Cellular changes during cold-pressed ‘Hass’ avocado oil extraction : a thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology, at Massey University, Auckland campus, New Zealand. EMBARGOED until 1 May 2021.
Cellular changes during cold-pressed extraction of ‘Hass’ avocado (Persia americana Mill.) and ‘J5’ olive (Olea europaea L.) were investigated to understand how each step in the process affects oil release from the tissue and to ascertain if and how cold-pressed oil yields were influenced by cellular changes. Electrical impedance spectroscopy (EIS), electrical conductivity, light microscopy and rheological measurements were used to examine avocado and olive flesh and pulp structure at defined processing steps during both commercial and laboratory-based cold-pressed oil extraction. Light microscopy revealed most parenchyma cells in the fruit flesh were ruptured after the destoning and grinding steps. Concomitantly, a significant reduction in electrical resistance and a concurrent increase in conductivity of pulp tissue occurred when cells were ruptured during the destoning and grinding process. Malaxing assisted aggregation of oil into larger droplets, observed by microscopy.--Shortened abstract