Optimizationonfermentation Processof Mulberry Fruit Vinegarand Extraction Of Pigments From Mulberry Pomace

Mulberry is not only rich in nutrients such as sugar,vitamins,organic acids,proteins,polyphenols and trace elements,but also contains functional ingredients such as resveratrol and anthocyanins and so on.It gives mulberry higher nutritional value and plays a positive role in maintaining human health.At present,the development of mulberry is mainly used in food and chemical industry.In terms of food,mulberry can be processed into fruit wine,fruit vinegar,jam,fruit tea,yogurt and so on.As an acidic condiment,mulberry fruit vinegar has high nutritional value and is deeply loved by consumers.Therefore,the study on mulberry fruit vinegar can not only better utilize the resources,but also enrich the varieties of fruit vinegar products.In chemical industry,the natural pigments in fruits and vegetables can be extracted and utilized,which has good coloring effect.At present,most of the processing of mulberry is used for juicing,and the rest of the pomace is generally discarded,resulting in a great waste of resources.However,mulberry pomace are rich in natural pigments.Therefore,the extraction of pigment from mulberry pomace can not only obtain high-quality natural pigment,but also help to avoid the waste of resources.In this paper,fruit vinegar was fermented from mulberry by liquid fermentation.Based on the single factor experiment,the response surface was used to optimize the fermentation process to obtain the best process parameters.Meanwhile,the headspace solid phase microextraction and gas chromatography-mass spectrometry(SPME-GC/MS)were used to detect and analyze the changes of flavor substances in the fermentation process of mulberry fruit vinegar.Through the relative odor activity value(ROAV)to quantized and evaluate the contribution of different volatile substances to the overall flavor to determine the key flavor compounds.Moreover,ethanol was used to extract the pigment from the mulberry pomace with the assistance of ultrasonic technology.Response surface method was used to optimize the extraction process and improve the extraction rate of pigment.The obtained experimental results are as follows:(1)On the basis of single factor experiment,acetic acid fermentation was optimized by response surface methodology.The results showed that optimum fermentation parameters were as follows:initial alcoholicity 10.5%vol,liquid amount 22%,inoculation amount 9%,fermentation temperature 34.5℃.Under this condition,the acetic acid was up to 60.162g/L after 7 days of fermentation.The order of influence on acetic acid yield was:fermentation temperature>initial alcoholicity>liquid amount>inoculation amount.The obtained mulberry vinegar product has dark red color,pure vinegar taste and sweet and sour fruit juice taste,with typical flavor of mulberry vinegar.The content of volatile acid was 5.4 g/100mL,reducing sugar was 1.1 g/100mL,and total ester was 1.3 g/100mL.(2)Using the SPME-GC/MS,respectively to the mulberry juice,alcohol fermentation,acetic fermentation flavour compounds of three stages were analyzed.The ROAV method was used to determine the key flavor compounds at the same time.The results show that there were 8 kinds of ester substances,2 kinds of alcohol substances,3 kinds of aldehyde substances,3 kinds of acids substances in the mulberry juice,relative contents were 8.65%,4.28%,47.44%,11.46%,respectively.There were 22 kinds of ester substances,8 kinds of alcohol substances,3 kinds of aldehyde substances,8 kinds of acids substances in the mulberry wine,relative contents were 59.8 8%,1 0.23%,2.05%,8.69%,respectively.There were 17 kinds of ester substances,9 kinds of alcohol substances,7 kinds of acids substances in the mulberry vinegar,relative contents were 37.53%,24.64%,20.82%,respectively.During the whole fermentation process,the changes of esters first increased and then decreased,the changes of alcohols gradually increased,the changes of aldehydes gradually decreased,and the changes of acids first decreased and then increased.The results of the ROAV showed that caprylic aldehyde,as a key compound in mulberry juice,has a strong fruit aroma and the lowest threshold,which played a major role in the formation of the flavor of the mulberry juice.Isoamyl acetate has fresh and sweet fruit aroma,which plays a key role in the formation of the flavor of mulberry wine and mulberry vinegar.(3)On the basis of single factor experiments,using the ultrasonic assisted extraction of mulberry pomace pigments.Response surface methodology was used to optimize the extraction process of mulberry pomace pigments.The results showed that the optimum extraction parameters were:ethanol concentration 65%,ultrasonic time 29 min,ultrasonic power 59 W,solid-liquid ratio 1:4.Under this condition,with three-level extraction method,the extraction ratio was up to 93.17%.The order of influence on extraction ratio was as follows:solid-liquid ratio>ethanol concentration>ultrasonic power>ultrasonic time.