|
| Specimen | Experimental criterion | Spectral region λ (nm) | Source (power (W)) and modulation frequency (Hz) | Region or centers absorbing (CA) λ (nm) | Mathematical analysis | Significant findings/results | Country |
|
| Red lettuce and chard seeds | Pieces of fresh fruit were used. | 250–750 | Xenon lamp
P = 700 W
(chopper, 17 Hz) | 600, 300 | None | By using PAS, aged seeds in vegetable were evaluated. Nonaged seeds had higher β values than aged seeds (Pardo et al.) [58]. | Mexico |
| Acai, cupuaçu, Brazil nut, and persimmon | Pieces of fresh fruit were used. | 200–400 | Xe arc lamp
P = 1000 W
(chopper, 30 Hz) | 218.4, 224.6, 227.2, 207.1, 218.4, etc. | Spectral deconvolution | By using PAS, band peaks were found corresponding to phenolic acids: p-hydroxybenzoic, gallic, protocatechuic, vanillic, cinnamic, p-coumaric, caffeic, and ferulic (Neto et al.) [59]. | Brazil |
| Persian lime juice (Citrus latifolia) | Persian limes were divided into four categories: the highest quality, the second-class, the third-class, and waste-class. | 300–800 | Xe lamp
P = 1000 W
(chopper, 17 Hz) | 314, 359, 445, 496, 684 | Second derivative | The level of photoacoustic signal is diminished depending on the quality of lemon evaluated. The lower quality corresponds lower photoacoustic signal level. The band of greatest absorption for lemon juice was found at 300–400 nm, related to the flavonoid region (Corzo-Ruiz et al.) [60]. | Mexico |
| Chili pasilla peppers (Capsicum annuum L.) | Chile pasilla was used dehydrated. | 250–700 | Xe lamp
P = 1000 W
(chopper, 17 Hz) | 265–400 | None | Photoacoustic signal increases as a function of the dehydration time; the authors relate the flavonoid region between 265 and 400 nm (Zendejas-Leal et al.) [61]. | Mexico |
| Maize (Zea mays L.): White, yellow, and blue | Sample adapted to the cell size (6 mm). | 300–800 | Xe lamp
P = 700 W | 300–350
300–450
300–460 | Variance analysis and least significant difference (LSD) test | Indicated a ratio of the absorbance bands of each maize evaluated (white, yellow, and blue colors), with components such as flavonoids, flavonols, carotenoids, and anthocyanins (Domínguez-Pacheco et al.) [46]. | Mexico |
| Buckwheat grain meal | Whole meal was prepared from the grain. | 250–600 | Xe lamp
1000 W
(chopper, 17 Hz) | 280, 378 | Standard deviations, correlation | Using PAS, it was possible to observe two absorbent peaks at 280 and 378 nm related to protein content and rutin, respectively (Dóka et al.) [49]. | Hungary
Netherlands
Italy |
| Mushrooms Agaricus brasiliensis | A volume of 80 mm3 of each sample was used. | 270–1000 | Xe arc lamp
P = 1000 W
(chopper, 16 Hz) | 300–400
475 | Multivariate analysis, linear correlation | Flavonoids show at least two absorbance bands: one ranging from 240 to 280 nm and another from 300 to 400 nm. The correlation between the PA absorption spectra of the samples and their total phenolic content was found. The phenolic content of the samples was linearly associated with its normalized PA signal at 475 nm (De Oliveira et al.) [17]. | Brazil |
| Maize (Zea mays L.) | The seeds used were three: crystalline white maize, crystalline yellow corn, and floury blue maize. | 300–800 | Xe lamp
P = 700 W
(chopper, 17 Hz) | 350 | Statistical analysis | It was indicated, the main absorption center was found at 350 nm of wavelength, and it was associated to the presence of flavonoids and flavonols. At 470 nm, the absorption centers could be due to the presence of carotenoids, and at 650 nm, the absorption centers are associated mainly with the presence of anthocyanins (Domínguez-Pacheco et al.) [46]. | Mexico |
| Maize (Zea mays L.) | Prior to the study, the seed lot was standardized in size and color. | 270–500 | Xe lamp
P = 700 W
(chopper, 17 Hz) | 350 | Statistical analysis | The optical absorption coefficient of two growing regions in Mexico was found to have a similar behavior in all grains (Rodríguez-Páez et al.) [62]. | Mexico |
| Maize (Zea mays L.) | The seed varieties used were crystalline and floury. | 325–700 | Xe lamp
P = 700 W
(chopper, 17 Hz) | 350
650 | Variance analysis | From the photoacoustic signal, the optical absorption coefficient (β) and optical penetration length (lβ), both as a function of the wavelength, were measured, identifying differences between the floury and crystalline seeds β value at 650 nm (Hernández-Aguilar et al.) [63]. | Mexico |
| Maize seed (Zea mays L.) | The seed genotypes had bluish pigmentation. | 330–800 | Xe lamp
P = 1000 W
(chopper, 17 Hz) | 450 | Phase resolved | PA signal phase can be used to characterize layers at different depths. The authors reported the optical absorbance spectra at different light modulation frequencies and compared these spectra with the ones obtained from the phase-resolved method in order to separate the optical absorption spectra of seed pericarp and endosperm. Absorption band in the range of 550–750 nm is attributed to anthocyanins in the aleurone layer (Hernández-Aguilar et al.) [47]. | Mexico |
| Curcuma curry mustard | The samples were placed in the photoacoustic cell without previous preparation. In the case of mustard, it was placed on filter paper. | 280–700 | Xe lamp
P = 700 W
(chopper, 17 Hz) | 290–540
318, 345, and 535 | First derivative | The curcuma and “curry” have a higher optical absorbance spectrum obtained by PAS when compared to the optical absorption spectrum of mustard at the range of 300 to 670 nm. The maximum absorption peaks in the samples evaluated from calculating the first derivative of the absorbance spectra were found at 318, 345, and 535 nm (Hernandez et al.) [64]. | Mexico |
| Chili pasilla peppers (Capsicum annuum L.) | Pasilla chili peppers were studied in three different stages: green, red, and dried. | 300–800 | Xe lamp
P = 1000 W
(chopper, 17 Hz) | 330,354, and 367 | None | The photoacoustic signal was directly proportional with the wavelength. Absorbance spectra qualitatively show that the green stage is richer in flavonoids and that decrease and degrade as the peppers ripen (Barrientos-Sotelo et al.) [65]. | Mexico |
| Malting barley seeds | The seeds were photosensitized by soaking them for one hour in methylene blue. | 400–700 | Xenon lamp
P = 700 W
(chopper, 17 Hz) | 575 | Statistical analysis | By photoacoustic spectroscopy, it is possible to obtain the optical absorption coefficient of barley seeds at different conditions: in natural color and dyed with methylene blue. Also, it is possible to define the optical range where the samples are optically opaque or optically transparent (Pérez Reyes et al.) [66]. | Mexico |
| Maize grains (Zea mays L.) | Grains were obtained from the central part of the ear of corn for each variety; blue maize and yellow maize were used. | 325–800 | Xe lamp
P = 700 W
(chopper, 17 Hz) | 348, 502,623, 671, etc. | First derivative | Both varieties show distinct maxima absorption peaks, which correspond to zero values in the first derivative of β (optical absorption coefficient). For the blue maize grain, maximum absorption peaks were observed at (348, 502, 623, and 671) nm. In the case of the yellow maize grain, maximum absorption peaks were observed at 392 nm and 505 nm (Molina et al.) [50]. | Mexico |
| Dutch-processed cocoa powder | Grating chocolate samples was the only preparatory step required. | 300–650 | Xe lamp
P = 1000 W
(chopper, 17 Hz) | No peaks | Standard deviations, correlation | The obtained spectrum features no characteristic peaks in the investigated wavelength range. There is a trend of decreasing PA signal with increasing wavelength based on the shape of spectrum (Dóka et al.) [67]. | Hungary, Netherlands |
| Beans (Phaseolus vulgaris L.) | The varieties used were cultivated during the spring-summer agricultural cycles of the years 2002, 2001, 2006, 2002, and 2006 in different regions of Mexico | 350–750 | Xe lamp
P = 700 W
(chopper, 17 Hz) | 350–450 | Variance analysis | β decreases with increasing wavelength, being reported the highest absorbance band in a range of 350–450 nm. Significant statistical differences were found between the photoacoustic signals obtained from each variety of beans at 408 nm (Sanchez-Hernandez et al) [68]. | Mexico |
| Maize (Zea mays L.) grains | Corn adjusted to a size: diameter and thickness of 6 and 3 mm, respectively. | 325–800 | Xe lamp
P = 700 W
(chopper, 17 Hz) | 350 | Analysis of the variance, first derivative | The spectrum reported by the authors presented the highest absorbance band in a range of 325–400 nm (Molina et al.) [48]. | Mexico |
| Lyophilized apricots (Prunus armeniaca L.) | The fruit of seven apricots were examined at 80 % of their commercial maturity, and sample volume was of 0.25 cm3. | — | Xe lamp
P = 1000 W
17 Hz | 470, 450 | Standard deviations, correlation | PAS appears to be the most favourable technique to determine total carotenoid content, among others (Dóka et al.) [69]. | Hungary
Croatia
Netherlands
Belgium |
| “Tortillas” | The samples were homogenized in color and sizes, ordering the measurement, same side of the “tortilla”. | 350–700 | Xe lamp
P = 700 W
(chopper, 17 Hz) | 360–400 | Analysis of variance and model of Paulet and Chambron (1979) | The authors indicate that PAS was able to find the optical absorption coefficients (β) of colors of different tortillas from the photoacoustic signals amplitude and using the Rosencwaig and Gersho model. PAS is simple to use, requires only a small quantity of sample for analysis, and involves a minimum preparation (Hernández et al.) [55]. | Mexico |
| Maize (Zea mays L.) | The seeds were homogenized in terms of size, shape, and color and dimensions adjusted to the size of the PA cell (6 mm, diameter). | 320–700
620–700 | Xe lamp
P = 700 W
and modulated
(chopper, 17 Hz) | 350–390
Metil red: 450–
590 | Model of Rosencwaig and Gersho test Tukey | PAS was considered as a potential diagnostic tool for the characterization of the seeds, and it was possible to find the optical absorption coefficient β for maize seeds. In addition, conventional reflectance measurements (obtained with the integrating sphere) were performed to validate PAS absorption measurements. The results show that the absorbance spectra and reflection data of the seed samples are complementary (Hernández-Aguilar et al.) [70]. | Mexico |
| Coffee grains (adulterated) | The beans were roasted (210°C) during a time of 6 to 7 min. The adulteration was carried out, adding beans and barley. | 300–800 | Xe arc lamp
P = 1000 W
(chopper, 17 Hz) | 300–450
700–800 | Derivatives and differences | The photoacoustic technique allows spectroscopic studies of adulterated coffee from a direct analysis of solid samples of coffee powder, barley soya, and beans. Significant differences are observed, in terms of form, between 300 and 450 nm, where the behaviour of the carotenes and β-carotenes change as the adulterant (bean) is added. Similarly, the region of 700 to 800 nm corresponding to the absorption of the alkaloid “caffeine,” is also attenuated (Salcedo et al.) [71]. | Colombia |
| Dried pastas | Pastas prepared with different amounts of eggs were studied | 400–550 | Xe lamp
P = 1000 W
(chopper, 17 Hz) | 470 | Correlation
Regression | PAS can be proposed as a new analytical tool for a rapid screening/control of the total carotenoid concentration in pastas (Dóka et al.) [72]. | Hungary, Netherlands
Croatia |
| Dyes in commercial products: brilliant blue (B), sunset yellow (S), and tartrazine (T) | Solutions of gelatine powder (peach and lemon flavors, dissolved in hot water) and juice powder (citrus fruit flavor, dissolved in water,) were used. | 350–750
350–550
350–600 | Xe arc lamp
P = 800 W
(chopper, 20 Hz) | 600–680
380–490
430–540
620, 510, 452 | Deconvolution from Gaussian | Photoacoustic spectroscopy allowed the simultaneous determination of brilliant blue, sunset yellow, and tartrazine as binary mixtures in gelatin and juice powders, with a very good agreement between the values determined by using first derivative spectrophotometry. The PAS technique can be applied for the determination of the selected dyes in commercial food products (Coehlo et al.) [16]. | Brazil |
| Acai (Euterpe oleracea) seeds | C. gloeosporioides fungus-infected acai seed samples were used as small pastilles 6 mm in diameter and 1 mm in thickness to standardize its form. | 250–1000 | Xe arc lamp
P = 150 W | 300–350
650–900 | Fit to the data when they were obtained as a function of frequency | Differences between the photoacoustic spectra of the infected seed were found. Superior PA spectral curve was for the sample (treated), intermediary PA spectral curve is for sample (with fungus scraps), and inferior PA spectral curve is for sample (fungus infected). Characteristics peaks and bands were observed in the range from 650 to 900 nm ascribed to organic compounds with carboxylates and amines (functional groups) forming the typical metabolic structures of the fungus (Rezende et al.) [73]. | Brazil |
| Maize (Zea mays L.) | The seeds used were of the following colors: white, yellowish, and bluish. | 600–710
500–750 | Xe lamp
(chopper, 17 Hz) | 650 | Statistical analysis | PAS technique demonstrated to be a useful for the study of the effects in liquid chlorophyll of seedling leaves which came from irradiated maize seeds. The bluish-colored seed had the highest optical absorption coefficient and a negative laser light response, when it was treated before sowing (Hernández-Aguilar et al.) [74]. | Mexico |
| Wheat grains (Triticum aestivum L.) | Wheat seeds from different productive cycles and measured area of 4 × 6 mm were used without prior preparation. | 350–800 | Xe lamp
(chopper, 17 Hz) | 350 | None | Photoacoustic spectrum decreases as a function of the frequency, and differences are obtained in the spectra of the deteriorated and nondeteriorated grain, where the authors reported lower optical absorption in the young seed when compared with the older one due to deterioration in the older seed because of the presence of fungi or bacteria during storage, and this fact produces dark regions and, as a consequence, a higher optical absorption (Pacheco et al.) [51]. | Mexico |
| Wheat | Two seed conditions were used: treated with methylene blue and untreated. | 600–700 | Xe lamp
P = 1000 W
(chopper, 17 Hz) | 650 | Statistical analysis | The PA spectroscopy was demonstrated as a suitable technique to study the optical absorption coefficient β of wheat seeds with and without photosensitizer (Hernández-Aguilar et al.) [75]. | Mexico |
| Maize (Zea mays L.) | Maize seeds were irradiated by a diode laser. | 400–500 | Xe lamp
P = 1000 W
(chopper, 17 Hz) | 471–478 | Statistical analysis | The PA method was demonstrated as a technique capable of studying the effect caused by irradiation (diode laser radiation at 650 nm) of maize seeds. PA signals were related in the range of 471 to 478 nm with β-carotene and lutein, the natural pigments present in the seedling leaf of maize (Hernández-Aguilar et al.) [76]. | Mexico |
| Coffee | Organic and conventional green coffee beans were used. | 300–800 | Xe arc lamp
P = 1000 W | 432–718, 725–740, 743–772 | Derivative subtraction and ANOVA | Statistical differences were found between certain ranges of wavelength of the spectra of each type of coffee. The PAS technique allows a spectroscopic analysis of organic opaque samples (Delgado et al.) [77]. | Colombia |
| Water | PA spectrum were recorded under the laboratory conditions (T =−10°C, P = 3.5105 Pa). | 200–1100 | Xe arc lamp
P = 500 W | 226, 244, 289, 302, 326, 744,844, 920,974 | None | The distilled water is transparent between the wavelengths 326 to 920 nm. The strong absorption peak was found at the wavelength 226, 289, and 974 nm (Kapil et al.) [78]. | India |
| Corn (seedlings) | Irradiated seeds presowing with laser diode. | 600–700 | Xe lamp
1000 W
(chopper, 17 Hz) | 650, 680 | Statistical analysis | Significant statistical differences were found in the amplitude of the photoacoustic signal when seedling leaves from irradiated seeds were measured, comparing the points corresponding to chlorophylls “a” and “b,” i.e., at 680 and 650 nm (Hernández et al.)[79]. | Mexico |
| Coffee | The coffee roasting was done in a temperature range between 200 and 210°C. | 510–775 | Halogen lamp
P = 1000 W | 630 and 670 | Second derivative | The amplitude of the PA signal contained several absorption centers; in this case, those corresponding to the chlorophyll pigments were identified. To identify them more clearly, the criterion of the second derivative was used (Delgado et al.) [80]. | Colombia
Mexico |
| Red sorghum (Sorghum bicolor L.) flours | Grains were surface-sterilized by washing and stirring them in a 5% aqueous solution of sodium hypochlorite, later the grains were dried. | 250–550 | Xe lamp
300 W
(chopper, 16 Hz) | 285, 335 | Correlation | PA spectra show two characteristic bands: the first one (centered at 285 nm) is due to aromatic amino acids in sorghum flour, while another, close to 335 nm, is due to the flavonoids and phenolics acid present in the pericarp of sorghum flour. The PA signal decreases with increasing wavelength across the entire spectral range studied (Dóka et al.) [53]. | Hungary
Netherlands |
| Water, hexagonal ice, and snow | Snow (surface hoar) was prepared in the laboratory by injecting warm moist air plus water vapor in a cold chamber. | 200–1100 | Xe arc lamp
P = 300 W | 320, 971–974 | None | PA spectrum of distilled water shows a strong absorbance in the ultraviolet UV region below 320 nm and another strong absorbance maxima at the wavelengths 971–974 nm, in the near infrared NIR region. Between the wavelengths 320–922 nm, distilled water is transparent. In general, the overall PA signal strength is greater in ice as compared to snow (Kapil et al.) [81]. | India |
| Mango | None | 200–400 | Xe arc lamp
P = 1000 W | 220, 250–280, 330–370 | None | Indicated the presence of three bands at ∼ 220, 250–280 and 330–370 nm in good agreement with conventional optical absorption spectrum attributed to the flavonoid type of biomolecules called quercetin (Lima and Filho) [56]. | Brazil |
| Wheat and rice (pathogens) | Spores were extracted from the infected seeds. | 200–800 | High-pressure Xe lamp
P = 300 Watt | 232, 292, 372, 552, 652, 272, etc. | None | The authors show that PA spectroscopy is a suitable nondestructive technique for distinguishing pathogens of different genera and species. This technique proved useful for differential diagnosis of various seed-borne pathogens of wheat and rice (Gupta et al.) [82]. | India |
| Milk (fresh and oxidized) | The whole milk powder of different compositions (composition: 27% fat, 26% protein, 5% water, 36% lactose, and 6% ash) was used and was oxidized by exposing it to UV radiation and heat in the presence of air. | 250–500 | Xe lamp
300 W
(20 Hz) | 290
320–360 | Correlation | The authors indicated that PAS is a method for routine and rapid assessment of peroxide value in oxidized whole milk powder. Absorbent peaks were found at 290 nm associated with the presence of aromatic amino acids in the milk powders. Spectral changes by oxidation were in 320–360 nm (Dóka et al.) [41]. | Hungary
Netherlands |
| Pericarp of maize (Zea Mays L.) | The material evaluated was obtained of maize grain nixtamalized. | 300–700 | Xe lamp | 400–450 | Spectrum differences | The optical absorbance spectra reveal the presence of flavonoids in the pericarp which are sensitive to the action of alkaline cooking and which are characterized by an absorbance band between 400 and 450 nm that provide the characteristic coloring yellowish to these biopolymers (Hernandez et al.) [83]. | Mexico |
| Pericarp of maize (Zea Mays L.) | Cooked corn was used from which the pericarp was extracted to evaluate it. | 300–700 | Xe lamp
(chopper, 17 Hz) | 300–350
375–450 | Spectrum differences | Absorbance spectrum in the region of 300–800 nm in these films is constituted by the superposition of two absorbent centers: one corresponding to the absorption in the UV region of 300–350 nm for cellulose in the epidermis and the other in the region of 375–450 nm corresponding to the pigments present in the pericarp that are sensitive to an alkaline medium (Hernández et al.) [84]. | Mexico |
| Skimmed milk powder and whey powder | Pure skimmed milk and whey powders; mixtures were made at 5, 7.5, 10, 15, and 20%. | 300–600 | Xe Lamp
P = 450 W
Modulation Frequency, 30 Hz | 370 | Subtraction correlation | The unknown amount of foreign whey powder can then be determined from a previously made calibration curve by PAS. So, is useful for detection of adulterated milk by whey powder (Dóka et al.) [40]. | Hungary
Netherlands |
| Pb304 adulterant in ground sweet red paprika (Capsicum annuum) | The amount of Pb304 in mixture was 0.5, 1, 2, and 2.5 g. | 320–700 | Xe lamp
300 W
(chopper, 54 Hz) | 545 | None | Demonstrated that the PAS as potential technique to identify samples adulterated with lead tetraoxide (Dóka et al.) [43]. | Hungary
Netherlands |
| Paprika (Capsicum annuum) seasoning products of paprika | Pericarps of red, yellow, and green ripe paprika were dried and made powder to be evaluated. | 200–800 | Xenon arc lamp
P = 1 KW | 220–550
540 | Histogram | The spectrum of yellow paprika reveals in the visible region four absorptions, two maxima at 411 and 435 nm and two shoulders at about 442 and 483 nm. The maximum at 411 nm can be attributed to the absorption of capsorubin, whereas the predominance of the yellow-colored carotenoids in diverse concentrations determines the maximum at 435 nm (zeaxanthin and cryptoxanthin) and the absorption at 442 nm (β-carotene, zeaxanthin, and lutein). The red pigments capsorubin and capsanthin are responsible for the absorption at 540 nm (Vinha and Haas) [85]. | Germany |
| Eggs | Egg powders irradiated by 60Co (0, 2.5, 5, 10, and 20 kGy). | 240–530 | Xe lamp
300 W
(chopper, 56 Hz) | 275, 480 | Correlation | Points out that the PAS technique has possibilities to evaluate the changes due to irradiation in egg powders (Dóka et al.) [42]. | |
| Strawberries | Strawberries of different stages of maturity were used and selected according to their size and color, ranging from white (unripe) to dark red (overripe). | 250–750 | Xe arc lamp
P = 1000 W
47, 107, and 190 Hz
Light intensity = 139 W·m−2 | 510
278 | Fitted curve | The authors demonstrate the potential of photoacoustic spectroscopy in the assessment of the maturity of strawberries using the spectral ratio of anthocyanin and protein bands. It is worth noting that it is a direct and nondestructive technique that might be extended to other horticultural crops (Bergevin et al.) [57]. | Canada |
| Annatto | Extracts of pigments were obtained by applying soybean oil or acetone as solvent. | 200–1200 | High-pressure Xe arc lamp
P = 1000 W | 260
442, 467, and 498 | Fitted curve | The absorbance peaks at 442, 467, and 498 nm were assigned to bixin in solution, whereas the peak at about 260 nm was mainly due to the absorbance of soybean oil (Haas and Vinha) [86]. | Germany |
| White bread flour, rye flour, soya flour, and dried pea flour | Samples of different colours were used: white, yellow, green, and brown. | 350–700 | Xenon lamp | 370, 385,410, and 475 | None | Indicated discrimination of different flours based on origin, color, and grain size is possible; they suggested its usefulness for quality control purposes (Favier et al.) [52]. | Netherlands
Hungary |
| Milk protein | Milk protein concentrates containing ferrogluconate at 27, 136, 1230, and 12000 ppm were used. | 300–700 | Xe lamp
P = 1600 W
(chopper, 30 Hz) | 348, 380, and 552 | Model Rosencwaig and Gersho | The authors demonstrated that PA measurements (range visible light) on milk protein concentrates are capable of determining Fe content in the form of ferrogluconate (Dóka et al.) [39]. | Hungary |
| Corn (Zea mays L.) | Specimens were exposed to different concentrations of aluminum. | 350–800 | Xe arc lamp
P = 1000 W
20 Hz | 680 | None | It was found that the most of the spectral differences lie in the region dominated by the chlorophyll band, with a maximum at 680 nm (Marquezini et al.) [87]. | Brazil |
| Bean plants (Phaseolus vulgaris L. cv. Fori GS) | Bean leaves were treated with herbicides. | 380–720 | High-pressure Xe lamp
P = 450 W
Modulation frequency of 22 Hz | 475, 675 | Statistic analysis | The photoacoustic spectrum of bean leaves was decreased with the use of herbicides. When the leaves were immersed in paraquat, the ratio of the photoacoustic signals, PA67S/PA475, decreased significantly. Benzonitrile and diuron also decreased the intensity of the photo acoustic spectrum. The changes induced by benzonitrile were less obvious than those induced by diuron. (Szigeti et al.) [88]. | Hungary |
| Milk powder | The PA measurements were performed at room temperature T = 298°K. | 200–630 | Xe lamp
1000 W
(chopper, 20–1000 Hz) | 280 | None | PA spectra of tablets of milk powder showed one peak at 280 nm corresponding to the absorption of proteins and a smaller band in the visible (400–500 nm) that might be assigned to milk carotenoids (Nsoukpog-Kossi et al.) [38]. | Canada |
| Skimmed milk, partly skimmed milk (2% fat), whole milk (3.25% fat), and other milk products | Cheddar cheese was placed in the photoacoustic cell in the form of a small disc 14 mm in diameter and 1 mm thick. For the other products, a small quantity was put in filling the cell. | 250–440 | Xe arc lamp
P = 1000 W | Fat absorption band: 250–260 protein peaks 280 | Substraction of spectrum | The authors demonstrated the possibility of using photoacoustic spectroscopy for milk product analysis (Martel et al.) [30]. | Canada |
| Glycine max | The sample used was an intact leaf cut in the form of discs of 5 mm diameter. | 300–800 | Xe arc lamp
P = 1000 Watts
MF = 25 Hz | 450, 680 | Phase-resolved | It was proposed that photoacoustic spectroscopy is an important tool for the investigation of insoluble plant components. The author reported the spectrum of the leaf with the characteristic absorbance bands of the waxy cuticle, carotenoids, and chlorophyll (Nery et al.) [89]. | Brazil |
| Green coffee | Coffee beans freshly ground and roasted and compacted into a disk-shaped sample chamber in the PA cell holder were used. | 340–610 | Xe lamp
P = 400 W
30 Hz | 360 nm | None | Photoacoustic spectroscopy was proposed as possible nondestructive alternative for in situ assessment of water-soluble compounds in green or roasted coffee beans (Reis et al.) [90]. | Brazil |
| Seedlings of maize mutants | Samples were cut immediately before placing them in a photoacoustic cell. | 300–800 | Xe lamp
P = 450 W
32 Hz | 320 | Deconvolution | Photoacoustic spectroscopy was proposed as a simple, direct, nondestructive alternative for both qualitative and quantitative assessment of plant mutations. It is a method important to the resources available to the plant geneticist (Lima et al.) [91]. | Brazil |
Flower petals
Blue larkspur
Red poppy petal | None. | 380–750 | MF = 500 Hz | 380–420
and
500–650
400–580 | Scattered transmisión
Diffuse reflectance
Transmision | The results indicated coincidences in the spectra obtained with all the techniques used, coinciding in all with the wavelength of the maximum peak of the signal (Li et al.) [92]. | China |
| Leaves (species of Euphorbia) | The twigs of these plants were cut under water, washed in distilled water, and the leaves were dried (purple pigmentation in leaves). | 400–740 | Spectrometer model 6001 (EG & G)
Modulation frequency = 40 Hz | 545, 675 | Average | The photoacoustic absorbance spectra presented absorbent centers at 545 and 675 nm, which were related to anthocyanins and chlorophylls (Veeranjaneyulu and Das) [93]. | India |
| Wheat lignin | Twigs of plants were cut under water, washed in distilled water, and the fresh wheat stems (culms) were obtained from mature, presenescent plants raised in growth chambers. Small sections of wood and field-dried culm were washed. | 250–450 | Xe lamp
P = 1000 W
Modulation frequency = 150 Hz | 350 | None | It was proposed that photoacoustic spectroscopy is an important tool for the investigation of insoluble plant components. Absorbance bands in the 300 to 400 nm region may be attributable to chemically modified or degraded lignin components resulting from natural aging of the polymer. Chemical modification of lignin is known to occur when lignocellulosic materials are exposed to near-UV light (Gould) [94]. | USA. |
| Lettuce (chloroplast membranes) | The chloroplast suspension was adsorbed on cotton wool and measurement. | 400–720 | Xe arc lamp
P = 450 W
770 and 72 Hz | 580, 680 | Normalized | The authors related the chlorella component at the wavelength of 580 nm, and the highest absorbance peak of the obtained spectrum was found at 680 nm (Cahen et al.) [33]. | Israel |
| Spinach | Spinach leaf of 10 mm in diameter were cut and mounted on the support plate. | 250–700 | Xe Lamp
P = 1000 W | 450, 650 | Differentiation | The author demonstrated that the major absorbing components in the spinach are the chlorophylls. The chlorophylls are similar to the haemoproteins and contain a porphyrin ring, this being chelated to magnesium at the ring center (Adams et al.) [34]. | England |
| Green leaf | — | — | -— | — | — | Rosencwaig found Soret band at 420 nm, the carotenoid band structure between 450 and 550 nm, and the chlorophyll band between 600 and 700 nm [29]. | USA |
| Marine algae | — | — | — | — | — | PAS can reduce the amount of material required and could reduce the time required for the identification of plant species (Rosencwaig and Hall) [32]. | |
Black-eyed susan
Red rose petals | — | 200–800 | Xe Lamp
P = 4200 W | 340, 530 | None | Two maxima peaks are found: the first is due to cyanine (530 nm) absorption in the flower, and the second at 340 nm is due to some other ultraviolet-absorbing compound in the red rose petal. In the blackeyed susan, the base of the flower petal is rich in ultraviolet- absorbing flavanol glucosides. The technique can give useful information about photochemistry (Harshbarger and Robin) [30]. | USA |
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