The aim of this study was to investigate the effects of in vitro digestion on the phenolic contents and antioxidant activities of citrus peels. Three different varieties of citrus peels (mandarin, ponkan and red tangerine) were treated with simulated gastric fluid (SGF) and simulated intestinal fluid (SIF). The results showed that the SGF or SIF treatments of the citrus peels did not significantly increase the total phenolic content (TPC) or total flavonoid content (TFC), except for that of the TFC of ponkan peel treated with SGF. However, simulated in vitro digestion did improve the antioxidant activities measured with FRAP and ABTS methods. The effect of SGF was more positive than those of SIF for the FRAP assay, but the opposite was true for ABTS. Notably, both simulated digestion techniques decreased the DPPH free radical scavenging abilities. Simulated digestion in vitro changed the antioxidant activities of the citrus peels.
Summary
The study aimed to investigate the mechanism of the colour change of carambola puree by high pressure processing (HPP), and the effects on its flavour, antioxidant properties and other physicochemical properties. The results showed that the colour change of carambola puree after HPP (200, 400, 600 and 800 MPa, for 15 min at 25 °C) was caused by both the enzymatic browning inhibition and the β‐carotene release promotion. The physical and chemical properties also varied after HPP treatment, in which the potential of hydrogen (pH) value and the total soluble solids decreased with the pressure. With the increase of pressure, the content of total phenols and flavonoids increased to a certain extent, and the antioxidant activity also increased. HPP could destroy the cell structure and form microscopic pores in the tissue, which might cause changes in physical and chemical properties. Compared with untreated samples, HPP could improve the characteristic flavour and quality of the sample itself, and it has a great application prospect in the production of carambola puree.
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