Study On The Shelf-life Extension And Quality Maintenance Of Semi-dried Noodles

Semi-dried noodles,as a novel instant noodle product with medium-high moisture content,meeting consumers’demand for nutrition,health,quality,and taste,show huge market potential in the noodle industry.However,due to the medium-high moisture content,initial microbial quantity,and abundant nutrient substances,semi-dried noodles are prone to spoilage and deterioration during storage at room temperature.Therefore,the effects of phosphate salts,p H and packaging methods on the shelf-life and quality characteristics of semi-dried noodles,as well as the underlying mechanisms were investigated in this paper.The purpose of this study was to provide theoretical guidance for the shelf-life extension and quality maintenance of semi-dried noodles.Firstly,the effects of four types of phosphate salts（SHMP,sodium hexametaphosphate;STPP,sodium tripolyphosphate;TSPP,sodium pyrophosphate;MSP,sodium dihydrogen phosphate）on the shelf-life and quality characteristics of semi-dried noodles were investigated.Microbial analysis showed that 0.2%SHMP,0.4%STPP and 0.3%TSPP extended the shelf-life of noodles from 3 days to 4 days,while 0.2%or 0.3%MSP extended the shelf-life of noodles from 3 days to 5 days.Nuclear magnetic resonance（NMR）analysis revealed that phosphate salts decreased the water mobility in noodles.Cooking and texture analysis showed that TSPP increased the cooking loss of noodles,while STPP and TSPP increased the water absorption of noodles.SHMP,TSPP and MSP increased the hardness of noodles.The rheological test showed that STPP had the strongest effect on improving the rheological properties of dough.The SDS extractable protein（SDSEP）under non-reducing and reducing condition showed that SHMP,STPP and TSPP could induce disulfide bond cross-linking between proteins in semi-dried noodles.STPP and TSPP increased the peak viscosity of starch in semi-dried noodles,while SHMP and MSP decreased the peak viscosity.Thermal properties analysis indicated that STPP and TSPP increased the gelatinization enthalpy（ΔH）of starch in noodles,while SHMP and MSP decreased theΔH.Furthermore,confocal laser scanning microscopy（CLSM）and scanning electron microscopy（SEM）showed that SHMP,STPP,and MSP strengthened the gluten network formation,while TSPP weakened the network.Secondly,the effects of p H on the shelf-life and quality characteristics of semi-dried noodles were investigated.Microbial analysis showed that the inhibitory effect of p H on the total plate count was ranked as follows:p H 4>p H 10>p H 5=p H 9>p H 7=p H 8>p H 6.The inhibitory effect of p H on the mold/yeast counts was ranked as follows:p H 9>p H 10>p H 6=p H 8>p H 4>p H 7=p H 5.With the increase of p H（p H 4-10）,the water mobility in noodles increased first and then decreased,reaching the maximum at p H 7;the cooking loss of noodles decreased first and then increased,reaching the minimum at p H 6;the hardness and tensile force of noodles increased significantly（p<0.05）.During the later storage period,the hardness of noodles at p H 4-8 decreased significantly（p<0.05）,while the hardness of the noodles at p H 9-10 did not decrease.With the increase of p H（p H 4-10）,the SDSEP value in noodles first decreased and then increased,and the protein covalent cross-linking degree was the highest at p H 8;the starch viscosity in semi-dried noodles first increased and then decreased,reaching the maximum at p H 8;Furthermore,CLSM showed that the microstructure of gluten network in the semi-dried noodles was getting denser and denser,and it was the densest at p H9.Thirdly,the effects of packaging methods on the shelf-life and quality maintenance of semi-dried noodles were investigated.Both deoxidizer and O₂/CO₂ adsorbent could extend the shelf-life of semi-dried noodles to more than 40 days.And deoxidizer had stronger inhibition on the total plate count and mold/yeast counts in semi-dried noodles.The inhibitory effect of packaging materials on the total plate count was ranked as follows:aluminum foil>PA/CPP=PE/PET>PA/PE.During the storage period of 0-20 days,the moisture content of semi-dried noodles in different packaging material groups decreased first,then increased,and then decreased again.The barrier of PA/PE was poor,and noodles lost more moisture during storage.During the storage period of 5-10 days,the transverse relaxation time(T₂₂)of the semi-dried noodles in all packaging material groups increased significantly（p<0.05）,and the T₂₂ of the semi-dried noodles in the aluminum foil group increased the least.During the storage period of10-20 days,the T₂₂ of the semi-dried noodles in the aluminum foil group did not change significantly（p>0.05）,while that in other packaging material groups decreased significantly（p<0.05）.During the storage period of 0-10 days,the hardness and chewiness of semi-dried noodles in all packaging material groups increased significantly（p<0.05）,while the aluminum foil group had the smallest increase.During the storage period of 10-20 days,the hardness and chewiness of all packaging material groups decreased significantly（p<0.05）,with the smallest decrease in the aluminum foil packaging group.Finally,the effects of comprehensive preservation on the shelf-life and quality maintenance of semi-dried noodles were investigated.Using 0.2%SHMP and 0.4%STPP as compound phosphate salts,adding 0.6%alkaline salt to adjust the p H of noodles to 9,and using deoxidizer combined with aluminum foil packaging,the shelf-life of semi-dried noodles at room temperature could be extended from 3 days to more than 120 days.And the edible quality of noodles could be maintained well during storage.