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Controversial – general public concern, requires dose is regulated. Thermal Preservation. Blanching: severity-mild. Exposes food to boiling water or steam for a short time. It kills microorganisms to some extent, but not enough to be considered safe. Purpose: inactivate enzymes, wilt vegetables, drive off oxygen and other gases. Used with other methods like freezing, dehydration and canning. Pasteurization: severity-moderate. Thermal process that uses temperatures of 72c for 15 seconds (High Temperature Short Time HTST). Purpose: reduce the microbial load to a safe level. Low-acid foods -> pathogens, acid foods -> spoilage microbes. Spoilage microorganisms can still survive (proteolytic and lipolytic spoilage generates off-flavours). Refrigeration slow down growth of spoilage microorganisms. Commercial sterilization: severity – high. Thermal process that uses a minimum of 121c moist heat for 15 minutes. Purpose: destroy all viable microorganisms (spoilage microorganisms, pathogens, clostridium botulinum). Some thermophilic spores may survive but they are non-viable. Commercially sterile -> absence of viable microorganisms. Clostridium botulinum: extremely heat resistant spores, produces a deadly neurotoxin, anaerobic, cannot grow well at a pH of 4.6 or less. Ultra High Temperature (UHT) + aseptic packaging (food packaged in pre-sterilized containers in a sterile environment). Purpose: shorter processing times -> higher quality product. Shelf life is > 6 months even at room temperature. Every particle of food requires the time-temperature combo. Cold point: food particle that takes the longest to reach the desired time-temperature combination. Heat transfer characteristics are dependent on many factors: 1. Viscosity/consistency: affects mechanism of heat transfer. Viscous foods -> conduction- molecule to molecule in straight line (slow). Non-viscous foods -> convection – fluid motion fluid heats along the hot wall of the container and rises (fast). Semi-viscous foods -> both. Conduction -> center of can, convection -> 1/3 from the bottom of the can. 2. Chemical composition. Certain constituents have a protective effect on microorganisms. (sugars, fats, proteins, salt etc). certain constituents decrease the resistance of microorganisms. (spices, acidulants, antimicrobial compounds). Lower time-temperature combinations required. 3) container size, shape and composition. Cans, retortable pouches, tetra pak, glss jars or bottles, plastic. Thermal Death Curves (TDC): microorganisms are not killed instantaneously. Microbial death- logarithmic order of death. Under constant thermal conditions the same % of microbial population will be destroyed in a given time interval regardless of the size of the surviving population. Commercial sterilization (CS): survivor curve or Thermal Death Rate Curves (TDRC). If a given temp. kills 90% microbial population in the 1stminute of heating, 90% of remaining population will be killed in the 2ndminute, 90% remaining in the 3rd. D-value (decimal reduction time): time (in minutes) at a particular temperature required to kill 90% of a microbial population. Z-value: in the real world we don’t have instantaneous heat to 121c. product may be already