Eureka! Institutional Repository

The purpose of the present work was the production of kefir powders and the study of the effect of the drying method and the addition of various carriers (possible thermoprotectants), on specific properties of the powders and the reconstituted samples. More specifically, 6 different kefir samples were produced, (control, a sample that remained for 4 days in the refrigerator until it was dried, and samples to which kefiran, gum arabic, inulin and fructo-oligosaccharides were added). The drying was carried out by spray drying at two different inlet temperatures (140°C and 180°C) and by freeze drying (lyophilization). For the purpose of the present work, the powders were reconstituted to 100% of the original moisture content. According to the results, almost all the freeze-dried (FD) samples showed a higher percentage of moisture than both SDA (low inlet temperature) and SDB (high inlet temperature) samples, except for FD IN, which showed a lower moisture content than that of the corresponding SDA sample and FD KEF, which only showed a higher moisture content than the corresponding SDB sample. SDB KEF, SDB IN, SDB GA and SDB TR showed a lower moisture content in comparison with the corresponding SDA samples. All the reconstituted samples showed a very significant decrease in apparent viscosity and at the same time a considerable increase in the rheological behavior index, compared to the fresh samples. Spray drying at both inlet temperatures produced powders with small particles and a narrow particle size distribution, with a peak at around 10μm, while a small percentage of larger particles were also present. In contrast, the reconstituted SDA and SDB samples showed a unimodal distribution, with a peak slightly above 10μm. The different composition of the samples due to the different carriers and the different inlet temperatures did not affect the particle size of the powders and the reconstituted samples. Powders produced by spray drying showed a spherical shape with a porous surface. In contrast, the freeze-dried powders exhibited an irregular shape and uneven surface. Reconstitution of both SDA and SDB samples, as well as FD samples, did not affect the morphology of the particles of the powders.