Mechanisms of retention of organic volatiles in freeze‐dried systems *

Abstract

Retention of organic volatiles was studied in freeze-dried systems containing various carbohydrates ranging in molecular weight from glucose to dextrans. On the basis of the freeze-drying experiments and studies on sorption and desorption after drying, a mechanism for the retention and /or loss of volatiles .during drying was postulated. The mechanism involves formation of 'microregions' in the dry cake in which the volatile is entrapped. The space between the microregions is freely passable by the volatile. The total amount of volatile retained under given conditions depends on the moisture profile during drying, and on the effective vapour pressure of the volatile in the system.The present paper considers the following molecular aspects of the formation of microregions in freeze-drying of solids :(1) orientation of the molecules of the solid with respect to volatile molecules prior to or during freeze-drying;(2) effects of size and polarity of the volatile on orientation of surrounding carbohydrate molecules ;(3) effects of mobility of these molecules under conditions of drying;(4) molecular and environmental factors which control the moisture level at which the microregions become sealed, and subsequently impermeable to the volatile.

Properties of oregano (Origanum vulgare L.), citronella (Cymbopogon nardus G.) and marjoram (Majorana hortensis L.) flavors encapsulated into milk protein-based matrices

“…Operating conditions as well as the nature of core flavoring and coating carrier are the main determinant factors in the retention of volatile constituents (Flink & Karel, 1970a, 1970bRosenberg et al, 1990;Voilley, 1995). It was reported that proteins possess sufficiently high binding capacity for flavor compounds (Franzen & Kinsella, 1974;OÕNeil, 1996).…”

Effects of carbohydrate crystallization on stability of dehydrated foods and ingredient formulations

“…The effect of amorphous sugars on aroma retention during storage has been extensively investigated (Chirife, Karel, & Flink, 1973;Flink & Karel, 1972). Senoussi, Dumoulin, and Berk (1995) showed that diacetyl retention decreased sharply in a lactose matrix, when about 60% of lactose crystallized.…”

Structure related changes during moistening of freeze dried apple tissue

“…Unexpected high retention of volatiles in model systems and foods was observed in early studies on freeze drying by Karel (1970, 1972) and Chirife and Karel (1973) among others. A strong decrease in the retention of volatiles following moisture adsorption and structural collapse was evidenced (Chirife & Karel, 1974;Flink & Karel, 1972;To & Fink, 1978). It was proposed that volatiles may become entrapped in the amorphous matrices resulting from rapid dehydration and that the release of entrapped volatiles may be triggered by structural collapse.…”