![]() Lethal rates when plotted against process time can be used to calculate the F or P value of a thermal process. Calculate the lethal rate at 110° C compared to that at 121.11° C (Tr), given that the most heat-resistant organism present has a Z value of 10° C. Use of this equation can be illustrated using the following example. The z-value measured in ☌ is the reciprocal of the slope of the thermal death curve for the target microorganism or spore 10° C is the value frequently used in F o calculations performed on low-acid foods. ![]() The lethal rate is a dimensionless number and can be calculated using equation 1 (Stobo, 1973) and is a relative term that compares the microbial killing effect at a measured temperature to one minute at the reference temperature.Įquation 1, Lethal rate = 10 (T-Tr)/z where T is the temperature, in Celsius, at which the lethal rate is calculated and Tr is the reference temperature at which the equivalent lethal effect is compared. This can be expressed by calculating lethal rate. ![]() The logarithmic reduction in time required to kill the same number of microorganisms as the temperature is increased has been well described. salmonella can survive several hours at high temperatures in molten chocolate.īecause microorganisms in foods are exposed to lethal temperatures as they reach the target processing temperature, during holding and during cooling, it is necessary to calculate the cumulative effect of heat on microbial destruction during both heating and cooling as well at the holding time at the target temperature to obtain a true estimate of the lethal effects of a heat treatment process. Note fat, sugar, salt and chocolate content have a major effect on the sensitivity of microorganisms to heat in general they markedly increase their resistance to heat e.g. The lethal effect of high temperatures on microorganisms is dependent on several factors, including temperature, holding time, pH and water activity. One of the calculators will also upload CSV files of a thermal process and provides a facility for free, independent validation of a thermal process. In general, the more values, the more accurate the value for F or P will be. The area under the time-lethality curve is determined by numerical integration using the industry standard method, the trapezoid rule or the more accurate Simpson's rules or both for comparative purposes. The lethality calculators convert temperature readings to lethal rates, plot the lethal rates against time, and determine appropriate lethality values or chemical indicators for a heat process whether using hot water, saturated steam or dry heat. Determine the accuracy of 3 algorithms for predicting the concentration of lactulose in milk after defined heat treatment.Calculator for determining the lethality (F, B* values) and chemical changes (C* value) for generic high-temperature processes using the Trapezoid and Simpson's rules.Calculator for determining the lethality (F, B* values) and chemical changes (C* value, formation of HMF, Lactulose, Furosine, and destruction of thiamine) in heated milk integrated using the Trapezoid and Simpson's rules.Calculator for determining the lethality (F, value) of a thermal process using the Trapezoid and Simpson's rules. This unique calculator works with thousands of pasted values e.g.These calculators are listed on the Calculators and Models page under Thermal Processing e.g. ![]() The Dairy Science and Food Technology website contains several free, On Line calculators, for determining the cumulative lethality (F, B*, P or PU) of thermal processes, the concentration of Thermal Process Indicators (TTI) following UHT treatment of milk and several other process indicators. ![]()
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