Browsing by Subject "Viscosity"

Wheat bran is obtained after conventional milling of wheat grains for the production of white flour, which is an important source of dietary fiber, vitamins and minerals, but still remains underutilized in food manufacturing. In spite of the increasing evidence about the health effects of whole-meal and fiber-rich foods, refined white flour is still preferred. Bran also has a negative influence on dough rheology, texture and the sensory quality of bread, which limits its use in bran bread baking. The use of starter culture for sourdough fermentation can drive the fermentation process and confer specific changes on the matrix. Exopolysaccharides (EPS) produced by some lactic acid bacteria (LAB) are important due to their physicochemical properties affecting dough rheology and bread texture, as well as their health-promoting potential. The screening of EPS-producing strains has been carried out mostly on wheat and rye sourdough, and very few studies have considered different matrices. The objective of this work was to determine and compare whole-wheat flour and wheat bran fermentation by two strains of LAB (Leuconostoc spp. and Weissella spp.) in the presence of added sucrose and without, and to study the effect of sourdough obtained with a selected EPS-producing LAB strain on the quality of bread and its shelf-life. Sourdough quality was studied by means of microbiological, rheological and chemical analysis by comparing the growth and acidification performance in the different matrices, and by evaluating EPS production using viscosity measurements. The physical and mechanical properties of fresh bread made using the best EPS producer LAB were investigated to study the product shelf-life by using the seed replacement method and texture analysis test. The results showed that dough prepared with Weissella confusa with added sucrose had a positive impact on viscosity, as well as providing mild acidic sourdough leading to better bread quality properties, whereas in the presence of Leuconostoc pseudomesenteroides, no positive viscosity has observed in whole-wheat sourdough. Bran sourdough samples with Weissella confusa showed a higher volume, better color and shelf-life during storage than samples with un-soured bran, confirming the effect of sourdough and the positive role of EPS on the functional properties of high-fiber bread making.

Cereal β-glucans are soluble non-starch polysaccharides. Both the health benefits and industrial applications of β-glucan have been correlated to its capability of forming viscous solutions. Oxidative degradation has been demonstrated to be the critical factor that causes the viscosity drop of β-glucan solutions. In oats and barley, more than 90% of the phytate was found in the soluble fiber fraction, most of which is β-glucan. Phytate has chelating ability to form phytate-mineral complexes. Therefore, phytate has the potential to suppress iron-catalyzed oxidative reactions and is hypothesized to protect β-glucan from oxidative degradation. The aim of this research was to study the role of both intrinsic and added phytate in the oxidative degradation kinetics of β-glucan. Fenton reaction was used to induce oxidation in both oat β-glucan (OBG) and barley β-glucan (BBG) solutions. Degradation of OBG and BBG was indicated by the decrease in molecular weight and viscosity. When the concentration of hydrogen peroxide kept constant, the extent of OBG degradation was found to be greater with increased iron concentration. Most degradation occurred in the beginning of the oxidation and OBG degradation in the initial 3 hours fitted well in the second order kinetics. The reaction rate constant (k) which stands for the degradation rate demonstrated a positive relationship with the iron concentration. Intrinsic phytate in OBG had a protective effect on β-glucan degradation induced by Fenton reaction. After phytate removal by ion exchange resin, degradation of OBG solution became faster with the same amount of oxidative reagents. As to the degradation kinetics, under the same oxidative condition, the k value increased after phytate removal. Added phytic acid also had a protective effect on the degradation of BBG solution, but the effect was not as strong as the intrinsic phytate in OBG. Furthermore, the strength of the protection was related to the PA/iron ratio. When the PA/ iron ratio was 2:5 , there was no protective effect of added phytic acid observed on the degradation of BBG. When the PA/ iron ratio was 2, the added phytic acid had protective effect. When PA/ iron ratio was 1:5, the added phytic acid had a more profound protective effect. In summary, our results demonstrated that both intrinsic phytate and additional phytic acid had a protective effect against the oxidative degradation of β-glucan. Addition of phytic acid in a proper ratio is of importance to maintain the stability of products containing β-glucan. Phytate or phytic acid is commonly considered as an antinutrient related to the mineral bioavailability in food intake. This study however showed an anti-oxidant effect of phytate in β-glucan solutions which suggests that it may have a beneficial effect in physicological conditions.