Escherichia coli ATCC25922 and Staphylococcus aureus ATCC25923 were used as test strains for screening of antimicrobial lactic acid bacteria from kefir grains. The fermentation supernatant of the selected isolate was processed into a freeze-dried powder. When used at a concentration greater than 6.250 mg/mL, the unpurified antimicrobial peptides had a strong bacteriostatic effect. The strain was identified as Lactobacillus casei by 16S rDNA gene sequencing. Raw whole milk was fermented by inoculating this strain at 2, 3 or 4 g/100 mL, and stored at 4 ℃ for 30 days. The pH and syneresis of fermented milk decreased with increasing inoculum size, whereas the titratable acidity, hardness, viscosity and water-holding capacity increased. The fermented milks with inoculum amounts of 3 and 4 g/100 mL did not significantly differ in sensory evaluation scores, both higher than that inoculated at 2 g/100 mL.

Set skim yogurt was supplemented with inulin as a fat replacer to improve its texture and organoleptic properties. The water-holding power, rheological properties, color and sensory evaluation of yogurt prepared from skim milk powder with added inulin were measured and compared with those of control samples (whole milk yogurt). The rheological properties and sensory evaluation of the yogurt with 3.0% inulin was similar to those of control samples, but the water-holding power was lower than that of control samples. Whey syneresis occurred in none of the yoghurt samples. It was concluded that addition of 3.0% inulin resulted in high overall acceptability and showed good potential for commercial application.