constitute 4–8% of the kernel and about 25 and 70% of the cell wall polysaccharides
of the endosperm and aleurone layer, respectively [162]. These hemicelluloses have
little nutritional significance for nonruminant organisms (e.g., chicken and pigs) as
they lack the appropriate digestive enzymes. Undigested arabinoxylans increase the
viscosity of the digesta in the gut and are known to have anti-nutritive effects. The
high viscosity in the chicken intestine impairs penetration of digestive enzymes and
ultimately decreases nutrient absorption. This results in an inefficient use of the feed
and poor growth of the chicken. Moreover, the high viscosity may also support
pathogenic conditions, especially in broiler chicks [35]. Addition of hemicellulases
to the feed releases oligosaccharides which have prebiotic effect and stimulate the
growth of beneficial bacteria in the gut, and this promotes the chickens’ health
[195, 196]. The use of xylanases, preferably together with mannanases, in feed
formulation alleviates the anti-nutritive effects imposed by the arabinoxylans
[196, 197]. Moreover, xylanases help in the degradation of the cereal cell walls
and improve nutrient accessibility [198]. The enzymes eliminate sticky excreta
problems and significantly contribute to reducing waste problems by lowering the
water content of the droppings. In addition, the efficient use of the grain decreases
the manure output, which is beneficial to the environment.
The ruminant animal feed nutritional quality can be improved with addition of
xylanases in the feed. This is believed to be due to an increase in cellulose
accessibility to ruminant digestion by removing the xylan component of the feed.
It makes the digestion complete and improves the feed conversion efficiency
[199]. In a similar way, most feed ingredients such as soybean meal, copra meal,
palm kernel meal, and legumes contain mannan. Because of its indigestive nature, it
negatively affects the growth performance of the animals. Thus, addition of
mannanases to the feed can improve the feed digestibility by degrading the mannan
and improve productivity [200].
Hemicellulases used as feed additives are known to be active around moderately
acidic pH, especially if it is meant to be active in the digestive tract of the animals
where the pH is about 5. However, if the enzyme is intended to improve the feed
quality before feeding (during pelleting and storage), it should not be necessarily
active at low pH. This has brought the possibility of using enzymes that are active in
the neutral range. Even, the potential of alkaline active hemicellulases as feed
additives has been positively evaluated [201]. Thus, alkaline active hemicellulases
which are active in a wide range of pH can be considered for feed applications.
6.7 Food
In bread-making, xylanases improve dough development time, consistency, extensibility, and resistance to breakdown. It improves the desirable texture, loaf volume,
and shelf life of the baked bread [162, 202]. However, all xylanases are not useful for
this purpose. Xylanases that digest and solubilize water-unextractable arabinoxylans
with only little effect on water-extractable arabinoxylan are the most preferred.
Alkaline Active Hemicellulases
277
of the endosperm and aleurone layer, respectively [162]. These hemicelluloses have
little nutritional significance for nonruminant organisms (e.g., chicken and pigs) as
they lack the appropriate digestive enzymes. Undigested arabinoxylans increase the
viscosity of the digesta in the gut and are known to have anti-nutritive effects. The
high viscosity in the chicken intestine impairs penetration of digestive enzymes and
ultimately decreases nutrient absorption. This results in an inefficient use of the feed
and poor growth of the chicken. Moreover, the high viscosity may also support
pathogenic conditions, especially in broiler chicks [35]. Addition of hemicellulases
to the feed releases oligosaccharides which have prebiotic effect and stimulate the
growth of beneficial bacteria in the gut, and this promotes the chickens’ health
[195, 196]. The use of xylanases, preferably together with mannanases, in feed
formulation alleviates the anti-nutritive effects imposed by the arabinoxylans
[196, 197]. Moreover, xylanases help in the degradation of the cereal cell walls
and improve nutrient accessibility [198]. The enzymes eliminate sticky excreta
problems and significantly contribute to reducing waste problems by lowering the
water content of the droppings. In addition, the efficient use of the grain decreases
the manure output, which is beneficial to the environment.
The ruminant animal feed nutritional quality can be improved with addition of
xylanases in the feed. This is believed to be due to an increase in cellulose
accessibility to ruminant digestion by removing the xylan component of the feed.
It makes the digestion complete and improves the feed conversion efficiency
[199]. In a similar way, most feed ingredients such as soybean meal, copra meal,
palm kernel meal, and legumes contain mannan. Because of its indigestive nature, it
negatively affects the growth performance of the animals. Thus, addition of
mannanases to the feed can improve the feed digestibility by degrading the mannan
and improve productivity [200].
Hemicellulases used as feed additives are known to be active around moderately
acidic pH, especially if it is meant to be active in the digestive tract of the animals
where the pH is about 5. However, if the enzyme is intended to improve the feed
quality before feeding (during pelleting and storage), it should not be necessarily
active at low pH. This has brought the possibility of using enzymes that are active in
the neutral range. Even, the potential of alkaline active hemicellulases as feed
additives has been positively evaluated [201]. Thus, alkaline active hemicellulases
which are active in a wide range of pH can be considered for feed applications.
6.7 Food
In bread-making, xylanases improve dough development time, consistency, extensibility, and resistance to breakdown. It improves the desirable texture, loaf volume,
and shelf life of the baked bread [162, 202]. However, all xylanases are not useful for
this purpose. Xylanases that digest and solubilize water-unextractable arabinoxylans
with only little effect on water-extractable arabinoxylan are the most preferred.
Alkaline Active Hemicellulases
277