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Benefits of Sourdough

Starch / Glycaemic Index (GI) and Insulin Index (II)

Dietary carbohydrate is the major source of plasma glucose. An increase in the amount of rapidly digestible carbohydrate in the diet causes a rapid increase in blood glucose levels and a large demand for insulin in the postprandial period. The major carbohydrate sources in the Western diet contain rapidly digestible starch, and many common starchy foods like bakery goods, breakfast cereals, potato products and snacks produce high glycaemic responses. There are strong indications that the large amounts of rapidly available glucose derived from starch and free sugars in the modern diet [foods with high Glycaemic Index (GI) and high Insulin Index (II)] lead to periodic elevated plasma glucose and insulin concentrations that may be a risk factor to health. 

In vitro, native starches are hydrolyzed very slowly, and to a limited extent, by amylases. When starch is used in food processing, starch gelatinization, i.e. the process of disrupting starch crystalline structure with heat and moisture, usually results in a decrease or loss of the slow digestion property of native cereal starches. Gelatinized starch will exist for example in bakery products in a partially or completely amorphous state. Thus, the more gelatinized starch is, the more rapidly it will be digested. In many common starchy foods, such as in regular white wheat bread, the starch is highly gelatinized and product structure very porous, resulting in rapid degradation of starch in the small intestine and a very rapid rise of blood glucose level (high GI).

Several mechanisms have been proposed to be involved in sourdough processing contributing to reduced starch digestibility. Formation of organic acids, especially lactic acid, during fermentation has been suggested to be a main reason. The physiological mechanisms for the acute effects of acids appear to vary. Whereas lactic acid lowers the rate of starch digestion in bread, acetic and propionic acids appear instead to prolong the gastric emptying rate. Chemical changes taking place during sourdough fermentation have been postulated to diminish the degree of starch gelatinization, which would partly explain the lower digestibility of sourdough-fermented cereal foods. Sourdough fermentation has been also shown to promote the formation of resistant starch, which has slower digestibility. 

There also may be other mechanisms for the sourdough to regulate GI/II of the products. pH-dependent proteolysis generally occurs during sourdough fermentation producing significant amounts of peptides and amino acids in the sourdough. These may have a role in regulating glucose metabolism. Furthermore, the results of Katina et al. demonstrate that sourdough fermentation increases the amount of free phenolic compounds, which may also have an impact on lowering the GI/II.

Sources

Kati Katina and Kaisa Poutanen (2013), Chapter 9: Nutritional Aspects of Cereal Fermentation with Lactic Acid Bacteria and Yeast. In: Marco Gobbetti, Michael Gänzle (eds) Handbook on Sourdough Biotechnology. Springer Science+Business Media New York

Barclay AW, Petocz P, McMillan-Price J, Flood VM, Prvan T, Mitchell P, Brand-Miller JC (2008) Glycemic index, glycemic load, and chronic disease risk – a meta-analysis of observational studies. Am J Clin Nutr 87:627–637

Björk I, Granfeldt Y, Liljeberg H, Tovar J, Asp NG (1994) Food properties affecting the digestion and absorption of carbohydrates. Am J Clin Nutr 59:699S–705S

Zhang G, Venkatachalam M, Hamaker BR (2006) Structural basis for the slow digestionproperty of native cereal starch. Biomacromolecules 7:3259–3266

Östman E (2003) Fermentation as a means of optimizing the glycaemic index – food mechanisms and metabolic merits with emphasis on lactic acid in cereal products. Ph.D. thesis, Lund University, Department of Applied Nutrition and Food Chemistry

Zhang G, Sofyan M, Hamaker BR (2008) Slowly digestible state of starch: mechanism of slow digestion property of gelatinized maize starch. J Agric Food Chem 56:4695–4702

Fardet A, Leenhardt F, Lioger D, Scalbert A, Rémésy C (2006) Parameters controlling the glycaemic response to breads. Nutr Res Rev 19:18–25

Liljeberg H, Lönner C, Björck I (1995) Sourdough fermentation or addition of organic acids or corresponding salts to bread improves nutritional properties of starch in healthy humans. J Nutr 125:1503–1511

Liljeberg H, Björck I (1998) Delayed gastric emptying rate may explain improved glycaemia in healthy subjects to a starchy meal with added vinegar. Eur J Clin Nutr 52:368–371

Scazzina F, Del Rio D, Pellegrini N, Brighenti F (2009) Sourdough bread: starch digestibility and postprandial glycemic response. J Cereal Sci 49:419–421

Proteins

Protein degradation (Proteolysis) by sourdough fermentation has been found to be higher than in just yeasted doughs. During dough fermentation, the proteolysis by Lactic Acid Bacteria releases small peptides and free amino acids, which are important for rapid microbial growth and acidification and as precursors for the flavor development of leavened baked products. Furthermore, this proteolytic activity might be used as a tool to reduce certain allergen compounds. Cereal proteins are one of the most frequent causes of food allergies. Wheat proteins may induce a classical allergy affecting the skin, gut or respiratory tract, exercise-induced anaphylaxis, occupational rhinitis or asthma, and protein modification with fermentation offers possibilities to reduce their allergy-causing properties .

Intensive degradation of prolamin of wheat and rye has also opened new possibilities to use these cereals even as part of gluten-free diets. Controlled proteolysis in wheat and rye doughs was suggested to reduce gluten levels to such an extent that the products were tolerated by celiac patients. It was shown in a 60-day clinical trial that biscuits and cakes produced using a hydrolyzed wheat product made using sourdough lactobacilli and fungal proteases were not toxic to patients with celiac disease. By degrading prolamins of wheat or rye with a proteolysis-intensive sourdough process, it is possible to produce good quality gluten free bread with sourdough technology. 

Recently, it has been demonstrated that sourdough fermentation can promote the formation of bioactive peptides. Bioactive peptides are defined as specific protein fragments that have positive effects on body functions or conditions and that may influence human health. Usually, bioactive peptides correspond to specific sequences from native proteins, which are released through hydrolysis by digestive, microbial, and plant proteolytic enzymes, and their levels generally increase during food fermentation. Coda et al. summarized that bioactive peptides, on the basis of in vitro and in vivo studies, have demonstrated a large spectrum of biological functions, such as opioid-like, mineral-binding, immunomodulatory, antimicrobial, antioxidative, antithrombotic, hypocholesterolemic, and antihypertensive activities. The ability of selected lactic acid bacteria to produce antioxidant peptides during sourdough fermentation by using various cereal flours as substrates was demonstrated.

Rizzello et al. exploited the potential of sourdough lactic acid bacteria to release lunasin, an anticarcinogenic peptide, during fermentation of cereal and non-conventional flours. Sourdough-originated lunasin was identified in their study and the concentration of lunasin was shown to increase up to two to four times during fermentation.

Cereal proteins are one of the most frequent causes of food allergies.

Sources

De Angelis M, Coda R, Silano M, Minervini F, Rizzello C, Di Cagno R, Vicentini O, De Vincenzi M, Gobbetti M (2006) Fermentation by selected sourdough lactic acid bacteria to decrease coeliac intolerance to rye flour. J Cereal Sci 43:301–314

Rollán G, De Angelis M, Gobbetti M, de Valdez GF (2005) Proteolytic activity and reduction of gliadin-like fractions by sourdough lactobacilli. J Appl Microbiol 99:1495–1502

Palosuo K (2003) Update on wheat hypersensitivity. Curr Opin Allergy Clin Immunol 3:205–209

Di Cagno R, De Angelis M, Auricchio S, Greco L, Clarke C, De Vincenzi M et al (2004) Sourdough bread made from wheat and nontoxic fl ours and started with selected lactobacilli is tolerated in celiac sprue patients. Appl Environ Microbiol 70:1088e1096

Gobbetti M, Rizzello C, Di Cagno R, De Angelis M (2007) Sourdough lactobacilli and celiac disease. Food Microbiol 24:187–196

Rizzello CG, De Angelis M, Di Cagno R, Camarca A, Silano M, Losito I et al (2007) Highly efficient gluten degradation by lactobacilli and fungal proteases during food processing: new perspectives for celiac disease. Appl Environ Microbiol 73:4499–4507

Greco L, Gobbetti M, Auricchio R, Di Mase R, Landolfo F, Paparo F, Di Cagno R, De Angelis M, Rizzello CG, Cassone A, Terrone G, Timpone L, D’Aniello M, Maglio M, Troncone R, Auricchio S (2011) Safety for patients with celiac disease of baked goods made of wheat flour hydrolyzed during food processing. Clin Gastroenterol Hepatol 9(1):24–29

Coda R, Rizzello CG, Pinto D, Gobbetti M (2012) Selected lactic acid bacteria synthesize antioxidant peptides during sourdough fermentation of cereal flours. Appl Environ Microbiol 78(4):1087–1096

Rizzello CG, Nionelli L, Coda R, Gobbetti M (2012) Synthesis of the cancer preventive peptide lunasin by lactic acid bacteria during sourdough fermentation. Nutr Cancer 64:111–120

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