Microencapsulation is a proven technique used to convert food flavours into a more useable and shelf-stable solid form. For the purposes of this study one of the food flavour compounds, limonene, has been microencapsulated within the β-cyclodextrin.
Information on the sorption isotherm behaviour of β-cyclodextrin and/or the β-cyclodextrin flavour (Limonene) complex is non-existent. Sorption characteristic is an essential "tool" within the food processing industry to predict both the stability and its capability to be processed during food manufacture.
This research was undertaken to study the sorption isotherms of the complex powder with a variable amount of Limonene flavour volatile loads. The percentages of flavour proportions complexed with the β-cyclodextrin were 3%, 7.50% and 9.68% (dry basis). The sorption data of the complex powder was fitted to various predictive mathematical models. The parameters of the models were determined by linear and non-linear regression analysis. In addition, the effect of temperature on the net isoteric heat of sorption was analysed by the Clausius-Clapeyron equation.
The predictive mathematical models studied in this thesis were the two parameter models namely the BET, Halsey, Henderson, Oswin, and Smith. The three parameter model studied was the GAB model, and the four parameter model studied was the double power Peleg model. In predicting a suitable mathematical model, the maximum acceptable % relative mean error was considered 10%. The (co-efficient of determination) values were also compared. All the models except the double power Peleg model were compared mathematically using both the linear and non-linear regression analysis methods. The results of this study indicated that the β-cyclodextrin is hydrophilic, and that moisture is strongly "attracted" or showed high affinity to the β-cyclodextrin torus shaped molecule. The other observation made was that the desorption isotherm moisture levels were very high (approximately 1 5% dry basis) at a water activity of 0.1. At the same water activity, the moisture content of β-cyclodextrin, during adsorption was averaged at approximately 6% dry basis.
When the % relative mean error values and coefficients of determination were compared, the GAB model fitted the best for both the BCD (Beta-cyclodextrin) and BCD complexes. The Henderson and Smith model results also showed to be acceptable, with most % relative mean error values below 10% and reasonably high coefficient of determination values above 0.92. The Oswin, and Halsey equations performed poorly for the adsorption isotherm results, but performed very well for the desorption isotherms. The Smith and BET equations proved to perform better with adsorption isotherms. However, the most acceptable equations for both the adsorption and desorption isotherms were the GAB and Henderson equations.
The values for the double power Peleg model were very comparable with the GAB model for both the adsorption and desorption of the BCD and BCD complexes used in the linear regression analysis. However, the GAB model did outperform the double power Peleg model for the desorption results for both the BCD and BCD complexes.
The sorption behaviour of the micro-encapsulated complex was influenced strongly by the amount of limonene oil. At the same equilibrium humidity condition, the dry basis moisture of the complex decreased as the amount of limonene in the complex was increased. The increased percentages of limonene oil complexed with BCD probably lowered the strength of high energy binding sites with water. The curves started to resemble sigmoid type II curves rather than the type I Langmuir curves as observed in the case of pure BCD. The degree of hysteresis also changed, and became less pronounced as the temperature and limonene contents micro-encapsulated with BCD increased.