Browsing by Subject "exopolysaccharides"

Aflatoxin B1 (AFB1) is a naturally occurring toxic compound produced by various types of fungi. The presence of AFB1 in food and feed can lead to severe illness, which makes it a serious threat to humans and animals. Due to global climate change, the cases of AFB1 contamination in food will increase since high temperature and humidity favour fungal growth and the production of AFB1. The bioavailability of AFB1 can be decreased by adsorption or biotransformation. Adsorption happens by the utilization of different AFB1 binding agents, which can be either mineral and organic or biological adsorbents. Mineral and organic adsorbents are only used in feed since they may also bind to nutrients. Biological adsorbents are being studied more actively since they maintain the nutritional value of the food. Studies show that Lactic acid bacteria (LAB) can be used to bind AFB1 from contaminated foods. The aim of this research was to study the capacity of different LAB (viable and nonviable) to adsorb (bind) AFB1 under different pH conditions. The research first evaluated the binding ability of AFB1 by 13 viable and nonviable LAB strains at pH 7. The best binding strains were selected for further study at pH 3 to mimic gastric pH. The AFB1 binding with cells was performed at 25℃ for 90 min. To determine the binding capacity, the solutions were centrifuged and free AFB1 in the supernatant was extracted with acetonitrile, and quick, easy, cheap, effective, rugged, and safe (QuEChERS) method was used to clean up the samples. AFB1 concentration was determined by ultra-performance liquid chromatography and fluorescence detection (UPLC-FLD). The LAB strains used in this research were shown to have the ability to bind AFB1. Binding efficacy of AFB1 depended on the bacterial strain. Viability and pH also affected the binding ability. All nonviable cells showed better binding ability (44.9–71.3%) compared to the viable cells (29.0–49.4%). The strains also had better binding capacity at lower pH regardless of the cell viability. The highest binding efficacy (71.3%) was achieved by the nonviable cell of Lactobacillus helveticus FAM 22155 at pH 3. The results of this thesis showed that some LAB strains bind AFB1 and that the binding is stable under stomach conditions. Studies to investigate the stability of the binding under simulated upper and lower gastrointestinal (GI) tract conditions (in vitro digestion) and in vivo studies are needed in order to provide further evidence of the applicability of LAB in lowering the bioavailability of AFB1.

Partial replacement of wheat flour with faba bean flour enhances the nutritional quality of wheat bread, but simultaneously weakens the gluten network, decreases the bread volume and increases bread hardness. The flour can be fermented with lactic acid bacteria, capable of producing exopolysaccharides (EPS), to improve the technological properties for baking. The aim of the research was to produce a bread rich in protein by replacing 30 % of the wheat flour with faba bean flour, which was fermented by EPS-producing Weissella confusa or Leuconostoc pseudomesenteroides -lactic acid bacteria to improve the baking quality. The effect of native and fermented faba bean flour to the properties of dough and bread was studied. Water absorption and rheology of the dough was analyzed with farinograph and Kieffer test of Texture Analyser. The volume of the breads was measured by rapeseed replacement method, and the texture of the breads by using TPA-test of Texture Analyser. The protein content of the total energy value of the bread was determined by calculations. As expected, native faba bean flour decreased the stability and elasticity of the dough compared to the 100 % wheat dough. The volume of wheat - faba bean bread decreased 11 % and the crumb texture was 38 % harder compared to the wheat bread. Fermentation of faba bean flour increased the water absorption and decreased the extensibility of the dough compared to the dough with native faba bean. Fermentation with W. confusa increased the bread volume by 21 % and decreased the bread hardness by 12 % compared to the breads with native faba bean. The volume of the breads with W. confusa-fermented faba bean was increased by 8 % even compared to the 100 % wheat bread. Yet the breads fermented with L. pseudomesenteroides had considerably decreased volume (-15 %) and increased hardness (+116 %) compared to the breads with native faba bean. The difference was hypothesized being caused by more intense acidification and possibly the different structure and amount of EPS. In this study 30 % of wheat flour was successfully replaced with faba bean, resulting a bread rich in protein and with a texture similar to 100 % wheat bread, as the faba bean flour was fermented with EPS-producing W. confusa -lactic acid bacteria. New methods for analyzing the rheology of EPS-containing dough would be beneficial for estimating the baking quality.

Faba bean flour is a sustainable and relatively inexpensive way to make protein rich food in comparison with meat products, because it has high proteins content (rich in lysine (30%)) and considerable amounts of vitamins, minerals and dietary fibre. Even rough faba bean is widely cultivated and consumed, few data is available concerning the suitability to be fermented. The objective of this master’s thesis was to study the potential of sourdough fermentation of faba bean with selected lactic acid bacteria for in situ production of dextrans as texture forming components for various food applications. In this study, the growth and dextran formation by Leuconostoc and Weissella in faba bean sourdoughs were investigated. Eight lactic acid bacteria belonging to genera Leuconostoc and Weissella characterized for slime formation were used as starters for in situ formation of exopolysaccharides in faba bean flour. The growth of lactic acid bacteria, pH and acidity, and viscosity of different sourdoughs were analyzed. An enzyme assisted method and acid hydrolysis were used to analyze dextran content with further quantification by HPAEC-PAD. The amount of dextran formed by Leuc. pseudomesenteroides DSM 20193, Leuc. mesenteroides subsp mesenteroides LMG 7939, Leuc. Citreum DSM 5577, W. cibaria LMG 17699, and W. cibaria Sj1b varied from 1.86 to 4.22 g kg-1 (wet weight), which allows the possibilities to use dextran as alternatives for hydrocolloids in food applications. The synthesized dextran increased significantly viscosity of sourdoughs. After fermentation, the amount of raffinose family oligosaccharides (RFO) were decreased. The results of the sourdough fermented faba bean flours showed that Leuc. pseudomesenteroides DSM 20193 and Leuc. Mesenteroides subsp mesenteroides LMG 7939 were the most potential strains to produce dextrans and increase viscosity properties.