Characterizing the Impact of Postharvest Temperature Stress on Polyphenol Profiles of Red and White-Fruited Strawberry Cultivars

All living organisms have developed mechanisms that help them prevent internal stress and survive under harsh conditions. For fruits, specifically strawberries, stress is fought against primarily by increasing the synthesis of polyphenols, which are secondary plant metabolites with bioactive activity. Characterizing these bioactive compounds and the differences between strawberry cultivars can be vital for strawberry breeders. Furthermore, understanding the mechanisms that trigger the synthesis of polyphenols and their levels within different strawberry cultivars will provide breeders with tools to successfully identify cultivars with higher resistance to pre- and postharvest stressors. To gain that understanding, this study aimed to characterize the polyphenol profiles of three major Florida strawberry cultivars (‘Florida Radiance, Sweet Sensation® ‘Florida127’, and ‘Florida Brilliance’) as well as a new white-fruited variety (‘Florida Pearl’) using an HPLC-DAD. First, to determine the impact of temperature stress on strawberries, ‘Florida Radiance’ and Sweet Sensation® ‘Florida127’ were stored at 1, 10, and 20°C and respiration rate (RR), water loss, total phenolics, anthocyanins, ascorbic acid, and total and individual sugar contents measured on the day of harvest and after 3 and 7 days of storage. Second, the impact of postharvest temperature stress on the polyphenol profiles of ‘Florida Radiance’ and Sweet Sensation® ‘Florida127’ was evaluated. Finally, polyphenol profiles were characterized, and total polyphenol and anthocyanin contents of ‘Florida Brilliance’ and ‘Florida Pearl’ were measured on the day of harvest and after 9 days at 1°C. To obtain an analytical color representation of the differences between the red and white-fruited berries, color attributes (L*a*b* system) were also measured for ‘Florida Brilliance’ and ‘Florida Pearl’. Results showed that ‘Florida Radiance’ and Sweet Sensation® ‘Florida127’ cultivars stored at 20°C had higher respiration rates and water loss. They experienced a more significant decline in all secondary and primary metabolites than counterparts held at 1 or 10°C. Polyphenol profiles for ‘Florida Brilliance’ and ‘Florida Pearl’ were significantly different. Compared to ‘Florida Brilliance’, pelargonidin-3-glucoside was not detected in ‘Florida Pearl’, which seemed to have been “replaced” by a larger concentration of kaempferol-3-glucoside. Overall, the results showed that strawberry cultivars differ significantly in their polyphenol profiles at harvest. Besides, postharvest temperature stress showed that higher stress temperatures lead to a greater decline in the polyphenol profiles and contents of primary and secondary metabolites. The effects of UV rays were indirectly studied in ‘Florida Brilliance’ and ‘Florida Pearl’ as preharvest stress. There was an evident change in the polyphenol profiles with an increasing UV index, particularly in the white-fruited strawberries. The results from this study can ultimately help with the further development of new strawberry genotypes. At the same time, they provide valuable information about the optimal growing and postharvest storage conditions for the white-fruited ‘Florida Pearl’