Fermentazione pasta acida (IV parte)
Reologia della pasta acida: influenza dei Lattobacilli
“Effects of LAB to dough structure
The structural effects of sourdough in wheat-based system may first be due to the direct influence of low pH on structure-forming dough components, such as gluten, starch, arabinoxylan etc. (Angioloni et. al., 2006). Dough is very sensitive to changes in ionic strength and pH and such changes could have direct impact on the constituents of dough (Clarke et al., 2002). The drop in pH value caused by the produced organic acids influences the viscoelastic behaviour of dough. A correct description of the changes in dough behaviour is necessary to maintain handling and machinability in industrialized production (Wehrle et. al., 1997). A number of earlier studies have examined influence of acids and different pH values on the dough properties. All of these confirmed that changes in the absolute pH value of sourdough significantly influence sourdough components.
The pH profile may affect the time frame during which the acid influences the constituent ingredients of the dough. The changing pH values during sourdough fermentation period may also afford passage through a range of pH values close to the optimum for various enzymes present in the dough system. It is so-called secondary (indirect) effect of sourdough acidification (Clarke et al., 2004). The activity of proteolytic and amylolytic enzyme present may be influenced to a greater degree by the pH profile of the biological acidification fermentation period in contrast to the rather instantaneous nature of the chemically acidified regime. Optimum activity of these enzymes, which play significant role in changes of dough constituents, achieve optimum activity at pH 4-5 for the proteolytic and pH 3.6 – 6.2 for the amylolytic enzymes (Belitz & Grosh, 1992). Other enzymes that might affect the structural components of the dough the activity of which is pH dependent include peroxidases, catalases, lipoxigenases and polyphenol oxydases (Belitz & Grosh, 1992; Clarke et. al., 2002). Results obtained by the the fundamental rheological tests, baking tests, and farinograms show that activity of some enzymes in the biologically acidified dough led to structural changes in the dough (Corsetti et. al., 2000; Clarke et. al., 2002; Clarke et. al., 2004). Corsetti et. al. (2000) also reported that even limited photolytic degradation of wheat proteins affects the physical properties of gluten, which in turn can have a major effect on bread firmness and staling.
Gas production during fermentation of sourdough has been marked as a one of the most important parameters to affect on sourdough structure and rheology. Hammes and Gänzle (1998) have noted that the contribution of yeasts and LAB to the overall gas volume differs with the type of starters and the dough technology applied. These authors have also reported that gas formation by the sourdough microflora is only of minor importance if baker’s yeast added. Clarke et. al. (2002) proved that the amount of gas produced by the sourdough microorganisms does not contribute remarkably to the increase in loaf specific volume. However, Hammes & Vogel (1995) indicated certain differences connected to the type of used LAB starter. Thus, obligately heterofermentative Lb. pontis significantly higher influenced to the gas formation in sourdough than facultatively hetrofermentative Lb. plantarum. (A Grounded Guide to Gluten: How Modern Genotypes and Processing Impact Wheat Sensitivity – Chapter Fermentation and microbial enzymes – Lisa Kissing Kucek, Lynn D. Veenstra, Plaimein Amnuaycheewa, and Mark E. Sorrells. Comprehensive Reviews in Food Science and Food Safety Vol. 14, 2015).”
Authors have argued that the most important contribution of sourdough fermentation is not the microbial protease activity, but lowering of the pH to levels optimal for wheat endoprotease activity (Hartmann and others 2006; Ga ̈nzle and others 2008; Lopo- nen and others 2009). Cysteine proteases operate in a pH range of 3 to 6, with optimal gliadin hydrolysis at 4.25 (Bottari and others 1996). A pH of 4.0 allowed more of the 33-mer degradation in wheat, emmer, einkorn, and rye, although degradation in bar- ley was more efficient at pH 6.5. Similarly, the optimal pH for yeast enzymatic activity in degrading wheat fructose was 4.5 to 5 (Nilsson and others 1987). Escriva and Martinez-Anaya (2000) demonstrated that the fructosan degradation in 2 sourdough cul- tures was related to the culture’s acidification ability. Acidic conditions alone can help degrade prolamins in wheat and rye (Kanerva 2011). (A Grounded Guide to Gluten: How Modern Genotypes and Processing Impact Wheat Sensitivity – Chapter Fermentation and microbial enzymes – Lisa Kissing Kucek, Lynn D. Veenstra, Plaimein Amnuaycheewa, and Mark E. Sorrells. Comprehensive Reviews in Food Science and Food Safety Vol. 14, 2015).”
“Changes in pH values caused by production of lactic acid also influence on the rheological properties of dough (Wehrle et al., 1997). Dough with containing acid has been characterized by increased phase angle and reduced complex modulus indicative of overmixing (Wehrle et al 1997). Small physical and chemical changes in the gluten network can result in significant changes in rheological properties. Clarke et al. (2002) were concluded that addition of sourdough prepared either from a single strain starter culture or a mixed strain starter culture had significant impact on the rheological properties of wheat flour dough. Koceva Komlenić et al (2010) investigated the influence of chemical and biological acidification on dough rheological properties. According to their experimental results, rheological properties strongly depend on acidification type. Dough with lower pH value showed less stability during mixing, decreased extensibility and gelatinization maximum. In general, the rheological properties of dough greatly improved when the sourdough was added. Influence of Acidification on Dough Rheological Properties Daliborka Koceva Komlenić, Vedran Slačanac and Marko Jukić Faculty of Food Technology, Josip Juraj Strossmayer University of Osijek, Croatia 2012- www.intchopen).”