Oxalic acid alleviates chilling injury and positively influences post-harvest parameters of sweet bell pepper by affecting glycine betaine accumulation, cells respiration rate and NADPH oxidase enzyme activity during cold storage

Bell pepper as tropical crop and warm-season vegetable is sensitive to cold storage under temperatures below 7.5 °C. The purposes of the current study were to investigate the influence of pre-harvest treatment of oxalic acid (OA 0, 1, 5, 10, and 15 mM) on some of most important morphological, physiological and bio-chemical characteristics of red bell pepper cv. "2090 Westland" at post-harvest stage, and assessment of mechanisms and enzymatic pathways of crop response to OA treatments. OA treatments greatly reduced the chilling index, and the positive effects of treatments enhanced by increasing the concentration of OA. The energy level (ATP content) of pepper fruits decreased with extending storage duration, but OA treatment maintained the ATP content of fruits. On 24 d of storage, the highest and lowest activity rate of NADPH oxidase enzyme was recorded in control and 10 mM-treated fruits. Extending storage duration led to a significant increase in cells respiration rate, but this increase was more pronounced in control. Oxalic acid as low-risk and environmentally friendly compound could be an appropriate choice to apply as pre-harvest treatment in order to extend shelf-life of bell pepper fruits during cold storage under 4 ºC. The most important mechanisms reaction of OA are enhancing of enzymatic and non-enzymatic antioxidant activities, increasing the accumulation rate of osmoprotectants and regulation of energy metabolism of cells. Pre-harvest treatment of OA 10 mM could be introduced as efficient technique to overcome adverse effects of chilling stress on post-harvest characteristics of bell pepper.