Emerging technologies to improve fooddrying: ethanol,freezing, pulsed electric field and ultrasound applied to dekopon and orangepeel

Abstract

Citrus fruits are of great importance for human consumption as well as for industrialization and to develop technologies that aim to improve their conservation and creating alternatives for the reuse of by-products of these fruits from the agro-industrial productive chain is of extreme importance in the environmental and technological axis. Therefore, this work aims to study the influence of drying techniques as well as the application of pretreatments in dehydration of dekopon (Citrus retiulata “Shinarui”) and orange peels (Citrus sinensis). In the first article, the effects of ethanol as a pretreatment to convective drying (50 and 70 °C; 2.0 m/s) of dekopon slices were studied, with reductions in drying time and total color difference, greater retention of phenolic compounds and ascorbic acid and better antioxidant capacity with ethanol application. The second article deals with the effects of convective drying (50 °C) and atmospheric freeze-drying (-10 °C) assisted by ultrasound (US; 20.5 kW/m³) on orange peel cv. Valencia Late. US significantly reduced the drying time, and drying at 50 °C showed better results of the technological properties of the alcohol insoluble residue (water and oil retention capacity and swelling capacity). In the third article, the influence of pulsed electric fields (PEF - 200 and 600 μs) and US during the drying of orange peel (50 °C) was evaluated. Shorter drying times and changes in the color of the dry samples were obtained with the application of US and PEF 200 μs, respectively. All treatments with PEF showed a similar percentage of ascorbic acid, and only at 600 μs produced a reduction in the retention of antioxidant activity. The combined effect of the techniques showed a significant increase in the retention of phenolic compounds. The fourth article studies the influence of PEF on the drying kinetics of orange peel and the parameters of the mathematical model that was used. The application of US as well as its effect associated with PEF reduced the drying time. The De coefficient was higher in the US experiments and in the combination between US and PEF. The last article discusses the influence of freezing (slow and fast) and US on the drying kinetics of orange peel and on the parameters of the mathematical model. US applications as well as their effect combined with freezing reduced the drying time. The De coefficient was statistically higher in the US experiment compared to the control.