Luis Medina-Torres

Study of the antioxidant properties of extracts obtained from nopal cactus (Opuntia ficus-indica) cladodes after convective drying

BACKGROUND The process of convective drying was evaluated in terms of the bioactive compounds contained in nopal samples before and after dehydration. Total polyphenol, flavonoid, flavonol, carotene and ascorbic acid contents were determined in undehydrated and dehydrated samples. Two drying temperatures (45 and 65 °C) and two air flow rates (3 and 5 m s(-1) ) were evaluated. The rheology of samples under the best drying conditions was also studied, since it provides important information regarding processing (mixing, flow processing) as well as the sensory attributes (texture) of rehydrated samples. RESULTS Non-Newtonian shear-thinning behaviour was observed for samples dried at 45 °C, while samples dried at 65 °C showed shear-thickening behaviour, possibly caused by thermal chain scission of high-molecular-weight components. CONCLUSION The best conditions for bioactive compound preservation were a drying temperature of 45 °C and an air flow rate of 3 m s(-1) , resulting in 40.97 g phenols, 23.41 g flavonoids, 0.543 g β-carotene and 0.2815 g ascorbic acid kg(-1) sample as shown in table 3.

Effect of air flow rate on the polyphenols content and antioxidant capacity of convective dried cactus pear cladodes (Opuntia ficus indica)

The interest in nopal has encouraged the use of dehydration; there are few studies about the effect of process parameters on the nopal polyphenol content and antioxidant activity. The objective of the present work was to evaluate the effect of air-drying flow rates on the amount and antioxidant capacity of extracts of Opuntia ficus indica cladodes. Nopal was dried at 45°C and air flow rates of 3 and 5 m/sec. Samples were analyzed for moisture, total polyphenol, flavonoid, and flavonol contents, chain-breaking activity, inhibition of low-density lipoprotein and deoxyribose oxidation. Nopal drying at an air flow rate of 3 m/sec showed higher values of phenols, flavonoids and flavonols. The best value of low-density lipoprotein inhibition and deoxyribose was found at 1,000 µg/ml. The air flow rate affected the amount of polyphenols and the OH· radical scavenging, but did not modify the chain-breaking activity and the low-density lipoprotein inhibition activity.

Rheological and physical properties of spray-dried mucilage obtained from Hylocereus undatus cladodes.

This study examines the rheological behavior of reconstituted spray-dried mucilage isolated from the cladodes of pitahaya (Hylocereus undatus), the effects of concentration and its relationship with physical properties were analyzed in reconstituted solutions. Drying process optimization was carried out through the surface response method, utilizing a factorial 2(3) design with three central points, in order to evaluate yield and rheological properties. The reconstituted mucilage exhibited non-Newtonian shear-thinning behavior, which adequately fit the Cross model (R(2)>0.95). This dynamic response suggests a random coil configuration. The steady-shear viscosity and dynamic response are suitably correlated through the Cox-Merz rule, confirming the mucilages stability of flow. Analysis of the physical properties of the mucilage (Tg, DTP, and particle morphology) explains the shear-thinning behavior.

Effect of high-pressure homogenization on the physical and antioxidant properties of Quercus resinosa infusions encapsulated by spray-drying.

Quercus resinosa leaves are used in northern Mexico as a refreshing beverage rich in polyphenolic compounds. These leaves show astringency and hence need taste masking for incorporating in a food product. They also interact with many other food components and are not very stable to food processing environments, thus it is important to protect them and a common way is by encapsulation. In the present study the use of encapsulation by spray-drying of Quercus resinosa leaves infusions was evaluated. Q. resinosa leaves were collected, air dried, and milled prior to infusion preparation. Lactose-sodium caseinate blends at 3 different proportions (11 : 4%, 9 : 6%, and 7 : 8%) were dispersed with a constant amount of lyophilized infusion (0.075%) and processed under high-pressure homogenization (0, 100, 200, 300 MPa). Total phenolic content, DPPH kinetic analysis, deoxy-D-ribose oxidation inhibition, rheological evaluation, and particle size analysis were performed to evaluate the obtained capsules. High antioxidant activity was shown by capsules despite their very low concentration when inhibiting deoxy-D-ribose oxidation. Chain breaking rate was related to polyphenolic concentration in capsules. Using lactose-caseinate blends produces capsules of submicron to nanometer size that retain the good antioxidant capacities of original infusions.

Effect of cholesterol and triglycerides levels on the rheological behavior of human blood

Important public health problems worldwide such as obesity, diabetes, hyperlipidemia and coronary diseases are quite common. These problems arise from numerous factors, such as hyper-caloric diets, sedentary habits and other epigenetic factors. With respect to Mexico, the population reference values of total cholesterol in plasma are around 200 mg/dL. However, a large proportion has higher levels than this reference value. In this work, we analyze the rheological properties of human blood obtained from 20 donors, as a function of cholesterol and triglyceride levels, upon a protocol previously approved by the health authorities. Samples with high and low cholesterol and triglyceride levels were selected and analyzed by simple-continuous and linear-oscillatory shear flow. Rheometric properties were measured and related to the structure and composition of human blood. In addition, rheometric data were modeled by using several constitutive equations: Bautista-Manero-Puig (BMP) and the multimodal Maxwell equations to predict the flow behavior of human blood. Finally, a comparison was made among various models, namely, the BMP, Carreau and Quemada equations for simple shear rate flow. An important relationship was found between cholesterol, triglycerides and the structure of human blood. Results show that blood with high cholesterol levels (400 mg/dL) has flow properties fully different (higher viscosity and a more pseudo-plastic behavior) than blood with lower levels of cholesterol (tendency to Newtonian behavior or viscosity plateau at low shear rates).

Properties of the Entomoparasitic Nematodes (Heterorhabditis bacteriophora) Liquid Culture using a Helicoidal Ribbon Agitator as Rheometric System

The rheological parameters: flow behaviour index n, flow consistency index K and effective viscosity ηe were estimated for the entomoparasitic nematodes Heterorhabditis bacteriophora liquid broth at different culture maturation times. The nematode or nematodes were cultivated during 20 days in a bioreactor, and the growth media inside the bioreactor was enriched with protein and fat sources. Rheological parameters for the heterogeneous suspension were estimated with mixer principles employing a helical ribbon agitator fixed to a rheometer. As the culture matured, n decreased from 0.8 to 0.2 (-) and K increased up to 1200 mPa•sn; ηe showed a non-Newtonian (n<1) behaviour, ηe reached peak values of 0.32 Pa•s for a rotational speed of 0.5 revolutions per second (rps) and 0.048 Pa•s for 2.5 rps. Rheological properties reported here could be more reliable as compared to those reported for non-homogeneous liquid fermentations where estimations were performed with conventional geometries (i.e. concentric cylinders) which are appropriate for homogeneous systems but not for non-homogeneous ones.

Mixing and tempering effect on the rheological and particle size properties of dark chocolate coatings Efecto del mezclado y temperado sobre las propiedades reológicas y de tamaño de partícula de coberturas de chocolate oscuro

Chocolate coatings are semisolid suspensions of fine particles from sugar, cocoa, non fat milk solids in an oily phase. Processing steps of chocolate include mixing, refining, conching, tempering, molding, and packing. Tempering is a directed pre-crystallization that consists of shearing chocolate mass at controlled temperatures. The effect of mixing and tempering process on the particle size distribution and rheological behavior of dark chocolate coatings were evaluated. Each sample was melted (65 °C, 15 min) and tempered following three different procedures usually recommended for chocolate. Proximate composition analysis, specific surface area, mean particle diameter, consistency index (K), flow index (n), G′, G″ and electron micrographs (4000×) were obtained. All samples followed Casson flow model and (n) showed a pseudoplastic behavior. Higher values of K were shown by tempering process 3. Shear increased chocolate storage module (G′) and its stability. Samples without tempering and shearing have shown higher values of particle size. Las coberturas de chocolate son suspensiones semi-sólidas de partículas pequeñas de azúcar, cacao, sólidos no grasos de leche en una fase oleosa. Los pasos del procesamiento de chocolate incluyen mezclado, refinación, conchado, temperado, moldeo y empacado. El temperado es una pre-cristalización directa que consiste en cizallar la masa de chocolate a temperaturas controladas. Se evaluó el efecto del mezclado y del temperado sobre la distribución del tamaño de partícula y el comportamiento reológico de coberturas de chocolate obscuro. Las muestras fueron fundidas (65 °C, 15 min) y temperadas siguiendo tres procedimientos recomendados. Se determinaron el análisis proximal, área superficial específica, diámetro medio de partícula, índice de consistencia (K), índice de flujo (n), módulos viscoelásticos (G′ y G″), y se usó micrografía electrónica, SEM (4000×). Todas las muestras presentaron un comportamiento al flujo ajustado al modelo de Casson. Los cambios de K estuvieron en función del proceso de temperado usado, pero (n) mostró cambios en su comportamiento pseudoplástico. Los mayores valores de K se obtuvieron para el temperado 3 y los menores para el temperado 1. El corte incrementó el módulo de almacenamiento (G′) y en consecuencia su estabilidad. Las muestras sin temperado y corte mostraron el mayor tamaño de partícula (9.17 μm).

On the pulsating flow behavior of a biological fluid: human blood

In this work, the rectilinear flow of a complex fluid (human blood) under a pulsating time-dependent pressure gradient is analyzed. A first approximation of the real case of blood flowing in a vein is described. The normalized pressure gradient simulates the pumping work of the heart while the flow geometry (circular tube) is assumed rigid, smooth, and cylindrical. The rheological behavior of blood with different cholesterol levels is modeled using the Bautista–Manero–Puig (BMP) constitutive equation. According to the analytical solution, a flow enhancement is predicted to first order which represents the optimum pumping work of the heart which governs the flow of blood in the entire body. This work is a contribution to the understanding of the complex rheology involved in the discontinuous pressure-driven flow of blood in the human body.

Rheology and gel point of the enzymatic hydrolysis of urea in the presence of urease

This study reports on the rheology of the gelation kinetics of raw chitosan (CTS) solutions (2% w/v) produced by enzymatic hydrolysis of urea at different urea concentrations (40, 50, 60, 80, and 100 mM) in the presence of urease at 1 U/mL. Viscoelastic parameters and pH values were evaluated during gelation process and the rheological properties of CTS hydrogels produced were monitored after 24 h at 37°C to simulate human body temperatures. pH measurements suggest that above some critical urea concentration (50 mM) the time required (tgel) to reach the critical pH gelation shows no dependence on urea concentration (tgel was ca. 70 minutes). Above 50 mM of urea concentration, CTS hydrogels exhibit an elastic modulus G′ higher than the viscous modulus G″ with no frequency dependence characteristic of a gel behavior. Gelation kinetics analyzed by rheology suggest that the G′ (i.e., structure) development depends on urea concentration during solution neutralization.

Rheology of the ultrasound-induced gelation in poloxamer aqueous solutions

The rheological behavior of the ultrasound-induced gelation of poloxamer aqueous solutions (Pluronic F-127, Sigma-Aldrich) is analyzed in this work. A new rheometric technique is proposed in which ultrasonic pulses are applied to the sample under shear flow. An ultrasonic transducer was adapted to the lower plate of a controlled-stress rheometer with a parallel-plate fixture (AR-1000 TA Instruments). Solutions were tested under linear oscillatory-shear flow at constant angular frequency in time sweeps with and without ultrasound. The mechanical response of the ultrasound-formed gels was evaluated under linear oscillatory and instantaneous stress relaxation tests. Results suggest that these solutions produce “weak gels” according to the Winter-Chambon criterion.