The freeze-drying of orange juice for the preparation of reference materials

Summary

The possibility of producing fruit juice reference materials is conditioned by the availability of a method which allows the transformation of the original juice or concentrate into a better physically stable form. Therefore a feasibility study of the transformation of orange juice by freeze-drying was carried out. In general, the obtained powder is hygroscopic, and tends to agglomerate into large solid lumps. Under optimal conditions of freeze-drying combined with redrying of the powder before closing the bottles, a slightly cohesive but physically stable yellow orange powder can however be obtained. Compared to the original juice, this shows no loss of reducing sugars and has a normal glucose-fructose ratio. Moreover, most aminoacids e.g. asparagine, methionine, lysine and arginine are not affected by freeze-drying. Based on the study of a limited number of important fruit juice parameters, it may be concluded that freeze-drying seems very promising in order to obtain an orange juice reference material, which after redissolution in water keeps the original chemical orange juice properties.