Research And Application Of Microbial Fermentation Technology Of Kelp Paste

The algae production in China was increasing year by year,among which Fujian kelp production has been the first in China for many years.Due to the backward processing technology of kelp,its application in deep processing of kelp products was limited.Kelp was a high-quality raw material for paste products.Adding a certain proportion of bacteria to ferment during processing can not only improve its quality characteristics such as nutrition,flavor and health care,but also inhibit the growth of harmful bacteria during fermentation,prolong shelf life and improve food safety,which was loved by most consumers.Therefore,in this paper,kelp was used as raw material,and mixed fermentation technology of Aspergillus oryzae and Aspergillus niger was used to prepare kelp paste.The optimal fermentation parameters of kelp paste were studied by response surface method.On this basis,the quality index and microbial colony structure and composition of kelp paste at different fermentation times were determined,the correlation between microbial flora and quality index was constructed,the formation mechanism of characteristic flavor in kelp paste fermentation was clarified,and the microbial fermentation control technology of kelp paste was established to obtain a high-quality kelp paste product,which provided a certain degree for the development and deep processing of kelp paste.The main research contents and results were as follows:(1)kelp paste was prepared by mixed fermentation of Aspergillus oryzae and Aspergillus niger,and the effects of material ratio,koji ratio,salt concentration and salt water addition on amino nitrogen in kelp paste were investigated.On this basis,the response surface method was used to optimize the optimum technological parameters of kelp paste.The results showed that the optimum fermentation technological parameters of kelp were as follows: 3:1 of the ratio of kelp to soybean,2:1 of the ratio of Aspergillus oryzae to Aspergillus niger,14.5% of salt concentration,and77% of the amout of brine addition.The fermentation temperature was34℃,the fermentation time was 10 d,and the amino nitrogen value was0.76%±0.04%,which was basically consistent with the theoretical prediction value.The results met the standard requirements of Q/FHTY0043S—2023 《Fermented Kelp Paste》.(2)The quality characteristics of kelp paste during fermentation(0 d,10 d,20 d,30 d,40 d,50 d)were studied by electronic nose,electronic tongue,HS-SPME-GC-MS and LC-MS.The results of physicochemistryical indexes and nutrient composition analysis showed that the contents of amino nitrogen,total acid,ammonium salt and ash increased gradually with the fermentation time,while the p H value,moisture,fat,protein and carbohydrate decreased gradually with the fermentation time,and the sodium content was 2.63 ～ 2.64 g/100 g.The results of electronic nose analysis showed that nitrogen oxides and short-chain alkanes such as methane were the main causes of odor,and the difference in aroma characteristics may be caused by benzene,nitrogen oxides,ammonia,alkanes,alcohol ether aldehydes and ketones,organic sulfides and long-chain alkanes.The results of electronic tongue analysis showed that umami,salty and richness were the main taste indexes of kelp paste.The results of HS-SPME-GC-MS analysis showed that 27 volatile flavor substances were identified in kelp paste,including aldehydes,alcohols,acids and ketones,among which the contents of hexanal,2-octenal,2-decenaldehyde and other important fishy substances in kelp decreased gradually during fermentation.The results of LC-MS analysis showed that 707 kinds of non-volatile flavor substances were identified,including 246 kinds of lipids and lipid-like molecules(34.78%)and 217 kinds of organic acids and their derivatives(30.69%).The generation of their metabolites was mainly related to the degradation and metabolism of fats and carbohydrates.Through topological analysis,10 important metabolic pathways,such as alanine,aspartic acid and glutamic acid metabolism,tricarboxylic acid cycle,arginine and proline metabolism,were screened out,and 43 different metabolites participated in the metabolism.Among the different metabolites,glutamic acid and aspartic acid metabolism were the important sources of umami flavor,alanine and proline metabolism were the important sources of sweetness,the arginine metabolism was the important source of bitterness.At the same time,citric acid in organic acid can produce synergistic effect with malic acid,which makes the taste of kelp paste more abundant.(3)16S rRNA high-throughput sequencing and fluorescence quantitative PCR were used to study the dynamic changes of flora in kelp paste during fermentation(10 d,20 d,30 d,40 d and 50 d),and to construct the correlation between bacteria or fungi in kelp paste and quality indicators.The results of bacterial research showed that Proteobacteria and Firmicutes were the main phylum,then the relative abundance of Proteobacteria was low from 30 to 50 days.At the genus level,the bacteria were mainly Enterobacter,Enterobacter,Pediococcus,Bacillus,marine Bacillus,Bifidobacterium,Lactobacillus,Weiss and Enterococcus.Bacteria such as Bacillus,Lactobacillus,Weiss,Lactobacillus,Enterococcus,and Pediococcus were positively correlated with the good flavor of kelp paste,such as fruity aroma,fruity aroma,floral aroma,creamy aroma,grassy aroma,etc.Among them,Weiss can effectively inhibit the production of odorous substances such as valeraldehyde and hexanal in kelp paste,and Pediococcus was negatively correlated with biogenic amines,which can effectively inhibit the formation of biogenic amines and improve food safety.The results of fungal research showed that Aspergillus oryzae and Aspergillus niger were related to many organic acids in non-volatile flavor substances,such as L-glutamic acid,N-succinyl-L-glutamic acid,L-arginine,N-acetyl-L-glutamic acid,L-aspartic acid,bitter L-methionine,sweet lysine,sour citric acid,malic acid and succinic acid,which enrich kelp paste.At the same time,Aspergillus oryzae and Aspergillus niger were positively correlated with various biogenic amines,so the extension of fermentation time can effectively reduce biogenic amines and improve the safety of kelp paste.On the basis of the correlation between flora and quality index,the optimum time for mixed fermentation of Aspergillus oryzae and Aspergillus niger in kelp paste was determined to be 40 days.