9-1

M. F. PATTERSON¹, M. Linton¹, E. Black², G. F. Fitzgerald², and A. L. Kelly³. (1) Agriculture, Food and Environmental Science Div., Northern Ireland Dept. of Agriculture and Rural Development, Food Microbiology Branch, Newforge Ln., Belfast, BT9 5PX, United Kingdom, (2) Dept. of Microbiology, Univ. College Cork, National Univ. of Ireland, Cork, Ireland, (3) Dept. of Food and Nutritional Sciences, Univ. College Cork, National Univ. of Ireland, Western Rd., Cork, Ireland

High pressure processing has the potential to produce high quality foods that are microbiologically safe and with an extended shelf-life. However, different microbial species vary in their response to high pressure. In general terms, the pressure resistance of bacterial spores > ascospores > viruses> yeasts> vegetative cells. However, there can be wide variation among different species, and even within strains of the same species. Therefore, an understanding of how pressure affects microbial cells and the factors that can influence resistance is important when designing optimum processing conditions for pressure treatment of foods. This paper will discuss proposed mechanisms for microbial inactivation, with particular emphasis on bacterial spores as these are particularly pressure resistant. This problem must be overcome before it will be possible to produce shelf-stable pressure treated foods. For example, it has been reported that ungerminated spores can survive pressure treatments of over 1000 MegaPascals (MPa) for more than 1 hr at room temperature. However, spore germination can be induced at lower pressures rendering them more sensitive to inactivation, and this has led to a number of proposed treatment strategies. These include the combination of pressure with heat, with and without the addition of antimicrobial agents. For example, a combination of 500 MPa high for 2 cycles, each of 5 min, at 40⁰ C resulted in > 6 log unit germination and a 2.5 log inactivation in Bacillus subtilis spores in milk. The addition of nisin (500 IU/ml) prior to this pressure treatment resulted in a 7.6 log germination and a 5.9 log inactivation of the spores in milk.

Session 9, Mechanisms and modeling of bacterial spore inactivation by high pressure processing
2:30 PM - 5:30 PM, Sunday PM Room 391

2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana