In this research, the effects of various essential oils including; mint (Mentha spicata), bee balm
(Mentha longifolia), eucalyptus (Eucalyptus camaldulensis) and ziziphora (Ziziphora tenuior L) as well
as the concentration of high methoxyl pectin (stabilizer) on quality, sensory, rheological and
microbiological characteristics of probiotic drinking yoghurt was investigated. Drinking yoghurt was
prepared according to standard method with different essential oils. Acidity, pH, serum separation,
rheological and sensory properties and viability of probiotics bacteria (Lactobacillus acidophilus and
Bifidobactrium animalis subsp. lactis) in final products were assessed at a 7 days interval during the
storage period (28 days). The results showed that high methoxyl pectin prevented serum separation
in drinking yoghurt at a level of 0.5% and were effective at this concentration without any undesirable
effect on the taste and odour of the product. A gradual increase in acidity (from 0.75 to 1.2) was
observed whereas a decline in pH (from 4.3 to 3.77) was noted in all the samples. Considering the
sensory effect of the essential oils, the best treatment with overall acceptability was obtained in
samples with ziziphora essential oils. Number of probiotics culture in all samples decreased during
storage (from 2.5×109 and 1.1×109 at first day to 7.9×106 and >106 for Bifidobactrium animalis and
Lactobacillus acidophilus, respectively) and significant difference were observed between all samples
and control (P< 0.05). Probiotic drinking yoghurt containing mint essential oils had the highest viable
count of probiotic bacteria (7.9× 106) and samples with eucalyptus exhibited lowest viable count of
probiotic bacteria (1.6× 106) at end of storage time. Bifidobactrium animalis subsp. lactis seemed more
stable than Lactobacillus acidophilus.