Water activity and glass transition in dairy ingredients

Abstract

-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.

Hidrólise Da Lactose E Produção De Leite Em Pó: Aspectos Tecnológicos

“…Respectivamente: interior da câmara de secagem após 1 hora de operação (1) e entrada do ciclone após 1 hora de operação (2). (SCHUCK et al, 2005a).…”

“…Porém, se este mesmo pó apresentar 4,4% (m/m) de umidade, a sua TTg passa a ser de 45 ºC. Este decréscimo ocorre devido a uma maior porcentagem de água no produto (SCHUCK et al, 2005a).…”

“…Como apresentado na Tabela 1, estes monossacarídeos apresentam uma TTg menor que a da lactose, visto que a TTg de um carboidrato é inversamente proporcional ao seu peso molecular (ROOS, 1993). Considerando que a TTg do produto lácteo é a resultante dos seus componentes, o LPD apresenta uma TTg menor que a do leite em pó tradicional (SCHUCK et al, 2005a).…”

Processing of Mozzarella cheese wheys and stretchwaters: A preliminary review

“…Among sugars, it is of interest to note that glucose and galactose have lower glass transition temperatures than lactose. Schuck et al [49] developed a stickiness and caking sensitivity index that, on the basis of the characteristics of a powder (glass transition and change in thermal capacity) and the process, makes it possible to assess the risk of stickiness and/or caking.…”

Studying of Properties and Storability of Dry Whey Obtained With the Use of Electric Spark Treatment

“…Полученные результаты согласуются с литературными данными [14,16], в которых указано, что скорость физико-химических из-менений в продукте, в том числе реакции Майара, снижается при уменьшении разности между температурой хранения и температу-рой стеклования.…”