Abstract
The aim of this work was to hydrolyze kidney bean (Phaseolus vulgaris L.) protein isolate (KBPI) using pepsin (P7000) to obtain kidney bean protein hydrolysates (KBPH) with different degrees of hydrolysis (DH). Antioxidant and antibacterial activities of KBPH against selected pathogenic and spoilage bacteria were evaluated. In addition, applying KBPH as a potential preservative in minced beef during cold storage was studied. The extent of protein degradation by pepsin was determined by measuring DH and SDS-PAGE. KBPH obtained after 6 h of hydrolysis had the highest DH (33.7%), while KBPH obtained after 1, 2, 3, 4 and 5 h had DH values of 11.6, 15, 20.7, 25.6, and 30, respectively. The highest antiradical activity of KBPH (85% for DPPH center dot and 80% for ABTS(+) assay) was recorded after 6 h of hydrolysis. The hydrolyzate with the highest antibacterial activity (DH = 33.7%) was selected for the antibacterial evaluation in situ and in vitro. The antibacterial activity of KBPH (100 mg/mL) with a different degree of hydrolysis on bacterial growth was evaluated using the disc-diffusion method. KBPH reduced the growth of gram-positive bacteria by 70-75% and the bacterial growth of gram-negative bacteria by about 78-80%. Total viable, psychrotrophic bacterial and coliform bacterial counts were determined in beef samples enriched with KBPH (100 and 200 mu g/g) during storage at 4 degrees C for 15 days. Samples supplemented with 200 mu g/g KBPH kept the level of the total viable count at 5.7 and 6.55 log after 12 and 15 days of storage, which increased the secured storage time to be 14 or 15 days instead of 7 or 8 days in the case of the control sample. The results could be useful to formulate functional peptides from KBPI that could be applied in novel foods and nutraceuticals.