Milk protein interactions with fruit polyphenols – bioavailability on in-vitro digestion : A Dissertation submitted in partial fulfilment of the requirements for the Degree of Master of Science in Food Innovation at Lincoln University

Nguyen, Binh
Abstract
Abstract withheld for embargo reason
Keywords
milk proteins; polyphenols; fruit; interaction; antioxidant activity; in-vitro digestion; bioavailability; Food Science
Fields of Research
0908 Food Sciences; 090802 Food Engineering; 090899 Food Sciences not elsewhere classified; 090801 Food Chemistry and Molecular Gastronomy (excl. Wine)
Date
2021
Type
Dissertation
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Restricted item - embargoed until 01 March 2023
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file embargoed until 2023-03-02
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Abstract Although polyphenols are secondary metabolites, polyphenols are interested in research due to their beneficial health effects. A diet containing phenolic compounds helps to inhibit or interrupt the oxidation process and thereby mitigate disease risks such as cancer, cardiovascular diseases, and type 2-diabetes mellitus. Phenolic compounds have a chemical structure with aromatic rings bonded to the hydroxyl groups, including phenolic acids, flavonoids, stilbenes, and lignans, according to their carbon skeleton's nature. Antioxidant activity in PCs is decided by its structure particularly, the aromatic rings and the hydroxyl groups. The benzene ring plays a role in stabilizing antioxidant molecules, while the hydroxyl group contributes to antioxidant function by producing an acid-free radical. Thus, PCs with antioxidant properties are applied in a variety of food products for health benefits. Recently, many commercial dairy products enriched with fruit have been introduced to the food market worldwide. Berry fruits, grapes and kiwifruit have a rich source of polyphenols that are added to milk and dairy products. PCs can interact with the protein in a food matrix and form complexes, leading to changes in the structure and function in both polyphenols and proteins. The associations of milk proteins and PCs can be both of non-covalent and covalent interaction, including hydrogen bindings, hydrophobic links, and van der Waals, and hydrophobic interactions. Resulting in affecting the bioavailability and antioxidant of polyphenols. Besides, the gastrointestinal conditions also have impacts on polyphenols' bioavailability and antioxidant capacity. However, the effects of protein-polyphenol interactions on bioavailability as well as antioxidant activity of fruit polyphenols have not been comprehensively studied. Also unknown is the optimal ratios of milk proteins to polyphenols to maximize bioavailability and antioxidant activity. To elucidate the impacts of protein-polyphenol interaction on bioavailability and antioxidant activity of polyphenols during digestion. Boysenberry and fruit complex are fortified with milk at a varied ratio to evaluate. Before digestion, protein-polyphenol mixtures have a higher phenolic content (TPC) and antioxidant ability (AA) in comparison to milk controls, but lower than fruit polyphenol control. The addition of polyphenol in milk helps enhance phenolic content and antioxidant activity; however, the protein-polyphenol interaction has negative effects on polyphenol content and their function. Among milk proteins, casein was reported to have a lower interaction with polyphenol. After digestion, TPC of protein-polyphenol mixtures is observed to have a significant decrease when compared to mixtures before digestion. The changes in TPC are caused by the effects of enzymes and pH conditions in in-vitro gastrointestinal digestion. It is worth noticing that AA nearly stays unchanged after digestion. Besides, the increase in the proportion of polyphenols in milk does not increase TPC and AA of polyphenol due to a saturated binding. Thereby, fortification of polyphenol in milk is a potential result. Casein expresses lower impacts to polyphenol, which is evaluated as a good carrier. Casein should enhance in food matrix in comparison to whey proteins. However, a ratio of polyphenol added in milk should be further studied.