Handbook of Vitamin C Research

194Magdalena Stevanović and Dragan UskokovićHowever, this technique leads to low encapsulation efficiencies for water-soluble drugs [90,110].The solvent evaporation technique was used to investigate effects of varyingtemperature, core-to-wall ratio and the presence of plasticizsers (triethyl citrate) on themicroencapsulated ascorbic acid [96]. Results showed that the presence of plasticizerdecreased the release rate. Two core-to-wall ratios used were 1:1 and 3:1. No significanteffect was found. Similarly, the two temperatures used for solvent evaporation of 28°C and55° C, showed no significant effect on the release rate. The spray drying technique used fourdifferent polymer-coating materials, whether singly or as a mixture. They were gel, starch,ethyl cellulose and β-cyclodextrin. The results showed that ascorbic acid loss during spraydrying was 20%. Each of the various coating materials resulted in capsule sizes mostlybetween the 90-280μm fractions. However, the encapsulated ratio of ascorbic acid was notvery high, less than 50%. This means that less than 50% of ascorbic acid used in thetechnique was actually microencapsulated.5.4. Spray DryingSpray-drying is a well-known technique that generates solid powders from solution orsuspension and has special applications in the pharmaceutical industry in manufacturing drugdelivery systems and controlled release formulations. Consisting of a single step process thatinvolves atomisation of the liquid feed which is injected into a drying chamber containing hotair or nitrogen. The droplets instantly dry into solid particles that are subsequently collectedin the drying chamber. The two factors that can influence the properties of the output materialare the spray-dried particle formulation factors and the spray-drying parameters [111]. Spraydryingwas used as preparation method of vitamin C/Eudragit® microspheres [71]. VitaminC/Eudragit® microspheres obtained by this method showed potential for delivery of vitaminC by oral rout [71]. Spray-drying was, also, used by Finotelli and co-workers for obtainingmicrocapsules with different content of ascorbic acid for application in the food industry asfortification [112].5.5. Homogenization of Water and Organic PhasesSpherical nanoparticles of the poly (D,L-lactide-co-glycolide) (PLGA) in the size range110-170 nm were produced using physicochemical method with solvent/non-solvent systems[1, 17, 113]. The encapsulation of the ascorbic acid in the PLGA polymer matrix wasperformed by homogenization of water and organic phases (modified precipitation method)(Figure 6). The PLGA commercial granules have been dissolved in acetone and after that theaqueous solution of the ascorbic acid has been added in PLGA solution in acetone whilecontinuously been homogenized. Concentration of ascorbic acid in water was varied in orderto obtain particles with different ratio of PLGA and ascorbic acid (PLGA/ascorbic acid85/15%wt, PLGA/ascorbic acid 70/30%wt, PLGA/ ascorbic acid 50/50%wt and PLGA/ascorbic acid 30/70%wt) [1, 113]. The introduction of 15% of ascorbic acid does notinfluence the size, while further increase of ascorbic acid concentration increases the size of