The Effects of Conventional and Microwave Drying on Drying, Rehydration and Fermentation Kinetics and Viability of Kefir Grains

Tez Türü: Yüksek Lisans

Tezin Yürütüldüğü Kurum: Yıldız Teknik Üniversitesi, Kimya-Metalurji Fakültesi, Kimya Müh.Bölümü, Türkiye

Tez Danışmanı: Dilek Kılıç

Tezin Onay Tarihi: 2023

Tezin Dili: İngilizce

Özet:

In the present work, the effects of microwave and oven drying methods and drying conditions on the drying, rehydration, and fermentation kinetics of kefir grains as well as the microbial viability of grains were investigated.

Kefir grains were dried at various oven temperatures (30°C, 37°C, and 45°C) and microwave powers (100W, 180W, and 300W). Microwave drying reduces the drying time by 90% compared to conventional drying. The rehydration studies showed that the water absorption capacity of grains dried by microwave is higher than those dried by the oven. Moisture diffusivity was observed to increase with drying temperature (0.37x10-10 - 1.69x10-10 m2/s) and microwave power (3.17 x 10-10 - 16.96 x10-10 m2/s).

The results showed that drying methods and conditions do not affect the fermentation ability of kefir grains and fermentation rates obtained with dried kefir grains are very close to the rate obtained with fresh kefir grains. The cell count analysis (yeast counts and lactic acid bacteria counts) showed that microwave drying and oven drying do not affect the viability of kefir grains to a detrimental extent. Compared to spray and freeze drying, the survival rate in microwave and oven drying (around 90% for both LAB and yeast) was significantly high.

As a result of the modelling studies, it was determined that the drying kinetics could be represented by the 1st order kinetic model (Lewis model) while the rehydration and fermentation kinetics could be represented by the pseudo 1st order kinetic model.

Keywords: Kefir, Drying, Microwave, Rehydration, Fermentation, Kinetics