Effects of Different Pretreatment Methods on Browning and Drying Characteristics of Hot Air-Dried Daylily Buds

This experiment investigated the effects of soaking treatment (for 45 min) with different color fixatives (0.1 g/100 mL citric acid, 0.2 g/100 mL citric acid, 0.2 g/100 mL sodium bicarbonate, and 1.0 g/100 mL sodium chloride solution) after blanching for two minutes on the browning inhibition and drying characteristics of daylily buds during hot air drying. The color, nutrient composition and microstructure of dried products were characterized, and the chemical structure was analyzed by Fourier transform infrared (FTIR) spectroscopy. The pretreatment conditions for dried daylily buds with improved commodity value were determined using principal component analysis (PCA). Results showed that the browning inhibitory effect of steam blanching was better than that of hot water blanching. The decreasing order of the browning inhibitory effects of color fixatives was 0.2 g/100 mL citric acid solution > 0.1 g/100 mL citric acid solution > 1.0 g/100 mL sodium chloride solution > 0.2 g/100 mL sodium bicarbonate solution. Daylily buds pretreated with 0.2 g/100 mL citric acid solution showed the highest drying rate, and the dried product had high rehydration ratio. Collectively, the dried product prepared by steaming followed by soaking with 0.2 g/100 mL citric acid solution had good quality with respect to color, flavonoid and polyphenol contents and microstructure. PCA indicated that the contents of polyphenols and 5-hydroxymethylhydrate were highly correlated with color and browning degree, and chewiness had the highest correlation with hardness. Out of the eight principal components, two (the first one included polyphenol content, browning degree and color difference, and the second one included hardness and 5-hydroxymethylfurfural content) were extracted, which could well reflect the comprehensive information on the quality of dried daylily buds. This study can provide theoretical and technical references for the deep processing of daylily buds.