Cellular Changes in “Hass” Avocado Mesocarp During Cold‐Pressed Oil Extraction

Abstract

The aim of this study was to understand factors affecting oil release from "Hass" avocado cells during the cold-pressed oil extraction process. Early-season "Hass" avocado fruit and pulp were sampled from a commercial extraction process. Light microscopy and electrical impedance spectroscopy were used to examine avocado flesh structure at defined steps during the extraction process (destoning, grinding, malaxing, and decanting). Most parenchyma cells were ruptured during destoning, grinding, and mixing before malaxing. In contrast, the other oil bearing cells, idioblast cells, appeared to remain unruptured and intact during the extraction process. The greatest reduction in electrical resistance was observed after the destoning step. There were also significant differences between the resistances of flesh after destoning, grinding, and prior to malaxing samples. Malaxing for two hours assisted the process of oil aggregation, which led to a greater oil yield. These findings will help to develop methods to enhance oil extraction from early-season "Hass" avocado fruit.

The impact of fruit softening on avocado cell microstructure changes monitored by electrical impedance and conductivity for cold‐pressed oil extraction

“…The total oil content in the avocado flesh can be determined using a solvent extraction method, to compare with the oil yield from the cold‐pressed extraction method. The total oil in the avocado flesh was extracted using an accelerated solvent extraction (ASE) system to provide the total oil content present (Yang et al, ).…”

“…Cold‐pressed avocado oil, a popular culinary oil, is extracted for this purpose from the fresh avocados using only mechanical means to liberate the oil from the fruit flesh and to separate the oil from the aqueous fraction. The oil is mostly found in the avocado flesh parenchyma cells (Platt‐Aloia & Thomson, ; Yang et al, ). The oil is first released from these oil bodies after grinding (Yang et al, ), the next step called malaxing helps to allow the oil droplets to come together to form larger droplets, which results in ease of recovery and improved oil yields (Wong, Eyres, & Ravetti, ).…”

“…The oil is mostly found in the avocado flesh parenchyma cells (Platt‐Aloia & Thomson, ; Yang et al, ). The oil is first released from these oil bodies after grinding (Yang et al, ), the next step called malaxing helps to allow the oil droplets to come together to form larger droplets, which results in ease of recovery and improved oil yields (Wong, Eyres, & Ravetti, ). The degree of fruit ripening, monitored by fruit softness, can affect cold‐pressed avocado oil yields and oil quality (Woolf et al, ).…”

“…The structure of different fruit tissues can be monitored by measuring the electrical properties (Ando, Mizutani, & Wakatsuki, ; Bauchot, Harker, & Arnold, ; Harker & Dunlop, ; Harker & Forbes, ; Ohnishi, Shimiya, Kumagai, & Miyawaki, ; Sugiyama, , ; Wu, Ogawa, & Tagawa, ; Yang et al, ; Yang, Hallett, Oh, Woolf, & Wong, ). Electrical impedance spectroscopy (EIS) is a fast and simple technique to evaluate cell structure in fruits (Wu et al, ).…”

“…Rapid techniques for monitoring the degree of cellular disruption and the release of oil will assist processors to maximize extraction yields and possibly reduce extraction times. Yang et al () reported that EIS could be used to monitor avocado microstructural changes during cold‐pressed oil extraction. For human consumption, it is recommended to ripen avocado fruit to a firmness of 65–95 firmometer value (Fv) (White, Woolf, Hofman, & Arpaia, ).…”