Meliza Lindsay Rojas

Ultrasound pre-treatment enhances the carrot drying and rehydration

The present work aimed to describe the mechanisms involved in the enhancement of the drying and rehydration process of carrot slices caused by the pre-treatment using the ultrasound technology. For that, carrot slices of 4mm of thickness were pre-treated for 30 and 60min using an ultrasonic bath (41W/L; 25kHz). The convective drying process was performed at 40 and 60°C with 2.0m/s of air velocity, while the rehydration process was performed at 25°C. The Henderson & Pabis model was used to describe the drying kinetics and the Peleg model to describe the rehydration process of the carrots slices. As a result, the drying and rehydration kinetics were described, at the different conditions of process, correlating the results with the main effects that the ultrasound cause as a pre-treatment (cell bloating and micro-channels) and the air-drying temperature. Depending on the length of the pre-treatment, the effects caused by the ultrasound in the following processes were different. In addition, it was corroborated that when the drying temperature is increased, less evidenced is the ultrasound effect. The ultrasound, when is applied for long times, enhanced the drying and further rehydration rate at low temperatures, due to the tissue damage. Moreover, vacuum-packed samples were pre-treated with ultrasound in order to exclude the water gain and to evaluate only the micro-channels formation effect. It was concluded that the ultrasound pre-treatment enhances the drying and rehydration processes; however, future optimization studies are recommended.

Using ultrasound technology for the inactivation and thermal sensitization of peroxidase in green coconut water

Green coconut water has unique nutritional and sensorial qualities. Despite the different technologies already studied, its enzymatic stability is still challenging. This study evaluated the use of ultrasound technology (US) for inactivating/sensitizing coconut water peroxidase (POD). The effect of both US application alone and as a pre-treatment to thermal processing was evaluated. The enzyme activity during US processing was reduced 27% after 30min (286W/L, 20kHz), demonstrating its high resistance. The thermal inactivation was described by the Weibull model under non-isothermal conditions. The enzyme became sensitized to heat after US pre-treatment. Further, the use of US resulted in more uniform heat resistance. The results suggest that US is a good technology for sensitizing enzymes before thermal processing (even for an enzyme with high thermal resistance). Therefore, the use of this technology could decrease the undesirable effects of long times and/or the high temperatures of the conventional thermal processing.

Other Mass Transfer Unit Operations Enhanced by Ultrasound

Ultrasound is a promising technology, which has been used in many mass transfer unit operations with excellent results, such as drying, osmotic dehydration, extraction, hydration, salting/brining, and desalting. During a mass transfer unit operation, external and internal resistances can exist. Then, the reduction of both is necessary to accelerate the process. Ultrasound can reduce one or both resistances by different mechanisms such as acoustic cavitation, the sponge effect, microchannel formation, and others. Furthermore, the ultrasound enhancement differs in each unit operation. Consequently, the use of this technology for assisting the entire process or as a pretreatment can change the way the process is improved.

Ultrasound Processing of Fruit and Vegetable Juices

Abstract The quality of juices is defined by their physical, enzymatic, microbiological, and sensory stability. Many studies have evaluated the use of ultrasound as an alternative for processing fruit and vegetable juices, taking advantage of the physical and chemical effects resulting from the use of this technology. Ultrasound can improve the juice consistency (apparent viscosity), color, cloudiness stability, and sensory acceptance, as well as enhancing the microbial and enzymatic stability and the biocompounds stability. The changes in microscopic structure, the consequent changes in composition, and the relative magnitude of the coexistent forces in the system influence the obtained properties and stability. Therefore, the combination of several factors makes each ultrasound process and its corresponding final effects on a juice a particular case, which makes this technology interesting and promising.

Evaluating the Guo–Campanella viscoelastic model

Biological materials are characterized by complex structures and compositions, leading to viscoelastic behavior. Their viscoelastic characterization is important for the evaluation, design, and optimization of processes to ensure high quality products. Proposals of methodologies of analysis and modeling are critical steps in studying the rheological properties of these materials. In this context, a new model, the Guo-Campanella Model, was recently proposed to describe the stress-relaxation behavior of biological material. This work is an independent and impartial evaluation of this new model. It considers 10 different samples, comprising in natura and processed foods, from both plant and animal bases. For comparison, a Generalized Maxwell Model and the Peleg Model were also evaluated. The Guo-Campanella Model fitted the stress-relaxation data of evaluated products well, demonstrating its validity for describing the viscoelastic behavior of biological materials with different structures, sources, and processing. Finally, the Guo-Campanella Model parameters were evaluated and their interpretations and possible uses described. It was shown that the Guo-Campanella Model can be successfully used for future studies. PRACTICAL APPLICATIONS The stress-relaxation assay is a common technique for characterizing the viscoelastic properties of biological materials. The results obtained are generally evaluated using such compound models as the Generalized Maxwell model. Although this approach is interesting from a fundamental point of view, it results in many parameters to evaluate, thus increasing the complexity and limiting the interpretation. In this sense, the Guo-Campanella Model has only two parameters, which facilitates interpretation, especially for practical applications. This work validated this model, also contributing to its interpretation by discussing the meaning of its parameters. Consequently, this is potentially useful for future studies on food properties and process design.

Ultrasound processing of guava juice: Effect on structure, physical properties and lycopene in vitro accessibility

The present work evaluated the effect of high-power ultrasonication on the structure and properties of guava juice. The microstructure, concentration of lycopene, in vitro accessibility of lycopene and physical properties (pulp sedimentation, turbidity and colour) were evaluated. The results of this study demonstrate that the ultrasonication disrupts the guava cells, releasing their content and altering the juice properties. Although this processing decreases the total amount of lycopene in guava juice, the release of lycopene from the cells increased its in vitro accessibility. Furthermore, the size reduction of the dispersed pulp particles improved the physical stability of the juice, avoiding pulp sedimentation without significant colour changes during storage. In conclusion, it is suggested that ultrasonication is an interesting alternative to improve the physical and nutritional properties of fruit juices.