Anthocyanins are among the most abundant polyphenols in fruits and vegetables and exhibit potent antioxidant activity. Our previous studies suggested that anthocyanins present in the gastrointestinal tract (GIT) of rats exert chemopreventive effect on colon cancer. Since such effect was dose dependent, it is important to examine the stability and transformation of anthocyanins in the GIT. Based on some in vitro studies and limited in vivo evidence, we hypothesized that anthocyanins were moderately stable under the influence of digestive enzymes and physiological conditions in the GIT, and their chemical structures determine the stability, accessibility, biotransformation, and health-promoting effects.
To validate our hypothesis a series of studies were conducted. We first examined the transit, stability, transformation, and uptake of black raspberry anthocyanins in rat GIT. Our results suggest that ingested anthocyanin glycosides remained relatively stable in the GIT lumen and were efficiently taken up into the GIT tissues with limited transfer to the plasma compartment. We also observed selective degradation of cyanidin-3-glucoside in the small intestine lumen, which was tentatively attributed to β-glucosidase activity in the small intestine.
In order to eliminate interferencing non-anthocyanin compounds in bioassays, a novel mixed mode cation-exchange/reversed-phase (MCX) solid-phase extraction (SPE) technique was developed for high purity isolation of anthocyanins. The new technique achieved above 99% anthocyanin purity while maintaining excellent yield (93.6 ± 0.55%) and low cost.
To elucidate the effect of intestinal enzymes on anthocyanin digestion, an in vitro model was employed. Cell-free extract of pig small intestinal mucosa and crude extract of lactase containing foods/supplement were examined with respect to their β-glycosidase activities on highly purified anthocyanins. Selective degradation of anthocyanin glucosides and galactosides was observed in the presence of small intestinal mucosa cell-free extract and lactase supplement extract, respectively. The type of aglycone also substantially affected the resistance of anthocyanins to enzymatic degradation.
The outcome of this dissertation demonstrates that chemical structure of anthocyanins greatly affects their stability in the GIT. Such information will contribute to the exploration of anthocyanin's health benefits in vivo, and may eventually facilitate the development of value added foods/nutraceuticals that promote the healthiness of people.