Chapter 24
Avocado Oil: The Color of Quality Downloaded by UNIV OF CALIFORNIA SAN DIEGO on January 14, 2016 | http://pubs.acs.org Publication Date: June 13, 2008 | doi: 10.1021/bk-2008-0983.ch024
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M. Wong , O. Ashton , C. Requejo-Jackman , T. McGhie , A. White , L. Eyres , N. Sherpa , and A. Woolf 2
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Institute of Food, Nutrition, and Human Health, Massey University, Auckland, New Zealand The Horticulture and Food Research Institute of New Zealand, Auckland, New Zealand Oils and Fats Group, Ν. Z. Institute of Chemistry, Auckland, New Zealand 2
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Cold pressed extra virgin avocado oil is a relatively new culinary oil. This chapter will review the importance of the fruit, and postharvest and processing practices on the color quality of the oil. Cold pressed avocado oil extracted from the 'Hass' cultivar (Persea americana Mill.) has a very intense green color which contributes to its unique appearance and identity. The color is attributed to chlorophyll pigments (up to 60 μg g ) extracted into the oil from the flesh tissue and also from skin tissue present during the extraction process. The oil also contains high concentrations of carotenoid pigments, the predominant carotenoid being lutein (~2 μg g ). The concentration of pigments in the oil depends on cultivar, maturity, ripeness, fruit storage before extraction, type of tissue extracted and the processing conditions used. As the fruit ripen, the pigment concentrations decline in the skin and flesh. Storage of avocado oil results in a loss of chlorophyll, dependent on temperature, light and oxygen levels, while carotenoids are relatively stable. With the decline in chlorophylls, the oil changes color from emerald green to yellow/gold. To retain the color quality of avocado oil, maintenance of high pigment concentrations during and after extraction is important. -1
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© 2008 American Chemical Society
In Color Quality of Fresh and Processed Foods; Culver, Catherine A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2008.
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Downloaded by UNIV OF CALIFORNIA SAN DIEGO on January 14, 2016 | http://pubs.acs.org Publication Date: June 13, 2008 | doi: 10.1021/bk-2008-0983.ch024
Introduction The commercial production of cold pressed extra virgin avocado oil is a relatively recent development worldwide. Previously, avocado oil has been extracted using high temperature and solvents primarily for cosmetic purposes and not for culinary purposes. The production of a high quality, edible, cold pressed avocado oil requires retention of important pigments and healthful compounds as well as minimisation of oxidation. In order to achieve this, all aspects of oil production must be considered, including preharvest and postharvest effects on fruit, processing techniques, and oil storage practices. There is very little published information on the extraction of avocado oil and aspects affecting the oil quality. This chapter will briefly review the existing literature on avocado fruit and avocado oil extraction, which includes recently published and unpublished research from the authors.
Avocado Fruit Production The avocado originated in southern Mexico and was domesticated several thousand years ago in Central America. It was cultivated from the Rio Grande to central Peru before the arrival of Europeans (7). Historically, the avocado has also been referred to as alligator pear, vegetable butter, butter pear and midshipman's butter. The flesh of an avocado can contain as much as 25 - 30% oil by fresh weight and the flesh is normally consumed fresh. World production of avocado in the 2004/2005 season is summarised in Table I. The main avocado producers in the northern hemisphere are Mexico, United States (primarily California), Israel and Spain, and in the southern hemisphere Chile, South Africa, Australia and New Zealand. Other countries such as Peru and Argentina are also large producers of avocados and production in South East Asia is increasing (2). Most countries are orientated to exporting the fresh fruit, with the remaining fruit sold on the domestic market. The 'Hass' cultivar accounts for >90% of avocado production in Mexico, Chile, United States and New Zealand and >75% of the production in Spain and Australia (Table I). Thus, 'Hass' is generally the main focus of research and development worldwide. 'Hass' is the preferred cultivar grown because of its superior yields and fruiting characteristics (7). Other major cultivars grown in approximate order of priority include 'Fuerte', 'Ryan', 'Pinkerton' and 'Edranol'.
In Color Quality of Fresh and Processed Foods; Culver, Catherine A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2008.
330 Table I. Main producers of avocados worldwide in 2004/2005 marketing year" . 6
Production Exported Processed % of crop (metric tonnes) (metric tonnes) (metric tonnes) Ήass' cultivar
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on January 14, 2016 | http://pubs.acs.org Publication Date: June 13, 2008 | doi: 10.1021/bk-2008-0983.ch024
Australia
32,000
320
1,200
75
Chile
177,000
136,412
300
93
Israel
77,000
45,000
1,000
32
934,282
180,165
25,000
95
New Zealand
22,000
15,000
1,850
98
South Africa
85,000
38,000
13,600
36
Spain
55,000
48,000
n.r.
75
162,721
1,431
n.r.
95
Mexico
United States
n.r. - none reported. Marketing year varies for each country: Australia, New Zealand and Spain, July/June; Chile and South Africa, January/December; Mexico, August/July; United States, November/October. Source of data: 3, 4, 5.
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Avocado Fruit Development and Ripening
Determination of Fruit Maturity Avocados are unique in that they do not ripen on the tree and thus can be held on the tree for very long periods, as much as two years from flowering. As the avocado fruit matures on the tree, the main physiological changes are increase in size, increase in dry matter content and an increase in lipid (oil) content. The latter two changes are highly correlated and are used as horticultural measures of commercial maturity (6). Measurement of dry matter is the most common method employed as it is simple, cheap and rapid to determine. Fruit harvested with a low % dry matter is likely to have a poor taste, and if harvested at very low dry matter values (
