Egounlety et al 7 observed soaking the soybean for 12 to 14 hours reduced about

Egounlety et al 7 observed soaking the soybean for 12

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Egounlety et al . 7 observed soaking the soybean for 12 to 14 hours reduced about 25% raffinose and 20% stachyose, the loss of sucrose in soaking liquids was even more than that of raffinose when during the prepartion of tempeh. Prinyawiwatkul et al . 25 reported when soaking cowpea in 1: 6 water (cowpea: water, w/w) at 25 for 24 hours the sucrose and stachyose decreased by 39% and 18.4% respectively. Ruiz-Terán et al . 17 found that when the soybeans were hydrated in water at 100 for 30 min the oligosaccharides losses in the hydration water was 45 g/kg initial dry soybean. Different results in oligosaccharides content detected in soaking water might be attributed to different varieties, 23,26 volume of soaked water, soaking temperature and soaking time. 7,25 Soaking is an important operation during the prepara- tion of soybean sheet. Soaking can make the dry beans absorb a certain volume of water, which facilitated the following grinding process. Li 13 believed soaking made the seed soft, the seed structure loose, the protein easily extracted, the seed components diffuse into water. This contributes to the detectable sugar in the soaked water. Washing the soaked soybeans in water could flow away the foam and ash in the soaked soybeans, which is an usual practice in soybean sheet processing. Ruiz-Terán et al . 17 reported in their study that washing the soaked soy- beans at 60 reduced the oligosaccharides content dur- ing preparation of tempeh. Egounlety et al . 7 reported the combined effect of soaking, dehulling, washing and cook- ing reduced more than half of oligosaccharides in prepara- tion of bean tempeh. Grinding method might influence the oligosaccharides concentration in soymilk. Lasekan et al . 27 reported that by a fine milling the sugar content in two sorghum cultivars would be increased. Filtrating separated non-soluble soybean residue from soymilk which guaranteed the good quality of soybean sheet. A certain amount of oligosaccharides was left in the soy residue. Inevitably this lead to certain loss of oligosaccharides. In the sheet formation process, as water evaporates with time dry matter in the soymilk increased and the film thickness as well as the weight of the soybean sheet in- creased too. This was the major reason accounting for the increasing tendency in oligosaccharides content in final soybean sheets recovered later in the process ( Figure 4 ) . The results from the present study indicate that soybean oligosaccharides are easily subjected to loss with various treatments, including soaking, grinding, filtrating, boiling while the last step of sheet formation accounted for the highest loss. The by-product in soybean sheet production, the sweet slurry which contains large amount of oligosaccharides, are is not fully utilized. The analysis of loss profile im- plies possible ways to improve technology for production of oligosaccharides enriched soy-sheets, and whilst arouses attention to make full use of the by-products in the processing of the soybean sheet.
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