Modeling drying kinetics of dominga grapes

Air drying kinetics of grapes (Dominga variety) were determined at 30, 40 and 50°C and velocities of 0.45 and 0.60 m/s, using a pilot tunnel tray drier. The air relative humidity ranged from 3 to 35%. The characteristic drying curves presented a single falling-rate behavior. Several models were attempted to fit the drying data. The effect of temperature on grape drying kinetics was also quantified. Air velocity had no significant effect on drying rates, in the tested range. The exponential model presented the best fit, and a drying rate and equilibrium moisture content were obtained for each isothermal experiment Temperature influence on drying rate followed an Arrhenius type behavior. A one-step non-linear regression to all the data allowed to obtain an activation energy of 31.8 :!:0.3 kJ/mol and a mean equilibrium moisture content of 0.338 :!:0.007 kg water/kg d.m. The developed model is crucial for simulating drying times of Dominga grapes

Modelling and optimization of the processing of a healthy snack bar made of grape and tomato pomaces

A snack made of 36% by-products of grape and tomato pomaces was developed, also including other ingredients such as oats, chia, quinoa, honey, and peanut butter. The recipe was defined as tasty and healthy by a focus group. The snack was produced by using forced air at three different drying temperatures (50 °C, 60 °C and 70 °C). The Newton, Page, Henderson & Pabis, and Midil-li-Kucuk models fit the drying curves well. The average values for the Newton’s model drying constants were: k50= 2.71x10-1 ± 3x10-3 min-1; k60= 2. 76x10-1 ± 4x10-3 min-1 and k70= 3.91x10-1 ± 8x10-3 min-1; at 50 °C, 60 °C and 70 °C, respectively. The product’s quality was assessed over storage, regarding water activity and texture (hardness, springiness, cohesiveness, chewiness and resilience). The three tested processing temperatures did not influence the final product’s quality differently. Since there are no significant differences between initial and final water activity and texture attributes for any temperature, and they were mainly unaltered over storage, the snack bar was considered stable during this period. This new snack which includes by-products from the food industry reduces food waste and contributes to a circular economy model, simultaneously presenting environmental and economic advantages.info:eu-repo/semantics/publishedVersio

A fruit snack including grape and tomato pomaces: assessment of the effect of temperature on drying characteristics and quality during storage

info:eu-repo/semantics/publishedVersio

Integrated approach on solar drying, pilot convective drying and microstructural changes

Solar drying of foods is an old technique, still used nowadays. Nevertheless, the mathematical approach of the complex phenomena involved is not completely integrated. Drawbacks appear in modelling heat transport, specially related to the huge variability of meteorological factors. The great dependence of the heat and mass transfer model parameters on water content is also frequently forgotten. Macroscopic changes (e.g. shrinkage) that occur during drying processes, are usually not considered in mass transfer equations, also affecting the predictive ability of the models. The objective of this work was to develop the mathematical basis and considerations for integrating heat and mass transfer phenomena, taking into consideration macroscopic changes and their correlation to changes at microscopic level (e.g. cellular shrinkage), that might occur during solar drying of grapes

Simulation of food solar drying

This chapter discusses the simulation process of food solar drying, presenting the basic issues of mass and heat transfer under time-varying conditions. Food drying embraces several phenomena, and scientists do not completely understand its underlying mechanisms. However, mathematical simulation and modelling provide comprehensions to improve the knowledge on the drying mechanisms, allow the prediction of the drying behaviour as well as being essential tools in the design of solar drying equipment. The major difficulty in simulating food solar drying arises from variable meteorological conditions that change air temperature, moisture and velocity inside the solar equipment, during the drying process. Therefore, an integrated mass and heat transfer model under dynamic conditions is presented, and appropriate assumptions are discussed. A meteorological model and desorption isotherms are taken into consideration as well. The integrated model includes food’s shrinkage, changing boundary conditions and variable thermal properties and water diffusivity with time and space (non-isotropic characteristics).info:eu-repo/semantics/acceptedVersio

Quantification of microstructural changes during first stage air drying of grape tissue

Microstructural changes in cells of Ruby grape (Vitis vinifera) quarters were monitored during first stage of convective air drying, under a stereo-microscope. A gradual overall shrinkage of grape cells was observed during the process. The cellular parameters: area, perimeter, major and minor axis length, Feret diameter, elongation, roundness and compactness, were quantified by image analysis. It was verified that cell dimensions suffered modifications during drying, but their shape remained unchanged. These microstructural changes showed a smooth exponential decrease with time, and a first-order kinetic model was satisfactorily fitted to the data. Temperature increased the rate of cellular shrinkage and this effect followed an Arrhenius type behaviour. Increasing temperature from 20 to 60 C resulted in a 350% increase of the area change rate. For the parameters related to cellular dimensions, the magnitude of the values were 10 3 min 1 for the rate of change at 40 C and 3 kJ/mol for the activation energ