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Enzyme Research
Volume 2015, Article ID 573721, 10 pages
http://dx.doi.org/10.1155/2015/573721
Research Article

Immobilization of Papain on Chitin and Chitosan and Recycling of Soluble Enzyme for Deflocculation of Saccharomyces cerevisiae from Bioethanol Distilleries

1Department of Biological Science, University of State of São Paulo (UNESP), 19806-900 Assis, SP, Brazil
2Food Engineering Faculty, State University of Campinas (UNICAMP), 13083-970 Campinas, SP, Brazil

Received 3 September 2014; Revised 28 November 2014; Accepted 28 November 2014

Academic Editor: Denise Freire

Copyright © 2015 Douglas Fernandes Silva et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Yeast flocculation (Saccharomyces cerevisiae) is one of the most important problems in fuel ethanol production. Yeast flocculation causes operational difficulties and increase in the ethanol cost. Proteolytic enzymes can solve this problem since it does not depend on these changes. The recycling of soluble papain and the immobilization of this enzyme on chitin or chitosan were studied. Some cross-linking agents were evaluated in the action of proteolytic activity of papain. The glutaraldehyde (0.1–10% w·v−1), polyethyleneimine (0.5% v·v−1), and tripolyphosphate (1–10% w·v−1) inactivated the enzyme in this range, respectively. Glutaraldehyde inhibited all treatments of papain immobilization. The chitosan cross-linked with TPP in 5 h of reaction showed the yield of active immobilized enzyme of 15.7% and 6.07% in chitosan treated with 0.1% PEI. Although these immobilizations have been possible, these levels have not been enough to cause deflocculation of yeast cells. Free enzyme was efficient for yeast deflocculation in dosages of 3 to 4 g·L−1. Recycling of soluble papain by centrifugation was effective for 14 cycles with yeast suspension in time perfectly compatible to industrial conditions. The reuse of proteases applied after yeast suspension by additional yeast centrifugation could be an alternative to cost reduction of these enzymes.