Xue DuFollow

Date of Award

Summer 8-10-2018

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Food and Nutrition Sciences

Advisor

Angela Myracle

Second Committee Member

Beth Calder

Third Committee Member

Harold B. Dowse

Additional Committee Members

L. Brian Perkins

Jennifer J. Perry

Abstract

Diabetes is a global health problem. The consumption of dietary polyphenols may help to decrease the risk of type 2 diabetes and slow the progression of diabetic complications. Aronia (Aronia melanocarpa) and elderberry (Sambucus nigra L. ssp. canadensis) fruits are rich in polyphenols and exhibit health-promoting properties, but they are underutilized. Aronia and elderberries are rarely consumed raw due to the astringent mouth feel. New food products are needed to increase their consumption. Kefir, a fermented dairy beverage, was chosen to be the matrix for incorporating berries due to: 1) the protein matrix can help mask the astringency; 2) an acidic environment is beneficial for the stability of phenolic compounds; 3) fermentative microorganisms may be able to increase the bioavailability of polyphenols.

The first objective of this research was to develop new palatable products using underutilized berries and different sweeteners (sucrose, stevia and monk fruit extracts). Sensory evaluations were conducted to assess consumer acceptability of berry-containing kefirs. The results showed that aronia and elderberry kefirs sweetened with stevia or sucrose were all accepted by consumers where sucrose was the best-accepted sweetener. The second objective was to assess the health-promoting characteristics of the berry-containing kefirs. Aronia kefirs contained high levels of total phenolics and anthocyanins. Elderberry kefirs were moderate in total phenolics. All kefirs exhibited antioxidant capacity. The third objective was to evaluate the diabetes-beneficial properties of aronia kefir using an in-vitro digestion model. The impacts of fermentation on aronia polyphenols were also assessed. The results showed that the levels of bioaccessible polyphenols were elevated during digestion and the antioxidant capacity increased. Fermentation enhanced the inhibitory activity of aronia kefir on α-glucosidase but did not alter its weak inhibition on pancreatic α-amylase. Specific inhibition of α-glucosidase may decrease the absorption of carbohydrates and contribute to blood glucose control without side effects compared to pharmaceutical agents, such as acarbose.

In conclusion, new berry-containing kefirs were well-accepted by the consumers and the consumption of berry-containing kefirs may help to reduce oxidative stress and aid in blood glucose control. In addition, fermentation may be a good strategy to increase the bioavailability of dietary polyphenols.

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