Study On Preservation Treatments And Quality Improvement Of Wet Rice Noodles

Rice noodles are traditional food in Asian countries.It is mainly made from indica rice,made by extrusion forming or powder cutting.Rice noodles are popular among local people because of their convenient consumption and smooth taste.However,the wet rice noodles have high moisture content,and easy to be contaminated by microorganisms during the production process.In addition,it is not suitable to use high pressure or long time sterilization.Therefore,it is an urgent issue to delay the growth of the microorganisms and quality deterioration of wet rice noodles.The main research contents were as follows:Firstly,determined the optimum condition of acid leaching process was 1%citric acid solution for 2 min.On the basis of acid leaching,combined with biological preservative（ε-poly-L-lysine hydrochloride）and water bath sterilization to extending the shelf life of wet rice noodles.The results showed that the optimal addition amount ofε-poly-L-lysine hydrochloride was 0.02%,and the optimal water bath time was 20 min.The wet rice noodles prepared by compound preservation technology did not detected microorganisms within three months of storage.The second part was to explore the effects of acid leaching treatment（CA）,acid leaching combined withε-polylysine hydrochloride treatment（PL）and acid leaching combined with water bath treatment（SY）on the dominant spoilage microorganisms and microbial diversity of wet rice noodles,and take distilled water immersion as control group（CK）.The results showed that the dominant spoilage bacteria in different treatment groups were Bacillus and Enterobacter.Yeast was the main spoilage fungi in the early stage of storage,and mold in the late stage.The results of 16S r DNA indicate that the dominant spoilage bacteria in CK group were Pantoea,Sphingomonas and Bacillus.Different preservative treatments can significantly reduced the diversity of bacterial community.Among which,CA reduced the relative abundance of Sphingomonas and Bacillus,significantly.PL had good inhibitory effect on all three dominant bacterial genus.ITS r DNA results showed that Rhizopus,belongs to Mucoromycota,was the dominant spoilage fungi in CK,however the relative abundance decreased obviously after preservation treatments.While Ascomycota,with strong resistance to stress,became the dominant phylum after preservation treatments.This study provide a theoretical basis for the exploration of preservation technology of wet rice noodles.The third part was to improve the ediable evaluation quality of wet rice noodles,acetate starch,monoglyceride and guar gum were added into rice flour respectively.The optimal processing parameters were determined by single factor test and orthogonal test.The quality of wet rice noodles was evaluated by texture,cooking loss and sensory evaluation.The results showed that the optimal proportion of starch acetate,glyceryl monolaurate and guar gum was20%,0.3%and 0.2%,respectively.Under these conditions,the wet rice noodles with improved quality had high rehydration rate,minimum cooking loss,high hardness,good chewiness and the best sensory score.The results showed that the quality of wet rice noodles with the best ratio was improved significantly.The last part was to explore the effects of compound modifiers on long-term retrogradation and quality deterioration of wet rice noodles.The compound wet rice noodles and control samples were stored at 25℃for 12 weeks.The results showed that the moisture content of wet rice noodles decreased during storage,while,water activity increased.The content of freezing water increased,and the transverse relaxation time T₂₂ of weak binding water shifted to the right.This indicated that the combination of water and non-aqueous substances in wet rice noodles became less tight,water holding capacity decreased and quality deteriorated during storage.In addition,the sensory score,rehydration rate,brightness and whiteness of wet rice noodles decreased during storage.Cooking loss,texture characteristics and broken rate increased during storage.However,the compound improvers could inhibit quality deterioration and water migration.It has no obvious effect on color difference and p H.X-ray diffraction showed that the compound quality improvers could change the long-range order of starch structure,increase the crystallinity of short-term retrogradation,and reduce the crystallinity of long-term retrogradation.Fourier transform infrared spectroscopy（FTIR）showed that the intermolecular or intramolecular hydrogen bonds of starch were reduced,but the short-range order was not changed.It was found by scanning electron microscope（SEM）that the addition of starch and guar gum could make the rice noodles form larger pores and network structure.This experiment studied the effects of different preservation methods on the microbial growth and microbial community structure of wet rice noodles.On the basis of microbial controlled effectively,improving the quality of wet rice noodles and monitoring the long-term storage stability.This study provides theoretical basis for the industrialization of wet rice noodles.