Preharvest Applications of Oxalic Acid and Salicylic Acid Increase Fruit Firmness and Polyphenolic Content in Blueberry (Vaccinium corymbosum L.)

Blueberry exports that imply transport times of more than 25 d deteriorate their quality. The use of elicitors in preharvest has shown positive effects on the quality of berries such as grapes. The objective of this study was to evaluate preharvest applications (21, 14, and 7 d before harvest) of oxalic acid (OA) and salicylic acid (SA) on fruit firmness and phenolic compounds in blueberry. The treatments of 0, 2, and 4 mM OA in ‘Kirra’ and 0, 2, and 4 mM SA are in ‘Stella blue’. With the earlier preharvest application, ‘Kirra’ presented better firmness than ‘Stella blue’; however, 2 mM OA and SA in both cultivars increased fruit firmness, maintaining its weight and diameter with respect to the control. It should be noted that the treatment with 2 mM SA generated a 100% increase in polyphenolic content and antioxidant capacity (p < 0.05) in ‘Stella Blue’, with values close to 140 mg gallic acid 100 g−1 and 80 mg 100 g−1 fresh weight (FW), respectively. In Kirra, OA treatments did not have a significant impact on the polyphenol content, but 4 mM OA increased by 100% and 20%, total anthocyanin and antioxidant capacity of blueberry fruit, respectively. Based on our results, three pre-harvest applications of OA and SA during the fruit development until the beginning of ripening improve fruit firmness by up to 20% at different times of harvest.