Baroprotection of vegetative bacteria by milk constituents: A study of Listeria innocua |
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| Affiliation: | 1. Department of Microbiology, University College Cork, Ireland;2. Department of Food and Nutritional Sciences, University College Cork, Ireland;1. NIZO Food Research, Kernhemseweg 2, 6718 ZB Ede, The Netherlands;2. FrieslandCampina, Stationsplein 4, 3818 LE Amersfoort, The Netherlands;1. Department of Chemical and Materials Engineering, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand;2. Department of Chemical Engineering, University of Riau, Pekanbaru 28293, Indonesia;2. Smithfield Foods Inc., Smithfield, VA 23430;3. Food Safety and Intervention Technologies Research Unit, and;4. Office of the Area Director, United States Department of Agriculture, Agricultural Research Service, Eastern Regional Research Center, 600 E. Mermaid Lane, Wyndmoor, PA 19038 |
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| Abstract: | The baroprotective effect of milk constituents on Listeria innocua 4202 treated at 350 or 500 MPa for 5 min was examined. High-pressure (HP) treatment of L. innocua 4202 (1×109 cfu mL?1) resulted in complete inactivation in simulated milk ultra-filtrate (SMUF), a ～5.0 log reduction in phosphate-buffered saline and a ～2.9 log reduction in milk. The addition of micellar casein to SMUF increased survival of the bacterium by 3 logs, compared with SMUF alone, but the protective effect was negated if the minerals associated with the casein micelles were removed. The colloidal minerals calcium (30 mm), magnesium (5 mm), citrate (10 mm) and phosphate (20 mm), suspended in SMUF increased survival by ～3.3, ～1.7, ～3.3 and ～3.5 logs, respectively. The buffering capacity of the suspending medium was found to be a key factor in microbial baroresistance. Buffering by phosphate and citrate in milk may protect microorganisms against changes in pH during HP treatment, whereas the divalent cations calcium and magnesium may protect cell membranes against HP. |
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