Molecular techniques used in fermentation of Chinese vinegar
Chinese vinegar is produced by solid state fermentation of cereals or fruits. The main cereals used in fermentation of vinegar are sorghum & rice. The raw materials used in fermentation determine the flavour of the different types of vinegar. Chinese vinegar contain organic such as polyphenols, amino acids, melanoidins, organic acids and sugars that have anti_flammatory and antibacterial properties that protect the body the body from diseases. Nutrients such as amino acids and sugars provide energy to the body, improve immune system, osmoregulation and regulate cell metabolism. The different types of Chinese vinegar include Sichuan bran vinegar, Jiangzhe Rose vinegar, Zhenjiang aromatic vinegar and Shanxi old mature vinegar just to mention a few.
The solid state fermentation process
In koji preparation fermentation occurs aerobically through the reaction of Aspergillus oryzae, Monascus and Rhizopus fungi on the soaked grain with the help of yeast. Alcohol fermentation is commenced by the action of cultured yeast which converts liquefied starch material into ethanol. In this process temperatures are maintained below twenty-eight degrees Celsius to regulate ethanol evaporation. There is rapid increase of ethanol as other aromatic compounds accumulate. Alcohol fermentation goes up to 10 days. Acetic acid fermentation occurs anaerobically. Acetic acid bacteria produce aldehyde hydrogenase and ethanol hydrogenase which oxidize ethanol to acetic acid and esters are produced. Ethyl acetate is the main ester produced which is the characteristic flavour of Chinese vinegar. Other aromatic compounds of vinegar include isoamyl acetate, phenylethyl alcohol, phenylethyl acetate and 4 Vinylguaiacol. Volatile organic acids and non-volatile organic acids are produced which determine the difference in flavour of different types of vinegar. However, some aromatic compounds are lost due to the heat generated by acetic acid, anaerobic fermentation and decomposition by supplementary bacterial materials. Heterocyclic, hydrocarbons, ketones and aldehydes enrich the flavour of the vinegar as they increase. The main organic acids are malic acid, acetic acid, lactic acid and succinic acid.
Solid phase microextraction method is used to extract some volatile organic compounds.
Chinese liquor
It is commonly known as Baijiu which is among the world`s most consumed spirit and one of the oldest liquor that is distilled. It`s distillation and fermentation process is unique and multiplex as compared to the distillation of other liquors. The process involves saccharification and spontaneous fermentation simultaneously. The starter used is Jiuqu in the fermentation and distillation of Chinese liquor which occurs under the condition of solid state. In this preparation of Jiuqu the enzymes produced by microorganisms ferment the liquor. This component not only contribute to the taste of the liquor, but also primarily stimulate microbial consortium. Chinese liquor constitutes more ethanol that any other liquor cause of its unique process of distillation and fermentation. The flavour of the liquor is achieved through aging of liquor when stored. Chinese liquor has the most major flavour compounds besides having a rich flavour. This liquor is used in ceremonies as it is a symbol of happiness in the Chinese culture. Sorghum cereal is a raw material in Chinese liquor distillation and fermentation.
The process involves inoculation of the cooked cereal by crushed Daqu. Various types of Daqu are classified according to flavour and temperature control characteristics. One of the rich flavour liquor contains compounds of esters which are formed under the influence of Monascus spp. Each flavour of Daqu liquor has its own distinctive taste. Daqu constitutes microorganisms such as bacteria, yeast, actinomycetes and moulds. Enzymes produced by Daqu specifically amylase breaks down complex sugars into simple forms of sugars. In addition, amino acids and peptides determine the taste and aroma of the liquor. Due to the diverse starters, fermentation period and raw material used, different types of Chinese liquor has wide range of flavours. However, poor fermentation and deficient standardisation in the recent years has raised concerns on the safety and quality of the liquor. In addition, some toxins are formed during storage which are hazardous to human health if consumed. Aerobic fermentation risks contamination by microbial toxins.
Distillation process
The starter Daqu is prepared from pure wheat under high temperatures or from a mixture of peas and barley under medium temperatures. The grains are mixed with water and broken down into soluble starch to create a uniform mixture. Daqu is shaped into blocks and incubated in chambers under controlled temperatures. Maturation of the Daqu takes place during the storage period. During fermentation, Jiuqu which contains microorganisms such as yeast and bacteria and enzymes facilitates hydrolysis of raw materials into alcohol and flavour compound. Distillation of brewed grains combined with soaked raw grains occurs under solid state condition.the purpose of the fresh grains is to provide microorganisms and enzymes. The alcohol component ethanol is distilled together with the flavour compounds. The liquor is collected for branding, storage and further mixing respectively.
Pu-erh tea
It is a Chinese ancestral tea that has health advantages such as preventing the occurrence of cancer and promote loss of waist fat. This type of tea is produced as a result of solid state fermentation of green tea leaves that have been sun-dried. The caffeine level in pu-erh tea is influenced by the fungi present during anaerobic fermentation. Microorganisms degrade the caffeine content in pu-erh tea through inoculated fermentation. Strains such as theophylline has anti-inflammatory effects on the breathing system thus is effective in treatment of long term difficult pulmonary diseases and asthma is found in pu-erh tea. Theophylline is produced as a result of inoculated fermentation. Caffeine content in aerobic fermentations declines more as compared to anaerobic fermentation. This is because the fungus component in aerobic fermentation converts caffeine into theophylline. Among the five fungal strains from aerobic fermentation, A. niger is the principal fungi which provide the quality of pu-erh tea.
Fermentation process
in aerobic fermentation, sun-dried green tea leaves are soaked in distilled water to the achieve the required moisture content then stored. For sampling of the leaves to take place, they are turned over. Another set of leaves are soaked in distilled water classified into groups and stored in air tight contains for anaerobic fermentation to occur under room temperature. The samples are collected at different intervals and divided into two parts. One part is dried for four hours at high temperatures for examination of chemical elements. The other segment is stored at four degrees Celcius for identification and characterization of fungi.
Fermented vegetable products
The most popular fermented vegetables are olives, cucumber pickles and sauerkraut. Fermented vegetable products have long shelf life and do not require refrigeration. Vegetables are soaked in salty water a process known as brining which inhibits the growth of spoilage microbiota. Majority of vegetables are fermented by lactic acid bacteria since it improves and maintains the nutritional value of the vegetables. The nutrient components present in vegetable provides favourable medium for lactic acid bacteria fermentation. Probiotic supplement is advantageous to the body as it improves the immune system, boost the function of gastrointestinal tract, lower the cholesterol serum and reduces the risk of colon cancer. Lactic acid bacteria produce principle components such as exopolysaccharides and bacteriocins that promote essential characteristics such as flavour, texture and durability. In addition, it removes the toxics present in pickled products thus limiting the health risks. Fermented vegetables atre used as a source of probiotics as the retain various lactic acid bacteria
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