Studies on the nutritional value of the oils and mesocarp of avocado (Persea americana) and impact of soil quality on elemental composition.
This study covered both the Hass and Fuerte varieties of avocado pears. The quality of extracted avocado oil produced by different extraction techniques was assessed to determine the effect the extraction method had on the nutritional and storage value of the oil. While microwave extraction produced the highest yield of oil (70.0 %), supercritical fluid extraction produced oil with a wider range of fatty acids. Although the Hass variety produced a higher oil yield, oil extracted from the Fuerte variety was shown to have a higher monounsaturated fatty acid to saturated fatty acid ratio, which makes the latter oil more beneficial to health. Oils of the Fuerte variety also possessed a higher concentration of co-extracted metals, which makes it more susceptible to lipid oxidation. The overall choice for the most efficient extraction method was microwave extraction as it produced the highest yield and quality of oil. The impact of soil quality on elemental uptake into locally grown avocado fruit sampled from six different locations was determined. Of the 14 selected metals investigated, avocado fruit was found not to accumulate Cd, Co, Cr, Pb and Se. Generally, the concentration of elements in both varieties of fruit was in the order of Mg > Ca > Al > Zn > Fe > Mn > Cu > Ni > As. Relative bioaccumulation plots were used to establish the essential and non-essential elements for normal growth of avocado fruit. It was found that the plant has an involuntary uptake mechanism for As due to similarity in ion species to P, which is an essential element. The impact of soil quality parameters pH, cation exchange capacity and soil organic matter were determined and their impact on plant-soil interactions was analysed. Statistical analysis revealed a plethora of metal interactions at the plant-soil interface. However, the plant was still seen to control uptake of specific elements such as Cu, Fe and Ca, due to its physiological requirements. CEC was found to have a greater effect on availability of elements than pH and SOM. Geoaccumulation indices indicated moderate enrichment of Pb in soils; however this result had no bearing on the elemental uptake of the fruit at all sites. Comparisons to recommended dietary allowances (RDAs) for human diet reveal the average contribution of avocado to be 70% and 45% for Cu and Mn, respectively. Low levels of As was found in fruit which warrants continued monitoring of this element in the plant due to its similarity to P.