Encapsulation and real-time release characteristics of spray dried l-menthol

Abstract

The objective of this research was to understand the effects of octenyl succinic anhydride (OSAn) substitution level of carbohydrate encapsulation materials on the capsule characteristics and real-time release of l-menthol from spray dried powder. Spray dried l-menthol powder was prepared from modified dextrin and gum acacia of varying levels of OSAn substitution. Physical properties of the microcapsules and encapsulation matrices were determined by: constructing moisture sorption isotherms, particle sizing, density measurement via pycnometry, and by total and surface menthol content of the finished powders. Real-time menthol release and moisture uptake profiles were accomplished by using dynamic vapor sorption (DVS) coupled with either Tenax trapping and gas chromatography (GC) or proton transfer reaction mass spectrometry (PTR-MS). It was found that as OSAn substitution of carbohydrates increases, total and surface menthol appeared to increase and decrease, respectively. The particle size of the finished spray dried powder was influenced by spray dryer infeed solids concentration with higher solids leading to larger particle size. Microcapsule density did not appear to be affected by OSAn substitution or carrier type. Menthol release profiles varied greatly with carrier material used. Increased OSAn substitution (up to 3% treatment level) of the carrier material resulted in a significantly greater, but not earlier burst of menthol release. For most samples, the characteristic burst of menthol was followed by a decrease in release which was attributed to an observed matrix collapse. Moisture uptake rates of the powders were related to corresponding menthol release rates. As OSAn substitution increased for gum acacia (Acacia seyal), a trend of increased moisture uptake rate with menthol release rate was evident. However, for the dextrins, the moisture uptake rate had no influence on the rate of menthol release. The degree of OSAn substitution did not affect moisture sorption characteristics for dextrin samples. For gum acacia, increased levels of OSAn substitution resulted in a decreased affinity for moisture in the range of 0.3 to 0.7 aw.