Pectin, carrageenan help increase hardness, springiness, gumminess of extruded fruit.

Although extrusion technology has been used extensively to create carbohydrate-based snack foods, the use of extrusion to create a fruit-based snack product is a relatively new area of research. The benefits of an extruded fruit product include the health appeal of a fruit-based snack, the convenience of a ready-to-eat product and the ease of production which extrusion provides. Extruded fruit pieces can be used in ready-to-eat cereals. Extruded fruit purees can enhance the nutritional quality of candies, baked goods and frozen treats.

University of Missouri scientists investigated the moisture content, water activity, texture profile and shelf life of an extruded strawberry-based snack. The snack contained 27% strawberry puree, strawberry powder in a range of 37.25% to 39.25%, 31% glycerol, up to 2% pectin, up to 2% carrageenan, up to 1% citric acid and up to 1% potassium sorbate. The formulations were produced using a twin-screw extruder.

The ingredients were mixed together and heated to 80 C in a heating kettle-mixer before they were manually transported to the extruder. Researchers kept the processing conditions constant for all formulations--25 rpm and 65 C to 149 C in five of the nine zones. The researchers found that as the concentrations of pectin and carrageenan increased, the values for hardness, springiness and gumminess increased significantly, and the values for adhesiveness and moisture content decreased significantly.

The values for cohesiveness and water activity did not significantly change. High levels of pectin and carrageenan, combined with high levels of citric acid and potassium sorbate, yielded the highest values for hardness, springiness and gumminess and the lowest values for water activity (0.500 aW), adhesiveness and cohesiveness.

Over the five-month shelf life of the product, all formulations showed a significant increase in hardness, springiness and gumminess as well as a decrease in moisture content of 5% to 7%, water activity from 0.556 Aw to 0.490 Aw, adhesiveness and cohesiveness.

Further information. Fu Hung Hsieh, Department of Biological Engineering, University of Missouri, 248 Agricultural Engineering Building, Columbia, MO 65211; phone: [phone]; email: [e-mail].