Lemon Oil to -Cyclodextrin Ratio Effect on the Inclusion Efficiency of -Cyclodextrin and the Retention of Oil Volatiles in the Complex Bhesh R. Bhandari,* Bruce R. D’Arcy, and Lien Le Thi Bich School of Land and Food, Food Science and Technology, University of Queensland, Gatton, QLD 4345, Australia Microencapsulation of lemon oil was undertaken with -cyclodextrin using a precipitation method at the five lemon oil to -cyclodextrin ratios of 3:97, 6:94, 9:91, 12:88, and 15:85 (w/w) in order to determine the effect of the ratio of lemon oil to -cyclodextrin on the inclusion efficiency of -cyclodextrin for encapsulating oil volatiles. The retention of lemon oil volatiles reached a maximum at the lemon oil to -cyclodextrin ratio of 6:94; however, the maximum inclusion capacity of -cyclodextrin and a maximum powder recovery were achieved at the ratio of 12:88, in which the -cyclodextrin complex contained 9.68% (w/w) lemon oil. The profile and proportion of selected flavor compounds in the -cyclodextrin complex and the starting lemon oil were not significantly different. Keywords: Microencapsulation; lemon oil; -cyclodextrin; flavor volatiles INTRODUCTION Microencapsulation of flavors in a -cyclodextrin molecule is one of the most effective methods for protecting flavors against oxidation, heat degradation, and evaporation (Hedges et al., 1995; Szente and Szejtli, 1988; Reineccius, 1989; Pagington, 1985). This protec- tion is due to the fact that the flavor molecules are tightly held within the -cyclodextrin molecule. The interaction between -cyclodextrin (host) and flavor molecules (guests) may involve total inclusion or as- sociation with only the hydrophobic part of the molecule (Shahidi and Han, 1993; Szejtli et al., 1979). Various flavor compounds have different degrees of polarity, molecular size, and chemical compositions. Therefore, flavoring compounds may possess a particular config- uration of complex formation with -cyclodextrin. Szente and Szejtli (1988) reported that short-chain esters and aldehydes are not suitable for complexation with -cy- clodextrin. In a similar way, Reineccius and Risch (1986) found that smaller molecules are less retained than larger molecules. Additionally, they found zero inclusion of the flavor compound isoeugenol in -cyclo- dextrin. The variable retention property of -cyclodex- trin may sometimes produce an unbalanced flavor profile for certain flavor powders that are prepared using -cyclodextrin, particularly when small molecules are involved. There have been reports of numerous flavor com- pounds being encapsulated using -cyclodextrin (Pag- ington, 1986). However, most of the studies are limited to total flavor retention and stability during storage. As each flavoring material is composed of individual flavor compounds in various proportions, the final note offered by the product will depend on maintaining the original flavor composition during processing. The aim of this study was, therefore, to microencapsulate lemon oil using -cyclodextrin, and to investigate the overall characteristics, including the profile of flavor volatiles, of the complex as affected by the ratio of lemon oil to -cyclodextrin used during the complexation process. MATERIALS AND METHODS Raw Materials. Cold pressed lemon oil stored at 4 °C and -cyclodextrin (Japan Food and Chemical Pty. Ltd., Tokyo) were used as raw materials in the microencapsulation process. The concentration of volatiles in the lemon oil was 97.63% as determined by GC-MS analysis using the internal standard tetradecane. The moisture content of the -cyclodextrin was 9.94% as determined by the vacuum-drying method (AOAC, 1990). Complexation Process. A precipitation method used by Reineccius (1989) was used to prepare the lemon oil-- cyclodextrin complex. Fifty grams ((0.01) of -cyclodextrin was dissolved in 500 mL of an ethanol to water (1:2) mixture maintained at 55 °C ((2 °C) on a hot plate. A predetermined quantity of lemon oil dissolved in ethanol (10% w/v) was then slowly added to the warm -cyclodextrin solution. During addition of the lemon oil solution, the -cyclodextrin solution was continuously stirred (magnetic stirrer) and the tempera- ture maintained at 55 °C ((2 °C). The heating was stopped following this addition, and the resultant mixture was covered and stirred for 4 h. The final solution was refrigerated overnight at 4 °C. The precipitated -cyclodextrin-oil complex was recovered by filtration. This precipitate was dried in a convection oven at 50 °C for 24 h. The powder was then removed from the oven and allowed to air-dry at 25 °C for an additional 24 h in order for the powder to reach its equilibrium moisture content. The final powder at equilibrium was weighed. The amount of powder recovered (dry basis) was calculated by deducting its moisture content. Finally, the lemon oil powder was stored at 25 °C in an airtight bottle. The following five starting ratios of core material (lemon oil) to -cyclodextrin were used: 3:97, 6:94, 9:91, 12:88, 15: 85. Each starting ratio was prepared and investigated in triplicate. Subsequently, each of the investigated parameters (e.g., total oil, surface oil) were studied in duplicate for each prepared sample. Moisture Determination. The moisture content of the lemon oil powder was analyzed by drying a powder sample (3-4 g) in a vacuum oven at 70 °C for 24 h, under pressure <6.7 kPa (AOAC, 1990). Capillary GC-MS Analysis. The concentrated extracts were analyzed by a standard GC-MS procedure using a * Address correspondence to this author. E-mail: bb@burger.uqg.uq.edu.au. Facsimile: +61 7 5460 1171. 1494 J. Agric. Food Chem. 1998, 46, 1494-1499 S0021-8561(97)00605-5 CCC: $15.00 © 1998 American Chemical Society Published on Web 03/24/1998