Abstract:In this study，fresh apples were used as raw materials to investigate the changes in quality and flavor during apple fermentation under strictly controlled conditions of high temperature（50-90 ℃）and humidity（50%-90% relative humidity）.Compared with fresh apples，significant changes occurred in appearance，color，texture，and taste.The results showed that the total color difference（ΔE）increased significantly from 29.07±1.04 to 50.11±0.93 during the fermentation process，indicating that the color of the apples changed to dark brown.Sucrose，fructose，and glucose content decreased to（6.64±0.78），（77.04±0.58）mg/g DM，and（24.75±0.73）mg/g DM，respectively，while reducing sugar content increased to（409.36±0.64）mg/g DM.In terms of enzyme activities，polyphenol oxidase（PPO）activity peaked at the beginning of the fermentation period and then started to decrease，while superoxide dismutase（SOD）activity and phenylalanine ammonia-lyase（PAL）activity peaked and decreased in the middle of the fermentation period.Peroxidase（POD）activity remained stable throughout the fermentation.The total phenolic content of black apples increased 1.45-fold compared to fresh apples，and the 5-hydroxymethylfurfural content increased significantly to（16.21±0.36）mg/g DM at the late fermentation stage，with a significant increase in antioxidant activity but a decrease in total flavonoid content.Analysis of volatile flavor substances revealed that high temperature fermentation reduced the content of alcohols and esters and promoted the formation of compounds such as aldehydes，which，as a major product of the Maillard reaction，contributed significantly to the overall flavor of black apples.