Secagem de polpa de figo-da-índia.

Abstract

This study aimed to produce cactus pear in powder form by thin-layer drying in an oven. Whole cactus pear pulp was manufactured from ripe fruit and characterized as to total solid content, water content, total soluble solids, titratable acidity, pH, ascorbic acid, total sugars, reducing sugars, ashes, water activity, density and color. Formulations composed of cactus pear pulp added with modified starch at concentrations of 20, 25 and 30% were prepared. Next, thin,layers (0.5 cm thick) were placed in trays and dried in an air-circulation oven at temperatures of 50, 60 and 70 °C. Kinetic drying curves were determined and models proposed by Lewis, Page, Henderson & Pabis, Logarithmic and Midilli et al. were fit to these curves. The dry samples were removed from the trays and ground to obtain powder samples. The latter were characterized as to pH, titratable acidity, total sugars, reducing sugars, ascorbic acid, water activity, total soluble solids, luminosity (L*), redness (+a*) and yellowness (+b*). Powder samples were also assessed for hygroscopic behavior, determining moisture adsorption isotherms at 20 °C and fitted the Oswin, GAB and Peleg models to experimental data. Whole cactus pear pulp exhibited high moisture content and water activity, low ascorbic acid content, low acidity and elevated total soluble solid content. The different formulations were satisfactorily dehydrated, resulting in finely-granulated powders. The Lewis, Page, Henderson & Pabis, Logaritmico and Midilli et al. models fit well the experimental data, and can be used to predict drying kinetics. The model that best fit experimental data with respect to moisture adsorption isotherms of the powder samples was that proposed by Peleg. Depending on formulation and drying temperature, moisture adsorption isotherms were classified as type I or I I . Total soluble solids, as well as total and reducing sugars of the powder samples were not influenced by drying temperature or starch concentration. Furthermore, they exhibited low ascorbic acid content and were considered low-moisture foods (aw < 0.60).