| Grain protein is the byproduct after grain processing, which is abundant and cheap. As lack of some biosynthesis pathway and incomplete protein hydrolase, Lactobacillus acidophilus (LA) has severe nitrogen source requirement. In this paper, three kinds of grain protein (wheat, rice and corn) were used as the materials, which were catalyzed by alkaline protease to obtain the peptides. Then, the peptides were added into the culture media. The growth-stimulation effect of grain protein peptides on the LA was studied, in which the growth activity was taken as the assessment index. Furthermore, from the aspect of biological metabolism, the effects of peptides on the growth status, lactic acid production and exopolysaccharides (EPS) production were also studied, in order to evaluate the effect on the critical enzyme activities during the synthesis of lactic acid and EPS. Finally, the antioxidant activity of grain protein peptides were studied, containing oxygen radical absorbance capacities (ORAC) scavenging activity, DPPH free radical scavenging activity and reducing power. The main results were as follows:(1) Alkaline protease was employed to catalyze the three kinds of grain proteins, and then the hydrolysate was separated through ultrafiltration. The peptides with different molecular weights were obtained. The growth-stimulation effects of these peptides on LA were evaluated. The rice protein peptide was thoroughly studied, containing its degree of hydrolysis (DH), molecular mass and amino acid composition. The result showed that the growth-stimulation effect of rice protein peptide was better than that of corn and wheat protein peptides. The peptides with molecular mass of less than 1ku showed the best growth-stimulation activity than others. There was not good correlation between DH and growth-stimulation activity of peptides. As to the rice protein peptide with molecular mass of less than lku, there was a higher amino acid proportion and more glutamic, isoleucine and leucine.(2) During 72h fermentation process, the influences of three kinds grain protein peptides (Mw<1ku, XM-Ⅰ, DM-Ⅰ and YM-Ⅰ) on the cell viability, lactic acid production and the activities of Lactate dehydrogenase (LDH) were studied. Through the comparison study of OD622, pH values and cell viability, the peptides (Mw<lku) could increase the cell concentration and OD622, but decrease the pH values, in which the DM-1 showed the most significant influence. There was not significant impact on the cell viability after addition of peptides. However, after addition of peptides, the lactic acid concentration increased, especially in the sample with DM-Ⅰ (16.66g/L). Three kinds of grain protein were able to improve the key enzyme activity of LDH in the glycolytic pathway.(3) During 72h fermentation process, the influences of three kinds grain protein peptides (Mw< 1ku) on the EPS production, monosaccharide composition and UDP-glucose pyrophosphorylase (UGP) activity were studied. The result showed that the addition of different grain protein peptides could increase the EPS production. And the EPS was composed of glucose, mannose and galactose. The addition of protein peptides (Mw< 1ku) could also increase the activity of UGP.(4) The antioxidant activities (ORAC scavenging activity, DPPH free radical scavenging activity and reducing power) of different peptides were studied. The result showed the source as well as molecular mass of peptides had influence on their antioxidant activities. Three kinds of antioxidant activities of grain protein peptides showed different strength orders. Overall, compared with the wheat protein peptide, the antioxidant activities of rice and corn protein peptides were better. After ultrafiltration, the peptide with Mw<lku revealed better antioxidant activity than other components. |
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