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On-tree indexing of ‘Hass’ avocado fruit by non-destructive assessment of pulp dry matter and oil content

Ncama, Khayelihle, Magwaza, Lembe S., Poblete-Echeverría, Carlos A., Nieuwoudt, Hélène H., Tesfay, Samson Z., Mditshwa, Asanda
Biosystems engineering 2018 v.174 pp. 41-49
avocados, chemometrics, computer software, dry matter content, freeze drying, harvesting, lipid content, mesocarp, models, nutritive value, orchards, ovens, pulp, spectrometers, statistical analysis, temperature, water content
Commercial harvest maturity of ‘Hass’ avocado fruit is estimated based on dry matter content (DM). Typically, a few samples representing the entire orchard are destructively analysed using time-consuming procedures such as oven or freeze drying the fruit's mesocarp. However, the maturity parameter of avocado, that is known to have a direct link to nutritional quality, is oil content (OC). This study was conducted to develop models for indexing maturity of on-tree avocado using a portable visible to near-infrared spectrometer. Rapid non-destructive models for assessing OC, DM and moisture content (MC) of avocado fruit were successfully developed using The Unscrambler® X chemometric software. Models robustness was assessed in an independent test set. There were non-significant differences (p > 0.05) between destructive and non-destructively assessed OC in terms of means (42.45 and 41.91%), standard deviations (4.79 and 4.87%) and coefficients of variation (11.34 and 11.62%) from the independent test set. The predictability of OC was associated with its high extractability caused by drying samples at high (75 °C) temperatures. The heat-drying technique can be used by other researchers to increase extractability and hence, the predictability of avocado OC during calibrations of alike non-destructive models. Commercial application of the developed models can improve maturity indexing since OC, DM and MC can be easily assessed without harvesting of sample fruit.