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Soybean Processing for Soymilk and By-product Utilization using Membrane Technology.

Vishwanathan, K. H. (2012) Soybean Processing for Soymilk and By-product Utilization using Membrane Technology. Doctoral thesis, University of Mysore.

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Abstract

The investigation was focused on developing an efficient protocol for the extraction of soymilk and effective utilization of its by-products, besides improving the understanding on the critical process steps involved. Wet grinding of hydrated soybean was carried out with mixer grinder, stone grinder and colloid mill which revealed that particle size had a profound effect on the protein recovery in the extracted milk. Greater particle size reduction was achieved with mixer grinder and colloid mill owing to the type of predominant grinding forces involved (cutting and shearing) compared to stone grinder (compressive). Examining the suitability of classical Kick’s, Rittinger’s and Bond’s laws developed for dry grinding revealed that they are applicable after the initial break up during wet grinding of soybean. During wet grinding, linoleic acid oxidizes in the presence of air catalyzed by lipoxygenase and the reaction products cause objectionable beany or grassy flavour. Although lipoxygenase can be easily inactivated by thermal means, it leads to reduced protein solubility and recovery. In the present study, inactivation of lipoxygenase has been attempted by grinding at low and high temperatures, and employing a chelating agent (curcumin). These approaches showed varying degree of success and grinding soaked bean at 70 °C along with emulsified curcumin was the most effective approach in inactivating lipoxygenase to the extent of 95%, along with a matching protein recovery of 87% to that of conventional hot extraction. Besides, the fortified soymilk obtained in the process exhibited greater polyphenolic and antioxidant activities, and reduced hexanal content signifying the multiple benefits. Okara, a by-product obtained during processing soybean for soymilk is a rich source of protein, but underutilized. The high quality of protein suggests that protein concentrate/isolate could be produced from okara. Initial studies were focused to understand the influence of multi-step grinding on particle size and protein extractability. Protein recovery from unclassified primary ground soy granules and okara flakes was ~84%. Introduction of secondary grinding of coarse fraction helped to improve the overall protein recovery by 6.8% in soybean and 3.3% in okara, indicating the benefits of the proposed approach for practical applications. The potential of membrane technology has not been attempted for the recovery of okara proteins although it offers superior functional properties in the product over acid precipitation techniques. Studies conducted in a cross-flow membrane system using microfiltration (MF; pore size 200 and 450 nm) and ultrafiltration (UF; MWCO 50, 100 and 500 kDa) membranes to eliminate non-protein impurities improved the protein content from 68% to 81%. Although, normalized flux in MF-450 (117 LMH/MPa) was close to UF-500 (118 LMH/MPa), the latter was selected based on higher average flux (47 LMH) offering the advantage of reduced processing time. However, the final protein content in okara (~80%) did not reach the target value of protein isolate (90%) unlike in the case of soy extract, owing to the greater presence of soluble fibres that were retained by the membrane. Tofu-whey generated in large volumes during coagulation of soymilk carried away ~37% of bean polyphenols including isoflavones. Ultrafiltration (100 kDa) in diafiltration mode recovered ~82% polyphenols and ~86% isoflavones from tofu-whey while completely eliminating the true proteins. Nanofiltration (G10) of ultrafiltered-whey did not lead to concentration but resulted in isoflavones enrichment in the retentate with a 2-fold increase in its purity. Combination of UF and reverse osmosis (RO) processes eliminated the larger impurities and reduced the bulk of tofu-whey, facilitating further processing in to high purity products.

Item Type: Thesis (Doctoral)
Uncontrolled Keywords: processing soybean, soymilk, membrane technology
Subjects: 600 Technology > 08 Food technology > 22 Legumes-Pulses > 05 Soya bean
600 Technology > 08 Food technology > 05 Processing and Engineering
Divisions: Food Engineering
Depositing User: Food Sci. & Technol. Information Services
Date Deposited: 14 Nov 2013 10:53
Last Modified: 28 Aug 2018 06:16
URI: http://ir.cftri.com/id/eprint/11302

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