Study On The Preservation Of Fresh Wet Noodles

Fresh wet noodles are popular with consumers because of their excellent palatability,flavour and nutrition.However,the high moisture content makes it susceptible to rapid spoilage due to microbial infestation during storage,and the short shelf-life is still an urgent issue for the industry.Therefore,this study investigated the effects of different water,wheat flour with different bacterial contents,chitosan oligosaccharides and hydrothermal treatment on the microbial shelf-life and quality of fresh wet noodles during storage at 4℃.And the underlying mechanisms of quality changes was investigated in order to provide a theoretical basis for the production of fresh wet noodles with longer shelf-life and better quality.Firstly,the effect of three types of water(plasma activated water,slightly acidic electrolytic water and ozonated water)on the microbial shelf-life and quality characteristics of fresh wet noodles was investigated.The results showed that the shelf-life of fresh wet noodles(6 d at the control group)was extended by 3 d,3 d and 6 d,respectively,at 4℃.All three groups of water enhanced the initial L~*and acidity of fresh wet noodles,reducing the PPO activity and p H at the same time.The determination of textural properties showed that the plasma activiated water reduced the hardness of fresh wet noodles to 4258.82 g,while the hardness of noodles made with slightly acidic electrolytic water and ozonated water reached 4640.17 g and 4817.53g,respectively.In the sensory evaluation,the fresh wet noodles made with ozonated water obtained the highest evaluation score.Also,the effect of wheat flour with different bacterial contents on the microbial shelf-life of fresh wet noodles was investigated.The decrease in the initial bacterial content of wheat flour significantly(p<0.05)prolonged the shelf-life of the fresh wet noodles at 4℃.At the same time,the reduction in the bacterial content of wheat flour significantly(p<0.05)inhibited the change in acidity of fresh wet noodles during storage.Secondly,the effect of chitosan oligosaccharides(COS)on the microbial shelf-life and quality of fresh wet noodlse was investigated.Microbiological results showed that the addition of COS significantly(p<0.05)prolonged the microbial shelf-life,reaching 9 d,12 d,12 d and15 d(0%,0.1%,0.3%and 0.5%COS),respectively.The addition of COS significantly(p<0.05)increased the initial acidity and inhibited the change of acidity during storage.With the increase concentration of COS,the cooking loss of fresh wet noodles increased significantly(p<0.05),while the L~*,hardness,tensile strength and tensile distance of noodles decreased,thereby reducing the sensory quality.X-ray diffraction patterns(XRD)showed that the addition of COS decreased the relative crystallinity of starch in noodles;the analysis of differential scanning calorimetry(DSC)showed that the enthalpy of gelatinization(ΔH)reduced to 4.4 J/g when the addition of COS reached 0.5%.According to the confocal laser scanning microscope,the gluten network of cooked noodles tended to be loose and discontinuous with the addition of COS increased;At the same time,the content of non-reducing SDS-EP and free-sulfhydryly group content increased from 38.89%and 2.40μmol/g of the control group to 47.49%and 2.87μmol/g,respectively,indicating that COS inhibited the disulfide bond cross-linking of gluten proteins during noodles’cooking.In addition,the composite effect of COS and ozonated water was studied.The results showed that ozonated water further extended the shelf-life of fresh wet noodles to 15,18 and21 days(0.1%,0.3%and 0.5%COS),respectively.Based on the addition of COS,ozonated water effectively improved the L~*,hardness and tensile strength of noodles,effectively improving the sensory quality.CLSM analysis indicated that gluten network affected by COS was more compact after being treated with ozonated water.Ozonated water promoted the covalent crossling of gluten proteins,resulting in significant(p<0.05)decreases in SDS-EP and free-sulfhydryl group content.Thirdly,the effect of hydrothermal treatments at different temperatures(60,70 and 80°C)and times(10,20 and 30 min)on the microbial shelf-life and quality of fresh wet noodles was investigated.The results showed that the microbial shelf-life of the noodles treated at 80°C could reach 50 d.The hydrothermal treatment significantly(p<0.05)decreased PPO activity and effectively maintained the stability of L~*.With the increase of temperature and time,the cooking loss and water absorption rate of noodles decreased significantly(p<0.05),while the hardness increased significantly(p<0.05).In addition,the degree of gelatinization of fresh wet noodles treated at 80℃for 30 min reached 31.91%,which meant the noodles still maintained the character of“raw”.The results of DSC and XRD showed that hydrothermal treatment increased the gelatinization temperature of starch in noodles,while the enthalpy of gelatinization(ΔH)and the relative crystallinity decreased.In addition,hydrothermal treatment promoted the cross-linking of gluten protein networks,and reduced the content of SDS-EP and free sulfhydryl groups to 56.52%and 2.81μmol/g,respectively,at 80℃-30 min.Finally,the effect of composite preservation on the microbial shelf-life and quality of fresh wet noodles was investigated.The combination of ozonated water,0.5%COS and hydrothermal treatment(80℃-30 min)extended the shelf-life of fresh wet noodles from 10 d to more than 93d,stably maintaining p H,acidity,textural properties and sensory quality during storage.