Reference Number: 16
The stability of vitamers: thiamine, riboflavin, nicotinic acid, nicotinamide, pantothenic acid, pyridoxine and pyridoxal, as well as soluble and insoluble dietary fiber was studied in a rye sourdough bread process. The vitamer concentrations were measured in raw materials (rye flours, white and red rye malt, yeast) and the rye sourdough breads made from them by means of LC–MS and stable isotope dilution assay. The content of dietary fiber was determined using a standard enzymatic-gravimetric method. During baking, the concentration of vitamins decreased by 20–45% in the case of thiamine, 25–50% in the case of nicotinic acid, 45–65% in the case of pyridoxal in both breads, 50% in the case of riboflavin and 15% in the case of pyridoxine only in fine rye bread. In contrast, the content of nicotinamide increased during processing by ten fold, presumably due to microbial activity during sourdough fermentation. The ratio of soluble to insoluble dietary fiber increased during rye sourdough processing.
Significance of the study
Dietary fibre is an indigestible form complex of carbohydrates. It is an important functional component, the content of which can change during rye bread processing. Soluble dietary fibres are those complex carbohydrates that can be broken down by enzymes during the process of digestion. Insoluble fibres are those that cannot be broken down but act as the main source of food to the millions of microbes present within our guts. Rye flour contains more insoluble fibre compared to soluble fibre.
The current study showed that in sourdough fine rye breads, the experimentally measured total dietary fibre was higher than that of the raw materials used and this phenomenon has been observed in other studies as well. The reason for the increase in total fibre could be attributed to the formation of resistant starches (insoluble fibre) during the fermentation and bread-making process. Although the levels of fibre increased, levels of B vitamins decreased in the final bread. This could be due to the effect of high temperatures during the baking process that may result in the degradation of these specific B vitamins.