M. Di Matteo

Effect on orange juice of batch pasteurization in an improved pilot-scale microwave oven.

The effects on orange juice batch pasteurization in an improved pilot-scale microwave (MW) oven was evaluated by monitoring pectin methyl-esterase (PME) activity, color, carotenoid compounds and vitamin C content. Trials were performed on stirred orange juice heated at different temperatures (60, 70, 75, and 85 degrees C) during batch process. MW pilot plant allowed real-time temperature control of samples using proportional integrative derivative (PID) techniques based on the infrared thermography temperature read-out. The inactivation of heat sensitive fraction of PME, that verifies orange juice pasteurization, showed a z-value of 22.1 degrees C. Carotenoid content, responsible for sensorial and nutritional quality in fresh juices, decreased by about 13% after MW pasteurization at 70 degrees C for 1 min. Total of 7 carotenoid compounds were quantified during MW heating: zeaxanthin and beta-carotene content decreased by about 26%, while no differences (P < 0.05) were found for beta-cryptoxanthin in the same trial. A slight decrease in vitamin C content was monitored after MW heating. Results showed that MW heating with a fine temperature control could result in promising stabilization treatments.

An ultrasound technique for monitoring the alcoholic wine fermentation

In this paper an ultrasonic technique, usually used in non-destructive-testing (NDT), is applied to the monitoring of alcoholic wine fermentation. This technique consists in placing a test tube, containing the analyzing fluid, between two matched ultrasonic piezoelectric transducers, one used as transmitter and the other as receiver. The transmitter generates an ultrasonic wave in the liquid sample which is received by the receiver; the attenuation and the delay of the received signal in respect to the transmitted one are used to characterize the testing fluid. As first experiments this technique was applied to some test solutions of saccharose in water, ethanol in water and of both solvents in water, in order to evaluate the method applicability and resolution. Best results are obtained by the propagation velocity measurement, with a resolution less than 2%. The method was then applied to monitor the wine fermentation: the propagation velocity in the must was measured every day and the results were related to chemical analyses. The obtained results show that the propagation velocity has the same behaviour of the saccharose concentration, putting in evidence the possibility of monitoring the process state by measuring the ultrasound propagation velocity.

Kinetics of carotenoids degradation and furosine formation in dried apricots (Prunus armeniaca L.)

The kinetics of carotenoid and color degradation, as well as furosine formation, were investigated in apricot fruits during convective heating at 50, 60 and 70°C. Degradation of carotenoids and color, expressed as total color difference (TCD), followed a first and zero order kinetic, respectively. The activation energy (Ea) for carotenoids degradation ranged from 73.7kJ/mol for 13-cis-β-carotene to 120.7kJ/mol for lutein, being about 91kJ/mol for all-trans-β-carotene. Violaxanthin and anteraxanthin were the most susceptible to thermal treatment. The furosine evolution was fitted at zero order kinetic model. The Ea for furosine formation was found to be 83.3kJ/mol and the Q10 (temperature coefficient) varied from 1.59 to 4.14 at the temperature ranges 50-60°C and 60-70°C, respectively.

Mathematical Model with Shrinkage of an Eggplant Drying Process

In this paper, the effect of a pretreatment on an eggplant drying process is investigated by using a suitable developed mathematical model with shrinkage. The objective is to assess the role of volume variation due to changes in pore structures in the dehydration processes. Parameters assessing eggplant quality are also taken into account and collected both with and without pretreatment. The built model is used to analyze evolutions of dehydration processes carried out at two temperatures to provide evidences of the advantages of using pretreatment to assure high quality of end products.

Drying Kinetics, Quality Changes and Shrinkage of Two Grape Varieties of Italy

Two varieties of grapes, white grape and red grape grown in the Campania region of Italy were selected for the study of drying characteristics, moisture diffusion, quality changes (colour) and shrinkage behaviour. Comparisons were made with treated and untreated grapes under constant drying condition of 50o C in a conventional drying system. This temperature was selected to represent farm drying conditions. Grapes were purchased from a local market from the same supplier to maintain the same size of grapes and same properties. An abrasive physical treatment was used as pretreatment. The drying curves were constructed and drying kinetics was calculated using several commonly available models. It was found that treated samples shows better drying characteristics than untreated samples. The objective of this study is to obtain drying kinetics which can be used to optimize the drying operations in grape drying.

Nanoclay based enhancers for microwaveable polymeric packaging

Polymeric materials are good candidates for microwaveable packaging thanks to their transparency to microwaves (MW). In addition, a great interest is devoted to developing innovative solutions based on systems that act as susceptors or heating enhancers to improving the characteristics of polymers in cooking/heating in MW ovens. This work was focused on design, production and characterization of nanocomposite multilayer poly(ethylene terephthalate) (PET) films suitable for microwaveable food packaging applications. The matrices used were two PET copolymers modified respectively with carbon black (ULTRA STD) and with titanium oxide (ULTRA NA). Nanocomposite co-extruded multilayer films were produced using different percentages of Cloisite® 20A (C20A). Films were analyzed in order to evaluate the effect of nanoclay on the morphology, the barrier properties and the effectiveness of the systems in reducing the cooking times of meat products. Morphological analyses showed that intercalation increases by increasing the clay percentage in ULTRA STD based systems. Gas and water vapor permeability analyses showed, for both ULTRA STD and ULTRA NA matrices, a more significant improvement in systems with the lowest concentration of nanofiller. The cooking tests have pointed out that the selected matrices are efficient in reducing cooking times and that even low concentration of C20A acts as heating enhancer of PET.

PET based nanocomposite films for microwave packaging applications

In recent years, changes in life standards have promoted the diffusion of Ready to Cook (RTC) and Ready to Eat (RTE) products for microwave ovens. However, the main limits in microwave (MW) ovens usage are often related to the proper choice of packaging materials suitable for such technology. In fact, packages for microwaveable RTC and RTE foods should ensure adequate preservation of the product before cooking/heating such as high barriers to gases and aromas and adequate control of water vapor transmission. In addition, microwaveable packaging material must be transparent to MW, thermally stable and resistant to the mechanical stress induced by the accumulation in the head space of volatile substances produced during the cooking. Polymeric materials are good candidates for microwaveable packaging thanks to their transparency to MW. In the last years a great interest is devoted to developing innovative solution based on the use of additives or systems that act as susceptors or heating enhancers for improv...

An Amperometric Biosensor for the Determination of Lactic Acid During Malolactic Fermentation

A lactate oxidase amperometric biosensor was developed and optimized for the malolactic fermentation monitoring during winemaking process. Lactate oxidase enzyme was immobilized on prussian blue modified screen-printed carbon electrode in order to reduce the electrochemical interferences due to the high content of electroactive compounds abundant in wine and must, such as polyphenols and ascorbic acid. The lactate oxidase biosensor developed showed high sensitivity (852 μA M-1) and a detection limit for lactic acid of 0.005 mM (0.45 mg L-1) The operational stability and the life time of the biosensors were also evaluated equal to 8 h and 30 days respectively. Finally the biosensor in flow injection system was used for lactic acid analysis during malolactic fermentation of a red wine and the results were compared with those registered by ion chromatography with good agreement with two sets of data.

Experimental analysis and mathematical modelling of the effect of starch gelatinization on chestnuts rehydration

The paper presents an experimental and modeling study of the rehydration process of air-dried chestnuts. Sorption curves are obtained for chestnuts dried at 40, 60, and 80 C immersed in water at 90 C and differential scanning calorimetry (DSC) measurements are performed to characterize the evolution of the starch gelatinization process on the transport of water during rehydration. In this way, stages of the rehydration process governed by different physical mechanisms are identified. A large growth in the absorption rate is observed at intermediate times due starch gelatinization while slow absorption is found at large times due to the swelling of the sample. A mathematical model is therefore presented enabling to describe the effect of diffusion, swelling and starch gelatinization. Parametric estimation of the model parameters is performed by nonlinear regression techniques providing indications on how to select processing conditions so as to achieve desired characteristics of the final product..