Enhanced hydrolysis of Macrocystis pyrifera by integrated hydroxyl radicals and hot water pretreatment

Fuelling the future of sustainable sugar fermentation across generations

Biomanufacturing in the form of industrial sugar fermentation is moving beyond pharmaceuticals and biofuels into chemicals, materials, and food ingredients. As the production scale of these increasingly consumer-facing applications expands over the next decades, considerations regarding the environmental impact of the renewable biomass feedstocks used to extract fermentable sugars will become more important. Sugars derived from first-generation biomass in the form of, for example, corn and sugarcane are easily accessible and support high-yield fermentation processes, but are associated with the environmental impacts of industrial agriculture, land use, and competition with other applications in food and feed. Fermentable sugars can also be extracted from second- and third-generation feedstocks in the form of lignocellulose and macroalgae, respectively, potentially overcoming some of these concerns. Doing so, however, comes with various challenges, including the need for more extensive pretreatment processes and the fermentation of mixed and unconventional sugars. In this review, we provide a broad overview of these three generations of biomass feedstocks, outlining their challenges and prospects for fuelling the industrial fermentation industry throughout the 21st century.

Recent Advances in Bioutilization of Marine Macroalgae Carbohydrates: Degradation, Metabolism, and Fermentation

Marine macroalgae are considered renewable natural resources due to their high carbohydrate content, which gives better utilization value in biorefineries and higher value conversion than first- and second-generation biomass. However, due to the diverse composition, complex structure, and rare metabolic pathways of macroalgae polysaccharides, their bioavailability needs to be improved. In recent years, enzymes and pathways related to the degradation and metabolism of macroalgae polysaccharides have been continuously developed, and new microbial fermentation platforms have emerged. Aiming at the bioutilization and transformation of macroalgae resources, this review describes the latest research results from the direction of green degradation, biorefining, and metabolic pathway design, including summarizing the the latest biorefining technology and the fermentation platform design of agarose, alginate, and other polysaccharides. This information will provide new research directions and solutions for the biotransformation and utilization of marine macroalgae.

Aquaculture Production of the Brown Seaweeds Laminaria digitata and Macrocystis pyrifera: Applications in Food and Pharmaceuticals

Seaweeds have a long history of use as food, as flavouring agents, and find use in traditional folk medicine. Seaweed products range from food, feed, and dietary supplements to pharmaceuticals, and from bioenergy intermediates to materials. At present, 98% of the seaweed required by the seaweed industry is provided by five genera and only ten species. The two brown kelp seaweeds Laminaria digitata, a native Irish species, and Macrocystis pyrifera, a native New Zealand species, are not included in these eleven species, although they have been used as dietary supplements and as animal and fish feed. The properties associated with the polysaccharides and proteins from these two species have resulted in increased interest in them, enabling their use as functional foods. Improvements and optimisations in aquaculture methods and bioproduct extractions are essential to realise the commercial potential of these seaweeds. Recent advances in optimising these processes are outlined in this review, as well as potential future applications of L. digitata and, to a greater extent, M. pyrifera which, to date, has been predominately only wild-harvested. These include bio-refinery processing to produce ingredients for nutricosmetics, functional foods, cosmeceuticals, and bioplastics. Areas that currently limit the commercial potential of these two species are highlighted.

Bioethanol Production from UK Seaweeds: Investigating Variable Pre-treatment and Enzyme Hydrolysis Parameters

This study describes the method development for bioethanol production from three species of seaweed. Laminaria digitata, Ulva lactuca and for the first time Dilsea carnosa were used as representatives of brown, green and red species of seaweed, respectively. Acid thermo-chemical and entirely aqueous (water) based pre-treatments were evaluated, using a range of sulphuric acid concentrations (0.125-2.5 M) and solids loading contents (5-25 % [w/v]; biomass: reactant) and different reaction times (5-30 min), with the aim of maximising the release of glucose following enzyme hydrolysis. A pre-treatment step for each of the three seaweeds was required and pre-treatment conditions were found to be specific to each seaweed species. Dilsea carnosa and U. lactuca were more suited with an aqueous (water-based) pre-treatment (yielding 125.0 and 360.0 mg of glucose/g of pre-treated seaweed, respectively), yet interestingly non pre-treated D. carnosa yielded 106.4 g g^-1 glucose. Laminaria digitata required a dilute acid thermo-chemical pre-treatment in order to liberate maximal glucose yields (218.9 mg glucose/g pre-treated seaweed). Fermentations with S. cerevisiae NCYC2592 of the generated hydrolysates gave ethanol yields of 5.4 g L^-1, 7.8 g L^-1 and 3.2 g L^-1 from D. carnosa, U. lactuca and L. digitata, respectively. This study highlighted that entirely aqueous based pre-treatments are effective for seaweed biomass, yet bioethanol production alone may not make such bio-processes economically viable at large scale.

Seaweed Bioethanol Production: A Process Selection Review on Hydrolysis and Fermentation

The rapid depletion and environmental concerns associated with the use of fossil fuels has led to extensive development of biofuels such as bioethanol from seaweeds. The long-term prospect of seaweed bioethanol production however, depends on the selection of processes in the hydrolysis and fermentation stages due to their limiting effect on ethanol yield. This review explored the factors influencing the hydrolysis and fermentation stages of seaweed bioethanol production with emphasis on process efficiency and sustainable application. Seaweed carbohydrate contents which are most critical for ethanol production substrate selection were 52 ± 6%, 55 ± 12% and 57 ± 13% for green, brown and red seaweeds, respectively. Inhibitor formation and polysaccharide selectivity were found to be the major bottlenecks influencing the efficiency of dilute acid and enzymatic hydrolysis, respectively. Current enzyme preparations used, were developed for starch-based and lignocellulosic biomass but not seaweeds, which differs in polysaccharide composition and structure. Also, the identification of fermenting organisms capable of converting the heterogeneous monomeric sugars in seaweeds is the major factor limiting ethanol yield during the fermentation stage and not the SHF or SSF pathway selection. This has resulted in variations in bioethanol yields, ranging from 0.04 g/g DM to 0.43 g/g DM.

Evaluation of ultrasound assisted potassium permanganate pre-treatment of spent coffee waste

In the present study, novel pre-treatment for spent coffee waste (SCW) has been proposed which utilises the superior oxidising capacity of alkaline KMnO₄ assisted by ultra-sonication. The pre-treatment was conducted for different exposure times (10, 20, 30 and 40min) using different concentrations of KMnO₄ (1, 2, 3, 4, 5%w/v) at room temperature with solid/liquid ratio of 1:10. Pretreating SCW with 4% KMnO₄ and exposing it to ultrasound for 20min resulted in 98% cellulose recovery and a maximum lignin removal of 46%. 1.7 fold increase in reducing sugar yield was obtained after enzymatic hydrolysis of KMnO₄ pretreated SCW as compared to raw. SEM, XRD and FTIR analysis of the pretreated SCW revealed the various effects of pretreatment. Thermal behaviour of the pretreated substrate against the native biomass was also studied using DSC. Ultrasound-assisted potassium permanganate oxidation was found to be an effective pretreatment for SCW, and can be a used as a potential feedstock pretreatment strategy for bioethanol production.

Hydroxyl radical-aided thermal pretreatment of algal biomass for enhanced biodegradability

BACKGROUND

Algal biomass, known as a potential feedstock for biofuel production, has cell wall structures that differ from terrestrial biomass. The existing methods for processing algae are limited to conventional pretreatments for terrestrial biomass.

RESULTS

In this study, we investigated a novel hydroxyl radical-aided approach for pretreating different types of algal biomass. In this process, hydroxyl radicals formed by a Fenton system were employed in combination with heating to alter the crystalline structure and hydrogen bonds of cellulose in the algal biomass. FeSO4 and H2O2 at low concentrations were employed to initiate the formation of hydroxyl radicals. This method releases trapped polysaccharides in algal cell walls and converts them into fermentable sugars. The effects of temperature, time, and hydroxyl radical concentration were analyzed. The optimal pretreatment condition [100 °C, 30 min, and 5.3 mM H2O2 (determined FeSO4 concentration of 11.9 mM)] was identified using a central composite design. Complete (100 %) carbohydrate recovery was achieved with some algal biomass without formation of inhibitors such as hydroxymethylfurfural and furfural as by-products. Both microalgal and macroalgal biomasses showed higher enzymatic digestibility of cellulose conversion (>80 %) after the milder pretreatment condition.

CONCLUSION

Hydroxyl radical-aided thermal pretreatment was used as a novel method to convert the carbohydrates in the algal cell wall into simple sugars. Overall, this method increased the amount of glucose released from the algal biomass. Overall, enhanced algal biomass digestibility was demonstrated with the proposed pretreatment process. The new pretreatment requires low concentration of chemical solvents and milder temperature conditions, which can prevent the toxic and corrosive effects that typically result from conventional pretreatments. Our data showed that the advantages of the new pretreatment include higher carbohydrate recovery, no inhibitor production, and lower energy consumption. The new pretreatment development mimicking natural system could be useful for biochemical conversion of algal biomass to fuels and chemicals.