Oxalic acid: A blooming organic acid for postharvest quality preservation of fresh fruit and vegetables

Oxalic acid (OA) is a unique organic acid that commonly occurs in plants with distinct functions in modulating metabolic processes. To date, the role of OA has primarily been studied in the deactivation of copper-containing preservatives, detoxification of aluminium toxicity and remediation of organic pollutants. During the last two decades, OA has been considered as an antioxidant compound with focus on its potential to enhance crop yield, improve fruit quality, boost nutritional profile, and delay postharvest senescence in fruit and vegetables. It has been established that pre- and postharvest OA application delays ripening and senescence by down-regulating physiological processes such as water loss, ethylene production and respiration. OA treatment controlled adverse storage effects including chilling injury, enzymatic browning, as well as flesh softening by lowering oxidative stress. OA application has also been found to reduce decay in fresh fruit and vegetables by inducing systemic resistance against pathogens, decontamination from surficial microbial load and pesticide residues. Additionally, OA treatments have shown to effectively improve enzymatic and non-enzymatic antioxidants and maintain attributes for eating quality. Effectively, OA application has been deemed to be a potentially food-safe natural and suitable alternative to synthetic chemicals for up-regulating bioactive compounds in harvested fruit and vegetables and extending storability within the postharvest supply chain. This extensive review covers aspects of OA including its: history, chemistry, biosynthesis in plants, quantification in fruit and vegetables, crosstalk with ripening physiology, past attempts and recent advancements in storage life extension, safety as well as quality management of fruit and vegetables.