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Item 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(Massey University, 2019) Yang, ShuoCellular 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. Increasing malaxing time resulted in a decrease in the solid-like behaviour (G’) of fruit pulp and an increase in cold-pressed oil yield, which correlated with the oil droplets in the fruit paste coalescing together and becoming larger. Idioblast cells in avocado flesh appeared to remain unruptured and intact during the extraction process. In comparison to the cold-pressed oil extraction of ‘Hass’ avocado, olive oil was easier to recover from ‘J5’ olive during cold-pressed extraction (at lower temperatures and for shorter times) as the olive paste was less viscous allowing the oil droplets to aggregate more easily. Processing of avocado fruit at three different stages of ripening (minimally-, fully- and over-ripe) produced higher oil yields and decreased oil quality (based on % free fatty acids and peroxide value) with riper fruit. Intact fruit and fruit pulp from the over-ripe fruit had higher conductivity and lower electrical resistance values, which indicated more cell rupture occurred when softer, riper avocado fruit are processed. For avocado fruit at six different stages of maturity (harvested between September and April during the 2016/17 season), light microscopy results showed there were more unbroken parenchyma cells in early season, less mature fruit. Polysaccharides in the cell walls were more strongly bound to cellulose in early-season avocado fruit. Late season fruit had more cell disruption during extraction corresponding to higher conductivity and lower electrical resistance values; hence higher extraction yields with increasing maturity. No significant compositional changes of the polysaccharides in the cell walls occurred during malaxing, which indicated that the malaxing step only promoted aggregation of the oil droplets. The malaxing temperature and ultrasound treatment at 20–25 kHz did not assist with cellular disruption during extraction. Higher malaxing temperature reduced the viscosity and increased the mobility of oil droplets and oil droplets were more likely to collide and aggregate to form larger droplets, reducing the G’ of the pulp tissue. The oil yield significantly increased from 1.05% to 13.43% with malaxing temperature increasing from 30 to 50 ⁰C, for early season fruit. Ultrasound treatment at 20–25 kHz decreased the G’ of the avocado pulp and helped the oil to aggregate. In conclusion, the avocado flesh cellular structure ruptured more easily in softer and late maturity fruit contributing to increased oil yields. Malaxing time, temperature and ultrasound treatment at 20–25 kHz influenced the degree of oil aggregation in fruit pulp and therefore improved the cold-pressed oil yield. Olive pulp was less viscous or less solid like during malaxing, resulted in faster oil agglomeration.Item Pigment composition of 'Hass' avocado and the extracted oil : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology in Food Technology at Massey University(Massey University, 2005) Ashton, Ofelia Batalla OrlingaThe changes in the concentration of pigments in the skin and the three pulp sections of the Persea americana (Hass var.) and the extracted oil up to 13 days after harvest at 20°C were identified and quantified by High Pressure Liquid Chromatography (HPLC). In the fresh tissue, seven pigments identified belonging to the carotenoid family were lutein, β-carotene, neoxanthin, violaxanthin, zeaxanthin, antheraxanthin and α-carotene. Chlorophyll a and chlorophyll b, pheophytin a and pheophytin b, chlorophyllide a and chlorophyllide b were identified and measured. In the oil extracted using Accelerated Solvent Extraction (ASE), lutein and antheraxanthin were identified. Neoxanthin, violaxanthin and zeaxanthin were not present. The [β-carotene and α-carotene were not tested due to the limitation of the method used in the oil determination. Chlorophyllide a and chlorophyllide b were absent. In the pulp starting from the dark pulp adjacent to the skin towards the stone, the carotenoid and chlorophyll concentrations in the fresh tissue and the extracted oil both showed a decreasing pattern. The highest oil yield was found to be between days 6 and day 8 after harvest. The pigment composition patterns of the avocado fresh tissue correspond to that of the extracted oil. There was an on-going increase in the concentration of the total anthocyanins in the avocado skin. The major anthocyanin identified was cyanidin 3-O-glucoside. Cold pressed avocado oil in the laboratory and in a commercial factory with different levels of skin included during the malaxing were produced. The peroxide value, free fatty acid value, fatty acid composition and antifungal diene were measured to determine the quality of avocado oil with different levels of skin. These showed that the addition of skin had no effect on the quality of oil produced. The addition of skin during cold pressed extraction increased the pigment levels. The stability of factory cold pressed avocado oil with added skin was investigated using accelerated shelf life testing. The addition of skin during avocado oil production in the factory shortened the shelf life. Storage of avocado oil under dark and at lower temperatures (≤20°C) provided greater stability for avocado oil pigments. The levels of antifungal diene in the avocado oil were undetectable. The comprehensive data regarding pigment composition obtained in this research may be of used in food technology, nutrition, postharvest management and gene technology. Keywords: avocado fruit, avocado oil, pigments, colour, carotenoids, chlorophylls, anthocyanin, lutein, chlorophyll a chlorophyll b, chlorophyllides, pheophytins, accelerated solvent extraction, cold pressed extraction, diene, peroxide value, shelf life.Item The oxidation stability of extra virgin avocado oil : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology in Food Science at Massey University(Massey University, 2002) Sherpa, NimmaExtra virgin avocado oil (EVAO) is extracted from avocado fruit with minimal processing. It contains a wide range of non-lipid compounds that have a profound affect on oil stability. The deterioration of oil quality is due to autoxidation and photooxidation reactions that occur during oil storage. The objectives of this research were to determine the effect of prooxidant factors (light, temperature, oxygen level) on oil oxidation and quality; make recommendations for oil processing and packaging procedures to minimise oxidation; predict the shelf life of the oil and to determine the effect of commercial antioxidants on oil oxidation. An accelerated oxidation reactor was developed to test the effects of fluorescent light, elevated temperature and varying oxygen levels on the peroxide value (PV) (initially 0.96 ± 0.03 meq/kg oil) and chlorophyll content (initially 16.2 ± 0.1 ppm) of EVAO. The production and packaging processes of Olivado NZ. were analysed for exposure to oxidation promoting factors. EVAO was exposed to dark storage at 50°C and 60°C in order to determine Q10 values for oil oxidation. Several commercial antioxidants were evaluated by examining their affect on EVAO using the Rancimat oil stability index analysis and hot air oven testing. It was found that fluorescent light at 4500 lux and aeration with dry air strongly accelerated the oxidation (determined by PV) and reduced the chlorophyll content of EVAO. The average effect of 4500 lux fluorescent light compared to 0 lux over seven hours was a PV increase of 4.5 ± 1.4 meq/kg oil and decrease in chlorophyll content by 0.9 ± 0.3 ppm. The average effect of aerated EVAO compared to EVAO stored at ambient oxygen levels over seven hours was a PV increase of 3.5 ± 1.7 meq/kg oil and a chlorophyll content decrease of 0.3 ± 0.2 ppm. Exposure to an elevated temperature of 60°C for seven hours did not cause a significant increase in PV. Recommendations were made to minimise the exposure of the oil to light, aeration, water and fruit sediment during production and packaging in order to minimise oxidation of the oil. Due to the breakdown of natural antioxidants and alternative side reactions that occurred at elevated test temperatures but not at ambient temperatures, the shelf life of the oil could not be defined. EVAO containing ascorbyl palmitate at a level of 100 ppm had a peroxide value 80 % less than control EVAO with no antioxidants after 500 hours storage at 60°C. Ascorbyl palmitate has GRAS status and was concluded to be the most effective antioxidant of those tested in EVAO.