Off-flavor and Loss of Aroma in Young Coconut Fruit During Cold Storage are Associated with the Expression of Genes Derived from the LOX Pathway and Badh2

Abstract

Dissatisfaction with the flavor quality of young aromatic Thai coconut ‘Nam-Hom’ usually grows when stored at 2–4°C after harvest, represented by off-flavor development and aroma loss. To understand the mechanism of postharvest flavor deterioration, young coconut fruit were stored at 4°C and 25°C for 15 days. Sensory evaluation was performed, volatile compositions were analyzed, enzyme activities and transcript levels of genes related to the synthesis of volatiles were investigated. Off-flavor was observed after six days of storage at 4°C and tended to be more serious after that. A total of 45 volatiles were identified in the young coconut fruit. Partial least square discriminant analysis (PLS-DA) revealed two volatiles, 1-heptanol, 1-octanol, and nonanal, which were associated with off-flavor development. Transcript levels of CnLOX1, CnHPL1, and CnADH2, relating to the volatile production catalyzed by the LOX pathway, increased during storage at low temperatures. Their respective enzyme activities were also found to increase. The loss of the aromatic nature of young ‘Nam-Hom’ coconut at 4°C was found to be associated with an increase in CnBadh2 gene expression, resulting in a lower 2-acetyl-1-pyrroline (2-AP) content as compared to that at 25°C. Wrapping the fruit with polyethylene (PE) instead of polyvinyl chloride film reduced the off-flavor by reducing the oxygen concentration; consequently, this prevented enzyme activities and expression of genes from the LOX pathway. However, the loss of the aromatic nature of young ‘Nam-Hom’ coconut fruit at low temperature storage could not be mitigated with PE packaging.