Residual moisture content as related to collapse of freeze-dried sugar matrices

PABLO BONELLI; CAROLINA SCHEBOR; ANA LEA CUKIERMAN; MARÍA DEL PILAR BUERA; JORGE CHIRIFE

JOURNAL OF FOOD SCIENCE

Institute of Food Technologists

Año: 1997 vol. 62 p. 693 - 695

0022-1147

Amorphous sugars were prepared by freeze-drying 20% (w/w) aqueoussolutions of lactose, sucrose, trehalose and maltose. The dried sampleswere further dehydrated over P2O5 for 1 wk at 25, 35 or 457C, and theresidual moisture content was determined using oven drying or a thermogravimetricbalance. Results indicated a small amount of residualmoisture (usually 1–2%) which was not removed by the desiccationtreatment for 1 wk at 257C over P2O5. The dried samples, heated at atemperature near the published ‘‘anhydrous’’ glass transition temperatures(Tg) exhibited different behavior depending on whether they wereheated in open or sealed vials. Structural collapse, a sharply visibleshrinkage of the matrix, was found in all samples in sealed vials, whilethose samples in open vials did not collapse. Thus, removal of the lastamount of residual moisture by heating in uncovered vials increased Tg,preventing or delaying collapse.