Study On The Key Technologies For Processing Mulberry Vinegar Rich In Anthocyanins

Fermented mulberry vinegar is a kind of vinegar for beverage made by alcoholic and acetic acid fermentation of mulberry as the main raw material.The effect of oxygen and enzymes result in significant loss of anthocyanins during the acetic acid fermentation,leading to mulberry vinegar with low anthocyanin contents and dark color.To address this problem,a new idea was proposed to produce anthocyanin-rich mulberry vinegar by separating the anthocyanins and alcohol from mulberry wine then using the separated alcoholic solution as the raw material for the acetic acid fermentation in order to avoid the loss of anthocyanins.Based on the aforementioned idea,mulberry vinegar was produced by firstly subjecting mulberry pulp to enzymatic treatment and alcoholic fermentation to obtain mulberry wine.Subsequently,the wine was treated with vacuum dealcoholing technology to obtain concentrated fermented mulberry brot h and alcoholic solution.The submerged semi-continuous process was used to obtained a high-acid spirit vinegar through acetic acid fermentation of the distilled alcoholic solution.Finally,mulberry vinegar was obtained by blending the concentrated fermented mulberry broth and the high-acid spirit vinegar.The key technologies affecting total anthocyanin contents,acetic acid yield and acetification rate were investigated.The main contents and results are as follows:(1)The indexes of juice yield and anthocyanin extraction as affected by the enzymolysis effect of PC-3,acid pectinase and EX-V on the mulberry pulp were evaluated.EX-V was found to be the most beneficial pectinase.Using anthocyanin extraction as an index,a mathematical model was established using response surface methodology to model the relationship between the amount of anthocyanin extraction and the enzymatic treatment parameters based on results from a single factor experiment.Taking the optimum parameters by the software and p ractical production maneuverability into consideration,the optimum enzymolysis parameters were enzyme addition 0.048 g/kg,reaction temperature 45.6℃ and reaction time of 1.25 h.Under these conditions,the anthocyanin extraction was 1.54 times higher than that of the control.(2)A high-yield Gluconacetobacter entanii acetic acid bacteria(with the accession number CCTCC NO:M 2017563)was isolated from a high-acid vinegar broth obtained from Zhenjiang,Jiangsu.In addition,the effects of ethanol and acetic acid concentration on the growth and acetic acid fermentation of the strain(HSMC-9)in the enriched medium and initial fermentation medium was investigated.The results showed that the strain grew fastest in the enriched medium without acetic acid but with 2%(v/v)ethanol.The fermentation performance of the strain was optimal when the ethanol and acetic acid in the initial fermentation medium were 4% and 1%(v/v)respectively.Besides,the fermentation performance of strain HSMC-9 was preliminarily tested.It was found that the acetification rate of the strain was 2.72 g/(L·h)and the total acidity of the fermentation broth reached 98.30 g/L after fermentation to 32.42 h,making the strain suitable for using in the production of high-acid vinegar.(3)Using CM 50 vacuum concentrator with low temperature,mulberry wine was dealcoholized under the operating parameters of vacuum of 0.096 MPa,evaporation temperature of 28℃,hot-water temperature of 45℃ and cold-water temperature of 8℃.Studying the changes in the retention rate of anthocyanin and the residual rate of ethanol in the mulberry wine during dealcoholation,the better dealcoholation time was 20 min and the dealcoholation effect of mulberry wine was verified under this condition.It was found that the anthocyanin retention rate and residual rate of ethanol of the concentrated fermented mulberry broth were 99.5% and 5% respectively and the expected effect was achieved.(4)The effects of stirring speed,aeration volume and feeding strategy on the start-up fermentation to obtain a better operation plan was studied.The better speed control scheme was obtained with the oxygen content of the fermentation broth as the inspection index.The optimum aeration volume was 0.8 vvm using acetification rate and final acidity as indexes.With respect to the growth and acetification rate curves of the strain,the better feeding strategy was as follows.Four times feeding operations were carried out during the start-up fermentation.The first feed was carried out at 12 h of fermentation.The difference between total concentration and total acidity was referenced to determine subsequent feeding time.When the difference was between 10~15,the second feeding was carried out.Subsequently,when the difference was less than 10,the third and fourth feedings were performed.The speeds of the four feeding operations were 40,50,35,30 mL/(L·h)respectively.Besides,the fermentation performance of the strain during split fermentation was studied.It was found that the acetification rate of the strain maintained 1.62~2.44 g/(L·h)and the total acidity of the fermentation broth maintained 96.0 g/L,thus making it suitable for using in semi-continuous fermentation process to produce high-acid vinegar.(5)The effects of acidity on anthocyanin stability,antioxidation,color and sensory quality of mulberry vinegar was investigated.The suitable acidity of mulberry vinegar was found to be 50 g/L.(6)The concentrated fermented mulberry broth,spirit vinegar and water were blended in the ratio of 9:17:7 to obtain mulberry fruit vinegar with acidity of 50.9 g/L.The total anthocyanin content of colorful mulberry vinegar was 752.8mg/L,which was 1.09 times higher than that of the mulberry vinegar produced by the conventional process.