Tofu with long shelf life and preparation method thereof

A preparation method of a tofu, comprising

• soaking and pulping soybeans, adding a defoamer, filtering and removing dregs to obtain soy milk;
• boiling the soy milk to obtain boiled soy milk;
• performing a primary cooling on the boiled soy milk to obtain primary cooled soy milk with a temperature of 60-75° C.;
• homogenizing and deaerating the primary cooled soy milk to obtain homogenized and deaerated soy milk;
• sterilizing the homogenized and deaerated soy milk by ultra-high temperature (UHT) to obtain sterilized soy milk;
• performing a second cooling on the sterilized soy milk to obtain second cooled soy milk with a temperature of 8-15° C.;
• performing, by using an inline mixing pump, inline mixing on the second cooled soy milk and a composite coagulant to obtain a mixture, wherein the composite coagulant is a mixed aqueous solution of sterilized strong base-weak acid salt and coagulant, a weight ratio of the sterilized strong base-weak acid salt to the coagulant is (1.25-2.10):(2.35-2.95), a weight concentration of the sterilized strong base-weak acid salt is 1.25-2.10%, and a weight concentration of the coagulant is 2.35-2.95%;
• the coagulant is gluconate lactone or a combination of the gluconate lactone and MgCl2, and an additive amount of chloride ions in the coagulant does not exceed 0.26% (w/w) of a mixed coagulant aqueous solution;
• the sterilized strong base-weak acid salt is sodium pyrophosphate or sodium lactate;
• and a temperature of the mixed aqueous solution is 8-15° C., and an addition amount of the mixed aqueous solution is not less than 13% of a weight of the soy milk;
• filling the mixture into an aseptic packaging box to obtain sterile filled soy milk;
• and
• using intermittent microwave to heat the sterile filled soy milk for a period of 10-12 min for solidification, and then cooling to obtain the tofu, wherein in a first half of the period, the sterile filled soy milk is heated with 350 W microwave per minute for 30 seconds, with an interval of 30 seconds, and in a second half of the period, the sterile filled soy milk is heated with 70 W microwave per minute for 30 seconds, with an interval of 30 seconds.

A preparation method of a tofu, comprising the following steps:

• soaking soybeans to obtain soaked soybeans;
• pulping the soaked soybeans according to a ratio of the soybeans to water of 1:6 to obtain soybean pulp;
• adding monoglyceride to the soybean pulp, to obtain foam-removed soybean pulp, wherein a weight ratio of the monoglyceride to the soybeans is 0.5%;
• filtering the foam-removed soybean pulp to remove dregs in the foam-removed soybean pulp, to thereby obtain soy milk with a solid content of 10.5%;
• heating the soy milk at a temperature of 115° C. for 5 min to obtain heated soy milk;
• performing a primary cooling on the heated soy milk to obtain primary cooled soy milk with a temperature of 70° C.;
• homogenizing and deaerating the primary cooled soy milk under a pressure of 20 MPa and a vacuum of 0.05 MPa, to obtain homogenized and deaerated soy milk;
• sterilizing the homogenized and deaerated soy milk by UHT at 134° C. for 5 seconds, to obtain sterilized soy milk;
• performing a second cooling on the sterilized soy milk to obtain second cooled soy milk with a temperature of 10° C.;
• performing, by using an inline mixing pump, inline mixing on the second cooled soy milk and a composite coagulant sterilized by membrane filtration to obtain a mixture, wherein the composite coagulant is added in a form of an aqueous solution, and a water temperature of the aqueous solution is 10° C., an addition amount of the aqueous solution of the composite coagulant is 13.7% of a weight of the soy milk, and the aqueous solution of the composite coagulant contains 1.7% sodium citrate and 2.5% gluconolactone;
• filling the mixture into an aseptic packaging box to obtain sterile filled soy milk;
• and
• using intermittent microwave to heat the sterile filled soy milk for a period of 12 min for solidification, and then cooling to obtain the tofu, wherein in a first 6 min, the sterile filled soy milk is heated with 350 W microwave per minute for 30 seconds, with an interval of 30 seconds, and in a second 6 min, the sterile filled soy milk is heated with 70 W microwave per minute for 30 seconds, with an interval of 30 seconds;
• wherein the step of using intermittent microwave to heat the sterile filled soy milk for the period of 12 min for solidification, and then cooling to obtain the tofu comprises the following steps, which are implemented in sequence:
• using the intermittent microwave to heat the sterile filled soy milk to make a center temperature of the sterile filled soy milk increase to a temperature of 90° C.;
• keeping the temperature at 90° C. for 5 min to obtain heated soy milk, and
• cooling the heated soy milk to a room temperature to thereby obtain the tofu.