There are many kinds of apple cider vinegar beverages on the market, but apple cider vinegar based on fermentation is rare. Most of them are pure raw material blended apple cider vinegar drinks, and some are even blended with vinegar essence, saccharin, and essence.
Apple cider vinegar is made from apple juice through alcoholic fermentation and acetic acid fermentation. The global industrial production of fruit vinegar mainly adopts liquid submerged fermentation technology. The nutritional and flavor quality of fruit vinegar mainly comes from the microbial transformation and metabolic by-products of sugar and other components during the fermentation process, as well as the original phytonutrients, natural original fruit aroma, natural pigments and vitamins of the fruit, while the sugar is completely transformed into Acetic acid is important, but it should not be the ultimate purpose. On the contrary, in the stage of aerobic acetic acid fermentation, after meeting the acetic acid conversion index of the fruit vinegar product, if the fermentation time can be shortened to carry out moderate fermentation, the alcohol volume fraction and acetic acid concentration during the fermentation process can be controlled, and the bad flavor formed by continuous oxidative metabolism can be avoided. , to minimize the damage of long-term chemical oxidation in the fermentation substrate to polyphenols and other phytonutrients, natural original fruit aroma and natural pigments, etc., which will significantly improve the health care and flavor quality of fruit vinegar.
Organic acids are important nutrition, flavor and characteristic components in apple cider vinegar, which endow fruit vinegar with a unique flavor. There are two sources of organic acids; one part is inherent in apple raw materials, such as tartaric acid, oxalic acid, citric acid, malic acid, fumaric acid, succinic acid; Ketoglutarate, etc. Volatile aroma components are the main aspects of aroma, and are the intuitive and important sensory qualities of fruit vinegar. The volatile aromatic components in fruit vinegar mainly include acids, alcohols, esters, aldehydes, ketones, terpenes, terpenes, etc.
The differences in the chemical and aroma profiles of moderately and entirely fermented apple vinegar were investigated. The total phenols content, and organic acid and aroma profiles were determined and analyzed using Folin-Ciocalteu colorimetry and high performance liquid chromatography(HPLC), respectively．
The volatile aroma components were extracted by headspace solid·-phase micro-extraction (HS-SPME)and identified by gas chromatography-mass spectrometry (GC-MS)．The total phenols content in the moderately fermented sample was 2l％higher than that in the entirely fermented one．The organic acids species in two vinegar samples were exactly the same，but their contents were different. The moderately fermented vinegar contained higher levels oftartaric acid,citric acid and fumaric acid while the entirely fermented one contained higher levels ofpyruvic acid,malic acid,a-ketoglutaric acid,lactic acid,acetic acid and succinic acid. The moderate fermentation could provide the vinegar with more abundant aroma-active compounds．A total of 37 volatile compounds were detected,including citronellol, nerol, butanoic acid ethyl ester, 4-methyl-3-hexyl acetate ester,and 2-methylbutyl acetate, which were also detected in the apple juice. The moderate fermentation method could be an effective way to develop apple vinegar with high quality because ofits protective effects on total phenols and aroma compounds．
