Effect of malaxing time and temperature on rheological properties of 'Hass' avocado pulp and oil yield during oil extraction

'Hass' is the main avocado cultivar grown worldwide. The extraction yield of avocado oil is dependent on pre‐ and postharvest factors as well as processing and extraction conditions. During a cold extraction process, avocado flesh is ground and then slow mixed or malaxed (≤50°C) to release oil from cells, and to aggregate and coalesce the oil droplets. The influence of malaxing conditions, including time and temperature, on oil yield, changes to cell integrity and oil aggregation in 'Hass' avocado fruit pulp was investigated with electrical impedance spectroscopy, electrical conductivity, light microscopy, and rheological measurements at different times during the avocado harvest season. Cell integrity, measured by electrical resistance and conductivity values, did not change with increasing malaxing temperature, which indicated that malaxing temperature did not assist cellular disruption or oil release during malaxing. Malaxing time and temperature reduced the viscosity, increased the mobility of oil droplets, and reduced the storage modulus (G′) of the pulp tissue. The longer time and higher temperatures during malaxing resulted in more oil droplets coalescing leading to increased aggregation to form larger droplets which were easier to separate during centrifugation. The oil yield increased by ≈130% as the malaxing temperature increased from 30 to 50°C, but the actual yield was also influenced by time of harvest during the season.