By Erica Faber – Orchard Productivity Manager
The following is an overview of factors that adversely impact fruit quality and shelf life with tips to ensure you minimise risk to your fruit and ultimately your pack out.
Avocados are one of the few fruits that do not actually ripen on the tree and have to be picked for the ripening process to begin. This is known as climacteric fruit. Studies indicate that C7 sugars and other metabolites are responsible for inhibiting the ripening process of the fruit while on the tree.
Also, unlike other fruit, avocados accumulate oil instead of sugars and the oil content increases as the fruit matures on the tree. Oil content was previously used as an indicator of fruit maturity but testing has shifted to dry matter content for determining maturity as there is a very close correlation between dry matter and oil content and dry matter testing yields quicker results and is more economic to do.
In New Zealand, fruit needs to test at an average of 23% dry matter for local and 24% for export markets before harvest can commence. These values ensure minimum oil content and fruit that the consumer will find both tasty as well as buttery and smooth. It is the content of oil and the profile of fatty acids that determine fruit quality for avocados unlike other fruit where the balance of sugars and organic acids are used to determine quality. Harvesting too soon when the oil content is not yet high enough will result in watery, tasteless avocados.
Once harvested, the ripening process commences. Even though the fruit has been picked, it is still “alive” so to speak and continues to respire; absorbing oxygen and giving off Ethylene, carbon dioxide, water and heat. The increase in Ethylene production is accompanied by numerous complex changes resulting in fruit softening, flesh colour change as well as the synthesis of aroma and flavor chemicals. Cooling of the fruit soon after harvest is therefore important to slow down the ripening process as well as moisture loss.
CORRECT HANDLING PROCEDURES FIELD HANDLING
In many countries Hass fruit is snap picked. However in New Zealand, Hass is snip picked to a pedicel length of 5mm. This not only reduces moisture loss and fungal disease entry but also differentiates the fruit from windfall or stolen fruit which either have no stem / button or a long stem. Cutting the pedicel too long though will cause scratching and abrasions on neighboring fruit, affecting pack out.
After picking, the fruit must be carefully and gently handled. When transferring the fruit from the picking bag to crates or bins, a drop height higher than 10cm will cause bruising leading to localized softening. Bruise severity increases with increasing fruit drop heights and will often only manifest after a few days. Any mechanical damage caused during field handling and transportation will affect the fruit’s cosmetic appearance impacting your pack out and also acting as entry points for postharvest pathogens that cause decay and rots. It is important therefore to ensure pickers have short nails, and bags, bins and crates have no sharp edges or protrusions and that there are no stray twigs in the bags or bins as all of this can result in scratches, cuts and abrasions on the fruit.
Also ensure that your access roads are well maintained and tractor speeds are at a minimum so as to avoid the fruit jostling around in the bins.
Bins that are overfilled will also cause compression damage and bruising.