Effect of various food processing techniques on the retention of loquat phenolics and their antioxidant capacity during in vitro digestion

Loquat (Eriobotrya japonica Lindl.) is a perishable fruit with a huge potential for processing. In this study, the effects of food processing techniques and in vitro gastrointestinal digestion on the phenolics of loquat products were investigated. For this purpose, the results of processed loquat products including juice, nectar, leather, pulp, and jam were compared to the control loquat samples. Spectrophotometric and chromatographic methods were used to analyze the total phenolic (TPC) and total flavonoid contents (TFC), individual phenolic compounds (chlorogenic acid, p-coumaric acid, epicatechin) as well as total antioxidant capacity by DPPH and CUPRAC assays. The TPC and TFC of loquat products varied from 61.2 +/- 5.4 to 855.7 +/- 36.0 mg GAE/100 g and 37.2 +/- 1.6 to 979.5 +/- 65.3 mg CE/100 g, respectively. As in total phenolics, flavonoids, and antioxidants, the highest chlorogenic acid, p-coumaric acid, and epicatechin contents were obtained in loquat leather as 201.20 +/- 9.99 mg/100 g, 47.50 +/- 2.21 mg/100 g, and 46.87 +/- 0.28 mg/100 g, respectively. In addition to these, after in vitro gastrointestinal digestion, it was revealed that loquat leather had the highest TPC, TFC, and total antioxidant capacity values compared to other samples. Results have indicated that the phenolic content of fresh loquat fruits could be improved or protected, mainly by processing into leather and/or jam. Thus, the product scale for this fruit can be increased by obtaining foods with high nutritional value.