Production of bioethanol from food waste: Status and perspectives

There is an immediate global requirement for an ingenious strategy for food waste conversion to biofuels in order to replace fossil fuels with renewable resources. Food waste conversion to bioethanol could lead to a sustainable process having the dual advantage of resolving the issue of food waste disposal as well as meeting the energy requirements of the increasing population. Food waste is increasing at the rate of 1.3 billion tonnes per year, considered to be one-third of global food production. According to LCA studies discarding these wastes is detritus to the environment, therefore; it is beneficial to convert the food waste into bioethanol. The CO₂ emission in this process offers zero impact on the environment as it is biogenic. Among several pretreatment strategies, hydrothermal pretreatment could be a better approach for pretreating food waste because it solubilizes organic solids, resulting in an increased recovery of fermentable sugars to produce bioenergy.

Isolation of Polygalacturonase-Producing Bacterial Strain from Tomatoes (Lycopersicon esculentum Mill.)

Background

Polygalacturonase (EC 3.2.1.15) enzyme aids in microbial spoilage of fruits and vegetables. It is very important to find economical ways to producing the enzyme so as to achieve maximum yield in industries due to its use at different areas of production process.

Methods

Isolation of polygalacturonase-producing bacterial strain from tomatoes (Lycopersicon esculentum Mill.) was studied. Polygalacturonase-producing bacterial strains were isolated and screened from tomatoes stored at normal laboratory temperature (25 ± 2°C). They were identified based on their morphological, biochemical, and molecular characteristics. The enzyme produced was partially purified by the ammonium sulphate precipitation method. Molecular weights and optimum conditions for best enzyme activity were obtained by SDS PAGE technique.

Results

Five bacterial isolates resulted after screening. Bacterial strain code B5 showed highest polygalacturonase activity. Optimum conditions for polygalacturonase PEC B5 were maintained at pH 4.5; temperature 35°C; substrate concentration 0.3 mg/ml, and best activity at less than 5 min of heating. The enzyme PEC B5 was found to weigh 65 kDa and 50 kDa for crude and partially purified aliquots, respectively. The result of 16S rRNA gene sequencing revealed bacterial strain code B5 as Enterobacter tabaci NR146667 having 79% similarity with the NCBI GenBank.

Conclusion

Microorganisms should be developed for large-scale production of enzymes in developing countries.

Multi-criteria decision analysis of waste-to-energy technologies for municipal solid waste management in Sultanate of Oman

The Sultanate of Oman faces challenges, like rapid growth of waste generation, which calls for an optimum waste management strategy. Oman has witnessed the production of 1.5m t of municipal solid waste in 2012, which is expected to elevate to 1.89m t in 2030. This rapid increase needs to be tackled to reduce the generation rates along with the environmental impacts. Currently, there are no treatment facilities in Oman other than limited recycling, and therefore dumping waste into the landfill is the only ultimate way to dispose solid waste. Hence, this study is an initiative to improve the waste managing system in Oman by proposing optimum waste-to-energy technology using an analytical hierarchy process, manually and through expect choice software as well. In the present study, the identified important parameters were considered in an analytical hierarchy process model to rank the waste-to-energy technology alternatives. Based on the survey conducted, the most important criteria were environmental and economic, with the local priority vector of 0.400 and 0.277, respectively. This research concludes that the most suitable waste-to-energy technology for Oman, on the basis of the identified criteria, is anaerobic digestion followed by fermentation and incineration, which will help to reduce the amount of waste, greenhouse gas emissions and developing and maintaining costs of landfills.

Recent trends in bioethanol production from food processing byproducts

The widespread use of corn starch and sugarcane as sources of sugar for the production of ethanol via fermentation may negatively impact the use of farmland for production of food. Thus, alternative sources of fermentable sugars, particularly from lignocellulosic sources, have been extensively investigated. Another source of fermentable sugars with substantial potential for ethanol production is the waste from the food growing and processing industry. Reviewed here is the use of waste from potato processing, molasses from processing of sugar beets into sugar, whey from cheese production, byproducts of rice and coffee bean processing, and other food processing wastes as sugar sources for fermentation to ethanol. Specific topics discussed include the organisms used for fermentation, strategies, such as co-culturing and cell immobilization, used to improve the fermentation process, and the use of genetic engineering to improve the performance of ethanol producing fermenters.

Advances in yeast systematics and phylogeny and their use as predictors of biotechnologically important metabolic pathways

Detection, identification and classification of yeasts have undergone a major transformation in the last decade and a half following application of gene sequence analyses and genome comparisons. Development of a database (barcode) of easily determined DNA sequences from domains 1 and 2 (D1/D2) of the nuclear large subunit rRNA gene and from ITS now permits many laboratories to identify species quickly and accurately, thus replacing the laborious and often inaccurate phenotypic tests previously used. Phylogenetic analysis of gene sequences is leading to a major revision of yeast systematics that will result in redefinition of nearly all genera. This new understanding of species relationships has prompted a change of rules for naming and classifying yeasts and other fungi, and these new rules are presented in the recently implemented International Code of Nomenclature for algae, fungi, and plants (Melbourne Code). The use of molecular methods for species identification and the impact of Code changes on classification will be discussed, as will use of phylogeny for prediction of biotechnological applications.