Stability of flavonoids and ascorbic acid Part 1: Development of an integrated approach for the stability testing of flavonoids and ascorbic acid in powders Part 2: Stability studies of a variety of anthocyanins and ascorbic acid in liquid and powder forms

Megan E West, Purdue University

Abstract

The research contained in this thesis is presented in two related parts. The first part focuses mainly on method development for better detecting and quantifying interactions between flavonoids and ascorbic acid, especially in powdered forms exposed to differing levels of moisture. The second part describes an in depth study of the most important flavonoid-ascorbic acid interactions identified using the approaches developed in part one, namely anthocyanin-ascorbic acid interactions. In part one, an integrated approach for determining the stability of flavonoids and ascorbic acid in powders was developed. A rapid analyte solubility procedure served to decide whether HPLC, GLC, or NMR would best serve to measure stability. Both the flavonoid under study and ascorbic acid were measured in one analysis with any of the determinative methods. Seventeen flavonoids of differing type and ascorbic acid were used to demonstrate the utility of the method. The approach was applied to monitor the effects of storage relative humidity on the stability of several flavonoid powders with and without ascorbic acid. Results showed that quercetin, luteolin, taxifolin, naringenin, and naringin were stable for as long as 8 weeks in RHs up to 98%, ascorbic acid was significantly destroyed in the presence of quercetin, taxifolin, and taxifolin at 98% RH. Both grape anthocyanins and ascorbic acid were unstable in the presence of each other at 98% RH. The approach developed and described in part one not only led to the further studies described in part two of this thesis, but also should be of value to other researchers working to better define the stability of flavonoids in food and supplement systems. In part two, the stability of anthocyanins and ascorbic acid were further studied in detail for both solutions and powders. The stability of cyanidin 3-glucoside, highly purified and present in semi-purified extracts also containing cyanidin 3-(6"-malonoyl)glucoside, petunidin 3-glucoside, delphinidin 3-glucoside, delphinidin 3-(6"-acetoyl)glucoside, and/or delphinidin 3-(6"-coumaroyl)glucoside in combination with ascorbic acid was determined in solution at differing pH and temperature levels and dry powders at different relative humidity. Results generally confirmed the mutual destruction of anthocyanins and ascorbic acid in solution with increasing pH and temperature, however improved stability of acylated anthocyanins and those with differing flavylium cores was not observed. With powders, stability was related to increasing levels of moisture, but results did not necessarily parallel those recorded for liquids. Key assays included HPLC analyses of individual anthocyanins and ascorbic acid as well as CIELAB color measurements, including the generation of color swatches. The latter were found to be a very useful tool for evaluating and preserving results. The results of this research should further the efforts toward the use of anthocyanins as replacers for synthetic colorants, especially in those products likely to contain meaningful levels of ascorbic acid, such as powdered beverages.

Degree

Ph.D.

Advisors

Mauer, Purdue University.

Subject Area

Food Science

COinS