Quince phenolics and dietary fibers: changes during in vitro digestion

The present study aimed to optimize the extraction conditions of quince phenolic compounds, and to investigate the changes in quince soluble-insoluble dietary fiber and phenolic compounds under in vitro gastrointestinal digestion conditions.

Extraction optimization of quince phenolic compounds was done with a three-stage method consisting of fractional factorial design, steepest ascent/descent method, and central composite design. The effect of quince phenolic extract on α-glucosidase, α-amylase, and pancreatic lipase inhibition was examined. In addition, the phenolic profile of the extract was determined. Quince phenolic compounds and dietary fiber fractions were subjected to in vitro digestion in the oral, gastric, small intestine, dialysis, and large intestine. The glucose absorption capacity during the intestinal digestion of dietary fibers was evaluated.

The highest amounts of total phenolics (881 mg gallic acid equivalent/100 g), total flavonoids (337 mg catechin equivalent/100 g), and chlorogenic acid (95.22 mg/100 g) were in the gastric phase followed by the small intestine phase. In addition, high antioxidant capacity (1151 mg trolox equivalent/100 g) was observed in the gastric phase. In the large intestine stage, 98% release of caffeic acid was observed. In addition, quince soluble dietary fiber absorbed glucose (69.15 mg/g dietary fiber) during small intestine digestion.

When the values of the bioaccessibility and recovery index were examined, a great amount of the phenolic compounds were recovered by the oral, gastric, small intestine and large intestine phases. Quince soluble dietary fiber was significantly more effective than insoluble ones on glucose absorption in the small intestine digestive medium. The changes that quince phenolic compounds and dietary fiber fractions undergo during the in vitro digestion process should be supported by in vivo studies to support their effects on health.