Application of Endo-β-1,4,d-mannanase and Cellulase for the Release of Mannooligosaccharides from Steam-Pretreated Spent Coffee Ground

Thermophilic β-mannanases from bacteria: production, resources, structural features and bioengineering strategies

β-mannanases are pivotal enzymes that cleave the mannan backbone to release short chain mannooligosaccharides, which have tremendous biotechnological applications including food/feed, prebiotics and biofuel production. Due to the high temperature conditions in many industrial applications, thermophilic mannanases seem to have great potential to overcome the thermal impediments. Thus, structural analysis of thermostable β-mannanases is extremely important, as it could open up new avenues for genetic engineering, and protein engineering of these enzymes with enhanced properties and catalytic efficiencies. Under this scope, the present review provides a state-of-the-art discussion on the thermophilic β-mannanases from bacterial origin, their production, engineering and structural characterization. It covers broad insights into various molecular biology techniques such as gene mutagenesis, heterologous gene expression, and protein engineering, that are employed to improve the catalytic efficiency and thermostability of bacterial mannanases for potential industrial applications. Further, the bottlenecks associated with mannanase production and process optimization are also discussed. Finally, future research related to bioengineering of mannanases with novel protein expression systems for commercial applications are also elaborated.

Evaluation of Valorisation Strategies to Improve Spent Coffee Grounds' Nutritional Value as an Ingredient for Ruminants' Diets

Lignin in animal diets is a limiting factor due to its low digestibility. This study assessed the effects of thermal or mechanical pre-treatments and enzymatic hydrolysis on spent coffee grounds' (SCG) nutritional value and digestibility. A first trial studied the effect of thermal pre-treatment and hydrolysis with removal of the liquid part and a second trial studied mechanical pre-treatment and hydrolysis with and without removal of the liquid part. Autoclaving did not improve the enzymatic performance nor the nutritional value. Hydrolysis reduced the digestibility of the solid phase and impaired its ruminal fermentation efficiency. Hydrolysates without removing the liquid part improved its nutritional value, but not compared with unprocessed SCG. Grinding increased crude protein and reduced crude fibre and protein, which led to greater fermentation and in vitro digestibility. Thus, grinding emerges as the most promising valorisation strategy to improve SCG nutritional characteristics and their use for animal feed, contributing to the circular economy.

Coffee by-products: An underexplored source of prebiotic ingredients

Consumers' demand for foods with high nutritional value and health benefits has fueled the development of prebiotic foods. In coffee industry, cherries transformation into roasted beans generates a large amount of waste/by-products (pulp/husks, mucilage, parchment, defective beans, silverskin and spent coffee grounds) that usually end up in landfills. The possibility to use coffee by-products as relevant sources of prebiotic ingredients is herein ascertained. As a prelude to this discussion, an overview of pertinent literature on prebiotic action was conducted, including on biotransformation of prebiotics, gut microbiota, and metabolites. Existing research indicates that coffee by-products contain significant levels of dietary fiber and other components that can improve gut health by stimulating beneficial bacteria in the colon, making them excellent candidates for prebiotic ingredients. Oligosaccharides from coffee by-products have lower digestibility than inulin and can be fermented by gut microbiota into functional metabolites, such as short-chain fatty acids. Depending on the concentration, melanoidins and chlorogenic acids may also have prebiotic action. Nevertheless, there is still a lack of in vivo studies to validate such findings in vitro. This review shows how coffee by-products can be interesting for the development of functional foods, contributing to sustainability, circular economy, food security, and health.

Bioconversion of spent coffee grounds to prebiotic mannooligosaccharides - an example of biocatalysis in biorefinery

Spent coffee ground (SCG), an agro-industrial waste, have a high content of polysaccharides such as mannan, making it ideal for utilisation for the production of nutraceutical oligosaccharides. Recently, there has been growing interest in the production of mannooligosaccharides (MOS) for health promotion in humans and animals. MOS are reported to exhibit various bioactive properties, including prebiotic and antioxidant activity. In this study, SCG was Vivinal pretreated using NaOH, characterized and hydrolysed using a Bacillus sp. derived endo-β-1,4-mannanase, Man26A, for MOS production. Structural analyses using Fourier-transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA) were conducted to assess the efficacy of the pretreatment. Lignin removal by the pretreatment from SCG was clearly shown by TGA. FT-IR, on the other hand, showed the presence of α-linked d-galactopyranoside (812 cm^-1) and β-linked d-mannopyranoside residues (817 cm^-1) in both SCG samples, signifying the presence of mannan. Hydrolysis of pretreated SCG by Man26A produced mannobiose and mannotriose as the main MOS products. The effect of simulated gastric conditions on the MOS was investigated and showed this product to be suitable for oral administration. Finally, the prebiotic effect of the MOS on the growth of selected beneficial bacteria was investigated in vitro; showing that it enhanced Lactobacillus bulgaricus, Bacillus subtilis and Streptococcus thermophilus growth. These findings suggest that SCG is a viable source for the production of MOS which can be orally administered as prebiotics for effecting luxuriant growth of probiotic bacteria in the host's digestive tract, leading to a good health status.

Production and characterization of thermostable acidophilic β-mannanase from Aureobasidium pullulans NRRL 58524 and its potential in mannooligosaccharide production from spent coffee ground galactomannan

The maximum yield of the crude mannanase from Aureobasidium pullulans NRRL 58524 was 8.42 ± 0.18 U mL-1 when cultured for 72 h in the optimized medium containing 3% (w v-1) defatted spent coffee grounds (SCG) and 0.67% (w v-1) ammonium sulphate. Two forms of mannanase were observed in the crude enzyme and the principal mannanase was enriched to apparent homogeneity via sequential filtration and anion exchange chromatography. The molecular mass of the enzyme was approximately 63 kDa as determined by SDS-PAGE. The enriched mannanase was active at high temperatures (45-75 °C) and a pH range from 3 to 6 with the maximum activity at 55 °C and pH 4.0. The enzyme was relatively thermostable with more than 75% of its initial activity remained after a 12 h incubation at 55 °C. The half-lives of the enriched mannanase were over 8 and 6 h at 60 and 65 °C, respectively. The enzyme was not adversely affected by chelator and most ions tested. This enzyme could hydrolyze both glucomannan and galactomannan and exhibited limited catalytic activity on beta-glucan. When the crude mannanase was used to hydrolyze galactomannan extracted from SCG, the maximum yield of reducing sugars mainly comprising of mannobiose (16.27 ± 0.84 mg 100 mg-1), and mannotriose (2.85 ± 0.20 mg 100 mg-1) was obtained at 58.22 ± 2.04 mg 100 mg-1 dry weight, under optimized condition (84.87 U g-1 mannanase, 41 h 34 min incubation at 55 °C and pH 4.0). These results suggested the prospect of the enzyme in mannan hydrolysis and mannooligosaccharide production at a larger scale.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03301-4.

Copra meal hydrolysis by the recombinant β-mannanase KMAN-3 and MAN 6.7 expressed in Escherichia coli

Hydrolysis products of defatted copra meal (DCM) hydrolysis were investigated with either recombinant β-mannanases from Klebsiella oxytoca KUB-CW2-3 (KMAN-3) or Bacillus circulans NT 6.7 (MAN 6.7). Morphological changes and functional groups of solid residues were also determined by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. Results revealed that the Michaelis-Menten constant (K m) and maximum velocity (V max) values of KMAN-3 on DCM were 2.4 mg/ml and 5.4 U/mg, respectively, while MAN 6.7 recorded K m and V max at 2.0 mg/ml and 4.3 U/mg, respectively. Both enzymes efficiently randomly hydrolysed DCM and produced a range of different manno-oligosaccharides (MOS). The profile of hydrolysis products was different for each enzyme used. Main products from hydrolysis of DCM by KMAN-3 and MAN 6.7 were various MOS including mannobiose (M2), mannotriose (M3), mannotetraose (M4), and mannose, whereas mannopentaose (M5) was only found from KMAN-3. Amount of M3 produced by KMAN-3 was about three times higher than from MAN 6.7. Total MOS yield for KMAN-3 was 1.5-folds higher than for MAN 6.7. SEM analysis showed that enzymatic hydrolysis with KMAN-3 and MAN 6.7 resulted in deconstruction of the DCM structure which generated a variety of MOS products. FTIR spectra revealed that the properties of both hydrolysed solids were not significantly different compared to the original DCM. Results suggested that KMAN-3 was a promising candidate for production of high MOS content from copra meal.

High-level expression of an engineered β-mannanase (mRmMan5A) in Pichia pastoris for manno-oligosaccharide production using steam explosion pretreated palm kernel cake

An engineered β-mannanase (mRmMan5A) from Rhizomucor miehei was successfully expressed in Pichia pastoris. Through high cell density fermentation, the expression level of mRmMan5A reached 79,680 U mL^-1. The mRmMan5A showed maximum activity at pH 4.5 and 65 °C, and exhibited high specific activities towards mannans. To produce manno-oligosaccharides, palm kernel cake (PKC) was pretreated by steam explosion at 200 °C for 7.5 min, and then hydrolyzed by mRmMan5A. As a result, the total manno-oligosaccharide yield reached 34.8 g/100 g dry PKC, indicating that 80.6% of total mannan in PKC was hydrolyzed. Moreover, the kilo-scale production of manno-oligosaccharides was carried out to verify the feasibility of mass production. A total of 261.3 g manno-oligosaccharides were produced from 1.0 kg of dry PKC. An effective β-mannanase for the bioconversion of mannan-rich biomasses and an efficient method for the production of manno-oligosaccharides from PKC are provided in this paper.

Structural Characterization and in Vitro Fermentation of β-Mannooligosaccharides Produced from Locust Bean Gum by GH-26 endo-β-1,4-Mannanase (ManB-1601)

Size exclusion chromatography of β-mannooligosaccharides (β-MOS) mixtures, obtained from ManB-1601 hydrolysis of locust bean gum, resulted in separation of oligosaccharides with various degrees of polymerization (DP 2, 3, and 5). The oligosaccharides were structurally [ESI-MS, FTIR, XRD, TGA, and NMR (¹H and ¹³C)] and functionally (in vitro fermentation) characterized. DP2 oligosaccharide was composed of two species, (A) mannopyranose β-1,4 mannopyranose and (B) α-1,6-galactosyl-mannopyranose, while DP3 oligosaccharide showed the presence of only one species, i.e. α-d-galactosyl-β-d-mannobiose. ManB-1601 was capable of cleaving near the branch points in the substrate, resulting in oligosaccharides with galactose at the terminal position apart from attacking unsubstituted β-1,4-glycosidic linkages. DP2 and DP3 improved the growth of three out of seven species of Lactobacillus while DP5 resulted in poor growth of all Lactobacillus spp. under in vitro conditions. DP2, DP3, and DP5 were found to inhibit the growth of Escherichia coli, Listeria monocytogenes and Salmonella typhi.

Optimization of High Solids Dilute Acid Hydrolysis of Spent Coffee Ground at Mild Temperature for Enzymatic Saccharification and Microbial Oil Fermentation

Soluble coffee, being one of the world's most popular consuming drinks, produces a considerable amount of spent coffee ground (SCG) along with its production. The SCG could function as a potential lignocellulosic feedstock for production of bioproducts. The objective of this study is to investigate the possible optimal condition of dilute acid hydrolysis (DAH) at high solids and mild temperature condition to release the reducing sugars from SCG. The optimal condition was found to be 5.3 % (w/w) sulfuric acid concentration and 118 min reaction time. Under the optimal condition, the mean yield of reducing sugars from enzymatic saccharification of defatted SCG acid hydrolysate was 563 mg/g. The SCG hydrolysate was then successfully applied to culture Lipomyces starkeyi for microbial oil fermentation without showing any inhibition. The results suggested that dilute acid hydrolysis followed by enzymatic saccharification has the great potential to convert SCG carbohydrates to reducing sugars. This study is useful for the further developing of biorefinery using SCG as feedstock at a large scale.

Novel β-1,4-Mannanase Belonging to a New Glycoside Hydrolase Family in Aspergillus nidulans

Many filamentous fungi produce β-mannan-degrading β-1,4-mannanases that belong to the glycoside hydrolase 5 (GH5) and GH26 families. Here we identified a novel β-1,4-mannanase (Man134A) that belongs to a new glycoside hydrolase (GH) family (GH134) in Aspergillus nidulans. Blast analysis of the amino acid sequence using the NCBI protein database revealed that this enzyme had no similarity to any sequences and no putative conserved domains. Protein homologs of the enzyme were distributed to limited fungal and bacterial species. Man134A released mannobiose (M₂), mannotriose (M₃), and mannotetraose (M₄) but not mannopentaose (M₅) or higher manno-oligosaccharides when galactose-free β-mannan was the substrate from the initial stage of the reaction, suggesting that Man134A preferentially reacts with β-mannan via a unique catalytic mode. Man134A had high catalytic efficiency (k_cat/K_m) toward mannohexaose (M₆) compared with the endo-β-1,4-mannanase Man5C and notably converted M₆ to M₂, M₃, and M₄, with M₃ being the predominant reaction product. The action of Man5C toward β-mannans was synergistic. The growth phenotype of a Man134A disruptant was poor when β-mannans were the sole carbon source, indicating that Man134A is involved in β-mannan degradation in vivo. These findings indicate a hitherto undiscovered mechanism of β-mannan degradation that is enhanced by the novel β-1,4-mannanase, Man134A, when combined with other mannanolytic enzymes including various endo-β-1,4-mannanases.