Physico-chemical and sensory properties of yogurt from ultrafiltreted soy milk concentrate added with inulin

The total solids required for yogurt preparation were obtained by soy milk microfiltration and ultrafiltration. Inulin was incorporated at the level of 20–70 g/L, and the soy milk containing inulin was fermented using conventional microorganisms. The chemical, physical and sensory properties of the products were evaluated. The membrane concentration of soy proteins leads to yogurts with an increase of 59 g/L of proteins and 15 g/L of vegetable fats, reducing ash and anti-nutrients content. The clot had high stability and protein concentration generated a buffer effect smoothing the acidity and the flavor obtained is more agreeable. In addition, the proteins were concentrated without thermal treatment. As the inulin content increased, creaminess and viscosity increased as well. The products prepared presented nice smell, flavor and color, being the sample with higher global acceptability the yogurt with 50 g/L of inulin (P < 0.05).     

A new amperometric biosensor for fructose determination based on epoxy-graphite-TTF-TCNQ-FDH-biocomposite

In this work a novel amperometric biosensor for fructose determination in solutions was developed. The device was constructed by the incorporation of a tetrathiofulvalene-tetracyanoquinodimethane organic conducting salt and fructose dehydrogenase enzyme, include in a polymeric matrix of epoxy resin and graphite powder. Because of the electrocatalytic function of the salt, the direct transfer of the electron between the reduced prosthetic group (PQQH₂) of the enzyme and the transducing material, was verified at a low working potential (150 mV vs. Ag/AgCl), where the interfering reactions were minimized. The response time at 90% of the steady state value was less than 20 s. The current response was directly proportional to the D-fructose concentration from 0.01 to 0.3 mmol/l with a detection limit of 0.005 mmol/l (signal/noise of 3) and a sensitivity of 1.9985 μA/mmol. The biosensor sensitivity diminishes when its surface is not polished between successive determinations, and remains constant (rsd=1.85, n=10) when the surface is polished between determinations. The effects of temperature and pH on the biosensor response were studied and analyzed; also the properties of the enzyme (Km _ap, I _max, Q₁₀) were determinate in this work. The biosensor was used to determine fructose in high fructose syrups and there were not significant differences between these results and those obtained by HPLC (p≤0.05). During 4 months, in intermittent determinations the biosensor kept 100% of its original sensitivity and after 18 months stored at 4°C, it only lost 32% of its sensitivity. The simplicity, low working potential, high stability and good performance of this biosensor shows a great potential for its use in the fructose determination.     

Effect of freezing on physical properties of whey protein emulsion films

The objective of this work was to study the effect of the freezing process on physical properties of whey protein emulsion films with different beeswax content dried at 5 °C. Thickness, microstructure, water vapour permeability, solubility in water, sorption isotherms and mechanical properties were measured in Control and Frozen films. The freezing process did not cause fractures or perforations in films, but films with beeswax showed a change in the appearance of the lipids after freezing. Only films with 40% of beeswax showed a significant increase in the water vapour permeability after freezing. The freezing process did not affect film solubility in water but produced small differences in the equilibrium moisture content values. In the puncture test, the freezing process increased puncture strength and deformation of films without beeswax but those parameters were not affected in films with beeswax. In tensile test, tensile strength and elastic modulus decreased, but elongation was not affected by freezing process. Principal component analysis accomplished an adequate condensation of the date grouping samples according to film formulation and treatment (Control and Frozen films). Indeed, the relationships of sample grouping and measured parameters were enlightened by principal component analysis. In conclusion, whey protein emulsion films were resistant to the freezing process (freezing, frozen storage and thawing) and could be a good alternative as a treatment to preserve the quality of frozen foods.     

Comparison of crumb microstructure from pound cakes baked in a microwave or conventional oven

Imaging, light microscopy and scanning electron microscopy were used to compare the microstructure of crumbs from pound cakes baked in a microwave or conventional oven. The microwave baking conditions for pound cake (240 W, 5 min) were established in previous research, conventional baked pound cakes were obtained using a swing oven at 180 °C for 40 min. Statistical differences in total cell, cell/cm² and mean cell area (P?0.05) were observed in the image analysis. Cells from microwaved pound cake crumbs were 20% larger. However, factor shape was 0.81 for both microwave and conventionally baked crumbs, and crumbs from both oven types were similar in appearance. Light microscopy revealed birefringence in crumbs from both types of pound cakes. Scanning electron microscopy revealed that the conventionally baked product had a greater amount of protein matrix however; the matrix structure of the crumb was comparable between microwave-baked and conventionally baked pound cakes. In conclusion, our results suggest that the unique aspects of pound cake dough, including its high content of fat, sugar and moisture, make it well suited to microwave baking.     

Physical and Antioxidant Characterization of Edible Films Added with Red Prickly Pear (<Emphasis Type="Italic">Opuntia ficus-indica</Emphasis> L.) cv. San Martín Peel and/or Its Aqueous Extracts

The aim of this research was to investigate the effect of the addition of peel powder and/or its aqueous extract on physical and antioxidant characteristics of carboxymethyl cellulose (CMC) edible films. Prickly pear peel powder and aqueous extract (2 and 4%) were characterized in color, bioactive compounds (betalains and total phenolic compounds), antioxidant capacity and reducing power. Edible films were prepared with CMC, glycerol, varying the dissolution medium (0, 2, or 4% aqueous extract from prickly pear peel) and peel powder (0, 1, or 2%) using a face-centered central composite design. Physical, mechanical, bioactive compounds, and antioxidant capacity properties were investigated in edible films. Prickly pear peel powder presented 58.8 ± 0.08 mg of betacyanins/100 g, 53.8 ± 0.2 mg of betaxanthins/100 g, 967.8 ± 20 mg Gallic acid equivalent (GAE)/100 g for total phenolic compounds, an antioxidant capacity equivalent to 420.9 ± 4.9 mg GAE/100 g and a reducing power of 879.1 ± 115.9 mg ascorbic acid equivalent (AAE)/100 g. High concentration of aqueous extract and peel powder in CMC films increased the bioactive compounds content, antioxidant capacity and reducing power. Films mechanical properties were not affected by the aqueous extract; nevertheless, were strongly affected by the peel powder. Response surface methodology was used to optimize edible films formulation with high antioxidant characteristics, being the optimal formulation 1.7% of peel powder plus 3.3% of aqueous extract. This study may be the base for exploitation of prickly pear peel as source of bioactive compounds with antioxidant capacity for their use in edible coatings.     

Gallic Acid‐Loaded Zein Nanoparticles by Electrospraying Process

Currently, electrospraying is a novel process for obtaining the nanoparticles from biopolymers. Zein nanoparticles have been obtained by this method and used to protect both hydrophilic and hydrophobic antioxidant molecules from environmental factors. The objective of this work was to prepare and characterize gallic acid‐loaded zein nanoparticles obtained by the electrospraying process to provide protection to gallic acid from environmental factors. Thus, it was related to the concentration of gallic acid in physicochemical and rheological properties of the electrosprayed solution, and also to equipment parameters, such as voltage, flow rate, and distance of the collector in morphology, and particle size. The physicochemical properties showed a relationship in the formation of a Taylor cone, in which at a low concentration of gallic acid (1% w/v), low viscosity (0.00464 ± 0.00001 Pa·s), and density (0.886 ± 0.00002 g/cm³), as well as high electrical conductivity (369 ± 4.3 µs/cm), forms a stable cone‐jet mode. The rheological properties and the Power Law model of the gallic acid‐zein electrosprayed solution demonstrated Newtonian behavior (n = 1). The morphology and size of the particle were dependent on the concentration of gallic acid. Electrosprayed parameters with high voltage (15 kV), low flow rate (0.1 mL/hr), and short distance (10 cm) exhibited a smaller diameter and spherical morphology. FT–IR showed interaction in the gallic acid‐loaded zein nanoparticle by hydrogen bonds. Therefore, the electrospraying process is a feasible technique for obtaining gallic acid‐loaded zein nanoparticles and providing potential protection to gallic acid from environmental factors.     

Occurrence of major and trace elements in powdered milk from Argentina

The concentrations of major and trace elements in Argentinean commercial powdered milk samples were determined with inductively coupled plasma mass spectrometry. Also the daily intake (DI) was calculated for adults and infants. The concentrations of B, Mg, Na, K and Ca were significantly higher in skimmed milk. Cu, Mo, Fe, Mn and Zn were significantly higher in infant formula. All the DIs were below the tolerable upper intake levels. The mean As concentration (26.0 ± 8.6 ng/g) in the powdered skimmed milk samples was slightly higher than in the others. Mean Pb concentrations ranged from 4.1 ± 2.1 to 13.5 ± 8.2 ng/g. The highest mean U concentration was 7.8 ± 2.6 ng/g for whole milk. This study contributes to the knowledge of major and trace elements in powdered milk and its contribution to the diet in Argentina.