Polyphenols accumulation effects on surface color variation in apple slices hot air drying process

Polyphenols are closely related to the nutritional value , flavor, and color of dried apple products. In present work, the correlation of polyphenol accumulation with apple slices browning in hot air drying (65 °C, 2 m/s air velocity) process was investigated. Polyphenols composition were distinguished in different apple varieties, among which chlorogenic acid, epicatechin were the most abundant constitutes, accounting for 44.47–75.45 g/100 g, 30.31–35.16 g/100 g of total polyphenols respectively in apple flesh. Browning characteristic distribution of 7 varieties dried apple in PCA analysis model were similar to their fresh counterparts. The average browning degree were 22.31 and 6.72 in dried and fresh apple slices respectively, revealing that hot air drying treatment accelerated and extended the effects of polyphenol enzymatic browning process. High chlorogenic acid and/or catechin content induced redness value ( a* value) variation, while lower total polyphenol content and higher polyphenol diversity mainly induced brightness ( L* value) and yellowness ( b* value) variation in drying process. Specifically, in Fuji apple slices, quercetin-3-O-galactoside significantly correlated to L* variation (r = 0.838, **P < 0.01), while catechin, chlorogenic acid, phlorizin successively contributed to the variation of a* (r = 0.877, 0.906, 0.848, **P < 0.01) and b* (0.919, 0.953, 0.906, **P < 0.01). These results would be the reference for predicting and controlling the color quality of dehydrated apple products by polyphenol content and composition.