Biomass, Volume 2, Issue 2 (June 2022) – 3 articles

The aerobic oxidation of biomass transformations into valuable chemical products via a green catalytic process is one of the most important protocols because of its low reaction temperature and high productivity rate. Recently, the introduction of small-sized Cu and Au nanoparticles (e.g., 1–3 nm) upon the surface of oxides can provide more catalytic active sites and then enhance the catalytic activity of aerobic oxidations significantly. The introduction of these metal nanoparticles is a kind of perfect catalyst for enhancing the efficiency of the activation of oxygen molecules and the separation of photo-generated holes and electrons during the photo-oxidation reactions. In this account, we summarize recent progress of the aerobic oxidation of biomass alcohol toward the production of highly valuable chemicals over supported catalysts of metal nanoparticles (NPs), including methanol conversion into methyl formate via photo-oxidation over CuO_x/TiO₂ nanocomposites, biomass ethanol transformation with biomass furfural to produce hydrocarbons biofuels over Au/NiO catalysts, and glucose oxidation to gluconic acid using Au/activated carbon (Au/AC) as catalysts. Furthermore, at the atomic level, to understand the structure-property correlations, insights into molecular activations of oxygen and biomass, and the investigation of active catalytic sites on photo/catalysts will be detailed and discussed. Finally, future studies are needed to achieve more exciting progress in the fundamental revealing of the catalytic reaction mechanisms and conversion pathway and the future perspective in industrial applications. Full article

Microalgae are known to have higher photosynthetic efficiencies when compared to land-based plants. The use of microalgae biomass as a protein source is attracting attention due to its interesting protein composition and sustainable character when compared to conventional animal and plant protein-based sources. Nonetheless, the existence of a rigid cell wall is typical for most microalgae species, and this presents a serious obstacle to a higher bioaccessibility of their valuable protein fractions. Depending on the cell wall composition, the gastrointestinal digestion process itself can result in different pathways of protein absorption. It is then important to understand how microalgae cell wall structure can be affected during traditional and industrial production of its biomass once these questions are often overlooked. This review intends to fulfill this gap by addressing the major impacts of innovative sustainable processing of microalgae biomass, giving particular attention to drying operations and cellular disruption methods based on electric field application—such as pulsed electric fields (PEF) and moderate electric fields (MEF). Using microalgae biomass as food supplements at its full potential depends on its protein digestibility patterns, and subsequently their bioaccessibility and bioavailability. The importance of using in vitro gastrointestinal systems to understand the impact of innovative downstream processing of microalgae biomass will be addressed. Full article

Coffee wastes have large amounts of by-products rich in phenolic compounds such as chlorogenic and caffeic acid, with potential applications for developing fine chemicals such as caffeic acid phenethyl ester (CAPE). A screening for microorganisms was undertaken in a coffee plantation environment to isolate native tropical species able to modify secondary metabolites present in this kind of biomass enzymatically. From the screening, 130 fungal strains could grow in lipase inducer media. Fungal strains were identified via ITS-based sequencing. Classification based on BLAST assigned 51 isolates to 12 different genera, including Absidia, Aspergillus, Cunninghamella, Fusarium, Metarhizium, Meyerozyma, Mucor, Neocosmospora, Papiliotrema, Penicillium, Rhizopus, and Trichoderma. DNA sequencing identified 14 putative extracellular lipases. According to the extracellular lipase activity, the most promising strain was identified as Fusarium sp. by DNA barcoding. Extracellular lipases from this strain exhibited maximal hydrolytic activity at a temperature of 45 °C, a pH of 7.00, and 200 ppm of NaCl, with an affinity towards substrates having carbon chain lengths of 8 or longer. Under these conditions, lipase instead of esterase activity is the main feature. The Km and Vmax values calculated using p-nitrophenyl palmitate (pNPP) as hydrolysis substrate were 0.003 mM and 299.8 μmol min⁻¹ mg⁻¹, respectively. Fusarium sp. lipases presented high stability during freeze–thawing, allowing the storage of enzyme solutions at −20 °C, but not as a lyophilized powder. According to our kinetic study, these lipases catalyzed CAPE hydrolysis, showing a progressive decrease in the concentration of the CAPE and a correspondent increase in the caffeic acid concentration as a product of this hydrolysis. Being able to carry out this type of reaction under mild conditions shows that Fusarium sp. lipases recognize CAPE as substrate and suggest CAPE synthesis (reverse reaction) and transformation can be engineered, using caffeic acid from coffee biomass, as a potential industrial application for these lipases. Full article