Bioactive compounds in soybean proteins and its applications in food systems

Abstract

Soybean has been one of the most important sources of vegetable-sourced proteins. Soybean protein isolate was isolated, characterized, transformed into methylated soybean protein (basic and hydrophilic nature) by esterification with methanol in the presence of hydrochloric acid (50 molar ratio), and tested for their antibacterial activity against pathogenic and spoilage bacteria. Alternatively, glycinin, basic subunit, and β-conglycinin were isolated from soybean protein and tested for their antimicrobial action. Supplementing raw milk with esterified soybean protein (0.5%) reduced the titratable acidity to 0.21, maintaining its pH at 6.4 after 8 days of cold storage compared to 4 days for untreated milk. Similar action was observed when raw milk was stored at room temperature for 10 h. Adding glycinin and the basic subunit to pasteurized milk inoculated with the three bacteria L. monocytogenes, B. subtilis, and S. enteritidis (ca. 5 log CFU/mL) could inhibit their propagation after 16–20 days storage at 4°C by 2.42–2.98, 4.25–4.77, and 2.57–3.01 log and by 3.22–3.78, 5.65–6.27, and 3.35–3.72 log CFU/mL, respectively. The antifungal activities of soy protein fractions glycinin and β-conglycinin against the pathogenic fungus Penicillium digitatum, either in vitro or in situ (postharvest orange fruit), were evaluated and compared with the fungicide rhizolax. These results suggest that a soy protein fraction containing mainly β-conglycinin can be used as an effective environmentally friendly fungicidal agent against postharvest fungal infections. Native and modified soybean fractions can be used to control the undesirable bacteria and fungus in food improving its safety.