Antioxidant Activity Of Milk Fermented With Lactic Acid Bacteria From Different Fruits

Bioactive peptides can be generated from milk protein by fermentation with lactic acid bacteria (LAB). In this study LAB were isolated from different food samples. Among 300 LAB isolates, 205 isolates showed clear zone on modified MRS-CaCO3 agar, catalase negative and Gram positive, that were considered as LAB and used for this study. Twenty out of 205 isolates that showed proteolytic activity on skim milk agar produced peptides in skim milk hydrolysate (SMH) and show free radical scavenging activity ranging from 11 to 50.8% (v/v) after 24 to 72 h of fermentation, respectively as determined by 1,1-diphenyl-2-picrylhydrazyl (DPPH) method. Ferrous chelating activity (FCA) of SMH showed similar values for EDTA after 24 h fermentation but decreased after 72 h for all LAB isolates with values between 10.3 to 97.6% (v/v) for 24 to 72 h, respectively. The IC50 DPPH value of SMH-Lactobacillus plantarum1 (SMH1) was higher (2.92 mg/ml) than that of Leuconostoc mesenteroides (SMH2) and Lactobacillus plantarum ATCC8014 (SMH3) 8.81 and 4.53 mg/ml, respectively. The IC50 FCA values of SMH1 and SMH2 were 0.46 and 0.69 mg/ml, respectively greater than SMH3 (IC50 value 0.74 mg/ml) but lower than EDTA. All isolates showed poor reducing power (RP) compared to ascorbic acid. L. mesenteroides and L. plantarum1 isolated from non-dairy sources have probiotic and antioxidative properties which could benefit consumers. The proteolytic activity of SMH was significant affected (p ≤ 0.05) by the strains of LAB used. The SMH1 was higher inhibit the cell proliferation of cancer cells than SMH2 and SMH3 with values 20.63, 26.32 and 32.63%, respectively at concentration of SMH 200 μg/ml compared with the untreated control cells. The amino acid compositions for all SMH were significantly (P ≤ 0.05) rich in glutamic acid, proline, lysine and leucine.However, the total hydrophobic amino acids content in SMH2 was higher (13.98%) than SMH1 and SMH3 (12.72%, and 8.23%), respectively. Aromatic amino acids along with hydrophobic amino acids contribute to antioxidant activity. The crude protein extracts of SMH generated by three LABs isolates were partially purified by ammonium sulfate precipitation and dialysis. The peptides from most active fractions collected by reverse phase high-performance liquid chromatography (RP-HPLC) were sequenced by electrospray ionization mass spectrometry (ESI-MS/MS). The application of antibrowning agents is one of the most effective methods for controlling the browning reaction in fruits and vegetables. Therefore, the effect of antibrowning agents (Ascorbic acid, Citric acid, SMH1, SMH2 and SMH1+SMH2) on Chinese pear and potato slices was investigated. The results indicate that the slices of Chinese pear and potato treated with combining SMH1+SMH2 inhibited browning reaction comparable to ascorbic acid as shown by reduction of total phenol content. Therefore, It can be concluded that this local LAB isolates have the potential to be used to generate peptides in SMH and have the antioxidant and antibrowning activities, a dual function of bioactive peptides that would be useful in the formulation of functional foods.