Digestibility of starch and protein in fonio sourdough bread

Highly glycemic index of wheat bread causes rapid increase of blood glucose level which is harmful for people with chronic diseases such as type II diabetes and obesity. Consumption of whole grain bread rather than bread from refined wheat flour is an alternative way to reduce the risk of chronic disease. In Africa, the occurrence of chronic diseases is on the rise and therefore alternative products based on whole grain flour are needed. Furthermore, due to climate change the smart solution would be to utilize flour from cereal grains that are produced locally rather than being imported. Fonio is one of the oldest cereal in West Africa. Gluten-free fonio is always consumed as whole grain flour which is beneficial for digestion and cardiovascular function. Sourdough fermentation is known as a processing that can influence starch and protein digestibility in bread making. Moreover, sourdough is needed to enhance the quality of whole grain fonio bread. Utilization of sourdough fermentation is a potential method to improve the texture, sensory and nutritional qualities of bread. The aim of this thesis work is to evaluate the protein and starch digestibility of wheat bread with 40% whole grain fonio sourdough. In this study, breads were prepared and used for protein and starch digestibility studies. Freeze-dried samples were used for total starch and protein contents analysis. Moisture content of the breads was also analyzed to calculate the weight of samples needed for in vitro starch and protein digestibility. Pancreatic amylase was used to determine the starch in vitro digestibility. Breads with 1g starch were incubated at 37℃ with continuously shaking after which the reducing sugar content was determined. Glycemic index was calculated based on the starch hydrolysis percent. Protein in vitro digestibility was measured by pepsin and pancreatin. Breads were incubated at 37℃ with constantly shaking. The un-digested protein was determined by Dumas method. The protein digestibility was calculated with the total protein content. Phytate content was tested by the phytate content kit from Megazyme. Compared to wheat bread, fonio breads all had lower starch digestibility. This phenomenon was mainly caused by the wholegrain which increases the content of dietary fiber and enzyme inhibitors. For sourdough bread, there was a slight decrease of starch hydrolysis percent compared to control fonio bread. Sourdough enhanced the solubility of dietary fiber which therefore increased viscosity of chyme. Higher viscosity of chyme affects the glucose uptake and enzyme contact which consequently contributed to reduction of starch digestibility. Furthermore, the produced organic acids especially acetic acid may contribute to the lower starch digestibility of sourdough bread. Glycemic index of sourdough fonio bread was the lowest one among all the bread samples. For protein digestibility, fonio breads all had lower protein digestibility compared to wheat bread. However, there was an increase of protein digestibility by sourdough fonio bread. LAB protein metabolism to get enough nitrogen resources may explain this. The lower content of phytate in sourdough fonio bread may also influence the protein digestibility. In conclusion, sourdough fonio bread has lower starch digestibility than wheat bread and can enhance protein digestibility compared to fonio bread without sourdough.