Determination of physicochemical and bioactive properties of strawberry kefir powder produced by foam mat drying method

Kefir, one of the fermented milk products, is a product that has been intensively researched in recent years due to its beneficial effects on health resulting from its nutritious content and probiotic properties and is in demand by consumers who are conscious of healthy nutrition. Creating consumption alternatives to ensure that kefir reaches more consumers can meet the demands of these consumers. In addition to alternative products, creating storage methods other than cold storage for foods directs food producers to search for the advantages it provides in terms of storage and transportation. Drying, one of the oldest food preservation methods, can cause quality losses in the nutritional value and physical properties of foods when applied with traditional methods. Therefore, the drying method to be applied should be selected meticulously in a food such as kefir due to its probiotic content. Other criteria to be considered in the selection of the drying method are that it is easy to apply and has low installation and operating costs. Foam mat drying method (FMD) is among the drying methods that have frequently come to the fore in recent years in the drying of liquid or semi-liquid foods. In the foam mat drying method, protein-based products are used as foam generators. Kefir has the feature of creating foam due to the proteins and protein derivatives it contains and it is thought that it can be used for foam mat drying. In this thesis study, it was planned to benefit from the foaming feature of kefir by mixing it with strawberry pulp in certain proportions and to dry it with the foam mat drying method. Thus, it was aimed to create an alternative new product in the form of instant powder with increased functional properties by adding fruit and to process kefir with a different preservation method that preserves its probiotic properties. Carboxymethyl cellulose (CMC) was added as a foam stabilizer and egg white powder (EWP) as a foam agent to the strawberry puree and kefir mixture in creating foam. Strawberry puree and kefir were used in two different ratios: C sample 66% Kefir-33% Strawberry Puree-0.50% CMC-0.50% EWP and K sample 74% Kefir-25% Strawberry Puree-0.50% CMC-0.50% EWP mixtures were prepared. Foamed mixtures were spread on drying trays, dried in a hot air dryer at 45 ˚C until the moisture content decreased below 3%, and ground to powder form. Physicochemical, microbiological, antioxidant, bioactive and sensory properties of the obtained powder products were evaluated. Moisture contents of the samples were found to be 2.71-2.89% for C and K samples, respectively; water activity values were 0.228 and 0.224; total soluble dry matter contents were 2-2.3%; pH values were 4.23-4.78. The differences between the bulk density, tapped density, flowability, adhesiveness, dispersibility, degree of caking, rehydration rate, hygroscopicity and solubility values of the powder product properties were not found to be statistically significant. From the color values, the L* value of the K sample was found to be high, while the a*, b*, Chroma and Hue angle values of the C sample were found to be higher. Total phenolic substance amount (4274 mg GAE/kg) and TEAC value (21.69 mg mM TE/g) were found higher in sample C. The highest total monomeric anthocyanin was observed in sample C (2545 mg/kg). In sensory evaluations, the differences between the pinkish color, strawberry odor, strawberry taste, strawberry aroma, fermented milk aroma and general liking parameters of samples C and K were found to be significant (p<0.05). Microbiological content, color values, moisture content, aw, pH, hygroscopicity values of powder samples stored in aluminum laminated packages at refrigerator temperature were examined at the end of 45 days. A slight increase was detected in the number of Lactobacillus spp., which was determined as 7.42 and 7.65 log cfu/g for samples C and K, respectively, at the beginning of storage, on the 45th day (p<0.05). In this study, strawberry kefir powder produced by foam mat drying method was developed as a new functional product different from existing products. The foam mat drying method was used for the first time in kefir drying. If applied on an industrial scale after optimisation studies and pilot studies, a practical and functional product for consumers can be brought to the food market and storage and transport costs can be reduced.