Effect of Fruit Maturity on Microstructural Changes and Oil Yield during Cold-Pressed Oil Extraction of 'Hass' Avocado

The aim of this study was to determine the effect of avocado fruit maturity (as estimated by time of harvest during the season) on cold-pressed oil yield. 'Hass' avocado fruit at six different stages of on-tree maturity (harvested between September and April 2016/2017) were processed in a commercial cold-pressed oil extraction plant. After destoning and grinding, the fruit pulp was malaxed for 120 min. Avocado pulp samples were examined by light microscopy, electrical conductivity, and electrical impedance spectroscopy. More intact parenchyma cells were observed by microscopy in early-season fruit. The greatest cell disruption occurred after the grinding step as shown by electrical resistance values. The late-season fruit were found to have higher conductivity and lower electrical resistance values which indicated more cell disruption occurred during extraction. Cell walls extracted from fruit harvested later in the season showed a higher yield of the water-soluble polysaccharides and a lower yield of the trans-1,2-diaminocyclohexane-N,N,N ',N '-tetraacetic acid (CDTA)-soluble polysaccharides. The cold-pressed oil extraction yield (g oil/100 g fresh flesh) was found to increase with fruit maturity from 10.4 in the early season to 22.5 (g oil/100 g fresh flesh) in the late season. The extraction efficiency (cold-pressed extraction yield/total oil content) also increased from early season (77.2%) to late season (96.6%). In conclusion, the avocado flesh cellular structure ruptured more easily in late-season fruit suggesting of a contribution to more oil release and improved extraction yields.