Effects of changes in homogenisation sequence and stage for sheep milk on physicochemical and microbiological properties and consumer acceptance of kefir

Abstract

The aim of this work is to contribute to the knowledge of the quality of kefir produced from sheep milk, with a particular focus on the effect of homogenisation conditions such as homogenisation sequence and homogenisation stage. The effect of single-stage (150 bar) or double-stage (150/30 bar) homogenisation, both prior to and after heat treatment at 85°C for 15 min, on the physicochemical and microbiological properties and consumer acceptance of kefir produced from sheep milk was investigated. Kefir produced from homogenised sheep milk was stored at 4°C for 30 days. Visual roughness, number of grains, mean perimeter of grains, apparent viscosity, and consistency coefficient were higher, and flow behaviour index and syneresis were lower in kefir produced from heat-treated and subsequently homogenised milk compared to those in kefir produced from milk homogenised before heat treatment, as well as in kefir produced from double-stage homogenised milk compared to those in kefir produced from single-stage homogenised milk. The homogenisation conditions for milk led to statistical differences in the microbiological counts of kefir, which were not microbiologically significant. The appearance and texture scores of the kefir samples increased when double-stage homogenisation was applied instead of single-stage homogenisation to the milk or when the milk was homogenised after heat treatment instead of before heat treatment. This study demonstrated that changing the homogenisation sequence and homogenisation stage for milk altered the physicochemical properties and consumer acceptance of kefir.