Abstract:
Soy residue or okara is a by-product of soymilk and tofu production process. It is usually available in a semi-solid form,
which gives an appearance of clumpy mass in absence of excessive moisture. However, okara still contains a large amount of protein
and fiber, which makes it suitable as a fortifying ingredient in many types of food products. However, raw okara deteriorates rapidly,
so it is necessary to introduce it to a suitable drying process in order to obtain dried okara, which has desirable characteristics, either in
terms of physical and nutritional properties, and long shelf-life. The objective of this research was to study the feasibility of drying okara
in a jet spouted bed of sorbent particles as well as to investigate the effects of various parameters, i.e., inlet air temperature, mass ratio of
sorbent particles to okara, superficial air velocity and initial bed height as well as the use of different types of sorbent particles,
on the drying kinetics, specific energy consumption and various quality attributes of the dried product viz. color, oxidation level, rehydration ability,
urease index and protein solubility. In addition, the effects of mass ratio of sorbent particles to okara and initial bed height on the hydrodynamic
behavior of a jet spouted bed of sorbent particles were also investigated.
Based on the results it was observed that the use of appropriate amount of sorbent particles could improve the spouting stability of the mixed bed.
Using sorbent particles (either in the case of passive or active sorbent) could enhance the drying rates, especially during a constant rate drying period.
It was also found that, when using the same amount of sorbent particles, the use of active sorbent (maltodextrin DE = 28) resulted in higher drying
rates than those obtained when using passive sorbent (silica gel beats). In the case of drying to produce dried okara for the animal feed industry it was
observed that dried okara underwent high-temperature drying without the use of sorbent particles had values of urease index and percentage of protein
solubility within the standard levels. Dried okara had acceptable values of oxidation and color changes. On the other hand, okara at low-temperature
with the use of active sorbent (maltodextrin) yielded dried okara, which had acceptable qualities in terms of rehydration ability, oxidation level and color
for use as an ingredient of human food products. Results obtained from this study can be used as a guideline to develop a dried okara production process
to obtain high-quality product for various applications.