【Megazyme】α-Amylase and β-Amylase

Like most cereals, barley contains starch as its primary storage polysaccharide. Starch must be released from within the barley endosperm, then broken down into smaller fragments in order to become useful for fermentation.

Once the cell wall has been broken down by enzymes like b-glucanase and xylanase, the starch hydrolases (another group of enzymes released by the grain during malting) are able to reach the starch molecules.

Each of the main starch hydrolases acts on different types of linkage within the starch chains, cutting the molecules into smaller fragments known as maltodextrins. The very smallest fragments are the fermentable sugars such as maltose and glucose.

Why does starch matter?

The abundance and activity of starch hydrolases has a direct impact on the fermentability of the later wort. Brewers and distillers who understand the enzyme content of their malts and mashes can exercise tighter control of their mashing and fermentation processes to ensure predictable production and consistent sensory characteristics with every batch.

Using enzymatic methods, it is possible to determine the total starch (K-TSHK, K-TSTA) content in any sample. This is useful for brewers and distillers wishing to understand the potential fermentability of their malts and worts.

Measurement of starch damage from grain milling and processing allows brewers and distillers to assess the accessibility of starch to starch hydrolases.

Cereal starches are composed of two types of polysaccharide chains: amylose and amylopectin.

Many of the starch properties relevant to maltsters are determined by the proportions of amylose and amylopectin present, for example gelatinisation, solubility, and mouthfeel of finished beverages.

a-Amylase is one of the three most important enzymes involved in starch hydrolysis, releasing fermentable sugars and maltodextrins from starch polysaccharide molecules. a-Amylase is an endo-acting enzyme which hydrolyses the a-1,4 bonds found in both amylose and amylopectin.

As the most thermostable of the starch hydrolases, a-amylase has a temperature optimum up to 70oC, which allows it to tolerate the temperatures involved in starch gelatinisation.

Around 90% of a-amylase persists through the mashing phase. The amount of a-amylase that survives after mashing is generally not the limiting factor in obtaining the maximal hydrolysis of starch for fermentation.

Like a-amylase, b-amylase cuts a-1,4 linkages in starch chains. However, b-amylase is an exo-acting enzyme, which means that instead of randomly cutting internal linkages in starch, it cuts from the end of the chain only.

b-Amylase liberates fermentable maltose molecules, which account for ~ 65% of the fermentable sugar in wort. a-Amylase and b-amylase work synergistically during mashing as b-amylase generally acts on the starch fragments liberated by the initial hydrolytic action of a-amylase.

See the Megazyme website for full details on our range of ultra-pure b-amylases.

Measurement of b-Amylase Activity

b-Amylase is the most abundant starch hydrolase present during malting, however it is significantly less thermostable than a-amylase. Just 40% of the initial b-amylase persists to continue liberating maltose at the end of mashing. Brewers therefore need to quantify the true activity of b-amylase: the presence of too little b-amylase has the potential to limit the fermentability of the resulting wort. This is a particular concern when brewing with adjuncts.