Nourhène Boudhrioua

Influence of ripeness and air temperature on changes in banana texture during drying

Abstract This study aims to characterize how the rheological properties of slices of Cavendish Grande naine bananas change during the hot air drying process. Since the degree of ripeness of fresh banana considerably affects the rheological properties of the dried product, changes in fresh banana were first of all monitored during storage at room temperature and humidity. This study made it possible to determine the parameters which discriminated between degrees of fruit ripeness––moisture content, sugar content in the pulp, firmness of the banana with peel (S) and peel color (a*). Two non-linear regression correlations linked S and a* to storage time. Glucose content was correlated with the values of S, a* and moisture content in order to avoid this measurement very time consuming. Secondly, the changes in rheological properties were monitored by penetrometry throughout the drying experiments. This study showed that a radical change in the rheological behavior of the slices occurred depending on the fruit ripeness after 4, 6 or 8 h of drying at 80 °C: they lost their deformability and became brittle. An analysis of the thermo-mechanical properties of the slices by dynamic mechanical thermal analysis showed that this abrupt change in the properties must be related to the product going below the glass transition temperature (Tg) as it is cooled after drying.

Moisture Sorption Isotherms, Thermodynamic Properties, and Glass Transition of Pears and Apples

Moisture sorption isotherms of apples and pears were determined at 30, 45, and 60°C and water activity (a w ) range of 0.04–0.83 using a standard static gravimetric method. The sorption isotherms of both fruits decreased with increasing temperature and exhibited type III behavior according to Brunauer–Emmett–Teller (BET) classification. The moisture desorption data fitted well with the Peleg model (0.997 ≤ r ≤ 0.999, 0.009 ≤ SE ≤ 0.071, and 4.840 ≤ p ≤ 13.779). The glass transition temperature (T g ) of both fruits decreased linearly with the increase in water activity (a w ). The variation in glass transition temperature versus water activity (T g ∼ a w ) and glass transition temperature versus solid fraction of pears and apples (T g ∼ W s ) were adequately predicted by Khalloufi et al.s model (0.998 ≤ r ≤ 0.999 and 0.007 ≤ SE ≤ 4.088) and the Gordon and Taylor model (0.879 ≤ r ≤ 0.979 and 9.798 ≤ SE ≤ 18.507). The thermal transition and desorption isotherms data were used to establish state diagrams of pear and apple and evaluate suitable fruits storage conditions.

Validation of a Method of Determination of Apparent Diffusivity Versus Composition in Solids

Abstract A method is presented for computing the values of apparent diffusivity in solids with respect to the concentration of the diffusing substance (water or sodium chloride). This method does not require any assumption upon the mathematical relationship between diffusivity and concentration. It can be applied to experimental measurements of local concentration versus position within the solid (profiles) with relatively few measurements (circa 10) and a mathematical smoothing of the experimental data by using an artificial neural network model. The method was first validated on simulated data obtained by using a constant diffusivity value and on experimental profiles when the relation between diffusivity and concentration was given. It was then applied to original experimental moisture profiles obtained by putting gelatin gels with different initial moisture contents into contact for up to 14 days. The method was also successfully applied to five sets of experimental moisture and sodium chloride profiles taken from the literature and obtained from different food products. Apparent diffusivities calculated by our method were found in agreement with those obtained by authors using different numerical methods to compute the diffusivity values.

Moisture and salt transfers during constant temperature drying of gelatin gels : Effects of composition and of water flux intensity

Adrying cell was set up to generate salt and moisture gradients in added and free salt gelatin gels maintained at constant temperature. Fluxes from 30 × 10 -6 to 280 × 10 -6 kg water m -2 s -1 were generated in the gels. The water and chloride profiles were measured by slicing and analysis of moisture and chloride. The experimental moisture and salt profiles were used to estimate the apparent diffusivities of water and chloride as a function of composition and process variables. At high and medium promoted water fluxes, salt transfers were accelerated. At low fluxes the rates of mass transfer were small and profiles were flatter. The experimental profiles showed a cross diffusion of moisture and salt occurring in the liquid phase for the investigated ranges of water flux. Water and chloride diffusivities varied respectively from 8 × 10 -10 to I × 10 -11 m 2 s -1 and from 8 × 10 -11 to 8 × 10 -10 m 2 s -1 for moisture and salt contents varying respectively from 0.6 to 9.5 kg water kg -1 anhydrous gel and from 2 to 8 g chloride 100 g -1 water. Moisture diffusivity depends on the initial structure and composition of the gel. It decreases with decreasing of moisture content. Chloride diffusivity remains relatively constant with chloride content. Moisture and chloride diffusivities measured at high and medium evaporated moisture fluxes in gelatin gels are higher than those measured at low moisture fluxes.

Effect of the process, temperature, light and oxygen on naringin extraction and the evolution of its antioxidant activity

Citrus co-products are rich in flavonones among them naringin. This compound exhibits several biological activities. These properties are mainly due to its antioxidant activity. The purpose of this work was in one hand to compare five technics of extraction conducted under different operating conditions and in the other hand, to analyse the effects of temperature, light and oxygen on naringin degradation and on the evolution of its antioxidant activity. The results obtained showed that the ultrasound assisted extraction leads to the highest naringin content and the thermal degradation of naringin occurs only for higher temperatures above 100 °C. Moreover, the naringin appears to be sensitive to an exposure to visible light (16.5 klux). The effect of the oxygen is less pronounced due to the lack of the enone structure and a hydroxyl group in position 3. The antioxidant activity of naringin is significantly affected by the light and high temperature.