Screening Of Aroma-production Bacteria And Study On Maillard Reaction

In this paper, strains producing aroma were obtained from Baiyunbian high temperature Daqu, systematic research was done with the fermenting characteristic of aroma-producing bacteria and its effect with Maillard Reaction, the main results as below:1) The strain of bacteria named BG05 which could produce aroma was screened from high temperature Daqu with the method of high-temperature and heat treatment, it produced strong aroma in wheat bran through solid fermentation for 15d or in wheat-extract medium by submerged fermentation for 6d. BG05 was identified to be Bacillus licheniformis by morphological characteristics, physiological and biochemical indicators and 16SrDNA sequence analysis. The analysis of physiological characteristics of BG05 showed that: the optimum growth temperature was 40℃and pH was 7.0, the bacteria reached its logarithmic groth phase after 5h, and reached its stable phase after 20h.2) The study on the mode of Maillard Reaction showed that BG05 had certain promoter action to Maillard Reaction, the fermentation products at 55℃for 2d after sterilization by membrane filtration smelled stronger aroma, there must be existence of some enzymes which can catalyze the Maillard Reaction. Selecting the different environmental conditions to study the influence factors of Maillard Reaction by aroma-production bacteria, The results indicated that the optimal fermentation conditions were as follows: fermentation temperature 55℃, fermentation time 8d, initial pH7.0, liquid ratio 1:0.7, inoculation level 10% .Fe3+ can promote Maillard Reaction more visibly than the other metal ions, Fe2+ can't promote Maillard Reaction.3)In order to investigate the reason of BG05 producing aroma,comparing BG05 and its mutants ZBG06 and ZBG12 which can't produce aroma in many aspects, the results showed that: The aroma-production bacteria can provide much more reducing sugar substances and free amino acids than the mutants by fermentation,the content of reducing sugar was 17.81% and free amino acids was 37.34mg/100g; The results of the mode Maillard Reaction showed that the mutants can promote Maillard Reaction hardly;The results of SDS-PAGE electrophoresis showed that the extracellular proteins are not the reason for aroma-production;All of the three strains'glucoamylase activities were about 200.00U/g, but the protease activity of aroma-production bacteria was 68.40U/g which much higher than its mutants.The original strain which could produce aroma was determined on the result of many factors.4)The differences of fermentation broth of BG05 and blank controller was analyzed by HPLC, the composition of fermentation broth was analyzed by GC-MS, the results showed that the fermentation broth included acids, alcohols, esters, aldehydes, ketones and heterocyclic; The furfural which contains more in maotai-flavor liquor than other liquors was detected. These aroma compounds including phenol, ethyl acetate, vanillin, 2, 3-Butanediol and furfural are the source of the fermentation broth's aroma.