Mannanase is a specialized enzyme belonging to the broader group of hemicellulases, which break down complex carbohydrates found in plant cell walls. Specifically, this enzyme is an endo-1,4-\(beta\)-mannanase (EC 3.2.1.78) that works by hydrolyzing mannan, a type of polysaccharide. Its biological function is to dismantle large sugar chains into smaller fragments. This activity is fundamental to the natural recycling of plant biomass and has been adapted for numerous industrial applications.
Basic Function and Substrate
The primary target of mannanase is mannan, a polysaccharide and major constituent of hemicellulose, the second most abundant natural polymer after cellulose. Mannan is a long chain of mannose sugar units linked by \(beta\)-1,4-glycosidic bonds, distributed in softwoods, seeds, and plant endosperm. Mannan forms include linear mannan, glucomannan (containing mannose and glucose), and galactomannan (containing mannose and galactose side chains).
Mannan serves as a structural component within the plant cell wall or as a carbohydrate reserve in seeds, such as those from guar and coffee plants. Mannanase initiates the breakdown of this large polymer by randomly cleaving the internal \(beta\)-1,4-linkages within the mannan backbone. This action, known as hydrolysis, uses water to split the molecular bonds.
The enzymatic degradation of mannan often requires the synergistic action of other enzymes, such as \(beta\)-mannosidase and \(alpha\)-galactosidase, for full deconstruction. Mannanase acts as the primary cleaving agent, breaking the polymer into manno-oligosaccharides (MOS) and simple mannose sugars. This process is necessary for nutrient cycling and is important in seed germination, mobilizing stored energy for the growing seedling.
Natural Sources and Commercial Production
Organisms across multiple biological kingdoms naturally produce mannanase to degrade plant material. The enzyme is found in plants, aiding in seed germination, and in some animals for digestion. The most prolific and commercially relevant sources are microorganisms, specifically fungi, bacteria, and actinomycetes.
Fungi, such as Trichoderma reesei, and bacteria, particularly species of Bacillus, are the preferred industrial sources due to their high activity and capacity for large-scale production. Commercial mannanase is typically produced through microbial fermentation, involving growing high-yielding strains in a controlled environment. Submerged fermentation, where microbes are grown in a liquid medium, is a common method, resulting in the enzyme’s secretion into the broth for purification.
Improving Efficiency in Animal Feed
Mannanase is economically significant as a feed additive in non-ruminant agriculture, primarily for poultry (broilers) and swine (pigs). Common feed ingredients, such as soybean meal, contain high levels of mannan that are poorly digested and act as an anti-nutritional factor. This undigested mannan increases the viscosity (thickness) of the digestive tract contents, interfering with the absorption of nutrients and energy.
The presence of intact mannan can also stimulate the animal’s innate immune system, triggering a metabolically costly immune response. By hydrolyzing the mannan, the enzyme simultaneously reduces intestinal viscosity for efficient nutrient uptake. It also removes the molecular structure that triggers the immune response, redirecting energy toward growth.
The addition of mannanase has demonstrated tangible improvements in performance metrics. Studies show that supplementation can improve the feed conversion ratio (FCR) by approximately one percent in broilers and up to six percent in pigs. This means less feed is required to achieve the same weight gain, linked to increased digestibility of dry matter, crude protein, and energy. The resulting manno-oligosaccharides created by the enzyme’s action can also function as prebiotics, promoting a healthier gut microbiota.
Broader Industrial Applications
Mannanase is valuable across several major industries due to its ability to break down complex plant polysaccharides.
Pulp and Paper
In the pulp and paper sector, mannanase is used in bio-bleaching to improve the brightness of softwood pulp. By degrading the mannan component of the wood fiber, the enzyme facilitates lignin removal during bleaching. This reduces the need for harsh, chlorine-based chemicals, making the process more environmentally sound.
Textiles
The textile industry utilizes mannanase to modify the surface of fabrics, particularly denim, achieving a stone-washed, softened effect. This avoids the mechanical damage caused by traditional pumice stones. The enzyme acts on guar gum and other mannan-containing sizing agents used in manufacturing, allowing for a gentler and more controlled finishing process.
Food and Beverage
Mannanase is also employed in the food and beverage industry to clarify products and enhance extraction yields. In fruit juice production, the enzyme breaks down mannan-based gums and clouding agents, leading to a clearer, more stable final product. It is also used in processing coffee extracts to reduce viscosity, which concentrates flavor components.