Chapter 9

A

Osmotic

Thermal (heat) processing

Heat can denature proteins , inactivate enzymes , and gelatinize starches.  Heat kills microorganisms by denaturing their proteins and inactivating their enzymes

 Sterilization (hospital)  Commercial sterility (food)  Pasteurization/blanching

: No living forms are alive or biologically No spores, no vegetative cells

Sterility can only be considered achieved when all parts of a product have been heated to 121 C (reached by using steam) and held at that temperature for 15 min

Under these very harsh conditions, foods would effectively become inedible and of very poor nutritional quality

Canning processing

Definition of commercial sterility: all pathogenic and toxin forming vegetative organisms are killed and their spores are inactivated, to the extent that they cannot reproduce. Commercial sterility is a practical level of sterility that ensures safety while maintaining the food’s quality attributes (flavor, color, texture, nutritional value) to a reasonable extent and gives a shelf life of >2 years.

Vegetative cells

), canning processes specifically target heat resistant spores of Clostridium botulinum

C. botulinum is ubiquitous and capable of growing in the anaerobic environment of canned food (hermetically sealed) and producing botulinum toxin, a deadly neurotoxin that kills if ingested in microgram quantities.  In high acid foods ( pH ≤ 4.6 ), spores of C. botulinum are incapable of germinating (i.e., of being reactivated to the toxin producing vegetative state).

temperatures higher than the boiling point of water are required to achieve commercial sterility (spores can survive for > 5 hours at 100 C).  High temperatures required to inactivate spores are provided by steam under pressure

 10 psi = 116 C  15 psi = 121 C  20 psi = 127 C

Pasteurization is a less severe heat treatment, usually below the boiling point of water  Pasteurization of milk targets vegetative cells of pathogenic microorganisms such as Mycobacterium tuberculosis that are relatively thermally resistant  Pasteurization results in a limited shelf life extension on its own as some food spoilage organisms, particularly spores , survive the process and are the source of new vegetative outgrowths.  Refrigeration is usually required to extend the benefits associated with pasteurization.

Blanching is a short heat process similar to pasteurization but its intent is to denature (knock out) deleterious enzymes in fruits and vegetables, such as:  polyphenol oxidase (enzyme responsible for enzymatic browning  lipoxygenases (produce off flavors by catalyzing lipid oxidation )  Blanching is commonly carried out prior to freezing, high pressure, or other non thermal processes to minimize enzymatic deterioration during processing and storage.

destruction of microorganisms/enzymes and maintenance of product quality attributes (flavor, nutritional value, color, texture, etc.).

Safety takes precedence over all else

 understanding time/temperature combinations and their effects on microorganisms of concern  understanding the heat penetration characteristics of a product  calculating appropriate thermal processes for the food product based on (1) and (2)  validating the efficacy of thermal processes

C. botulinum is too dangerous to use in step ( 4 ) so a less dangerous but even more temperature resistant spore former is used instead, such as:  Clostridium sporogenes PA 3679 (PA = putrefactive anaerobe), or  Bacillus stearothermophilus  Concept: If the spores of these organisms are adequately destroyed by a thermal process, then we should also be safe from C. botulinum , which is thermally less resistant.

121

1 million ( 10 6 ) spores in a can, a thermal process that results in the reduction of the spore population by 12 logarithmic cycles to 10 6 spores represents

Statistically, there is only one living spore in 10 6 cans.