Progress 10/01/02 to 09/30/05
Outputs
Outbreaks of foodborne illness associated with apple cider and dairy products have prompted research on the survival of Escherichia coli 0157:H7 and Listeria monocytogenes in these food systems, respectively. Current processing methods utilize heat for bacterial inactivation, and although effective, these applications may cause undesirable changes in the nutritional and sensorial properties of foods. Non-thermal processing technologies are emerging as promising alternatives. Ultrasound induced cavitation is lethal to many bacteria, especially when combined with other microbial reduction strategies such as heat. A 400W ultrasound generator was used to evaluate the effects of batch and continuous flow ultrasonic treatments on the natural flora and Listeria monocytogenes in milk as well as E. coli 0157:H7 in apple cider. Continuous flow ultrasound treatment, when combined with mild heat (57C), for 18 minutes resulted in a 99.999% reduction of L. monocytogenes in UHT milk,
99.999% reduction in total aerobic bacteria in raw milk, and a 99.999% reduction in E. coli 0157:H7 in pasteurized apple cider. Microstructural analysis revealed reduction of fat globule size as well as protein lipid interactions, which may be favorable.
Impacts
The results show that ultrasonic treatment coupled with mild heating might be a promising alternative method for milk treatment and apple cider pasteurization to preserve nutrients.
Publications
- D'Amico, D.J., Silk, T.M., and Guo, M.R. 2003. Effect of ultrasound treatment on the natural flora and microstructure of milk. IFT Annual meeting Book of Abstracts, p179.
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Progress 01/01/03 to 12/31/03
Outputs
Heat treatment is widely used to pasteurize milk and apple cider, although effective at killing pathogens, heat can impair the organoleptic and nutritional values of foods. The objective of this study was to assess the efficacy of ultrasound as an alternative means of processing milk and apple cider. Samples were treated using a digital sonifier and 110 W ultrasonic output power. During treatment samples were placed in circulating water baths minimizing temperature increases resulting from ultrasonic treatment. For continuous flow treatments, sample temperature was maintained by a temperature controlled circulating water bath flowing through a cooling jacket surrounding the treatment chamber. In addition UHT milk was inoculated with Listeria monocytogenes strain F5069 serotype 4b, and pasteurized apple cider was inoculated with an Escherichia coli 0157:H7 cocktail consisting of acid tolerant strains. Results listed are for samples individually treated for six minutes
at 100% amplitude. Sample treatment temperatures were 20 and 57C. Milk samples were plated to determine aerobic plate count (APC) levels and Listeria levels. Cider samples were plated to determine the survival of E. coli. Microbial levels in raw milk decreased 2.15 log CFU/ml at 20C ad 2.66 log CFU/ml at 57C in the batch operation. Reductions resulting from the continuous flow setup were 2.99 log CFU/ml at 20C, and 4.86 log CFU/ml at 57C. Listeria monocytogenes levels decreased 1.99 log CFU/ml at 20C and 3.47 log CFU/ml at 57C in the batch operation. Continuous flow treatment resulted in a 3.69 log CFU/ml reduction at 20C and 5.07 log CFU/ml reduction at 57C. Batch treatment of apple cider resulted in E. coli reductions 4.76 log CFU/ml at 20C and 6.03 log CFU/ml at 57C. The continuous flow setup yielded a reduction of 4.7 log CFU/ml at 20C. Microstructure analysis reveals that treatment effects are similar to homogenization and fat emulsification. Treatment also induced interactions
between compositional components that may be favorable. The results show that ultrasonic treatment might be a promising alternative method for milk treatment.
Impacts
The results show that ultrasonic treatment might be a promising alternative method for milk treatment and apple cider pasteurization to preserve nutrients.
Publications
- DAmico, D.J., Silk, T.M., and Guo, M.R. 2003. Effect of ultrasound treatment on the natural flora and microstructure of milk. IFT Annual meeting Book of Abstracts, p179.
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Progress 01/01/02 to 12/31/02
Outputs
Heat treatment is widely used to pasteurize milk and other fluid food products. Although heating can kill pathogens, it can cause undesirable side effects such as loss of nutrients, and unacceptable changes in color and flavor. The objective of this study is to use ultrasound as an alternative means to treat milk and other liquid food products. Samples were treated using a digital Sonifier (Model 450W, Branson Ultrasounics Co.) at a constant frequency (20 kHz) and 110 W ultrasonic output power that was measured calorimetrically with a thermocouple. Ultrasound treatment of raw milk resulted in 99.9% reduction of overall organisms after three minutes of sonification. Levels of Listeria monocytogenes inoculated milk samples reduced from 7.53 log CFU/ml to 6.04 log CFU/ml after three minutes of treatment. Further studies are needed to investigate the effects of ultrasound on pathogens in combination with mild heating. A continuous ultrsound treatment system will be set up
for this research.
Impacts
Results of this study show that ultrasound treatment may be a promising alternative method to the conventional treatment for the milk and apple cider industries to process their products without significant damages on nutrients.
Publications
- M.R. Guo, T. Silk, and J. Wu. 2002. Effect of ultrasound treatment on total bacteria and Listeria monocytogenes levels in milk. J. Dairy Sci. 85 (Suppl. 1): 380.
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