Experimental substantiation of the composition of gelatin mass for obtaining capsules with essential oils
Authors: Molokhova E. I. , Ponomareva E. I. , Sorokina Yu. V. , Alekseeva I. V. , Ryumina T. E. , Novikova V. V. , Golovanenko A. L. , Berezina E. S. , Ladutko Yu. M. 
Published: December 2021

Introduction. Soft gelatin capsules are a promising dosage form comprising essential oils as active agents. Joint research of the staff of the Perm State Pharmaceutical Academy, the Research Institute of Nutrition of the Ministry of Energy and Industry of the Republic of Tajikistan have proposed the composition of gelatin mass for encapsulation by the rotary matrix method. The mechanical and physical-technological parameters required to preserve the strength and elasticity of the capsule shell during the production process and storage are determined.

Aim. Study of the rheological properties of gelatin masses based on gelatin of different grades, as well as the migration of essential oils through capsule shells.

Materials and methods. Pharmaceutical active substances "Lipovitol" and "Limoneol" obtained in the Republic of Tajikistan were used as active substances introduced into the composition of soft gelatin capsules. Sunflower oil was used as the solvent. Gelatin samples were used to obtain gelatin masses: 1 – Foodchem (China), 2 – Brodnickie Zaklady Zelatyny Sp. zo.o. (Poland), 3 - Italgelatine s.p.a. (Italy), 4 – Ewald-Gelatine GmbH (Germany), 5 – Weishardt International (France); glycerol; sunflower oil. Gelatin mass for manufacturing soft capsules was prepared in a closed reactor. Capsules were prepared on an automatic encapsulation line RJWJ – 115 Soft Gelatin Encapsulator Machine (China). The structural and mechanical properties of soft gelatin masses were determined on a rotary viscometer RV type "Reotest 2" (Germany). The dynamics of the process of migration of essential oils and its components were studied by changing their amount in a capsule by chromato-mass spectrometry method on a chromatograph Varian CP 3800 with a quadrupole mass spectrometer 4000 MS as a detector (USA).

Results and discussion. When studying the rheological properties of model compositions, it was found that for all samples of gelatin masses there is a decrease in values of effective viscosity when the shear rate increases, which characterizes the tested samples as a structured dispersion system. Additional studies have shown that the gelatin masses have thixotropic properties. Samples of gelatin masses 3–5 had narrower hysteresis loops, while sample 5 the narrowest, restoration of the structure took place quite quickly. Capsules obtained from gelatin mass 3 and 4 samples had a strong seam and were well cut out of the tape. From the mass of sample 5, high strength ribbons were obtained, a high temperature was required to seal the capsules, in some capsules the seam was not glued on one side, as a result, the capsules were rigid and brittle. As a result of the study, the rheological optimum of the gelatin mass suitable for preparing capsules by a rotary matrix method was determined, which has boundaries in the ranges of shear rates of 0.556–243 s-1 and viscosity ranges of 11.46-5028.76 Pa ⋅ s and shear stress of 2788–2808 Pa developing at these rates. When studying the migration of active substances through the capsule shell, it was found that over three years of storage of capsules in a closed polymer can, the content of essential oil in Lipovitol capsules decreased by 4.88 %, in Limoneol capsules by 5 %, which indicates partial migration of oil through the gelatin shell. The content remained within the permissible deviations (±10 %). The content of essential essential oil components also remained within acceptable deviations throughout the shelf life.

Conclusion. The optimal composition of the shell for producing soft capsules by a rotary matrix method is justified. It was found that the rheological optimum of gelatin mass is characterized by viscosity ranges of 11.46-5028.76 Pa ⋅ s and shear stress of 2788–2808 Pa. According to the results of the study of the migration of essential oils through the shell, has been established the shelf life of soft gelatin capsules in glass jars made of dark glass and a temperature of 15 to 25 °C – 3 years.