Calor de sorbición y cambio en energía libre en pulpa de piña liofilizada

Two thermodynamic properties, the heat of sorption (Qs) and the Gibbs free energy change (∆G) were evaluated at several temperatures (5, 25, 30, 35 and 55°C) on freeze-dried pineapple pulp. It was found that 1) the heat of sorption follows the Clauslus-Clapeyron relationship; 2) the shape of the heat of sorption vs. the equilibrium moisture content curve was sigmoid; 3) the heat of sorption from adsorption data gave higher values than those from desorption data; and 4) the free energy change (∆G) is linearly related to the equilibrium moisture content. These two parameters are very important in dealing with food stability because it is possible to predict the water activity at any given temperature of either of these values is known.Dos propiedades termodinámicas, el calor de sorción (Qs) y el cambio en energía libre de Gibbs (∆G) fueron evaluadas a diferentes temperaturas (5, 25, 30, 35 y 55°C) en pulpa de piña liofilizada. Se encontró que: 1) el calor de sorbición sigue la relación de Clausius-Clapeyron; 2) la forma de la curva que representa la relación de calor contra humedad es sigmoide; 3) los calores de sorbición obtenidos de los datos de adsorción son más altos que los obtenidos de los datos de desorción; 4) los cambios en energía libre están linealmente relacionados con el contenido de humedad en equilibrio. Estos dos parámetros son muy importantes cuando se estudia la estabilidad de un alimento, ya que conociendo el valor de cualquiera de ellos es posible predecir la actividad de agua a cualquier temperatura

Rodajas de piña preservadas por métodos combinados

Pineapple slices were treated by two combined methods, packaged and stored at room temperature. The first preservation method consisted of blanching pineapple slices at 100° C for two minutes followed by a cooling period of 1.5 minutes at room temperature. The slices were then immersed in a 50% sucrose solution with 1,000 ppm of potassium sorbate and 150 ppm of sodium bisulfite. The osmotic treatment was done at room temperature (28.5 ± 1.5° C) for 24 hours. The treated slices were removed from the osmotic solution, the excess syrup from the slices was removed, and the product was later packaged in sealed plastic bags. The final water activity values ranged between 0.95 and 0.97 for the packaged product. For the second preservation method, the pineapple slices were blanched in saturated steam for 12 minutes and stored at 12° C until processing by combined methods. Sucrose solutions (55 and 60° Brix) with four different concentrations of potassium sorbate (100, 200, 300, or 500 ppm) were used as osmotic solutions. The water activity was 0.91 after the osmotic process and 0.88 after hot air drying. A shelf life of at least 30 days was observed for product prepared with both preservation techniques, and the sensory characteristics noted were similar to those in a commercially canned product (Del Monte canned slices). The inhibitory effect of potassium sorbate on yeast and mold growth was significant for concentrations above 300 ppm.Se trataron rebanadas de pina con dos métodos combinados y se almacenaron a temperatura ambiente para evaluar su vida útil. El primer método de preservación consistió en escaldar la fruta a 100° C por dos minutos y luego enfriarla a temperatura ambiente (28.5 ± 1.5° C) por 1.5 minutos. Tras el enfriamiento se procedió a colocar las rodajas en almíbar al 50% de sacarosa con 1,000 ppm de sorbato de potasio y 150 ppm de bisulfito de sodio. El tratamiento osmótico se hizo a temperatura ambiente por 24 horas. Las rodajas se sacaron del almíbar y se empacaron en bolsas plásticas luego de escurrir la mayor parte del almíbar. La actividad de agua del producto empacado fluctuó entre 0.95 y 0.97. En el segundo método de preservación, las rebanadas de piña se escaldaron en vapor saturado por 12 minutos y se almacenaron en refrigeración (12° C) hasta su tratamiento por métodos combinados. Se usaron soluciones de sacarosa de 66 y 60° Brix con cuatro niveles de sorbato de potasio (100, 200, 300, 500 ppm) para la deshidratación osmótica de las rebanadas. Una vez en equilibrio, se removieron las rebanadas de la solución de sacarosa y se secaron parcialmente con aire caliente por una hora. El valor de actividad de agua fuego del tratamiento osmótico fue de 0.91 y bajó a 0.88 luego del secado parcial con aire caliente. Para ambos métodos de preservación se observó un período no menor a 30 días durante el cual las características sensoriales del producto compararon favorablemente con las de productos comerciales de piña enlatada (Del Monte). El efecto inhibidor de sorbato de potasio sobre los hongos y las levaduras fue evidente a concentraciones mayores de 300 ppm

Procesamiento no térmico de alimentos

Conventional approaches to process foods have proven to offer very safe products but, in some cases, the quality of the final product is significantly lower to the original one. Nonthermal processing of foods has emerged as a viable alternative to those conventional processing by offering safe products of excellent quality and at very reasonable cost. These emerging technologies utilize nonthermal microbial stress factors as the main inactivation mechanism. In some cases, external sources of heat or self-generated heat are utilized to supplement the main inactivation mechanism. This combination becomes very relevant in the case of the sterilization of low-acid foods by pressure assisted thermal processing (PATP). This article presents some of the most relevant nonthermal technologies where some of them are already in use by the food industry and others will be adopted in the very near future. It is the case; these nonthermal technologies could be used in combination among themselves or with other preservation approaches seeking synergistic effects in order to have shorter processes and very good quality food products.Los procesos comúnmente utilizados por la industria de alimentos ofrecen productos seguros pero, en muchos casos, la calidad de los mismos es significativamente peor a los productos no procesados. En forma reciente, se ha empezado a investigar en forma sistemática y desde un punto de vista científico, tecnológico y práctico, las llamadas tecnologías “no térmicas”. Las mismas utilizan como factores principales de inactivación microbiana estrategias que no utilizan el calor. El mismo puede utilizarse como suplemento o puede ser autogenerado por la tecnología utilizada, y a veces puede jugar un papel importante en el proceso como por ejemplo en la esterilización de alimentos de baja acidez utilizando altas presiones. En este trabajo se describen algunas tecnologías “no térmicas” que han adquirido mucha relevancia y que han sido incorporadas a las líneas de proceso en algunas industrias o que, eventualmente, serán incorporadas en un futuro muy cercano. Todas estas tecnologías tienen ventajas y desventajas, y ninguna de ellas es capaz de procesar todos los alimentos, sin embargo debido a la seguridad que ofrecen, la calidad del producto final y los costos involucrados en el uso de las mismas, las hacen una opción muy atractiva a los métodos convencionales, generalmente centrados en el uso del calor. Es del caso señalar que las tecnologías no térmicas pueden ser utilizadas en combinación entre ellas o con otras, buscando efectos sinérgicos lo cual redundará en procesos más cortos y la obtención de productos de mejor calidad

Study of strawberry flavored milk under pulsed electric field processing

Few studies exist on flavored milk processed by pulsed electric fields (PEF). The main concern is product stability. This study aimed to analyze the degradation of coloring agent Allura Red in strawberry milk under PEF. Four systems were tested containing Allura Red: two commercial milks and two model systems. PEF conditions were 40 kV/cm, 48 pulses (2.5 μs), and 55 °C; coloring agent was quantified via RP-HPLC. After processing, only minor changes were observed in color, Allura Red concentration, and pH. During storage (32 d) at refrigerated conditions (4 °C) commercial samples maintained pH above 6. Model systems dropped below pH 6 after 10 days of storage. Color of samples showed important decrease in a⁎; hue angle and chroma changed during storage. HPLC analysis reported a bi-phasic effect in Allura Red concentrations versus time. Concentration changed, reaching a maximum value during the middle of storage, possibly attributed to microbial growth, pH reduction, or interaction of proteins. However, PEF affected the stability of Allura Red in milk when additional ingredients were not added to the product

Study of strawberry flavored milk under pulsed electric field processing

Few studies exist on flavored milk processed by pulsed electric fields (PEF). The main concern is product stability. This study aimed to analyze the degradation of coloring agent Allura Red in strawberry milk under PEF. Four systems were tested containing Allura Red: two commercial milks and two model systems. PEF conditions were 40 kV/cm, 48 pulses (2.5 μs), and 55 °C; coloring agent was quantified via RP-HPLC. After processing, only minor changes were observed in color, Allura Red concentration, and pH. During storage (32 d) at refrigerated conditions (4 °C) commercial samples maintained pH above 6. Model systems dropped below pH 6 after 10 days of storage. Color of samples showed important decrease in a⁎; hue angle and chroma changed during storage. HPLC analysis reported a bi-phasic effect in Allura Red concentrations versus time. Concentration changed, reaching a maximum value during the middle of storage, possibly attributed to microbial growth, pH reduction, or interaction of proteins. However, PEF affected the stability of Allura Red in milk when additional ingredients were not added to the product

High-pressure Processing: Kinetic Models for Microbial and Enzyme Inactivation

High pressure processing (HPP) has become the most widely accepted nonthermal food preservation technology. The pressure range for commercial processes is typically around 100-600 MPa, whereas moderate temperature (up to 65°C) may be used to increase microbial and enzymatic inactivation levels. However, these industrial processing conditions are insufficient to achieve sterilization since much higher pressure levels (>1000 MPa) would be required to inactivate bacterial endospores and enzymes of importance in food preservation. The next generation of commercial pressure processing units will operate at about 90-120°C and 600-800 MPa for treatments defined as Pressure Assisted Thermal Processing (PATP), or Pressure Assisted Thermal Sterilization (PATS) if the commercial food sterilization level required is achieved. Most published HPP kinetic studies have focused only on pressure effects on the microbial load and enzyme activity in foods and model systems. Published work on primary and secondary models to predict simultaneously the effect of pressure and temperature on microbial and enzymatic inactivation kinetics is still incomplete. Moreover, few references provide a detailed and complete analysis of theoretical, empirical, and semi-empirical basis for the kinetic models proposed to predict the level of microbial and enzyme inactivation achieved. This review organizes these published kinetic models according to the approach used, and then presents an in-depth and critical revision to define the modeling research needed to provide commercial users with the computational tools needed to develop and optimize pasteurization and sterilization pressure treatments.Keywords: Primary and Secondary Models, High Pressure Processing, Kinetics, Microbial Inactivation, Pressure Assisted Thermal Processing, Enzyme Inactivatio

Transport Phenomena in Films and Coatings Including Their Mathematical Modeling

In the present chapter, two examples related to transport phenomena in films and coatings are discussed. One of them represents the heat and mass transfer process in fried foods that were covered with an edible coating based on methylcellulose (MC). This is an alternative to reduce oil uptake (OU) in fried foods due to its lipid-barrier properties. The following aspects are discussed: (1) mathematical modeling of heat and moisture transfer during the deep-fat frying of food, (2) experimental validation of the mathematical model with regard to the temperature profiles and the water losses from the food product, (3) analysis of the relationship between the OU measurements and microstructural changes developed, and (4) performance of applying an edible coating based on MC on a food model dough system. The mathematical model of the frying process based on the numerical solution of the heat and mass transfer differential equations under unsteady-state conditions was proposed and solved. It allows simulating satisfactorily the experimental data of temperature and water content during the different frying stages. OU was also linearly correlated with water loss at the initial frying stage. A simple equation for OU as a function of frying times was proposed, considering the microstructural changes developed during the frying process. The presence of MC coating reduced the OU, modifying the wetting properties and also becoming a mechanical barrier to the oil. The second example represents the mathematical modeling of potassium sorbate release from a starch biodegradable active film to a model food system represented by a gel in contact with the active film. Mass transfer partial differential equations in nonstationary conditions were numerically solved using the finite element method. The model assumes a constant initial mass of antimicrobial in the active film that diffuses through the film penetrating in the food system. The numerical solution allowed the determination of the diffusion coefficients of the antimicrobial agent in both, the film and the gel. Concentration profiles were simulated to predict the time period in which the antimicrobial concentration can be maintained above the critical inhibitory concentration in the packaged food. Experimental data of sorbate diffusion from active films and from a liquid solution to the semisolid medium were compared with the predicted concentration profiles. The model allows the simulation of nonstationary diffusion of different additives incorporated to polymeric matrixes, taking into account the preservative concentration in the film and the dimensions of the semisolid food system.Centro de Investigación y Desarrollo en Criotecnología de Alimento

Procesamiento no térmico de alimentos, discurso de D. Gustavo V. Barbosa-Cánovas en su Ceremonia de Investidura como doctor “honoris causa” por la Universidad Politécnica de Cartagena, 2010

En este artículo se examinan nuevas tecnologías no térmicas y su desarrollo en el que han trabajado en colaboración la industria, el entorno académico y el gobierno. Estos tres grupos trabajan conjuntamente con las agencias reguladoras para su uso en la industria alimentaria, con el fin de ofrecer productos de consumo alimentario seguros, nutritivos y sabrosos. Es del caso señalar que algunas regulaciones tradicionales para la pasteurización y esterilización se han modificado para dar cabida a estas nuevas tecnologías, donde el calor no es el principal factor de estrés para inactivar los microorganismos.De origen uruguayo y de abuelos españoles, ha desarrollado también su carrera en varias universidades norteamericanas. Sus trabajos en el campo de la Ingeniería de los Alimentos le hicieron merecedor en el año 2005 del premio más valorado en todo el mundo en Ciencia y Tecnología de Alimentos, que concede el prestigioso Instituto de Tecnología de Alimentación de los Estados Unidos. Su labor investigadora ha sido pionera en las técnicas de conservación de alimentos por métodos no térmicos y en procesado mínimo