The impact of refractance window drying conditions on the physical and microbiological properties of kefir powder

Abstract The growing globally interest in healthy nutrition has resulted in a significant progress in the development of specialised and novel dairy powders. Refractance window has received increasing attention as a novel food-processing technology that is used at laboratory and industrial scale for food dehydration. This study was conducted determine the effect of refractance window drying conditions on the physical and microbiological properties of kefir powder. Refractance window drying is an innovative drying system that effectively utilizes conduction and radiation as heat transfer mechanisms and provides rapid drying with high quality. No previous study was conducted to produce kefir powder using refractance window drying. In the present study, the physical and microbiological properties of kefir powders produced by refractance window drying and freeze drying were compared during storage at 4 °C for 90 days. High drying temperature and thin spreading caused more colour changes in the samples. Refractance window drying of kefir resulted in a powder that had good flowability and low cohesiveness. Moreover, refractance window drying provided much better wettability, hygroscopicity and solubility compared to freeze drying. The survival of Lactococci, Lactobacilli, acetic acid bacteria and yeast in the kefir powders produced by RW drying at 50 °C was higher other counterparts at the end of storage.