Texture of vacuum microwave dehydrated apple chips as affected by calcium pretreatment, vacuum level, and apple variety

The effects of calcium pretreatment, vacuum level, and apple variety on the texture of apple chips, processed using a combination of air drying and vacuum microwave dehydration (VMD), were determined. Pretreatment of apple slices by immersion in 1-5% aqueous CaCl2 significantly increased crispness of chips as determined by instrumental and sensory analysis; however above 1%, chips were perceived as bitter. Higher vacuum applied during VMD significantly lowered density and increased crispness of chips. This effect was mediated by the vaporization of water in the interior of the chip, which caused expansion of the tissue. Chips made from Fuji apples had higher calcium contents, and were crisper than Red and Golden Delicious apple chips. Microstructure of the chips evaluated by scanning electron microscopy indicated that chips with thicker cell walls and large internal voids were crisper.