Effects of Autoclaving and Freeze-Drying on Physicochemical Properties of Plectranthus esculentus Starch Derivatives.

The goal of this research was to assess the effects of autoclaving followed by freeze-drying on acetylated xerogel (AXS) and carboxymethylated (CMS) derivatives of Plectranthus esculentus starch as potential vaccine stabilizers. Starch extracted from tubers of P. esculentus were modified by single (carboxymethylation) and dual (acetylation followed by xerogel formation) methods. The derivatives were formulated into vaccine stabilizer suspensions, autoclaved, and freeze-dried without additives or antigen. The derivatives and freeze-dried products were assessed by physical appearance, titration, moisture content (MC), TGA, DSC, XRD, SEM, and FTIR analyses. The degrees of substitution (DS) of the CMS and AXS derivatives were 0.345 and 0.033, respectively. Modification significantly reduced the MC of the derivatives. Freeze-dried AXS (FAXS) had lower MC than freeze-dried CMS (FCMS). The lower degree of hydrophilicity/MC of AXS and FAXS was confirmed by TGA and FTIR band intensities and shifts. Reduction in DSC water desorption/evaporation enthalpies (ΔH) from - 1168.8 mJ (NaS) to - 407.48 mJ (AXS) confirmed the influence of modification on moisture. FTIR confirmed acetylation and carboxymethylation of the derivatives by the presence of 1702.9 cm-1 and 1593 cm-1 bands, respectively (FTIR). Increasing concentrations of the derivatives yielded uncollapsed/unshrunken lyophilisates. SEM and XRD showed that modification, autoclaving, and freeze-drying yielded beehive-like microstructures of FCMS and FAXS that were completely amorphous. Processing (autoclaving and freeze-drying), therefore, enhanced the amorphousness of the starch derivatives which is required in vaccine stability during processing and storage. These findings indicate that these starch derivatives have potential as novel vaccine stabilizers.

Process and isothermal storage stabilities of a live veterinary vaccine formulated with Plectranthus esculentus tuber starch derivatives as stabilizers.

Comparability stability studies of a live Newcastle Disease LaSota vaccine were conducted post freeze-drying and during storage at 5±2, 25±2 and 37±1 °C to demonstrate the equivalence/inequivalence of stability profiles of vaccines stabilized with peptone (reference), trehalose and starch derivatives (acetylated xerogel and carboxymethylated) from Plectranthus esculentus tubers. Variations in moisture content during storage at 5±2 °C; physical collapse/shrinkage, partial microcollapse, and hydrophilicity of lyophilisates were prominent in starch stabilized vaccines without additives. Using the mean embryo infective dose (EID50) test, the derivatives and peptone stabilized vaccines had < 0.5 logEID50 loss in titre during freeze-drying. At the storage temperatures of 5±2, 25±2 and 37±1 °C, using peptone, acetylated xerogel starch, carboxymethylated starch, and trehalose, the average shelf lives of the vaccines were 23-55, 21-26, and 2.6-4.9 months respectively. Acetylated xerogel and carboxymethylated derivatives of Plectranthus esculentus tuber starch with/without additives were able to keep the live ND LaSota vaccine stable during freeze-drying at 1-3 % w/v. The stability of all the vaccines declined as storage temperatures increased. The acetylated xerogel stabilized vaccines were more stable than all of the others at 25±2 and 37±1 °C temperatures.