Progress in microbial biomass conversion into green energy

The increase in global population size over the past 100 decades has doubled the requirements for energy resources. To mitigate the limited fossil fuel available, new clean energy sources being environmental sustainable for replacement of traditional energy sources are explored to supplement the current scarcity. Biomass containing lignin and cellulose is the main raw material to replace fossil energy given its abundance and lower emission of greenhouse gases and NOx when transformed into energy. Bacteria, fungi and algae decompose lignocellulose leading to generation of hydrogen, methane, bioethanol and biodiesel being the clean energy used for heating, power generation and the automobile industry. Microbial Fuel Cell (MFC) uses microorganisms to decompose biomass in wastewater to generate electricity and remove heavy metals in wastewater. Biomass contains cellulose, hemicellulose, lignin and other biomacromolecules which need hydrolyzation for conversion into small molecules by corresponding enzymes in order to be utilized by microorganisms. This paper discusses microbial decomposition of biomass into clean energy and the five major ways of clean energy production, and its economic benefits for future renewable energy security.

Spent Craft Brewer's Yeast Reduces Production of Methane and Ammonia by Bovine Rumen Microbes

Methane and ammonia are byproducts of rumen fermentation that do not promote animal growth, and methane is a key contributor to anthropogenic climate disruption. Cows eructate every few breaths and typically emit 250–500 L of methane gas daily. Significant research is focused on finding diets and additives that lower the production of methane and ammonia. Emerging research has shown that humulones and lupulones, molecules that are found in the cones of hops (Humulus lupulus), have potential in this regard. These molecules, which are also key flavor components in beer, are biologically active: they are known inhibitors of Gram-positive bacteria. Ruminants' sophisticated digestive systems host billions of microorganisms, and these systems' outputs will likely be affected in the presence of brewer's yeast (Saccharomyces cerevisiae). So-called spent yeast is produced during the beer-brewing process and contains humulones and lupulones in concentrations that vary by beer style, but it is generally discarded as waste. Our research suggests that adding spent craft brewer's yeast to rumen microbes by single time-point 24-h in vitro incubations suppresses production of methane and ammonia. This project examines the correlation between the quantities of hop acids in spent yeast and the production of methane and ammonia by bovine rumen microbes in vitro. We determined, by HPLC, the hop acid concentrations in spent yeast obtained from six beer styles produced at a local brewery. We performed anaerobic incubation studies on bovine rumen microbes, comparing the effects of these materials to a baker's yeast control and to the industry-standard antibiotic monensin. Results include promising decreases in both methane (measured by GC–FID) and ammonia (measured by colorimetric assay) in the presence of craft brewer's yeast, and a strong correlation between the quantities of hop acids in the spent yeast and the reduction of methane and ammonia. Notably, two of the yeast samples inhibited methane production to a greater degree than the industry-standard antibiotic monensin. Our results suggest that spent brewer's yeast has potential to improve ruminant growth while reducing anthropogenic methane emission.

Valorisation of Brewer’s Spent Yeasts’ Hydrolysates as High-Value Bioactive Molecules

Brewer’s spent yeast (BSY) is produced by the beer industry and has high nutritional value and great potential for producing high-value molecules, such as peptides, for nutraceutical, food and feed applications. In the present research, Flavourzyme® and Protamex® enzymes were selected for protein hydrolysis based on previous studies. The optimum conditions for the enzymatic hydrolysis were defined by response surface methodology (RSM) by the Box–Behnken design composed of four variables: temperature, pH, enzyme dosage and time. Protein content, hydrolysis degree and the anti-microbial and antioxidant bioactivities of obtained hydrolysates were quantified. Obtained results show that time, enzyme dosage and pH had the highest effect on protein extraction yield (PEY), degree of hydrolysis (DH) and antioxidant activity. Response variables ranged from 13.7 to 29.7% for PEY, from 6.3 to 35.7% for DH and from 0.65 to 1.65 g for Trolox equivalent antioxidant capacity. Antimicrobial activity, measured as minimum inhibitory concentration, against Aeromonas salmonicida, Bacillus cereus, Bacillus subtilis and Salmonella enterica, ranged from 6.25 to 50 mg/mL. Antioxidant and antimicrobial activity showed the potential use of BSY hydrolysates as an ingredient for functional foods.

Inclusion of yeast waste as a protein source to replace soybean meal in concentrate mixture on ruminal fermentation and gas kinetics using in vitro gas production technique

This experiment was conducted to investigate the utilisation of yeast waste as protein source to replace soybean meal in concentrate mixture on kinetic of gas, rumen ammonia-nitrogen and digestibility of nutrients by using in vitro gas production technique. The experimental design was a completely randomised design and the dietary treatments were replacing soybean meal with yeast wastein concentrate at the ratio of 100:0, 75:25, 50:50, 25:75 and 0:100, respectively. Yeast waste was obtained from KSL Green Innovation Public Co. Limited, Thailand. The gas production was recorded at 0, 0.5, 1, 2, 4, 6, 8, 12, 16, 24, 48, 72 and 96 h of incubation. The yeast waste contained 26.4% crude protein. Gas production from soluble fractions (a), gas production from the insoluble fraction (b), potential extent of gas production (a+b) and the gas production rate constants for the insoluble fraction (c) were not altered when increasing concentration of yeast waste replacing soybean meal (P > 0.05). Cumulative gas production (at 96 h of incubation) ranged from 69.3 to 72.8 mL and was similar among treatments. Ruminal NH3-N concentration was linearly increased (P < 0.05) whereas ruminal pH did not alter when inclusion various levels of yeast waste replacing soybean meal, which ranged from 15.2 to 19.1 mg/dL and 6.90 to 6.94, respectively. In vitro dry matter digestibility and in vitro organic matter digestibility did not changed by increasing levels of yeast waste in the diets (P > 0.05), except only in vitro dry matter digestibility at 12 h, which higher in soybean meal:yeast waste at 25:75 ratio (P < 0.05). Furthermore, propionate (C3) molar was linearly higher when compared between inclusion yeast waste and the control group whereas acetate was decreased quadratically (P < 0.05) and protozoal population tended to be decreased (P = 0.07) when increasing the level of replacing yeast waste. In conclusion, yeast waste could replace soybean meal in concentrate mixture with no negative effect on gas kinetics, rumen fermentation and in vitro digestibility, and therefore its use in animal feeding would contribute to a reduction in environmental pollution.

Hops (Humulus lupulus L.) Bitter Acids: Modulation of Rumen Fermentation and Potential As an Alternative Growth Promoter

Antibiotics can improve ruminant growth and efficiency by altering rumen fermentation via selective inhibition of microorganisms. However, antibiotic use is increasingly restricted due to concerns about the spread of antibiotic-resistance. Plant-based antimicrobials are alternatives to antibiotics in animal production. The hops plant (Humulus lupulus L.) produces a range of bioactive secondary metabolites, including antimicrobial prenylated phloroglucinols, which are commonly called alpha- and beta-acids. These latter compounds can be considered phyto-ionophores, phytochemicals with a similar antimicrobial mechanism of action to ionophore antibiotics (e.g., monensin, lasalocid). Like ionophores, the hop beta-acids inhibit rumen bacteria possessing a classical Gram-positive cell envelope. This selective inhibition causes several effects on rumen fermentation that are beneficial to finishing cattle, such as decreased proteolysis, ammonia production, acetate: propionate ratio, and methane production. This article reviews the effects of hops and hop secondary metabolites on rumen fermentation, including the physiological mechanisms on specific rumen microorganisms, and consequences for the ruminant host and ruminant production. Further, we propose that hop beta-acids are useful model natural products for ruminants because of (1) the ionophore-like mechanism of action and spectrum of activity and (2) the literature available on the plant due to its use in brewing.