Xylanases are glycoside hydrolases enzyme with genetically single chain glycoproteins that catalyze the hydrolysis of glycosidic bonds in complex sugars. Xylanases range from 6--80 kDa, active between pH=4.5--6.5 and at temperature between 40 and 60 C (Butt, et al., 2007). These enzymes are produced by some microorganisms to cleave xylans (substrate), a major constituent of hemicellulose. Three major enzymes, endoxylanases, exoxylanases and -xylosidases, act synergistically and are required for the breakdown of xylan backbone in hemicellulose. Endoxylanases (EC 3.2.1.8) cleave the -1,4 bonds of xylan backbone. Exoxylanases (EC 3.2.1.37) hydrolyse -1,4 bonds of xylan from the inside non-reducing ends randomly and release xylooligosaccharides. The xylooligosaccharides and xylobiose obtained then will be cleaved by -Xylosidases to release xylose (Raveendran, et al., 2018).
Xylanases which can be produced by different sources differ in their requirements for temperature, pH, etc. for optimum functioning. Xylanases are produced by organisms such as algae, protozoa, molluscs, crustaceans, insects, bacteria, plant seeds, and many fungi in the genus Aspergillus. However, fungi are the major sources of xylanase due to their high content and extracellular release of the enzyme, such as Aspergillus (Raveendran, et al., 2018).
 For several decades, the biotechnological use of xylanolytic enzymes has increased and can be applied to many industries. The important applications of xylanases are in the paper industries, feed industries, food industries, pharmaceutical industries, and bio-fuel (Kumar, et al., 2017). In food industry, xylanases are used for bread making (dough conditioning), the production of corn starch, clarification of fruit juice and wine; animal feeds, and alcoholic fermentation.
XYLANASE IN BAKING
Enzymes play a key role in baking industry and xylanase has been widely used in bread making with other enzymes as bread improvers (Beg, et al., 2001). Xylanases are added to dough to help break down polysaccharides (hemicellulose) in the wheat flours. Xylanase transforms water insoluble hemicellulose into soluble form, which increases the binding of water in the dough and leaving the dough softer and easier to knead. This enzyme also makes the dough more tolerant to different flour quality parameters and variations in processing methods (Harris and Ramalingam, 2010). Thus, they help stabilize the dough, make it more flexible, and improve gluten strength.
Xylanase also affects bread volume. The positive effect of xylanase on bread volume is due to the redistribution of water from the pentosan (xylan) phase to the gluten phase. The increase in the volume of the gluten fraction increases its extensibility, which will result in better oven spring. The improving effect of pentosanase on bread volume may be associated with a better gas retention during proofing, probably due to the action of enzyme in reducing the viscosity of the gelling starch and allowing greater and longer expansion in the oven before enzyme inhibition and protein denaturation (Butt, et al., 2008).
They can also increase the specific bread volume by delaying crumb formation and this improves the quality of bread (Raveendran, et al., 2018). Doughs treated with xylanase have improved dough handling properties, such as increasing moisture retention and shelf-life by reducing the staling rate , as well as improved sensory qualities and resistance to fermentation (Harris and Ramalingam, 2010). They appear to be particularly effective in straight dough process. Therefore, decreasing the dough firmness, increasing volume and creating finer and more uniform crumbs (Butt, et al., 2008).
Hence, xylanase along with protease, lipase and -amylase are significantly effective for obtaining bread with higher specific volume in microwave oven, as compared to the bread with no enzyme added. The texture profile analysis was greatly modified by xylanases and the firmness of breadcrumb was reduced. These enzymes improve the strength of the gluten network and therefore, improve the quality of bakery products (Butt, et al., 2008).
References:
Kumar, D., et al. 2017. Xylanases and their industrial applications: A review. Biochemical and Cellular Archives. Vol. 17, No. 1, pp. 353-360.
Harris, A. D. and Ramalingam, C. 2010. Xylanases and its Application in Food Industry: A Review. Journal of Experimental Sciences Vol. 1, Issue 7, Pages 01-11.
