Optimization of Heat Pump Dryer Conditions on Bioaccessibility of Some Secondary Metabolites of Cornelian Cherry-Capia Pepper Pestil

Özkan-Karabacak, Azime; Durgut-Malçok, Senanur; Tunçkal, Cüneyt; Tamer, Canan Ece; Pandiselvam, Ravi

doi:https://doi.org/10.1155/2023/5443962

Journal of Food Biochemistry

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Abstract Introduction Materials and Methods Results and Discussion Conclusion Data Availability Additional Points Conflicts of Interest Acknowledgments References Copyright Related Articles

Research Article | Open Access

Volume 2023 | Article ID 5443962 | https://doi.org/10.1155/2023/5443962

Optimization of Heat Pump Dryer Conditions on Bioaccessibility of Some Secondary Metabolites of Cornelian Cherry-Capia Pepper Pestil

Azime Özkan-Karabacak,^1,2Senanur Durgut-Malçok,³Cüneyt Tunçkal,⁴Canan Ece Tamer,³and Ravi Pandiselvam⁵

Academic Editor: Snehasis Chakraborty

Received31 Jul 2023

Revised24 Oct 2023

Accepted06 Nov 2023

Published29 Nov 2023

Abstract

Pestil is a traditional and functional snack produced by removing moisture from fruit pulp using different methods. Although solar drying is common in traditional pestil drying, modern drying methods are preferred in industrial production. As one of these methods, heat pump drying (HPD) is considered to be the most favorable technique owing to its notable efficiency in the drying process and low energy consumption. Additionally, it has the capability to accurately regulate drying conditions, thereby enhancing the overall quality of the dried foods. The aim of this study was to investigate the effects of HPD conditions on drying kinetics and quality profile (total monomeric anthocyanin (TMA) content, total phenolic content (TPC), antioxidant capacity (AC), and carotenoid content) and their in vitro bioaccessibility of the cornelian cherry-capia pepper pestil. Also, it was aimed to produce high-quality pestil having bioactive properties by optimizing HPD conditions. Drying temperature (40–50°C) and cornelian cherry concentration (30–40%) were selected as independent variables for the response surface methodology (RSM). After in vitro digestion, pestil samples have higher bioaccessible β-carotene, α-carotene, lutein, and AC (especially for the DPPH method), whereas the drying process reduced the bioaccessibility of TPC in pestil samples. Using a RSM, we found that the way the responses (TMA, TPC, AC, and carotenoids) were related to the independent variables can be best explained by quadratic (Qc), reduced quadratic (RQc), and reduced cubic (RCc) models. These models had high R² values, which mean they can accurately predict the outcomes. The optimal condition of responses with composite desirability of 0.852 was drying temperature at 46.68°C and 44.94% cornelian cherry concentration.

1. Introduction

Pestil is a traditional snack produced by removing moisture using different drying methods from fruit pulp. Pestil production is an important method to increase the shelf life and/or to add value to the fruit pulp [1]. Moreover, pestils are low in moisture so these snacks can be stored for a long period and their shipping is very economic [2]. The production methods and steps may show differences according to the geographical regions; also the ingredients of pestil such as sugar, starch, flour, honey, or milk may vary [3].

The taste of pestils are usually sweet because producers prefer fruits such as mulberry, grape, apricot, and plum for production of pestil, and when the water content is reduced, flavor of fruits and sugar content are concentrated [4]. Consumers’ tendency towards natural, traditional, and healthy snacks has been increased. For this reason, health-conscious consumers desire different forms of pestil which are rich in minerals, fiber, antioxidant capacity, and energy [5, 6]. Pestils prepared with both fruit and vegetable mixtures and spices are not available in the market. This deficiency has shed light on our study for producing an alternative pestil (without added sugar and salt) containing cornelian cherry (Cornus mas L.), capia pepper (Capsicum annuum), onion (Allium cepa L.), garlic (Allium sativum L.), and some spices (sumac, chili powder, dry mint, black pepper, and cumin).

Cornelian cherry is a fruit with sour and sweet taste, containing polyphenols such as gallic acid, rutin, resveratrol, quercitrin, chlorogenic acid, and quercetin. Thanks to these polyphenols, cornelian cherry, which has high antioxidant capacity, is also rich in anthocyanins (i.e., pelargonidin-3-glucoside, cyanidin-3-glucoside, cyanidin-3-rutinoside, delphinidin-3-galactoside, and cyanidin-3-galactoside). In addition to this, the fruit has carotenoids (i.e., lutein and alpha-carotene). Cornelian cherry has antimicrobial, anti-inflammatory, anticancer, antidiabetic, and antiatherosclerotic actions [7, 8]. Capia pepper is known to be a good source of carotenoids such as β-carotene, β-cryptoxanthin, alpha-carotene, and lutein, and also capsaicinoids, quercetin, and luteolin. Fresh, cooked, powder, sauce, and puree forms of capia pepper are generally consumed [9, 10]. The ascorbic acid present in 100 g fresh pepper (130 mg) is 1.5–2 times more than the ascorbic acid content of orange. In addition to this, capia pepper which is rich in vitamins as A, C, and E and folate having cell protection property and preventive effect for degenerative diseases [11]. Onions have high amounts of flavonoids, fructan, and organosulfur compounds. These components have strong antioxidant capacity. Also, it prevents cardiovascular diseases, having antimicrobial effects for pathogenic microorganisms and anti-inflammatory effect [12]. Garlic with high amounts of allicin, polyphenol, and organosulfur compounds has been traditionally used against viral diseases [13]. Spices with a sharp and intense aroma are obtained from flowers, fruits, seeds, and roots of tropical plants. They have high antioxidant activity and prevent oxidative deterioration [14].

Incorrect drying may lead to irreversible damage to product quality. Sun drying has some advantages such as attractive appearance and texture, but this method induces the slow drying process, exposures to environmental contamination, and microbial contamination [15]. Therefore, the modern drying methods are used for the drying process such as freeze drying, vacuum drying, spray drying, hot air drying, microwave drying, and heat pump drying (HPD) [16–18]. The main goals of drying are to maximize energy savings, increase productivity, and enhance product quality. As a result of its low energy usage, the HPD system is the most advanced system. Heat pump dryers are renowned for their remarkable energy efficiency, reaching a maximum of 91.95%, as well as their minimal power consumption, which falls within the range of 60% to 80%. Moreover, these dryers are cost-effective, possess outstanding drying capabilities with efficiency levels of up to 95%, and exhibit a high coefficient of performance (COP), reaching up to 5. Additionally, they operate at low drying temperatures, not exceeding 80%, resulting in quick drying times. Furthermore, these dryers maintain a low relative humidity, ranging from 10% to 80%, and have the ability to preserve the nutritional value of the dried items [19]. Also, this method ensures high-quality product and controlled drying conditions. Finally, it provides lower operating cost compared to conventional hot air dryers [17, 20].

Since 2000, optimization studies have become more significant in the field of food engineering in order to improve the performance of food processing and consumer acceptance of the final product. This procedure is employed in a number of applications, including the optimization of pasteurization, extraction, extrusion, and drying conditions [21]. RSM, an efficient statistical technique for optimization, can be used to reduce the number of experiments. Optimization of process parameters such as temperature, time, air velocity, and material thickness is vital for drying studies in order to produce high-quality products [21, 22].

Recent studies have demonstrated the application of RSM in optimizing HPD of fruits and vegetables. These applications have yielded significant findings regarding drying efficiency and product quality. For example, in Özkan Karabacak et al.’s [23] study, the effects of HPD on bioaccessibility of TPC and AC of melon slices were optimized with selected independent variables of drying air temperature (35–45°C), air velocity (5–9 m/s), and slice thickness (0.5–1 mm). They claimed that the melons’ higher bioaccessibility and optimal drying conditions protected their TPC and AC. In another study about the optimization of a different HPD temperature of shiitake mushrooms using RSM, it was concluded that the optimum drying conditions of shiitake mushrooms were determined as 35°C, 45°C, 55°C, and 65°C for 2.4 h, 3.3 h, 5.6 h, and 2.6 h, respectively [24]. Tomato slices also benefited from RSM-optimized drying, exhibiting improved color, sensory attributes, and preservation of lycopene and ascorbic acid content [25]. These studies highlight the efficacy of RSM in maximizing drying efficiency and enhancing the quality and nutritional value of HPD applied fruit and vegetable products.

The increasing trend towards natural and healthy snacks improves the popularity of these products that are not containing added sugar and salt. For this reason, the pestil that we produced in our study, consists of a mixture of fruit and vegetable and extracts of onion, garlic, and spices designed for a new snack option for consumers and producers. The aim of this study is to determine the antioxidant capacity (AC), total phenolic content (TPC), total monomeric anthocyanin (TMA) content, and carotenoid profile and their bioaccessibility of heat pump dried cornelian cherry-capia pepper pestil and to optimize all these quality parameters by RSM for the first time.

2. Materials and Methods

2.1. Materials

Cornelian cherries were obtained from a local bazaar in Bursa. Capia pepper, garlic, onion, and spices were bought from a market in Bursa. Apple pectin was obtained from Penguen A.Ş., Bursa.

2.2. Preparation of Cornelian Cherry-Capia Pepper Pestil Samples

First, the cornelian cherries and capia peppers were washed. The cornelian cherries pits taken out using a strainer, and the seeds were removed from the capia peppers. The capia peppers were then cooked in steam for 10 minutes. After that, both the cornelian cherries and capia peppers were ground up using a domestic blender. In our study, since RSM was applied, 13 different production trials were conducted. The amounts of cornelian cherry pulp changed between 27.93 and 42.07% (Table 1). After keeping the amounts of other ingredients to be added as a constant, the remaining amounts were completed to 100% with capia pepper pulp. Garlic (2%) and onions (20%) were grated and pressed to get their juice. This juice (10 mL), along with 1 g of each spice (black pepper, chilli pepper, mint, thyme, sumac, and cumin), were mixed together and left in a closed glass jar for 4 hours at room temperature. Then, the juice was filtered and separated from the spices and added to the cornelian cherry and capia pepper mixture. Apple pectin was dissolved in hot water (75°C) (0.05%) and 40 mL of this solution added to the abovementioned blend. Finally, the mixture was boiled at 98°C for 10 minutes. After cooling to room temperature (24 ± 0.05°C), pestil pulp was spread uniformly (8 × 8 cm, 3 mm thickness) and dried by HPD.

2.3. Drying System Procedure

The heat pump dryer designed and manufactured by Yalova University, Air Conditioning and Refrigeration Technology Program laboratory (Figure 1). The HPD system operates as a closed-loop conduit system during the drying process, with no external air intake. It is comprised of two interconnected cycles, namely, the refrigerant cycle and the drying air cycle. The refrigerant cycle, which is a crucial component of the system, is composed of four primary elements. The compressor (1-2) is where compression work is done and temperature and gas pressure are raised; the condenser (2–4) is where temperature and gas pressure are lowered; the capillary tube (3–5) is where gas pressure is lowered; and the evaporator (4–6) (between 1 and 5°C) is where liquid refrigerant boils with lower pressure. The thermostat regulates the drying temperature within the system. Solenoid valves enable gas to flow through the exterior condenser (3′) when the thermostat reaches the appropriate drying temperature. Gas flow to the exterior condenser stops when the drying temperature drops below the specified level. The system runs in the 1°C difference range, and this operation is automatic. Thanks to an axial fan, there is constant air flow in the air side process even in the absence of an external air input. The air duct contains an internal condenser and evaporator. The air heated by the internal condenser enters the drying cabinet at point (A) and exits at point (B) carrying the moisture that the product has absorbed. Point (C) condenses at point (D) because of the evaporator and releases its moisture after passing through the evaporator inlet. As the drying air goes through the evaporator, it cools. The internal condenser (E) needs to have its temperature raised once more. While it dries, this process continues. Temperature and relative humidity during the drying process are measured at one-minute intervals owing to the data logger (j) depicted in Figure 1 from the positions indicated in the air process. The only heat source utilized in the HPD system is the gas heat in the condenser. As a result, the compressor has to work harder and use more energy. The load cell (k) allowed for the recording of the product’s weight loss at intervals of three minutes.

HPD was run about 30 minutes before the drying process for stabilizing drying conditions. Pestils were dried at different temperatures (37.93–52.07°C) with a constant drying air velocity (1.0 m/s) (Table 1). Testo 405-V1 and Testo 410-2 were used for determining the air flow rate of drying trials. After the system was stabilized, 225 g pulp of cornelian cherry-capia pepper pestil was drained into mold of certain size (thickness: 3 mm, width: 8 cm, and length: 8 cm). The samples were placed in the tray. After starting the drying process, weight loss was measured by using the load cell. All data were recorded by using a computer at four-minute intervals by using the indicator. Relative humidity and temperature were determined and also enthalpy values (h) were measured from the psychometric diagram. The ambient temperature of the drying system was 24 ± 1°C, and the humidity was determined as 55 ± 5% on average. Until the moisture content of cornelian cherry-capia pepper pestils decreased to 0.090 ± 0.02 g water/g dry matter, the drying process was continued. All experiments were performed in three replications.

2.4. Analysis Methods

2.4.1. Physicochemical Analyses

Physicochemical analyses were carried out in both pulp and pestils. Refractometer (RA–500 KEM) determined the water soluble dry matter (Brix°). pH was measured by using Mettler Toledo Sevencompact pH/Ion pH meter. Moisture content of samples was determined by using the drying oven method [26]. Shimadzu (UV 1208) spectrophotometer was used for the antioxidant capacity (AC), total phenolic content (TPC), and total monomeric anthocyanin (TMA) analyses.

2.4.2. Total Phenolic Content (TPC) Analysis

The Folin–Ciocalteu technique was used to calculate TPC. First, a vortex (Vortex Mixer Classic, Velp Scientifica, Usmate, Italy) was used to combine 0.5 mL of extract, 1.5 mL of distilled water, and 0.5 mL of Folin–Ciocalteu reagent in capped glass tubes for 15 s. After waiting for 5 minutes, 1 mL of saturated Na₂CO₃ (35%, w/v) solution was added, and the tube’s contents were stirred before being left in the dark for 30 minutes. At 700 nm, the samples’ absorbance was determined. “mg gallic acid equivalent (GAE)/100 g dry weight (dw)” was used to indicate the results [27].

2.4.3. Antioxidant Capacity Analysis

Using the DPPH, FRAP, and CUPRAC techniques, AC was calculated. 0.1 mL sample was added to 3.9 mL of DPPH solution and vortexed for 30 seconds using a vortex (Vortex Mixer Classic, Velp Scientifica, Usmate, Italy) in the DPPH method. For 30 minutes, tubes were stored in a dark place. By measuring the decrease in absorbance of the DPPH solution in the presence of various concentrations of trolox (10–100 μmol/L), a trolox calibration curve (R² = 0.9997) was generated [28]. In the FRAP procedure, 100 mL of the sample or the control was combined with 300 mL of distilled water and 3 mL of the FRAP reagent (daily produced). For 30 minutes, extracts, test samples, and a blank were incubated at 37°C. The instantaneous measurement of absorbance was at 595 nm. According to the calibration curve, the results were calculated to be µmol trolox equivalent (TE)/g dw (R² = 0.9934) [29]. 100 mL of the sample was combined with 900 mL of distilled water and CUPRAC reagent in the CUPRAC procedure. CuCl₂, neocuproine, and ammonium acetate solutions were combined in exactly the same proportions to create the CUPRAC reagent. At 450 nm, absorbance was determined after 30 minutes [30]. The results were presented as μmol TE/g dw (R² = 0.9933).

2.4.4. Total Monomeric Anthocyanin (TMA) Analysis

TMA was determined by the pH differential method. First, 0.1 mL sample and potassium chloride buffer (0.025 M, pH 1) were mixed in a test tube. Briefly, 0.1 mL sample and sodium acetate buffer (4.5 M, pH 4.5) mixed in another test tube. Absorbance of the samples was measured at 512 nm and 700 nm. The result was calculated as follows:where A = (A λ₅₁₂- λ₇₀₀) pH_{1, 0}-(A λ₅₁₂- λ₇₀₀) pH_4,5, MW = molecular weight of the relevant anthocyanin (for cyanidin-3-glucoside: 449.2), DF = dilution factor, € = coefficient of absorbance (for cyanidin-3-glucoside: 26900), and l = spectrophotometer cuvette of layer thickness (cm) [31].

2.4.5. Extraction of Carotenoids

Briefly, 5 mL of a liquid called hexane, acetone, and ethanol (50 : 25 : 25) was mixed together and added to 5.00 ± 0.01 g of a sample. Then, the mixture was shaken. After that, supernatant was collected and took into a test tube. This material was evaporated by using nitrogen. The residue was dissolved using with THF : methanol (50 : 50 v/v) before HPLC-DAD analysis [32].

2.4.6. Analysis of Carotenoids with the HPLC-DAD Method

Samples were put into HPLC after being filtered with a 0.45 mm membrane filter. The column of C18 (25 cm × 4.6 mm, 5 μm) was the immobile phase. For spectral measurement at 475 nm, flow rate of 1 mL/min, and an injection volume of 10 μL, methanol/acetonitrile (90 : 10 v/v) was used as the mobile phase. Temperature of the column was 30°C, and the program duration was 30 min. Retention time in the column and characteristic spectra of carotenoids were used for the identification of carotenoids. For determination of the amount of carotenoids, β-carotene and lutein standards (Sigma (St. Louis, MO, USA)) were used [32].

2.4.7. In Vitro Digestion

The in vitro digestion model is a simulation of gastrointestinal digestion procedure. First, for simulating mouth digestion, homogenized pestil sample was mixed with saliva fluid (different concentrations and volumes of potassium chloride, mono potassium phosphate, sodium bicarbonate, magnesium chloride hexahydrate, ammonium carbonate, and hydrochloric acid mixed; pH 7), α-amylase, CaCl₂, and distilled water. After this, material was incubated by using shaking water bath at 37°C for 2 min. Second, for simulating gastric digestion, mouth phase was mixed with gastric fluid (different concentrations and volumes of potassium chloride, mono potassium phosphate, sodium bicarbonate, sodium chloride, magnesium chloride hexahydrate, ammonium carbonate, and hydrochloric acid mixed; pH 3), pepsin, and CaCl₂. The pH of the gastric phase was adjusted to 3 with HCl (1 mol/L). The gastric phase was incubated by using shaking water bath at 37°C for 2 hours. Finally, this gastric phase was mixed with intestinal fluid (different concentrations and volumes of potassium chloride, monopotassium phosphate, sodium bicarbonate, magnesium chloride hexahydrate, and hydrochloric acid mixed; pH 7), pancreatin, bile, and CaCl₂. The pH of intestinal phase was adjusted to 7 with NaOH (1 mol/L). Intestinal phase was incubated by using a shaking water bath at 37°C for 2 hours. After simulated gastric digestion and small intestinal digestion, the sample was centrifuged at 3500 rpm for 10 minutes, filtered, and the supernatant was collected for analysis [33].

2.4.8. Experimental Design

For the purpose of determining the best formula of cornelian cherry-capia pepper pestil, RSM was used. Totally, 13 different experiments were carried out using the experimental design (Table 2 and Table 1). In this research, RSM was applied with the central composite design. The effects of cornelian cherry pulp concentration (%) and drying temperature (°C) on the AC (DPPH, FRAP, and CUPRAC), total phenolic content, profile of carotenoids and their in vitro bioaccessibility, and total monomeric anthocyanin content were investigated. Two factors and their levels (1 and −1) were determined for creating experimental design. Mean of “1” is high value and mean of “−1” is low value of parameters (Table 2). The independent variables of cornelian cherry pulp concentration and drying temperature were determined through preliminary experiments. As a result of these preliminary experiments, cornelian cherry pulp concentration and drying temperatures that produced significant differences in the final product were evaluated in the study. All computational values were examined using the Design Expert 9 software. Using a 5% test of significance, the impact of the investigated factors on the individual response was assessed and explained.

According to equation (2), β₀, β_i, β_ii, and β_ij describe intercept, linear, Qc, and interaction regression terms, respectively, and ε defines the error. X_i and X_j are the independent variables, and Y is predicted response variable in RSM optimization. Three-dimensional graphics were established to monitor the influences of factors on each response visually, besides optimum levels for each factor were evaluated.

2.4.9. Sensory Analysis

Sensory evaluation was performed with 13 panelists from Bursa Uludag University Food Engineering Department, Türkiye. This evaluation was carried out in two sessions. All samples were coded with 3-digit numbers. Panelists evaluated color intensity, brightness, homogeneous appearance, odor of cornelian cherry, odor of capia pepper, odor of onion and garlic, odor of spice, flavor of cornelian cherry, flavor of capia pepper, flavor of onion and garlic, flavor of spice, sourness, umami, bitterness, sweetness, surface flatness, toughness, chewiness, and resilience stickiness. They used a 7-points scale.

2.4.10. Statistical Analysis

All results were statistically calculated by ANOVA using SPSS 15.0 (SPSS Inc., USA). These results were determined at a 5% significant level. To measure significant differences () between means, Duncan’s multiple range test was utilized. All analyses were carried out with two replications.

3. Results and Discussion

3.1. Brix and pH of Cornelian Cherry-Capia Pepper Pulp

The pH values of cornelian cherry-capia pepper pulp were found to be between 3.64 ± 0.09 and 3.85 ± 0.12, and brix values of pestil samples were found to be between 12.10 ± 0.17 and 16.33 ± 0.15 (Table 3). Saygı [34] measured the pH value of cornelian cherry and found it to be between 2.24 and 3.14. Yilmaz et al. [35] reported that the water soluble dry matter (brix) of cornelian cherry was between 12.53 and 21.17%. According to Tural and Koca [36], pH and brix values of cornelian cherry lies between 3.11–3.53 and 12.50–21.00%, respectively. In our study, pulp of capia pepper and cornelian cherry were mixed to prepare pestil samples; also, this pulp included some spices and extract of garlic and onion. These components could change pH and brix value of the pulp.

3.2. TPC of Cornelian Cherry-Capia Pepper Pulp, Pestil, and Their In Vitro Bioaccessibility

The TPC of cornelian cherry-capia pepper pulp ranged from 1116.07 ± 299.54 to 3351.70 ± 245.08 mg GAE/100 g dw (Figure 2), with the highest TPC value observed in sample 8 (35% cornelian cherry, drying at 52.07°C) (). Phenolic compounds are known to be sensitive to oxidation and heat treatments [37], but food processes can lead to the release of constituents in the food matrix, resulting in increased TPC [38]. In our study, the TPC values of the cornelian cherry-capia pepper pestil samples varied between 1845.90 ± 56.92 and 2515.40 ± 176.20 mg GAE/100 g, with some samples showing decreases and others showing increases in TPC after drying (). These variations may be attributed to differences in chemical structures, oxidative enzyme activities, and extraction efficiencies [39, 40]. Similar observations have been reported in studies on other dried fruits, such as apricot pestil [41], pomegranate pestil [7], and blackthorn pestil [42]. In these studies, the drying process generally increased the TPC values, although variations were observed depending on the drying method and conditions. It is noteworthy that dried fruits may exhibit lower TPC values compared to fresh ones due to the breakdown of cellular constituents during the drying process [43]. In summary, the variations in TPC values observed in our study and previous studies can be attributed to the specific ingredients, drying methods, and employed process conditions. Some factors, such as chemical structures (phenolic compounds, carbohydrates, and water), oxidative enzyme activities (polyphenol oxidase, peroxidase, and catalase), and extraction efficiencies (solvent selection, extraction time, and temperature), can help explain the changes in TPC values and optimize drying processes to enhance the phenolic content of the final product while minimizing undesirable reactions that may lead to phenolic compound degradation.

In this study, the effects of in vitro gastric digestion and in vitro small intestinal digestion on the presence and quantity of phenolic compounds were investigated. The results revealed different responses of the samples to the digestion processes, highlighting the scientific rationale behind the observed outcomes. First, it was found that sample 2, consisting of 40% cornelian cherry and dried at 40°C, exhibited the highest total phenolic content (TPC) value among the samples subjected to gastric digestion (Figure 2). Conversely, gastric-digested sample 6, containing 42.07% cornelian cherry and dried at 45°C, showed the lowest TPC value. Gastric digestion increased the TPC value in sample 2, whereas it caused a decrease in TPC values of samples 1, 3, 5, 6, 8, 10, 12, and 13 than the undigested samples (). Previous studies have also reported an increase in TPC values after gastric digestion. For instance, Kamiloglu and Capanoglu [44] observed an increase in TPC values of grape molasses, apricot, and plum pestils after gastric digestion, ranging from 11% to 164% higher than undigested samples. Similarly, Suna [18] investigated the changes in TPC values of in vitro digested medlar pestil samples dried using different methods (hot air, microwave, and vacuum). Their findings showed that the TPC values after small intestinal digestion of microwave- and vacuum-dried medlar pestil samples were higher than those of the undigested ones. Furthermore, in vitro small intestinal digestion led to a minimum TPC value in sample 6 (42.07% cornelian cherry, drying at 45°C) (), as depicted in Figure 2. Except for sample 3, the TPC values of all in vitro small intestinal digested pestil samples were lower than those of gastric-digested and undigested samples (). When comparing the TPC values after in vitro gastric and small intestinal digestion, it was observed that the reduction ranged between 16.92% and 70.57%. These results provide insights into the changes that phenolic compounds undergo during the digestion processes. The observed effects vary among different samples, and it is worth noting that the combination of phenolics with other molecules, such as polysaccharides, as highlighted by Heleno et al. [45], may pose challenges in their passage through dialysis membranes. Also, since the drying process involves thermal treatment, the temperature may affect the degree of degradation and in vitro bioaccessibility of dietary polyphenols. Similarly, drying reduced the TPC values and in vitro bioaccessibility of jujube fruit [46] and coffee beans [47]. Oxidation and cellular degradation events have been suggested as the cause of this decrease [48].

3.3. RSM Model for TPC Results

The RCc model for TPC is expressed by the following equation:

The signs “+” and “−” and magnitude of terms emphasize the effect of parameters on responses. Negative sign of parameter shows antagonistic effect, and positive sign of parameter shows synergistic effect [49]. From equation (3), linear term of cornelian cherry pulp concentration (X₁) had positive effect, but drying temperature (X₂) had negative effect on TPC value. According to this result, when comparing sample 1 (30% cornelian cherry, drying at 40°C) and sample 3 (30% cornelian cherry, drying at 50°C), sample 1 showed a higher TPC value than sample 3. Also, when this comparison was applied to sample 3 (30% cornelian cherry, drying at 50°C) and sample 4 (40% cornelian cherry, drying at 50°C), sample 4 had a higher TPC value than sample 3. This situation demonstrated that cornelian cherry pulp concentration had a positive effect, and the drying temperature had a negative effect on the TPC value. Qc term of both parameters had also negative effect. TPC value was significantly negatively influenced by the drying temperature (X₂); also, cornelian cherry pulp concentration (X₁) was the highest efficient on TPC value ().

Contour surface diagrams denoted the relationship of parameters and analysis results of cornelian cherry-capia pepper pestil. Figure 3a shows the interaction between cornelian cherry pulp concentration and drying temperature for undigested pestil samples. From Figure 3, while cornelian cherry concentration was increased, TPC value also increased. However when drying temperature was increased, lower TPC values were obtained.

(a)

(b)

(c)

Equations (4) and (5) showed TPC value of after gastric and small intestinal digestion, respectively.

Linear term of cornelian cherry pulp concentration had negative effect on TPC value of both two equations. Also, while drying temperature was increased, TPC values of samples subjected to in vitro gastric and small intestinal digestion increased. The effects of cornelian cherry pulp concentration on TPC values of samples subjected to gastric and small intestinal digestion are indicated in Figures 3(b) and 3(c), respectively.

3.4. AC of Cornelian Cherry-Capia Pepper Pulp, Pestil, and Their In Vitro Bioaccessibility

3.4.1. DPPH

AC of pulp and pestil samples was evaluated by using the DPPH method. The AC values of the pulp samples ranged from 19.97 ± 0.61 to 40.21 ± 0.45 μmol TE/g dw (Figure 4), with the highest AC value observed in sample 6 (42.07% cornelian cherry, drying at 45°C). The DPPH results of the pestil samples were lower than those of the pulp samples in each experiment (). This finding is consistent with a study conducted by Kc et al. [50] on lapsi fruit pestil. The decrement in the antioxidant activity of pestil samples after drying may be attributed to the breakdown of biologically active compounds at drying temperatures, resulting from chemical, enzymatic, or thermal decomposition [51].

Among the undigested pestil samples, the maximum DPPH value (7.05 μmol TE/g dw) was found in sample 10 (35% cornelian cherry, drying at 45°C), while the minimum DPPH value (6.47 μmol TE/g dw) was found in sample 7 (35% cornelian cherry, drying at 37.92°C) (). Özkan Karabacak [42] reported DPPH values ranging from 5.67 to 6.47 μmol TE/g dw for blackthorn pestil samples dried using various methods, while Suna [18] measured DPPH values of medlar pestils ranging from 6.30 to 6.87 μmol TE/g dw. The variations in DPPH results could be attributed to differences in process conditions, raw materials, and ingredients. Tontul and Topuz [7] determined DPPH values of pomegranate pestil ranging from 1.87 to 2.42 g TE/100 g dw.

After in vitro gastric and small intestinal digestion, the DPPH results of all of the cornelian cherry-capia pepper pestil samples were higher than those of the undigested samples (). This finding is consistent with the finding of Özkan Karabacak [42] study, which reported increased DPPH bioaccessibility after drying of blackthorn pestils. Additionally, Oliveira and Pintado [52] observed an increase in antioxidant activity of strawberry and peach-enriched yogurts after small intestinal digestion. The decrease in DPPH values during small intestinal digestion, compared to gastric digestion, could be described by the deprotonation of hydroxyl groups in phenolic compounds, which is influenced by the pH of the environment. The gastric stage has an acidic property, while the intestinal environment is mildly alkaline. The decrease in AC values after simulated small intestinal digestion may be attributed to the degradation of polyphenols and anthocyanins due to pH changes during the intestinal digestion process [53].

3.4.2. RSM Model for DPPH Results

The RQc model for AC determined by the DPPH method is expressed by the following equation:

From equation (6), linear terms of cornelian cherry pulp concentration had positive effect, whereas drying temperature had negative effect on DPPH value of undigested samples. Qc terms of both parameters had negative effect and the effect of cornelian cherry pulp concentration was more effective than the drying temperature (). Sample 4 (40% cornelian cherry, drying at 50°C) had more cornelian cherry pulp concentration value than sample 3 (30% cornelian cherry, drying at 50°C). Also, the DPPH value of sample 4 was higher than that of sample 3.

Equation of Y₅ and Y₆ indicated that linear term of cornelian cherry concentration and interaction of cornelian cherry concentration and drying temperature had negative effect on DPPH results after gastric and intestinal digestion. However, linear term of drying temperature had positive effect on DPPH value determined after gastric and intestinal digestions (Figures 5(b) and 5(c)). When comparing in vitrogastric-digested sample 7 (35% cornelian cherry, drying at 37.93°C) and sample 8 (35% cornelian cherry, drying at 52.07°C), a higher DPPH value was observed in sample 8, where the drying temperature was higher. As this result shows the positive effect of drying temperature on in vitrogastric-digested samples, the same conclusion can be reached in Figure 5(b).

(a)

(b)

(c)

3.4.3. CUPRAC (μmol TE/g dw)

The CUPRAC results of the pulp samples showed a range between 21.27 ± 0.54 and 66.88 ± 1.28 μmol TE/g dw (Figure 6). The maximum CUPRAC value (58.94 μmol TE/g dw) was observed in undigested sample 6 (42.07% cornelian cherry, drying at 45°C), while the minimum CUPRAC value (46.79 μmol TE/g dw) was found in undigested sample 13 (35% cornelian cherry, drying at 45°C) (). The drying process resulted in increased CUPRAC values for samples 3, 4, 10, 11, and 12 (). These findings are consistent with those of the previous studies on the effects of drying conditions on fruit quality, as reported by Özkan Karabacak et al. [23] and Paramanandam et al. [54]. The increase in antioxidant activity after drying can be attributed to the release of phytochemicals at high temperatures. Variations observed in the values of postgastric and small intestinal digestion samples can be attributed to differences in environmental pH values, among other factors. Additionally, changes resulting from an increase in cornelian cherry pulp concentration can be explained by alterations in the chemical composition of compounds in the sample during digestion. Some compounds may become more or less reactive with CUPRAC reagents due to structural changes, leading to fluctuations in the observed antioxidant capacity [54]. In an optimization study on HPD of melon slices, Özkan Karabacak et al. [23] observed an increase (1–30%) in antioxidant activity after drying, when investigating the effects of independent variables such as drying air temperature, air velocity, and slice thickness.

In our study, after in vitro gastric digestion, an increase in CUPRAC values was observed for samples 5, 8, and 11 compared to undigested samples (). However, the CUPRAC results of the small intestinal digested samples were lower than gastric-digested ones for samples 4, 5, 6, and 7 (). The highest CUPRAC values after gastric and small intestinal digestion were found in sample 5 (27.93% cornelian cherry, drying at 45°C) and sample 8 (35% cornelian cherry, drying at 52.07°C), respectively. These findings are in line with the study conducted by Suna [18], who reported that the CUPRAC values of undigested hot air-dried medlar pestil samples (at 60°C and 70°C) were 96.10 and 70.22 μmol TE/g dw, respectively. After in vitro gastric digestion, these values changed to 93.41 and 89.42 μmol TE/g dw, while after in vitro small intestinal digestion, they changed to 64.85 and 95.55 μmol TE/g dw, respectively. The observed decrease in postdigestion CUPRAC values for the medlar pestil dried at 60°C and the increase for the medlar pestil dried at 70°C indicate the significance of drying temperature on the AC of in vitro digested samples. In our study, sample 8 was dried at the highest temperature (52.07°C), while sample 7 was dried at the minimum temperature (37.93°C). Similar to the findings of Suna [18], the CUPRAC values of the samples after intestinal digestion indicated a similar trend to the drying temperature. The maximum CUPRAC value was found in intestinal digested sample 8 (71.08 μmol TE/g dw), while the minimum CUPRAC result was determined in intestinal digested sample 7 (34.26 μmol TE/g dw).

3.4.4. RSM Model for CUPRAC Results

The Qc model for AC determined by the CUPRAC method is expressed by the following equation:

From equation (8), linear terms of cornelian cherry pulp concentration and drying temperature had positive effect on CUPRAC value. While Qc term of drying temperature had a positive effect, Qc term of cornelian cherry pulp concentration had a negative effect on CUPRAC value. Cornelian cherry pulp concentration of sample 5 (27.93% cornelian cherry, drying at 45°C) was lower than that of sample 6 (42.07% cornelian cherry, drying at 45°C). Also, sample 5 had a lower DPPH value than sample 6. When the cornelian cherry pulp concentration and drying temperature increased together, higher CUPRAC value was obtained (Figure 7(a)).

(a)

(b)

(c)

According to equations (9) and (10), cornelian cherry pulp concentration had negative influence on CUPRAC values of after gastric and small intestinal digestion. However, drying temperature had a positive effect on CUPRAC values of in vitro gastric and small intestinal digested samples. Equation (10) indicated that linear term of drying temperature had a positive effect on CUPRAC values of after small intestinal digestion. Sample 8 had the highest drying temperature (52.07°C). Also, CUPRAC value of small intestinal digested sample 8 showed the highest result. Figure 7(c) demonstrates this result.

3.4.5. FRAP

The FRAP results of the pulp samples ranged from 140.70 ± 7.11 to 266.66 ± 3.27 μmol TE/g dw (Figure 8). The maximum FRAP value for the pulp samples was observed in sample 6 (42.07% cornelian cherry, drying at 45°C), while the minimum FRAP value was found in sample 12 (35% cornelian cherry, drying at 45°C) (). In the pestil samples, the AC determined by the FRAP method ranged from 150.10 ± 1.15 to 186.72 ± 5.55 μmol TE/g dw. Only undigested sample 12 showed an increment in FRAP values after drying when compared with the all samples (). Similar findings with sample 12 were reported by Deng et al. [55], Michalska et al. [56], and Zielinska and Markowski [57], who observed that drying treatment increased AC of red pepper, plum powders, and blueberries, respectively.

After gastric digestion, a significant increase was observed in the FRAP values, as well as in the other AC results, except for sample 2 (). However, variable results were obtained after small intestinal digestion. The maximum FRAP value was found in in vitro small intestinal digested sample 3 (207.74 μmol TE/g dw), while the minimum FRAP value was found in in vitro small intestinal digested sample 13 (124.05 μmol TE/g dw). According to Figure 8, when comparing the FRAP values of gastric and small intestinal digested samples, in vitro gastric digestion showed higher results, except for sample 10. The results of an in vitro digestion revealed that the fruit pestil matrix appeared to have a protective impact on most antioxidant compounds, preventing their degradation during gastrointestinal digestion so that they could retain their antioxidant capability upon entering the colon. These substances may function as antioxidants in the intestine or undergo biotransformation and absorption in the large intestine/colon [58].

3.4.6. RSM Model for FRAP Results

The Qc model for AC was explained by the FRAP method is expressed by the following equation:

From equation (11), both cornelian cherry pulp concentration and drying temperature had positive effect on FRAP value. Even Qc term of drying temperature had a positive effect, and Qc term of cornelian cherry pulp concentration had a negative effect on FRAP value. Linear term of cornelian cherry pulp concentration had the highest effect on FRAP value (). From the contour diagram (Figure 9(a)), when cornelian cherry pulp concentration and drying temperature increased, higher FRAP value was obtained. In addition, interaction of both linear parameters had a positive effect on FRAP results.

(a)

(b)

(c)

According to equations (12) and (13), linear terms of cornelian cherry pulp concentration had negative correlation with FRAP value of after gastric and small intestinal digested samples. Qc terms of both parameters had positive effect on FRAP values of digested samples. Figures 9(b) and 9(c) demonstrate that when drying temperature increased; FRAP values of both gastric and small intestinal digested samples also increased.

3.5. TMA Content of Cornelian Cherry-Capia Pepper Pulp and Pestil

The total monomeric anthocyanin (TMA) content of the cornelian cherry-capia pepper pulp samples ranged from 11.14 to 28.29 mg/kg (Table 4). The maximum TMA value was observed in sample 6 (42.07% cornelian cherry, drying at 45°C), while the minimum TMA value was found in sample 12 (35% cornelian cherry, drying at 45°C) (). Comparing the TMA content between the pulp and pestil samples, it is evident that the drying process led to an increase (between 4.53 and 9.19 times) in the TMA content of the pestil samples compared to the pulp samples. This finding is supported by previous studies on the effects of drying on TMA content. For example, Deng et al. [55], Michalska et al. [56], and Zielinska and Markowski [57] reported similar results, showing that drying fruits at higher temperatures and for shorter periods increased their anthocyanin content.

The TMA content of the cornelian cherry-capia pepper pestil samples ranged from 81.19 ± 14.42 to 156.39 ± 17.78 mg/kg. It is worth noting that the specific samples with higher cornelian cherry pulp ratios (e.g., sample 6 containing 42.07% cornelian cherry) exhibited the highest TMA content. This suggests that the composition of the fruit pulp in the pestil samples played a significant role in determining the TMA content. Overall, these results demonstrate the impact of the drying process and fruit pulp composition on the TMA content of cornelian cherry-capia pepper pulp and pestil samples.

Additionally, drying temperature had a significant effect on the TMA results. For instance, sample 1 (30% cornelian cherry, drying at 40°C) had a higher TMA content than sample 3 (30% cornelian cherry, drying at 50°C), and sample 2 (40% cornelian cherry, drying at 40°C) had a higher TMA content than sample 4 (40% cornelian cherry, drying at 50°C). This finding is consistent with that of a previous study on dried blood-flesh peach pulp using hot air drying at different temperatures (50, 60, and 70°C) [59]. The study reported that as the temperature increased to 70°C, the TMA content decreased due to the thermal degradation of anthocyanins. It was also noted that cyanidin-3-glucoside (C3G), identified as the predominant anthocyanin in cornelian cherry, is sensitive to thermal treatment [59]. Contrarily, comparing the two samples (sample 8 at 52.07°C and sample 11 at 45°C), in which the amount of cornelian cherry pulp concentration (35%) remained constant and the temperature varied, an increase in TMA value with the increased drying temperature was exhibited. However, this increase is statistically insignificant (). Some researchers have reported that C3G may be positively affected by temperature, possibly due to the acceleration of molecular movement and the increased extraction rate of C3G at higher temperatures [60].

3.6. RSM Model for TMA Results

The Qc model for TMA content is expressed by the following equation:

From equation (14), linear terms of cornelian cherry pulp concentration (X₁) had negative effect, but drying temperature (X₂) had positive effect on TMA results. When compared TMA value of pulp and pestil samples, an increase was determined in all samples. When Qc term of drying temperature () increased, TMA values was also increased. Drying temperature was more effective than cornelian cherry pulp concentration on TMA values. In addition, according to Figure 10, increase of drying temperature also caused increase of TMA content. Similarly, when purple waxy corn kernels were dried using a tunnel dryer, the measured TMA at 60°C (2215.87 mg/100 g) was found to be lower than that at 65°C (2452.93 mg/100 g). The reason for this could be attributed to the application of a longer drying process to reach the desired moisture levels at a lower temperature. Prolonged drying processes might lead to the degradation of anthocyanins, thus explaining these results [61].

3.7. Carotenoid Profile

In order to identify the changes in the carotenoid profile of the samples, calculations were made with β-carotene, α-carotene, and lutein standards. β-carotene, α-carotene, and lutein contents of undigested pestil samples ranged from 25.90 to 112.10, 22.20 to 84.48, and 1.26 to 5.05 mg/100 g dw, respectively (Table 5). Table 5 also shows that the content of β-carotene was max 2.5 times higher than the content of α-carotene and max 54 times higher than that of lutein in pestil samples. According to the carotenoid results of the pulps, the highest values were obtained from sample 6. This result can be associated with the fact that the highest cornelian cherry pulp ratio was in the recipe of sample 6 (42.07% cornelian cherry, drying at 45°C). After drying, β-carotene, α-carotene, and lutein content of the samples decreased to a range of 54–87%, 22–84% and 73–96%, respectively. The reason of the reduction in carotenoids may be related to their sensitivity to heat, oxygen, light, and enzymes [62]. According to a previous study by Colle et al. [63], oxidation is by far the predominant factor contributing to the degradation of carotenes. It is thought that oxidation is primarily a free radical process that results in an irreversible reaction and increases the levels of breakdown products such as epoxides, apocarotenones, and apocarotenals. Different studies reported the decrease in carotenoids after the drying process of carrots [64], pumpkins [62], mango cultivars [65], commercial coriander varieties [66], carrot, sweet potato, and yellow bell pepper [67]. Moreover, further research by Mazzeo et al. [68] found that the overall carotenoid content of fruits and vegetables degrades by 8–10% when they are cooked or processed.

In order to determine the bioaccessibility of the pestil samples, the changes in the amounts of β-carotene, α-carotene, and lutein released in the stomach and small intestine were investigated after the digestion through simulation (Table 5). β-Carotene, α-carotene, and lutein could not be detected in the samples after gastric digestion. According to earlier research on the in vitro release characteristics of β-carotene, the amount of β-carotene degradation increased with lowering pH and achieves a maximum at pH = 5 in an acidic environment (pH = 3–7) [69]. Courraud et al. [70] also reported that acidic conditions in the gastric phases highly affect the sensitivity of carotenoids according to alkaline conditions. However, an increase was observed in all carotenoid components after small intestinal digestion. These increments for β-carotene, α-carotene, and lutein ranged from 7.33 to 15.20, 7.52 to 16.73, and 7.03 to 22.34 times, respectively, when compared with undigested samples. Studies indicate that different carotenoids exhibit varied ratios of bioaccessibility. Lutein is easier to dissolve in water than α-carotene, β-carotene, and lycopene. This is because lutein is made up of substances that like water more, while the other substances are made up of substances that like oil more. Also, lutein can be found in different parts of food and interacts with other molecules in a different way [71].

Similar results with this study were presented in a recent study examining the bioaccessibility of carotenoids in carrot chips dried using a combination of instant pressure drop drying, hot air, and freeze drying [72]. As a result of the study, carotenoids in dried carrot chips were found to be more bioaccessible than those in fresh samples, although fresh carrots contained higher carotenoids than dried ones. By altering the natural food matrix during food processing, Courraud et al. [70] have also shown that technological methods like cooking or boiling vegetables enhance carotenoid bioavailability.

3.8. RSM Model for Carotenoid Results

The RCc model was significantly () fitted to the undigested β-carotene response and was expressed by the following equation:

Cornelian cherry pulp concentration (X₁) showed positive correlation on undigested β-carotene value of the pestil samples, while drying temperature (X₂) showed negative correlation. Their interaction term (X₁X₂) positively affected the undigested β-carotene value of the samples. While the Qc terms of cornelian cherry pulp concentration () affected the result positively, drying temperature () affected the result negatively. Although cornelian cherry pulp concentration and drying temperature affected the second-order interaction term (X₁) positively, the cubic term of drying temperature () negatively affected the result.

It can be seen from 3D surface graph (Figure 11(a)), β-carotene decreases with the increase in drying temperature, while β-carotene increases with the increase in the amount of cornelian cherry.

(a)

(b)

(c)

(d)

(e)

The RCc model for undigested α-carotene content is described by the following equation:

From equation (16), linear terms of cornelian cherry pulp concentration had a positive effect but drying temperature had a negative effect on undigested α-carotene content. As in the β-carotene result, the increase in Qc term of drying temperature decreased the undigested α-carotene content, while the increase in the amount of cornelian cherry pulp used in the recipe increased the undigested α-carotene content. This relationship is also seen in the 3D graph (Figure 11(b)). The second-order interaction term was positively affected undigested α-carotene content.

The Qc model significantly fitted to the undigested lutein content and can be described by the following equation:

From this equation and its 3D surface graph, it can be seen that undigested lutein content of the pestil samples was negatively influenced by the increments in cornelian cherry pulp concentration (X₁) and drying temperature (X₂). At low drying temperature and low cornelian cherry pulp concentration, the undigested lutein value was at its highest value (Figure 11(c)). Moreover, their interaction terms (X₁X₂) and Qc term of drying temperature () negatively affected undigested lutein content. However, undigested lutein content of pestil samples had positive correlation with the Qc term of cornelian cherry pulp concentration ().

RSM models were also applied to determine the best fitted models for in vitro bioaccessibility of carotenoids. While no model was fitted to small intestinal digested β-carotene contents, the Qc model significantly fitted to the simulated small intestinal digested α-carotene and lutein responses and their models can be described by equations (18) and (19), respectively.

From these equations and their 3D plot graphs (Figures 11(d) and 11(e)), it can be understood that at high level of cornelian cherry pulp concentration (X₁), the simulated small intestinal digested α-carotene and lutein values were the highest. In both of the equations, the interaction term of cornelian cherry pulp concentration and drying temperature (X₁X₂) positively affected the simulated small intestinal α-carotene and lutein values. While simulated small intestinal digested α-carotene content was negatively affected by the Qc term of cornelian cherry pulp concentration (), drying temperature () showed a positive effect on it. Both of the Qc terms of cornelian cherry pulp concentration () and drying temperature () had a negative effect on simulated small intestinal digested lutein content.

3.9. Sensory Analysis

Sensory analysis results showed that there was no statistical difference between brightness, odor of cornelian cherry, flavor of spice, umami, bitterness, sweetness, surface flatness, and chewiness parameters of the samples (Figures 12–15) (). Sample 2 (40% cornelian cherry, drying at 40°C) had the best score for colour intensity, homogeneous appearance, and elasticity parameters. For odor of capia pepper, odor of spice, flavor of capia pepper, sourness and stickiness criteria, sample 13 (35% cornelian cherry, drying at 45°C) had the highest score. Also, sample 7 (35% cornelian cherry, drying at 37.92°C) had the best score for odor of onion and garlic and flavor of onion and garlic; sample 5 (27.92% cornelian cherry, drying at 45°C) had the best score for flavor of capia pepper; sample 8 (35% cornelian cherry, drying at 52.07°C) had the best score for stiffness criteria.

3.10. Fitting the Model

Central composite matrixes of independent variables are indicated in Table 2. Cornelian cherry pulp concentration and drying temperature were used for optimization formula. Different levels of parameters light the way for determining the best formula for cornelian cherry-capia pepper pestil. Table 6 shows regression analysis including regression coefficient, lack of fit, R², adjusted R², values, and consequently proper models. The lack of fit test was not significant in each case, indicating that the models were sufficiently accurate for predicting the responses for any combination of independent factors within the tested ranges. According to the value (), every term in the models was significant. Additionally, R² generally needs to be greater than 80% to be considered a well-fitting model [73]. According to these parameters, the RCc model was determined as the best model for TPC (undigested and simulated gastric digestion), DPPH (simulated small intestinal digestion), CUPRAC (simulated gastric and small intestinal digested), FRAP (undigested and simulated gastric digestion), TMA, β-carotene (undigested), and α-carotene (undigested). The Qc model was fitted for TPC (simulated small intestinal digestion), CUPRAC (undigested), FRAP (simulated small intestinal digestion), lutein (undigested), α-carotene (simulated small intestinal digestion), and lutein (simulated small intestinal digestion). Also, the RQc model was observed as the best model for DPPH (undigested and simulated gastric digestion). A quadratic model is a mathematical model that describes how a response variable depends on the levels of independent variables. In this model, the independent variables have first-order (linear) terms and second-order (quadratic) terms [74]. The reduced quadratic model is a one-step simplified version of the quadratic model [75]. A reduced cubic model is used to examine the effects of independent variables on responses in more detail. In this model, the independent variables have first-order (linear), second-order (quadratic), and third-order (cubic) terms [76]. The regression coefficient, denoted as R², represents the proportion of the variation in the dependent variable that can be accounted for by the model. It is generally recommended that a good fitting model should have an R² value exceeding 80% [77]. High R² and adjusted R² values showed good agreement between experimental and predicted values. The highest R² and adjusted R² were determined in Y6 (DPPH—simulated small intestinal digestion) as 0.9869 and 0.9685, respectively. The lowest values were found in Y4 (DPPH—undigested) as 0.7008 and 0.5512, respectively.

3.11. Optimization

According to their impacts on the final product’s quality, the replications were given equal importance in order to maximize the values of the independent variables (cornelian cherry concentration and drying temperature) for the production of high-quality cornelian cherry-capia pepper pestil. Table 7 lists the employed parameter, experimental, and predicted outcomes. The optimal drying temperature of 46.68°C, the cornelian cherry concentration of 44.94%, and the composite desirability of 0.852 were shown to be necessary for designing of functional pestil.

4. Conclusion

Although cornelian cherry has many bioactive compounds beneficial for human health, it has very astringent and sour taste, which makes it difficult to use in the food industry. For this reason, the use of cornelian cherry fruit in pestil production will develop a new functional product for consumers. Also, capia pepper, extracts of onion-garlic, and spices improved flavor and bioactive properties of the product. According to this study, drying has varying effects on TPC values. Also, the TPC values of in vitro gastric-digested samples were determined to be generally higher than those of in vitro small intestinal digested samples (). DPPH results of after in vitro gastrointestinal digestion showed generally higher values than undigested ones. However, variable results were obtained in CUPRAC and FRAP values after digestion of pestil samples. TMA content in pestil samples increased by 81.19% and 156.39% after drying. The results also showed that although the β-carotene, α-carotene, and lutein content of the samples decreased with drying, in vitro gastrointestinal digested pestil samples had more bioaccessible carotenoids than undigested samples. Considering these findings, it can be said that drying may be an alternative strategy to increase bioaccessibility of carotenoids and AC. Cornelian cherry-capia pepper pestil that we produced in our study, consisting of a mixture of fruit and vegetable also does not containing added salt and sugar for a new and innovative snack for consumers and producers. The optimum parameters of 46.68°C for drying temperature and 44.94% for cornelian cherry pulp concentration were predicted by RSM with composite desirability of 0.852. This study offers a theoretical and experimental framework for future research on the relationship between cornelian cherry content and variable HPD temperature for pestil samples. The focus of this work is on the performance of the drying process, specifically how varied temperatures and cornelian cherry concentrations affect it. Unquestionably, other variables (such as relative humidity and air speed) and responses (such as cost of the product and other quality characteristics of the product) are recommended to be taken into account in the future.

Data Availability

The data used to support the study are available from the corresponding author upon request.

Additional Points

Practical Applications. The research presented in this study holds promising practical applications for the food industry, offering new opportunities to create functional and health-enhancing snacks for consumers. The utilization of HPD to produce cornelian cherry-capia pepper pestil presents an avenue for developing premium functional snacks. RSM used in this study provides a systematic approach for optimizing HPD conditions. The optimized drying conditions result in a product with increased bioaccessibility of bioactive compounds, including carotenoids and antioxidants, potentially providing consumers with improved health benefits. The pestil, consisting of a blend of fruit and vegetable components and free from added salt and sugar, offers a nutritious and innovative alternative to conventional snacks. Its unique flavor profile and rich bioactive properties can cater to the evolving preferences of health-conscious consumers. Implementing this experimental framework can help food manufacturers to achieve consistent high quality in their pestil products.

Conflicts of Interest

The authors declare that they have no conflicts of interest.

Acknowledgments

The first author gratefully acknowledges the Scientific Research Project Office of Bursa Uludag University (Project no. FHIZ-2021-411) for providing financial support.

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