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

摘要

The impact of avocado fruit firmness on cold-pressed oil recovery was investigated using a laboratory oil extraction unit. Intact, ground flesh and the malaxed (mixed) fruit pulp samples were collected during the extraction process to evaluate cell structure by electrical impedance spectroscopy, electrical conductivity, and light microscopy. The intact flesh of soft fruit at 105 firmometer value (Fv; over ripe) had the lowest electrical resistance compared to fruit with a firmness of 55 Fv (minimally ripe). The grinding step resulted in the greatest reduction in electrical resistance, suggesting the greatest cellular disruption in this step. Additionally, intact fruit and fruit pulp from fruit at 105 Fv had a higher conductivity and a lower electrical resistance value, which indicated more cell rupture occurred when softer, riper avocado fruit were processed. A greater number of unbroken parenchyma cells remained in samples from firmer fruit at various sampling points during the extraction process. Practical applications Parenchyma cells in the mesocarp of soft ripe "Hass" avocado were easier to disrupt during cold-pressed extraction. Extraction yield of oil, using the cold-press method, increased with riper avocados. However, the cold-pressed oil quality decreased with avocado fruit ripeness, based on percentage of free fatty acids and peroxide value. Electrical impedance spectroscopy (EIS) was found to be a useful technique for following mesocarp cellular changes during the extraction of oil.