Effect of Drying Aids on the Quality Properties of Kefir Powder

The biological and nutritional value of kefir makes it imperative to widen its customer reach by extending its shelf life, enabling its storage and transport at ambient temperatures, and reducing its packaging cost requirements. A well-documented and widely used food processing method that can achieve the above-mentioned outcomes is spray drying through the formulation of kefir powder, with quality attributes that will closely resemble that of the original product. In the present work, a variety of drying carriers (trehalose, fructo-oligosaccharides, maltodextrin, gum arabic, and whey proteins) were studied with regard to their effect on the properties of powdered and reconstituted kefir samples. Particularly, the physicochemical characteristics (moisture content, pH, acidity, color), powder properties (bulk density, tapped density, water solubility index, insoluble matter), adsorption isotherms, particle size distribution, microbiological properties, and structural characteristics of the samples were evaluated. Gum arabic and maltodextrin produced kefir powder samples with the lowest moisture content. Spray drying affected a reduced acidity and, as a consequence, an increased pH in the reconstituted samples, especially without any carrier addition and with trehalose and fructo-oligosaccharides irrespective of their concentration. Desirable color attributes were achieved on the kefir powder samples with trehalose, fructo-oligosaccharides, and maltodextrin regardless of their concentration in the product. Fructo-oligosaccharides, added at 3%, gave the highest values of bulk density, while whey proteins, due to their nature, exhibited the lowest. All carriers tested improved the water solubility index when compared to the control sample. The sample with 10% whey proteins exhibited the lowest moisture adsorption compared to the control at the highest relative humidity environments employed for the test. In the absence of agglomeration, powder granule size and structural morphology were not affected by the carriers. The survival of lactococci in the powdered kefir samples, in comparison to the control product, was higher in the case where 4% trehalose or 5 to 10% whey proteins were added. On the contrary, yeast populations decreased significantly during drying and they were not affected by the presence of the different carriers. As shown by the findings of the present study, trehalose proved to be the most effective carrier, among the others used, for producing high-quality kefir powder products. However, further work is required with regard to the keeping quality of the product during long-term storage.