Effect of cold storage temperature and silicon dips on physico-chemical properties of a new mandarin selection "M37" fruit

Abstract

Newly developed mandarin selection ―M37‖ has the potential to become a future export soft citrus cultivar. However, the selection is highly susceptible to chilling injury, which normally reduces post-storage quality and marketability of citrus fruit. Silicon (Si), applied at post-harvest as potassium silicate (K2SiO3), has potential to mitigate against chilling injury. So far, the effect of Si on ―M37‖ mandarin chilling susceptibility is unknown. Therefore, the aim of the study was to investigate the effect of cold storage temperature and postharvest potassium silicate dips on the chilling susceptibility and physico-chemical properties of new mandarin selection ―M37‖ fruit. The experiment was carried out in a factorial, arranged in a completely randomised design (CRD) with three replicates. Treatment factors were: 2 x cold storage temperature (-0.6±1 and 4.5 ±1°C) and 4 x potassium silicate concentration (0, 50, 100 and 150 mL L-1 K2SiO3). Fruit were dipped in different potassium silicate solutions (0, 50, 100 and 150 mL L-1) for 30 minutes, air dried, waxed; and thereafter, stored for 28 days at -0.6 and 4.5°C with 85-90% relative humidity. After withdrawal from cold storage, fruit were held at ambient temperature (±23°C) for 7 days (shelf-life); during shelf-life fruit were evaluated for chilling injury, physical properties (weight loss and firmness loss) and biochemical properties (electrolyte leakage, total soluble acids (TSS), titratable acids (TA) and TSS: TA ratio). The results showed that fruit were highly susceptible to chilling injury after storage at 0.6°C when compared with 4.5°C. However, treating fruit with postharvest potassium silicate dips improved their chilling susceptibility, especially with 50 and 100 mL L-1 K2SiO3 concentrations. Electrolyte leakage was lower for fruit treated with K2SiO3 compared to the control across all the storage temperatures. Although, ―M37‖ fruit stored at 4.5°C showed higher weight loss, firmness loss, TSS and TSS: TA ratio when compared with -0.6°C storage. Fruit firmness increased with the increase in potassium silicate concentrations during storage at -0.6 and 4.5°C; with the highest firmness loss occurring on fruit treated with 150 mL L-1 than control. Similarly, TSS increased concomitant with K2SiO3 concentration. Although, TA decreased with increasing K2SiO3 concentrations for fruit stored at 4.5°C; resulting in higher TSS: TA ratio. In conclusion, postharvest silicon dips effectively improved the storability of ―M37‖ mandarin fruit, preserved quality and extended the cold storage period. xi

Keywords: Biochemical properties; Chilling injury; Firmness loss; Potassium silicate dips; Weight loss