1,721,179 research outputs found
Staling and water dynamics in high-gluten bread
No full textStaling indicators (texture, amylopectin retrogradation, water status and proton molecular mobility) in a high-gluten bread (25% flour substitution and water absorption at 500 Brabender Unit) were compared to a control during 1 week of storage. The contribution of macroscopic crumb to crust water migration on frozen water, molecular mobility and retrograded amylopectin was evaluated in bread loaves and bread crumb stored in NMR tubes. High-gluten bread was softer and had increased volume, cohesiveness, springiness, moisture and frozen water contents than the control, with comparable amylopectin retrogradation. An increased proton molecular mobility was observed in fresh high-gluten bread. In condition of no occurrence of macroscopic water migration, proton molecular mobility indicated reduced changes in breads during storage, suggesting the important role played by migration in the staling process. These changes were further reduced in the high-gluten bread, indicating an influence of the larger moisture content but also a contribution of gluten in regulating molecular changes
Effect of physico-chemical and molecular mobility parameters on Staphylococcus aureus growth
No full textThe role played by water activity, ‘mobility’ and physico‐chemical properties of the media in modulating microbial response has been the object of large debate in the scientific community. In this study, Staphylococcus aureus growth parameters (lag phase and cell density at 24 h) in brain heart infusion (BHI) and BHI:NaCl (1:1) were analysed in their correlation with physico‐chemical/mobility parameters descriptive of the media [solid content, aw, kinematic viscosity, 17O NMR (R2, Pbw and inline image)]. In these high moisture content, liquid and ‘homogeneous’ media S.aureus growth related to all the physico‐chemical and molecular mobility parameters analysed in a similar manner and it was found to be influenced more significantly by added NaCl than by the physico‐chemical and molecular mobility of the media. Staphylococcus aureus growth parameters correlated better with aw (relatively independent of NaCl concentration) than with any other parameter considered in this study
Effect of Long-Term Storage on Water Status and Physicochemical Properties of Nutritionally Enhanced Tortillas
No full textThe effect of functional ingredients (carrot juice, whole soy flour, and whole kamut flour) and storage (180 days) on physicochemical properties (texture and amylopectin recrystallization) and water status (moisture content, water activity, ice melting peak thermal properties, and proton nuclear magnetic resonance (1H NMR) mobility) of tortillas has been studied. Different formulations significantly changed the parameters studied during storage resulting in larger changes than in the standard formulation (STD) that, therefore, may be considered the most stable product. The properties of whole kamut tortillas were very similar to those of standard sample while the formulation that contained carrot juice lead to an increased system rigidity observable both at macroscopic (textural properties), macromolecular (significantly reduced), and molecular (1H FID) levels. A decrease of moisture content, water activity, endothermic transition ~0 °C, and an increase of 1H NMR mobility (1H T2 pop A and C) were observed in soy-containing products [(soy enriched (SOY) and carrot, soy, and kamut (CSK)]. SOY and CSK had very low water activity, presented the highest 1H NMR molecular mobility and underwent the most marked changes during storage suggesting that water activity cannot be taken as a sole indicator of food stability as very important modifications occurred in tortillas at molecular level
The effect of different convection cooking methods on the instrumental quality and yield of pork Longissimus dorsi
No full textThe effect of different cooking methods (natural convection, NC, forced convection, FC and forced convection/steam combined, FC/S) on selected physical properties of cooked pork Longissimus dorsi samples were compared. FC/S treatment was significantly faster (∼19 min) than NC and FC cooking treatments (∼27 min). The overall cook values at the center of all samples (calculated taking into consideration the cooling phase) were comparable and might explain the similar tenderness found among samples that underwent significantly different thermal histories. The weight loss of the FC/S samples was significantly higher than in the other cooking methods while the color of the surface was paler than the NC and FC ones
Effect of bran on bread staling: Physico-chemical characterization and molecular mobility
No full textHigh fibre breads were produced with the addition of durum wheat bran fractions (regular bran and a fraction extracted from the most internal bran layer) and their physico-chemical properties and water status were characterised during storage. Bran enriched breads exhibited similar properties during storage, they were harder, less springy and less cohesive than the control. Water status was strongly affected by bran addition, independently of bran composition: water activity, moisture and frozen water content (measured by Differential Scanning Calorimetry) were generally higher in the bran samples than in the control bread during storage. Amylopectin retrogradation was significantly larger in the presence of bran fractions. 1H NMR mobility (T2 number of populations and relaxation times) was different in the high fibre breads as compared to the control sample. The changes in protons mobility observed upon storage indicated an influence of bran on water/gluten/starch molecular domains and their dynamics, that may have affected the development of the gluten network resulting in different textural properties
Bread staling: Effect of gluten on physico-chemical properties and molecular mobility
No full textThree gluten enriched breads were produced (5% and 15% gluten samples where water was adjusted with farinograph determination, and a 15% sample with the same water amount of the control). The effect of gluten on bread staling (7 days) was evaluated, focussing on texture, amylopectin retrogradation, water status and 1H molecular mobility.
The addition of gluten at higher levels (15%) resulted in breads, that retained higher softness, springiness and cohesiveness upon storage. Crumb moisture content was not affected by gluten but at a macromolecular level (DSC) 15% samples showed higher frozen water content. NMR measurements showed a significant effect of gluten on proton T2 relaxation time distributions, revealing a larger presence of protons strongly interacting with water and a more pronounced proton exchange with increasing storage time. The results suggested that, in the presence of gluten, a larger amount of water might be available to plasticize the crumb structure, resulting in a softer product
Staling of gluten-free breads: physico-chemical properties and 1H NMR mobility
No full textFour gluten-free (GF) breads produced using commercial GF mixes with different formulations were characterized during 1 week of storage and compared to wheat-flour-based bread (STD), in terms of texture (texture profile analysis), amylopectin retrogradation (differential scanning calorimetry) and water status (moisture content, frozen water content by differential scanning calorimetry and 1H nuclear magnetic resonance—NMR mobility by a low-field spectrometer). GF fresh breads were significantly harder, less cohesive and less springy than STD. Water status indicated higher water availability in GF breads, depending on formulation, with higher moisture and frozen water content that was also reflected in a higher molecular mobility (1H spin–spin NMR relaxation time). Furthermore, limited changes in moisture and frozen water contents were observed in GF bread, and therefore, textural changes in these GF products were mostly related to retrograded amylopectin. Statistical analysis with PCA (principal component analysis) allowed to identify the most important factors in the GF bread staling process. The effect of formulation (GFs vs STD) was related to water status descriptors and the effect of storage to textural properties, retrograded amylopectin parameters, as well as the mobility of the more rigid protons
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