Recovery of polyphenols and mannoproteins from enological by-products: evaluation of their potential application for glycemic control

Abstract

Starch is the main carbohydrate in the human diet and its digestion is one of the primary sources of increasing post-prandial blood glucose. Starch digestion begins in the oral cavity with the action of the salivary α-amylase, which releases maltose by producing the hydrolysis of β-1,4 glycosidic bonds. Starch is further hydrolyzed along the digestive tract, releasing glucose that enters the bloodstream. Blood glucose levels need to be balanced, since high glucose levels have been associated with a wide range of health risks, such as oxidative stress, insulin resistance and type II diabetes, obesity and cardiovascular diseases. Intake of dietary polyphenols has shown potential to modulate post-prandial glucose index due to their ability to inhibit digestive enzymes such as α-amylases and β-glucosidases, among other effects [1, 2]. Therefore, fortification of foods with polyphenols could help control the glycemic response. The winemaking industry produces large amounts of by-products, like grape pomace and wine lees, which can be revalorized as sources of grape-derived polyphenols and mannoproteins (MPs), contributing to the environmental sustainability of the wine industry. Polyphenols are known for producing unpleasant sensations for the consumer, such as bitter taste and astringency. MPs are yeast polysaccharides that can act as flavor modulators, so their combination with polyphenols may help overcome this issue by reducing polyphenol-induced bitterness and astringency. In view of this, the objective of this work was to obtain a polyphenol-rich extract and MPs from white grape pomace and lees, respectively, and analyze their effects on the activity of human salivary α-amylase. The results obtained showed that the polyphenol-rich extract was able to reduce α-amylase activity, probably by forming soluble enzyme-phenolic compound complexes. MPs partially decreased the inhibitory effect of polyphenols by decreasing enzyme-phenolic compound interactions. The combined addition of polyphenols and MPs still caused an important inhibition of α-amylase activity, indicating that MPs could be used as potential flavor modulators. Furthermore, MP characteristics played a role in their ability to counteract the enzymatic inhibition caused by polyphenols. These results open the possibility to the valorization of winemaking by-products as sources of useful compounds with potential applications for developing glycemic-modulating functional foods.

References

[1] Freitas, D.; Le Feunteun, S. (2019). Inhibitory effect of black tea, lemon juice, and other beverages on salivary and pancreatic amylases: What impact on bread starch digestion? A dynamic in vitro study. Food Chem., 297, 124885

[2] Sun, L.; Warren, F. J.; Gidley, M. J. (2019). Natural products for glycaemic control: Polyphenols as inhibitors of alpha-amylase. Trends Food Sci. Technol., 91, 262-273