γ-Aminobutyric acid treatment reduces the chilling injury and quality deterioration of Chinese olives during cold storage through regulating the metabolisms of respiration and energy

Abstract

Chilling injury (CI) is one of the main symptoms of quality deterioration in cold-stored Chinese olives, leading to the rapid declines of nutrition and commercial value. This work explored the efficacy of 1.0 mM γ-aminobutyric acid (GABA) treatment on the respiratory and energy metabolisms in Chinese olives during cold storage at 2 °C and its relationship with CI development and quality attributes. The Chinese olives were immersed in distilled water and 1.0 mM GABA solution for 10 min, respectively. Compared with the control samples, the GABA-treated Chinese olives presented lower levels of fruit CI index and weight loss percentage, and lower contents of pericarp carotenoid and pulp reducing sugar. Conversely, the GABA-treated samples showed a higher percentage of the commercially acceptable fruit, a higher pericarp h° value, higher levels of pericarp chlorophyll and pulp total soluble solids, titratable acidity, tannin, vitamin C, total soluble sugar, and sucrose. Additionally, the GABA-treated samples showed lower respiration rate, lower activities of phosphoglucose isomerase, succinate dehydrogenase, cytochrome C oxidase, and ascorbic acid oxidase, lower values of nicotinamide adenine dinucleotide (NAD) and the reduced form of NAD (NADH), and lower content of adenosine monophosphate, but higher activities of glucose-6-phosphate dehydrogenase + 6-phosphogluconate dehydrogenase, nicotinamide adenine dinucleotide kinase, H⁺, Ca²⁺, and Mg²⁺-ATPase, higher values of nicotinamide adenine dinucleotide phosphate (NADP) and the reduced form of NADP (NADPH), and higher contents of adenosine triphosphate, adenosine diphosphate, and energy charge. These findings elucidate that the alleviating effects of GABA on the CI occurrence and quality deterioration in Chinese olives during cold storage are related to the inhibition of respiratory metabolism and the maintenance of a higher energy status.