Fermentation performance and nutritional assessment of physically processed lentil and green pea flour

Authors: BYANJU, BIBEK - Iowa State University; Hojilla-Evangelista, Milagros - Mila; LAMSAL, BUDDHI - Iowa State University

Submitted to: Journal of the Science of Food and Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/25/2021
Publication Date: 3/31/2021
Citation: Byanju, B., Hojilla-Evangelista, M.P., Lamsal, B.P. 2021. Fermentation performance and nutritional assessment of physically processed lentil and green pea flour. Journal of the Science of Food and Agriculture. https://doi.org/10.1002/jsfa.11229.
DOI: https://doi.org/10.1002/jsfa.11229

Interpretive Summary: The demand for plant-based proteins has risen exponentially in the alternative proteins market; however, for legumes (for example beans, peas, soybeans), the presence of antinutritional factors (ANF, compounds that diminish the nutritional quality of the food) is one of the obstacles for their widespread acceptance as food ingredient. Fermentation is a low-cost processing technology that can reduce ANF and enhance the nutritional and quality aspects of food ingredients. A physical technique that is gaining popularity in the food processing industry is high-power sonication (applying sound wave energy), which causes cellular breakage that improves the extraction of proteins, sugars, and other nutrients and will impact fermentation. In this research, we found that applying high-power sonication or precooking the legumes before fermentation reduced some ANF in green pea, lentil and soybean flours, which in turn, improves protein availability. In the current work, we first precooked green peas, lentils and soybeans and then ground them into flour or milled the beans into flour and then sonicated each flour at low or high power before subjecting all the treated samples to fermentation by two common probiotic bacteria. We found that both untreated and treated (precooked or sonicated) flours of soybean, green pea, and lentil supported the growth of the probiotic bacteria during fermentation. We also found that precooking and sonication before fermentation notably reduced the amounts of the ANF in the resulting products. Our results demonstrated that precooking or sonication combined with fermentation are effective techniques for decreasing ANF in legume flours, which can lead to improved protein nutritional quality. This research is useful to food ingredient processors and academic and industry researchers for designing efficient ANF removal methods that consequently broadens the uses of plant-based proteins.

Technical Abstract: A significant amount of nutrients, including dietary fibers, proteins, minerals, and vitamins are present in legumes, but the presence of anti-nutritional factors (ANFs) like phytic acid, tannins, and enzyme inhibitors impact their availability. These ANFs could be reduced or modified with physical/ biochemical processes, for example, extrusion, sonication, and fermentation. In this research, the effect of a combination of a physical process (sonication or precooking) 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 ratio (substrate: water) and fermented. Physically modified flours were inoculated with Lactobacillus plantarum and Pediococcus acidilactici at 108 CFU/mL and fermented in shake flasks for 72 h at 37°C, and 200 rpm. The microbial growth and pH were measured at 6, 12, 24, 48, and 72 h. The pH dropped from 6.5 to 4.5 during the initial 24 h and microbial growth reached around 1013 CFU/mL at 24 h. The population doubling time for L. plantarum was shortest on precooked green pea flour (0.94 h) and longest on 4 min sonicated green pea flour (2.46 h). Similarly, the doubling time for P. acidilactici was the least for precooked lentil (0.9 h) and greatest for 2 min sonicated green pea flour (1.36 h). Total phenolic contents were significantly (p<0.05) reduced for all physically modified and fermented substrates compared to non-fermented controls. Trypsin inhibitory activity (TIA) was reduced significantly for all the substrates except for unsonicated soybean and lentil fermented with L. plantarum and P. acidilactici. When physical processing was done, there was a decrease in TIA. Phytic acid content decreased for physically modified soybean and lentil but not significant for green pea. Even though there was a decrease in ANFs, there was no significant change in in vitro protein digestibility for all substrates except for unsonicated L. plantarum fermented soybean flour and precooked L. plantarum fermented lentil.