Hydrogen production and consumption of organic acids by a phototrophic microbial consortium

Abstract. The main problem of hydrogen production via anaerobic fermentation is the very low production rate due to severe hydrogen-consuming reactions. Hydrogen partial pressure is a major factor influencing reactions of hydrogen production and consumption. To study the influence of H2 concentration on hydrogen production and consumption, H2 was mixed with N2 at initial concentrations of 20%, 40%, 60%, 80%, and 100% to sparge the fermentation broth. The results showed that H2 concentration had significant influence on these reactions, changing the pathway of glucose hydrolysis and acidification. With increasing H2 concentration in the sparging gas, the pathway of glucose acidogenesis hydrolysis transferred from mixed acid production (propionic acid and butyric acid) to propionic acid production. When the H2 concentration was 20% and the N2 concentration was 80%, the production rates of propionic acid and butyric acid were highest (0.76 and 0.41 mmol mmol-1 glucose consumed d-1, respectively) and accounted for 100% of total soluble metabolic products. When the H2 concentration in the sparging gas was more than 40%, the production rates of propionic acid and butyric acid decreased, and glucose degradation was inhibited. In addition, due to propionic acid type fermentation and high hydrogen partial pressure, acetogenesis was not feasible thermodynamically, resulting in a low production rate of H2 during the whole fermentation process. When the initial H2 concentration in the sparging gas was 40%, the production rate of H2 was highest, (0.42 mol mol-1 glucose consumed d-1). In addition, the theoretical production rate of H2 calculated from the production of soluble metabolic products was less than the actual value. This resulted from the co-existence of homoacetogenesis and acetic acid oxidation due to the bidirectionality of homoacetogens, establishing a new symbiotic relationship. Keywords: Anaerobic fermentation, Hydrogen consumption, Hydrogen partial pressure, Hydrogen production, Sparging.

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Identification of the Microbial Consortium in Sri Lankan Buffalo Milk Curd and their growth in the Presence of Prebiotics

Journal of Food Science and Technology Nepal ◽

10.3126/jfstn.v9i0.12579 ◽

2016 ◽

Vol 9 ◽

pp. 20-30 ◽

Cited By ~ 1

Author(s):

N. Dekumpitiya ◽

D. Gamlakshe ◽

S. I. Abeygunawardena ◽

D. Jayaratne

Keyword(s):

Microbial Consortium ◽

Value Added ◽

Buffalo Milk ◽

Lactobacillus Delbrueckii ◽

Sri Lankan ◽

A Value ◽

Production And Consumption ◽

Bacillus Spp ◽

The Difference ◽

Lactobacillus Delbrueckii Subsp

The production and consumption of traditionally fermented buffalo milk curd provides many economical and food security benefits to both producers and consumers in the country. To improve this traditional product as a value-added product, an investigation was conducted to elucidate the microbial consortium associated with curd using culturable techniques and the microbial load was quantified in the presence of prebiotics. Twenty six samples of curd were analyzed to isolate microorganisms. The two major LAB groups present in the samples were characterized as Lactobacillus and Streptococcus. LABs were further identified as Lactobacillus delbrueckii subsp. lactis, L. planatarum, L. helviticus, Lactobacillus delbrueckii subsp. bulgaricus and L. casei subsp casei, Streptococcus thermophiles and S. lactis. Saccharomyces cerevisiae, Micrococcus spp., and Bacillus spp. were also present in this microbial consortium The addition of two types of commercially available prebiotics improved the counts of Lactobacillus in curd samples, despite the difference in the prebiotic compounds.

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