Today, consumers tend to eat fresh food with high nutritional and health benefits. Food, in addition to eliminating hunger and providing essential nutrients, should improve the health and physical and mental health of the consumer. Probiotics are living microorganisms that have a healthy effect if they are consumed alive and sufficiently. Using appropriate prebiotic compounds and selecting suitable carriers for probiotics can increase the growth and activity of these beneficial bacteria. Soybeans and their products are considered to be good carriers for probiotic microorganisms that can play an effective role in increasing the viability of probiotic bacteria. The purpose of this study was to investigate the effects of inulin prebiotic and antioxidant green tea on increasing the viability time of Bifidobacterium longum in synbiotic soy ice cream.

In order to produce synbiotic soy ice cream, the green tea extract in concentrations of 1, 2 and 3% and inulin in proportions of 1, 2 and 3% and also probiotic bacteria Bifidobacterium Longum in the amount of 107 Cfu/ml were added to synbiotic soy ice cream formulation. Therefore, 10 treatments were designed according to completely randomized design with three replicates. Tests of determination the percentage of polyphenolic compounds, percentage of total acidity, percentage of increasing overrun, peroxide number (mEq/Kg), viscosity evaluation (cp), color assessment (lighting, redness and yellowness index), sensory assessments (odor, taste, texture and overall acceptance) were performed one day after production and the survival rate of Bifidobacterium Longum (Cfu/ml) of soybean ice cream samples done during 21 days of storage at -18°C. For data analysis of the results of the tests, Duncan's test for comparison means at probability level of 5% was used by Minitab version 16 software.

The results showed that increasing the concentration of inulin and green tea extract in the synbiotic soy ice cream formulation, overrun, yellowness index (b*), lighting index (L*), score of sensory indexes including odor, taste, texture and overall acceptance decreased and acidity, the viability rate of Bifidobacterium longum, viscosity and redness index (a*) increased. Bifidobacterium longum population after 21 days of storage in all treatments, including control, was higher than 106 Cfu/ml. In contrast to inulin increase in the concentration of green tea extract had a significant effect on the reduction of peroxide index. The sensory indices of the treatment containing 1% green tea extract and inulin were not significantly different with the control sample and were presented as superior treatment in this study. Sensory indexes of treatments containing 1% green tea extract and inulin were not significantly different with the control sample and were presented as a superior treatment in this study.

By using 1% green tea extract and 1% inulin can be possible to produce a synbiotic soy ice cream with optimal qualitative and sensory properties with good health properties.