Effects Of Tea Soup Extraction Conditions On Milk Tea Quality And Whey Protein Properties

China’s tea market scale continues to expand,and the milk tea which is prepared with freshly brewed tea soup and fresh milk is more and more popular among consumers.It not only meets consumers’ taste requirements,but also conforms to the current trend of healthy eating.The quality of milk tea is not only related to the selection of raw materials,but also affected by the processing technology.Extraction is an important part in the production of tea soup,and the extraction conditions are related to the subsequent processing steps and product quality.In this study,tea soups which were prepared at different extraction conditions were used as the raw material.The effects of extraction conditions on the sensory quality of tea soup and the flavor and properties of milk tea were studied.Then,the interaction between tea soup and whey protein was studied,so as to further explore the influence of tea soup on the structure and functional properties of whey protein.Combining the preparation process of tea soup with the flavor and properties of milk tea and finding the relationship between the two factors can provide a certain reference for improving the sensory quality and functional properties of new tea drinks.The main research contents are as follows:The effects of extraction conditions on the sensory quality of tea soup were studied by measuring the quality components of tea soup.The results showed that with the prolongation of extraction time,the contents of tea polyphenols,amino acids,sugars,and caffeine in the tea soup continued to increase,and the extraction rate was fast at first and then slowed down,which may be related to the decreasing concentration gradient in the tea soup.Under the same extraction time,as the extraction temperature increased,the brightness of the tea soup decreased,the greenness weakened,and the yellowness deepened.With the increase of the extraction temperature,the extraction amount of ester catechin and bitter amino acid increased,and the bitterness of the tea soup was aggravated.The effects of extraction conditions on the quality of milk tea were studied by measuring the taste indexes,flavor substances,antioxidant activity and stability of milk tea.The results showed that with the increase of extraction temperature,the types of flavor substances in milk tea increased from38 to 45.In addition,the increase of the extraction temperature led to the enhancement of the antioxidant activity of milk tea,but the content of ester catechins also increased,resulting in increased bitterness and poor stability of the milk tea.Considering the quality of milk tea and economic benefits comprehensively,the optimal extraction time was 30 min and the extraction temperature was 65 °C.The interaction between tea soup and whey protein was studied by ultraviolet-visible absorption spectroscopy,fourier transform infrared spectroscopy and fluorescence spectroscopy.The results showed that both EGC and EGCG in tea soup could interact with whey protein to form complexes,and the interaction force between EGCG and whey protein was stronger than that of EGC.Tea polyphenols were rich in tea soups,which changed the structure of whey protein.The content of α-helix and β-sheet of whey protein decreased,while the content of β-turn and random coil increased.There was static quenching between EGC,EGCG and whey protein,and the interaction between them was mainly hydrophobic.The effects of different tea soups on the functional properties of whey protein were studied by measuring solubility,foamability,foam stability,emulsifying activity and emulsifying stability.The results showed that the tea soup extracted at low temperature was helpful to improve the functional properties of whey protein,while the high concentration of tea polyphenols in the tea soup extracted at high temperature was not conducive to maintaining the stability of the system.Then by combining with in vitro simulated digestion,the effects of tea soups on whey protein digestibility and antioxidant activity were studied.The study found that the addition of tea soup reduced the digestibility of whey protein and enhanced the antioxidant activity of the whey protein system.When the digestion time was the same,the inhibition of the whey protein digestibility by the tea soup was enhanced with the increase of the extraction temperature.The degree of hydrolysis of whey protein in the intestinal digestion stage was higher than that in the gastric digestion stage.In addition,with the increase of extraction temperature,the antioxidant activity of the system was enhanced,and the antioxidant activity in the gastric digestion stage was stronger than that in the intestinal digestion stage.