The Trapezoidal Integration Method for Calculating Fo Values in Fishery Products Canning

A mathematical method in which the time-temperature data are used to measure changes I in lethality during heating and cooling. By using standard time intervals the lethal value: is computed in stages and the cumulative L value for the process is found without the need for graphical representation of the heating and cooling curves.

Calculating Fo Values in Fishery Products Canning: The improved general method

A plot of temperature versus time is made on specially constructed lethal rate paper which has on its left-hand vertical axis product temperature (on a log scale) while on the other vertical axis is drawn lethal rate (on a linear scale). Thus for each temperature can be shown the corresponding lethal rate. Time is plotted along the horizontal axis, using a convenient scale.

The Principles of Canning for Fishery Products: Calculating Fo Values

Thermocouple probe

To be sure of commercial sterility the Fo value at the SHP, the thermal centre of the container, must be sufficient to kill all Clostridium botulinum and reduce survival probabilities for other more heat resistant bacteria to an acceptable level. It is assumed that bacterial spores will randomly contaminate the fish and that therefore they may be located at the SHP. Although a pessimistic approach, this caters for the ``worst case`` scenario on which product safety must be based.

The Principles of Canning for Fishery Products: Lethality of Heat During Heating and Cooling

Clostridium botulinum

Although by convention the sterilising effect of a process is expressed in standard units of minutes at 121.1 ºC (the symbol used is Fo), the product inside a can does not instantaneously reach processing temperature and in some cases of conduction heating, the temperature at the thermal centre of the can never reaches that of the heating medium (which need not be at 121.1 ºC).

The Principles of Canning for Fishery Products: Bacterial Spores Heat Resistance

It is desirable that the test organism in comparative thermal death time determinations be one which grows readily on the ordinary culture medium, with the production of an abundant yield of spores in a minimum time.

It should, furthermore, be an organism which has a characteristic type of growth, or should possess some readily determinable which will serve to differentiate it from contaminants likely to be encountered.

The Principles of Canning for Fishery Products: Selection of Thermal Processing Conditions

The purpose of sterilizing cans of fishery products is to rid the container and the contents of all pathogenic micro-organisms and to prevent. spoilage by non-pathogenic contaminants under normal storage conditions. Selection of processing conditions necessary to fulfill these criteria is based upon experimental studies in which the rate of heat penetration to the slowest heating point (SHP) of the container is measured during simulated retorting cycles.

The Principles of Canning for Fishery Products Preservation

What is Canning?

Canned fish

Canning is a method of preserving food in which the food is processed and sealed in an airtight container, providing a typical shelf life ranging from 1 year to 5 years and under specific circumstances a freeze dried canned product can last as long as 30 years and can still be safely consumed. The process was first developed as a French military discovery by Nicolas Appert in 1810. The packaging prevents microorganisms from entering and proliferating inside.