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In the present thesis a study of hydrocolloids derived from olive plant matrices took place. The main source of these raw materials was the solid wastes from olive oil mills, low value by-products of the food industry which were first fully or partially composted before being used in this study. Those extracts were characterized via various physicochemical methods, such as SEC and FT – IR. The characterization showed that the extracts from composted olive oil mill waste are hydrocolloids negatively charged, comprised mostly of high molecular polysaccharides and some proteins. Subsequently, in order to assess their capacity to being used as emulsifiers in the food industry, the extracts from olive plant matrices were added as emulsifying agents to prepare O/W emulsions. The study of these emulsion showed that the extracts can be used as emulsifiers providing quite stable emulsions over time with relatively small droplet size distribution. Because of this they could be used in real products for the food industry. All of the above were confirmed by the measurements of static light scattering, zeta potential, interfacial tension phenomena and with laser confocal microscopy (LSCM). The same procedure with the same measurements was performed on all partially composted samples. In this case, the results of the emulsions study showed prospects of their being used as emulsifiers in acidic foods with a short shelf life, unlike in the case of fully composted waste which were stable for a longer period. In addition, all of the samples were studied for a period of 6 months, from the beginning of composting until its completion, in order to identify differences in their composition and emulsifying ability. In this case, the results of the interfacial phenomena were statistically analyzed to determine the optimum pH of the extraction as well as the optimum composting time. The results of this analysis showed statistically significant differences between the samples according to composting time and extraction pH, however, in the case of time, no reliable conclusions can be drawn as further study of the hydrolysis of proteins is needed to determine their effect on interfacial tension, and therefore the emulsifying capacity of the samples