Physicochemical Properties of Kefir Manufactured by a Two-Step Fermentation

Abstract

The objective of this study was to assess the physicochemical and sensory changes of a kefir manufactured by a two-step fermentation (MTY, 1 st step: 37 o C for 9 h; 2 nd step: 24 o C for 15 h) and compare it with kefirs produced by two conventional methods (GTY, fermentation at 37 o C for 24 h; KEY, 22 o C for 24 h). Rapid changes in pH and titratable acidity (TA) were observed in samples from all three manufacturing methods during fermentation process and storage period. Lactic acid bacteria (LAB) counts of MTY increased gradually up to 12 h of fermentation, reaching 9.28 Log CFU/mL, with maximum value observed in this experiment of 9.48 Log CFU/mL. The LAB counts of all samples decreased significantly during storage. The highest viscosity was observed for MTY (1750-1771 cPs), compared with the lowest viscosity observed for KEY (1250-1277 cPs). The viscosity of all samples increased slightly during storage (1250-1805 cPs, p<0.05), as well as carbon dioxide content (0.01-1.36%, p<0.05), except for GTY. The most significant increase in alcohol concentration during storage period was seen in MTY from 0.01% to 1.36% (p<0.05). MTY scored significantly higher in most items of the sensory analysis, indicating that the product manufactured by the two-step fermentation method is more acceptable compared with conventionally produced kefirs.

Survival of Escherichia coli O157:H7 and Staphylococcus aureus during the fermentation and storage of kefir

“…The number of LABs during storage did not change significantly. Similar results were reported in Yoo et al (2013) as well. Kang et al (2013) reported that the number of LABs did not change much during storage for 9 days.…”

“…There was no significant difference in bacterial inoculated samples either. Similar results were obtained from Yoo et al (2013). On another study, Özdestan & Üren (2010) reported that pH values changed between 4.11 and 4.53 in the kefir samples and the TA values varied between 0.65% and 1.05%.…”

“…During fermentation, the pH slowly decreased in all kefir samples. Yoo et al (2013) obtained similar results in the kefir they produced with different methods. The researchers reported that pH dropped slowly during fermentation.…”

“…Similar to the results of this study, Beukes et al (2001) reported an average of 8 log 10 cfu mL -1 LAB counts in traditional South African fermented milk. Yoo et al (2013) found that the number of LAB increased during fermentation of kefir, the LAB number increased from 4.29 Log 10 cfu mL -1 to 8.52 Log 10 cfu mL -1 , and then their development slowed down. These values are higher than those in our study.…”

Optimization of Milk Type and Physical Factors for Reduction of Alcohol Content in Kefir

“…The pH and TA values found in this study are considered to be in the acceptable range of a commercial yogurt (Kang et al, 2013). These results for kefir are in agreement with the findings of Yoo et al, (2013).…”