The growing environmental concerns have intensified interest in renewable sources, promoting the use of agro-industrial residues as alternative substrates for the production of materials, chemicals, and bioenergy. Among these residues, cheese whey stands out due to its high content of lactose, proteins, and minerals, and is widely used in microbial fermentations to produce industrially relevant compounds such as enzymes. Likewise, lignocellulosic wastes like sugarcane bagasse have proven effective as carbon sources for cellulase production, while corn steep liquor has been employed as an inexpensive nitrogen source. Studies involving Bacillus licheniformis SMIA-2 have demonstrated its potential to produce enzymes such as proteases, avicelase, and carboxymethyl cellulase (CMCase) using agro-industrial residues, including passion fruit peel flour, cheese whey, and sugarcane bagasse supplemented with corn steep liquor. Replacing conventional inputs with industrial by-products not only reduces enzyme production costs but also contributes to minimizing the environmental impact caused by residue disposal. This review highlights the importance of agro-industrial residue valorization as a sustainable and economically feasible strategy for microbial enzyme production.
Keywords: Bacilllus licheniformis, Agro-industrial residues, Cheese whey, Sugarcane bagasse, sustainable bioprocesses
The sharp growth of Brazilian agribusiness has placed it in a prominent position in the country's development process. Since 1980, the generation, adaptation, transfer, and adoption of technological innovations have enabled significant productivity gains, especially in the grain sector, whose production has doubled.1 The significant advances in agribusiness performance have led to an increase in the consumption of inputs and the generation of waste in agricultural and agro-industrial activities. Since the 1980s, scientific research has pointed to the worsening of global environmental problems, such as the destruction of the ozone layer, the greenhouse effect, and the compromise of biodiversity, in addition to the local impacts resulting from the generation of liquid and solid waste. These problems have required a rethink of the development model, which was shown to be limited by its effects on sustainability.2 Waste generation is associated with waste in the use of inputs, losses between production and consumption, and materials generated throughout the agro-industrial chain that have no evident economic value. It is estimated that, on average, 20% to 30% of the grain, fruit, and vegetable harvest in Brazil is wasted on the way from the farm to the consumer. Data on the type and volume of waste generated in global agribusiness without added value are scarce.3
Waste can represent a loss of biomass and nutrients, in addition to increasing the polluting potential associated with inadequate disposal, which, in addition to polluting soil and water bodies when compounds are leached, causes public health problems. On the other hand, the high cost associated with the treatment, transportation, and final disposal of the waste generated has a direct effect on the price of the final product. Special attention has been given to minimizing or reusing waste and establishing new uses for agricultural products and byproducts to replace non-renewable resources. As a result, green chemistry, clean chemistry, environmentally benign chemistry, or self-sustainable chemistry is already a reality, especially in countries with a highly developed chemical industry and strict control over pollutant emissions. A good example is the growing adoption of the biorefinery concept, whose logic is analogous to oil refineries and integrates processes aimed at the total valorization of the raw material.4 The application of agro-industrial waste in bioprocesses, in addition to providing alternative substrates, also helps to solve the pollution problems that their disposal in the environment could cause. With the advent of biotechnological innovations, mainly in the area of enzyme technology and fermentation, many new avenues have been opened for their use.5 The use of low-cost waste as substrates in the production of enzymes is especially interesting for countries where agro-industrial waste is abundant. The objective of this review work is to present how agro-industrial waste was used to produce substrates for the production of commercial enzymes, in addition to helping to solve the problem of environmental pollution.
A narrative review was carried out on “Agro-industrial residues: importance and applications in the production of microbial enzymes,” focusing on the production of enzymes of great commercial interest produced by Bacillus licheniformis SMIA-2. The review was based on material obtained through research on several research platforms. The selected articles on the subject were analyzed, seeking answers to the objectives that followed this study, following the criteria of relevance and applicability to the study.
Environmental impacts of agro-industrial waste
The Resolution of the National Environmental Council (CONAMA) nº 01/86, of 01/23/86 (article 1º), defines environmental impact as:
(...) any change in the physical, chemical and biological properties of the environment (...) resulting from human activities that, directly or indirectly, affect: the health, safety and well-being of the population; social and economic activities; biota; the sanitary and aesthetic conditions of the environment; and the quality of environmental resources.
These impacts can be reversible or irreversible and have positive or negative effects. According to ROCCA6 inadequate treatment of industrial waste contributes to the worsening of environmental problems, due to the non-use of products released into rivers. It should be noted that, even when operating satisfactorily, effluent retention tanks contain some amount of blood, fat, solids from the intestinal contents of animals, fragments of tissue, among other residues. Therefore, it is necessary to minimize waste through economically advantageous practices, which offer the possibility of environmental control.7
Across the world and especially in Brazil, whose economy is strongly based on agribusiness, large amounts of waste are generated by food processing industries. However, these materials, although mostly considered to be serious environmental problems, can serve, in many cases, as rich sources of bioactive compounds, including antioxidant and antimicrobial substances. "These residues can be considered potential sources of these natural compounds, so that, when used, they result in greater economic gains, simultaneously reducing the impact of their disposal on the environment.6
Whey protein
Historically, whey has always been considered a waste product with low economic value. Its large volume of production represents one of the biggest problems for the dairy industry. Throughout Brazil, most small and medium-sized cheese producers are unable to find a suitable destination for whey, and there is a huge lack of technologies that enable the use of its proteins. Because it contains a high quantity of nutrients, it is considered a highly polluting material, with a biological oxygen demand (BOD) of 30,000 to 50,000 mL-1.8 With the trend towards clean and environmentally friendly processes in food production, there has been a growing concern about finding economic applications for the whey obtained from cheese production.9
The aqueous portion of milk that separates from the curd or casein during conventional cheese production is cheese whey, an opaque, yellow-green fluid that retains about 55% of the milk's nutrients.10,11 Approximately 85-95% of the volume of milk used in cheese production results in whey, which contains about half of the total milk solids, represented by water-soluble proteins, mainly albumins and globulins, salts, fat and lactose,10 found in the following proportions: 6.0-6.5% of total solids, of which about 4.5-5.0% lactose, 0.8-1.1% protein, 0.03-0.1% fat, 0.5-0.8% mineral matter and 0.2-0.8% lactic acid.12,13 In terms of volume and depending on the techniques used in production, between nine and twelve liters of whey can be produced, with an average of ten liters for each kilo of cheese produced.14-16
Among the waste generated in the food industry, whey stands out, which is a residual liquid obtained from the coagulation of milk intended for the manufacture of cheese or casein.17 Whey is a byproduct of the cheese and casein industry, has high functional and nutritional value and, when properly processed, either as a concentrate or protein isolate, is an excellent ingredient for the manufacture of various industrialized foods. A substantial amount of whey is discarded annually in Brazil, in the form of industrial waste, causing a serious environmental problem.18
The discharge of whey, in addition to causing damage to nature, also corresponds to an unacceptable waste given its nutritional characteristics. Whey is an important source of low-cost proteins and lactose that could be better utilized to generate direct and indirect jobs, increase the income of entrepreneurs in the sector and create greater circulation of capital, in addition to reducing costs with effluent treatment and environmental damage.19,20 Furthermore, according to RICHARDS,21 discarding whey without efficient treatment is not only an environmental crime, but also rejecting an ingredient that has high quality. In Brazil, data on the availability of whey is highly imprecise, but much of the cheese is produced by small companies that, in order to avoid the cost of treating this effluent and without effective supervision by the authorities, opt to partially use this byproduct as animal feed, discarding the excess directly into rivers.22,23 The composition of whey provides several applications in the food industry, but it is not yet fully explored. There is a need for greater incentives for the use of whey due to its nutritional value, the enormous volume of production due to the full expansion of cheese factories, and the benefits of reducing the volume of waste to be treated by these industries.24
Brazil is seeking to increase the processing of whey to meet the domestic demand for whey powder in the dairy beverage, bakery, biscuit, pharmaceutical and animal feed industries, and consequently reduce its need to import the product. Thus, the production of whey powder can be considered an economic alternative, generating employment and also a source of income for the producer.25
The reuse of waste is a management alternative for agribusinesses, and in the case of whey, it generates significant results, since the proportion of whey produced in the manufacture of cheese is, on average, ten liters of liquid waste for each kilo of cheese manufactured. Considering the large volume of whey produced by dairies, the cost of treatment that allows its disposal into the environment becomes very high. On the other hand, with the advent of new technologies for drying whey, it is possible to take advantage of its main components, that is, lactose and soluble proteins, and thus transform a cost into income generation through the production of inputs for other industrial sectors.25 The production of microbial enzymes using whey has been carried out by several researchers,11,26,27 and enzymatic productivity has increased with the use of this substrate. Several studies have been developed using whey for the production of hydrolytic enzymes to make the production of these enzymes viable.28,29 Currently, environmental legislation has become increasingly strict. Dairy industries are looking for alternatives to use cheese whey.30 Among the various techniques for using cheese whey, it stands out as a substrate for fermentation, and is also a very interesting raw material in the production of various products such as ethanol,31,32 yeast extract,12 lactic acid,33,34 dairy beverages,9 among others.
Passion fruit peel flour
Brazil is the world's leading producer of passion fruit (Passiflora edulis Sims), with a production of approximately 172.3 thousand tons per year. Approximately 90% of passion fruit peels and seeds from the juice and pulp industries are discarded, despite containing a large amount of fiber, pectin, and oil. The remainder is used for various purposes, such as in the preparation of animal feed and in the manufacture of sweets.35
Passion fruit is a widely consumed fruit in the world and in Brazil. Its pulp contains ascorbic acid and carotenoids.36 Its peel accounts for 60% of the fruit and contains pectin (21.5%), tryptophan, fatty acids, and amino acids.37 Regarding the by-products of the juice industry, the main one is the fruit peel, which has been shown to have great potential for substances in its composition, especially soluble fibers.38,39
Passion fruit peel, which represents 52% of the fruit's mass composition, can no longer be considered an industrial waste, since its characteristics and functional properties can be used to develop new products.40-43 Due to the significant production of juice, the peels, as a major waste, have become a burden to the environment. Therefore, it is necessary to find a viable way to transform the peels into useful products or to dispose of them properly, seeking a positive environmental impact.40,44
Passion fruit peel flour is a byproduct of juice factories. It is widely used for animal feed and discarded as industrial waste. Considering that in the manufacture of pectin by the food industry, the entire peel is extracted,45 a rational and efficient use of this waste as a substrate for the production of microbial proteins could yield satisfactory results in the production of feed20 and microbial proteins,46 also contributing to minimizing the problems of losses in the industrialization of tropical fruits.20
Sugarcane bagasse
Sugarcane bagasse is the result of the process of grinding the extracted stalk to obtain the juice, which undergoes processes until sugar and alcohol are obtained. For each ton of sugarcane harvested, approximately 30% of bagasse is produced.47 Bagasse is a byproduct from which only some constituents of the original material remain, and, in the case of sugarcane, the fiber and some amount of sugar remain. The chemical composition of bagasse varies according to several factors, including the variety of sugarcane, the type of planting soil, and the harvesting and handling techniques.48 Sugarcane bagasse may contain 32 to 44% cellulose, 27 to 32% hemicellulose, 20 to 24% lignin, and 4.5 to 9.0% ash.49
Sugarcane bagasse is the main agro-industrial residue in Brazil, with approximately 250-280 kg produced per ton of processed sugarcane. Despite the great potential of this lignocellulosic biomass (60-70% carbohydrates) for the production of fuels and chemical products, part of what is generated is burned in sugar mills and alcohol distilleries to generate energy, a smaller fraction is used for animal feed, and a large part is discarded as agricultural waste. The main composition of sugarcane bagasse consists of two polysaccharide fractions (cellulose and hemicellulose) and a polyphenolic macromolecule (lignin). The most abundant component is cellulose (33-36%), a polysaccharide consisting of a linear chain made up of several β(1,4)-D-glucose units linked in such a way as to generate crystalline regions that, consequently, increase its resistance to hydrolytic processes. Hemicellulose, the second predominant fraction (28-30%), is a heteropolysaccharide that has a varied composition according to its source. Hemicellulose from sugarcane bagasse is composed of heteroxylans, with a predominance of xylose, which can be chemically hydrolyzed more easily than cellulose. Lignin is a complex structure formed by the polymerization of aromatic alcohols. It is resistant to enzymatic attack and degradation, and thus its content and distribution are recognized as the most important factors that determine the recalcitrance to cell wall hydrolysis.50,51 The lignin present in lignocellulosic biomass can also bind to the enzymes that degrade it, thus becoming an inhibitor of these enzymes.52
Corn steep liquor
Corn steep water, a major byproduct of the corn milling industry, is a cheap substrate available on a large scale,53 capable of providing an additional nitrogen source, providing peptides and amino acids readily available for cell metabolism. This byproduct of the corn starch processing industry is a source of carbohydrates, amino acids, peptides, vitamins, phosphate, and metal ions54 and was therefore used in the culture medium to replace yeast extract and peptone, high-cost nitrogen sources. This residue has been satisfactorily used for a variety of fermentations such as the production of solvents, antibiotics, and enzymes.55
The industrial wet milling process is the second largest sector of corn grain consumption after animal feed, using 12% of the total produced.56 This involves chemical, biochemical transformations, and mechanical operations to separate the corn grain into its relatively pure fractions: germ, fiber, starch.57
The primary products of wet milling are food and industrial starches, which can be converted into syrups and ethanol. Co-products include corn oil and products intended for the production of animal feed, such as corn gluten meal, corn germ meal, fibers and soaking water, the latter being soluble solids removed during soaking and concentrated by evaporation. The resulting soaking water, usually sold at 50% solids, is rich in vitamins, especially B complex. Combined with other ingredients, these items are used in the formulation of specific feeds according to the destination of the animals.56
Considering that the substrate for microorganism growth corresponds to 30-40% of the cost of enzyme production on an industrial scale,58 several studies have shown the potential of using corn steep water as a source of nitrogen and carbon for enzyme production by thermophilic microorganisms.22,29,59-65
The Brazilian economy is one of the most important in the world based on agriculture, producing and exporting coffee, sugar cane, soybeans, cassava, fruits, among others. However, the large production of these agricultural products generates a large amount of waste, which when accumulated leads to environmental deterioration and loss of resources, with a significant contribution to the problem of recycling and conservation of biomass.66
In recent decades, there has been a growing search for the use of agro-industrial waste, due to the incessant demand for agricultural activities. Several processes have been developed to use these materials, transforming them into chemical compounds and products with high added value such as alcohol, enzymes, organic acids, amino acids, etc.66-69
In the search for alternative solutions to the problem of waste disposal, many industries have opted to use microorganisms as reducing agents for organic matter in these materials or for the elimination or reduction of toxic compounds, with thermophilic enzymes being widely used in these processes.70,71
The application of agro-industrial waste in bioprocesses, on the one hand, provides alternative substrates and, on the other, helps to solve the pollution problems that their environmental disposal could cause. With the advent of biotechnological innovations, mainly in enzyme and fermentation technology, many new avenues have been opened for their use.67
Several agro-industrial residues are used as alternative sources of substrates for enzyme production, due to local availability and because they represent an alternative source of low commercial value, especially when the objective is to produce these enzymes on a large scale.72 Approximately 40% of the costs of enzyme production by fermentation correspond to the culture medium. The use of alternative culture media for the production of proteases by Bacillus has been reported in many scientific studies. These media can be obtained from several sources such as shrimp and crab shell powder,73 fish meal,74 soybean meal,58,75 amaranth seed flour,76 chicken feathers,77 arrowroot,78 cheese whey and corn steep liquor.22,28,29,64
Brazil is the world's largest producer of sugarcane, with a production of 620.4 million tons in the 2018/2019 harvest.79 This production is considerable, leading to the conglomeration of by-products, mainly sugarcane straw, fresh leaves, and bagasse.79 Among the lignocellulosic raw materials, agroindustrial materials stand out due to their residue nature. Straw is found on the surface of the planted area after harvesting, and this residue includes leaves, tips, stems, and roots. The fibers of these materials are made up of cellulose, hemicellulose, and lignin.80 Although bagasse can be used to generate energy or as an animal supplement, there is still a large surplus that can be used to produce various goods for society. Some alternatives for its use as raw material are the production of ethanol, paper and cellulose, acoustic coatings, pressed wood, agricultural fodder, alcohol, alkaloids, and enzymes.81,82
Currently, the surplus of bagasse available for other uses is between 7 and 10% of the total bagasse (approximately 280 kg of bagasse per ton of sugarcane). The remaining bagasse obtained in sugarcane processing is used as primary fuel in the generation of steam and electricity.79 Replacing pure cellulose commonly used as an inducing substrate for enzymatic synthesis with relatively cheaper substrates such as sugarcane bagasse has been shown to be effective in reducing the production cost of cellulases.83
The research group of HUMBIRD84 in their study suggested that the carbon source used in enzyme production could represent more than 50% of the total cost of the enzyme, if pure glucose were used. Another major problem is the generation of waste in the fruit processing industry that, after processing, generates by-products, which often do not have a specific destination, becoming environmental contaminants and, consequently, generating operational costs for companies, as they require treatment for disposal.
The greatest economic relevance of the passion fruit comes from the industrialized product in the form of whole or concentrated juice, due to its sensory characteristics and also its nutritional aspects.85
Brazil is a major producer of passion fruit. A large part of this production is used for juice extraction, with the main residues being the peels and seeds, which correspond to 65 to 70% of the weight of the fruit.35 Approximately 90% of the passion fruit peels and seeds from the juice and pulp industries are discarded, although they contain a large amount of fiber, pectin and oil, with the remainder being used for various purposes, such as in the preparation of animal feed and in the manufacture of sweets.35
Passion fruit peel contains a large amount of compounds such as cellulose, pectin and others, and large nutritional supplements are not necessary for adequate microbial development, as they function as inducers for the production of extracellular enzymes, such as cellulases, xylanases, pectinases and others.5 Thus, the production of cellulases through bioprocesses using passion fruit peel is one of the many ways to exploit them profitably.
Passion fruit peel flour has demonstrated the benefits of using cosubstrates to increase enzymatic activity.86 In addition, corn steeping water, a major byproduct of the corn milling industry, is a cheap substrate available on a large scale,53 capable of providing an additional nitrogen source, providing peptides and amino acids readily available for cell metabolism.
This byproduct of the corn starch processing industry is a source of carbohydrates, amino acids, peptides, vitamins, phosphate and metal ions54 and was therefore used in the culture medium to replace yeast extract and peptone, high-cost nitrogen sources. This residue has been successfully used for a variety of fermentations such as the production of solvents, antibiotics and enzymes.55
The industrial wet milling process is the second largest sector of corn grain consumption after animal feed, using 12% of the total produced.56 This involves chemical, biochemical transformations and mechanical operations with the objective of separating the corn grain into its relatively pure fractions: germ, fiber and starch.57
The primary products of wet milling are food and industrial starches, which can be converted into syrups and ethanol. Co-products include corn oil and products intended for the production of animal feed, such as corn gluten meal, corn germ meal, fibers and soaking water, the latter being soluble solids removed during soaking and concentrated by evaporation. The resulting soaking water, usually sold at 50% solids, is rich in vitamins, especially B complex. Combined with other ingredients, these items are used in the formulation of specific feeds according to the destination of the animals.56 MAKKY87 investigated the production of cellulases (avicellase) by the thermophilic Geobacillus stearothermophilus when cultivated on “in natura” sugarcane bagasse and treated with alkali. The maximum activity of the enzyme expressed was 1.99 U/mL and 1.06 U/mL in the treated and untreated bagasse, respectively. LADEIRA63 reported the production of cellulases by Bacillus sp. SMIA-2 was cultivated at 50oC in submerged cultures containing sugarcane bagasse. The maximum activity of avicelase (0.83 U/mL) and carboxymethylcellulase (0.29 U/mL) was reached after 120 h and 168 h of culture incubation.
The production and characterization of cellulases by Bacillus sp. C1AC5507 using sugarcane bagasse as a carbon source was reported by PADILHA88 The cellulase (carboxymethylcellulase) presented a molecular weight of approximately 55 kDa, and its activity varied between 0.14 and 0.37 U/mL.
Cellulases
Cellulases are extracellular enzymes capable of acting on cellulosic materials, promoting their hydrolysis. They are highly specific biocatalysts that act together to release sugars, of which glucose is the one that arouses the greatest industrial interest.89 The cellulolytic enzyme complex is divided into three groups according to its site of action on the cellulosic substrate: β-1,4-endoglucanases (EC 3.2.1.4), β-1,4-exoglucanases (EC 3.2.1.91) and β-glucosidases (EC 3.2.1.21).90 Avicelases (exoglycanases) act progressively on reducing or non-reducing ends of cellulose, with greater affinity for insoluble or microcrystalline cellulose, releasing glucose and mainly cellobiose as products. They are capable of acting on microcrystalline cellulose, shortening polysaccharide chains.91 Exoglycanases do not act on soluble celluloses because there is a stereochemical hindrance caused by the groups. Exoglycanases act on crystalline cellulose (Avicel), producing a slow and gradual reduction in its degree of polymerization. Thus, activity tests on Avicel characterize exoglycanases,92 while for the activity of endoglycanases, carboxymethyl cellulose is used,93 making it possible to differentiate between these enzymes. Carboxymethylcellulases (endoglucanases) are enzymes of the cellulolytic complex that cleave the bonds of the less compacted (amorphous) regions of cellulose, reducing the length of the fiber and generating new free ends. Endoglucanase, classified with EC 3.2.1.4, has the systematic name, according to the IUBMB – International Union of Biochemistry and Molecular Biology, 1,4-β-D-glucan-4-glucanohydrolase, also known as carboxymethylcellulase (CMCase). It is the enzyme of the cellulolytic complex responsible for initiating hydrolysis. This enzyme randomly hydrolyzes the internal regions of the amorphous structure of the cellulosic fiber, breaks the bonds within the cellulose chain, releasing glucose, cellobiose, and cellodextrins, creating non-reducing ends for subsequent action of the exoenzymes. Endoglucanase is the cellulolytic enzyme responsible for the rapid solubilization of the cellulosic polymer, due to its fragmentation into oligosaccharides.94,95 Cellulases have a wide range of applications and are used in the food industry in processes of extracting fruit juice, seed oils and clarifying juices; in the production of animal feed, thus increasing its digestibility; in the textile industry for defibrillating fabrics and fading denim; and in the paper and cellulose industries.96
Proteases are enzymes involved in the conversion of proteins into amino acids and peptides. Their production is a property of all organisms and they are generally constitutive, although over time they become partially induced.97 KUMAR and TAKAGI98 cite proteases as essential constituents in all forms of life on Earth, including prokaryotes, fungi, plants and animals.
Also called proteinases or peptidases, proteases constitute one of the most important groups of industrial enzymes with applications in different industries worldwide.99 Alkaline proteases have been intensively studied due to their potential use in various industrial sectors such as the food, pharmaceutical, leather, detergent, diagnostics, waste management and recovery of silver used in X-ray films.100
Microorganisms contribute to two-thirds of the production of proteases commercialized in the world. There is a long list of microorganisms that produce proteases, but a small number are commercially exploited due to the fact that some have toxic and pathogenic characteristics. A large number of bacteria, fungi and yeasts are known to produce serine-type alkaline proteases.98 However, few microorganisms have been recognized as commercial producers, with only microorganisms that produce substantial quantities of extracellular enzymes being of greatest industrial importance.101 Conclusive research found in the literature shows that the genus Bacillus sp is the largest commercial source of proteases. This fact is due to the relative ease of isolating microorganisms of this genus from various sources, making them a focus of attention in biotechnology.102 A large number of Bacillus species from exotic environments have been explored for the production of proteases. Strains of B. licheniformis, B. subtilis, B. amyloliquifaciens and B. mojanensis can be cited as potential producers.98-101 Thus, the genus Bacillus contains a large number of industrially important species and provides approximately half of the current commercial production of enzymes.
Amylases
Amylases, both in the eukaryotic and prokaryotic groups, act as one of the main enzymes responsible for obtaining energy for metabolic functions, from starch as a carbon source. However, in most eukaryotes, these enzymes act in specific tissues or organs, related to the organism's nutrition, which makes their extraction and purification for commercial use unfeasible in most cases.58 Thus, microorganisms emerge as a simple and cheap alternative for the production of these enzymes, since they require minimum nutritional and maintenance conditions, present high production efficiency, in addition to secreting the enzymes into the extracellular environment.103
A wide variety of microorganisms produce one or more types of amylases, and it is known that amylases produced by thermophilic microorganisms have more thermostable characteristics than those produced by mesophilic microorganisms. These thermostable amylases are of great interest in the starch processing industry, since the gelatinization temperature of starch is around 70ºC. 104,105
Amylases are extracellular enzymes since starch, the substrate of amylases, has a high molecular weight and cannot pass through the microbial cell membrane. Thus, amylases are produced inside the cell and subsequently secreted into the environment. However, for the microorganism to accelerate the synthesis of these enzymes, the cell receives a signal through low molecular weight fragments, formed by the action of small quantities of constitutively produced enzymes.106 Amylases are widely distributed in nature and, in addition to being responsible for recycling the carbon contained in starches in general, they play an important role in the starch processing industry.107 One of the processes that uses amylases is the conversion of starch into dextrins, maltose, glucose and fructose. Dextrins are used in clinical formulations, as material for enzymatic saccharification, stabilizers, thickeners, etc. Maltose is used in confectionery, soft drinks, brewing, fermentation for ethanol production, and the manufacture of jellies and ice creams. Glucose is used in soft drinks, baking, breweries and fermentation for ethanol production and fructose is used in soft drinks, jams, yogurts and canned fruits.108
The Brazilian thermophilic strain of Bacillus sp. SMIA-2 produced good levels of avicelase and CMCase in submerged fermentation, using sugarcane bagasse and corn steep water as low-cost substrates. Enzyme production began in the exponential growth phase, reaching a maximum at 120 h for avicelase and 168 h for CMCase.63 The characteristics presented by avicelase and CMCase from Bacillus sp. SMIA-2 demonstrate that these enzymes can be very useful in biotechnological applications. This same Bacillus produced protease when cultivated in a solution (0.5% w/v) of whey powder and supplemented with passion fruit peel flour (0.25% w/v) and reached a maximum at 72 h.109-112
- a. Agro-residues are effective substrates for enzyme production.
- b. Cheese whey and bagasse reduce microbial enzyme costs.
- c. Bacillus sp. SMIA-2 utilizes low-cost agro-industrial wastes.
- d. Valorization of residues supports sustainable bioprocesses.
The authors thank the Brazilian Agencies CNPq and CAPES for financial support and Pró-Reitoria de Inclusão e Pertencimento da Universidade de São Paulo-USP.
This Research Article received no external funding.
Regarding the publication of this article, the author declares that they have no conflicts of interest.
