Cristina Ferrero

Effect of hydrocolloids on starch thermal transitions, as measured by DSC

Differential scanning calorimetry (DSC) was used to analyze the influence of different hydrocolloids (xanthan, guar, and locust bean gums, carboxymethylcellulose and sodium alginate) on the gelatinization of corn starch in systems with starch concentration ranging between 0.1 and 0.7 g starch/g mixture. The reduction of available water produced a shift in gelatinization temperature, especially of the conclusion temperature. The effect was more marked for ionic hydrocolloids. The influence of hydrocolloids on glass transition temperature (Tg) of gelatinized starch suspensions and on the glass transition temperature of the maximally freeze-concentrated solute/unfrozen water matrix (T′g) was also studied.T′g onset values ranged between −4.5 and −5.5‡C for corn starch pastes with and without hydrocolloids. Those hydrocolloids that increased the viscosity of the unfrozen matrix inhibited additional ice formation during thawing (devitrification).Starch concentration and final heating temperature were found to be relevant factors affecting the kinetics of amylopectin retrogradation during frozen storage at −4‡C. Xanthan gum failed to prevent amylopectin retrogradation; this observation could be attributed to the fact that gums act outside the starch granule, while amylopectin retrogradation takes place within the granule.

Pectins as Breadmaking Additives: Effect on Dough Rheology and Bread Quality

The effect of two types of pectins with different degrees of esterification on dough and bread characteristics was analysed. A high methoxyl pectin (HMP) and a low methoxyl pectin (LMP) were assayed in dough without or with salt (2%) at levels ranging from 0.25% to 2.0%. Farinographic water absorption increased when pectins were incorporated in dough with salt, whereas this effect was not observed in dough without salt. Pectin addition diminished the stability of dough in all cases. Texture profile analysis showed that pectins softened the dough, particularly when salt was added. Cohesiveness was also higher in doughs with salt at the maximum level of hydrocolloid addition. In dough with salt, HMP decreased the elastic and viscous moduli, while the values for tan (δ) were increased with respect to control. SEM micrographs showed that dough with pectin has a filamentous structure. In the breadmaking process, dough with HMP showed a better performance, leading to higher specific volumes and softer crumbs both in fresh and stored bread.

Enzymes Action on Wheat–Soy Dough Properties and Bread Quality

High levels of soy flour added to wheat bread produce negative effects on gluten network formation, dough properties, and on bread final quality. The objective of this study was to assess the influence of three enzymes, transglutaminase (TG), glucose oxidase (GOX), and endoxylanase (XYL), on dough properties and final quality of high-protein breads. The addition of TG and GOX increased the mixing stability and maximum resistance of dough, decreased its extensibility, and produced stronger and more consistent dough samples. XYL incorporation produced opposite results. XYL addition and the lowest GOX dose increased bread volume significantly and decreased initial crumb firmness, while high doses of TG (0.3%) produced detrimental effects on bread volume and crumb firmness. In conclusion, XYL and GOX 0.001% addition improved the final quality of soy-fortified breads, but XYL was the best additive to improve dough properties, bread volume, and quality.

EFFECT OF MIXING TIME ON STRUCTURAL AND RHEOLOGICAL PROPERTIES OF WHEAT FLOUR DOUGH FOR BREADMAKING

The effect of mixing time on two Argentinean commercial flours (FI and FII) was studied. Both flours showed a similar electrophoresis profile but different content of free sulfhydryls. Rheology of dough obtained from flours (DI and DII) revealed that DI presented a more elastic matrix. FI required more than 8 min for an optimum development of gluten, while DII was already fully developed (development time: 7.3 min). Up to 16 min of mixing, DI matrix maintained the sheet like structure while DII showed a more filamentous one, characteristic of a weak and over kneaded dough. This weakness of gluten network obtained from FII was accompanied by a depolymerization process.

Rheological and Microstructure Characterization of Composite Dough with Wheat and Mesquite (Prosopis spp) Flours

Rheological behavior and microstructural characteristics of composite dough with wheat and mesquite flours (from Prosopis alba) were analyzed by response surface methodology. A central composite design was applied varying proportions of water (50 to 80 g each 100 g wheat flour) and mesquite flour (0 to 70 each 100 g wheat flour). Texture profile analysis showed that increasing the amount of mesquite flour and decreasing the amount of water led to less cohesive and more resilient doughs. Stress relaxation curves were fitted with a Maxwell model and relaxation times were obtained. These parameters resulted higher for those formulations low in mesquite content and high water levels. Composite dough showed a typical viscoelastic behavior with higher elastic moduli (G’) when mesquite flour ratio in the mixture was increased. 1H-RMN T2 relaxation assays revealed higher mobility in samples with high amounts of water and minimum level of mesquite. A farinograph was adequate to obtain optimum water amounts and showed that addition of mesquite led to less stable dough respect to control wheat dough. By using confocal laser scanning microscopy with fluorescent probes rhodamine B and fluoresceine isothiocyanate, a poor gluten network development or protein aggregation was observed when water contents were far from optimum.

Wheat Varietal Flours: Influence of Pectin and DATEM on Dough and Bread Quality

The effect of two additives, high methoxyl pectin (P) and the emulsifier diacetyl tartaric acid esters of monoglycerides commonly named DATEM (D) and their mixture (P+D) on dough properties and baking performance of two varietal Argentinean wheat flours (‘Buck Pronto’ [BP]; ‘Klein Escudo’ [KE] was analyzed. Rheological characterization of dough (alveogram, farinograms, texture profile analysis-TPA, and rheometric assays), with and without additives, was performed. SEM was used to evaluate the microstructure of dough. Baking performance was analysed by bread volume measurements, shape ratio of loaves (width/height), and the hardness of crumb and crust. Assays on dough showed differences in alveographic force (W) and in most of the texture profile analysis parameters. Assays on bread showed that BP specific volume was improved with the addition of P and P+D, but shape ratio was only improved with the mixture of P+D. Breads from KE flour with additives presented, in all cases, showed higher volumes and a better shape ratio than those obtained with the control sample. Hardness of KE crumb was diminished by all additives but BP crumb was softened only with the addition of P and P+D. All sensory parameters were improved for both types of bread, particularly with D and P+D.

A Comparative Study of Commercial Modified Celluloses as Bread Making Additives

The effect of commercial modified celluloses: microcrystalline cellulose, carboxymethyl cellulose, and hydroxypropylmethyl cellulose on bread quality attributes and their potential protective effect with respect to bread staling were analyzed. Two levels of gums were assayed (0.5 and 1.5 g/100 g flour). The best performance was obtained with carboxymethyl cellulose and hydroxypropylmethyl cellulose F 4 M at both levels; these gums led to higher specific volumes and a better crumb texture as measured by texture profile analysis. In general, crumbs were softer, more cohesive, and resilient and exhibited lower chewiness values. Other gums like microcrystalline cellulose and hydroxypropylmethyl cellulose F50 did not improve bread quality on the same extent. Mechanical spectra obtained by dynamic mechanical analysis assays indicated a marked change in molecular mobility when carboxymethyl cellulose was present. Bread staling was evaluated by texture profile analysis, moisture loss, and calorimetric assays. Gums did not avoid retrogradation and even exhibited an accelerating effect, probably due to changes in water retention and migration during storage. However, in most cases, final crumb hardness in samples with hydrocolloids was lower than that in the control sample.