Production of α-galactosidase by thermophilic fungus Humicola sp. in solid-state fermentation and its application in soyamilk hydrolysis

Properties and applications of α-galactosidase in agricultural waste processing and secondary agricultural process industries

Agriculture products form the foundation building blocks of our daily lives. Although they have been claimed to be renewable resources with a low carbon footprint, the agricultural community is constantly challenged to overcome two post-harvest bottlenecks: first, farm bio-waste, a substantial economic and environmental burden to the farming sector, and second, an inefficient agricultural processing sector, plagued by the need for significant energy input to generate the products. Both these sectors require extensive processing technologies that are demanding in their energy requirements and expensive. To address these issues, an enzyme(s)-based green chemistry is available to break down complex structures into bio-degradable compounds that source alternate energy with valuable by-products and co-products. α-Galactosidase is a widespread class of glycoside hydroxylases that hydrolyzes α-galactosyl moieties in simple and complex oligo and polysaccharides, glycolipids, and glycoproteins. As a result of its growing importance, in this review we discuss the source of the enzyme, production and purification systems, and enzyme properties. We also elaborate on the enzyme's potential in agricultural bio-waste management, secondary agricultural industries like sugar refining, soymilk derivatives, food and confectionery, and animal feed processing. Insight into this vital enzyme will provide new avenues for less expensive green chemistry-based secondary agricultural processing and agricultural sustainability. © 2023 Society of Chemical Industry.

Microbial production and biotechnological applications of α-galactosidase

α-Galactosidase, (E.C. 3.2.1.22) is an exoglycosidase that target galactooligosaccharides such as raffinose, melibiose, stachyose and branched polysaccharides like galactomannans and galacto-glucomannans by catalysing the hydrolysis of α-1,6 linked terminal galactose residues. The enzyme has been isolated and characterized from microbial, plant and animal sources. This ubiquitous enzyme possesses physiological significance and immense industrial potential. Optimization of the growth conditions and efficient purification strategies can lead to a significant increase in the enzyme production. To boost commercial productivity, cloning of novel α-galactosidase genes and their heterologous expression in suitable host has gained popularity. Enzyme immobilization leads to its greater reutilization, superior thermostability, pH tolerance and increased activity. The enzyme is well explored in food industry in the removal of raffinose family oligosaccharides (RFOs) in soymilk and sugar crystallization process. It also improves animal feed quality and biomass processing. Applications of the enzyme is in the area of biomedicine includes therapeutic advances in treatment of Fabry disease, blood group conversion and removal of α-gal type immunogenic epitopes in xenotransplantation. With considerable biotechnological applications, this enzyme has been vastly commercialized and holds greater future prospects.

Enzyme-based processing of soybean carbohydrate: Recent developments and future prospects

Soybean is well known for its high-value oil and protein. Carbohydrate is, however, an underutilized major component, representing almost 26-30% (w/w) of the dried bean. The complex soybean carbohydrate is not easily hydrolyzable and can cause indigestibility when included in food and feed. Enzymes can be used to hydrolyze the carbohydrate for improving soybean processing and value of soybean products. Here the enzyme-based processing developed for the following purposes is reviewed: hydrolysis of different carbohydrate-rich by/products from soybean processing, improvement of soybean oil extraction, and increase of nutritional value of soybean-based food and animal feed. Once hydrolyzed into fermentable sugars, soybean carbohydrate can find more value-added applications and further improve the overall economics of soybean processing.

A novel promising strain of Trichoderma evansii (WF-3) for extracellular α-galactosidase production by utilizing different carbon sources under optimized culture conditions

A potential fungal strain of Trichoderma sp. (WF-3) was isolated and selected for the production of α-galactosidase. Optimum conditions for mycelial growth and enzyme induction were determined. Basal media selected for the growth of fungal isolate containing different carbon sources like guar gum (GG), soya bean meal (SM), and wheat straw (WS) and combinations of these carbon substrates with basic sugars like galactose and sucrose were used to monitor their effects on α-galactosidase production. The results of this study indicated that galactose and sucrose enhanced the enzyme activity in guar gum (GG) and wheat straw (WS). Maximum α-galactosidase production (213.63 UmL⁻¹) was obtained when the basic medium containing GG is supplemented with galactose (5 mg/mL). However, the presence of galactose and sucrose alone in the growth media shows no effect. Soya meal alone was able to support T. evansii to produce maximum enzyme activity (170.36 UmL⁻¹). The incubation time, temperature, and pH for the maximum enzyme synthesis were found to be 120 h (5 days), 28°C, and 4.5–5.5, respectively. All the carbon sources tested exhibited maximum enzyme production at 10 mg/mL concentration. Among the metal ions tested, Hg was found to be the strongest inhibitor of the enzyme. Among the chelators, EDTA acted as stronger inhibitor than succinic acid.

Optimization of Culture Conditions for Some Identified Fungal Species and Stability Profile of α-Galactosidase Produced

Microbial α-galactosidase preparations have implications in medicine and in the modification of various agricultural products as well. In this paper, four isolated fungal strains such as AL-3, WF-3, WP-4 and CL-4 from rhizospheric soil identified as Penicillium glabrum (AL-3), Trichoderma evansii (WF-3), Lasiodiplodia theobromae (WP-4) and Penicillium flavus (CL-4) based on their morphology and microscopic examinations, are screened for their potential towards α-galactosidases production. The culture conditions have been optimized and supplemented with specific carbon substrates (1%, w/v) by using galactose-containing polysaccharides like guar gum (GG), soya casein (SC) and wheat straw (WS). All strains significantly released galactose from GG, showing maximum production of enzyme at 7th day of incubation in rotary shaker (120 rpm) that is 190.3, 174.5, 93.9 and 28.8 U/mL, respectively, followed by SC and WS. The enzyme activity was stable up to 7days at −20°C, then after it declines. This investigation reveals that AL-3 show optimum enzyme activity in guar gum media, whereas WF-3 exhibited greater enzyme stability. Results indicated that the secretion of proteins, enzyme and the stability of enzyme activity varied not only from one strain to another but also differed in their preferences of utilization of different substrates.

Purification and characterization of α-galactosidase from white chickpea (Cicer arietinum)

Glycosylated α-galactosidase (melibiase) has been purified from white chickpea ( Cicer arietinum ) to 340-fold with a specific activity of 61 units/mg. Cicer α-galactosidase showed a M(r) of 45 kDa on SDS-PAGE and by MALDI-TOF. The optimum pH and temperature with pNPGal were 4.5 and 50 °C, respectively. The K(m) for hydrolysis of pNPGal was 0.70 mM. Besides hydrolyzing the pNPGal, Cicer α-galactosidase also hydrolyzed natural substrates such as melibiose, raffinose, and stachyose very effectively; hence, it can be exploited commercially for improving the nutritional value of soy milk. Galactose was found to be a competitive inhibitor. The property of this enzyme to cleave the terminal galactose residues can be utilized for converting the group B erythrocytes to group O erythrocytes.

Purification and characterization of a thermostable α-galactosidase from Thielavia terrestris NRRL 8126 in solid state fermentation

Several seeds and husks of some plants belonging to leguminosae, Graminae, Compositae and Palmae were evaluated as carbon substrates to produce α-galactosidase (α-Gal) by the thermophilic fungus, Thielavia terrestris NRRL 8126 in solid substrate fermentation. The results showed that Cicer arietinum (chick pea seed) was the best substrate for α-Gal production. The crude enzyme was precipitated by ammonium sulphate (60%) and purified by gel filtration on sephadex G-100 followed by ion exchange chromatography on DEAE-Cellulose. The final purification fold of the enzyme was 30.42. The temperature and pH optima of purified α-Gal from Thielavia terrestris were 70 °C and 6.5, respectively. The enzyme showed high thermal stability at 70 °C and 75 °C and the half-life of the α-Gal at 90 °C was 45 min. Km of the purified enzyme was 1.31 mM. The purified enzyme was inhibited by Ag2+, Hg2+, Zn2+, Ba2+, Mg2+, Mn2+ and Fe2+ at 5 mM and 10 mM. Also, EDTA, sodium arsenate, L-cysteine and iodoacetate inhibited the enzyme activity. On the other hand, Ca2+, Cu2+, K+ and Na+ slightly enhanced the enzyme activity at 5 mM while at 10 mM they caused inhibition. The molecular weight of the α-Gal was estimated to be 82 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This enzyme displays a number of biochemical properties that make it a potentially strong candidate for biotechnological and medicinal applications.

Production and Optimization of Cellulase Enzyme Using Aspergillus niger USM AI 1 and Comparison with Trichoderma reesei via Solid State Fermentation System

Novel design solid state bioreactor, FERMSOSTAT, had been evaluated in cellulase production studies using local isolate Aspergillus niger USM AI 1 grown on sugarcane bagasse and palm kernel cake at 1 : 1 (w/w) ratio. Under optimised SSF conditions of 0.5 kg substrate; 70% (w/w) moisture content; 30°C; aeration at 4 L/h · g fermented substrate for 5 min and mixing at 0.5 rpm for 5 min, about 3.4 U/g of Filter paper activity (FPase) was obtained. At the same time, comparative studies of the enzymes production under the same SSF conditions indicated that FPase produced by A. niger USM AI 1 was about 35.3% higher compared to Trichoderma reesei. This shows that the performance of this newly designed SSF bioreactor is acceptable and potentially used as prototype for larger-scale bioreactor design.

Response surface methodology for optimizing the fermentation medium of alpha-galactosidase in solid-state fermentation

AIMS

Alpha-galactosidase is applied in food and feed industries for hydrolysing raffinose series oligosaccharides (RO) that are the factors primarily responsible for flatulence upon ingestion of soybean-derived products. The objective of the current work was to develop an optimal culture medium for the production of alpha-galactosidase in solid-state fermentation (SSF) by a mutant strain Aspergillus foetidus.

METHODS AND RESULTS

Response surface methodology (RSM) was applied to evaluate the effects of variables, namely the concentrations of wheat bran, soybean meal, KH(2)PO(4), MnSO(4).H(2)O and CuSO(4).5H(2)O on alpha-galactosidase production in the solid substrate. A fractional factorial design (FFD) was firstly used to isolate the main factors that affected the production of alpha-galactosidase and the central composite experimental design (CCD) was then adopted to derive a statistical model for optimizing the composition of the fermentation medium. The experimental results showed that the optimum fermentation medium for alpha-galactosidase production by Aspergillus foetidus ZU-G1 was composed of 8.2137 g wheat bran, 1.7843 g soybean meal, 0.001 g MnSO(4).H(2)O and 0.001 g CuSO(4).5H(2)O in 10 g dry matter fermentation medium.

CONCLUSIONS

After incubating 96 h in the optimum fermentation medium, alpha-galactosidase activity was predicted to be 2210.76 U g(-1) dry matter in 250 ml shake flask. In the present study, alpha-galactosidase activity reached 2207.19 U g(-1) dry matter.

SIGNIFICANCE AND IMPACT OF THE STUDY

Optimization of the solid substrate was a very important measure to increase enzyme activity and realize industrial production of alpha-galactosidase. The process of alpha-galactosidase production in laboratory scale may have the potential to scale-up.

Effect of cultivating conditions on alpha-galactosidase production by a novel Aspergillus foetidus ZU-G1 strain in solid-state fermentation

The work is intended to achieve optimum culture conditions of alpha-galactosidase production by a mutant strain Aspergillus foetidus ZU-G1 in solid-state fermentation (SSF). Certain fermentation parameters involving moisture content, incubation temperature, cultivation period of seed, inoculum volume, initial pH value, layers of pledget, load size of medium and period of cultivation were investigated separately. The optimal cultivating conditions of alpha-galactosidase production in SSF were 60% initial moisture of medium, 28 degrees C incubation temperature, 18 h cultivation period of seed, 10% inoculum volume, 5.0 approximately 6.0 initial pH of medium, 6 layers of pledget and 10 g dry matter loadage. Under the optimized cultivation conditions, the maximum alpha-galactosidase production was 2 037.51 U/g dry matter near the 144th hour of fermentation.

Induction and characterization of an unusual alpha-D-galactosidase from Talaromyces flavus

An extracellular alpha-d-galactosidase from Talaromyces flavus CCF 2686 with extremely broad and unusual acceptor specificity is produced exclusively in the presence of the specific inducer--6-deoxy-D-glucose (quinovose). The procedure for the preparation of this very expensive substance has been modified and optimized. Surprisingly, any of other common alpha-D-galactosidase inducers or substrates, e.g., D-galactose, melibiose and raffinose, did not stimulate its production. The crude alpha-D-galactosidase preparation was purified by anion-exchange chromatography and three isoenzymes with different substrate specificities were identified. The main isoenzyme (alphaGal1) was further purified by cation-exchange chromatography and fully characterized. When compared with other alpha-galactosidases and also with other isoenzymes produced by T. flavus, it showed a markedly different regioselectivity and also negligible hydrolytic activity towards melibiose. Moreover, it was active on polymeric substrates (locust bean gum, guar gum) and significantly inhibited by alpha-D-galactopyranosyl azide, D-galactose, D-xylose, melibiose, methyl alpha- and beta-D-galactopyranoside and lactose.

Extracellular alpha-galactosidase from Debaryomyces hansenii UFV-1 and its use in the hydrolysis of raffinose oligosaccharides

Raffinose oligosaccharides (RO) are the factors primarily responsible for flatulence upon ingestion of soybean-derived products. ROs are hydrolyzed by alpha-galactosidases that cleave alpha-1,6-linkages of alpha-galactoside residues. The objectives of this study were the purification and characterization of extracellular alpha-galactosidase from Debaryomyces hansenii UFV-1. The enzyme purified by gel filtration and anion exchange chromatographies presented an Mr value of 60 kDa and the N-terminal amino acid sequence YENGLNLVPQMGWN. The Km values for hydrolysis of pNP alphaGal, melibiose, stachyose, and raffinose were 0.30, 2.01, 9.66, and 16 mM, respectively. The alpha-galactosidase presented absolute specificity for galactose in the alpha-position, hydrolyzing pNPGal, stachyose, raffinose, melibiose, and polymers. The enzyme was noncompetitively inhibited by galactose (Ki = 2.7 mM) and melibiose (Ki = 1.2 mM). Enzyme treatments of soy milk for 4 h at 60 degrees C reduced the amounts of stachyose and raffinose by 100%.

Influence of cultivating conditions on the alpha-galactosidase biosynthesis from a novel strain of Penicillium sp. in solid-state fermentation

AIMS

The work is intended to achieve optimum culture conditions of alpha-galactosidase production by a mutant strain Penicillium sp. in solid-state fermentation (SSF).

METHODS AND RESULTS

Certain fermentation parameters involving incubation temperature, moisture content, initial pH value, inoculum and load size of medium, and incubation time were investigated separately. The optimal temperature and moisture level for alpha-galactosidase biosynthesis was found to be 30 degrees C and 50%, respectively. The range of pH 5.5-6.5 was favourable. About 40-50 g of medium in 250-ml flask and inoculum over 1.0 x 10(6) spores were suitable for enzyme production. Seventy-five hours of incubation was enough for maximum alpha-galactosidase production. Substrate as wheat bran supplemented with soyabean meal and beet pulp markedly improved the enzyme yield in trays.

CONCLUSIONS

Under optimum culture conditions, the alpha-galactosidase activity from Penicillium sp. MAFIC-6 indicated 185.2 U g(-1) in tray of SSF.

SIGNIFICANT AND IMPACT OF THE STUDY

The process on alpha-galactosidase production in laboratory scale may have a potentiality of scaling-up.

Biochemical engineering aspects of solid state bioprocessing

Despite centuries of use and renewed interest over the last 20 years in solid-state fermentation (SSF) technology, and despite its good potential for a range of products, there are currently relatively few large-scale commercial applications. This situation can be attributed to the complexity of the system: Macroscale and microscale heat and mass transfer limitations are intrinsic to the system, and it is only over the last decade or so that we have begun to understand them. This review presents the current state of understanding of biochemical engineering aspects of SSF processing, including not only the fermentation itself, but also the auxiliary steps of substrate and inoculum preparation and downstream processing and waste disposal. The fermentation step has received most research attention. Significant advances have been made over the last decade in understanding how the performance of SSF bioreactors can be controlled either by the intraparticle processes of enzyme and oxygen diffusion or by the macroscale heat transfer processes of conduction, convection, and evaporation. Mathematical modeling has played an important role in suggesting how SSF bioreactors should be designed and operated. However, these models have been developed on the basis of laboratory-scale data and there is an urgent need to test these models with data obtained in large-scale bioreactors.

Temperature control in a continuously mixed bioreactor for solid-state fermentation

A continuously mixed, aseptic paddle mixer was used successfully for solid-state fermentation (SSF) with Aspergillus oryzae on whole wheat kernels. Continuous mixing improved temperature control and prevented inhomogeneities in the bed. Respiration rates found in this system were comparable to those in small, isothermal, unmixed beds, which showed that continuous mixing did not cause serious damage to the fungus or the wheat kernels. Continuous mixing improves heat transport to the bioreactor wall, which reduces the need for evaporative cooling and thus may help to prevent the desiccation problems that hamper large-scale SSF. However, scale-up calculations for the paddle mixer indicated that wall cooling becomes insufficient at the 2-m(3) scale for a rapidly growing fungus like Aspergillus oryzae. Consequently, evaporative cooling will remain important in large-scale mixed systems. Experiments showed that water addition will be necessary when evaporative cooling is applied in order to maintain a sufficiently high water activity of the solid substrate. Mixing is necessary to ensure homogeneous water addition in SSF. Automated process control might be achieved using the enthalpy balance. The enthalpy balance for the case of evaporative cooling in the paddle mixer was validated. This work shows that continuous mixing provides promising possibilities for simultaneous control of temperature and moisture content in solid-state fermentation on a large scale.

A simplified material and energy balance approach for process development and scale-up of Coniothyrium minitans conidia production by solid-state cultivation in a packed-bed reactor

Production of conidia of the biocontrol fungus Coniothyrium minitans by solid-state cultivation in a packed-bed reactor on an industrial scale is feasible. Spore yield and oxygen consumption rate of C. minitans during cultivation on oats and three inert solids (hemp, perlite, and bagasse) saturated with a liquid medium were determined in laboratory-scale experiments. The sensitivity of the fungus to reduced aw, and the water desorption isotherms of the four solid materials were also determined. C. minitans is very sensitive to reduced aw: 50% inhibition of respiration was found at aw 0.95, spore formation was completely inhibited at aw 0.97. A simplified mathematical model taking into account convective and evaporative cooling was used to simulate temperature and moisture gradients in the bed during cultivation. Adequate temperature control can be achieved with acceptable air flow rates for all four solid matrices. Moisture control is the limiting factor for cultivation in a packed bed. Oats cannot be used due to the shrinkage and aw reduction caused by evaporative cooling. Of the three inert supports tested, hemp provides the best spore yield and control of water activity, due to its high water uptake capacity. A spore yield of 9 x 10(14) conidia per m(3) packed bed can be achieved in 18 days, using hemp impregnated with a solution containing 100 g dm(-3) glucose and 20 g dm(-3) potato extract. Sufficient water is predicted to be available after 18 days, to allow a higher initial nutrient concentration, which may lead to higher spore yields.