Biomedical Engineering Reference
In-Depth Information
12.2
Sourdough and Product Quality
Current knowledge of the effect of carbohydrate metabolism, exopolysaccharide
production, and amino acid conversion allows the targeted selection of starter cul-
tures for improved bread quality (see Chap.
7
). The availability of genome sequences
for sourdough-adapted lactobacilli [
7,
17,
18
] not only furthers the understanding of
the microbial ecology of sourdoughs, but also facilitates the elucidation of addi-
tional metabolic pathways converting amino acids, lipids, and phenolic compounds
and their effect on bread quality. The elucidation of the effect of individual meta-
bolic pathways on bread quality is supported by the development of tools related to
comparative genomics, proteomic and transcriptomic analyses, and the develop-
ment of novel tools for metabolic re-engineering of sourdough lactic acid bacteria
[
7,
8,
18
]. A more comprehensive analysis of the effect of strain-specific metabolic
traits on product quality in combination with a decrease of the expense associated
with genomic analyses for starter cultures will facilitate
in silico
strain selection as
a complement for the evaluation of cultures in application trials.
12.3
Sourdough and Nutrition
The comparison between baked goods made with baker's yeast or chemical leaven-
ing and those made with sourdoughs clearly evidences that sourdough bread is more
digestible and has a higher bioavailability of minerals because substantial degrada-
tion of cereal components (e.g. proteins and phytate) occurs during fermenta-
tion [
19
]. This is already an undisputable reason for the preferred use of sourdough.
However, public policy and industrial product development in developed countries
are no longer predominantly related to the need to meet basic nutritional require-
ments by an increased bioavailability of macro- and micronutrients. In contrast,
nutritional intervention or the formulation of functional food aims to prevent or to
mitigate chronic diseases that are highly prevalent in developed countries. Chronic
diseases that are substantially influenced by diet include inflammatory bowel dis-
ease, diabetes, celiac disease as well as cardiovascular diseases, obesity and the
metabolic syndrome. Consequently, the formulation of functional food products has
become an important component in industrial product development and product
diversification. Examples include gluten-free products, products with reduced
sodium content or an increased level of dietary fibre, and food enriched with anti-
oxidative or bioactive compounds.
Wheat flour-based products such as bread, biscuits and breakfast cereals are
characterized by relatively high values of glycaemic index and insulin index.
Sourdough fermentation or the addition of soluble fibres represent the most promis-
ing tools to decrease starch digestibility and, consequently, the values of glycaemic
index and insulin index. Various mechanisms are responsible for this effect but these
remain to be elucidated in depth [
20,
21
]. Sourdough fermentation represents an
indispensable biotechnology for making wholegrain bread, especially rye bread,
