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38 April 2019 Tablets & Capsules being the shell plasticizer. As the fig- ure shows, the glycerin-plasticized softgels increased in hardness by 360 percent after six months, whereas the softgels plasticized with sorbitol-sor- bitan solution only increased in hard- ness by 30 percent. Formulators should choose plasti- cizers and their ratios carefully, con- sidering factors such as the gelatin quality, the capsule size, and the nature of the liquid fill. Many different tools are available to quantify plasticizer activity. One well-known method is to conduct differential scanning calorimetry (DSC) studies with isolated films [2]. This method gives access to important values, including the shell's specific melting enthalpy, melting temperature, and glass tran- sition temperature. The specific melting enthalpy indicates the crys- tallinity of the formulated gelatin and can help formulators in adjust- ing the relative levels of the excipi- ents in the shell to obtain the neces- sary gelling for film formation and sealing. Table 1 shows DSC data illustrating the impact of glycerin, sorbitol-sorbitan, and a 50/50 blend of the two on isolated gelatin films. Both excipients demonstrated a remarkable ability to soften gelatin. Formulations containing sorbitol-sor- bitan as the sole plasticizer had a lower impact on the gelatin's melting temperature and a greater impact on its melting enthalpy than formula- tions containing glycerin at the same concentration. As the data show, sor- bitol-sorbitan solution can also be used in combination with glycerin. Because sorbitol-sorbitan solution is less hygroscopic than glycerin, as shown in Figure 4, it offers various advantages for softgel production and storage. First, softgels made with sorbitol-sorbitan solution require 10 to 20 percent less drying time after production than softgels plasticized with glycerin, which reduces production costs. Second, since softgels made with sorbitol-sorbitan solution are less hygroscopic than those made with glycerin, they are more able to resist challenging storage condi- Table 1 DSC data for isolated 180-bloom gelatin films without and with 33 percent plasticizers Melting temperature (°C) Melting enthalpy (J/g) Gelatin without plasticizer 97.8 19.0 Gelatin with 33 percent glycerin 57.6 13.2 Gelatin with 33 percent Polysorb 90.0 8.8 Gelatin with 16.5 percent glycerin and 16.5 percent Polysorb 75.0 13.4 Figure 3 Shell hardness over time for softgels plasticized with glycerin versus softgels plasticized with sorbitol-sorbitan solution (Polysorb 85/70/00) Shell hardness (N) 7 6 5 4 3 2 1 0 Glycerin Polysorb Initial 1 month 6 months Figure 4 Hygroscopicity of sorbitol-sorbitan versus glycerin 80 70 60 50 40 30 20 10 0 Water content (%) Relative humidity (%) 0 20 40 60 80 100 Polysorb Glycerin