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Use ultrasound to release galactosidase from yogurt bacteria and improve viability of probiotics.

Probiotic bacteria are a mixed culture of microorganisms which, when consumed by humans, affect the host beneficially. Effective yogurt contains at least 100 million to 1 billion live probiotic bacteria per mL. Probiotic yogurt holds a satisfactory position in the dairy market, and there is a clear trend to increase its consumption in the next few years.

Researchers at Washington State University used sonification to rupture yogurt bacteria and improve the viability of probiotics. This ultrasonification technique, in which the yogurt bacteria are ruptured to release more galactosidase and improve the viability of probiotics, should encourage more consumers to buy yogurt, which exerts health benefits beyond inherent basic nutrition as it improves lactose absorption in the human gut.

Two different cultures, YO Mix 236 and DPL ABY 611, supplied by Danisco, were used in this research. These cultures consisted of Streptococcus thermophilus and Lactobacillus delbruekii ssp. Bulgaricus. They were sonicated using an ultrasonic processor for 3, 4 and 5 minutes at 16 kHz.

The investigators studied physicochemical and rheological characteristics, enzymatic activity, microstructure and probiotics viability. They used a thermocouple in the treatment chamber to monitor the temperature throughout the experiments. The ultrasound wave was kept constant at 100% for all treatments. They used sonicated and unsonicated yogurt samples for making yogurt. The probiotics studied were Lactobacillus acidophilus and Bifidobacterium longum.

The results demonstrated that the probiotics grow better in sonicated yogurt than in unsonicated yogurt, indicating the availability of more nutrients for the probiotics due to a greater availability of galactosidase. The viability of probiotics increased by 2 log cycles in sonicated yogurt, compared to just one-half log cycle in the unsonicated yogurt. There is a clear trend that galactosidase activity increases due to sonification, improving the viability of probiotics. The activity increased 4.73 times in sonicated yogurt compared to 3.28 times in unsonicated yogurt.

Further information. Stephanie Clark, Department of Food Science, Washington State University, FSHN Building, Room 118, 100 Dairy Rd., Pullman, WA 99164; phone: 509-335-4215; fax: 509-335-4815; email:
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Publication:Emerging Food R&D Report
Date:Aug 1, 2008
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