Sporopollenin microcapsules for microencapsulation of living cells
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Sporopollenin microcapsules for microencapsulation of living cells Shwan A. Hamad,1 Amro K.F. Dyab,1,2 Simeon D. Stoyanov3 and Vesselin N. Paunov*,1 1 Surfactant & Colloid Group, Department of Chemistry, University of Hull, Hull, HU6 7RX, UK. 2 Surfactant Research Chair, Chemistry Department, College of Science, King Saud University, P.O.Box - 2455, Riyadh - 11451, Kingdom of Saudi Arabia. 3 Unilever Foods and Health Research Institute, Olivier van Noortlaan 120, 3133 AT Vlaardingen, The Netherlands. ABSTRACT We used sporopollenin prepared from Lycopodium Clavatum to encapsulate living yeast cells as a model for probiotics. The microencapsulation of cells was achieved by using the trilite scars of the sporopollenin microcapsules which can open up by compressing the sporopollenin into a pellet. Such compressed pellets were exposed to an aqueous suspension of yeast cells in the presence of a biocompatible surface active agent which allowed living cells to be loaded inside the sporopollenin particles by the influx of liquid to the sporopollenin interior as the deformed microcapsules re-inflated to their original state. We demonstrated that the cells viability and biological activity is preserved after the microencapsulation in the sporopollenin. Such microencapsulation technology could find application in preserving cells from mechanical stress and aggressive environments which can be used in protection of probiotics in food formulations. INTRODUCTION The term sporopollenin was first coined by Zetzsche [1] to describe the material which essentially forms the major part of the outer highly resistant coat (exine) of pollen grains. Pollen powder consists of monodisperse pollen grains, which contains the sperm cells of seed plants. Sporopollenin has been recognized as one of the most resistant material of bioorganic origin [2] against both biological and chemical decay. Preserved individual sporopollenin grains have been discovered in 500 million year old sedimentary rocks [3]. Pollen grains come in variety of morphologies, where the shapes, size and surface features depend on the plant species. Many pollen grains have nearly spherical morphology with the smallest size of around 6 µm. The pollens of the Lycopodium clavatum (running pine) are shaped like a three-sided pyramid which forms a trilite scar and round shape on the opposite side of the particle which is covered by a honey-comb structure of rims. These complex particles have diameter of about 28 µm [4]. Sporopollenin can be isolated from the pollens by consecutive alkaline and acidic solvent treatments, which remove the inner cellulose layer but preserve the exine morphology. The exact chemical structure of sporopollenin is still questioned but the analytical evidence suggests that the main component is an oxidized polymer of carotenoids and their esters [3e]. Bohne et al.[5] studied the structure and the diffusion properties of sporopollenin microcapsules prepared from pine pollen and demonstrated that the sporopollenin exine contains two inner layers (endexine an
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