Catherine Bonazzi

Effect of Temperature and Cultivar on Polyphenol Retention and Mass Transfer during Osmotic Dehydration of Apples

Several cultivars of apples (Malus domestica) were chosen for their variable concentrations and compositions in phenolic compounds. Cubed samples (1 cm3) were subjected to osmotic dehydration, and the effect of temperature was studied at 45 and 60 degrees C. Water loss, sucrose impregnation, and the evolution of some natural components of the product were followed to quantify mass transfer. Ascorbic acid and polyphenols were quantified by HPLC for several osmotic dehydration times and regardless of the quantity of impregnated sugar. Changes in antioxidant components differed as a function of the nature of molecules. Their concentrations decreased in line with temperature, and few differences were observed between cultivars. Processing at a lower temperature (45 degrees C) caused a total loss in ascorbic acid but allowed the retention of between 74 and 85% of initial polyphenols, depending on the cultivar. Cultivars containing highly polymerized procyanidins (such as Guillevic) experienced less loss. Hydroxycinnamic acids and monomeric catechins displayed the most marked changes. Leaching with water into the soaking solution was the principal mechanism retained to explain these losses.

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.

DYNAMIC OPTIMAL CONTROL OF BATCH RICE DRYING PROCESS

ABSTRACT The drying of paddy rice may result in quality degradation, expressed as a head kernel yield, leading to significant commercial depreciation of the product. A mathematical model of the drying and of the quality degradation process was combined with a dynamic optimization algorithm to determine the drying conditions (air temperature and relative humidity as functions of time) that ensured the highest possible final product quality for a specified drying time and a specified final moisture content. The robustness of the optimal drying strategy with respect to the initial state of the product, to the model parameters and to the initialization of the optimization algorithm was verified. The compromise between the highest achievable final quality and the allowed total drying time was studied. The combination of simulation and optimization yielded a new insight in the rice drying process and in the quality preservation strategies.

A COMPARTMENTAL MODEL OF THIN-LAYER DRYING KINETICS OF ROUGH RICE

ABSTRACT Rough rice at about 21% (wet basis) was dried at various conditions of temperatures and evaporating capacities of air. The influence of both parameters on drying rate has been studied. At high temperatures, high drying rates can be achieved with low evaporating capacities. In addition, desorption isotherms of rough rice were measured at 35, 60 and 85°C and the experimental isotherms data were fitted using a modified Pfost equation. A compartmental model was developed to simulate the grain moisture content. Heat and mass transfer coefficients were optimized using a Nelder & Mead method. Internal mass transfer coefficient was written as an exponential function of the average moisture content and temperature of the grain and the external mass transfer coefficient as a function of air temperature. The compartmental approach predicts very well the average moisture content with a mean error of about 5% in static and dynamic conditions.

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.

MOISTURE DIFFUSION IN GELATIN SLABS BY MODELING DRYING KINETICS

ABSTRACT The aim of this work is to improve the knowledge concerning moisture mobility in gelatin slabs, through the evaluation of moisture diffusivity (function of temperature and moisture content) by modeling of drying kinetics The first part of this work is devoted to the determination of the gel characteristics needed for a good modeling. Drying experiments were then carried out on a pilot drier according to a central composite design with 3 factors (temperature, moisture content and pH). Moisture diffusivity was finally calculated by fitting a model to the drying experiments. The chosea model (a conventional diffusive model with variable diffusion coefficient, solved by finite difference calculations in a solid-related frame of coordinates) did not perfectly fit the experimental results. It especially under-estimates moisture gradients at the surface of the gel

The effect of different osmotic agents on the sensory perception of osmo-treated dried fruit

Summary To increase the attractiveness of dried fruit, the osmotic dehydration method (DIS) was used to fortify the structural matrix of fruit tissues with health-promoting compounds. The aim of these studies was to determine the impact of different osmotic agents on the sensory perception and acceptability of osmo-dried and osmo-freeze-dried sour cherries, blackcurrants, and apples. The osmo-dried fruits, thus manufactured, were subjected to profile sensory analysis. With the exception of basic fruit taste, all the sensory attributes investigated were influenced significantly by the osmotic agent used for fruit impregnation before drying. We proved that the osmotic solution significantly influenced the taste and/or texture profile of the dehydrated fruit and affected their sensory acceptability, but the changes depended on species and drying method. In general, dried fruit pre-treated with sucrose (S), inverted sugar (IS), or de-acidified fruit juice (DeAFJ) were characterised by having a predominantly sweet taste, while those treated with concentrated apple juice (JF) had high acidity. Oligofructose (OF) applied to freeze-dried fruit created a high level of crispness in the final product. Polyols such as galactosorbitol (GALSOR) and sorbitol (SOR) could not be recommended for osmotic impregnation of fruit due to a sensation of increasing hardness that lowered consumer acceptability of the product.

APPLICATION OF FUZZY RULES-BASED MODELS TO PREDICTION OF QUALITY DEGRADATION OF RICE AND MAIZE DURING HOT AIR DRYING

ABSTRACT The concept of modelling using a rules -based approach is introduced and developed for die prediction of the quality degradation of grains during hot air drying. It is men validated on two typical examples of quality degradation during drying: the head kernel yield of paddy rice and the wet-milling quality of maize. The linguistic approach gives a representation of die experts understanding of phenomena and leads to a good kinetic model after identification of die parameters using genetic algorithms. This study also points out die robustness of die model prediction, even if noisy data are used, and its ability to predict transient behaviours under certain conditions.

Apple polyphenoloxidase inactivation during heating in the presence of ascorbic acid and chlorogenic acid.

It was recently reported that during osmotic dehydration of ascorbic acid (AA)-treated apple cubes, losses in AA and phenolics could partly arise from enzymatic oxidation, provided polyphenoloxidase (PPO) was still active under the processing conditions. To determine the impact of dehydration temperatures on PPO action, as well as chemical and enzymatic oxidation reactions, apple PPO inactivation alone or with AA (1mM) and/or chlorogenic acid (CG, 3mM), as well as AA and CG levels evolution, during heating of the model solutions at 45 and 60°C were investigated. At pH 3.8, PPO was still functional, keeping 61 and 4% residual activity after 2h of heating at 45 and 60°C, respectively. The combined treatment of heating and AA was more effective in reducing PPO activity, while incubation at 60°C with AA and CG minimised the losses of PPO activity. CG remained stable during heating, even in the presence of AA which, in turn, was more affected by heating. Thus, during heating, provided PPO remained active with enough available O2 in the model systems, CG oxidation and coupled oxidoreduction with AA could readily develop.

Superheated Steam Drying: An Overview of Pilot and Industrial Dryers with a Focus on Energy Efficiency

According to the principle of sustainability, modern industry should preserve nonrenewable energy sources and develop more efficient processes, especially in terms of energy consumption. The depletion of fossil energy reserves, the environmental impact of greenhouse gases, and the possible threats of environmental taxes are the main reasons to develop new processes in general, and new drying processes in particular, for the existing industries. Using superheated steam as a drying medium instead of hot air can improve the energy efficiency by reusing the energy from exhausted steam and prevent gas emission into the atmosphere by condensation. The present review is focused on both lab-scale pilots—including impingement jet, fluid bed, kiln, fixed bed, and flash drying—described in the literature and existing industrial facilities, with a specific analysis focused on energy efficiency. The usefulness of superheated steam drying pilots for experimental research and for the design of industrial dryers is analyzed. The impact on quality specifications of the dried product for different operating conditions is also presented. Documentation on industrial superheated steam dryers is very rare. Nevertheless, this work presents and analyses the key data available for superheated steam drying of beet, alfalfa, industrial pulp, and paint sludge. Energy recovery and process integration, with a focus on specific technological challenges for industrial dryer implementation, are also presented. This document will result in a discussion of some new ideas for possible R&D in superheated steam drying.