Sterilization‐in‐place of concentrated nutrient solutions

Abstract

Sterilization-in-place (batch sterilization) behavior of concentrated nutrient solutions was quantified for various nutrient solutions of fermentation processing interest. Experimental observations of sterilization temperatures and corresponding pressures suggested that sterilization pressures were substantially lower for concentrated nutrient solutions than for water. This effect was believed to be directly related to the lower vapor pressure and lower activity coefficient of these concentrated nutrient solutions. Using thermodynamic data for the specific nutrient, pressures and temperatures, calculated as a function of nutrient concentration, compared favorably with observed values. This method permits estimation of the expected sterilization pressure for concentrated nutrients for which no experimental observations have yet been made at the sterilization temperature of interest. Estimate accuracy, ranging from 0.006 to 0.06 bar, can be enhanced if one set of experimental temperature/pressure values is known at the expected sterilization scale. The potential impact of the nature of concentrated nutrient solutions on steam-in-place vessel headspace temperature distributions, D-values of B. stearothermophilus, and overall sterilization effectiveness is also discussed. The low vapor pressure of concentrated nutrient solutions was hypothesized to directly impact air removal effectiveness and sterilization performance during batch sterilization. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 62:501–508, 1999.