Mariana Alves

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.

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.