Acetic Acid Fermentation Research Articles

Optimization of a Process for Preparation of Base Wine for Cider Vinegar Production

Apple juice is used to prepare cider vinegar a traditional fermented product consumed world over. An attempt has been made to optimize the alcoholic fermentation of apple juice by Saccharomyces cerevisiae var. ellipsoideus UCD 595 for subsequent acetic acid fermentation to prepare cider vinegar, with respect to initial concentration of TSS, DAHP and sulfur dioxide content, using RSM. It was found that the fermentability of the different runs varied according to the initial sugar and DAHP concentration. The optimum base wine quality characteristics: TSS (4.03 °B), rate of fermentation (0.42 °Brix/24 h), ethanol (6.05%), titratable acidity (0.43%), volatile acidity (0.021%), phenolics (149.76 mg/100 g), pH (3.43), reducing sugars (107.88 mg/100 gm), total sugars (0.377%) and residual sulfur dioxide (28.77 ppm) with 0.837 desirability, were obtained using 14 °B initial TSS, 0.1% DAHP and 50 ppm sulfur dioxide. Verification experiments were conducted to compare predicted and actual values, which revealed near concurrence among them; confirming that models used were capable of reasonably and accurately predicting the dependent variables. Hence, these conditions are considered optimum for the alcoholic fermentation to produce a desirable level of alcohol in the shortest time for subsequent conversion into cider vinegar by acetic acid fermentation.

저온 알코올 발효를 통한 고품질 복숭아 식초의 생산

As health benefits of traditional vinegar is newly recognized, vinegar products are being developed with new and enhanced functionalities to meet customers’ diverse demand. Meanwhile, peach is one of the crops with largest production in Korea but neither its preservation nor its processing is simply done. For the development of a new vinegar product using peach, the present study focused on improving an alcoholic fermentation process using a new cold-tolerant Saccharomyces cerevisiae strain isolated from peach. Specifically, alcoholic fermentation of peach concentrates was performed at a control (30℃) or a low (10℃) temperature, followed by conventional acetic acid fermentation at 25℃, to investigate the effect of low-temperature alcoholic fermentation (LTAF) on the final vinegar quality. We measured free amino acid contents and flavor compound profiles, and performed sensory evaluation of the vinegar products. As a result, the LTAF vinegar had higher free amino acid contents and lower off-flavor intensity than those in the control vinegar. Moreover, overall preference of the LTAF vinegar was significantly higher than the control vinegar. In conclusion, the present study demonstrated that a promising potential of using the LTAF process for the development of high quality vinegar products.

Dynamic microbial succession of Shanxi aged vinegar and its correlation with flavor metabolites during different stages of acetic acid fermentation

Shanxi aged vinegar (SAV), one of the famous Chinese vinegars, is produced by multispecies solid-state fermentation in which the acetic acid fermentation stage (AAF) is especially important. However, how bacterial succession and their metabolites change along with the different stages of AAF is still poorly understood. In this study, we investigated the dynamic bacterial succession and flavor formation in three batches of SAV using high-throughput sequencing and metabolomics approaches. It is interesting to find that AAF can be divided into three stages based on its bacterial community succession (early stage, days 0–4; medium stage, days 5–21; and later stage, days 22–26). Pantoea, Pediococcus, Lactococcus and Rhizobium played an important role in the early stage; Lactobacillus was dominant in the medium stage (67.72%); and Acetobacter, Komagataeibacter and Kroppenstedtia were the key bacteria in the later stage. A total of seven organic acids and 42 volatile constituents (esters, alcohol, ketones and aldehydes) were detected during the AAF. Spearman correlation analysis showed a significant correlation between the bacterial community and these flavor metabolites during the AAF of the SAV. This is the first report to explore the relationships between volatile flavor metabolites and bacterial community succession by a three-staged method and provide theoretical support for a flavor formation mechanism in traditional SAV.

Improving the acetic acid tolerance and fermentation of Acetobacter pasteurianus by nucleotide excision repair protein UvrA.

Acetic acid bacteria (AAB) are widely used in acetic acid fermentation due to their remarkable ability to oxidize ethanol and high tolerance against acetic acid. In Acetobacter pasteurianus, nucleotide excision repair protein UvrA was up-regulated 2.1 times by acetic acid when compared with that without acetic acid. To study the effects of UvrA on A. pasteurianus acetic acid tolerance, uvrA knockout strain AC2005-ΔuvrA, uvrA overexpression strain AC2005 (pMV24-uvrA), and the control strain AC2005 (pMV24), were constructed. One percent initial acetic acid was almost lethal to AC2005-ΔuvrA. However, the biomass of the UvrA overexpression strain was higher than that of the control under acetic acid concentrations. After 6% acetic acid shock for 20 and 40min, the survival ratios of AC2005 (pMV24-uvrA) were 2 and 0.12%, respectively; however, they were 1.5 and 0.06% for the control strain AC2005 (pMV24). UvrA overexpression enhanced the acetification rate by 21.7% when compared with the control. The enzymes involved in ethanol oxidation and acetic acid tolerance were up-regulated during acetic acid fermentation due to the overexpression of UvrA. Therefore, in A. pasteurianus, UvrA could be induced by acetic acid and is related with the acetic acid tolerance by protecting the genome against acetic acid to ensure the protein expression and metabolism.

Key pathway of methane production and characteristics of stable carbon isotope of the Tuojia River waterbody.

This study aimed at exploring the key pathway of methane production and clarifying the composition and distribution of carbon (C) isotopes in the Tuojia River waterbody in Hunan Pro-vince. We estimated CH4 concentrations and fluxes of four reaches (S1, S2, S3 and S4) by a two-layer diffusion model and gas chromatography. The spatial and temporal distribution of CH4 flux and its relationship with environmental factors were examined. The key pathway of CH4 production was investigated by stable C isotope method to analyze the distribution characteristics of 13C isotope (δ13C) of water dissolved CH4 and seston/benthic organic matter. There was significant seasonal variability in water pH, with mean value of (7.27±0.03). The concentration of dissolved oxygen (DO) showed strong seasonal and spatial variations, with the range of 0.43-13.99 mg·L-1. The maximum value of DO occurred in S1 and differed significantly in summer and autumin. In addition, DO differed significantly in winter and other seasons in S2, S3 and S4. The concentration of dissolved organic carbon (DOC) showed a gradual increasing trend from source to estuary. The highest concentration of DOC (8.32 mg·L-1) was found in S2, while the lowest was observed in S1 (0.34 mg·L-1). The electrical conductivity (EC) and oxidation-reduction potential (ORP) of water ranged from 17 to 436 μS·cm-1 and from -52.30 to 674.10 mV, respectively, which were significantly different among the four reaches (P＜0.05). Water ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3--N) concentrations were in the ranges of 0.30-1.35 (averaged 0.90±0.10) mg·L-1 and 0.82-2.45 (averaged 1.62±0.16) mg·L-1, respectively. The dissolved concentration and diffusion flux of CH4 ranged from 0 to 5.28 μmol·L-1 and from -0.34 to 619.72 μg C·m-2·h-1, respectively, with significant temporal and spatial variations. They showed a similar trend among reaches. Their values were highest in spring, followed by in winter and lowest in summer and autumn. Spatially, the CH4 concentration and flux followed the order of S2>S3>S4>S1. The correlation analysis showed that CH4 flux was positively correlated with NH4+-N and DOC. The pathway of CH4 production of all reaches was dominated by acetic acid fermentation, while there were obvious differences among the four reaches. The contribution of CH4 from acetic acid fermentation was greatest (87%) in S1, followed by S4(81%), S2(78%) and S3(76%). The mean value of the δ13C for dissolved CH4, seston organic matter and benthic organic matter was -41.64‰±1.91‰, -14.07‰±1.06‰ and -26.20‰±1.02‰, respectively. There was a positive correlation between the δ13C of dissolved CH4 and benthic organic matter, whereas the δ13C value of dissolved CH4 was negatively correlated with CH4 flux.

내산성이 우수한 Acetobacter pasteurianus AFY-4 균주를 이용한 다래 식초 초산발효 최적화

Acetobacter pasteurianus AFY-4 was isolated from fermented vinegar in Hongcheon-gun, Gangwon-do. The A. pasteurianus AFY-4 strain had a higher tolerance to low-pH. Optimization of acetic acid fermentation of hardy kiwi (Actinidia arguta) was conducted using the A. pasteurianus AFY-4 strain based on the response surface methodology (RSM). The optimization of acetic acid fermentation for producing hardy kiwi vinegar was determined by five levels of initial ethanol, initial acetic acid, and acetic acid bacteria (AAB) inoculum volume, using the central composite design. The acetic acid yield and residual ethanol for acetic acid fermentation of hardy kiwi optimized by the RSM were significantly different. The optimal conditions for acetic acid fermentation of hardy kiwi vinegar were 8.95% of the initial ethanol, 1.86% of the initial acetic acid, and 25.02% of the AAB inoculum volume.

Role of a membrane-bound aldehyde dehydrogenase complex AldFGH in acetic acid fermentation with Acetobacter pasteurianus SKU1108

Acetic acid fermentation is widely considered a consequence of ethanol oxidation by two membrane-bound enzymes-alcohol dehydrogenase and aldehyde dehydrogenase (ALDH)-of acetic acid bacteria. Here, we used a markerless gene disruption method to construct a mutant of the Acetobacter pasteurianus strain SKU1108 with a deletion in the aldH gene, which encodes the large catalytic subunit of a heterotrimeric ALDH complex (AldFGH), to examine the role of AldFGH in acetic acid fermentation. The ΔaldH strain grew less on ethanol-containing medium, i.e., acetic acid fermentation conditions, than the wild-type strain and significantly accumulated acetaldehyde in the culture medium. Unexpectedly, acetaldehyde oxidase activity levels of the intact ΔaldH cells and the ΔaldH cell membranes were similar to those of the wild-type strain, which might be attributed to an additional ALDH isozyme (AldSLC). The apparent KM values of the wild-type and ΔaldH membranes for acetaldehyde were similar to each other, when the cells were cultured in nonfermentation conditions, where ΔaldH cells grow as well as the wild-type cells. However, the membranes of the wild-type cells grown under fermentation conditions showed a 10-fold lower apparent KM value than those of the cells grown under nonfermentation conditions. Under fermentation conditions, transcriptional levels of a gene for AldSLC were 10-fold lower than those under nonfermentation conditions, whereas aldH transcript levels were not dramatically changed under the two conditions. We suggest that A. pasteurianus SKU1108 has two ALDHs, and the AldFGH complex is indispensable for acetic acid fermentation and is the major enzyme under fermentation conditions.

Producing Acetic Acid of Acetobacter pasteurianus by Fermentation Characteristics and Metabolic Flux Analysis.

The acetic acid bacterium Acetobacter pasteurianus plays an important role in acetic acid fermentation, which involves oxidation of ethanol to acetic acid through the ethanol respiratory chain under specific conditions. In order to obtain more suitable bacteria for the acetic acid industry, A. pasteurianus JST-S screened in this laboratory was compared with A. pasteurianus CICC 20001, a current industrial strain in China, to determine optimal fermentation parameters under different environmental stresses. The maximum total acid content of A. pasteurianus JST-S was 57.14 ± 1.09g/L, whereas that of A. pasteurianus CICC 20001 reached 48.24 ± 1.15g/L in a 15-L stir stank. Metabolic flux analysis was also performed to compare the reaction byproducts. Our findings revealed the potential value of the strain in improvement of industrial vinegar fermentation.

Nuclear magnetic resonance- and gas chromatography/mass spectrometry-based metabolomic characterization of water-soluble and volatile compound profiles in cabbage vinegar

Non-targeted metabolomic analyses employing nuclear magnetic resonance- and gas chromatography/mass spectrometry-based techniques were applied for an in-depth characterization of cabbage vinegar, an original agricultural product made from cabbage harvested in Tsumagoi, Japan. Water-soluble and volatile metabolite profiles of cabbage vinegar were compared with those of various vinegars: rice vinegar, grain vinegar, apple vinegar, and black vinegar (Japanese kurozu made of brown rice). Principal component analysis (PCA) of the water-soluble metabolites indicated that cabbage vinegars belonged to an isolated class by the contributions of fructose, pyroglutamic acid, choline, and methiin (S-methylcysteine sulfoxide). Regarding the volatile compounds, the PCA data represented that rice, black, and apple vinegars were characterized by most of the dominant volatiles, such as acetate esters, alcohols, ketones, and acids. Cabbage and grain vinegars were included in the same class although these two vinegars have different flavors. Orthogonal partial least squares-discrimination analysis exhibited the differences in volatile compound profile between cabbage and grain vinegars, revealing that cabbage vinegars were characterized by the presence of sulfides (dimethyl sulfide, dimethyl disulfide, and dimethyl trisulfide), nitriles (allyl cyanide and 4-methylthio-butanenitrile), 3-hexene-1-ol, and crotonic acid. The time-course changes in these highlighted compounds during the acetic acid fermentation of cabbage vinegar suggested that pyroglutamic and crotonic acids were produced through fermentation, whereas choline, methiin, sulfides, nitriles, and 3-hexene-1-ol were derived from cabbage, suggesting the key role of these compounds in the unique taste and flavor of cabbage vinegar.

Design of Intelligent Household Fruit Vinegar Fermentation Device and Optimization of Key Parameters

Compared with carbonated beverages, fruit vinegar was gradually becoming more favored by consumers, because of their higher nutritional functions. But its popularization was limited by higher selling price. This article described a fruit vinegar fermentation device that can be used at home and also introduced the design principles, composition and operation methods. Furthermore, taking apple vinegar as an example, the key parameters of fermentation were determined by single-factor and orthogonal tests. In alcohol fermentation, the fermentation time, fermentation temperature and inoculation amount were 72 h, 30°C and 0.07%, respectively. In acetic acid fermentation, the fermentation temperature, ventilation and bacteria amount were 32°C, 4 L/min and 0.18%, respectively. The refreshing and fermented apple vinegar could be obtained with the total acid content of 3.6 g/100 mL. The kinetic formula between the content of acetic acid and fermentation time was calculated and acetic acid content of fruit vinegar could be determined by controlling fermentation time according to the formula. So, the device could produce different content of acetic acid of fruit vinegar automatically, without manual operation. The study was sufficient to provide reference and experience for further popularization of fruit vinegar.

Development and Metabolite Profiling of Elephant Garlic Vinegar.

Elephant garlic (Allium ampeloprasum var. ampeloprasum), which belongs to the Alliaceae family along with onion and garlic, has a flavor and shape similar to those of normal garlic but is not true garlic. Additionally, its properties are largely unknown, and its processing and product development have not been reported. In this study, we focused on using elephant garlic to produce a new type of vinegar, for which the market is rapidly growing because of its health benefits. First, we evaluated the effects of elephant garlic addition on acetic acid fermentation of rice wine by Acetobacter pasteurianus. In contrast to normal garlic, for which 2% (w/v) addition completely halted fermentation, addition of elephant garlic enabled slow but successful fermentation of ethanol to acetic acid. Metabolite analysis suggested that sulfur-containing volatile compounds were less abundant in elephant garlic than in normal garlic; these volatile compounds may be responsible for inhibiting acetic acid fermentation. After acetic acid fermentation, vinegar with elephant garlic did not have any sulfur-containing volatile compounds, which could positively contribute to the vinegar flavor. Moreover, the amino acid profile of the vinegar suggested that nutritional and sensory properties were more enhanced following addition of elephant garlic. Thus, elephant garlic may have applications in the development of a new vinegar product with improved flavor and quality and potential health benefits.

레몬그라스 식초의 초산발효 특성과 항산화 활성

This study investigated acetic acid fermentation properties and antioxidant activity of vinegar by addition of lemon grass to develop high quality vinegar by using lemongreass. Traditional brown rice wine contained 5% lemongrass powder and had an alcohol content of 7.2%. The wine was fermented by Acetobacter. sp. RIC-V and made into lemongrass vinegar (LV). The pH and total acidity of the LV were 3.13% and 7.21%, respectively. Fructose was detected whereas glucose, sucrose, and maltose were not detected. Among organic acids, acetic acid was highest at 3658.6 mg%; trace amounts of lactic acid, citric acid, malic acid, tartaric acid, and oxalic aicd were detected. Of the 17 free amino acids, glutamic acid, histidine, alanine, and proline were mainly detected. To conduct total polyphenol content and ABTS radical scavenging activity, 3% and 5% lemongrass powder (P3LV, P5LV) and 1%, 2%, and 3% of lemongrass extract (E1LV, E2LV, E3LV) were added to LV, respectively. Total phenolics increased as the added lemongrass powder and extract increased. Total phenolics were 490.9, 559.4, and 895.7 μg gallic acid equivalents/mL in brown rice vinegar, LV, P5LV. ABTS radical scavenging activities were 43.2%, 58.0%, and 91.0% in brown rice vinegar, LV, P5LV, respectively. These results show that lemongrass vinegar has considerable potential as a high quality functional vinegar with antioxidative effects.

Diversity and dynamics stability of bacterial community in traditional solid-state fermentation of Qishan vinegar

Qishan vinegar is a typical Chinese fermented cereal product that is prepared using traditional solid-state fermentation (SSF) techniques. The final qualities of the vinegar produced are closely related to the multiple bacteria present during SSF. In the present study, the dynamics of microbial communities and their abundance in Daqu and vinegar Pei were investigated by the combination of high throughput sequencing and quantitative PCR. Results showed that the Enterobacteriales members accounted for 94.7%, 94.6%, and 92.2% of total bacterial sequences in Daqu Q3, Q5, and Q10, respectively. Conversely, Lactobacillales and Rhodospirillales dominated during the acetic acid fermentation (AAF) stage, corresponding to the quantitative PCR results. Lactobacillus, Acetobacter, Weissella, Leuconostoc and Bacillus were the dominant and characteristic bacterial genera of Qishan vinegar during AAF process. Redundancy analysis suggested that Lactobacillales and Rhodospirillales had a positive correlation with humidity and acidity, respectively. These results confirmed that the bacterial community structure could be affected by physiochemical factors, which determined the unique bacterial composition at different fermentation stages and showed batch-to-batch consistency and stability. Therefore, the conformity of bacterial community succession with physiochemical parameters guaranteed the final quality of Qishan vinegar products. This study provided a scientific perspective for the uniformity and stability of Qishan vinegar, and might aid in controlling the manufacturing process.

The use of a micro- and ultrafiltration cascade system for the recovery of protein, fat, and purified marinating brine from brine used for herring marination

In this study we analyzed the composition of post-production marinating brines (MB) from the marination of fresh and frozen herring in marinating brines comprising 6–10% NaCl and 3–4% acetic acid. After 7days of marination in a 1-step or 2-step marinating process, NaCl levels in MB decreased by ∼33% and acetic acid by ∼60% compared to fresh marinating brine. The post-production marinating brines contained NaCl (37–43g/dm3), acetic acid (14–18g/dm3), total dry matter (64–73g/dm3), fat (5–27g/dm3), and protein (14–26g/dm3). Their turbidity was in the range of 307–2427 NTU, while pH <4.7. Psychrophilic, mesophilic, acetic, and lactic acid fermentation bacteria were found.The recovery of protein, fat, and purified marinating brine was tested in a cascade membrane system, using microfiltration (polypropylene bag 25μm) and ultrafiltration (UF) performed with ceramic membranes with cut-offs of 150kDa and 1kDa. In the permeate we observed no changes in pH, NaCl and acetic acid levels; it was clear (turbidity at 1 NTU) and sterile. The permeate recovery coefficient was 0.50, and its reuse can reduce the use of NaCl and acetic acid in the production of marinating brines by about 20–25%. The highest rejection coefficient for protein content (average 0.30) and fat content (from 0.66 to 1.00) was observed for the membrane with a cut-off of 150kDa. Overall recovery after both stages of UF was 0.60 for total protein and 0.40–0.69 for total fat.In conclusion, the tested membrane system recovered biomolecules (protein and fat) and the permeate. This makes it an alternative technical solution thanks to which post-production marinating brine may be re-used and not just discharged as effluent.

Unraveling the correlation between microbiota succession and metabolite changes in traditional Shanxi aged vinegar

Shanxi aged vinegar (SAV) is a well-known vinegar produced by traditional solid-state fermentation and has been used in China for thousands of years. However, how microorganisms and their metabolites change along with fermentation is unclear. Here, 454 high-throughput sequencing and denaturing gradient gel electrophoresis were used to investigate the composition of microbial community. Metabolites were further analyzed by gas chromatography–mass spectrometry and high–performance liquid chromatography. Results showed that the composition of bacterial community changed dramatically at different stages of fermentation. The bacterial genera (relative abundance > 0.1%) decreased from 17 in daqu (starter used in starch saccharification) to 2 at the 12th day of alcohol fernemtation (AF). 15 bacterial genera at the 1st day of acetic acid fermentation (AAF) decreased to 4 genera, involving Acetobacter (50.9%), Lactobacillus (47.9%), Komagataeibacter (formerly Gluconacetobacter, 0.7%) and Propionibacterium (0.1%) at the 7th day of AAF. The structure of fungal community was more homogeneous. Saccharomyces and Saccharomycopsis were predominant in AF and AAF. A total of 87 kinds of nonvolatile metabolites were detected. Canonical correspondence analysis showed a significant correlation between the microbiota succession and the formation of metabolites during the fermentation of SAV. This study provides detailed information for the fermentation mechanism of traditional SAV.

Acetobacter pasteurianus metabolic change induced by initial acetic acid to adapt to acetic acid fermentation conditions.

Initial acetic acid can improve the ethanol oxidation rate of acetic acid bacteria for acetic acid fermentation. In this work, Acetobacter pasteurianus was cultured in ethanol-free medium, and energy production was found to increase by 150% through glucose consumption induced by initial acetic acid. However, oxidation of ethanol, instead of glucose, became the main energy production pathway when upon culturing ethanol containing medium. Proteome assay was used to analyze the metabolism change induced by initial acetic acid, which provided insight into carbon metabolic and energy regulation of A. pasteurianus to adapt to acetic acid fermentation conditions. Results were further confirmed by quantitative real-time PCR. In summary, decreased intracellular ATP as a result of initial acetic acid inhibition improved the energy metabolism to produce more energy and thus adapt to the acetic acid fermentation conditions. A. pasteurianus upregulated the expression of enzymes related to TCA and ethanol oxidation to improve the energy metabolism pathway upon the addition of initial acetic acid. However, enzymes involved in the pentose phosphate pathway, the main pathway of glucose metabolism, were downregulated to induce a change in carbon metabolism. Additionally, the enhancement of alcohol dehydrogenase expression promoted ethanol oxidation and strengthened the acetification rate, thereby producing a strong proton motive force that was necessary for energy production and cell tolerance to acetic acid.

Vinegar production from post-distillation slurry deriving from rice shochu production with the addition of caproic acid-producing bacteria consortium and lactic acid bacterium

To establish a zero emission process, the post-distillation slurry of a new type of rice shochu (NTRS) was used for the production of health promoting vinegar. Since the NTRS post-distillation slurry contained caproic acid and lactic acid, the effect of these two organic acids on acetic acid fermentation was first evaluated. Based on these results, Acetobacter aceti CICC 21684 was selected as a suitable strain for subsequent production of vinegar. At the laboratory scale, acetic acid fermentation of the NTRS post-distillation slurry in batch mode resulted in an acetic acid concentration of 41.9g/L, with an initial ethanol concentration of 40g/L, and the acetic acid concentration was improved to 44.5g/L in fed-batch mode. Compared to the NTRS post-distillation slurry, the vinegar product had higher concentrations of free amino acids and inhibition of angiotensin I converting enzyme activity. By controlling the volumetric oxygen transfer coefficient to be similar to that of the laboratory scale production, 45g/L of acetic acid was obtained at the pilot scale, using a 75-L fermentor with a working volume of 40L, indicating that vinegar production can be successfully scaled up.

Effects of gas condition on acetic acid fermentation by Clostridium thermocellum and Moorella thermoacetica (C. thermoaceticum).

Fermentation with acetogens can be affected by cultivation gas phase, but to date, there is not enough evidence on that matter for Clostridium thermocellum and Moorella thermoacetica. In this work, the effects of sparged CO2 as well as sparged and non-sparged N2 on these microorganisms were studied using glucose and cellobiose as substrates. It was revealed that sparged CO2 and non-sparged N2 supported growth and acetic acid production by C. thermocellum and M. thermoacetica, while sparged N2 inhibited both of the microorganisms. Notably, part of the sparged CO2 was fermented by the co-culture system and contributed to an overestimation of the products from the actual substrate as well as an erring material balance. The best condition for the co-culture was concluded to be N2 without sparging. These results demonstrate the importance of cultivation conditions for efficient fermentation by anaerobic clostridia species.

Effect of aspartic acid and glutamate on metabolism and acid stress resistance of Acetobacter pasteurianus

BackgroundAcetic acid bacteria (AAB) are widely applied in food, bioengineering and medicine fields. However, the acid stress at low pH conditions limits acetic acid fermentation efficiency and high concentration of vinegar production with AAB. Therefore, how to enhance resistance ability of the AAB remains as the major challenge. Amino acids play an important role in cell growth and cell survival under severe environment. However, until now the effects of amino acids on acetic fermentation and acid stress resistance of AAB have not been fully studied.ResultsIn the present work the effects of amino acids on metabolism and acid stress resistance of Acetobacter pasteurianus were investigated. Cell growth, culturable cell counts, acetic acid production, acetic acid production rate and specific production rate of acetic acid of A. pasteurianus revealed an increase of 1.04, 5.43, 1.45, 3.30 and 0.79-folds by adding aspartic acid (Asp), and cell growth, culturable cell counts, acetic acid production and acetic acid production rate revealed an increase of 0.51, 0.72, 0.60 and 0.94-folds by adding glutamate (Glu), respectively. For a fully understanding of the biological mechanism, proteomic technology was carried out. The results showed that the strengthening mechanism mainly came from the following four aspects: (1) Enhancing the generation of pentose phosphates and NADPH for the synthesis of nucleic acid, fatty acids and glutathione (GSH) throughout pentose phosphate pathway. And GSH could protect bacteria from low pH, halide, oxidative stress and osmotic stress by maintaining the viability of cells through intracellular redox equilibrium; (2) Reinforcing deamination of amino acids to increase intracellular ammonia concentration to maintain stability of intracellular pH; (3) Enhancing nucleic acid synthesis and reparation of impaired DNA caused by acid stress damage; (4) Promoting unsaturated fatty acids synthesis and lipid transport, which resulted in the improvement of cytomembrane fluidity, stability and integrity.ConclusionsThe present work is the study to show the effectiveness of Asp and Glu on metabolism and acid stress resistance of A. pasteurianus as well as their working mechanism. The research results will be helpful for development of nutrient salts, the optimization and regulation of high concentration of cider vinegar production process.

Effect of Yeast and Acetic Fermentation on Phytochemical and Antioxidant Properties of Jackfruit Pulp(Artocarpus heterophyllus L.)

Jackfruit (Artocarpus heterophyllus L.) is one of the important tropical fruits in Malaysia, mainly used for fresh consumption because of its good source of energy, deliciously sweet in taste, proteins, dietary fiber, minerals and vitamins. To date, there is lack of fermentation study reported on jackfruit. Hence, the aim of this work is to evaluate the phytochemical content and antioxidant properties of fermented jackfruit which was subjected to acetic acid bacteria and yeast fermentation individually for a duration of 7 days. The changes in the pH value, brix value, total reducing sugar content, total phenolic and total flavonoid content were examined for both yeast and acetic acid fermented jackfruit samples. Few antioxidant activities such as ferric reducing antioxidant power (FRAP) value and 2,2-diphenyl -1- picrylhydrazyl (DPPH) free radical scavenging activity were also analyzed to determine the differences in the respective properties of jackfruit pulp after being subjected to yeast or acetic acid fermentation. There is a slight change on brix value and DPPH free radical scavenging activity (31.05-33.17% radical scavenging activity) for both yeast and acetic acid fermented samples. However, acetic acid fermented jackfruit exhibited higher total reducing sugar content (23.24 mg glucose/mL) and total phenolics content when compared to yeast fermented jackfruit sample. Both yeast and acetic acid fermented jackfruit samples showed higher FRAP value (0.435 -0.48 mg ascorbic acid/mL) than unfermented jackfruit sample (0.372 mg ascorbic acid/mL) except for total flavonoid content which exhibited a decreasing trend after fermentation.