From being ubiquitously featured on brunch menus, to filling our grocery aisles, the humble avocado has become a staple “superfood” nowadays. The persea americana, or avocado, is mostly produced as a fruit. Infamous for its ephemeral ripe state, avoidance of cosmetic waste and high fat content has lead to the production of avocado oil (AO) (M. Wong, 2010).
- Global production and major producing countries
A significant increase in production and consumption of avocados since 1950 has lead to it being one of the most economically fruitful tropical fruits, with a 52% increase since 1999 and a gradual increase in production in the past 10 years (See. Table 5.) (Schaffer, 2013; Wong, Eyres et al., 2014). USA consumption of avocados has overtaken Europe’s since the 1990s and continued to boom in the new millennium. This is partially due to local production (California, Hawaii) and its publicized nutritive qualities (Schaffer, 2013).
Mexico is currently the leading producer of avocados worldwide with an approximate avocado production of 1.8-1.9MMT for 2017/2018 (FAOSTAT; Flores, 2017). Other leading producers include the Dominican Republic, Colombia, New Zealand, Chile and Peru (Dávila, Rosenberg et al., 2017; M. Wong, 2010; Schaffer, 2013).
Industrial processing results in a 21-30% oil yield (Dávila et al., 2017). The yield relies heavily on the properties of the avocado with pre-harvest and postharvest variations impacting the oil content and composition (Ferreyra, Sellés et al., 2016). The Hass avocado cultivar represents 90% of global production with its mature flesh containing 32% oil and the seed 2%, though on average 18% (Fulgoni, Dreher et al., 2013; Wong et al., 2014).
Avocados ripen off the branch, therefore they are harvested when mature, but not ripe (Magwaza & Tesfay, 2015). The ripeness of the avocado influences the oil content of the fruit and therefore the extractable oil potential. This can be achieved when the fruit is ripe; after 8 days post-harvest (Villaseñor-Mora, Martínez-Torres et al., 2017). Immature harvest leads to mediocre shrivelled skin, watery flavour with stringy, rubbery texture and limited oil yield (Magwaza & Tesfay, 2015). Over-matured fruits result in accelerated ripening, leading to increased susceptibility to physical damage and diseases (Magwaza & Tesfay, 2015). Maturity is assessed via the color, firmness, sweetness of the fruit, though recent technology has lead to the use of refractometry or thermal emissivity for assessment of oil content (Magwaza & Tesfay, 2015; Villaseñor-Mora et al., 2017).
The oil extracted from the fruit also varies depending on timing of harvest, with later harvest increasing yield: (75%-90%) (M. Wong, 2010; Ozdemir & Topuz, 2004; Schaffer, 2013). Additionally, other factors impact the composition of the oil such as temperature (lower temperature increases MUFA), crop location, the variety (Hass, or Fuerte) and ripening period (Ozdemir & Topuz, 2004; Schaffer, 2013), (Ferreyra et al., 2016).
Different AO products share a common series of pre-treatment steps: washing, de-skinning/stoning, and processing steps: mashing, thermal conditioning and malaxing, then oil extraction (solvent, high-temperature, decanting) and purification (Ashton, Wong et al., 2006; Qin & Zhong, 2016).
Common extraction methods include chemical and high temperature extractions. Solvent extraction uses a 3:2 ratio of ethanol to hexane, resulting in high yield and quality (95% oil extracted/oil content) (Costagli & Betti, 2015). Depending on the product and use, some require pre-treatments including drying, which may decreases the oil quality (oxidation and destruction of phytochemicals) and/or increases overall yield (M. Wong, 2010; Qin & Zhong, 2016). Newer technology introduced supercritical extraction which results in yellow oil from 35MPa of pressured CO2 (less extracted chlorophyll) (Qin & Zhong, 2016; Schaffer, 2013). Depending on the extraction treatment and final use of the oil, different refining processes are necessary: refining, bleaching and deodorizing.
A novel New Zealander extraction method has become popularized since 1990’s resulting in cold-pressed oil. The extraction process for avocado oil is similar to that of olive oil as it is an aqueous extraction process, however it requires different pre-treatments (washing, destining, de-skinning, thermal conditioning and kneading) and decanter centrifugation and vertical centrifuges to remove excess moisture (Costagli & Betti, 2015; M. Wong, 2010; Schaffer, 2013). This results in oil rich in avocado flavour and phytonutrients. Skin and seed removal are necessary prior to extraction, the flesh is then ground into a paste at 45-50ºC, still considered cold-pressed, for 40-60min (M. Wong, 2010). Afterwards, the oil and aqueous phases are separated via high-speed decanting centrifugation (M. Wong, 2010). In the case of EVAO, after extraction, minimal processing is required, which allows for the flavour, color and nutritional qualities to remain (Wong et al., 2014).
- Basic Chemistry
AO is an odourless yellow oil (M. Wong, 2010). Its FA composition is similar to that of olive oil due to its high oleic acid content (Schaffer, 2013). Around 76% MUFAs (oleic and palmitoleic acids), 12% PUFAs (linoleic and linolenic acids) and 12% SFAs (palmitic and stearic)(M. Wong, 2010). It contains α-tocopherol as the main antioxidant (70-190mg/kg oil) with β-, γ-, and δ-tocopherols also present, but in minute quantities (<10mg/kg oil). Phytosterols can also be found including β-sitosterol (2.23–4.48 mg/g oil)(M. Wong, 2010). Additionally, levels of vitamin A and K can be found in the oil (Dreher & Davenport, 2013). The quality of the oil ultimately depends on the quality of the extracted fruit, with low FFA (<0.5% oleic acid) and low peroxidase value (<2meq/kg) when extracted from mature undamaged fruit (M. Wong, 2010).
- Nutritional Qualities
The avocado fruit is known to contain many beneficial fats and phytonutrients, however only the oil contains the lipid-soluble fraction of these chemicals (i.e. anthocyanins and chlorophyllides cannot be found in AO)(Ashton et al., 2006). In addition to its high MUFA content, the oil contains many phytochemicals including carotenoids such as lutein (0.5-3.3mg/kg oil, 70% carotenoids) and zeaxanthin, polyphenols, tocopherols and phytosterols (Ashton et al., 2006; Lu, Arteaga et al., 2005; M. Wong, 2010; Schaffer, 2013). Virgin coconut oil and crude avocado oil contain chlorophylls (which may undergo oxidation). Increased carotenoid and chlorophyll content can be achieved by introducing avocado skin the extraction mash (11.1mg/kg vs. 46.9mg/kg and 22.3mg/kg vs. 69.8mg/kg, respectively) (Qin & Zhong, 2016). CPAO (Hass cultivar) also appears green due to chlorophyll (11-19mg/kg oil) and carotenoids (1.0-3.5mg/kg oil).
- General Uses
Similarities in FA composition between AO and OO allows for AO to be a replacement to the latter. Its high smoke point (>250°C unrefined and >270°C refined) and heat stability renders it ideal for frying (Berasategi, Barriuso et al., 2012; M. Wong, 2010). The carotenoid bioavailability is increased due to the lipid nature of oil and can subsequently increase absorption from foodstuffs it is added to (Unlu, Bohn et al., 2005).
Similarly to coconut oil, avocado oil can also be processed into biofuel (Eryilmaz et al., 2016).
AO is used in the cosmetic industry for its high vitamin E concentration and moisturizing characteristics (Lin, Zhong et al., 2017; Schaffer, 2013). AO and its by-products can also be introduced in treatments of skin disorders (See Table 6.).
Animal and human studies suggest AOs MUFA aids in diabetic and hypercholesterolemics profiles (See Table. 6.). Additionally, the lutein content may promote ocular health (Abdel-Aal el, Akhtar et al., 2013). Piascledine, or avocado soybean unsaponifiables (by-products of the saponification treatment), is used as an oral supplement treating osteoarthritis, and alternative to HRT, though glucosamine content may lead to allergic reaction (Christiansen, Bhatti et al., 2015; Oryan, Mohammadalipour et al., 2015; Panahi, Beiraghdar et al., 2011). Additionally, it has been reported to aid in cutaneous wound healing (Oryan et al., 2015) (See Table 6.).
- By-products and other uses
The remaining pulp from processing may be used as fertilizer. It can also be incorporated into animal diet (poultry, sheep) due to its consistent crude protein content (similar to maize), high SFA and linoleic acid. However high non-digestible fiber leads to lower growth rate, rendering it inappropriate as feed (M. Wong, 2010; Skenjana, 2012).
The seed (15-16% avocado weight) contains high dietary fiber, FAs, polyphenols, steroids and other extracts that may be utilized in pharmacological settings (Dennis & Savitri, 2017; Leite, Brito et al., 2009). It has also been used to control pest due to its antifungal properties (Leite et al., 2009).
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