Accurate information about sourdough is sorely needed. In the UK there is no legal definition of ‘sourdough’ and some unscrupulous manufacturers are exploiting confusion about what it is to sell products that may deliver few, if any, of the benefits claimed for this way of making bread.
As a contribution to clearing the confusion, here are two important summaries of the potential benefits of sourdough bread fermentation from some of the world’s leading sourdough researchers. These benefits depend on the action of sourdough yeasts and lactic acid bacteria during extended dough fermentation (over several hours). They are therefore not delivered by breads containing small additions of dried (often specifically deactivated) ‘sourdough powder’ but not given more than minimal fermentation at the dough stage. Claims, whether direct or by implication, for functional or nutritional benefits from such bread products, are likely to be seriously misleading.
1. Gobbetti M. et al. How the sourdough may affect the functional features of leavened baked goods. Food Microbiology 37 (2014) 30–40
‘Sourdough fermentation may affect the functional features of leavened baked goods…fermentation through sourdough may
- stabilize or increase the functional value of bran fractions and wheat germ
- decrease the glycaemic response of baked goods
- improve the properties and bioavailability of dietary fibre complex and phytochemicals
- increase the uptake of minerals
- produce new nutritionally active compounds, such as peptides and amino acid derivatives (e.g. gamma-amino butyric acid) with various functionalities, and potentially prebiotic exo-polysaccharides.
Wheat flour digested via fungal proteases and selected sourdough lactobacilli has been demonstrated to be probably safe for coeliac patients.’ (edited)
2. Gänzle, M.G. Enzymatic and bacterial conversions during sourdough fermentation. Food Microbiology 37 (2014) 2–10
‘The use of sourdough in bread making influences all aspects of bread quality. The technological effects of sourdough on the flavour, texture, shelf-life, and nutritional quality of bread are dependent on bioconversion of flour components at the dough stage (Table 1).
Two main factors differentiate sourdough processes from straight dough processes. First, the presence of lactic acid bacteria adds the metabolic potential of this heterogeneous group of organisms to the meta- bolic potential of yeasts (Decock and Capelle, 2005; De Vuyst and Neysens, 2005).
Second, the fermentation time of sourdough processes ranges from 8 hours (sponge doughs) to over 144 hours (Brandt, 2007). This long fermentation time compared to straight dough processes allows for a substantial contribution of endogenous enzymes to biochemical conversions at the dough stage.’ (emphasis added)
Role in microbial physiology
Contribution to bread quality
|Carbohydrate conversion and metabolism|
|Metabolic energy (maltose, sucrose)||Texture (starch)|
|Cofactor regeneration (fructose)||Water binding, reduction of staling (starch, pentosans, exopolysaccharides)|
|Protection against environmental insults (oligosaccharides, exopolysaccharides)||Taste and shelf life (organic acids)
Generation of reducing sugars for flavour generation during baking
|Biofilm formation (exopolysaccharides)||Dietary fibre and prebiotic oligosaccharides|
|Protein conversion and metabolism|
|Nitrogen source||Volume (gluten)|
|Metabolic energy (alanine)||Taste and flavour (glutamate, ornithine, other amino acids)|
|Acid resistance (Gln, Glu, Arg)||Bioactive compounds (g-aminobutyrate)|
|Cofactor regeneration (Glu, glutathione); and protection against oxidative stress (Cys)||Bioactive peptides (taste-active, ACE-inhibitory)|
|Conversion of phenolic compounds|
|Metabolic energy (hydrolysis of flavonoid hexosides)||Elimination of anti-nutritive factors (enzyme inhibitors)|
|Removal of noxious compounds||Elimination of bitter taste (tannins)
Increased bioavailability of phenolics as antioxidants
|Metabolic energy (cofactor regeneration)||Control of lipid oxidation (taste, flavour)|
|Membrane homeostasis (synthesis of unsaturated and hydroxy fatty acids)||Formation of antifungal compounds|
The work of Michael Gänzle and Marco Gobbetti and colleagues over many years is gratefully acknowledged by all those trying to make bread that is really better for individuals, their communities and the environment.
Prepared on 20/1/2016 by Andrew Whitley