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Journal of Dairy Science

Evaluation of biopreservatives in Greek yogurt to inhibit yeast and mold spoilage and development of a yogurt spoilage predictive model

A.J.Buehler, N.H.Martin, K.J.Boor, M.Wiedmann

Milk Quality Improvement Program, Department of Food Science, Cornell University, Ithaca, NY 14853.


Dairy products, including cultured dairy products such as cheese and yogurt, are susceptible to fungal spoilage. Traditionally, additives such as potassium sorbate have been used to control fungal spoilage; however, with consumer demand for clean-label products, other strategies to control fungal spoilage (e.g., biopreservatives) are increasingly being used in dairy formulations. In order to help the dairy industry better evaluate biopreservatives for control of fungal spoilage, we developed a challenge study protocol, which was applied to evaluate 2 commercially available protective cultures for their ability to control yeast and mold spoilage of Greek yogurt. Greek yogurt formulated with and without protective cultures was inoculated with a cocktail consisting of 5 yeasts and 1 mold to yield inoculum levels of 101 and 103 cfu/g of yogurt. The inoculated yogurts were stored at 7°C and fungal counts as well as time to visible growth, on the yogurt surface, of mycelium mold colonies or yeast were determined over shelf-life. Whereas fungal concentrations increased to spoilage levels (≥105 cfu/g) in all yogurt formulations at both inoculum levels by d 23 of storage at 7°C, no surface mold was observed over 76 d in any of the products formulated with protective cultures. Control yogurts without biopreservatives all showed surface mold by d 23. In order to allow industry to better evaluate the business effects of improved control of surface mold growth that can be achieved with protective cultures, we developed a Monte Carlo simulation model to estimate consumer exposure to visible mold growth in yogurt formulated without fungal inhibitors. Our model showed that initial mold contamination rate has the largest effect on the model outcome, indicating that accurate data on contamination rates are important for use of these models. When air plates were used, in a proof-of-concept approach, to estimate initial contamination rates in a small yogurt manufacturing operation, our model predicted that 550 ± 25.2 consumers (±standard deviation) would be exposed to visible mold growth for every 1 million cups of yogurt produced. With initial contamination rate data for individual facilities, this model could be used by industry to estimate the number of consumers exposed to visible mold spoilage and could allow industry to better assess the value of mold-control strategies.

Keywords: protective culture, yeast, moldyo, gurt.

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