Study On Fermentation Performance Of Different Starter Culture And Evaluation Of Its Functional Bioactivity In Yogurt

In modern society,cardiovascular diseases have seriously threatened human health,especially hypertension and heart disease.People control their blood pressure by taking conventional antihypertensive drugs,but related studies report that taking antihypertensive drugs for a long time will bring some side effects and potential harm to human body.Therefore,relevant scholars began to study the hypotensive functional foods.Angiotensin Convening Enzyme(ACE)is an important regulator of blood pressure.Excessive ACE can cause the rise of blood pressure.ACE inhibitory peptides are short peptides that can inhibit ACE activity,control and reduce blood pressure.Studies have found that some yogurt contains bioactive peptides that can inhibit the rise of blood pressure.Frequent consumption of yogurt can prevent hypertension.In the process of yogurt fermentation,casein in yogurt is hydrolyzed by protease of lactic acid bacteria into macropeptides,free amino acids and functional active peptides,including antioxidant peptides and ACE inhibitory peptides.ACE inhibitory peptides have many advantages,such as good antihypertensive effect,specificity,safety and no side effects on human body.In recent years,ACE inhibitory peptides have been extensively studied.The production of functional yogurt is inseparable from high-quality starter.Therefore,it is imperative to develop functional starter with independent property rights and high activity and to produce yogurt with high biological activity.In this paper,we first select the fermentation performance of different ratios of Streptococcus thermophilus(St)KLDS S1 and Lactobacillus bulgaricus(Lb)KLDS 1.0907,and select the excellent fermentation ratio on the laboratory scale.Then we studied the traditional fermentation agent strain.Fermentation performance after compounding with Lactobacillus acidophilus(La)KLDS 1.0901 and Lactobacillus helveticus(Lh)KLDS 1.8701,acid production capacity,vigor,post-acidification ability,viscosity production,flavor-producing ability,etc.The indicators and sensory characteristics were measured,and compared with the foreign Hansen starter,the fermentation performance of the yogurt starter was evaluated,and the antioxidant peptide and ACE inhibitory peptide in the active peptide of the yogurt were in vitro tested and structurally analyzed.A functional starter with excellent fermentation performance and antioxidant and antihypertensive functions.The yogurt fermented by Streptococcus thermophilus KLDS S1 and Lactobacillus bulgaricus KLDS 1.0907 at the ratio of 1:0,0:1,1:1,3:1 and 1:3 showed that compared with the other four starters,the fermentation speed of the starter with the ratio of ball to Bacillus 1:3 was faster,the p H of the starter decreased to 4.83 at 4 h and 4.83 at 6 h,and the titration acidity reached 75.During storage at 4 C,the acidification of the starter with a ratio of 1:3 was slow,the p H decreased from 4.49 to 4.4,and the sensory score was 83.Therefore,the optimal ratio of Streptococcus thermophilus KLDS S1 and Lactobacillus bulgaricus KLDS 1.0907 was 1:3.The viscosity and hardness of yogurt improve its texture.La KLDS 1.0901 and Lh KLDS 1.8701 were added to the traditional starter to ferment yogurt and four strains jointly fermented yogurt.The results showed that the viscosity and hardness of yogurt co-fermented by St KLDS S1,Lb KLDS 1.0907 and Lh KLDS 1.8701 were similar to those of Hansen starter.St KLDS S1,Lb KLDS 1.0907 and La KLDS 1.0901 co-fermented yogurt,the number of live lactic acid bacteria reached 1.51×108 cfu/m L,and the content of acetaldehyde and diacetyl were relatively high,22.80 mg/L and 6.747 mg/L,respectively.St KLDS S1,Lb KLDS 1.0907 and Lh KLDS 1.8701,La KLDS 1.0901 co-fermented yogurt coagulated for 4 hours during fermentation,and the p H dropped to 4.6 at 5 hours.The titration acidity reached 73,the total reducing power,DPPH scavenging rate and ABTS+ free radical scavenging rate were 0.260,59.7% and 41.13%,respectively.During storage,ACE inhibition rate reached 92.1%,similar to the trend of Hansen starter,and the sensory evaluation score was relatively high.By preparing a water-soluble extract,separating different molecular weight antioxidant peptides and ACE inhibitory peptides and detecting their activity.The results showed that the ACE inhibitory peptides of the four strains co-fermented yogurt were the highest,which was 80% higher than Hansen starter.The short peptide with molecular weight >10 KDa had the highest total antioxidant activity,which was 0.3857.The short peptide with a molecular weight of 3~10 KDa has the highest ABTS+ radical scavenging rate of 18.97%.St KLDS S1,Lb KLDS 1.0907 and La 1.8701 co-fermented yogurt,the short peptide with a molecular weight of 3~10 KDa has the highest DPPH free radical scavenging rate of 37.10%,which is higher than Hansen starter.Structural analysis showed that the structures of antioxidant and ACE inhibitory peptides in yogurt were different,but their molecular weights were less than 1000 Da,and the length of peptide segments was 5-10,mainly from β-CN.The structure of yogurt antioxidant peptide is similar to that of ACE inhibitory peptide,that is,it contains more hydrophobic and aromatic amino acids,such as proline and tyrosine;ACE inhibitory peptide contains valine,isoleucine and leucine at N-terminal,phenylalanine,alanine,valine and proline residues at C-terminal,and has antioxidant activity.It also has ACE inhibitory activity.This study concluded that the fermentation performance of Streptococcus thermophilus KLDS S1 and Lactobacillus bulgaricus KLDS 1.0907 was the best when they were compounded in a ratio of 1:3 and added Lactobacillus acidophilus KLDS 1.0901 and Lactobacillus helveticus KLDS 1.8701.They had the characteristics of strong acid production,high activity,strong ability to produce sticky and flavor substances,excellent quality of yogurt,high antioxidant activity and ACE inhibitory activity.Sex peptides are the most abundant,mainly from β-CN.They have strong free radical scavenging ability and ACE inhibition ability.Therefore,the combination of Streptococcus thermophilus,Lactobacillus bulgaricus,Lactobacillus acidophilus and Lactobacillus helveticus was screened as a high-quality functional starter.