Utilization of stevia as a sucrose substitute in soy probiotic yoghurt
Abstract
Stevia is extracted from the leaf of stevia rebaudiana Bertoni plant and is a natural sweetener that has potential to be used as a sucrose replacement in sweetened products. This study aimed to investigate the effect of sucrose substitute with stevia on the growth of Lb rhamnosus during soy milk fermentation. Commercially available stevia was used to replace sucrose (maintained at 8% in the control) at the rate of 0.2% stevia(T1), 0.7% stevia (T2), 1.2% stevia (T3) in the soy yoghurt. Yoghurt mixtures were separately heat treated (85°C/15 mins) cooled to inoculation temperature (42°C), inoculated with commercial yoghurt culture containing Streptococcus thermophilus and Lb rhamnosus and then incubated (40°C). The prepared soy yoghurt samples were tested for pH, acidity and Lb rhamnosus yoba counts at intervals of 0,2,4,6 and 24 hours. Consumer acceptability, viscosity and syneresis of the yoghurt were determined after 24 hrs. of fermentation. Lb. rhamnosus was able to grow to grow in the soy yoghurt up to 8.167 -8,283 log cfu/ml. the highest cell growth was observed in the yoghurt containing 8% sugar whereas the lowest was observed in yoghurt containing 1.2% stevia. There was a significant difference (p<0.05) in the cell counts of between the control (8% sugar) and yoghurt containing stevia. However, there was no significant difference (p>0.05) between yoghurt containing 0.7% and 1.2% stevia. The pH reduced with the growth of the Lb. rhamnosus Yoba up to 3.80-4.28, with 8% sugar yoghurt containing the lowest pH. The pH values were significantly different (p<0.05). Titratable acidity increased with fermentation to values of 0.203%-0.287% lactic acid. Yoghurt containing 1.2% was not accepted since it had acceptable scores below 5. The control (8% sugar) was liked most however, among the stevia treatments, yoghurt containing 0.7% stevia was the most liked. The study showed that replacement of sugar with stevia is possible and an acceptable probiotic soy yoghurt can be produced.