| Tofu is accepted by people because it contains rich soybean protein, unsaturated fatty acids and active component. Due to the presence of nutrients and high moisture, spoilage associated with bacterial growth is likely to be happened in a short period of time. Especially in the summer day, the high temperature makes tofu’s shelf-life even shorter, causes the difficulties in transit, preservation and consumption of tofu, which greatly limits the development of China’s tofu industry, and also brings some serious food safety issue. Currently in China, the production of tofu is lowly automated, the small-scaled enterprises will exist for a long time, so finding a proper natural food preservative is a relatively easy and convenient way to extend shelf-life of tofu under current conditions.In this research, we optimized the degradation conditions of chitosan which is a non-toxic broad-spectrum antimicrobial with large molecular weight, to get a kind of high antibacterial and water-soluble oligochitosan, which can be used to extend tofu’s shelf-life, and provide a theory basis for tofu’s manufacturing, The following were results of the study:1Optimization of degradation conditions of chitosan to get high antibacterial and water-soluble oligochitosanThe three single factors for chitosan degradation were optimizated by orthogonal experiments to get the high antibacterial and water-soluble oligochitosan, the optimal degradation condition were the concentration of H2O2:3%, the reaction time:60min, the reaction temperature:60℃. The molecular weight of the oligochitosan got through this condition is1.043×104, the degree of deacetylation is83.9%, and The chitosan and oligochitosan were analyzed by infrared spectrometry and found a little difference in their spectra. It is suggested that their basic structures be similar.2The effects of oligochitosan on3different types of tofuIn order to study the effect of oligochitosan on the commercial tofu,5different concentration of oligochitosan were added into3different types of tofu. The result shows that the effects of oligochitosan on preservation of marinated tofu and gypsum tofu were similar, only the addition of2.0%oligochitosan achieved better preservation effect. And the effect on GDL tofu’s fresh-keeping seems the best, the addition of2.0%oligochitosan increased the shelf-life at37℃of GDL tofu by8hours. But too more oligochitosans (≥1.5%) will weaken the flavor and taste of tofu. The addition of oligochitosan also increased the water content and springiness of tofu, but only within a certain range, oligochitosan is positive for the hardness, cohesiveness and chewiness of the marinated and gypsum tofu, and the GDL tofu’s hardness, cohesiveness and chewiness were decreased with the increase of oligochitosan. Therefore excessive doses of oligochitosan have a negative impact on the quality of tofu.3the study on the combination of oligochitosan and acidic solventFor the antibacterial properties of oligochitosan will be greatly improved in low pH condition, some kind of acidic solvent is considered to be added into the tofu to reduce the addition of oligochitosan, and the result showed that GDL was a proper one. Central composite design (CCD) was used to optimize the ratio of oligochitosan and GDL, the optimized ratio was:oligochitosan0.66%, GDL1.00%. And the preservative successfully inhibited the growth of bacterial, the total number of bacterial and coliform group were included, in the tofu. It also slowed down the tofu’s speed of acid dropping and softening. Tofu’s shelf-life was extended by nearly8h at37℃. And the sensory quality was kept fresh within12h. |
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