Effects of different drying and processing methods on vitamin C, color, phenolics, antioxidant activity, and mogroside V of Luo Han Guo (Siraitia grosvenorii) drink

Luo Han Guo fruit (LHG), native to Guangxi province of China, is rich in mogrosides, polyphenols, vitamins, and many other nutrients. Drying and processing methods are known to impact the final quality of food product. In this study, traditional hot-air dried Luo Han Guo (HAD-LHG) and low temperature-vacuum dried Luo Han Guo (LTVD-LHG) fruit samples were used to make Luo Han Guo aqueous drink that was subjected to high hydrostatic pressure processing (HHPP) and thermal pasteurization. Unpasteurized LHG drinks were used as controls. Color, vitamin C, total phenolic content, mogroside V content, and cellular antioxidant activity in HepG2 cells were measured and analyzed for the LHG drinks. Results showed that pH values of original LHG aqueous drink were highly affected by the drying methods of LHG fruit. HAD-LHG drink had pH values of 4.4 - 4.8, while pH values of LTVD-LHG were around 5.8 - 6.1. No significant differences of color parameters (L*, a*, b*, C*, hue, browning index) of LHG drink were found after treated by HHPP or thermal pasteurization. Whereas color indices were greatly affected by drying methods of LHG. The color of HAD-LHG drink was dark brown, and the color of LTVD-LHG drink was light yellow. The browning index of HAD-LHG drink (199 ± 8) was much higher than that of LTVD-LHG drink (21 ± 5). Drying methods of LHG fruit largely affected their vitamin C content, total phenolic content, and mogroside V content. LTVD-LHG had much higher vitamin C content and mogroside V content than HAD-LHG, but HAD-LHG drink exhibited significantly higher total phenolic content (499 ± 114 mg GAE/100 g dried LHG) than LTVD-LHG drink (136 ± 40 mg GAE/100 g dried LHG). Drink processing methods showed no significant effects on total phenolic content and mogroside V content of each LHG drink. The cellular antioxidant activity (CAA) values of HAD-LHG drink was not significantly affected by drink processing methods. But CAA values of LTVD-LHG drink would be decreased after thermal pasteurization when comparing to high pressure processing and unpasteurized control groups.