Studies on the nutritional value of the oils and mesocarp of avocado (Persea americana) and impact of soil quality on elemental composition.
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Date
2011
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Abstract
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.
Description
Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2011.
Keywords
Avocado., Persea., Soils--Quality., Theses--Chemistry.