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Defining Paenibacillus azoreducens (P8) and Acetobacter pasteurianus (UMCC 2951) strains performances in producing acetic acid
(2022-11-17)
Krusong, Warawut
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La China, Salvatore
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Pothimon, Ruttipron
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Gullo, Maria
In this study, spore-forming bacteria isolated from saccharified rice were selected for producing acetic acid. From the screening of 15 strains, P8 strain was chosen as a candidate. The strain was identified as Paenibacillus azoreducens by 16S rRNA analysis (99.85% similarity with P. azoreducens CM1T). Acetic acid is the main component of vinegar but also an industrial commodity produced by chemical synthesis. Sustainable routes for obtaining acetic acid are of great interest for decreasing the environmental impact generated by chemical syntheses. Biological acetic acid production is effective for vinegar production by acetic acid bacteria, but it cannot economically compete with the chemical synthesis for producing it as a pure commodity. Considering the need to improve the yield of pure acetic acid produced by microbial conversions, in this study, P8 strain was chosen for designing processes in different fermentation conditions. Tests were conducted in single and semi-continuous systems, using rice wine as substrate. Acetic acid produced by P8 strain was compared with that of Acetobacter pasteurianus (UMCC 2951), a strain known for producing acetic acid from rice wine. Even though the fermentation performances of P. azoreducens P8 were slightly lower than those of acetic acid bacteria usually used for vinegar production, results highlight its suitability for producing acetic acid. The final acetic acid produced by P. azoreducens P8 was 73 g/L, in a single stage fermentation, without losses. In nine cycles of semi-continuous regime the average of acetification rate was 0.814 (g/L/days). Two main attributes of P. azoreducens P8 are of relevance for producing acetic acid, namely the ability to grow at temperature higher (+ 37°C), than mesophilic acetic acid bacteria, and the absence of cytoplasmic assimilation of acetic acid. These features allow to design multiple strains cultures, in which P. azoreducens can acts as a helper strain. Based on our results, the new isolate P. azoreducens P8 can be propagated in fermenting broths for boosting acetic acid production, under the selected conditions, and used in combination with acetic acid bacteria to produce biological acetic acid, as a non-food grade commodity.
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Determination of antifungal volatile organic compounds of upland rice vinegar and their inhibition effects on Aspergillus flavus in dried chili pepper
(2022-04-01)
Pothimon, Ruttipron
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Krusong, Warawut
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Daetae, Pawinee
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Tantratian, Sumate
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Gullo, Maria
Determination of volatile organic components (VOC) produced in high acid upland rice vinegar was conducted using GC-MS. Acetic acid and ethyl acetate at 9.11% and 2.69% (v/v), respectively, were major VOC found in the vinegar while the others were isobutyl acetate, isobutyl alcohol, isoamyl acetate, isoamyl alcohol, phenethyl acetate and phenethyl alcohol. Subsequently, vinegar and VOC were tested, in vitro, for their inhibition on conidia germination of 103 conidia/mL of Aspergillus flavus. The exposure with 10% (v/v) of vapor-phase vinegar and pure acetic acid completely inhibited the germination of conidia with 30 min exposure, while VOC mixture of 9.11% (v/v) acetic acid, 0.08% (v/v) isoamyl alcohol, 0.45% (v/v) phenethyl alcohol and 0.01% (v/v) isobutyl alcohol with 45 min exposure could achieve the same target. Then, vinegar vapor was tested on the inhibition of conidia germination and aflatoxin production of A. flavus during 90 d subsequent storage of dried chili pepper. Complete inhibition of conidia germination and aflatoxin production were achieved with the 40 min exposure of 1.04 ± 0.03 mmol/L of vaporized vinegar. Our results showed that fumigation of upland rice vinegar containing antifungal VOC is a simple and an economical method for commercial preservation of dried chili pepper. Upland rice vinegar is a novel bio-fumigant for prevention of mycotoxin production in dried food and feed products during storage.
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Inhibition of Pantoea agglomerans contamination of fresh-cut jackfruit by exposure to weak organic acid vapors
(2021-03-01)
Pothimon, Ruttipron
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Podjanee, Uraiwan
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Krusong, Warawut
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Thompson, Anthony Keith
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Massa, Salvatore
Fresh-cut jackfruit, purchased from markets in urban areas of Bangkok, were examined for bacterial contamination. Pantoea agglomerans was the predominant contaminant bacterium occurring in 90% of the 30 samples tested; many with high loads. Inhibition of surface contamination of P. agglomerans by vinegar, lactic acid or citric acid, either as liquid or vapor, were tested in vitro. For liquid-phase exposure, vinegar had a higher inhibitory effect than the other two, both of which that gave only slight inhibition. Exposure to vinegar vapor containing 3.36 mmol L−1 acetic acid for 90 min gave complete inhibition of P. agglomerans. In order to test this vaporized vinegar treatment on the quality of jackfruit, non-inoculated samples, with or without vinegar treatment, were stored for 7 d at 5 ± 2 °C and then tested by a sensory evaluation panel. Results showed that in all the attributes tested, color, texture and overall acceptability, vaporized vinegar treated sample were preferred to non-treated samples. It was concluded that exposure of fresh-cut jackfruit to vaporized vinegar is a simple method of controlling surface bacterial contamination without detrimentally affecting their acceptability.
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Consecutive bacterial cellulose production by luffa sponge enmeshed with cellulose microfibrils of Acetobacter xylinum under continuous aeration
(2021-01-01)
Krusong, Warawut
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Pothimon, Ruttipron
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China, Salvatore La
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Thompson, Anthony Keith
The bacterial cellulose production (BCP) process, using cellulose microfibrils (CM) of Acetobacter xylinum enmeshed on luffa sponge matrices (LSM) as LSM-CM starter, has been successfully developed where the LSM-CM production process can be recycled through consecutive cycles in limited dissolved oxygen (DO) under continuous aeration. In this study, incremental aeration rates impacted the consecutive cycles. Gluconic acid production, during the process, resulting in the reduction of BCP, was increasingly generated at high aeration from 0.28 to 0.34% at 3 L/min to 0.83–0.97% and 1.52–1.99% at 6 and 9 L/min after 7 d culture at 30 ± 2 °C. To compensate for the negative impact of aeration, 0.10 and 0.15% (w/v) carboxymethyl cellulose (CMC) was found to create a microenvironment for recycled LSM-CM at both high aeration (6 and 9 L/min, respectively). Under nine consecutive BCP cycles, acceptable BC yields (from 5.54 ± 0.5 to 5.89 ± 0.5 g/L) were associated with high biomass at 6 L/min aeration. These results confirm that LSM-CM, combined with CMC called as LSM-CM-CMC, created microenvironments low in DO under high aeration rates and that the recycled LSM-CM-CMC with aeration is an alternative, sustainable, economic process that could be applied for mass BCP.
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Conducting High acetic acid and temperature acetification processes by Acetobacter pasteurianus UMCC 2951
(2020-11-01)
Pothimon, Ruttipron
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Gullo, Maria
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La China, Salvatore
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Thompson, Anthony Keith
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Krusong, Warawut
In this study Acetobacter pasteurianus strain UMCC 2951 was tested as a microbial starter to conduct acetification processes by repeatedly cultivation cycles under high temperature acetification at 40 ± 1 °C. Acid production and acetification rate increased with repeated cultures under high temperature acetification as adaptation period increased, but were still lower than acetification at 30 ± 1 °C. However, the addition of 0.15 % calcium chloride reduced the negative effects of 40 ± 1 °C on both acid production and acetification rate compared to 30 ± 1 °C. A strong decrease in fatty acids and phosphatidylethanolamine and increases in phosphatidylcholine and phosphatidylglycerol in cell membranes were found under high acid and high temperature acetification. In addition, transmission electron microscope images reveal a more compact cell wall when calcium chloride was added to the cultivation medium. The strategy used in this study confirmed that the use of acetic acid bacteria as microbial starters could be effective also at temperature above the optimal values, when acetification processes are managed through repeated semi-continuous cycles.
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Inhibitory impact of vapor-phase ethanol on conidia germination and mycelial growth of Aspergillus fumigatus on bread
(2019-01-01)
Krusong, Warawut
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Pothimon, Ruttipron
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Vichitraka, Assanee
Mold contaminated on bread sold in local market was isolated and identified as Aspergillus fumigatus. Then, the bio-control of ethanol on A. fumigatus for significantly reducing consumer health risk was investigated. Susceptibility of the mold to evaporated vapor-phase ethanol (EVE) was examined in vitro. Complete elimination of viable spore and inhibition growth spread on Potato Dextrose Agar at 30 ± 2 °C of were found with exposure for 15 min to EVE (10.80 ± 0.3 mmol/L). The effect of EVE on the susceptibility of artificial inoculated A. fumigatus on bread were further examined. While exposure to EVE affected the survival conidia, the degree of reduction depended on the inoculation level. Complete reduction was achieved for the low inoculation level (2.08 ± 0.04 log conidia/g) by EVE (60 min exposure, 19.27 ± 0.3 mmol/L) but susceptibility was reduced with the high inoculation level (5.4 ± 0.06 log conidia/g). Simultaneously, total aflatoxin production decreased, as EVE exposure increased. Scanning electron microscope images of inoculated bread, confirm the effects of EVE in reducing levels of viable conidia. Hence, EVE is shown to be an effective bio-fumigant for A. fumigatus mycelial growth and aflatoxin formation on bread, so effectively reducing the potential for consumer health risks due to this widespread fungus.

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