High voltage electrical discharges combined with enzymatic hydrolysis for extraction of polyphenols and fermentable sugars from orange peels

Acidogenic fermentation was applied to evaluate the potential recovery of biological monomers as precursors in bio-plastic production. Three residual organic substrates from high-volume beverage sectors (coffee, orange juice, beer) were assessed: spent coffee grounds (SCG), orange peels (OP), and brewers' spent grains (BSG). Batch fermentation tests were set up. SCG and OP were studied as single substrates and combined to evaluate yields of _target monomers (volatile fatty acids, ethanol, lactate) and to reveal interactions between the matrixes. NaOH pre-treatment was applied to SCG to enhance disruption of the lignocellulosic cell wall. BSG was studied without pre-treatment and following acid or alkaline pre-treatment, with acidogenic fermentation being initiated with two different initial pH values (7; 9). Acetogenic fermentation was achieved with all substrates, although with different yields of _target monomers. In terms of total biological metabolite production, following alkaline pre-treatment, OP and BSG, both fermented at an initial pH 9, showed the best performance, yielding 62.6 g and 62.0 g _target monomers per litre substrate. For all substrates, acetic and butyric acids were the most abundant products. In the case of OP fermentation, butyrate accounted for 57% (35.8 g/L) of the total. The BSG test with the highest total yield also achieved the highest acetate yield (36.7 g/L). The results confirm that OP and BSG should be considered a priority sustainable feedstock for the supply of biological monomers, particularly if polyhydroxyalkanoates are to be produced. SCG are better suited to aceto-oriented approaches, such as the production of polyvinyl acetate.

The objective of this study was to evaluate the potential of green solvents for extractions of bioactive compounds (BACs) and essential oils from wild thyme (Thymus serpyllum L.) using theoretical and experimental procedures. Theoretical prediction was assessed by Hansen solubility parameters (HSPs) and conductor-like screening model for realistic solvents (COSMO-RS), to predict the most suitable solvents for extraction of BACs. An experimental procedure was performed by nonthermal technology high voltage electrical discharge (HVED) and it was compared with modified conventional extraction (CE). Obtained extracts were analyzed for chemical and physical changes during the treatment. Theoretical results for solution of BACs in ethanol and water, as green solvents, were confirmed by experimental results, while more accurate data was given by COSMO-RS assessment than HSPs. Results confirmed high potential of HVED for extraction of BACs and volatile compounds from wild thyme, in average, 2.03 times higher yield of extraction in terms of total phenolic content was found compared to CE. The main phenolic compound found in wild thyme extracts was rosmarinic acid, while the predominant volatile compound was carvacrol. Obtained extracts are considered safe and high-quality source reach in BACs that could be further used in functional food production.

The development of lignocellulosic bioethanol plays an important role in the substitution of petrochemical energy and high-value utilization of agricultural wastes. The safe and stable expression of cellulase gene sestc was achieved by applying the clustered regularly interspaced short palindromic repeats-Cas9 approach to the integration of sestc expression cassette containing Agaricus biporus glyceraldehyde-3-phosphate-dehydrogenase gene (gpd) promoter in the Saccharomyces cerevisiae chromosome. The _target insertion site was found to be located in the S. cerevisiae hexokinase 2 by designing a gRNA expression vector. The recombinant SESTC protein exhibited a size of approximately 44 kDa in the engineered S. cerevisiae. By using orange peel as the fermentation substrate, the filter paper, endo-1,4-β-glucanase, exo-1,4-β-glucanase activities of the transformants were 1.06, 337.42, and 1.36 U/mL, which were 35.3-fold, 23.03-fold, and 17-fold higher than those from wild-type S. cerevisiae, respectively. After 6 h treatment, approximately 20 g/L glucose was obtained. Under anaerobic conditions the highest ethanol concentration reached 7.53 g/L after 48 h fermentation and was 37.7-fold higher than that of wild-type S. cerevisiae (0.2 g/L). The engineered strains may provide a valuable material for the development of lignocellulosic ethanol.