Effect Of Sourdough Fermented By Nisin Producing Lactococcus Lactis On Quality Of Fresh Noodles

Consumers prefer fresh noodles as they have a strong taste and fragrance,but the shelf life of fresh noodles is extremely short due to high water activity and nutrition.This study investigated impact of Lactococcus lactis subsp.lactis（L.lactis）fermented sourdough on the quality and shelf of fresh noodles,as well as the mechanism of sourdough delaying quality deterioration during storage at 4℃.This study can help to develop fresh noodles with unique flavor characteristics and provide theoretical and technical support for the extension of shelf life and quality maintenance of fresh noodles.L.lactis can grow and metabolize normally and produce nisin in situ in wheat flour.Sourdough fermentation profile including pH,total number of lactic acid bacteria colonies,organic acids and reduce sugar of Lactococcus lactis subsp.lactis were investigated.After 24h fermentation,pH value of sourdough decreased to 4.1,the number of lactic acid bacteria colonies was 8.5 Log CFU/g,the content of lactic acid reached 6.1 mg/g,the content of maltose reached 20.5 mg/g,the content of glucose reached 3 mg/g.After L.lactis CGMCC1.2030 fermented sourdough for 6 h,the highest nisin activity is about 400 IU/g.Storage experiments have shown that sourdough can prolong the shelf life and improve the quality of fresh noodles during storage.The shelf life of fresh noodles with sourdough was compared with the addition of lactic acid,nisin,calcium propionate,and lactic acid+nisin in fresh noodles.The shelf life of fresh noodles was in the following order（from the highest to the lowest）:sourdough>lactic acid+nisin>nisin>lactic acid>calcium propionate>blank group.The addition of sourdough increased the shelf life of fresh noodles by 83%,from 12 days to22 days at 4℃,compared to the blank control.Furthermore,fungal challenge test showed that sourdough inhibited the germination of spores of Penicillium expansum and Aspergillus flavus in artificially contaminated fresh noodles.The sourdough delayed the quality deterioration of raw noodles during storage at 4℃,while improving the appearance,cooking quality and texture of fresh noodles.Changes in fresh noodle quality and the effect of sourdough on the quality of fresh noodles stored at 4℃ was investigated.The optimal cooking time of fresh noodles with sourdough was prolonged,and the hardness of noodles increased significantly after cooking.After 12 days of storage,the b*value of fresh noodles with sourdough decreased from 12.35 to 8.47,and the number of black spots decreased by 15.48%,and the appearance was more uniform.The cooking loss was reduced by 15.48%compared with the blank group.The hardness of cooked noodles after cooking decreased by 25.96%compared with noodles before storage,and the chewiness decreased by about 18.57%.While the browning degree of fresh noodles in the blank group is more serious,and the cooking loss is lower than that before cooking.The hardness and chewiness of the strips decreased significantly after cooking.The hardness of cooked noodles decreased by 35.59%,and the chewiness decreased by 36.50%compared with those before storage.In addition,the addition of sourdough had a significant effect on the flavor of noodles,the alcohols content in the fresh noodles with sourdough decreased by 46.53%,the aldehydes content increased by 32.9%,and the ketones content was 11.8 times that of blank control.Among which,the hexanal content increased by 52.8%,the content of（E）-2-nonenal increased by 25.45%,and 2-undecanone,2,3-butanedione,and 3-hydroxy-2-butanone were added.The content of 2-pentylfuran in cooked noodles with sourdough increased by 58.18%compared with blank control.The water distribution in fresh noodles,the molecular weight distribution of gluten protein,the gluten network structure,the gelatinization characteristics of starch,the crystallinity and crystal structure of starch were determined,revealing that the relationship between the delayed quality deterioration of sourdough and the moisture,protein,and starch in the noodles.Results showed that T₂₂ of fresh noodles decreased and the water migration decreased after the addition of sourdough.In fresh noodles with sourdough,the amount of free thiol as well as glutenin and gliadin extracted by SDS were decreased,showing the degree of protein crosslinking enhanced.CLSM revealed that fresh noodles with sourdough addition had a more continuous and dense gluten protein network structure that might envelop starch granules tightly;SDS-PAGE analysis revealed that the subunit composition of gluten protein remained constant during storage.Gluten protein’sα-helix structure decreased while itsβ-turn and reverse parallelβ-fold structure increased after 12 days storage.The gelatinization characteristics of starch in fresh noodles were analyzed,and the result shows that gelatinization enthalpy value increased.The peak viscosity of starch increased,while the disintegration value decreased;the XRD pattern indicates that the crystalline structure of starch has not changed,but the crystallinity has increased.