Changes in Green Bean Phenolics, Flavonoids and Antioxidant Capacity during Industrial Freezing Process and in vitro Gastrointestinal Digestion

Abstract

Green bean (Phaseolus vulgaris) contains high amounts of phenolic compounds, and it is classified as one of the widely consumed vegetables, which is rich in antioxidant content and activity. The aim of this study was to determine the changes in total phenolic content, total flavonoid content and total antioxidant capacity in the samples taken from various production steps of the industrial freezing process of green beans, and to evaluate the bioaccessibility of phenolics, flavonoids and antioxidant capacity for raw material, waste and frozen product using the standardized in vitro gastrointestinal digestion model simulating the digestion in the mouth, stomach and intestine, respectively. Total phenolic content, total flavonoid content and total antioxidant capacity were determined using spectrophotometric methods and for the evaluation of total antioxidant capacity 4 different methods including ABTS, CUPRAC, DPPH and FRAP were used. Results showed that the total phenolic and flavonoid contents of the fresh green beans were preserved after industrial freezing process and their by-product that is separated as waste contains higher total flavonoid content and antioxidant capacity compared to raw material (117% and up to 97%, respectively) (p<0.05). In addition, after in vitro gastrointestinal digestion, frozen green beans and waste contained 12–23%, 143–148% and 10–230% more bioaccessible total phenolics, flavonoids and antioxidant capacity, respectively compared to fresh green beans (p<0.05). In conclusion, this study showed that food processing may affect the bioaccessibility of polyphenols.