RESUMO
BACKGROUND: Feed additives such as live yeast cultures have increasingly been used in ruminant feeds to improve animal performance and feeding efficiency. However, it is not clear how inactive combined yeast cultures affect ruminal gas production, fermentation kinetics and efficiency. Therefore, this study was done to determine the influence of incubating different substrates with a combined yeast culture + enzymatically hydrolyzed yeast (YC + EHY) on in vitro ruminal gas production, fermentation kinetics and metabolizable energy. Six contrasting substrates (Trichantera gigantea and Glircidia sepium leaves, Brachiaria hybrid (cv. Mulato II) leaf + stem and leaf only, Cynodon nlemfuensis and a commercial concentrate dairy feed) were incubated with and without YC + EHY in buffered rumen fluid and gas production measured at 2, 4, 6, 8, 10, 12, 15, 19, 24, 30, 36, 48 and 72 h post incubation. RESULTS: In vitro fermentation parameters (a, b, a + b and c) were unaffected by YC + EHY except for the lag phase in T. gigantea, which that reduced by 31.3% when it was incubated with YC + EHY. Supplementation with YC + EHY also did not affect metabolizable energy, 72 h organic matter digestibility, 24 h gas or CH4 production within substrate. However, cumulative gas and methane production at peak fermentation in the commercial concentrate feed was reduced by 20% when incubated with YC + EHY. CONCLUSION: It was concluded that YC + EHY has the potential to improve microbial colonization of T. gigantean substrates and reduce gas and methane production at peak fermentation in commercial concentrate feeds. © 2021 Society of Chemical Industry.
Assuntos
Rúmen , Saccharomyces cerevisiae , Ração Animal/análise , Animais , Dieta , Digestão , Fermentação , Metano/metabolismo , Rúmen/metabolismoRESUMO
AIMS: To calculate fermentation efficiency in a continuous ethanol production process, we aimed to develop a robust mathematical method based on the analysis of metabolic by-product formation. METHODS AND RESULTS: This method is in contrast to the traditional way of calculating ethanol fermentation efficiency, where the ratio between the ethanol produced and the sugar consumed is expressed as a percentage of the theoretical conversion yield. Comparison between the two methods, at industrial scale and in sensitivity studies, showed that the indirect method was more robust and gave slightly higher fermentation efficiency values, although fermentation efficiency of the industrial process was found to be low (~75%). CONCLUSIONS: The traditional calculation method is simpler than the indirect method as it only requires a few chemical determinations in samples collected. However, a minor error in any measured parameter will have an important impact on the calculated efficiency. In contrast, the indirect method of calculation requires a greater number of determinations but is much more robust since an error in any parameter will only have a minor effect on the fermentation efficiency value. SIGNIFICANCE AND IMPACT OF THE STUDY: The application of the indirect calculation methodology in order to evaluate the real situation of the process and to reach an optimum fermentation yield for an industrial-scale ethanol production is recommended. Once a high fermentation yield has been reached the traditional method should be used to maintain the control of the process. Upon detection of lower yields in an optimized process the indirect method should be employed as it permits a more accurate diagnosis of causes of yield losses in order to correct the problem rapidly. The low fermentation efficiency obtained in this study shows an urgent need for industrial process optimization where the indirect calculation methodology will be an important tool to determine process losses.
Assuntos
Bactérias/metabolismo , Etanol/metabolismo , Microbiologia Industrial/métodos , Bactérias/química , Etanol/análise , Fermentação , Modelos TeóricosRESUMO
Although numerous studies have examined many of the factors that affect the efficiency of batch ethanol fermentation, little attention has been paid to the influence of the biomass concentration on this efficiency. This paper shows that the influence of the biomass initial concentration on the fermentation efficiency depends on what is considered "produced ethanol". If only the ethanol present in the medium aqueous phase at fermentation completion is considered, the fermentation efficiency linearly decreases when the biomass initial concentration increases. If, however, the intracellular ethanol is also considered as produced ethanol, the fermentation efficiency is not affected by the biomass concentration.
Embora muitos estudos tenham avaliado muitos dos fatores que afetam a eficiência da fermentação etanólica, a influência da concentração da biomassa na eficiência do processo tem recebido pouca atenção. Esse trabalho mostra que a influencia da concentração inicial de biomassa depende do que se considera "etanol produzido". Se, terminada a fermentação, considera-se como etanol produzido apenas aquele existente na fase aquosa do meio, o rendimento da fermentação decresce linearmente quando a concentração inicial de biomassa aumenta. Entretanto, se o etanol intracelular também é considerado, a concentração da biomassa não afeta o rendimento da fermentação.