ABSTRACT
The aim of this work was to study the effect of blanching and ultrasound pretreatments on drying and quality characteristics of apple peel. Blanching was conducted in boiling water, ultrasound in a water bath, and drying in a batch tray dryer. The product obtained was ground into a flour, and assessed for color, water activity, proximate composition, sugars, and bioactive compounds. Results showed that effective moisture diffusivity increases with a decrease in product moisture content, being such dependence well described by a second order polynomial model. Average drying rate was higher and product moisture content was lower for blanched and sonicated flour, especially for the former. Such result suggests that blanching and ultrasound enhance water removal during drying of apple peel. Physical properties were significantly affected by pretreatments, being more intense red color and lower water activity obtained for sonicated flour. Nutritional and bioactive properties were also significantly affected by pretreatments, being lower sugar, higher protein, fiber, catechin and epicatechin content observed for blanched flour. Summarizing, blanching and ultrasound pretreatments improve drying of apple peel, both regarding process efficiency and product quality.
Subject(s)
Malus , Flour , Desiccation/methods , Fruit , WaterABSTRACT
Plant-based foods are recognized by their remarkable content of bioactive compounds. In an attempt to increase plant-based foods shelf-life, technologies like drying can be used. Foam-mat drying is a mild drying technology that removes water, usually by using hot air, from a foam obtained by the whipping of a liquid or semi-liquid food added with a foaming agent. There are several reports on the use of foam-mat drying for extending plant-based foods shelf-life, including reports on the effect of drying on their bioactive compounds. Therefore, this study aimed at reviewing the literature on the impact of foam-mat drying on plant-based foods bioactive compounds published in the last 10 years. Results show that short foam-mat drying time is beneficial to bioactive compounds retention. In addition, hot air temperature between 40-65 °C, foam thickness between 0.2 and 1 cm and the use of egg white as one of the foaming agents leads to high bioactive retention. Egg white is also the most used foaming agent. Regarding the mathematical models used for fitting the foam-mat drying kinetics, the Page model was shown as the most proper model. Foaming agent concentration is a delicate parameter, as its increase in foam formulation may beneficially enhance drying rates but, at the same time, it dilutes bioactive compounds and may cause their loss by oxidation. In conclusion, foam-mat drying stands out as a suitable technology for producing food powders with high bioactive retention.
