Maria João Barroca

Artificial neural network modelling of the antioxidant activity and phenolic compounds of bananas submitted to different drying treatments

Bananas (cv. Musa nana and Musa cavendishii) fresh and dried by hot air at 50 and 70°C and lyophilisation were analysed for phenolic contents and antioxidant activity. All samples were subject to six extractions (three with methanol followed by three with acetone/water solution). The experimental data served to train a neural network adequate to describe the experimental observations for both output variables studied: total phenols and antioxidant activity. The results show that both bananas are similar and air drying decreased total phenols and antioxidant activity for both temperatures, whereas lyophilisation decreased the phenolic content in a lesser extent. Neural network experiments showed that antioxidant activity and phenolic compounds can be predicted accurately from the input variables: banana variety, dryness state and type and order of extract. Drying state and extract order were found to have larger impact in the values of antioxidant activity and phenolic compounds.

Mass Transfer Properties of Pears for Different Drying Methods

In the present work, the mass transfer properties of pears were determined for three different drying systems (a solar stove, a direct solar drier, and a drying tunnel), using three calculation methodologies. The results obtained allowed concluding that the best methodology to calculate the mass transfer properties is based on Ficks equation, including shrinkage. The values of the diffusion coefficients in the solar drier and drying tunnel were similar, whereas in the solar stove the diffusivity was lower, indicating that the internal moisture transfer was less efficient. Regarding the mass transfer coefficient, this was higher in the solar drier, demonstrating a better efficiency of surface mass transfer.

Effect of Drying on the Textural Attributes of Bell Pepper and Pumpkin

The present work evaluates the effect of different drying treatments on the textural attributes of bell peppers (green and red) and of pumpkins (C. maxima and C. moschata), which were dried using different methods: freeze-drying and air drying at different temperatures. From the results obtained it is possible to conclude that with respect to pumpkin no dependence was found between the fiber orientation and the hardness of the fresh vegetable, but a significant dependence was observed on the location of the sample, with those samples situated closer to the skin showing higher values of hardness. As to the bell peppers, the hardness is higher for those measurements made from the external side when compared to those made from the internal side. As to the effect of drying on the texture of the vegetables, it was found that the increase in air drying temperature drastically reduces the hardness of all vegetables and that freeze drying has an intermediate effect between the vegetables dried at 30°C and 70°C. Moreover, the springiness tends to be higher in dried bell peppers but no significant effect was observed on this attribute in the case of pumpkins. With respect to cohesiveness, the results are similar to those for springiness, so that it is slightly higher in the dried bell peppers, but in the case of pumpkins no differences were found. Finally, the trends observed for chewiness follow those for hardness in all cases at study.

Study of the Solar Drying of Pears

ABSTRACT Four pear cultivars originating from Portugal (‘Amêndoa’, ‘Amorim’, ‘Carapinheira Branca’ and ‘S. Bartolomeu’) were dried in a solar drier, following a traditional sun drying method normally used in Portugal for the production of dried pears. The temperature and relative humidity inside the drier were recorded hourly throughout the whole process, while the moisture loss in the pears was evaluated with a variable frequency along the drying process, according to the drying rate. From the results obtained, it was possible to conclude that the conditions inside the drier are very favorable to drying, with periods in which the atmosphere is characterized by very high temperatures and very low relative humidities. Furthermore, the drying rates of the four cultivars of pears used in this study were investigated and it was observed that all of them present a similar kinetic behavior, thus enabling the use of alternative cultivars for the production of dried pears.

Artificial neural network modelling of the chemical composition of carrots submitted to different pre-drying treatments

The effect of various pre-drying treatments on the quality of dried carrots was evaluated by assessing the values of moisture, ash, protein, fibre, sugars and colour. The pre-drying treatments under investigation were dipping, either in ascorbic acid or sodium metabisulphite at different concentrations and pre-treatment times, as well as blanching. The experimental data was analysed using neural networks, so that relevant patterns in the data were found and conclusions drawn about each variable. The results showed that the type of pre-drying treatment (chemical or physical) had variable impact on the nutritional composition of the dried carrots but not on the colour parameters, which were found to be mostly unaffected by the pre-treatment procedure. Pre-treatment with chemical agents such as ascorbic acid or metabisulphite seem to have the least impact on the parameters studied. The results of the analysis by artificial neural networks confirmed these findings.

Effect of Drying on Total Phenolic Compounds, Antioxidant Activity, and Kinetics Decay in Pears

The polyphenols have been identified as food components sensitive to high temperatures; therefore, the application of heat treatments can lead to a significant reduction in the phenolic content and also on antioxidant capacity. The objectives of the present work were to investigate the decrease in total phenolic compounds and antioxidant activity in pears during air drying at different temperatures and to model the kinetics of those variations. The pears (cv. D. Joaquina) were dried at 60°C and 70°C in an electrical drying chamber with hot air at 0.5 m/s. Along drying several samples were collected for analysis, being submitted to multiple extractions with methanol and acetone solutions. The phenolic compounds were determined by the Folin-Ciocalteu method and the antioxidant activity was determined by the ABTS method. The results showed that three successive extractions with methanol followed by three extractions with acetone solution was necessary for an efficient quantification of the total phenolic compounds and antioxidant activity. The decrease along drying was found to be of about 40% for both parameters and for the two temperatures studied. Furthermore, a relatively strong relation was observed between total phenols and antioxidant activity. The mathematical modeling of the kinetics showed that a 3-parameter exponential decay function was the best function to describe the experimental data, and the kinetic constants were found to vary in the range 0.0136–0.0444 min−1.

Development of Fruit Jams and Juices Enriched with Fructooligosaccharides

In this work, fruit-derived products were enriched with a fructooligosaccharide, inulin, obtained from tubers of Jerusalem artichoke (Helianthus tuberosus). The products developed included juices and jams from various fruits and were analyzed in terms of chemical, microbiological, and sensorial properties right after production and again after storage. The comparison of the results before and after storage would allow establishing the conservation ability of the products developed. The results obtained allowed concluding that the products obtained contained a high content of inulin, which is a prebiotic compound with important benefits for gut health.

Comparative Study of the Drying of Pears Using Different Drying Systems

Different methods for the drying of pears, namely a solar stove, a solar dryer, and a tunnel dryer, were studied. All processes were conducted in three consecutive years to analyze if the behavior of each drying method showed evidence of a similar pattern, along with producing products similar to the traditional pears that are dried using direct sun exposure. The results showed that all methods led to a considerable reduction in drying time as compared to open-sun drying. Indeed, the drying time for the solar stove and the solar dryer showed a reduction of more than 40% while in the drying tunnel this reduction increased to more than 60%. In addition, it was also possible to conclude that the properties of the dried pears obtained by the three processes correspond to dried fruits similar to the traditional dried pears.

Solid-state studies and antioxidant properties of the γ-cyclodextrin·fisetin inclusion compound

Fisetin is a natural antioxidant with a wide range of nutraceutical properties, including antidiabetic, neuroprotecting, and suppression or prevention of tumors. The present work describes the preparation of a water-soluble, solid inclusion compound of fisetin with gamma-cyclodextrin (γ-CD), a cyclic oligosaccharide approved for human consumption. A detailed physicochemical analysis of the product is carried out using elemental analysis, powder X-ray diffraction (PXRD), Raman, infrared and 13C{1H} CP-MAS NMR spectroscopies, and thermal analysis (TGA) to verify fisetin inclusion and to present a hypothetical structural arrangement for the host–guest units. The antioxidant activity of the γ-CD·fisetin inclusion compound is evaluated by the DPPH assay.

Evaluation of the browning kinetics for bananas and pears submitted to convective drying.

The aim of this work was to evaluate the kinetics of colour change for bananas and pears dried in hot air at different temperatures, and also to test different kinetic models to verify which describe best the experimental data. Banana fruits from Madeira island and Costa Rica were and pears from cultivar D. Joaquina were peeled, cut and dried with hot air at 0.5 m/s and temperatures ranging from 50 to 70 oC, until reaching a final moisture content lower than 10% (wet basis). Along drying colour measurements were done using a tristimulus colorimeter measuring the CIELab coordinates, L*, a* and b*. The experimental data was then fit to different kinetic models found in literature (first order, second order and exponential rise functional). The results obtained showed that bananas undergo a more intense color change than pears. It was further observed that the increase in drying temperature lead in general to an increase in the colour degradation, being this effect more pronounced in the pears. As to the kinetics of color change, the exponential rise function showed the best fitting, and the values of the kinetic constant found with this model varied from 5.7023x10 to 1.0086 h.