Evaluation of hot water and menthyl jasmonate treatments for mitigation of chiling injary to improve 'hass' Avocado fruit skin colour

Abstract

Avocado fruit ‘Hass’ harvested during early-season and exposed to temperature at 5.5°C for 28 d are susceptible to chilling injury (CI); and therefore, develop poor skin colour during ripening. In ‘Hass’ avocado fruit, skin colour change during ripening is used by European market to indicate fruit ripeness and softness. Therefore, the aim of this study was to evaluate the use of hot water (HW) and methyl jasmonate (MJ) as postharvest treatment dips to mitigate CI; and thereby, enhance ‘Hass’ avocado fruit peel colour during ripening. Fruit were harvested randomly from 5 selected trees treated alike during early season (April 2018); and thereafter, transported to the laboratory. At the laboratory, experiments of this study were divided into 2: experiment (1) fruit were dipped into HW (38, 42 and 46°C for 30, 25 and 20 min, respectively); and experiment (2) fruit were dipped into MJ (10 and 100 µmol/L for 2 min) treatments. In both experiments after these treatments, fruit were allowed to dry for 60 minutes at ambient (±25°C) temperature and untreated fruit were used as control. Thereafter, fruit were stored at commercial shipping temperature (5.5°C) for up to 28 d. After removal from cold storage, fruit were ripened at ambient temperature (±25°C) and evaluated every after 2 d for weight loss, firmness loss, objective colour parameters (lightness-L*, chroma-C* and hue angle-h*), subjective colour (eye colour) and ripening percentage. However, chilling injury (CI) and electrolyte leakage (EL) were evaluated immediately after removal from cold storage. The results showed that HW significantly (P< 0.05) increased weight and firmness loss during ripening. Furthermore, HW reduced EL and external chilling injury (ECI) of ‘Hass’ avocado fruit during cold storage. In addition, the results showed that HW had significant effect (P< 0.05) on colour parameter L* and eye colour rating, but did not affect (P> 0.05) C* and h*. Avocado ‘Hass’ fruit subjected to HW at 42°C/25 and 46°C/20 min developed purple colour (eye colour rating 4.47 and 4.36, respectively) during ripening when compared with HW at 38°C/30 min and control fruit. Moreover, results showed that dipping fruit in 10 µmol/L had a significant effect (P< 0.05) on reducing weight loss during ripening. Methyl jasmonate (10 and 100 µmol/L) treatment reduced EL and alleviated external chilling injury (ECI) of ‘Hass’ fruit during cold storage. The results showed that MJ (10 and 100 µmol/L) treatments had significant effect (P< 0.05) on colour parameter L*, h* and eye colour rating, but did not affect (P> 0.05) C*. Furthermore, ‘Hass’ fruit treated with 10 and 100 µmol/L MJ reached the purple skin colour (eye rating 5.39 and 5.19, respectively) during ripening. Fruit dipped in MJ (10 µmol/L) had low weight loss when compared with fruit treated with MJ (100 µmol/L). In conclusion, the results of this study indicated that HW (42°C/25 minutes) and MJ (10 µmol/L) effectively alleviated external chilling injury; and therefore, improved ‘Hass’ skin colour development during ripening