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Abstract Fruit vinegar is a new beverage emerging in recent years because of its rich nutrition. At present, acetic acid bacteria are main strains used in the fruit vinegar production. Acetic acid bacteria are a general term for a class of bacteria that can oxidize ethanol to acetic acid. This paper mainly summarized the biological characteristics and research status of acetic acid bacteria for fruit vinegar brewing, in order to provide a theoretical basis for the selection of highquality acetic acid bacteria for fruit vinegar brewing.
Key words Fruit vinegar; Acetic acid bacteria; Biological characteristics
Received: July 16, 2019Accepted: October 29, 2019
Jinghong WANG (1980-), male, P. R. China, devoted to research about of brewing food research and development.
*Corresponding author. Email: [email protected].
Fruit is rich in various nutrients and has nutritional and healthcare functions, while fruit vinegar is an acid seasoning which is fermented from fruit as the main raw material［1］. Therefore, fruit vinegar has rich nutritional value and has functions such as fatigue resisting, blood pressure lowering, blood sugar lowering and blood fat lowering［2］. At present, the brewing of fruit vinegar has become a research hotspot.
Fruit vinegar is mainly brewed through several stages such as alcoholic fermentation, acetic fermentation and clarification. Sourness is the most important indicator of fruit vinegar［3］, and therefore, acetic fermentation is a key stage of fruit vinegar brewing. At present, the main strains for fruit vinegar brewing are acetic acid bacteria. Acetic acid bacteria are a general term for a class of bacteria that can oxidize ethanol to acetic acid. They are a group of obligate aerobic bacteria. Since the cell membrane of acetic acid bacteria contains a highly active acetate dehydrogenase and an acetaldehyde dehydrogenase complex, under aerobic conditions, acetic acid bacteria can oxidize ethanol to acetic acid［4］. Therefore, the choice of acetic acid bacteria plays a crucial role in the quality and flavor of fruit vinegar. At present, most scholars agree with the classification of acetic acid bacteria in Bergeys manual of Determinative Bacteriology (eighth edition), which divides acetic acid bacteria into Acetobacter and Gluconobacter［4,11,21］. Among them, Acetobacter includes three species: A. aceti, A. pasteeurianus and A. peroxydans, while Gluconobacter comprises only one species G. oxyeans［6］. The acetic acid bacteria currently widely used in fruit vinegar brewing mainly include A. baumannii and G. oxydans. In this paper, a brief review of the biological characteristics and application status of acetic acid bacteria for fruit vinegar brewing is given. Research Status of Breeding of Strains for Fruit Vinegar Production
At present, Chinas fruit vinegar industry still has a lot of room for development. An important factor restricting the development of fruit vinegar is the lack of special strains for fruit vinegar brewing with excellent acid production performance［7］. Most foreign countries use mixed bacteria with different properties for the production of fruit vinegar. For example, mixed fermentation with acetic acid bacteria including A. rancens, A. pasteurianus and A. suboxydans not only showed a high fermentation rate, but also formed esters and other organic acids, which enhanced the aroma and solid content of the product［8］. In Chinas fruit vinegar production, there are not many kinds of acetic acid bacteria cultivated in pure state. Most of the strains used are grain brewing strains, such as AS1.41 (A. rancens L.), A. rancens variant and HN 1.01 (A. lovaniense L.)［9］, but once put into the production of fruit vinegar, their acid production capacity, ethanol tolerance and other properties would declined, and the flavor of fermented fruit vinegar is not good. Therefore, in the research on the fruit vinegar strains, most acetic acid bacteria are directly selected from the vinegar mash, or the special strains commonly used in vinegar production are domesticated in highly acidic conditions and mutated［10］.
Biological Characteristics of Acetic Acid Bacteria and Their Application in Fruit Vinegar
Gluconobacter
Gluconobacter is an important genus of Acetobacteraceae, closely related to humans, first discovered and studied by Asai et al.［11］. There is only one species in Gluconobacter, namely, G. oxydans. Gluconobacter is movable or nonsporting flagellate bacterial population that oxidizes ethanol to acetic acid, but due to the lack of succinate dehydrogenase in the cell, it has no complete TCA cycle, and cannot further oxidize acetic acid or acetate into CO2 and H2O. However, this bacterium can catabolize Dglucose through the hexosephosphate pathway and produce 2ketogluconic acid and 5ketogluconic acid from Dglucose, and some strains can also produce 2,5diketoDgluconate. It has obvious ketogenic effect, and can oxidize polyols with different carbon chain lengths, such as glycerol, heptitol and octyl alcohol, into corresponding ketoses［12］.
In the process of fruit vinegar fermentation, sometimes it involves the interaction of multiple strains. Gluconobacter has incomplete oxidizing property, and the alcohols and aldehydes produced by it can reconcile the sour taste of vinegar and increase the flavor of fruit vinegar［13］. For example, Li et al.［13］ isolated and screened a G. oxydans strain E3 from naturally fermented fruit vinegar and tested it for fermentation characteristics. It was found that the optimum growth pH of strain E3 was 6, and the strain had good acid resistance, and could still grow when the pH was 3. Meanwhile, E3 could withstand the ethanol concentration of 6% v/v. When the concentration was 6% v/v, the acidity reached 4.12 g/ml after 6 d of fermentation. However, the heat resistance of E3 was not good, and the optimum growth temperature was 30 ℃. When the temperature exceeded 30 ℃, the acid yield of acetic acid bacteria rapidly decreased. Acetobacter
In the 8th edition of Bergeys manual of Determinative Bacteriology, Acetobacter is divided into three species: A. aceti, A. pasteurianus, and A. peroxydans. However, most of the strains currently used for industrial production of fruit vinegar are A. baumannii. At present, the strains produced in China for the production of fruit vinegar are mainly A. rancens AS1.41 and A. baumannii HN 1.01.
A. rancens AS1.41
In the early 1960s, there was only one strain in China, i.e., A. rancens AS1.41［14］. Microscopic examination showed that As1.41 acetic acid bacteria are mostly short rodshaped, straight or slightly curved, and round at both heads, and most of them appear in pairs and show no spores. A. rancens AS1.41 grows vigorously on glucose, yeast extract, and ethanol plate medium. After 2 d of culture, acid can be produced. If it is further cultured, acetic acid will be further oxidized and decomposed to form CO2 and H2O, and a white halo appears around the colony［15］. Shen et al.［16］ found through the optimization study of A. rancens As1.41 culture medium that when the ethanol concentration was greater than 6% v/v, the sour taste and acid production of As1.41 acetic acid were greatly reduced, the ethanol conversion rate was 96.1%, the acetic acid concentration could reached 3.79 g/100 ml, and the genetic performance was relatively stable. However, the AS1.41 strain also has shortcomings and is not suitable for liquid deep culture. If it is applied to the production of fruit vinegar, not only the acid production capacity is not ideal, but also the ethanol tolerance is to be improved. For example, Liu et al.［17］ studied the optimization of the fermentation process of acetic acid bacteria, and analyzed and compared the strain performances of A. rancens As1.41 and A. pasteurianus AC2005. They found that AC2005 was superior to AS1.41 in tolerance to ethanol and acetic acid. When the alcohol concentration was 2.7%, the acetic acid concentration was 2.6 g/ml, and the liquid loading was 40 ml, the ethanol conversion rate could reach 97.5%, and the highest acid yield reached 5.2 g/ml.
HN 1.01
HN 1.01 cells are ellipsoidal or short rodshaped, straight, round at two heads, single or paired when 0.7-1.0×101.4-1.9 micron, chained at young age, and show no spores and no flagella. In 1972, Shanghai Institute of Brewing Science isolated and cultured the excellent purebred "HN 1.01" acetic acid bacteria from the vinegar juice of Dandong vinegar factory, but the oxidation capacity was slightly weaker than that of AS 1.41 acetic acid bacteria［18］. Zhu et al.［19］ found that the strain had a higher ethanoloxidizing rate, and the conversion rate of ethanol to acid reached an average of 93.88%. Zhang et al.［19］ showed that the optimal acetic acid concentration of HN 1.01 was 2%, and the acetic acid yield of the acetic acid bacteria could reach 21.56 g/L after 24 h. Studies have shown that the specificity of HN 1.01 strain is not strong, and the flavor of fermented fruit vinegar is not good［10］. Lu et al.［20］ compared the bacteria with other acetic acid bacteria and found that the ethanol conversion rate was less than 70%, which was far lower than 87% of the QY7009 strain tested together. When the ethanol content reached 9%, the acid production capacity of HN 1.01 was even weaker and the ethanol conversion rate was lower. Prospects
Nowadays, with the improvement of peoples living standards, the nutritional value of fruit vinegar is gradually recognized by people, and the market demand for fruit vinegar is growing. At present, the research foundation of fruit vinegar in China is still limited, and there are inevitably many problems. For example, there is a lack of special fruit vinegar brewing strains in China. Most of the strains used for brewing are common strains in brewing vinegar, and the acidproducing capacity and ethanol tolerance of the strains need to be improved. Faced with such a broad development prospect of fruit vinegar industry, the selection of excellent strains is of great practical significance for improving the yield and quality of fruit vinegar. It is believed that with the maturity of molecular biology, genetic engineering and other technologies, more and more fruit vinegar brewing strains will be discovered to realize the industrialization of fruit vinegar brewing.
References
［1］ DONG YX, GUO DZ. Fruit vinegar development and fruit vinegar technology research［J］. New Product, 2001, 7(2): 123-125. (in Chinese)
［2］ YAO YJ, GONG HW, WANG EM. Healthcare function of fruit vinegar ［J］. The Beverage Industry, 2009, 12(9): 1-2. (in Chinese)
［3］ DONG SG. Screening of high quality fermentation strains and optimization of fermentation technology for apple vinegar and its beverage［D］. Qingdao: Ocean University of China, 2007: 1-105. (in Chinese)
［4］ SUN WL. The purification and identification of acetic acid bacteria［J］. China Condiment, 2011, 36(12): 72-75. (in Chinese)
［5］ FENG J, SHI QS, OUYANG YS, et al. Research progress on the polyphasic taxonomy of acetic acid bacteria［J］. Microbiology China, 2009, 36(9): 1390-1396. (in Chinese)
［6］ BOCHANAN RE, GIBBONS NE. Bergeys manual of determinative bacteriology［M］. Beijing: Science Press, 1984: 362-366. (in Chinese)
［7］ HOU AX. Breeding of excellent strains for fruit vinegar brewing and development of fruit vinegar beverage［D］. Hunan: Hunan Agricultural University, 2007. (in Chinese)
［8］ HU HP. Genetic classification and identification of acetic acid bacteria from Shanxi old vinegar and their production performance［D］. Shanxi: Shanxi Agricultural University, 2004. (in Chinese)
［9］ YAO C, YOU T. Research progress of producing strains and brewing technology of fruit vinegar ［J］. China Condiment, 2010, 35(12): 31-35. (in Chinese) ［10］ ZHOU GP, WANG FA, GAO B. Optimization of Selective Medium for Acetobacter and Separate of Good Strains［J］. China Brewing, 2004(6): 18-19. (in Chinese)
［11］ FENG J, SHI QS, OUYANG YS, et al. Research progress on Gluconacetobacter［J］. Journal of Microbiology, 2010, 30(2): 86-90. (in Chinese)
［12］ MILO KULHNEK. Microbial dehydrogenations of monosaccharides［J］. Adv Appl Microbiol, 1989, 34: 141-182.
［13］ LI Y, LIU YD, SU SY, et al. Identification of Acetobacter oxydans for fruit vinegar production and its fermentation characteristics［J］. China Brewing, 2012, 31(5): 242-246. (in Chinese)
［14］ ZHAO F, LI ZM, CHEN B. Research progress on the production of vinegar in our country［J］. Journal of Handan Polytechnic College, 2009, 22(4): 94-96. (in Chinese)
［15］ LI SH, XU X, ZHENG GQ. The daily change in Chla fluorescence parameters and the relationship between it and weather factors［J］. Agricultural Research in the Arid Areas, 2003, 21(2): 91-94. (in Chinese)
［16］ SHEN QH, BAI WJ. Study on optimized fermentation medium of acetic acid bacteria As1.41［J］. Journal of Anhui Agricultural Sciences, 2012, 40(36): 17455-17456, 17459. (in Chinese)
［17］ LIU HX, WANG M, WANG CX, et al. Technology optimization of acetic acid fermentation of Acetobacter pasteurium［J］. China Brewing, 2009, 204(3): 34-37. (in Chinese)
［18］ CHEN W. Study on breeding of highquality acetic acid bacteria, fermentation law of apple acetic acid and the effect of enzyme activity［D］. Shandong: Shandong Agricultural University, 2001. (in Chinese)
［19］ ZHU XM, XIA XL, YANG HL, et al. study on the key enzymes of ethanol oxidation and acetic acid production in Acetobacter pasteurianus HN 1.01 ［J］. Science and Technology of Food Industry, 2012: 1-6.
［20］ ZHANG B, LI MY, ZHANG ZP, et al. Effect of acetate concentration on production of acetic acid by acetic acid bacteria［J］. Academic Forum, 2008, (4): 38-39. (in Chinese)
［21］ HU HP, HAO L. Research progress on the breeding of acetic acid bacteria in vinegar industry［J］. Shanxi Food Industry, 2003, 3: 10-12. (in Chinese)
Key words Fruit vinegar; Acetic acid bacteria; Biological characteristics
Received: July 16, 2019Accepted: October 29, 2019
Jinghong WANG (1980-), male, P. R. China, devoted to research about of brewing food research and development.
*Corresponding author. Email: [email protected].
Fruit is rich in various nutrients and has nutritional and healthcare functions, while fruit vinegar is an acid seasoning which is fermented from fruit as the main raw material［1］. Therefore, fruit vinegar has rich nutritional value and has functions such as fatigue resisting, blood pressure lowering, blood sugar lowering and blood fat lowering［2］. At present, the brewing of fruit vinegar has become a research hotspot.
Fruit vinegar is mainly brewed through several stages such as alcoholic fermentation, acetic fermentation and clarification. Sourness is the most important indicator of fruit vinegar［3］, and therefore, acetic fermentation is a key stage of fruit vinegar brewing. At present, the main strains for fruit vinegar brewing are acetic acid bacteria. Acetic acid bacteria are a general term for a class of bacteria that can oxidize ethanol to acetic acid. They are a group of obligate aerobic bacteria. Since the cell membrane of acetic acid bacteria contains a highly active acetate dehydrogenase and an acetaldehyde dehydrogenase complex, under aerobic conditions, acetic acid bacteria can oxidize ethanol to acetic acid［4］. Therefore, the choice of acetic acid bacteria plays a crucial role in the quality and flavor of fruit vinegar. At present, most scholars agree with the classification of acetic acid bacteria in Bergeys manual of Determinative Bacteriology (eighth edition), which divides acetic acid bacteria into Acetobacter and Gluconobacter［4,11,21］. Among them, Acetobacter includes three species: A. aceti, A. pasteeurianus and A. peroxydans, while Gluconobacter comprises only one species G. oxyeans［6］. The acetic acid bacteria currently widely used in fruit vinegar brewing mainly include A. baumannii and G. oxydans. In this paper, a brief review of the biological characteristics and application status of acetic acid bacteria for fruit vinegar brewing is given. Research Status of Breeding of Strains for Fruit Vinegar Production
At present, Chinas fruit vinegar industry still has a lot of room for development. An important factor restricting the development of fruit vinegar is the lack of special strains for fruit vinegar brewing with excellent acid production performance［7］. Most foreign countries use mixed bacteria with different properties for the production of fruit vinegar. For example, mixed fermentation with acetic acid bacteria including A. rancens, A. pasteurianus and A. suboxydans not only showed a high fermentation rate, but also formed esters and other organic acids, which enhanced the aroma and solid content of the product［8］. In Chinas fruit vinegar production, there are not many kinds of acetic acid bacteria cultivated in pure state. Most of the strains used are grain brewing strains, such as AS1.41 (A. rancens L.), A. rancens variant and HN 1.01 (A. lovaniense L.)［9］, but once put into the production of fruit vinegar, their acid production capacity, ethanol tolerance and other properties would declined, and the flavor of fermented fruit vinegar is not good. Therefore, in the research on the fruit vinegar strains, most acetic acid bacteria are directly selected from the vinegar mash, or the special strains commonly used in vinegar production are domesticated in highly acidic conditions and mutated［10］.
Biological Characteristics of Acetic Acid Bacteria and Their Application in Fruit Vinegar
Gluconobacter
Gluconobacter is an important genus of Acetobacteraceae, closely related to humans, first discovered and studied by Asai et al.［11］. There is only one species in Gluconobacter, namely, G. oxydans. Gluconobacter is movable or nonsporting flagellate bacterial population that oxidizes ethanol to acetic acid, but due to the lack of succinate dehydrogenase in the cell, it has no complete TCA cycle, and cannot further oxidize acetic acid or acetate into CO2 and H2O. However, this bacterium can catabolize Dglucose through the hexosephosphate pathway and produce 2ketogluconic acid and 5ketogluconic acid from Dglucose, and some strains can also produce 2,5diketoDgluconate. It has obvious ketogenic effect, and can oxidize polyols with different carbon chain lengths, such as glycerol, heptitol and octyl alcohol, into corresponding ketoses［12］.
In the process of fruit vinegar fermentation, sometimes it involves the interaction of multiple strains. Gluconobacter has incomplete oxidizing property, and the alcohols and aldehydes produced by it can reconcile the sour taste of vinegar and increase the flavor of fruit vinegar［13］. For example, Li et al.［13］ isolated and screened a G. oxydans strain E3 from naturally fermented fruit vinegar and tested it for fermentation characteristics. It was found that the optimum growth pH of strain E3 was 6, and the strain had good acid resistance, and could still grow when the pH was 3. Meanwhile, E3 could withstand the ethanol concentration of 6% v/v. When the concentration was 6% v/v, the acidity reached 4.12 g/ml after 6 d of fermentation. However, the heat resistance of E3 was not good, and the optimum growth temperature was 30 ℃. When the temperature exceeded 30 ℃, the acid yield of acetic acid bacteria rapidly decreased. Acetobacter
In the 8th edition of Bergeys manual of Determinative Bacteriology, Acetobacter is divided into three species: A. aceti, A. pasteurianus, and A. peroxydans. However, most of the strains currently used for industrial production of fruit vinegar are A. baumannii. At present, the strains produced in China for the production of fruit vinegar are mainly A. rancens AS1.41 and A. baumannii HN 1.01.
A. rancens AS1.41
In the early 1960s, there was only one strain in China, i.e., A. rancens AS1.41［14］. Microscopic examination showed that As1.41 acetic acid bacteria are mostly short rodshaped, straight or slightly curved, and round at both heads, and most of them appear in pairs and show no spores. A. rancens AS1.41 grows vigorously on glucose, yeast extract, and ethanol plate medium. After 2 d of culture, acid can be produced. If it is further cultured, acetic acid will be further oxidized and decomposed to form CO2 and H2O, and a white halo appears around the colony［15］. Shen et al.［16］ found through the optimization study of A. rancens As1.41 culture medium that when the ethanol concentration was greater than 6% v/v, the sour taste and acid production of As1.41 acetic acid were greatly reduced, the ethanol conversion rate was 96.1%, the acetic acid concentration could reached 3.79 g/100 ml, and the genetic performance was relatively stable. However, the AS1.41 strain also has shortcomings and is not suitable for liquid deep culture. If it is applied to the production of fruit vinegar, not only the acid production capacity is not ideal, but also the ethanol tolerance is to be improved. For example, Liu et al.［17］ studied the optimization of the fermentation process of acetic acid bacteria, and analyzed and compared the strain performances of A. rancens As1.41 and A. pasteurianus AC2005. They found that AC2005 was superior to AS1.41 in tolerance to ethanol and acetic acid. When the alcohol concentration was 2.7%, the acetic acid concentration was 2.6 g/ml, and the liquid loading was 40 ml, the ethanol conversion rate could reach 97.5%, and the highest acid yield reached 5.2 g/ml.
HN 1.01
HN 1.01 cells are ellipsoidal or short rodshaped, straight, round at two heads, single or paired when 0.7-1.0×101.4-1.9 micron, chained at young age, and show no spores and no flagella. In 1972, Shanghai Institute of Brewing Science isolated and cultured the excellent purebred "HN 1.01" acetic acid bacteria from the vinegar juice of Dandong vinegar factory, but the oxidation capacity was slightly weaker than that of AS 1.41 acetic acid bacteria［18］. Zhu et al.［19］ found that the strain had a higher ethanoloxidizing rate, and the conversion rate of ethanol to acid reached an average of 93.88%. Zhang et al.［19］ showed that the optimal acetic acid concentration of HN 1.01 was 2%, and the acetic acid yield of the acetic acid bacteria could reach 21.56 g/L after 24 h. Studies have shown that the specificity of HN 1.01 strain is not strong, and the flavor of fermented fruit vinegar is not good［10］. Lu et al.［20］ compared the bacteria with other acetic acid bacteria and found that the ethanol conversion rate was less than 70%, which was far lower than 87% of the QY7009 strain tested together. When the ethanol content reached 9%, the acid production capacity of HN 1.01 was even weaker and the ethanol conversion rate was lower. Prospects
Nowadays, with the improvement of peoples living standards, the nutritional value of fruit vinegar is gradually recognized by people, and the market demand for fruit vinegar is growing. At present, the research foundation of fruit vinegar in China is still limited, and there are inevitably many problems. For example, there is a lack of special fruit vinegar brewing strains in China. Most of the strains used for brewing are common strains in brewing vinegar, and the acidproducing capacity and ethanol tolerance of the strains need to be improved. Faced with such a broad development prospect of fruit vinegar industry, the selection of excellent strains is of great practical significance for improving the yield and quality of fruit vinegar. It is believed that with the maturity of molecular biology, genetic engineering and other technologies, more and more fruit vinegar brewing strains will be discovered to realize the industrialization of fruit vinegar brewing.
References
［1］ DONG YX, GUO DZ. Fruit vinegar development and fruit vinegar technology research［J］. New Product, 2001, 7(2): 123-125. (in Chinese)
［2］ YAO YJ, GONG HW, WANG EM. Healthcare function of fruit vinegar ［J］. The Beverage Industry, 2009, 12(9): 1-2. (in Chinese)
［3］ DONG SG. Screening of high quality fermentation strains and optimization of fermentation technology for apple vinegar and its beverage［D］. Qingdao: Ocean University of China, 2007: 1-105. (in Chinese)
［4］ SUN WL. The purification and identification of acetic acid bacteria［J］. China Condiment, 2011, 36(12): 72-75. (in Chinese)
［5］ FENG J, SHI QS, OUYANG YS, et al. Research progress on the polyphasic taxonomy of acetic acid bacteria［J］. Microbiology China, 2009, 36(9): 1390-1396. (in Chinese)
［6］ BOCHANAN RE, GIBBONS NE. Bergeys manual of determinative bacteriology［M］. Beijing: Science Press, 1984: 362-366. (in Chinese)
［7］ HOU AX. Breeding of excellent strains for fruit vinegar brewing and development of fruit vinegar beverage［D］. Hunan: Hunan Agricultural University, 2007. (in Chinese)
［8］ HU HP. Genetic classification and identification of acetic acid bacteria from Shanxi old vinegar and their production performance［D］. Shanxi: Shanxi Agricultural University, 2004. (in Chinese)
［9］ YAO C, YOU T. Research progress of producing strains and brewing technology of fruit vinegar ［J］. China Condiment, 2010, 35(12): 31-35. (in Chinese) ［10］ ZHOU GP, WANG FA, GAO B. Optimization of Selective Medium for Acetobacter and Separate of Good Strains［J］. China Brewing, 2004(6): 18-19. (in Chinese)
［11］ FENG J, SHI QS, OUYANG YS, et al. Research progress on Gluconacetobacter［J］. Journal of Microbiology, 2010, 30(2): 86-90. (in Chinese)
［12］ MILO KULHNEK. Microbial dehydrogenations of monosaccharides［J］. Adv Appl Microbiol, 1989, 34: 141-182.
［13］ LI Y, LIU YD, SU SY, et al. Identification of Acetobacter oxydans for fruit vinegar production and its fermentation characteristics［J］. China Brewing, 2012, 31(5): 242-246. (in Chinese)
［14］ ZHAO F, LI ZM, CHEN B. Research progress on the production of vinegar in our country［J］. Journal of Handan Polytechnic College, 2009, 22(4): 94-96. (in Chinese)
［15］ LI SH, XU X, ZHENG GQ. The daily change in Chla fluorescence parameters and the relationship between it and weather factors［J］. Agricultural Research in the Arid Areas, 2003, 21(2): 91-94. (in Chinese)
［16］ SHEN QH, BAI WJ. Study on optimized fermentation medium of acetic acid bacteria As1.41［J］. Journal of Anhui Agricultural Sciences, 2012, 40(36): 17455-17456, 17459. (in Chinese)
［17］ LIU HX, WANG M, WANG CX, et al. Technology optimization of acetic acid fermentation of Acetobacter pasteurium［J］. China Brewing, 2009, 204(3): 34-37. (in Chinese)
［18］ CHEN W. Study on breeding of highquality acetic acid bacteria, fermentation law of apple acetic acid and the effect of enzyme activity［D］. Shandong: Shandong Agricultural University, 2001. (in Chinese)
［19］ ZHU XM, XIA XL, YANG HL, et al. study on the key enzymes of ethanol oxidation and acetic acid production in Acetobacter pasteurianus HN 1.01 ［J］. Science and Technology of Food Industry, 2012: 1-6.
［20］ ZHANG B, LI MY, ZHANG ZP, et al. Effect of acetate concentration on production of acetic acid by acetic acid bacteria［J］. Academic Forum, 2008, (4): 38-39. (in Chinese)
［21］ HU HP, HAO L. Research progress on the breeding of acetic acid bacteria in vinegar industry［J］. Shanxi Food Industry, 2003, 3: 10-12. (in Chinese)