## 3 Results and Discussion
### Effect of Polymer:Oil Ratio  
As complex coacervation results in the formation of core-shell microcapsules, one of the advantages of this process compared to conventional spray drying is a high loading (see, for example, the review by [PERSON] [19]). Here, we have investigated the degree of loading as determined by the Polymer:Oil ratio used in complex coacervation, and to what extent this affects size distribution and retention of peppermint oil following spray drying. Polymer:Oil ratios were varied from 1:2 to 2:1. Optical microscopy images and size distributions for microcapsules with different Polymer:Oil ratios before and after spray drying are shown in Figures 3 and 4 below, respectively. From the optical microscopy images in Figure 3, the tendency towards apparent loss of the largest capsules during spray drying is less for the highest Polymer:Oil ratio, with a similar narrowing of the differential number size distribution as discussed above (Figure 4). The differential volume size distributions show that the fraction of the largest floc population decreases with increasing Polymer:Oil ratio, with the population of flocs \(>80\)\(\mu\)m completely absent for Polymer:Oil = 2:1. This observed difference in dispersion flow behaviour might reflect changes in the viscoelastic properties of the polymer shell, with a thicker shell resulting in more rigid capsules with lower sticking probability. The microcencapsulation yield as a function of Polymer:Oil ratios after spray drying is shown in Figure 5. The coacervates prepared with ascorbic acid were stable during spray drying. None of the systems studied here showed any measurable loss of peppermint oil following the complex coacervation process (Table 1). In a 2004 study, [PERSON] et al. [26] encapsulated sunflower, lemon and orange oil by complex coacervation using whey protein isolate and gum Acacia as wall materials, reporting less than 20% loss of oil following the emulsification and coacervation steps. In order for better comparison of parameters such as wall thickness and crosslinker concentration, the spray drying parameters were kept constant for all the samples studied here. Also, unlike for conventional spray drying where microcapsules are formed during drying of the sprayed droplets, retention and encapsulation yield of oil in microcapsules formed by complex coacervation are expected to be less susceptible to spray drying parameters. From Table 1 and Figure 5 below, the mi  
Figure 4: Size distribution of peppermint oil complex coacervate microcapsules with different Polymer:Oil ratios before (**A**,**B**) and after (**C**,**D**) spray drying as measured using laser diffraction. Crosslinker concentration = 5% (_w:w_) with respect to BSA for all capsules. croencapsulation yield after spray drying generally increases with Polymer:Oil ratio, which is in agreement with other published work on microencapsulated essential oils [23, 25]. Note that for the data presented in Figure 5, crosslink concentration was kept constant at 5 wt% with respect to BSA. At lower Polymer:Oil ratios--especially for Polymer:Oil = 1:2, the high amount of peppermint oil relative to polymer suggests the formation of very thin microcapsule walls, which do not impart sufficient stability to prevent loss of oil during spray drying. Still, it should be noted that a Polymer:Oil ratio of 1:2 is much higher than what is generally found in the literature for spray drying of complex coaervate microcapsules, where Polymer:Oil ratios of up to 10:1 are reported [25]. Interestingly, it also appears that total polymer concentration affects microencapsulation yield, as shown for Polymer:Oil = 1:1 in Table 1 and Figure 5. Specifically, increasing the polymer concentration also increases the microencapsulation yield from 19% to 27% for 3 and 6 wt% polymer, respectively. This might be attributed to increased partitioning at the oil-water interface of coaervate nodules at higher polymer concentrations.