Effect of hot air drying on the polyphenol profile of Hongjv (Citrus reticulata Blanco, CV. Hongjv) peel: A multivariate analysis.

Hongjv peel (HP), a spice rich in polyphenols, is generally dried for its preservation. Hot air drying (HAD) at 50°C, 60°C, 70°C, and 80°C was performed in this study to dehydrate HP and it was found that the drying rate increased in line with the increase of HAD temperature. Absorbance analysis showed that HAD induced significant decreases in the total polyphenol content (TPC), total flavonoid content (TFC), and antioxidant activity of HP. Ultra performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) analysis found 18 phytochemicals in the HP, including 11 flavonoids, 6 phenolic acids, and 1 triterpenoid, while multivariate analysis revealed that chlorogenic acid, hesperidin, naringenin, and phloretin in the HP were influenced mainly by HAD. HAD-induced degradations were non-spontaneous, endothermic reactions, consistent with the first-order reaction kinetics. In addition, the results suggest that HAD is more likely to degrade polyphenols that include an ester bond or glucoside. PRACTICAL APPLICATIONS: Among the various methods of preservation used to process spices, HAD is still the most effective. The polyphenol of HP possesses numerous health benefits, including being anti-oxidative, anti-inflammatory, anticancer, antiproliferative, and other qualities. This study provides a method through which to obtain insight into the effects of HAD on polyphenols in food, and indicates potential targets to increase the polyphenol content in HP.