Biomedical Engineering Reference
In-Depth Information
of sourdough into a GF bread mixture was also shown to delay the firming process,
whereas chemical acidification increased the staling rate of the bread ([
44
] ;
Table
10.1
).
Thus, depending on the flour and the starter strains, sourdough fermentation can
be used for controlling the firming process of GF bread. However, the mechanism of
bread staling is still under discussion and virtually no studies address this complex
event in GF formulations. Therefore, more investigations are needed in order to
characterise the activity of flour and bacterial amylases in GF sourdoughs. Through
in depth investigations, it will be possible to identify the best process conditions for
retarding staling of GF bread by application of sourdough, i.e. type and amount of
added sourdough and its combination with commercial amylases and/or malts.
10.8
Sourdough as a Natural Tool for Improving
the Shelf Life of GF Bread
The distribution of dust and mould spores in the bakery environment is the main
cause of bread spoilage [
111
]. Bread spoilage represents a main issue for the baking
enterprises, in so far that it induces economical losses and health risks for the
consumers. The most common bread spoilage moulds are
Aspergillus
,
Cladiosporum
,
Endomyces
,
Fusarium
,
Monilia
,
Mucor
,
Penicillium
and
Rhizopus
[
111
] . An effec-
tive and natural way to improve the shelf life of bread consists in the application of
sourdough. Sourdough-associated LAB can produce various substances with anti-
fungal properties [
112,
113
]. Heterofermentative LAB release anti-fungal organic
acids, among which acetic and propionic acids are more effective than lactic acid
[
113
]. A mixture of organic acids, i.e. caproic, acetic, formic, propionic, butyric, and
n
-valeric acids, produced by
L. sanfranciscensis
CB1 were shown to be the main
factors responsible for its anti-mould activity against
Fusarium
,
Penicillium
,
Aspergillus
and
Monilia
[
108
] . Strains of
L. plantarum
were proven to have broad
anti-fungal activity, with 4-hydroxyphenlyllactic and phenyllactic acid being the
major inhibiting compounds produced by the sourdough-LAB [
114-
116
] . Ryan
et al. [
39
] also showed that addition of sourdough fermented with the anti-fungal
strain of
L. plantarum
allowed a reduction of the calcium propionate level in wheat
bread by around 30%, without any negative effects on the shelf life. Reutericyclin is
a low molecular weight antibiotic active against Gram-positive LAB and yeasts
produced in active concentrations by
L. reuteri
[
117
] . In addition,
L. reuteri
strains
can produce reuterin, an anti-microbial substance active against bacteria, yeasts and
fungi (reviewed by [
118
]). Sourdough LAB are also effective against rope spoilage
induced by
Bacillus
spp., because of production of organic acids and other unknown
anti-bacterial compounds [
119,
120
] .
Research on the application of sourdough for prolonging the shelf life of GF
breads is still in its infancy. Recently, Moore et al. [
44
] employed sourdough (20%)
fermented by the anti-fungal strain
L. plantarum
FST 1.7 in a composite GF bread
(Table
10.1
).
Lactobacillus plantarum
FST 1.7 retained its inhibitory activity against
