Hot water treatments improve 'Hass' avocado fruit quality after cold disinfestation

Abstract

The potential for hot water treatment (HWT) to improve quality of ‘Hass’ avocado following cold disinfestation for fruit flies, was investigated. Avocado fruit were placed in water at 38–42 °C for 20–60 min, disinfested for 16 days at 1 °C, then ripened at 20 °C. In the following season, fruit from another orchard were treated with hot water at 39–42 °C for 20–30 min, disinfested as above, then ripened at 16 °C. In both seasons, HWT significantly reduced skin damage caused by cold disinfestation, with 40 °C for 30 min, 41 °C for 20–30 min and 42 °C for 25–30 min giving the greatest reduction. Hot water treatments also reduced body rots in ripe fruit, with 40 and 41 °C for 30 min being consistently the most effective. Treatment at 42 °C increased body rots compared to the other HWTs in one season, and there was no benefit of HWT times longer than 30 min. The severity of vascular browning (VB) and mesocarp discolouration (MD) in ripe fruit was generally low, and increased following cold disinfestation. Hot water treatments reduced VB severity but had no effect on MD. Treatment at 41 °C for 25–30 min and 42 °C for 25 min increased the percentage of externally acceptable fruit (less than 5% of the skin area with defects) from 0 to about 80% 3 days after removal from disinfestation. The same treatment also increased the percentage of ripe fruit with acceptable flesh quality (less than 5% of the flesh with rots or disorders) from 0 to 16–20%, due mainly to reduced body rots. These results indicate the commercial potential of HWTs of about 41 °C for 25–30 min, or 42 °C for 25 min to improve avocado external and internal fruit quality following cold disinfestation.