SUMMARY—Explosion‐puffed apple pieces, because of their hygroscopicity, rapidly lose their crispness under humid conditions. A major cause of the loss of crispness is softening of the sugars, present in the glassy or amorphous state, as moisture is adsorbed. Of these sugars, sucrose has the highest softening point. Materials higher in sucrose content can tolerate more moisture at a given temperature before they soften than materials higher in monosaccharides. The sucrose content of apple pieces is 20—30 of the total sugars. The sucrose content of pieces for puffing was increased to 86 of the total sugars by the following treatment before puffing: The pieces were first soaked in tap water 3—6 hr to reduce monosaccharide content, then soaked in 20—40 sucrose solutions several hours to increase sucrose content by osmosis and counter‐diffusion of sucrose. The pieces were then partially dried, puffed and finally dried by conventional hot‐air drying to 2 moisture content. Comparison of untreated and treated pieces revealed that the untreated pieces lost their crispness at 4.3 moisture and the treated pieces at 6.6. When exposed to 75 R.H. and 72°F the untreated pieces remained crisp between 1 and 2 hr; at 75 R.H. and 90°F these pieces softened in less than 1 hr. However, the treated pieces exposed to 75 R.H. remained crisp 4—5 hr at 72°
展开▼
