The effect of sprouting of soybean and preparing soymilk and tofu on the yield, nutritional quality, antinutritional profile, colour attributes, organoleptic quality and texture profile (tofu) of four commonly used varieties of India were studied to assess the feasibility of using sprouting as a non-chemical, non-thermal tool to improve quality of soy products. Soymilk was prepared from sprouted and unsprouted seeds with process parameters of 121°C for 25 min. Coagulation of soymilk was done with 3% CaSO 4 at 80°C. Products from sprouted varieties showed an increase in protein (fb) of 7% in milk and 13% in tofu across varieties; a reduction in fat (fb) of 24% in milk and 12% in tofu; in trypsin inhibitor (db) of 73% in milk and 81% in tofu; in phytic acid (db) of 59% in milk and 56% in tofu across varieties. Tofu from sprouted seeds had higher protein and whiteness index but tofu strength was around 43% lesser than its unsprouted counterpart. Taste acceptability showed an increase of 10% and 6.3%; flavour of 23.2% and 11.6% and overall acceptability of 9.9% and 4.4% in milk and in tofu respectively from sprouted varieties. The improvements in composition and quality parameters was seen in all the varieties tested showing that sprouting could be beneficial for product development across varieties. The time and temperature used for production of soymilk was conventional (121°C for 25 min). Evaluation of time and/temperature reductions could be tried out to reduce the heat requirement and intensity, which could result in better nutritional and functional quality products
The effect of grinding cum blanching (GCB) of sprouted soybean at different temperatures on milk and tofu quality was studied. Three temperatures (121°C-T1,100°C-T2 and 80°C-T3) for GCB were used to produce soymilk and tofu from sprouted soybean which were analysed for the yield, nutritional, anti-nutritional profile, colour attributes, particle size, organoleptic quality and texture profile. Unsprouted Soybeans with GCB at 121°C served as control (C). There was significant difference (P<0.5) in trypsin inhibitor content in milk and ranged from 4.1 mg/g in T3 to 1.4 mg/g in T1.Optimal reduction in TI of 75-80 % was achieved in T2. There was significant difference (P<0.5) in protein extractability and ranged from 84.4 % in C to 93.9 % in T2. Hardness (N) of tofu was around 11.22 in C and reduced to 8.9, 8.6 and 4.4 in T1, T2 and T3 respectively. L values of soymilk ranged from 83.4 in C to 85.8 in T3; in tofu from 83.1(T3) to 87.2 (C) and decreased with the increase in heating temperature and time. Particle size d [3, 2] and volume d [4, 3] between treatments varied significantly (P<0.0001 and P<0.0038). Overall acceptability scores on 9 point hedonic scale for all treatments for milk and tofu were above 5. The texture scores of tofu for T3 were very low due to its soft structure. From the above investigations 100°C was the optimal temperature for GCB of sprouted soybean for the production of good quality soymilk and tofu.
Effect of roasting temperature and time on the hardness, moisture content and colour of whole-kernel of soybean was studied using response surface method (RSM). Colour of reference soy-butter (RSB) was used to indicate the time and temperature suitable for roasting soybean kernels to prepare soy-butter (SB). Temperature (160°C) and time (90 min) for roasting were identified, soybean kernels were roasted, subsequently made into SB and compared with RSB on the basis of nutrient content, particle size, colour and rheology. SB contained 45 g% protein and 34 g% fat on dry matter basis. There was a significant difference (P < 0.05) between RSB and SB on the basis of L* values, D 3,2 and D 4,3 . Rheology showed that SB samples behaved like a viscoelastic material. The mean apparent viscosity was significantly different (P < 0.0001) between SB (7.18 Pa.s) and RSB (4.72 Pa.s) which may be due to the significant difference in the particle size distribution (PSD). The Herschel-Bulkley model could successfully explain the rheological behaviour of SB.
The time and temperature of roasting of sprouted soybean was optimized using response surface method. The effect of roasting on sprouted whole kernel of soybean indicated that roasting time and temperature individually, as well as in combination, had a significant effect on hardness of roasted kernels. Sprouted soybean kernels were roasted at optimized temperature (127C) and time (37 min) and subsequently made into soy-butter (SB) and compared with reference soybutter (RSB) on the basis of nutrient content, particle size, color, sensory quality and rheology. SB contained 38 g/100 g protein and 34 g/100 g fat. There was significant difference (P < 0.05) between RSB and SB in L* values. Sprouting improved flavor scores and SB showed higher organoleptic acceptability compared with RSB on a 9-point hedonic scale. Rheology showed that SB behaved like viscoelastic shear thinning material; like Bingham plastic at lower shear rates and Herschel-Bulkley (HB) fluid at higher shear rates. PRACTICAL APPLICATIONSSoybean is an important crop due to its high protein content but soy products are not very popular due to problems of trypsin inhibitor, off-flavors, etc. Sprouting is a process known to improve the nutritional and functional quality while reducing the content of trypsin inhibitors and off-flavors of the bean and consequently of the product. SB, a comparatively new product of soybean, offers all positive attributes of soybeans, sprouting and sensory qualities of vegetable butters. A new process for manufacture of SB has been proposed in this paper. The nutrient quality, particle size and rheology have been studied. The process is simple and does not require any expensive or specialized equipment for commercial manufacture. Quality attributes of the product have been modeled so that effect of any change in process on the quality of product can be predicted or the manufacture process can be modified to achieve certain quality attribute.
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