Bio-Functionality Of Fremented Plum Juice By Lactic Acid Bacteria And Its Application As A Novel Acid-Coagulant Of Tofu

Tofu is essentially a protein gel formed by heating soymilk after coagulant addition. Coagulation process of soymilk is critical to the production of tofu, coagulant is critical to coagulation process. Currently coagulants include salt coagulant, enzymes coagulant and acids coagulant. Salt coagulant is widely used in traditional Chinese tofu processing. North tofu mainly made by the bittern as a coagulant has unique flavor, good texture, but its production process is difficult, yields is low; South tofu mainly made by gypsum as a coagulant has high yield and water holding capacity, but it is astringency and appears uneven texture phenomenon in the same cylinder. The problems of high prices and technical difficulties in preparation make application development of enzymes coagulant restricted. Acids coagulant mainly refers to glucono-δ-lactone (GDL), has now entered the industrial production. Tofu made by GDL has good quality, good texture, elasticity and good water holding capacity, but its light taste and soft texture is not suitable for cooking.As people’s requirements for natural food growing, researchers began looking natural organic acids to replace synthetic GDL. Green plum is famous for its abundant organic acids. After fermentation by L. plantarum 70810, organic acids such as lactic acid in plum juice increased, corresponding prebiotic function also improved. The fermented plum juice replacing GDL as acid coagulant has important and far-reaching significance.Specific studies and results were as follows:1. Preparation of fermented plum juiceSalted green plum with pectinase treatment was fermented by L. plantarum 70810. Optimiaed interrelated factors through single factor experiment and orthogonal test. With number of lactic acid bacteria and sensory evaluation as evaluation criterion, the results showed that the optimal formula was addition of sucrose at 4 g/100 mL, addition of carrot juice at 4% (v/v). Based on the formula, the best fermentation conditions were as follows: inoculation of 2% (v/v), fermentation temperature of 31℃, fermentation time of 2 d. Finally we got fermented plum juice with good taste and abundant lactic acid bacteria2. Bio-functionality assessment of fermented plum juiceEvaluated biofunctionality of plum fermented juice through in vitro antioxidant experiments and nematode life test. The results showed that fermented plum juice had some scavenging ability on DPPH radical, superoxide anion radical and hydroxyl radical. In addition, it also had a certain capacity to chelate metal ion. Plum fermented juice could prolong the life of Caenorhabditis elegans, and it was in a dose-dependent manner. Fermented plum juice could also improve nematode’s resistance to heat stress and oxidative stress.3. Process optimization of fermented plum juice tofuQuality of tofu was influenced by the ratio of soybean to water, addition of fermented plum juice, processing temperature, processing time and so on. Optimiaed the above factors through single factor experiment and orthogonal test. With hardness and holding water capacity as evaluation criterion, the results showed that the optimal processing conditions were as follows:addition of fermented plum juice of 20%, ratio of soybean to water of 1:4, processing temperature of 90℃, processing time of 25 min. Measured the shelf life of tofu prepared under the optimal conditions by pH, total number of bacteria and coliform. The results showed that the produced tofu had a shelf life of 12～16 h at 37℃, and its quality would not go bad in the next week at 4℃.4. Texture optimization of fermented plum juice tofuIn order to improve the low hardness and bad texture of tofu produced by fermented plum juice, added the natural edible gum and calcium salt to optimize texture. Using response surface method with response value of hardness and water holding capacity, the optimum adding amount of edible gum and calcium salts were determined. The results showed that the best adding amounts were calcium lactate at 2.91 mmol/L and carrageenan at 0.328 g/L, respectively. The Scanning electron microscope(SEM) micrographs indicated that the tofu-gel network structure was more compact than these of control without carrageenan and calcium lactate. Analysed the water distribution in tofu by low-field nuclear magnetic resonance (LF-NMR) technique. It showed that not easily flow water increased after addition of calcium lactate and carrageenan, which was related to water holding capacity. In addition, by measuring the viscosity changes of tofu, it indicated that curd speed greatly improved, curd time reduced.