Sonication assisted protein extraction from some legumes, and improvement of nutritional profile of ingredients through fermentation

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Byanju, Bibek
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Buddhi Lamsal
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The conventional protein extraction method uses alkali method by modulating pH in the range of 8.5- 9; however, the presence of cell wall, other polysaccharides, and location of protein inside the cell-matrix limits its extraction resulting in the recovery of approximately half of the available proteins. Several pretreatment or physical modification can be utilized to improve protein extraction. The present study aimed to apply physical modification such as high-power sonication and extrusion. Two studies were carried out: firstly, high-power sonication (HPS) was used as a pretreatment to improve the extraction of proteins and their effect on the physicochemical property was studied. Secondly, fermentation was used to improve the nutritional profile of physically modified (HPS and extrusion) legume-protein ingredients.The impact of high-power sonication as a pretreatment on the extraction of proteins from soybean flakes, and flours from soybean, chickpea, and kidney bean, and changes in physicochemical properties were evaluated. The substrates were dispersed in distilled water (1:10 w/v) and sonicated at two power densities (PD) of 2.5 and 4.5 W/mL for 5 min continuously. Proteins were extracted at pH range 8–8.5. PD 2.5 and 4.5 W/mL significantly increased protein extraction yields from soy flakes to 29.03% and 25.87%, respectively, compared to 15.28% for unsonicated, but did not increase for flours. Free sulfhydryl content for both sonicated and unsonicated soy flakes and flour were similar but increased in proteins from chickpea and kidney bean when HPS of 4.5 W/mL was applied, indicating the unfolding of protein structure. The protein band patterns for sonicated and unsonicated legumes proteins were found to be similar, indicating no peptide profile alterations by HPS. However, circular dichroism analysis showed changes in secondary structure composition in extracted kidney bean protein causing unfoldingxiiand destabilizing the native structure, but it remained unaffected for soy flakes and flour protein and chickpea protein.Legumes are rich sources of protein, carbohydrates, dietary fibers, and minerals, but their utilization has been limited because of several anti-nutritional factors (ANFs) and lower protein digestibility. To reduce the ANFs, physical modification of the substrates along with subsequent fermentation by L. plantarum and P. acidilactici were evaluated in the second study.ANFs like phytic acid, tannins, and enzyme inhibitors impact the availability of nutritional compounds and can be reduced or modified with physical/ biochemical processes, for example, extrusion, sonication, and fermentation. In this study, the effect of a combination of physical treatments (sonication/extrusion) and fermentation on some legume ANFs was evaluated. Flours of soybean, lentil, and green peas were sonicated for 2 and 4 min (power density ~ 2.5 W/mL) at a 1:8 (w/v) ratio (substrate: water) and fermented. Physically modified flours were fermented with probiotic bacteria namely Lactobacillus plantarum and Pediococcus acidilactici in shake flasks for 72 h at 37°C, and 200 rpm. All the substrates, modified and unmodified, effectively supported microbial growth which reached a peak of around 1013 CFU/mL at 24 h. Trypsin inhibitor activity (TIA) was reduced significantly for all the substrates except for unsonicated soybean, and lentil fermented with both microbes. TIA decreased when physical processing was done. Phytic acid content decreased notably for physically modified soybean and lentil but not for green pea. Total phenolic contents were significantly (p<0.05) reduced for all physically modified and fermented substrates compared to non-fermented controls. Even though there was a decrease in ANFs, there was no significant change in in vitro protein digestibility.

Fri May 01 00:00:00 UTC 2020