Summary:in this experiment,acidic electrolyzed water as antiseptic solution is used to research the disinfect effect and quality influence for tofu.The result shows tofu soaked in acidic electrolyzed water is beneficial for reducing microbes.

The soaked time about 20 minutes could make the microbe total number reduce from 3.64 log CFU/g to 2.34 log CFU/g.

More,the result of instrument shows acidic electrolyzed water has little influence for the hardness and color of tofu.

The result of sensory evaluation shows the soaking of acidic electrolyzed water basically does not influence with sensory quality of tofu.

Here are two species tofu in China,named Northern tofu and southern tofu.The northern is one of the main representative traditional bean product whose flavor,sense and good processing property is welcomed by people.but,most tofu producer is still the small-scale who has low efficiency,unstable quality and bad hygiene condition.

Tofu is easily go bad because of high water volume,high protein and fat.because tofu is not easily store and could not resolve the quality problem on the transportation,it only is sold in local to refrain from producing food.so,it is essential to research the keep-fresh technology to reduce loss.

Electrolyzed water is produced by electric field in special device,which make PH vale,ORP and ACC change to generate the special functional acidic electrolyzed water and alkaline electrolyzed water.Acidic electrolyzed water has a lot of functions alike high-effectiveness,instantaneous,wide scope,non-residue and convenient operation and use safeness,which is the extensive new disinfected technology in domestic and aboard.

This research,the northern as raw material,discusss the disinfect effect and quality influence for Acidic electrolyzed water in order to provide with a lot of theory data to keep it fresh.

1. Material and method

1.1 material and reagent

The northern from local supermarket.

Acidic electrolyzed water (pH：2.6 ±0.2、ORP=1016 ±24mV、ACC=49.2±3.8mg/L);

Running water(pH：7.6±0.3、ORP=365±10mV、ACC=4.3 ±0.8mg/L,glacial acetic acid,K2CR209,KI and soluble starch and KCL

1.2 method

1.2.1acidic electrolyzed water equipment

Electrolyzed generator to generate acidic electrolyzed water,NACL concentration is 1g/l,electrolyzed time 15 minutes.

PH value,ORP are measured by PH meter and reducing potential meter.The index of each sample is measured about 3 times,effective chlorine measured by iodine quantity method.

1.2.2 acidic electrolyzed water disinfect tofu 6 pieces of 25g tofu are divided two groups.One is soaked in electrolyzed water,another soaked in running water.3 pieces of tofu in every groups are soaked separately in 10.20.30 minutes in 100ml water and the contrast undone.Take them out to dry about 10 minutes to measure the number of bacteria.

By use of plate counting method measure the number of bacteria.Take 10g tofu after soaking under the sterile operation, and ground up to take into the triangle bottle with 90ml sterile saline.And dilute according to 10 times to full shake.

According to the rule GB4789.2-94,take inoculation of bacterial suspension into nutrient agar medium.

Count the number in eternal cultivat box in 37 degree.

1.2.3 the acidic electrolyzed water influence with the hardness and quality of tofu

Take 250g or so tofu in 2000ml beaker in proportion of 1:4 with acidic electrolyzed water ,separately soaked after 10.20.30minutes to measure the hardness and color of tofu and sensory evaluation.

1.2.3.1test color

The color of tofu is tested by color different meter according to the system of table color l*a*b ruled in 1976.l*is named brightness index,l*=0 black,l*=100white, higher value the l is,brighter the color is.+a*direction is red increase,-a*direction green increase,+b*direction yellow increase,-b*direction blue increase,VE ab*is the disparity of sample color.

1.2.3.2the hardness evaluation of tofu

Here is the second compression experiment by rheometer:sample is from tofu by sampler,the hardness of tofu is calculated by BOURNE method. 1.2.3.3sensary evaluation of tofu

According to the GB/T4195,10 over-graduated student from food college in China agriculture university,who know about the processing of tofu in technology and property.Before sensory evaluation,the sample is numbered in casual,and slice cube sample2cm*2cm*2cm,which is placed in the sheet plate with number to provide with judger in the laboratory with partition to evaluate.The hardness is sensed by teeth or tongue pressing the sample.Flavor is the particle intensity in mouth.

Taste is the bean flavor belonged with bean curd including the taste and flavor sensed by smell and mouth.Color is the sensory color by sense.Whole accept concluding color,flavor ,taste and hardness is the best.

2result and analysis

2.1the disinfect effect of electrolyzed water

It is advisable that the bacteria number of untreated tofu is 3.64log CFU/g.the treated is less than the untreated about 1.0 pair value,but that soaked running water is no difference with the untreated,which shows that running water with no disinfect effect and is less than electrolyzed water’s.From chart 1,it shows the number of bacteria is different in relation with different soak time.Tofu soaked in electrolyzed water about 20 minutes is least reaching 2.34 log CFU/g from 3 groups.Soak time 10 minutes preclude from the function of electrolyzed water.

The 30 minutes’ disinfect is lower following with contact time with tofu.

2.2the impact of tofu hardness soaked in electrolyzed water

The tofu texture has the important function for the quality and custom’s acceptability.Tofu is the protein gel substance whose hardness is one of the important texture.this experiment tested by rheometer has the impact fot tofu soaked in electrolyzed water.The experiment shows it is not obvious impact for hardness.After 30 minutes soak time ,the decline of hardness is not obvious,which show it could not affect the hardness in the condition of

soaking time 30 minutes.

2.3the impact of tofu color in electrolyzed water

The impact of tofu color soaked in electrolyzed water is tested by color different meter.From chart 4,the sensory evaluation is not differential from all indexes and contrast.In hardness,the soaked electrolyzed water is softer than the contrast from data(p〉0.05)in correspondence with the test apparatus.In flavor,because the electrolyzed water has the smell of sodium hypochlorite of kind,we could inspect if tofu soaked electrolyzed water has that.

From chart 4,the flavor is lower but not differential than the contrast(p〉0.05).The staff can not detect the odor.

In texture,the result of the soaked in electrolyzed water is the lowest but not differential.In clor,here is no difference among them in correspondance with the instrument test.The soaked in electrolyzed water is low impact for the color in vision.On the overall,tofu soaked in electrolyzed water is closed with the contrast with no difference (p〉0.05).In conclude,the acceptability of tofu has no impact at all for the soaked in electrolyzed water.

3.Conclusion

Electrolyzed water benefit the loss number of bacteria for tofu.the experiment result of soaking time shows that tofu soaked in electrolyzed water in 20 minutes could reach the better disinfect affect.Acidic electrolyzed water is less impact for the hardness,but a little impact for the color.The result of sensory evaluation shows the electrolyzed water could not impact the sensory quality of tofu.