Effects of Culture Conditions on Growth of Kefir Grains using Milk for Nutrition and Health: An Application of Response Surface Methodoly with Box-behnken Design.

Abstract

This combined process was successfully modeled by response surface methodology method with a Box–Behnken design. In this work, Box-Behnken Design of response surface methodology was used to investigate the effects of fat content in milk, incubation time and the number of rotations or shaking as culture conditions to for  growing kefir grains using milk as culture liquid. The implementation of first order factorial experiment was based on a 3^k Box- Benhnken experimental factorial design with one replicate. Response surface methodology was adopted to express the output parameter (Size of the kefir grain) that is decided by the input parameters (Number of rotations, Time and milk fat content) which yielded the response surface models. The effects of the culture conditions on growth of kefir grains using milk was studied by use of first order model. The adequacy of the first order model was examined by use residual analysis, the normal plot, the main affects plots, the contour plot, and ANOVA statistics F-test, t-test, R², and the adjusted R. The optimization of culture conditions was achieved by the help of the steepest ascent method to locate the optimal domain and direction of growth of kefir grains. The first order model was predicted using a D-optimal criterion which was used to evaluate the growth of kefir grains. The confidence level to check the growth of kefir grain was at 95%. The data was analyzed using R statistical software and excel. Data was presented using tables and graphs. Milk fat content and number of rotations per minute had a positive effects  while time had a negative effects on the growth of kefir grains using milk.

Keywords: Kefir grains; Response Surface Methodology; Box-behnken design; Culture conditions