Effects of Drying, Storage Conditions and Simulated Digestion on the Content of 5-Hydroxymethylfurfural in Dried Longan

To explore the formation pattern of 5-hydroxymethylfurfural (5-HMF) and the safety of dried longan during processing and storage, this study monitored the changes in 5-HMF content during drying and storage at different temperatures. The changes in the contents of reducing sugar, total acid and total free amino acid and browning degree during processing were determined and their correlation with 5-HMF content was analyzed. Moreover, the safety of dried longan was analyzed using in vitro simulated digestion experiments and a Caco-2 cell model. The results showed that as the drying temperature increased above 85 ℃, the 5-HMF content significantly increased (P < 0.05). The 5-HMF content was positively correlated with the total acid content and browning degree, but negatively correlated with the contents of total free amino acid and reducing sugar. During storage at different temperatures (4, 25, and 37 ℃), the 5-HMF level first increased and then decreased with storage time, and showed different increasing trends under different storage conditions. At 25 ℃, the 5-HMF content began to decline earliest and was lower overall. The 5-HMF content briefly increased during oral digestion, but significantly decreased during gastric and intestinal digestion. The water extract of dried longan inhibited the absorption of 5-HMF and counteracted the cytotoxicity of 5-HMF at 24 mmol/L to Caco-2 cells. These results indicated that optimizing the drying and storage conditions of dried longan can reduce the content of 5-HMF. In the case of normal consumption, the human digestive tract can reduce 5-HMF in dried longan, improving its safety for consumption.