Biomedical Engineering Reference
In-Depth Information
Sourdough microbiota and the lactic microbiota of the intestine of humans and
animals show remarkable overlap, indicating that intestinal lactobacilli are a poten-
tial source of sourdough-adapted strains [
1
]. The substrate availability of the upper
intestine of mammals that consume cereal-based foods, the major site of coloniza-
tion by lactobacilli in swine, poultry and rodents [
6
], is remarkably similar to sour-
dough. Sucrose and maltose are the major carbon sources and carbohydrate
metabolism by sucrose phosphorylase or levansucrase and maltose phosphorylase
contributes to the ecological fitness of lactobacilli. The intestinal origin of sour-
dough strains was recently demonstrated for
L. reuteri
, which is both a gut symbiont
and a stable member of sourdough microbiota [
1,
7
] . Several
L. reuteri
lineages
have evolved to become specific for their respective hosts, i.e. humans, swine, poul-
try or rodents [
7
]. Multi-locus sequence analysis and analysis of host-specific physi-
ological and genetic traits assigned five
L. reuteri
isolates from back-slopped
sourdoughs to rodent- or human-specific lineages. Comparative genome hybridiza-
tion revealed that the sourdough isolate
L. reuteri
LTH2584 is genetically highly
related to the rodent isolate
L. reuteri
100
-
23. Taken together, these results demon-
strate that sourdough isolates of
L. reuteri
that persisted in a back-slopped sour-
dough for over 50,000 generations initially originated from intestinal microbiota
[
8
] . Likewise,
L. rossiae
,
L. pontis
and
L. fermentum
were described as stable mem-
bers of intestinal and sourdough microbiota [
9
], and sourdough isolates of these
species may also originate from the intestine of animals.
The overlap of intestinal and sourdough microbiota allows the development of
probiotic cereal products employing probiotic lactobacilli as starter cultures. Vellie,
oat bran fermented with probiotic lactobacilli, provides a conceptual template for
such products [
10
]. Mesophilic lactobacilli are unlikely to originate from the intesti-
nal tract of mammals. However,
L. sanfranciscensis
was isolated from the intestinal
tract of fruit flies [
11
], which may provide a ubiquitous reservoir for the species.
Wheat and rye sourdoughs exhibit similar microbiota; their composition and
activity depends mainly on the process conditions (see Chap.
5
). Durum wheat sour-
dough, commonly used for bread baking in Southern Italy, was suggested to select
for obligate heterofermentative lactic acid bacteria owing to the higher levels of
maltose, sucrose and amino acids [
12
]. Moreover, cereal fermentations in Africa
and South Asia predominantly use sorghum, millet, corn, rice, or teff as raw materi-
als [
13
]. The dominant species of lactic acid bacteria in fermentations with these
substrates only partially overlap with wheat and rye sourdoughs [
14,
15
] . The higher
ambient temperature in tropical climates selects for thermophilic microbiota.
Substrate-derived factors such as the carbohydrate availability and the presence of
antimicrobial phenolic compounds also contribute to the establishment of divergent
and substrate-specific microbiota. However, the specific effect of the raw materials
on the microbial ecology of sourdough is currently not fully understood. The
industrialization of food production in developing countries will result in a more
standardized fermentation process and the production of starter cultures (see e.g. [
16
] ),
paralleling the development in the European baking industry in the past decades.
This development will also lead to an improved understanding of the microbial
ecology of cereal fermentations in tropical climates.
