Solar-augmented foam-mat drying of fruits

The foam-mat drying technique is used to dry fruit syrups into powder. Literature has indicated that solar energy has not yet been used in this field. Thus, it is the object of the present work to dry the foamed syrups of different fruits in a solar energy augmented drying unit. This leads to a saving in both energy and environmental pollution. An auxiliary heater, along with a control unit, is used to ensure drying at constant temperature. Foaming is effected by suitable edible additives and in some cases a stabilizer is needed as well. New techniques concerning the concentration and neutralization of fruit syrup were reached. The drying experiments were run on orange, lemon, grapefruit, tomatoes, strawberry, guava and apple. The results showed that foaming decreased the time of drying by 30.8–41.5% in the case of direct sun drying and by 47.1–73.2% in the case of solar drying compared to the drying time of unfoamed syrup. The present study showed that the solar-augmented foam-mat drying technique proves to be of sufficient efficiency and acceptability to replace spray drying which is known to be a highly complicated and energy-consuming technique.