Determining the dry matter is an essential measure with regard to food powders because:. it gives the dry matter content of the product, which can then be used to determine the material cost and commercial value of the powder . it gives the moisture (or water content) of the product, which is the difference between 100% total weight and the dry matter content. The dry matter content directly relates to the amount of water in a product. This in turn can be used to determine availability (water activity; cf. Chapter 11) and water mobility (glass transition; cf. Chapter 12) and consequently the biochemical stability, physical properties and flowability of the product.

-The glass transition temperatures (T g ) of various dairy powders were determined by differential scanning calorimetry among the sorptions isotherm, and were also calculated using the extended Couchman-Karasz equation, taking into account the dry values of T g and ∆Cp (heat capacity changes during glass transition) and the contents in each amorphous component category. The results obtained showed a statistically significant correspondence between measured and calculated T g inflection values: the model gives an approximate inflection value of T g corresponding to the measured one ± 14°C. This lack of fit can be explained both by the accuracy of measurement of T g and by not considering minor constituents of dairy powders (minerals and oligosaccharides) in calculation. From the values of T g and ∆Cp measured and/or calculated in this study, it is possible to anticipate the behavior of a dairy powder under given temperature (T) and water activity (a w ) conditions during drying and storage with regard to stickiness and caking. We propose the calculation of a stickiness and caking sensitivity index according to the values of [T -T g ] and ∆Cp, whose value is in agreement with the expected behavior of various dairy powders during drying and storage.

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