| Fresh wet noodles(FWNs)have a long history in China,and are loved by Chinese people because of their good taste,unique flavor,and rich nutrition.However,FWNs have high moisture content and rich nutrients,which make them very suitable for the growth of microorganisms and have a short shelf-life.Many studies mainly focus on the effects of various preservation methods on the inhibition of microorganisms and shelf-life of FWNs,but few studies focus on their effects on quality and the mechanism of quality effects.This paper mainly studied the effects of three preservatives commonly used in the industrial production of FWNs(ethanol,acids and acid salts,and alkaline salts)on the shelf-life and quality of FWNs,and explored the underlying mechanisms of changes in quality.Firstly,the research and analysis of the refrigerated FWNs sold in the supermarket channels in the Wuxi region were conducted.The results showed that the refrigerated FWNs in the market can be divided into two types: FWNs with short shelf-life(4～5 d)and FWNs with long shelf-life(30～90 d).Among them,the FWNs with short shelf-life usually do not add preservatives or only add a small amount of alkaline salts to improve their quality,and the p H value is 6.66～8.42.The commonly used preservatives in FWNs with long shelf-life are ethanol,acids and acid salts,and alkaline salts,of which ethanol is the most widely used.In addition,some FWNs with long shelf-life are adjusted the p H value to 4.84～5.11 or 9.41～9.46 by adding acids and acid salts or alkaline salts to prolong their shelf-life.Some FWNs with long shelf-life will also add water retention agent or deoxidizers for compound preservation.In terms of sensory properties,the sensory scores of FWNs with alkaline salts are generally higher than other samples.Secondly,the effect of adding ethanol on the microbial shelf-life and quality characteristics of FWNs were investigated.Ethanol could significantly inhibit the growth of microorganisms during the storage of FWNs at 4°C.When the additional amount of ethanol was 2%,4%,and6%,the microbial shelf-life of FWNs could be prolonged by 11 d,29 d,and 40 d,respectively.The addition of ethanol resulted in a significant(p<0.05)decrease in the water absorption,stabilization time,storage modulus(G’)and loss modulus(G’’)of the dough,and a significant(p<0.05)increase in the development time,weakening degree and creep strain.With the addition of ethanol,the hardness,breaking force,tensile distance,and water absorption of FWNs decreased significantly(p<0.05),while cooking loss increased significantly(p<0.05).Confocal laser microscope(CLSM)observation and gluten network analysis showed that the addition of ethanol inhibited the formation of gluten network in cooked FWNs,and the protein area,total protein chain length and number of connection points decreased significantly(p<0.05),and the porosity increased significantly(p<0.05).The results of reversed-phase highperformance liquid chromatography(RP-HPLC)showed that the addition of ethanol significantly(p<0.05)decreased the content of gliadin subunits,indicating that ethanol dissolved part of the gliadin.Changes in the content of SDS-extractable protein(SDS-EP)and protein subunits indicated that ethanol inhibited the cross-linking of protein.The results of nuclear magnetic resonance(NMR)showed that the addition of ethanol shifted the relaxation peak of water in FWNs to the right,enhanced water mobility and increased the content of free water.Thirdly,the effects of acids and acid salts(phosphoric acid,monosodium fumarate and fumaric acid)on the microbial shelf-life and quality characteristics of FWNs were investigated.The results showed that adding acids and acid salts to adjust the p H value of FWNs to 5.3 and4.7,respectively,could prolong their microbial shelf-life at 4°C by 5 d and 10 d.Adding acids and acid salts significantly(p<0.05)decreased the hardness and tensile distance of FWNs,and significantly(p<0.05)increased cooking loss and water absorption.CLSM analysis showed that the addition of acids and acid salts inhibited the formation of the gluten network in cooked FWNs.The contents of SDS-EP and free-SH in cooked FWNs increased significantly(p<0.05)with the addition of acids and acid salts,indicating that the formation of disulfide bonds was inhibited during the cooking of FWNs.The results of X-ray diffraction indicated that the addition of acids and acid salts resulted in the hydrolysis of the amorphous region of starch in the FWNs,and the pasting temperature,peak viscosity,and trough viscosity decreased significantly(p<0.05).In addition,the reduction in p H value caused by the addition of acids and acid salts was the main factor that affected the microbial shelf-life and quality of FWNs,but different types of acids and acid salts had no significant effect(p<0.05).Finally,the effects of additional amount of alkaline salts(mixed sodium carbonate and potassium carbonate 2:1)on the microbial shelf-life and quality characteristics of FWNs were studied.The results showed that the microbial shelf-life of FWNs at 4°C could be extended by7 d when the additional amount of alkaline salts was 1.5%.The addition of alkaline salts significantly(p<0.05)increased the hardness,breaking force,tensile distance,cooking loss,and water absorption of FWNs.The Angio Tool was used to fit and analyze the CLSM images,and the results showed that the addition of alkaline salts significantly(p<0.05)increased the protein area,total protein chain length and number of connection points,and significantly(p<0.05)decreased the porosity,the gluten network in cooked FWNs was denser.The ratio of β-elimination reaction and-SH oxidation reaction gradually increased with the addition of alkaline salts,so that the content of SDS-EP and free-SH in cooked noodles first decreased and then increased.The results of rapid viscosity analyzer(RVA)indicated that the pasting temperature,peak viscosity,trough viscosity,and final viscosity of starch all increased significantly(p<0.05)with the addition of alkaline salts. |
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