Chemical Pathway Analysis of Non-enzymatic Browning in Preserved Strawberry during Storage

In order to illustrate the chemical pathway of the browning of preserved strawberry during storage, commercial preserved strawberries were stored at 37, 25 or 4 ℃ and evaluated for color parameters and the contents of ascorbic acid, total phenol, three free sugars, five free amino acids and 5-hydroxymethyl furfural (5-HMF), and correlation and cluster analyses were performed as well. The results showed that for each temperature, the color parameters L*, a*, and b* of preserved strawberry all decreased with storage time, and the total color difference ΔE was 11.42–33.33 after 90 days of storage, suggesting that the color of preserved strawberry changed obviously during storage. Additionally, the contents of ascorbic acid, total phenol, free sugars, and free amino acids decreased in varying degrees, while 5-HMF content increased linearly. The correlation analysis showed that ΔE was significantly correlated with all color and chemical parameters except glutamine content (P < 0.05, P < 0.01, P < 0.001), indicating that the browning may result from a combination of ascorbic acid degradation, polyphenol oxidation and Maillard reaction. Using cluster analysis, the samples stored at higher temperature and for a longer period of time were distinguished from others, suggesting that the influence of storage temperature and period on the browning degree cannot be neglected. In conclusion, during storage, ascorbic acid, total phenol, free sugars and free amino acids are involved in the browning of preserved strawberry, despite the asynchrony. The results of this study provide a rationale for browning control of preserved strawberry.