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    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, Shuo
    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. 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.
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    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 Orlinga
    The 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.
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    International trends in fresh avocado and avocado oil production and seasonal variation of fatty acids in New Zealand-grown cv. Hass : a thesis presented in partial fulfilment of the requirements for the degree of Master in Applied Science in Agribusiness at Massey University
    (Massey University, 1999) Requejo-Tapia, L. Cecilia
    Intensive cultivation of avocados for commercial purposes began in California and Florida and later in Israel, South Africa and Chile. Although a range of avocado cultivars are grown, Hass is the world's most widely-grown and exported cultivar. Avocado fruit has shown good commercial perspectives and planted areas show a tendency to increase. World production of avocado has grown on average 4.3% (over 760.000 MT) between 1988 and 1998. The main producers of avocado are Mexico (34%), USA (8%), Dominican Republic (7%), Indonesia (6%) Brazil (4%) and Israel (4%), Chile (2.4%), Spain (3%) and South Africa (2%) which during 1997 contributed together to 70% of the world production. Avocado world trade has increased greatly from 57,576 tonnes in 1980 to 238,306 tonnes in 1997. In 1997, the main players in the export market were Israel, Mexico, South Africa, USA and Chile. The main importers of this fruit were in Europe: Belgium, France, The Netherlands, Sweden, Switzerland, the United Kingdom, Germany, Spain, and in America: the USA and Canada and in Asia: Japan has emerged as a strong market since 1995. Average prices paid per metric ton have decreased over the years as higher volumes of fruit are traded and new exporters enter into the business. Avocado producer countries will face major challenges because of increasing production and low prices over the short and medium term. With the exception of Mexico, Israel and the U.S. the rest of the studied country producers are fairly new in the industry, thus, they possess great potential for growing. In New Zealand avocados are mainly cultivated in the North Island specifically in the Bay of Plenty and Northland areas. The New Zealand avocado Industry is based on the Hass cultivar. Avocado trees in New Zealand continue to be widely planted and with the entrance of new growers, in the future, the orchard area will continue to increase. The avocado industry in New Zealand is export driven. New Zealand's main export markets are Australia and recently the United States. Actual Australian market dominance by New Zealand would be reduced in the following 5 years due to a constant increase in Australian domestic avocado production. Since 1996, the U.S. has become an important market of destination for New Zealand avocados. Traditional supplier of the U.S. market has been Chile and it represents New Zealand's main competitor In avocado export leader countries usually the local market is supplied with fruit that does not meet export (usually strict) quality requirements. Great increases in production and export volumes are expected, therefore, it is forecast that large volumes of low price rated avocados would exist and would force the industry to look for alternative uses for avocados. Those avocados rejected during classification for export markets mainly due to defects in cosmetic appearance might be used for avocado oil extraction. The oil industry generally considered a by- product of the fresh fruit industry. For the multiplicity of applications and high prices that it achieves, avocado oil represents an interesting industry that should be further researched. Lipids are an important part of the composition of avocado fruit for a range of reasons. They contribute significantly to the taste of the fruit, and are used indirectly as a means of defining maturity since they correlate highly with dry matter. Although there has been some work carried out in New Zealand examining lipid changes and maturity, there has been no examination of the fatty acid makeup of the lipids, how they vary between regions, and what the lipid content is later in a commercial season. Such information is important from a fruit quality, health and marketing points of view. On seven occasions between September 1998 and April 1999, fruit from two orchards located in Te Puke and the Far North were harvested and analysed for dry matter, lipid content and fatty acid composition. Dry matter assessments were carried out using the commercial method and, the lipid fraction was extracted using a modification of the Bligh and Dyer technique. Later, the fatty acid analysis of the lipids was carried out by gas chromatography. Average dry matter increased over the period of study (September to April). Dry matter for Te Puke fruit increased from 24.6% to 36.4%, while dry matter from the Far North fruit increased from 24.1% to 32.3% over the same period of time. Total lipid content increased from 17.2% to 31.3% in Te Puke and from 16.4% to 26.7% in the Far North from September to April. The results imply that fruit from Te Puke could be preferred from the point of view of oil extraction because higher yields can be obtained than from fruit from the Far North. It was found a high and positive relationship exists between total lipids and dry matter content in avocados. During the study period, fruit from Te Puke showed consistently higher lipid content (and dry matter content) than fruit from the Far North. At both sites, the beneficial monounsaturated oleic acid was the major fatty acid synthesised, however, fruit from Te Puke showed higher levels of oleic acid than fruit from the Far North. From the nutrition point of view the ratio of monounsaturated (oleic and palmitoleic acid) to saturated fatty acids (palmitic acid) and the ratio of polyunsaturated (linoleic and linolenic acid) to saturated fatty acids found for the Far North and Te Puke regions compare favourably with those of the recommended olive oil. Due to similarities in lipid composition between olive oil and avocado oil, it can be implied that the high concentration of monounsaturated fatty acids in avocado will be beneficial to lower blood lipids as olive oil does. The food industry makes use of avocado oil to prepare concentrated foods, while the cosmetics industry prepares lotions and soaps for hair and skin treatments. Lastly, prestigious laboratories are also analysing the property of the flesh and oil for medical purposes. The information compiled here confirms that avocado oil compares to olive oil and can be regarded as a high- value product from the nutritional and the commercial point of view. On current production trends in New Zealand, the likelihood of an oil-extraction plant is not remote. An oil industry in New Zealand would benefit the growers because it will absorb the surplus of avocados in the local market that otherwise would compete with their first grade fruit.