فاطمه شهدادی

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.