Samples of spray-dried soy milk powder were produced at various spray-dryer inletair
temperatures and characterized. Soybean seed (
Glycine max
TAX 1448 . 2E Var.)
was sorted, boiled for 40 min, manually dehulled, wet milled using plate mill and
sieved with muslin cloth to obtain water soluble extract (soy milk). The soy milk was
divided into two portions (samples A and B) and spray-dried using co-current spray
dryer at a constant feed rate (20.5 ml/sec) but at air-inlet temperatures of 204℃ and
260℃, respectively. Preliminary investigation carried out on this study showed that
samples produced at air inlet temperatures below 200℃ exhibited wet and
agglomerated particles. The recovered powdered samples were analyzed for
proximate composition, pH, available lysine, total solids, pack bulk density, viscosity,
solubility and wettability at different reconstituting water temperatures, and sensory
properties. Results showed that 38.60% and 45.55% yield (soy milk powder) were
achieved at the end of the process for samples A and B respectively. The samples
showed no significant differences (P ≥ 0.05) in some of these evaluated parameters
such as fat, ash and pH. Soy milk powder showed high protein content
(62.05±0.23%), fat (19.92±0.08%), ash (1.41±0.02 %) and available lysine
(5.02±0.29%), but low carbohydrate content (12.85±0.01 %) and moisture
(3.66±0.23%). The physical properties showed that the mean total solid of the
samples was 10.33±0.33%, pack bulk density (0.57±0.00 g/ml), while the mean
viscosity was 47 mpas. The sample spray-dried at 204℃ had solubilities of 48% and
78% at reconstituting water temperatures of 40℃ and 80℃, respectively while the
sample produced at 260‹C showed lower solubility of 38.46% and 45.01% when
temperature of reconstitution were 40℃ and 60℃, respectively. However, the sample
produced at 260℃ exhibited decreased solubility when the reconstituting water
temperature was raised above 60℃. Its solubility was 40.39% at reconstituting water
temperature of 70℃ which further decreased to 38% at 80℃. The wettability of the
samples steadily decreased as the reconstituting water temperature increased from 40
to 80℃. The wettability of the sample spray-dried at 204℃ decreased from 36 to 22
sec, while that of sample spray-dried at 260℃ decreased from 29 to 18 sec. Sensory
scores showed that the sample spray-dried at 204℃ was preferred to the sample
spray-dried at 260℃.
