Application of Response Surface Methodology to Improve Fermentation Time and Rheological Properties of Probiotic Yogurt Containing Lactobacillus reuteri
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- Bitaraf, M.S., Khodaiyan, F., Mohammadifar, M.A. et al. Food Bioprocess Technol (2012) 5: 1394. doi:10.1007/s11947-010-0433-2
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Response surface methodology was employed to investigate the combined effects of inulin addition (0–4% w/w), probiotic inoculum level (1–3% v/v), and fermentation temperature (37–45 °C) on fermentation time and rheological properties of nonfat-set yogurt. The rheological characteristics were measured by dynamic oscillatory rheometery. The second-order polynomial model was fitted to the fermentation time (Tf), structure strength (A value), resistance to mechanical force or yield stress (τy), and complex viscosity (ŋ*) of runs as the responses. Analysis of variance revealed that the quadratic models are well adjusted to predict the experimental data. Lack-of-fit tests were not significant and determination coefficients (R2) were higher than 88.6%. The results showed that fermentation time decreased with increasing inulin content, incubation temperature, and probiotic inoculum level. Rheological properties significantly influenced by independent variables. Inulin addition had a softening effect on yogurt. However, the effect of incubation temperature on structure strength was positive. Medium levels of probiotic inoculum resulted in stronger gels.