Preparation of fermentation media from agricultural wastes and their bioconversion into xylitol

Valorization of barley (Hordeum vulgare L.) brans from the sustainable perspective: A comprehensive review of bioactive compounds and health benefits with emphasis on their potential applications

Barley is an important source of sustainable diets for humans, while its brans is commonly disposed as wastes. The recycling of barley brans has become a key for facilitating the valorization of barley as a whole to achieve its sustainable development. This review summarized the value of barley brans as an excellent source of multiple functional components (phenolic compounds, β-glucan, and arabinoxylan), which conferred extensive health benefits to barley brans mainly including antioxidant, anti-obesity and lipid-lowering, anti-diabetic, and hepatoprotective properties. The utilization of barley brans reflected a great potential for sustainable development. Exploiting of food products and edible films containing barley brans or their bioactive compounds and non-food applications (preparation of bioactive substances, laccase enzymes, and biosorbents) have been attempted for supporting the zero-waste concept and circular economy. Considering their diverse applications, effective extraction techniques of bioactive compounds from barley brans and their safety are the priority of future research.

Biotransformation of grease waste into fatty acid by Penicillium chrysogenum SNP5 through media engineering and artificial neural network

Degradation of grease waste remains a challenging task. Current work deals with the biotransformation of grease waste into fatty acids under submerged fermentation using Penicillium chrysogenum SNP5 through media formulation and artificial neural network (ANN). Fermentation media was formulated to ameliorate the uptake of hydrocarbon by enhancing alkane hydroxylase (AlkB) activity, extracellular release of fatty acids and inhibiting beta-oxidation of fatty acid by regulating transketolase. Further, the process parameters of fermentation were optimized through Artificial Neural Network (ANN) using three critical variables viz; inoculum size (spores/ml), pH, and incubation time (days) while media engineering was done with the optimal supplementation of various medium components such as glucose, YPD, MnSO₄, tetrahydrobiopterin (THB) and phloretin. The maximum conversion of 66.5% of grease waste into fatty acid was achieved at optimum conditions: inoculums size 3.36 × 10⁷ spores/ml, incubation time 11.5 days, pH 7.2 along with formulated media composed of 1% grease in czapek-dox medium supplemented with 55.5 mM glucose, 0.5% YPD, 16.6 mM hexadecane, 1 mM MnSO₄, 1 mM THB, and 1 mM phloretin. The presence of long-chain fatty acids in purified extracts such as oleic acid and octadecanoic acid as end products has valued the evolved process as another source of alternative fuel.

Valorization of cereal by-product hemicelluloses: Fractionation and purity considerations

The biomass from cereal side streams is rich in valuable components, such as hemicelluloses. Among the hemicelluloses, arabinoxylans and β-glucans are the most acknowledged for potential health benefits. Numerous publications discuss the potential to use purified forms of these hemicelluloses for various applications. However, as the purification of hemicelluloses may not be economically feasible to upscale, sustainable and cost-effective methods are needed to make their valorization more realistic for industrial applications. Co-components present in hemicellulose-rich fractions may also provide added functionality, such as flavonoid content and antioxidant capacity. This review provides an overview on the feasibility of sustainably upscaling hemicellulose extraction processes, focusing on by-products from different cereal streams. We describe the hemicelluloses' physicochemical properties and provide various possible applications of pure and impure fractions from small scale to pilot and industrial scale. Furthermore, real case examples on the industrial utilization of cereal side streams are enclosed. This review provides pathways for future research for developing the hemicellulose extraction methods to obtain fractions with optimized purity, and offers suggestions to valorize them.

Fungal Biovalorization of a Brewing Industry Byproduct, Brewer's Spent Grain: A Review

The beer industry is a major producer of solid waste globally, primarily in the form of brewer's spent grain (BSG), which due to its low value has historically been diverted to livestock as feed or to landfills. However, its high moisture content and chemical composition positions BSG as an ideal candidate for further processing with microbial fermentation. Recent research has focused on filamentous fungi and the ability of some species therein to degrade the predominant recalcitrant cellulolignin components of BSG to produce valuable compounds. Many species have been investigated to biovalorize this waste stream, including those in the genuses Aspergillus, Penicillium, Rhyzopus, and Trichoderma, which have been used to produce a wide array of highly valuable enzymes and other functional compounds, and to increase the nutritional value of BSG as an animal feed. This review of recent developments in the application of filamentous fungi for the valorization of BSG discusses the biochemical makeup of BSG, the biological mechanisms underlying fungi's primacy to this application, and the current applications of fungi in this realm.

Improved upstream processing for detoxification and recovery of xylitol produced from corncob

This work deals with the development of an improved process for xylitol production from corn cob hydrolysate by biotechnological routes emphasizing the detoxification of corncob acid hydrolysate. The acid hydrolysate obtained by acid hydrolysis of corn cob was concentrated and detoxified by activated charcoal, membrane process and ion exchange resin process. The resultant partially purified corncob hydrolysate was used in fermentation. The fermentation of acid hydrolysate containing 56.5 g/L xylose was carried out in a 14 L fermenter at pH 4.5 for 48 h with 150 rpm stirring rate at 30 °C. A xylitol yield of 62% was achieved from the partially purified acid hydrolysate medium during fermentation using Candida tropicalis MTCC 6192. The purity of xylitol was increased to 92-94% upon downstream processing of carbonation, subsequently ion exchange process and activated charcoal.

Production of vinyl derivatives from alkaline hydrolysates of corn cobs by recombinant Escherichia coli containing the phenolic acid decarboxylase from Lactobacillus plantarum CECT 748T

The enzyme PAD from Lactobacillus plantarum CECT 748T decarboxylates some cinnamic acids namely p-coumaric acid (p-CA), caffeic acid (CA), and ferulic acid (FA) into their corresponding 4-vinyl derivatives (4-VD): 4-vinyl phenol (4-VP), 4-vinyl catechol (4-VC), and 4-vinyl guaiacol (4-VG), respectively, which are valuable food additives mainly employed as flavouring agents. The gene encoding this enzyme was cloned and overexpressed in Escherichia coli. Recombinant E. coli cells overproducing L. plantarum PAD showed a preference to degrade mainly p-CA and CA. Sterilized liquors obtained after alkaline hydrolysis of corn cob or alkaline hydrolysis of the solid residue coming from acid hydrolysis of corn cob were employed as growth media in fermentations performed in shaker or bioreactor. The fermentative process allowed converting 2222.8 mg/L p-CA into 993.9 mg/L 4-VP. The process described here allowed the production with a high-yield of a valuable food additive from a by-product of the food industry.

One step conversion of wheat straw to sugars by simultaneous ball milling, mild acid, and fungus Penicillium simplicissimum treatment

Wheat straw is one of the major lignocellulosic plant residues in many countries including China. An attractive alternative is the utilization of wheat straw for bioethanol production. This article mainly studies a simple one-step wet milling with Penicillium simplicissimum and weak acid to hydrolysis of wheat straw. The optimal condition for hydrolysis was ball milling 48 h in citrate solvent (pH = 4) with P. simplicissimum H5 at the speed of 500 rpm and the yield of sugar increased with increased milling time. Corresponding structure transformations before and after milling analyzed by X-ray diffraction, transmission Fourier transform infrared spectroscopy, and environmental scanning electron microscopy clearly indicated that this combined treatment could be attributed to the crystalline and chemical structure changes of cellulose in wheat straw during ball milling. This combined treatment of ball milling, mild acid, and fungus hydrolysis enabled the conversion of the wheat straw. Compared with traditional method of ball milling, this work showed a more simple, novel, and environmentally friendly way in mechanochemical treatment of wheat straw.

Maintenance and growth requirements in the metabolism of Debaryomyces hansenii performing xylose-to-xylitol bioconversion in corncob hemicellulose hydrolyzate

In order to improve the biotechnological production of xylitol, the metabolism of Debaryomyces hansenii NRRL Y-7426 in corncob hemicellulose hydrolyzate has been investigated under different conditions, where either maintenance or growth requirements predominated. For this purpose, the experimental results of two sets of batch bioconversions carried out alternatively varying the starting xylose concentration in the hydrolyzate (65.6 < or = S(0) < or = 154.7 g L(-1)) or the initial biomass level (3.0 < or = X(0) < or = 54.6 g(DM) L(-1)) were used to fit a metabolic model consisting of carbon material and ATP balances based on five main activities, namely fermentative assimilation of pentoses, semi-aerobic pentose-to-pentitol bioconversion, biomass growth on pentoses, catabolic oxidation of pentoses, and acetic acid and NADH regeneration by the electron transport system. Such an approach allowed separately evaluating the main bioenergetic constants of this microbial system, that is, the specific rates of ATP and xylose consumption due to maintenance (m(ATP) = 21.0 mmol(ATP) C-mol(DM) (-1)h(-1); m(Xyl) = 6.5 C-mmol(Xyl) C-mol(DM) (-1)h(-1)) and the true yields of biomass on ATP (Y(ATP) (max) = 0.83 C-mol(DM) mol(ATP) (-1)) and on xylose (Y(Xyl) (max) = 0.93 C-mol(DM) C-mol(Xyl) (-1)). The results of this study highlighted that the system, at very high S(0) and X(0) values, dramatically increased its energy requirements for cell maintenance, owing to the occurrence of stressing conditions. In particular, for S(0) > 130 g L(-1), these activities required an ATP consumption of about 2.1 mol(ATP) L(-1), that is, a value about seven- to eightfold that observed at low substrate concentration. Such a condition led to an increase in the fraction of ATP addressed to cell maintenance from 47% to 81%. On the other hand, the very high percentage of ATP addressed to maintenance (> 96%) at very high cell concentration (X(0) > or = 25 g(DM) L(-1)) was likely due to the insufficient substrate to sustain the growth.

The white-rot fungus Phanerochaete chrysosporium: conditions for the production of lignin-degrading enzymes

Investigating optimal conditions for lignin-degrading peroxidases production by Phanerochaete chrysosporium (P. chrysosporium) has been a topic for numerous researches. The capability of P. chrysosporium for producing lignin peroxidases (LiPs) and manganese peroxidases (MnPs) makes it a model organism of lignin-degrading enzymes production. Focusing on compiling and identifying the factors that affect LiP and MnP production by P. chrysosporium, this critical review summarized the main findings of about 200 related research articles. The major difficulty in using this organism for enzyme production is the instability of its productivity. This is largely due to the poor understanding of the regulatory mechanisms of P. chrysosporium responding to different nutrient sources in the culture medium, such as metal elements, detergents, lignin materials, etc. In addition to presenting the major conclusions and gaps of the current knowledge on lignin-degrading peroxidases production by P. chrysosporium, this review has also suggested further work, such as correlating the overexpression of the intra and extracellular proteins to the nutrients and other culture conditions to discover the regulatory cascade in the lignin-degrading peroxidases production process, which may contribute to the creation of improved P. chrysosporium strains leading to stable enzyme production.

Xylitol production from high xylose concentration: evaluation of the fermentation in bioreactor under different stirring rates

AIMS

To investigate the production of xylitol by the yeast Candida guilliermondii FTI 20037, in a bioreactor, from rice straw hemicellulosic hydrolysate with a high xylose concentration.

METHODS AND RESULTS

Batch fermentation was carried out with rice straw hemicellulosic hydrolysate containing about 85 g xylose l(-1), in a stirred-tank bioreactor at 30 degrees C, under aeration of 1.3 vvm (volume of air per volume of medium per min) and different stirring rates (200, 300 and 500 rev min(-1)). The bioconversion of xylose into xylitol by the yeast depended on the stirring rate, the maximum xylitol yield (YP/S = 0.84 g g(-1)) being achieved at 300 rev min-1, with no need to pretreat the hydrolysate for purification.

CONCLUSIONS

To determine the most adequate oxygen transfer rate is fundamental to improving the xylose-to-xylitol bioconversion by C. guilliermondii.

SIGNIFICANCE AND IMPACT OF THE STUDY

For the microbial production of xylitol to be economically viable, the initial concentration of xylose in the lignocellulosic hydrolysate should be as high as possible, as with high substrate concentrations it is possible to increase the final product concentration. Nevertheless, there are few reports on the use of high xylose concentrations. Considering a process in bioreactor, from rice straw hemicellulosic hydrolysate, this is an innovator work.

Improving laccase production by employing different lignocellulosic wastes in submerged cultures of Trametes versicolor

Laccase production by the white-rot fungus Trametes versicolor (CBS100.29) grown in submerged cultures was studied. Addition of different insoluble lignocellulosic materials into the culture medium in order to enhance laccase production was investigated. The lignocellulosic materials were grape seeds, grape stalks and barley bran, selected because of their availability and low cost, since they are agro-industrial wastes abundant in most countries. Barley bran gave the highest activities, a maximum value of 639U/l, which was 10 times the value attained in the cultures without lignocellulosics addition. The decolourisation of a model dye, Phenol Red, by the ligninolytic fluids obtained in the above-mentioned cultures was investigated. Grape stalk and barley bran cultures showed the highest ability to decolourise the dye, attaining a percentage of decolourisation of around 60% in 72 h.