Effect Of Fermentation Conditions On Bioactivities Of Mixed Peptides Derived From Yoghurt

Direct Vat Set Streptococcus thermophilus TA40(TA) and Lb.delbrueckii ssp. bulgaricus LB340(LB) was used as the starter bacteria toproduce Stirred yoghurt in different conditions. After a series of refrigeratedcentrifugation and ultrafiltration process， the mixed peptides fraction withmolecular weight (M.W.) less than3ku，(termed as pep3ku)， was collectedand analyzed of its molecular weight distribution and hydrophobic propertiesby using SEC and RPC methods. After characterization of specimens underdifferent fermentation conditions, T-AOC, DPPH radical scavenging and invitro ACE inhibitory assays were conducted on10ku and3ku samples undera chosen fermentation condition. The starter bacteria ratio factor was chosenbecause it was the most significant factor that affected pep3ku’s properties.Conclusions: the best pep3kuproducer in terms of yield concentrationand diversity was0:1and1:1groups. No peptides were found between1.4-3.5ku ranges. The amount of smaller peptides was affected bycombination ratios， major difference of larger peptides’ quantity liedbetween single strains and combinations. Group1:1produced the smallestpeptides and the most diverse M.W. distribution. With LB involved infermentation， the distribution density of peptides decreased，1:1and2:1groups produced more peptides of higher hydrophobicity，1:0and1:2groupsproduced more peptides of lower hydrophobicity. The starter bacteria ratio factor was the most significant factor thataffected pep3ku’s properties, other factors were not significantly affectingpep3ku in peptides concentration by ANOVA results, in molecular weightdistribution and hydrophobic properties by Wilcoxon sign test results; onlyripening factor had a significant effect on pep3ku’s hydrophobic properties.As results from T-AOC，DPPH radical scavenging and in vitro ACEinhibitory assays,1:2-3ku group showed the highest value in totalantioxidant capacity, which was equal to0.09mM FeSO4with about1mg/mL mixed peptides sample; meanwhile its DPPH radical scavengecapacity was highest among samples, the elimination rate was9.27%withabout1mg/mL mixed peptides sample.10ku samples exhibited higher ACEinhibition ratio than3ku samples in terms of non-lyophilized peptidesmixture, the highest ACE inhibitory rate was14.87%in group1:1-10ku.Considering that10ku samples contained more peptides than3ku samples,1:1-10ku sample should be less competitive than1:1-3ku sample, whichinhibited ACE at the rate of14.4%with2.12mg/mL.