| Asparagus(Gracilaria lemaneiformis)is rich in seaweed polysaccharides,proteins,amino acids and other nutritional active ingredients,as well as a variety of essential trace elements which are beneficial for the human health such as lowering blood lipids and anti-oxidation.Although the resources of asparagus in Fujian Province are abundant,asparagus is unfavourable for its heavy smell and poor palatability which effects its deep processing and market development.In this study,microbial fermentation was used to deodorize the asparagus.First,the microbial strains of the asparagus were selected for biological fermentation,then the effects of environmental conditions on the deodorization of the microorganism were studied and some volatile flavor components before and after the deodorization of asparagus were analyzed.Second,the changes of nutrient active substances such as the total acid,polysaccharide,polysaccharide content,p H value,protein,total sugar content of the asparagus slurry were studied and the biotransformation mechanism of the asparagus microbial fermentation was discussed.Finally,based on the deodorization technology of asparagus,asparagus cake with good flavor,moderate hardness and rich chewiness was made.The results of the study were as follows:1.The research on the biological deodorization technology of asparagus and the analysis of flavor substances.The suitable strains for biological deodorization of asparagus are selected as Saccharomyces cerevisia JJ4 and Lactobacillus paracasei subsp.paracasei RP38.The combination of deodorizing microbial strains is 1:1 Saccharomyces cerevisia JJ4 and Lactobacillus paracasei subsp.paracasei RP38.The optimal fermentation process parameters are as follows:add white sugar 2.0%(w/w),malic acid 0.2%(w/w),inoculum amount to 5%each,fermentation time 68 h and fermentation temperature 29?.Under this process conditions,asparagus has no fishy smell,has lact ic acid fermentation fragrance,flower fragrance,fruit fragrance and mellow fragrance.The effect of removing fishy smell and increasing fragrance is obvious.By HS-SPME-GC/MS technology,the main volatile flavor substances of asparagus are1,1,3,3-Tetramethylcyclopentane,cyclooctanol,1-methylcycloheptanol,octanal,3-octanone,capric acid,4-methyloctanoic acid.By compound bacteria RJ biolo gical deodorization,it mainly consumes 4-methyloctanoic acid,hydroxymethylfuranone,3-octanone,2-undecal,2-nonadecanone,n-nonanal,cyclooctanol,1-methylcycloheptanol,octanal,and caprylic acid etc;produced?-Phenylethanol,ethyl caproate,phenethyl acetate,ethyl decanoate,ethyl pentadecanoate,1-ethyl-1-methyl-cyclohexane,isoamyl octoate,ethyl nonanoate,Ethyl nonadenoate,etc.The main contribution of RP38 is that the biotransformation consumes3-octanone,4-methyloctanoic acid,heptadecane and other hydrocarbon acids with fishy smell,produces aromatic aldehydes and hydrocarbons such as 3-methylene-nonane,(E)-2-octenol,benzaldehyde,etc.The main contribution odf JJ4 is the consumption of 2-nonadecanone,hydroxymethylfuranone,cyclooctanol and other fishy substances for biotransformation,Ethyl nonanoate,?-phenethyl alcohol,ethyl decanoate,ethyl octanoate,ethyl caproate and other aromatic substances are produced.2.The effect of microbial fermentation on the nutrient active substances and functions of asparagus.The contents of crude polysaccharides,agar polysaccharides and sulfated polysaccharides in LG slurry are 0.315 g/100g,0.130 g/100g,and 0.035 g/100g,its content gradually increases and then stabilizes during the fermentation process;p H value and total sugar are 6.99 and 2.28 g/100g,both decreased significantly 3d before fermentation(P<0.05)and stable afterwards;the protein content was 0.068 g/100g,and it changed significantly after1 day of fermentation(P<0.05).Using Gel Permeation Chromatography(GPC)and Fourier Infrared Spectroscopy(FT-IR)to analyze the molecular weight and structure of the crude polysaccharides of asparagus.The results show the molecular weight of the crude polysaccharides of asparagus after fermentation has changed significantly,which from large molecular weight to small molecules that are more conducive to being absorbed by the human body.Fermentation dose not change the structure of the polysaccharides of asparagus,but can increase the content of sulfated polysaccharides.In addition,the antioxidant activity of the fermentation broth and crude polysaccharides of Asparagus is significantly enhanced after biological fermentation.The gel strength of asparagus slurry 3d before fermentation decreased from 69.45 g/cm~2 to35.15 g/cm~2,and change reached a very significant level(P<0.01).By comparing the gel strength of asparagus slurry before and after fermentation and different p H values,the resultsshow that the p H value is the main reason for the change of gel strength.3.Development of asparagus cake.Using fermented asparagus as raw material,develop a new product of asparagus cake.Through single factor and orthogonal test,the best gel formulation is obtained:pectin added is1.4%,carrageenan added is 0.5%.On the premise of the optimal formula,the research shows that the moisture content(y)and the hardness(x)of asparagus cake have a non-linear relationship during the drying process at 60°C.The equation is y=-0.7777x~2+16.38x+118.34,R2=0.9964.After sensory evaluation of asparagus cakes with different moisture content,the experiment found that the quality of asparagus cake is the best when the moisture content is 16.5±0.3%,and the dry end point of asparagus cake should be controlled at a hardness of 174?179 N/cm~2.This provides a quick detection and discrimination method for the dry end point of asparagus cake.Finally,the asparagus cake has moderate hardness and unique flavor,and all physical and chemical indicators meet the requirements of the standard DB36/T 1247-2020. |
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