Reconstitution characteristics of food powders and granules with emphasis on non fat dried milk : a thesis presented in partial fulfilment of the requirements for the degree of Master of Food Technology in Food Processing at Massey University, Palmerston North, N.Z.

Abstract

Reconstitution characteristics of food powders form a major determinant of consumer acceptance, particularly with the trend to instant foods. A working theory has been proposed to explain the mechanism of dispersion of any soluble food powder. A study was made of methods which may be employed to modify reconstitution characteristics. No significant improvement in the dispersibility of Non Fat Dried Milk (NFDM) could be achieved by a compression/repowdering process even though the particle density and porosity of the powder could be increased by this technique. When applied to spray dried instant coffee such process of compression, up to 150 psi, resulted in a small improvement in dispersibility while at the same time achieving a marked increase in the bulk density of the powder. The significance of this observation with regard to potential saving in packaging volume has been discussed. The most significant improvements in reconstitution characteristics of NFDM were achieved by a rewetting/redrying process. A granulation technique is described which has been successfully employed to simulate commercial instantising of powders. By means of this granulation technique it has been shown that by far the most important factors in agglomeration influencing the properties of the resultant "granules" are : 1. Rewetting moisture content at which granulation is achieved prior to redrying; 2. Particle or granule size of the final product. Optimum conditions for NFDM have been determined to be 11-12% rewetting moisture and a mean particle size of 200/u. This granulation technique has also been employed to study the effect of additives at agglomeration upon reconstitution properties of NFDM. Several commercial processes are in use, and are covered in patents, for the purpose of instantising NFDM and other food powders. Despite this, however, no study has previously demonstrated the critical nature of certain variables in this process as clearly as has been done in this study.