Title : The drying of avocado (Persea americana) slices
Abstract:
The Pollock (Persea americana) is a West Indian variety of avocado. The fruit is an oblong to pear-shaped green fruit that can weigh between 0.5 to 2.2 kg. Ripe avocados are highly perishable, and the pulp deteriorates rapidly when exposed to air, light and heat. Various preservation methods, including the use of preservatives, have been investigated in an attempt to extend the life of avocado pulp, which is very popular as a table fruit and in food preparations such as guacamole. The objective of this work was to investigate the drying of avocado pulp slices (1cm thick) using two methods; namely, hot-air (oven) drying at 60°C, and freeze drying. Samples were dried until constant weight was achieved, 24 and 72h, respectively. The initial moisture content and water activity (aw) values of fresh pulp averaged 3.16 g H2O/g DM (75.98% wb) and 0.889, respectively. Slices were oven-dried to an average moisture content of 0.06 g H2O/g DM (5.78% wb) after 24h, and a final average water activity of 0.606. Slices were dried in the freeze dryer to an average moisture content of 0.03 g H2O/g DM (3.47% wb) after 72h, and a final average water activity of 0.564. The pH of the dried slices averaged 5.38 and total soluble solids averaged between 0.01-0.02 g/g DM. With respect to the appearance of dried slices, freeze dried slabs were far superior in colour, texture and appearance and rehydration capacity, and more closely resembled fresh slices. Protein and fat content of freeze-dried slices averaged 0.13 and 0.90 g/g DM, respectively. For freeze drying. drying occurred in the falling rate period and drying rate constants (k1) averaged 0.151 1/h. The Verma model was found to best fit the MR data, based on the root mean square error (RMSE) and the chi-square statistic ( 2). The results show the clear potential for freeze drying to produce a natural, ready-to-use dried avocado pulp product without the use of heat, additives or preservatives.
