| Owing to high water content,wet raw noodles showed a short shelf life because of microbial spoilage and browning reaction.In order to prolong the shelf life of the fresh noodles,this study used different antisepsis and preservation technology to solve the problems above,as can provide a theoretical basis for industrial production.Main contents and results are as follows:1. Investigating the shelf life of blank group wet raw noodles and accelerated test conditions:(1) Mainly studied the total bacteria numbers,mould count and whiteness of blank group noodles stored at different temperatures (37℃,28℃,20℃and 4℃).The max-storage-time while the bacteria,mildew and whiteness all hadn't exceeded standard was determined as the shelf life of the wet raw noodle, while the products'shelf life were 4.4h,6.7h,21.6h,89h respectively;(2) Analysising the microorganism in noodles,it shown that G+,G-,coccus,becillus all of it have spore accounted for 60%~70%,30%~40%,95%,5%; Aspergillus strains is the majority of mildew,which includes the most uncommon Aspergillus accounted for 70%~ 80%,Aspergillus Oryzae,Rhizopus,Penicillium and Aspergillus Niger.The exploration above would provide a theoretical basis on the follow-up test.(3)To accelerate the testing speed,this article choose the temperature at which microbial grow and whiteness change both fairly fast. Considered synthetically,this article choose 28℃as the accelerated test temperature,then the shelf life of fresh noodles at 37℃,20℃,4℃are 0.66 times,3.2 times,13.3 times to the noodles at 28℃.2. Study on chemical method to prolong the shelf life of wet raw noodles(enhancement test,the shelf life of wet raw noodles was tested in environment 28℃,same below):(1)Ethanol,sodium diacetate,calcium propionate,propanediol etc.were tested for their bacteriostatic ability,the results suggest that sodium diacetate and Ethanol had excellent bacteriostatic ability among the reagents above.The orthogonal experiment results show that the optimum conditions of using chemical preservative was:2.5%Ethanol,0.4%sodium diacetat,0.02%calcium propionate,2%propanediol.The verification test under optimum conditions shows that the shelf life of wet raw noodles was over 22d (28℃);(2)The usage of capryl-monolyceride and calcium propionate as antiseptic was certificated by GB2760,and ethanol can also used in wet raw noodles as food accessories.Test results indicating that three kind of antiseptics had comfortable effect on inhibit mycete,while their abilities of inhibit mycete were:3%ehtanol(20h)>0.1%capryl -monolyceride(20h)>0.025%calcium-propionate(15h);(3)The results of study of antiseptics'effects on wet raw noodles suggest that chitosan and Nisin had limited affect to inhibit mycete before acidity adjustment.The addition level of chitosan was high,but the effect on mycete inhibit still not significant after acidity adjustment.Furthermore,acetic acid used as regulating acid agent could cause disagreeable taste in noodles,so chitosan is not suitable to be used as antiseptic. The addition level of Nisin was low, and its'mycete inhibit effect was significantly improved after acidity adjustment,so it was suitable as antiseptic in wet raw noodles, while the addition level was 0.02%. The addition level of natamycin was very low and has comfortable mycete inhibit effect,it was also suitable to be used as antiseptic in wet raw noodles,the usage dose was 0.002%.Prouducts using chemical method to retain freshness can get a long shelf life,but it may brings safe problems and can not prevent browning reaction.3. Physical methods for extending the shelf life of wet raw noodles: (1) Irradiation.Treated by 2kGy,4kGy,6kGy irradiation dose,the microorganisms in wet raw noodles are significantly suppressed,the shelf life can be extended to 3 ~ 5d,but the whiteness index only 20 ~ 25 at 24h,and sensory quality degraded seriously,so irradiation is not suitable used as preservative technology on wet raw noodles.(2)Heat treatment.Not using any preservatives,appropriate methods of dehydration and heat treatment are adopted to extend the shelf life of wet raw noodles.The optimum experimental conditions:dehydrated 3h in 35℃, RH = 75%,then 90℃heat treatment for 20min,thus the shelf life was up to 75h.In addition,heat treatment improved the whiteness of noodles markedly.Further tests showed that intermittent treatment had better performance,with the shelf life extended to 106h.(3)Packaging technology. Using deoxidizer packaging technology, the shelf life based on microbiological is extended to 24 ~ 38h, whiteness index extended to 33h.4. Comprehensive consideration of food safety and quality of products,a comprehensive selection experiments had been taken as following:(1)The combination of natural preservatives Nisin and heat treatment,the shelf life of noodles extended to 130h(5.4d),which was a satisfactory result.(2)The combination of oxygen packaging and heat treatment prolonger the shelf life of noodles to 192h (8d),which was the best result in this study.In summary,choose the combination of oxygen packaging and heat treatment as the preservation technology of wet raw noodles,thus the shelf life can prolong to 20d at 20℃,or over 80d at 4℃. |
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