Growth Kinetics of Staphylococcus aureus and Background Microorganisms in Camel Milk

Authors: XIE, ZHAOPENG - Fujian Agriculture And Forest University; PENG, YABO - Fujian Agriculture And Forest University; LI, CHANGCHENG - Fujian Agriculture And Forest University; LUO, XIAOJUAN - Fujian Agriculture And Forest University; WEI, ZHAOYI - Fujian Agriculture And Forest University; LI, XIAOTING - Fujian Agriculture And Forest University; YAO, YUKUN - Fujian Agriculture And Forest University; FANG, TING - Fujian Agricultural & Forestry University; Huang, Lihan

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/2/2020
Publication Date: 8/1/2020
Citation: Xie, Z., Peng, Y., Li, C., Luo, X., Wei, Z., Li, X., Yao, Y., Fang, T., Huang, L. 2020. Growth kinetics of Staphylococcus aureus and background microorganisms in camel milk. Journal of Dairy Science. 103/11. https://doi.org/10.3168/jds.2020-18616.
DOI: https://doi.org/10.3168/jds.2020-18616

Interpretive Summary: Staphylococcus aureus is a common foodborne pathogen that can produce heat-stable enterotoxins causing nausea, vomiting, diarrhea, and abdominal cramps in humans. It can be found in raw, under-processed, or cross-contaminated milk and other dairy products. This study was conducted to investigate the growth kinetics of S. aureus in camel milk. Predictive models for describing the growth behavior of this pathogen and background microorganisms in camel milk in a wide temperature range were developed and validated. These models can be used for conducting risk assessment and predicting the shelf-life in camel milk-consuming countries.

Technical Abstract: Staphylococcus aureus is a common foodborne pathogen that is ubiquitous in nature. Consumption of contaminated foods, such as dairy products, can lead to food poisoning caused by heat-stable staphylococcal toxins not easily destroyed during pasteurization. The objective of this study was to investigate the growth kinetics of S. aureus and background microorganisms in camel milk stored at different temperatures between 8 and 43°C using one-step kinetic analysis to estimate the kinetic parameters from the observed growth curves. The growth of S. aureus showed apparent lag, exponential, and stationary phases, while no or negligible lag phase was observed for the background microorganisms. Data analysis showed that the estimated minimum (Tmin), optimum (Topt), and maximum (Tmax) growth temperatures were 5.9, 42.0, and 49.2°C for S. aureus, and 3.0, 38.6, and 49.2°C for the background microorganisms, respectively. The estimated optimum specific growth rate (µopt) was higher for S. aureus (1.24 per h) than that for background microorganisms (0.995 per h). This study found that camel milk may inhibit the growth of S. aureus, as it exhibits smaller specific growth rate in comparison to that in cow’s milk or cooked potato. It also exhibits longer lag phase than that in cow’s milk at comparable temperatures. This unique property is probably related to the presence of some antimicrobial compounds naturally occurring in camel milk. The validation of the kinetic parameters and models showed that the root mean square error (RMSE) of prediction was only 0.5 log CFU/mL for both S. aureus and background microorganisms, suggesting that the models are reasonably accurate models. These models can be used for conducting risk assessments of S. aureus and predicting the general microbiological shelf-life of camel milk to prevent foodborne staphylococcal poisoning.