Effect of harvest season and time, ripening temperature and days on de-sychronisation of 'hass' avocado fruit skin colour change with softening during ripening

Abstract

Avocado ‘Hass’ fruit characteristically change skin colour from green to deep purple or black during ripening. However, there is an ongoing debate about the use of ‘Hass’ avocado fruit skin colour change as an indicator for ripening and whether pre- and post-harvest factors can alter this relationship. Thus, the aim of the study was to investigate the effect of harvest season, harvest time, ripening temperature and ripening days on ‘Hass’ avocado fruit skin colour change during ripening. The experiment was carried out as 2 x 3 x 3 x 5 factorial with three replicates. The experiment consisted of four treatment factors: 2 x harvest season (2014 and 2015), 3 x harvest time (May-early, June-mid and July-late), 3 x ripening temperature (16, 21 and 25°C) and 5 x ripening days (0, 2, 4, 6 and 8). Fruit were stored at industry recommended temperature of 5.5°C. After storage, fruit were ripened at 16, 21 and 25°C, therefore, evaluated at 0, 2, 4, 6 and 8 days for subjective and objective skin colour, fruit firmness, ripening percentage and chilling injury. Harvest season, harvest time, ripening temperature and ripening days had a significant effect (P<0.001) on ‘Hass’ avocado fruit skin subjective colour development during ripening. However, amongst the treatment factors; harvest time, ripening temperature and ripening days were the predominant factors in skin subjective colour development variation. Hence, late harvest fruit showed an improved skin colour development at higher temperature (25°C) at day 4 to ripening when compared with early and mid-harvest fruit. Moreover, skin lightness showed a decreasing trend during all harvest time and ripening temperature throughout days to ripening during 2014 and 2015 harvest season. Furthermore, ripening at higher temperature (25°C) resulted in rapid decrease on fruit firmness when compared with lower temperature (16°C), irrespective of harvest season and harvest time. In addition, mid-season fruit showed significantly higher chilling damage during the 2014 harvest season. In conclusion, the study showed that harvest season, harvest time, ripening temperature and ripening days factors had a significant influence on ‘Hass’ avocado fruit skin colour development, firmness and susceptibility to chilling injury.