| Corn is not only productive but also full of nutrition.Besides cooking it directly for consumption,corn can also be ground into corn flour.However,owing to its mucedin deficiency,which limits its ability to be processed,the applicability of corn flour has been severely limited.So the aim of this paper is improve the applicability of the corn flour by the method of lactic acid bacteria fermentation.The bacteria were Lactococcus lactis which separated from the natural fermented acid pulp,Lactobacillus plantarum which separated from the natural fermented sour soup,and Lactobacillus coryniformis which separated from a kind of yogurt,respectively.According to the optimizing of the fermentation process,we got the most suitable fermentation conditions were,the concentration of the fermentation liquid was 20%,the fermentation temperature was 37?,and the fermentation time was 4d,respectively.And comparing to the fermentation conditions,different lactic acid bacteria have minor impact on the fermentation effect of the corn flour.According to the analysis on the applicability of the fermentation and unfermented corn flour we can see that the fermented corn flour has lower water retaining capacity and higher gelation capacity,and it has lighter color.The fermented corn flour has smaller particles in size and in irregular shapes with many corner angles and broke particles in it.The glutein layer of the fermented corn flour was broken,leading to the starch particles in the fermented corn flour dissociated out.The fermented corn flour has better thermal stability and retrogradation resistance,and it has higher pasting temperature and pasting time,so the fermented corn flour needs more heat while the pasting process.When making corn dough with the fermented and unfermented corn flour respectively,the fermented corn dough is soft,and has better viscidity,elasticity,cohesiveness,gumminess,ductility,energy consumption for stretch and tensile resistance.So the fermented corn flour has better applicability and is more suitable to making flour foods.What's more,the aflatoxin B1 in the fermented corn flour is lower,so the lactic acid bacteria fermentation is a kind of effective method in secure.According to the analysis on the main ingredients and molecular structure of the fennentation and unfermented corn flour we can see that the main ingredients of dry matters are very different in content between the fermented and unfermented corn flour.The fermented corn flour has more starch and less other ingredients of dry matters.And the reducing of crude fiber and ash in the fermented corn flour making the fermented corn dough soft and improved its mouthfeeling.Starch in the corn flour was hydrolyzed during the fermentation process,leading to the molecular weight on average of the starch got lower,and the content of amylose got higher,so the amylopectin was the major substrate of the hydrolysis.The hydrolysis weaken the degree of crosslinking and crystalline of the starch in the corn flour,making the fermented corn flour a fluffy structure and easier to be made into corn dough.Glutelins in the fermented corn flour was nearly completely disappeared,which leading to the content of crude protein in the fermented corn flour got lower and the glutein layer of the fermented corn flour was broken.This is benefit to the starch particles in the fermented corn flour dissociated out,so the fermented corn flour has better water absorbing capacity and gelation capacity,with the properties similar to starch,and these properties make the fermented corn flour easier to be made into corn dough.Zein in the fermented corn flour is more stable on its secondary structure,this is benefit to the stability of the corn dough.According to the analysis on the mainly composition of the fermentation liquid with different fermentation time we can see that during the fermentation process of 1-7 days,total amount of the lactic acid bacteria in the fermentation liquid was in increasing in the early and in decreasing in the late.The pH value of the fermentation liquid decreased into a constant value and not changed any more,and content of lactic acid in the fermentation liquid increased into a constant amount but not changed any more.Content of reducing sugar and glucose in the fermentation liquid consistently reduced,and some other carbohydrate such as sucrose and maltose appeared in the late of the fermentation process.Content of soluble protein in the fermentation liquid reduced significantly,but content of amino acids in the fermentation liquid didn't changed significantly.Amount the amino acids,Asp,Thr,Ser,Val,Lys and His were the earlier growth factors for the lactic acid bacteria,and Glu,Gly,Ile,Tyr and Phe were the middle growth factors for the lactic acid bacteria,and Ala,Leu and Arg were the later growth factors for the lactic acid bacteria.Total amylase activity and total protease activity of the fermentation liquid decreased significantly as the fermentation time,until losing away.During the fermentation process,nutrition for the lactic acid bacteria not only comes from the original medium,but also comes from the corn flour.So the lactic acid bacteria changed the corn flour's molecular structure,in turn,it improved the applicability of the corn flour.But as the nutrition in the fermentation liquid deceased significantly,many lactic acid bacteria dead in the later fermentation process,leading to the fermentation liquid pollution and losing the fermentation effect,so the fermentation time should not be too long.Making a kind of corn cake using the fermented and unfermented corn flour respectively,we can see that comparing with the corn cake made by the original corn flour,the corn cake made by the fermented corn flour was soft with better elasticity and mouthfeeling,so the fermented corn flour got higher score on the sensory evaluation.What's more,the fermented corn cake has better inflation effect with beautiful appearance and spongy internal structure.Therefore the fermented corn cake was more popular amount people and it will be have broad market prospects. |
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