Alba S. Navarro

Effect of freezing rate on the rheological behaviour of systems based on starch and lipid phase

Abstract Starch gelatinized pastes with a lipid phase are important components of precooked frozen foods. These non-equilibrium systems undergo rheological modifications on freezing. The effect of freezing rate was analysed on different formulations containing wheat flour and com and wheat starches, shortening and xanthan gum. Gelation characteristics of the pastes were also studied. The viscoelastic behaviour of the formulations was analysed by their transient shear stress curves (τ versus time) obtained with a rotational viscometer. The Bird-Leider model fitted the experimental curves satisfactorily. Viscoelasticity and relaxation time parameters from the model quantified the rheological changes. High freezing rates maintained the textural characteristics of the unfrozen samples. Low freezing rates increased the viscoelasticity of the pastes and decreased their apparent viscosity. These changes would reduce consumer acceptibility of the product. Wheat proteins were responsible for the better performance of frozen wheat flour pastes. No effect of freezing rate was observed when xanthan gum was added to the pastes. Thus, the presence of the stabilizer (0.3%) reduces the negative effect of low freezing rates without losing product quality.

A comparative study of texture and rheology of Argentinian honeys from two regions

The rheological and textural properties of 26 eastern Argentinian honeys from two different regions (North and Central) were investigated. The viscosity curves of the samples were obtained using a rotational rheometer over a temperature range of 10 to 50C. The viscosity decreased with temperature and all honeys showed a Newtonian behavior. The temperature dependence of viscosity was described using the Arrhenius, Williams-Landel-Ferry, Vogel-Taumman-Fulcher, and Power Law models. The glass transition temperatures of honeys were measured with differential scanning calorimetry and values ranged from -42.63 to -47.71C. The glass transition temperature was also predicted with the Williams-Landel-Ferry model and no significant differences were observed with the experimental results. Rheological parameters were obtained by small amplitude oscillation experiments. Results indicated that the viscous modulus was higher than the storage modulus within all the frequency ranges assayed and honeys from the North region were more viscous. Results of the back extrusion test showed that honeys from the Central region are harder and both groups of honeys (North and Central) exhibited the same consistency and adhesivity. PRACTICAL APPLICATIONS The honey chain production starts with the extraction of the product from the combs, pumping it through pipes and finishes at the packaging of the product. During all these stages, honey viscosity is a key parameter to ensure proper processing and quality control, preventing the waste of economic resources. Determining honey viscosity is of great importance for the industry to select the equipment such as pumps, mixers, filters, centrifuges, heat exchangers, and optimization of industrial processes. The rheological and textural properties of honey are very important in terms of applications related to quality control and authenticity of honeys. Honey authenticity increases the trust of consumers to certified food products. Argentina is one of the leading honey producers and exporters in the world, but information on the rheological, thermal, and textural characteristics of Argentinian honey is very poor in the scientific literature.

Obtention and characterization of dried gels prepared with whey proteins, honey and hydrocolloids mixture: Development and characterization of a whey protein-honey-hydrocolloid snack

BACKGROUND Large amounts of honey and liquid whey derived from the dairy industry are produced in Argentina. Honey is exported in bulk and whey is transformed into whey protein concentrates and isolates. The objective of this work was to investigate the effect of pH, composition and storage time on the properties of dried gels with honey, whey proteins and hydrocolloids. RESULTS Color properties varied according to pH and composition. The fracture stress of dried gels prepared with corn starch was higher than that of gels prepared with guar gum in all conditions assayed. Youngs modulus was higher at pH 7 for both compositions and increased with storage time. Rubbery characteristics were found in dried gels with guar gum, while both corn starch and guar gum made the microstructure rougher. Multivariate analysis showed that samples could be grouped by pH. Panelists preferred pH 7 products over acidic ones, and no significant differences in sensory properties were found using either corn starch or guar gum in the formulation. CONCLUSION The results demonstrated that it is possible to generate a new product, which may open new applications for honey and whey in food formulations.