Flour Type

The flour in the sourdough is the substrate for the fermenting microorganisms. Wheat and rye flour are mostly used for sourdough making, but maize flour can also be used (28,69). The amount of fermentable carbohydrates in the flour varies with the type of cereal, but in particular with the activity of endogenous enzymes in the flour. The activities of amylases, xylanases, and peptidases are important for liberation of the fermentable low-molecular-weight carbohydrates and amino acids. In the dough stage, the a-amylase cannot degrade intact starch granules, but some granules are damaged during the milling process and may be partly degraded in the dough.

Starch is generally not degraded by LAB, and the content of fermentable mono- and disaccharides in rye flour can reach 5%, with maltose (3%) as the main part (70). Savola found that this content of free sugars decreased by 3% during sourdough fermentation.

However, Henry and Saini (71) found only small amounts of low-molecular-weight sugars in rye (0.7% sucrose and <0.1% of glucose, fructose, raffinose, and stachylose). The content of pentosans (arabinoxylans) in rye flour is high (6.5-12.2%) (72) compared to wheat flour (2-3%) (73), and they can be degraded to the pentoses xylose and arabinose by the corresponding enzymes during the bread-making processes (74).

The content of fermentable carbohydrates in wheat flour is 1-2% (67,75). The content of maltose increased during the sourdough fermentation from 1.5 to 2.4%, and the content of fructose from 0.05 to 0.45% in a sourdough fermented with Lc mesenteroides (75). The content of glucose was unchanged at the level of 0.17% as a result of a balance between bacterial consumption and hydrolysis by the enzymatic activity. No sucrose was detected in the samples, so the increase in fructose could not be caused by yeast invertase.

Most Lactobacillus isolated from sourdoughs are nonamylolytic, but amylolytic strains have been isolated from African fermented cereal products made from maize such as ogi, mawe, and kunu-zakki (76).

The extraction rate of the flour is one of the most important factors for determining the character of sourdough (77,78). With a high extraction rate (80-100%), the content of nutrients such as B vitamins and minerals increases compared to low extraction rate flour (65-75%), as does the buffering capacity of the flour primarily due to the phytic acid from the aleurone layer of the cereals. These factors can stimulate the growth and biochemical activity of the microflora in the sourdough, followed by a higher production of acids and flavor compounds. Rye flours have a generally higher extraction rate than wheat flours.

A linear relationship between ash content and TTA was found in wheat sourdough. The final TTA in sourdoughs made from wholemeal flour (ash 1.5%) was almost double the value compared to sourdoughs made from straight-grade flour (ash 0.55%), and the final pH was reached in less time in sourdoughs made from the low extraction flours (3).

Bread Making

Bread Making

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