Enzymes in bread making - Enzymes in Food Technology - page 115

Table 6.3 The effects of various amylases on staling.

Enzyme Mechanism Thermostability Softening Springiness

α -Amylase (A. oryzae) Mainly endo Low + Very limited

α -Amylase (A. niger) Mainly endo Intermediate + Little

α -Amylase (B. amyloliquefaciens) Endo High ++++ Negative

α -Amylase (Maltogenic) Exo and endo Intermediate ++++ Positive

β -Amylase (e.g. from wheat) Exo Low + Little

As can be seen in Fig. 6.6, maltogenic intermediate stable amylase has a significant effect
on crumb softness as function of storage time. A specific bacterial amylase even has a greater
effect on softness, but this same enzyme completely ruins the crumb elasticity (Fig. 6.6(b)),
whereas the maltogenic enzyme gives the crumb a relatively good springiness, even after
prolonged storage.
Fungal amylase and -amylase have a very limited effect on crumb softness and on crumb

resilience. The effects of these enzymes are comparable with effect of distilled monoglyc-
eride.
The maltogenic amylase has a thermostability which is in between those of fungal amy-
lase and bacterial amylase. 73 Therefore the enzyme is able to reduce retrogradation of
amylopectin. It can hydrolyze glucosidic linkages in gelatinized starch before it is inacti-
vated during the baking process. Since the enzyme is inactivated at the end of the baking
process, it does not excessively hydrolyze starch. Apart from the optimal thermostability of
this enzyme, it has other benefits compared with fungal or bacterial enzymes. 74
The enzyme can degrade amylase and amylopectin into maltose and longer maltodextrines,
and in doing so it does not need an unblocked non-reducing end. This indicates that the
enzyme is also capable of attacking starch through an endo-type mechanism. Besides that,
these maltodextrines are also assumed to have an anti-staling effect by specifically blocking
interactions between starch and gluten. 62, 63

β

The effects of various amylases on staling are

summarized in Table 6.3.

6.3 XYLANASES

Numerous studies have been performed to demonstrate the positive effects of pentosans-
modifying enzymes, which are presented by industry as pentosanases, xylanases, arabinoxy-
lanases and/or hemicellulases, here further referred to as xylanases. 29,75-78 The way these
enzymes are considered to have their effect is by reducing the water binding of WU-AX
and by solubilizing WU-AX and later also WE-AX into smaller molecules. 79, 80 Another
effect ascribed to xylanases is to offset reduced gluten coagulation caused by pentosans
by hydrolyzing the pentosans to an extent whereby this effect is not longer occurring. 81
Hamer 79 reported that the use of xylanases in a batter significantly improved gluten coagula-
tion. The resulting gluten also was shown to have a much better bread-making quality. This
effect was explained by the absence of any detectable pentosans in the remaining gluten,
whereas normally 2-3% pentosans were attached to gluten. These gluten-linked pentosans
were considered to have a steric hindrance effect on gluten coagulation. 82 Currently, indus-
trial xylanases are sold to the starch industry for processes whereby gluten and starch are
separated, which are based on this principle.