Epidemiological studies have clearly shown that whole-grain cereals can protect against obesity, diabetes, CVD and cancers. The specific effects of food structure (increased satiety, reduced transit time and glycaemic response), fibre (improved faecal bulking and satiety, viscosity and SCFA production, and/or reduced glycaemic response) and Mg (better glycaemic homeostasis through increased insulin secretion), together with the antioxidant and anti-carcinogenic properties of numerous bioactive compounds, especially those in the bran and germ (minerals, trace elements, vitamins, carotenoids, polyphenols and alkylresorcinols), are today well-recognised mechanisms in this protection. Recent findings, the exhaustive listing of bioactive compounds found in whole-grain wheat, their content in whole-grain, bran and germ fractions and their estimated bioavailability, have led to new hypotheses. The involvement of polyphenols in cell signalling and gene regulation, and of sulfur compounds, lignin and phytic acid should be considered in antioxidant protection. Whole-grain wheat is also a rich source of methyl donors and lipotropes (methionine, betaine, choline, inositol and folates) that may be involved in cardiovascular and/or hepatic protection, lipid metabolism and DNA methylation. Potential protective effects of bound phenolic acids within the colon, of the B-complex vitamins on the nervous system and mental health, of oligosaccharides as prebiotics, of compounds associated with skeleton health, and of other compounds such as alpha-linolenic acid, policosanol, melatonin, phytosterols and para-aminobenzoic acid also deserve to be studied in more depth. Finally, benefits of nutrigenomics to study complex physiological effects of the 'whole-grain package', and the most promising ways for improving the nutritional quality of cereal products are discussed.

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New hypotheses for the health-protective mechanisms of whole-grain cereals: what is beyond fibre?

Impact of sourdough on the texture of bread.

The production of sourdough bread can be traced back to ancient times. Sourdough is a mixture of flour and water that is fermented with lactic acid bacteria (LAB). Sourdough is an intermediate product and contains metabolically active yeast and LAB strains. The LAB that develop in the dough may originate from selected natural contaminants in the flour or from a starter culture containing one or more known species of LAB. Sourdough can be produced in bakeries or obtained from commercial suppliers. The microbial ecology of the sourdough fermentation is determined by ecological factors. Microbiological studies have revealed that more than 50 species of LAB, mostly species of the genus Lactobacillus, and more than 20 species of yeasts, especially species of the genera Saccharomyces and Candida, occur in this ecological niche. The sourdough microflora is composed of stable associations of lactobacilli and yeasts, in particular due to metabolic interactions. As shown for certain industrial sourdough processes, such microbial associations may endure for years, although the fermentation process runs under non-aseptic conditions. A reproducible and controlled composition and activity of the sourdough microflora is indispensable to achieve a constant quality of sourdough bread.

The sourdough microflora: biodiversity and metabolic interactions

Culturalable and non-culturable microorganisms naturally ferment majority of global fermented foods and beverages. Traditional food fermentation represents an extremely valuable cultural heritage in most regions, and harbors a huge genetic potential of valuable but hitherto undiscovered strains. Holistic approaches for identification and complete profiling of both culturalable and non-culturable microorganisms in global fermented foods are of interest to food microbiologists. The application of culture-independent technique has thrown new light on the diversity of a number of hitherto unknown and non-cultural microorganisms in naturally fermented foods. Functional bacterial groups ("phylotypes") may be reflected by their mRNA expression in a particular substrate and not by mere DNA-level detection. An attempt has been made to review the microbiology of some fermented foods and alcoholic beverages of the world.

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Review: Diversity of Microorganisms in Global Fermented Foods and Beverages

Lactobacilli in sourdough fermentation

Cereals are globally number one as food crops as well as substrates for fermentation Well known products are beer, sake, spirits, malt vinegar, and baked goods made from doughs leavened by yeasts or sourdough Fermentation processes are enabled by technological measures that act on the metabolically resting grains and direct ecological factors controlling the activity of lactic acid bacteria and yeasts Fermentable substrates originate from endogenous or added hydrolytic enzyme activities Examples of their management are malting, koji technology, addition of enzymes from external sources and sourdough, which stands on the origin of all fermentation When sourdough is continuously propagated under the conditions applied in bakery practice, a stable association of only few species of lactic acid bacteria (LAB) and yeasts achieve dominance and ensure a controlled process The variation of the ecological parameters acting on the microbial association such as the nature of cereal, temperature, size of inoculum, and length of propagation intervals leads in each case to a characteristic species association, thus explaining that altogether 46 LAB species and 13 yeast species have been identified as sourdough specific

Microbial ecology of cereal fermentations

Adaptability of lactic acid bacteria and yeasts to sourdoughs prepared from cereals, pseudocereals and cassava and use of competitive strains as starters.

The performance of Lactobacillus sanfranciscensis TMW 1.392 and its levansucrase deletion mutant TMW 1.392 Δlev in wheat dough was compared. The effects of both strains on dough and bread characteristics were determined in order to find benchmarks for in situ production of exopolysaccharides (EPS). Growth and acidification were lower in doughs prepared with the Δlev mutant than in those employing the wild type. Extensogram resistance of the dough was reduced and extensibility increased with the addition of L. sanfranciscensis levan. Added EPS positively influenced water absorption, bread volume and firming of the crumb. In situ production of EPS was not sufficient to achieve the same positive effects of EPS, as they partially overlapped with effects resulting from enhanced acidification. Control doughs were made to separate effects of predough, EPS and different metabolism/acidification. High acetic acid levels decreased extensibility and volume. High lactic acid levels negatively influenced crumb hardness and firming kinetics. The use of knock out mutants proved helpful to judge overall performance of a strain, although the interpretation of specific effects must consider all changes in its metabolism.

Performance of Lactobacillus sanfranciscensis TMW 1.392 and its levansucrase deletion mutant in wheat dough and comparison of their impact on bread quality

The effect of crude exopolysaccharides (EPS) of Lactobacillus sanfranciscensis strains on processing properties of wheat doughs was investigated and compared to the commercial available hydrocolloids guar gum and xanthan using straight dough method. In addition, the effect of swelling process occurring during fermentation and of in situ formation of levan on dough and bread properties was determined. The doughs supplemented with levan showed higher water absorption and lower stickiness than those supplemented with guar gum and xanthan. However, F(max) and l(max) resulting from extensibility measurements as well as peak viscosity during gelatinization were less affected. The use of chemically acidified sponge doughs resulted in increased stickiness and changes in the extension properties of the wheat doughs with decreasing pH. These negative effects were compensated by the addition of crude levan extracts. Addition of sourdoughs markedly decreased their stickiness but not their F(max) and l(max) resulting from extensibility measurements, as compared with chemically acidified sponge doughs. Enhanced in situ production of levan increased dough stickiness as well as increased resistance and decreased extensibility. This effect could be traced back to an enrichment of sugar or metabolites due to an altered metabolism of the bacteria. Breads produced from straight doughs supplemented with levan showed higher volumes as compared to commercial hydrocolloids.

Michael Seitter

Papers

Microbial ecology of cereal fermentations

Adaptability of lactic acid bacteria and yeasts to sourdoughs prepared from cereals, pseudocereals and cassava and use of competitive strains as starters.

Performance of Lactobacillus sanfranciscensis TMW 1.392 and its levansucrase deletion mutant in wheat dough and comparison of their impact on bread quality

Effect of exopolysaccharides produced by Lactobacillus sanfranciscensis on the processing properties of wheat doughs