Preliminary Studies On The Mechanism Of Methanol Formation And Pilot Test In Jujube Brandy

Jujube brandy, commonly known as "Zaogangzi", processes a brewing history for thousands of years in the traditional jujube region. Since the methanol content in the jujube brandy is far beyond the national regulations on distillation and the preparation, the production of this brandy has been always in the family cottage model, which cannot be traded in the market as a standardized commodity. On the basis of previous studies, this research studies the methanol content during the fermentation of jujube brandy and the dynamic trends of pectinmethylesterase activity; materials heat treatment on the influence of ethanol, higher alcohol contents in the jujube brandy; and the influence of the fermentation scale expansion on the methanol, ethanol and higher alcohol contents. This paper also aims at comparing the methanol, ethanol and higher alcohol in the condition of different fermentation scale and materials, in order to further clarify the formation of methanol in the brandy production, to improve the process conditions and to provide the theoretical basis and technical support for the development of jujube resource in our country. The main conclusions are as follows:1. A preliminary study on the relationship between the content of methanol in jujube brandy and the pectinmethylesterase in raw material.This study analyzes the enzyme activities of pectinmethylesterase and the dynamic trends of methanol in heat-treated group and control group during the fermentation, and designs pectinase treatment test. During the fermentation, the heat treatment has a huge impact on the activity of pectinmethylesterase and the dynamic trends of methanol: the highest value of enzyme activity in the untreated group is 1.35U/g, and the heated one is 0.47U/g. After 84 h of fermentation, the methanol content in the jujube brandy of the control group reached to 2.77g/L(100%,v/v), and the heated one is 0.36g/L(100%,v/v). The methanol content raises clearly with increase of the enzyme activity of pectinmethylesterase in pre-fermentation, relatively, the methanol content changes mildly with the decrease of the enzyme activity of pectinmethylesterase. After adding 0.08 m L pectinase in heat-treated material, the content of methanol reached to 4.58 g/L(100%,v/v), and the content of methanol in control group is 0.32g/L(100%,v/v). It shows that the heat treatment has no special effect on the substrate of pectinmethylesterase—pectinase, which also means that the decrease of the methanol content in jujube brandy, is caused by the pectinmethylesterase inactivation during the heat treatment.2. Pilot test demonstrates that the hydrolysis of pectin in raw material is the main way of methanol producedHeat treatment makes the mthanol content significantly reduced from 7.69 g/L(100%,v/v) to 0.54 g/L(100%,v/v) in pilot test. The four mainly higher alcohols in the jujube brandy are 1-propanol, iso-butanol, isomylalcohol and 2-methy-1-butanol, in which the isomylalcohol owns the largest proportion, about 50%. After the heat treatment, the contents of iso-butanol, 2-methy-1-butanol and isomylalcohol are highly increased, while the 1-propanol content is significantly decreased.3. Analysis the contents of methanol, ethanol and higher alcohols of jujube brandy in lab trial and pilot test, proved that larger fermentation scale significantly increased the methanol content, and using full jujube materials significantly reduced the methanol contentAfter the expansion of the scale of fermentation, the heat treatment leads to decrease of methanol content and ethanol content, in which the methanol content reduces from 7.69g/L(100%,v/v), ratio exceeding the national standard, to 0.54 g/L(100%,v/v), and the ethanol content decrease from 56.6v/v to 54.1 v/v; the influence on the higher alcohols differ from the laboratory scale, in the pilot test, the content of higher alcohols increases distinctly by the heat treatment, from 0.59 g/L to 0.91 g/L. and the research shows the trace of isopropanol, n-butanol, n-pentanol nor furfural. In the heat treatment, the proportion and the trend of higher alcohols basically stay the same. Compared with the full jujube raw material, the content of methanol and higher alcohols significantly increase using the jujube pit material in the fermentation.4. A preliminary study on the effect of three different aging containers of methanol, ethanol and higher alcohols in jujube brandy.In the aging process of 270 d, the test of the content of methanol, ethanol and higher alcohol has been made every 30 d. Statistical analysis shows that the three different aging containers do lower the content of methanol, ethanol and higher alcohol, which the index of the one of oak barrels reduces more significantly from 3.36g/L to 2.47g/L. The oak barrels can heave the content of higher alcohol in jujube brandy and the two other aging containers decrease the content of higher alcohol in jujube brandy.