132: Sequential Hot Air Drying and Deep-Bed Aeration for Dehydration of Off-Ground Harvest Almonds

Introduction

The off-ground harvest of almonds is considered as a promising method to mitigate dust generation and the concerns of quality and food safety associated with the current harvesting and drying method. Heated air drying followed by an efficient aeration practice could be a critical component to make the off-ground harvest method implementable. The objective of this study was to develop a sequential hot air drying and deep-bed aeration method for off-ground harvested almonds.

Methods

Almond samples from two different varieties, Monterey (MT) and Fretz (FZ), were used to conduct this study. The samples were dried from their initial moisture contents to target moisture contents (MC) of 9%,11% and 13% (wet basis) using a 6ft-high column dryer at step-down temperature (preheating at 80ºC and finishing drying at 60°C) and air speed of 1 m/s. The 11% and 13% samples were further dried to MC of 9% by aeration with ambient air at speed of 1 m/s. The control samples were also produced by using aeration to dry the almonds to 9% MC. The effect of hot air drying and deep-bed aeration conditions on the drying time, product quality, including color change, cavity, and concealed damage of dried almonds, was assessed. The microbial safety of dried almonds was evaluated using the dry rehydratable film method by following the procedure described in AOAC Official Method 990.12 and 966.23.

Results

The results showed the initial MC of the samples from MT and FZ varieties were 64.2±0.7% and 47.6±0.8%, respectively. It took 48, 44.8 and 36.2 h and 21.0,18.5, and 15.0 h to dry MT and FZ almonds from their initial MCs to the target MCs. The aeration times were 7.0, 11.5 h for MT almonds and 8.0 and 12.0 h for FZ almonds. The high temperature drying followed by deep-bed aeration had no adverse effect on dried product color. There were no differences in cavity, concealed damage, and microbial activity among the samples.

Significance

It was concluded that the sequential hot-air drying and deep-bed aeration method can be used to dry off-ground harvested almonds efficiently without affecting the product quality and safety.

Authors: Ragab Khir, Zhaokun Ning, Franz Niederholzer, Irwin Donis-Gonzalez, Zhongli Pan