Study On The Effect Of Microwave Combined With Alkali Soaking On The Quality Of LL Noodles

Noodles are a traditional staple food in China and other Asian countries.Noodles are popular with consumers because of their simplicity,rich nutrition and variety.LL(Long Life)noodles is a new type of instant cooked wet noodles,which has the advantages of fresh,smooth taste and convenient consumption.It is the first choice for people to eat healthy fast food.However,due to its high moisture content and rich nutrients,LL noodles is more susceptible to microbial contamination and spoilage,shortening the shelf life.Therefore,the aim of this project is to extend the shelf life and maintain the quality of the LL noodles.Firstly,the effect of microwave sterilization pretreatment technology on the physical and chemical indexes of wheat flour,as well as the shelf life and sensory quality of the LL noodles was investigated.Secondly,the effect of alkali soaking process on the preservation and quality characteristics of the LL noodles during storage was explored.Finally,the changes in the internal components of the LL noodles under different alkali soaking conditions were explored to reveal the mechanism of different alkali soaking treatments on the quality changes of the LL noodles and to provide certain theoretical basis and technical support for the mass production of the LL noodles.Firstly,the effect of microwave treatment on the microbial content and other physicochemical indexes of wheat flour was studied.And the LL noodles was prepared from microwave sterilized wheat flour.The optimum microwave sterilization time of wheat flour was determined by considering the shelf life and sensory quality of the LL noodles.The results showed that microwave treatment could significantly reduce the initial total plate count,molds and yeasts in wheat flour,and inhibit the activity of polyphenol oxidase(PPO),with the inhibition rate reaching 86% and 90% at 50 s and the inactivation rate of PPO reaching 61%respectively.After microwave treatment,the weakening degree of wheat flour increased,and the water absorption rate and stability time decreased.When microwaved for 60 s,the color of wheat flour became dark and yellow,the Browning degree deepened,and the powder clumping phenomenon appeared.The color and processing quality of wheat flour were not seriously damaged by microwave treatment for 50 s.Compared with the control group,the wheat flour treated with 50 s microwave for the preparation of the LL noodles could prolong the shelf life of the noodles by 2 times,and the sensory quality did not change much.Therefore,the wheat flour microwave treatment time of 50 s was selected for the subsequent experiment.Secondly,according to GB 2760-2014 Food Additive Use Standard,we selected foodgrade alkaline salts that are allowed to be added to noodles to make different concentrations of alkaline solutions for the LL noodles.The total plate count and sensory acceptability of the LL noodles after storage at 25℃ for 2 days were used as indicators.Four alkaline salts were selected as alkaline soaking solutions for the LL noodles,namely,tripotassium phosphate,trisodium phosphate,potassium carbonate and sodium carbonate,and the concentration ranges of the different alkaline soaking solutions were determined.Then,the effect of different concentrations of alkaline soaking solutions on the total plate count,p H value,color and initial cooking loss of the LL noodles were compared and analyzed.The results showed that all four alkaline soaking solutions could effectively inhibit the growth of microorganisms in the LL noodles.The shelf life of the LL noodles surface could be extended from 1 day to 6 days after being soaked with 15% tripotassium phosphate or 6% trisodium phosphate solution.The shelf life of the LL noodles was extended to 4 days after soaking with 6% potassium carbonate or6% sodium carbonate solution.After alkali soaking,the p H value of the LL noodles increased and maintained in the alkaline range,the brightness value decreased,and the yellowness value increased.When the concentration of alkali soaking solution was too high,the initial cooking loss of LL noodles is too high.Therefore,the optimum soaking concentrations of 15% for tripotassium phosphate and 6% for trisodium phosphate,potassium carbonate and sodium carbonate were selected and used for the subsequent tests and analyses.Thirdly,the effect of alkaline salts soaking treatments on the quality characteristics of the LL noodles during storage was investigated.The results showed that during the storage period(0-4 d),the alkali soaking treatment could increase the cooking loss and water absorption of the LL noodles after reheating,improve their adhesion and sensory quality.Among them,trisodium phosphate had the best effect on the quality improvement of the LL noodles.Under the trisodium phosphate soaking treatment,the LL noodles showed relatively low cooking losses,chewiness and sensory scores during storage,bright color,unique alkaline flavor and soft texture.Finally,the effect of alkali soaking solutions on the internal components and structure of the LL noodles during storage were discussed.The results showed that the interactions between the main components of the LL noodles were enhanced after the alkali soaking treatment,with an increase in the content of wheat gluten macromers(GMP)and disulphide bond content.The SE-HPLC peak and total SDS-EP values of the LL noodles decreased,the high molecular weight protein content increased.After alkali soaking,the conformation of the protein on the LL noodles changed.Among them,the proportion of ordered structure in the trisodium phosphate test group was the highest,reaching 50.76%,and the protein structure was the most stable.The gelatinization temperature and peak viscosity of starch increased.After alkali soaking,the moisture in the LL noodles was able to bind closely to the other solid components(starch,proteins,etc.).According to the scanning results of electron microscope,The internal and edge structures of the LL noodles were significantly different,with the most obvious microstructure in the tripotassium phosphate and sodium carbonate test groups,which showed large internal voids and a denser structure the closer to the edge.Among them,the gluten network structure of trisodium phosphate test group was the most dense,and the storage stability was better.