Biomedical Engineering Reference
In-Depth Information
and ethyl-acetate produced by
W. anomalus
[
133
] . Fungal contamination was
delayed by 28 days under pilot plant bakery conditions. Although indubitable
progress has been achieved in the making and storage of baked goods, fungal con-
tamination remains one of the main problems in terms of long-term shelf life of
bakery products. The search for novel methods of bio-conservation appears to be
one of the most promising tools in this regard, even though a combination of vari-
ous inhibitory compounds appears to be inevitable to markedly extend the storage
of leavened baked goods.
7.6.2
Antibacterial Compounds from Sourdough
Lactic Acid Bacteria
Antibacterial metabolites from lactic acid bacteria include reuterin and the organic
acids described above. However, the emphasis of research related to antibacterial
activities was placed on bacteriocins, ribosomally synthesized peptides with anti-
bacterial activity against closely related organisms, and reutericyclin. The pre-
vention of bread spoilage by rope-forming bacilli does not require the selection of
specific protective cultures. Growth of endospores of
Bacillus
spp. is readily inhib-
ited by modest acidification as is characteristic for sourdough bread [
134-
136
] .
Acetate and propionate are more effective against rope-forming bacilli than lactic
acid [
134
]. Remarkably, the bacteriocins nisin and pedicoin, either included as
additives, or generated in situ by bacteriocin-producing lactic acid bacteria, were
ineffective [
134
] .
Bacteriocin formation by sourdough lactic acid bacteria was described particu-
larly for strains of
L. sakei
,
L. plantarum
and
L. amylovorus
(for a review, see [
137,
138
] )
.
Bacteriocins appear not to be suitable for extending the shelf life of bread but
formation in sourdough fermentation was shown to enhance the stability of sour-
dough microbiota.
Lactococcus lactis
M30, a lacticin 3147-producing strain [
139
] ,
produced a bacteriocin during fermentation. The inhibitory activity persisted under
the low values of pH of sourdough and after thermal treatments that corresponded
to baking temperatures. Similarly, the bacteriocin-producing strain
L. amylovorus
DCE471 persisted for a long time during sourdough propagation [
140
] . The com-
petitiveness of
L. pentosus
2MF8, which synthesized a bacteriocin-like inhibitory
substance [
141
] and
Lc. lactis
subsp.
lactis
M30, which synthesized lacticin 3147
[
139
] were studied during sourdough propagation.
Lactococcus lactis
subsp.
lactis
M30 showed a larger spectrum of inhibition compared to
L. pentosus
2MF8, and did
not inhibit the growth of
L. sanfranciscensis
. After 20 days of back-slopping, the
persistence of
Lc. lactis
subsp.
lactis
M30 inhibited the indicator strain
L. plan-
tarum
20, without interference in the growth of
L. sanfranciscensis
CB1. The above-
described features of bacteriocins, together with the demonstration of the in situ
inhibitory activity, encourage the use of antimicrobial compounds to facilitate the
persistence of the starter cultures and the conditioning of the microbial interactions
that occur during sourdough fermentation.
