Drying Properties Of Bean Curd Residue And Its Applications In Noodle And Steam Bread

Bean curd residue is the by-product of tofu, soybean milk and other soybean products. It is rich in dietary fiber, protein, and other nutrient components. About 1.2 kg of fresh bean curd residue is produced from 1 kg of soybean processed for tofu. Approximately 2.8 million tons of bean curd residue are produced annually in China. For high moisture content, fresh bean curd residue putrefies very quickly. Bean curd residue sometimes used as animal feed, but most is dumped and burned as waste. Therefore, drying the fresh bean curd residue as soon as possible and developing the new application fields are necessary to full utilize this resource.This paper determined the nutrient components and antioxidant properties of bean curd residue, dried it with microwave-vacuum drying, freeze drying and hot-air drying, respectively, studied their drying characteristics, and applied it into the processes of noodle and steam bread. The results showed that:1. The contents of protein, insoluble dietary fiber, crude fiber, total sugar, reducing sugar, crude fat and ash are 17.84%, 36.29%, 5.90%, 37.40%, 2.57%, 9.62% and 3.85%, respectively. The contents of kalium, calcium, sodium, magnesium, manganese, zinc, iron, chromium and copper are 9.36 mg/g, 4.19 mg/g, 0.96 mg/g, 2.57 mg/g, 0.019 mg/g, 0.026 mg/g, 0.11 mg/g, 0.18 mg/100g and 0.67 mg/100g, respectively.2. The fresh bean curd residue were dried with microwave-vacuum drying, freeze drying, and hot-air drying, respectively. The drying time, rehydration property and flavonoid content of product were determined. The results showed that the drying time of microwave-vacuum drying was fastest (20 min), which is about 9.5% of hot-air drying and 2.8% of freeze drying. The rehydration of product from microwave-vacuum drying (5.66) was close to that of freeze drying (6.29), and distinctly higher than that hot-air drying (3.76). The flavonoid content of product from hot-air drying was highest (2.358 mg/g), the following was freeze drying (2.179 mg/g) and microwave-vacuum drying (1.995 mg/g). For the fast drying time and good quality of product, microwave vacuum drying has great potential for drying bean curd residue.3. Dry powder of bean curd residue was extracted by hot water (60℃) and 70% ethanol, respectively. The yields of water extract and ethanol extract were 16.45% and 9.53%. Generally, the antioxidant property of ethanol extract was higher than that of water extract. Ethanol extract showed higher antioxidant activity (78.13%) at 5 mg/mL,higher reducing power (1.268) at 10 mg/mL, higher scavenging ability on DPPH (64.77%) at 5 mg/mL. The difference of scavenging ability on hydroxyl radicals between ethanol extract and water extract was small (54.16-56.81% at 10 mg/mL). The two extracts showed weak scavenging ability on superoxide radicals. Naturally occurring antioxidant components in the extracts include total phenols (1.23-1.48%), flavonoids (5.59-7.43%) and polysaccharides (59.55-76.12%).4. By replacing part wheat flour with bean curd residue powder to produce noodle and steam bread, the effects of the adding amounts of bean curd residue and the improvers on the sensory qualities and textures of products were studied. The optimum parameters of noodle were wheat flour 75 g, bean curd residue powder 25 g, wheat gluten 3 g, sodium carboxymethyl cellulose 0.4 g, konjac flour 0.2 g, and salt 1 g. The optimal parameters of steam bread were wheat flour 85 g, bean curd residue powder 15 g, wheat gluten 1g, yeast 0.6 g, and fermentation time 120 min.