A Closer Look at Mannanase

Mannannases are enzymes that are responsible for breaking down the mannan portion of the hemicellulose structures found in plant cell walls.

Mannans are members of the hemicellulose family of nonstarch polysaccharides (NSPs). Mannans exist in the form of linear mannan, glucomannan, galactomannan, and galactoglucomannan. Mannans function as structural components in plant cell walls by binding cellulose. They also provide storage reserves of nonstarch carbohydrates in the cell walls and vacuoles of various plant tissues. Similar to other NSPs, monogastric animals possess no endogenous enzymes capable of digesting mannans.

Mannans are more highly concentrated in oilseeds than in grains. For instance, of the 9.9% total NSPs present in corn, only about 3% is made up of mannans..

Bach-Knudsen, Knud Erik, 1997. Carbohydrate and lignin content of plant materials
used in animal feeding. Anim. Feed Sci. Tech. 67: 319 - 338.

..whereas they represent approximately 8% of the total NSPs present in soybean meal.

NSP present in soybean meal (240g/kg).
Brillouet & Carré, 1983; Bach-Knudsen, 1997; Huisman et al., 1998.

However, even in oilseeds mannans do not account for nearly as large a percentage of the total NSPs as do pectins or cellulose. Nonetheless, mannanase enzymes have potential for improving oilseed digestibility, particularly when fed in conjunction with enzymes that express pectinase, cellulose, or α-galactosidase activity.

Mannanase enzymes primarily exist in the form of β-mannanase. This enzyme is responsible for cleaving β-1,4 linkages of mannan to release the sugar mannose. However, similar to other NSP structures, mannans have diverse and variable side chain structures comprised of β-1,4 linked mannosides, 1,4- β-glucopyranose, and α-galactose. Thus, for β-mannanase to function more efficiently, the presence of β-mannosidase, β-glucosidase, and α-galactosidase are required. As such, carbohydrase products which express multiple mannanase activities, as well as α-galactosidase should have a higher potential for degrading mannans and improving the digestibility of oilseeds.                                                  

Pectinase - Why is it Important?

Pectinases are enzymes that are probably unfamiliar to many people, as they are not as commonly offered in commercial nonstarch polysaccharide (NSP) degrading enzymes with the exception of multienzyme products. Very few pure or cocktail-type NSP degrading enzymes express pectinase activity. However, as pectins make up a large portion of the NSPs present in poultry rations, the importance of pectinase should not be overlooked.

Pectins are NSPs commonly associated with vegetable proteins. They are present in cereal grains as well, although to a much lesser extent. For instance, of the NSPs present in corn, only about 5-7% is made up of pectins.

Bach-Knudsen, Knud Erik, 1997. Carbohydrate and lignin content of plant materials
used in animal feeding. Anim. Feed Sci. Tech. 67: 319 - 338.

However, pectins account for the largest majority of the NSP content in soybean meal, as about 50-55% of the NSPs in soybean meal exists in the form of pectins.

Brillouet & Carré, 1983; Bach-Knudsen, 1997; Huisman et al., 1998.

Pectins exist as rhamnogalacturonans, arabinans, galactans and arabinogalactans. The majority of pectins present in the oilseeds typically used in monogastric diets are rhamnogalacturonans and arabinogalactans. As with other NSPs, monogastric animals possess no endogenous enzymes capable of digesting pectins.

Similar to other NSPs discussed in previous emails, pectins require multiple enzymatic activities to be broken down. This is because pectins exist as complex structures with highly-substituted and variable side chains (see below). For example, for rhamnogalaturonase to have access to its target substrate, first pectin acetylesterase must cleave the acetyl group attached to the polysaccharide. As such, NSP degrading enzymes which express multiple pectinase activities should have a higher potential for improving the digestibility of oilseeds.

		Pectin acetylesterase releases the acetyl residue linked to the galacturonic acid.
		Rhamnogalacturonase cuts the bonds between galacturonic acid and rhamnose in the rhamnogalacturonan region.
		Polygalacturonase cuts the linear chain of galacturonic acid in the homogalacturonan region.
		Pectin esterase releases the methyl residue linked to the galacturonic acid.

An Examination of β-glucanase

β-glucanase was first used in barley-based rations in Europe. Barley contains a large amount of soluble Non Starch Polysaccharides (NSP) in the form of β-glucans and arabinoxylans. These β-glucans result in poor nutrient absorption through large increases in gut viscosity. Thus, as early as the 1980s, β-glucanase enzymes began to be supplemented in barley-based rations to alleviate some of these detrimental effects.

Based on the β-glucan content of corn and soybean meal (see below), it would appear that there was little potential for improvement through β-glucanase supplementation in corn and soy-based poultry rations. However, this is somewhat misleading, as some β-glucanases function as cellulases.

Bach-Knudsen, Knud Erik, 1997. Carbohydrate and lignin content of plant materials used in animal feeding. Anim. Feed Sci. Tech. 67: 319 - 338.

Cellulose, one of the primary components of plant cell walls, represents a large portion of the NSP content of most cereal grains and oilseeds (see above). For instance, cellulose represents approximately 28% of the total NSP present in soybean meal and approximately 22% of the NSP present in corn. Cellulose consists of long chains of D-glucose subunits, linked by β-1, 4 linkages. For these β-1, 4 linkages to be separated, the activity of endo-1, 4-β-glucanase is required. As poultry do not produce this enzyme endogenously, it must be supplied in the ration.

It should be pointed out that it is very unlikely that cellulose can be degraded to its glucose subunits by an NSP degrading enzyme given the short transit time in the digestive tract of poultry. Rather, potential for improvements in digestibility exists through the ability of endo-1, 4-β-glucanase to elicit structural changes in the cell walls of grains and oilseeds, which could allow the bird’s endogenous enzymes better access to nutrients. 

Why Use Xylanase?

As mentioned in my previous email, this email will discuss the importance of xylanase enzymes.

Some of the Non starch polysaccharides (NSPs) typically present in grains and oilseeds are arabinoxylans and heteroxylans. Hence, there is potential for increasing dietary energy as well as improving digestion by supplementing xylanases in poultry diets.

Xylanase supplementation is often associated with diets based on wheat. This is largely because xylanases were first used with wheat-based poultry rations in Europe, as well as the fact that arabinoxylans make up a large portion of the NSP present in wheat.

Bach-Knudsen, Knud Erik, 1997. Carbohydrate and lignin content of plant materials used in animal feeding. Anim. Feed Sci. Tech. 67: 319 - 338.

Xylanases, however, also have potential benefits in corn and soybean meal based rations. Corn typically contains about 9.9% NSP on a dry matter basis, of which approximately 6% is made up of arabionoxylans (see above).

Soybean meal contains approximately 22% NSP, of which about 9% is made up of arabinoxylans.

Thus, the potential exists for xylanases to liberate energy from the NSP contained in corn and soybean meal-based rations.

One important consideration to remember regarding all enzymes is that they react with a specific substrate, and xylanases are no exception. As such, xylanases differ, and cannot be compared quantitatively from product to product. For instance, below it can be seen that an arabinoxylan typically requires four specific xylanase activities to be broken down to a simple sugar.

Click for detailed information

For different arabinoxylans, however (such as the highly branched arabinoxylans found in corn), a different sequence of xylanase activity is required to effectively break down the NSP.

Click for detailed information

Therefore, enzyme products which contain multiple xylanase activities should have higher potential for improving digestibility over a broader range of feedstuffs.

As arabinoxylans represent a large portion of the NSP present in most cereal grains and oilseeds, it is evident why so many commercial carbohydrase enzymes seek to express xylanase activity.


In our next Rovabio Mail, we will examine the enzyme β-glucanase.

Why Use Enzymes?

Recently, many carbohydrase or non starch polysaccharide-degrading (NSP) enzymes have become available commercially for use in poultry rations. Over 50% of poultry feed now contains supplemental NSP enzymes. NSP enzymes have clearly reached the “tipping point” of acceptability.

These products exist in several forms:

• Pure enzyme products which exhibit only one specific enzyme activity
• Blends of pure enzymes commonly referred to as “cocktails”
• Multi-enzymes (i.e., enzyme products produced from a single organism which expresses multiple enzyme activities)

Monogastric animals, such as poultry, possess endogenous enzymes which aid in the breakdown of different nutrients for digestion and absorption. For instance, poultry possesses protease which helps to break down protein, lipase which helps to digest fat, and amylase which helps to digest starch.

However, monogastrics have no endogenous enzymes capable of digesting non-starch polysaccharides. NSPs are complex carbohydrate structures which make up part of the cell walls of cereal grains and oilseeds. The two tables below show the amount of NSPs in various grains and oilseeds.

Bach-Knudsen, Knud Erik, 1997. Carbohydrate and lignin content of plant materials used in animal feeding. Anim. Feed Sci. Tech. 67: 319 - 338.

NSPs exert negative effects on digestion beyond their inability to be digested. NSPs exist in both soluble and insoluble forms. The soluble NSPs negatively impact digestion by forming viscous solutions in the gut, which can also result in issues such as wet droppings. The insoluble NSPs are thought to impede digestion by simply creating physical barriers which limit the access of endogenous enzymes to carbohydrates, fats and proteins.

As monogastrics possess no endogenous enzymes for NSP digestion, they must be provided in the diet. Feeding carbohydrase enzymes allows for improvements in digestibility, allowing poultry to utilize more of the energy and amino acids present in grains and oilseeds.

I will be writing a series of emails on various carbohydrase enzyme activities and why they are needed. In the next email, I’ll examine xylanases and how they work to break down a portion of the NSP found in grains like corn.