Flour Treatment : Enzymes


Fig. 123: Simplified representation of proteolytic enzymes attacking a protein molecule

3. Protease
Protease (also known as proteinase or peptidase) splits the protein strands of the gluten molecule (Fig. 123) and thus leads first to a softening and then to a complete collapse of the structure. Sometimes a rather surprising initial increase in viscosity or dough stability is observed. Although the causes are not clear, this may be due to improved water solubility at an early stage of hydrolysis when the main structure is still intact.

With short gluten structures a slight softening may well be desirable; in this case it has a similar significance to the use of cysteine. But unlike the amino acid, protease does not stop acting when the additive is used up. As a result, its effects increase with the fermentation time of the dough. That is why there is a considerable demand for enzyme preparations that do not contain even traces of protease. This fear may be exaggerated, at least if purified, single proteases are available: a single protease only acts on a few specific amino acid pairs (peptide bonds). Since there are 20 different amino acids, there are many combinations that cannot be hydrolysed by one particular protease. So the reaction will stop once all the suitable peptide bonds have been cut.

The use of proteases is less of a problem with flours that are rich in gluten. They are therefore used in bread improvers for burger buns or toast bread made from strong flour to achieve a smooth dough structure. Furthermore, proteases are very useful in the production of cracker, biscuit or wafer flours where elasticity of the gluten is undesirable but extensibility a prerequisite for proper processing.

Tab. 90: Lipids in wheat flour a

4. Lipolytic Enzymes
There are also frequent references to lipase, phospholipases and galactolipases. These enzymes split non-polar triglycerides present in flour (Tab. 90) into mono- and diglycerides and polar phospho- and galactolipids into more hydrophilic, i.e. more water-soluble lyso-forms (Fig. 124 - Fig. 126).

Fig. 124: Action of lipase on fat (triglyceride) molecules

Theoretically, this should lead to the in situ formation of emulsifiers with well-known effects. Interestingly, the amount of emulsifier formed in situ does not explain the positive effects on dough properties and baking behaviour. Presumably, the lipids affected by lipase are already located "in the right positions" (close to protein), at least once the dough has been prepared, where they are more effective than emulsifiers added to the flour. Surprisingly, no effect on crumb staling has be detected so far. In contrast to the above, the new molecules are possibly "in the wrong place" to prevent starch retrogradation, or the concentration is simply insufficient. The efficacy of monoglycerides in retarding staling is well-documented, but the typical dosage is 0.1 to 1% on flour.

Fig. 125: Action of phospholipases on lecithin (phosphatidyl choline)

Unfortunately, there is the problem of a possible impairment of taste due to the release of fatty acids. The author has occasionally noticed a rather cheesy smell in his baking laboratory, particularly when lipases were being tested in frozen butter croissants. For flour mills this is an obstacle because they do not have full control over the recipes used by their customers, the bakers.

Fig. 126: Action of galactolipase on monogalactosyl-diglyceride

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