Effects Of Mulberry Juice On Yogurt Quality And Interaction Between Mulberry Polyphenols And Casein

Mulberry,the fruit of Morus spp.,is rich in anthocyanin and nonanthocyanin phenolic compounds and can be served as a good additive for the development of functional foods.Casein,the most abundant protein in cow's milk,contains essential amino acids required by the human body and has rich nutritional value.It is cheap,easy to obtain,safe and stable.Recently,it is usually used to transport small active substances.In this study,the effects of mulberry juice on yogurt were firstly investigated,and then the casein and mulberry polyphenol/monomeric phenol composite system was used to explore the interaction between casein and mulberry polyphenol/monomer phenol and gastrointestinal digestion of casein-mulberry polyphenol complex.And it provides a theoretical basis for the development of functional dairy products rich in phenols..The main research results were listed as follows:1.Adding mulberry juice at 5%,10%,15% and 20%(v/v)to yogurt lowered the p H and hardness,increased the titratable acidity and water holding capacity,and stabilized the structure of the product.The contents of total phenols and total flavonoids and antioxidant activity of the yogurt increased in a dose-dependant manner with the incorporation of mulberry juice.2.Mulberry polyphenols and their monomeric phenols have a strong endogenous fluorescence quenching effect on casein.Among them,the quenching mechanism of MP,CA,C,FA and R on Cs were static quenching,while C3 R,C3G,EC and Cs may be covalently bonded.The thermodynamic analysis indicated that the forces between MP,CA and EC and Cs were hydrogen bonds and Van der Waals forces,between C3 G and R and Cs were hydrophobic interactions,and FA,C3 R and C and Cs through hydrogen bonds and hydrophobic interactions.Fourier transform infrared spectroscopy and circular dichroism chromatography demonstated that mulberry polyphenols and their monomeric phenols would change the secondary structure of casein,but wouldn't completely destroy the secondary structure of casein.The antioxidant activity of MP,C3 G,C3R,EC,FA,R,C and CA would decrease after interacting with Cs,i.e.produced antioxidant shielding phenomenon.3.Casein digestion was more obvious during the small intestine stage.The addition of mulberry polyphenols could inhibit casein hydrolysis,but the inhibitory effect was not significant.SDS-PAGE analysis showed that the addition of mulberry polyphenols did not change the enzymatic properties of casein.The circular dichroism explained that the secondary structure of casein and casein-mulberry polyphenol adducts were changed during in vitro digestion.Fluorescence spectrum analysis indicated that the red shift of the mulberry polyphenol-casein complex digestion product was greater than that of the casein digestion product,and the mulberry polyphenol produced a fluorescence quenching effect on casein.