By Dr. Jane Ambuko
Avocado has become increasingly important in Kenya as the leading export fruit which account for 74% of the export revenue from fruits. It is now considered as the ‘green gold’ – both for farmers and traders (especially exporters). Although most of the avocado producers target the lucrative export market, the domestic market is expanding gradually as consumers become more aware of the health and nutritional benefits of the ‘super fruit’.
The fruit is a rich source of health promoting nutrients and compounds including minerals, vitamins E and C, and β-carotene (pro-vitamin A), proteins, carbohydrates, fats and fiber (Fig 1.). It is noteworthy that avocado fruit contains approximately 2.5% protein which is significantly higher (2 – 10 times) than most fleshy fruits and vegetables. The fruit also contains a high oil content (10 – 20%), most of which is contained in the fleshy part of the fruit. It is also noteworthy that avocado contains more of the good fat – the monounsaturated fatty acids.F
Of the many components in avocado fruit, its oil content is a critical quality attribute which affects market acceptance both for industrial and culinary use. Oil content is also used as an index of maturity in avocado fruit.
The use of avocado oil has been predominantly in the cosmetic industry, mainly because of its stability and high content of vitamin E which is a key ingredient in beauty products. However due to consumer awareness about the health benefits of the super fruit, avocado is gaining even greater importance in culinary use.
What factors affect the oil content and therefore quality of avocado fruit?
Among the many other factors that affect the oil content and quality of avocado fruit, variety, crop production/orchard management practices, agro-ecological conditions and harvest maturity are key. Oil content varies with variety – some varieties contain more oil than others. The dominant varieties in the Kenyan export market (Fuerte and Hass) have an oil content ranging from 14 – 20% depending on production conditions and harvest maturity. Oil content in other common varieties such as Bacon, Puebla, Duke, Adrenol, Pinketon, Zultano ranges from 10 to 18%.
Like other fruits the quality of avocado fruit is affected by preharvest production factors including crop husbandry practices. These include water and nutrient management, pest and disease management and other orchard management practices. Therefore best fruit production and orchard management practices must be employed to ensure optimal fruit growth and development which subsequently affect fruit quality at harvest.
The agro-ecological conditions have an effect on avocado fruit growth and development and significantly affect the oil content. Kenya has diverse agro-ecological zones ranging from sub-humid to semi-arid. Due its wide adaptation, avocado fruit is produced in most of the agro-ecological zones in Kenya hence potential variation in quality of the fruits from the different AEZs. Unpublished studies (Boen, 2019) show that Hass avocado fruit produced in the less humid (dry) AEZs have higher oil content compared to those from the more humid (high potential) AEZs in Kenya. This means that even when avocado fruits possess similar physical attributes such as size and peel color, they may vary significantly in internal quality attributes including the oil content.
The same studies also showed that harvest maturity has a significant effect on avocado fruit quality attributes including oil content. Oil content was shown to increase gradually from <5% at 120 days after bloom (early harvest) to >13% at 180 days after bloom (late harvest).
The high demand for avocado fruit, especially in the export market often pushes farmers to harvest the fruits early in the season (often prematurely) to meet their contractual obligations. Knowledge of the maturity indices for various avocado varieties so as to guide farmers on when to harvest the fruit without compromising the quality is important.
Immature harvest not only affects the oil content but also negatively affect the eating and keeping quality of the fruit. Fruits that are harvested too early (prematurely) have low pulp dry matter, watery texture, poor flavor, shrivel during ripening and don’t ripen evenly. These attributes have negatively impacted traders and consumers perception of avocado fruit from Kenya.
As the global demand for avocado fruit continues to increase, more farmers (not only in Kenya) will increase production to take advantage of the market opportunities. For the avocado fruits from Kenya to compete favorably in the global market, efforts must be made to ensure that the factors that affect fruit quality are addressed.
There are various postharvest technologies and practices that can be applied to preserve quality after harvest. These include technologies for cold chain management, ethylene management, waxing to minimize gaseous exchange and water loss among others. However these technologies can only preserve the existent quality after the fruit is harvested. Therefore efforts must be made to ensure optimal quality at harvest and harvesting the fruit at the right stage of maturity. For Kenya’s avocado fruits to compete favorably in the market place (domestic and global), there is need for concerted efforts and interventions from various stakeholders including farmers, traders, policy makers and researchers.
The Author in a Senior Lecturer and Postharvest Specialist,
Department of Plant Science and Crop protection, University of Nairobi