Drying Kinetics and Quality of Soy Residue (Okara) Dried in a Jet Spouted-Bed Dryer

ABSTRACT

The objective of this study was to investigate experimentally the effects of various drying parameters, i.e., inlet air velocity, inlet air temperature, initial bed height and heating duration, on both the drying kinetics and various quality attributes of dried okara viz. percentage changes of the total protein content, color, urease index, as well as the specific energy consumption during drying in a jet spouted-bed dryer. It was observed that all drying conditions tested could reduce the amount of urease to an acceptable level and increasing the heating duration, air velocity, and hot air temperature led to a significantly higher rate of reduction of urease activity. The percentage change of the total protein content of okara undergoing different drying conditions was not significantly different, however. After drying, the redness of okara was the highest changing color index, but its absolute value was still much lower than those observed for the lightness and yellowness. Hence, dried okara appeared light-brown. The specific energy consumption of the process was found to be in the range of 3.69 to 5.89 MJ/kg evaporated water.

Keywords:

• Color
• Protein content
• Specific energy consumption
• Trypsin inhibitor
• Urease index

ACKNOWLEDGEMENTS

The authors express their sincere appreciation to the National Center for Genetic Engineering and Biotechnology (BIOTEC) for supporting the study financially. Thanks are also due to Sermsuk YHS Beverage, Co., Ltd., Chonburi, Thailand, for providing the raw material used in the study and also other support throughout the course of this study.

Notes

a, b, c, d and e in the same column with different superscripts means that the data are significantly different (p < 0.05).