Stability Of Polyphenols And Antioxidant Activity In Blueberry Yoghurt

Blueberries are rich in anthocyanins and other polyphenols,which have high nutrition,health value and can resistance to oxidative stress,anti-aging,anti-inflammatory,protect eyesight,antibacterial and other physiological activities,forti?cation of yoghurts with blueberry are favored by the market.The latest researches found that when polyphenols mixed with milk,its antioxidant activity of phenolic compounds would be affected,but the results are different.The effect of milk on the bioavailability of polyphenols in gastrointestinal digestion can also be affected to some extent,even to the nutritional value of the final product.In addition,the stability of polyphenols may also affect its ultimate biological utilization during storage period.So,it is practical significance to study the stability of polyphenols and antioxidant activity in blueberry yogurts during stroge and in vitro digestion.In this study,the stability and antioxidant activity of polyphenols in non-fat and full-fat blueberry yoghurts were studied during storage of 21 days at 4?,the blueberry preparation,non-fat and full-fat yoghurt as control.The total phenolics,total flavonoids and anthocyanin as the polyphenols stability indices,total antioxidant activity,DPPH and ABTS+ radical scavenging as the capacity of antioxidant indices,and analyze the variation and correlation of indices.To study the effects of gastrointestinal digestion on polyphenol stability and antioxidative activities of blueberry yogurt,gastrointestinal digestion test would be simulated use non-fat blueberry yogurt,and blueberry preparation and non-fat plain yogurt as control,the evaluation indices were same as above.Specific research contents and results are as follows:(1)Stability of polyphenols in non-fat and full-fat blueberry yogurt were studied under the condition for 21 days at 4?.The early stage of storage,total phenolics,total flavonoids and anthocyanin content of non-fat and full-fat blueberry yogurts were 46.14±1.28,41.63±0.84,9.01±0.11 mg/100 g and 47.20±1.17,41.91±0.77,8.98±0.10 mg/100 g.The content of polyphenols in blueberry yogurts decreased by 10.20%,9.92%,15.54% and 13.94%,11.45%,18.82% during storage,decrease was greater than the blueberry preparation(1.93%,3.46%,0.03%).The content of polyphenols during storage of blueberry yoghurt were significantly lower than in blueberry preparation(P<0.05).These results indicated that,yogurt system decreased the content and storage stability of blueberry polyphenols,and the stability in non-fat blueberry yogurt was slightly higher than that of full-fat blueberry yogurt.In addition,the degradation of anthocyanin in both blueberry yogurts were followed by first-order kinetics model,and their half-life were 86.64 and 69.31 drespectively.(2)The antioxidant activity of non-fat and full-fat blueberry yogurts were studied under refrigerated conditions at 4? for 21 days.The early stage of storage,total antioxidant activity,DPPH and ABTS+ free radical scavenging activity of non-fat and full-fat blueberry yogurts were44.51±1.20,59.49±1.48,61.39±1.07 mg/100 g and45.76±0.55,60.76±0.80,62.71±0.40 mg/100 g.The indices were significantly decreased by 6.52%,7.23%,4.91% and 11.20%,14.61%,8.01% in blueberry yogurts during storage,and higher than blueberry preparation(3.58%,4.17%,1.29%).The storage period of the antioxidant indices of blueberry yoghurt were significantly lower than that of blueberry preparation(P<0.05).The results showed that the yogurt system reduces the antioxidant activity of blueberry preparation,this may be related to the decrease of polyphenol content following the storage period.The correlation analysis of polyphenols content and antioxidant indices in non-fat and full-fat blueberry yogurts showed that,the total phenolics,total flavonoids contents was significantly positive correlated with the total antioxidant activity(P<0.05),and there was a positive correlation between anthocyanin and antioxidant index,but the correlation was not significant(P>0.05),which showed that the total phenolics,total flavonoids was closely related to the antioxidant activity,blueberry polyphenols may be its main antioxidant components.In addition,there was a significant positive correlation among the three antioxidant indices(P<0.01),which indicated that the correlation among these three antioxidant indexes were highly significant.(3)The effect of simulated gastrointestinal digestion on the stability of polyphenols in non-fat blueberry yogurt indicated that,total phenolics,total flavonoid and anthocyanin contents before digestion was 45.63±0.08,41.10±0.70,8.57±0.23 mg/100 g,which lower than that of blueberry preparation(62.67±0.69,48.48±1.27,9.96±0.06 mg/100 g),the effect of simulation oral digestion on the phenolics was not significant(P>0.05).During simulated gastrical digestion,the phenolics indices were significantly(P<0.05)improved by 204.30%,73.77%,18.44% compared with before digestion up to 120 min,and the total phenolics,total flavonoids content was higher than that of blueberry preparation,but anthocyanin was lower than that of blueberry preparation.Simulation of intestinal digestion process,total phenolics,total flavonoids content was increased significantly(P<0.05)by 198.03%,26.20% and remained relatively stable,while the anthocyanin content declining and lower than the level before digestion,which reduced by 22.75%,now the total phenols and anthocyanin content of non-fat blueberry yoghurt was higher than that of blueberry preparation,total flavonoids content was on the contrary.The results showed that the digestive enzymes and low p H could promote the release of polyphenols effectively in non-fat blueberry yogurt,but in the simulated intestinal digestion environment,the higher p H had great influence on the stability of anthocyanin.Protein-polyphenol interaction in yogurt system has protective effect of anthocyanins,which improve its tolerance in simulated intestinal environment,but this effect also reduced the potential bioaccessibility of flavonoids in non-fat blueberry yoghurt.(4)The effect of in vitro digestion on antioxidant activity of non-fat blueberry yogurtindicated that,the total antioxidant activity,DPPH and ABTS+ free radical scavenging capacity was 43.48±1.22,61.25±1.13,60.61±2.61 mg/100 g respectively before digestion,there was no significant effect of simulated oral digestion on antioxidant indices(P>0.05).The antioxidant indices in non-fat blueberry yogurt were significantly(P<0.05)improved by 104.97%,41.11%,77.07% respectively compared with before digestion up to 120 min,the total antioxidant activity was higher than that of blueberry preparation,DPPH and ABTS+ free radical scavenging capacity were lower.The total antioxidant activity and ABTS+radical scavenging capacity were significantly(P<0.05)increased by 41.11%,52.15% respectively compared with that before digestion,and the DPPH radical scavenging capacity was significantly(P<0.05)decreased 44.60%,now,total antioxidant activity and ABTS+ radical scavenging capacity of non-fat blueberry yoghurt were higher than that of blueberry preparation,DPPH free radical scavenging capacity was lower.From above,the antioxidant activity of non-fat blueberry yogurt was improved by simulated gastrointestinal digestion,but DPPH radical scavenging capacity was due to the steric hindrance caused by the hydrophilic protein in the process of digestion,which restrained the removal of the DPPH radical reaction.In addition,there might be exist the interaction amon various antioxidant substances in non-fat blueberry yogurt,lead to different results on non-fat blueberry yogurt and blueberry prepartion in three antioxidant evaluation indices.Correlation analysis results showed that,in the process of simulates gastrical digestion in non-fat blueberry yogurt,total phenolic,total flavonoids content and the three antioxidant activity evaluation indices were significantly correlated(P<0.05),the anthocyanin content and total antioxidation capability was significantly correlated(P<0.05),total phenol and flavonoids content were closely related to its antioxidant activity.In simulated intestinal digestion process,the phenolics content and antioxidant activity evaluation indices correlation was weak,these phenolics indies can't represent its potential antioxidant interaction.