Thermal Processing: Pasteurization, Sterilization, Commercial Retorting & Lethality Kinetics - Food Science Technology | Agrigyan

Biological indicators for validating high-temperature thermal sterilization:

• Bacillus subtilis spores are used to validate low-temperature decontamination or dry heat/radiation processes.
• Micrococcus flavus is a non-spore-forming coccus sensitive to heat.
• Geobacillus stearothermophilus (formerly Bacillus stearothermophilus) produces extremely heat-resistant thermophilic endospores ($D_{121} \approx 4\text{--}5\text{ min}$, $z \approx 10^\circ\text{C}$), making them the standard biological indicator for measuring thermal sterilization values and evaluating continuous aseptic holding tube performance in viscous liquid foods.
• Clostridium botulinum is the target public health organism ($D_{121} = 0.21\text{ min}$), but its dangerous neurotoxin makes it unsuitable for direct continuous pilot-plant validation assays.

Definitions of thermal processing parameters:

• The $F$ value (specifically $F_0$ at $121.1^\circ\text{C}$ or $250^\circ\text{F}$ with $z = 10^\circ\text{C}$) is defined as the equivalent heating time in minutes required to reduce a specified population of microbial cells or endospores to a desired sterility level.
• The $z$ value is the temperature change ($^\circ\text{C}$) required to alter the $D$ value by a factor of 10 (one logarithmic cycle).
• The $D$ value (decimal reduction time) is the time required at a given temperature to reduce microbial population by $90\%$ (1 log cycle).
• DRT is an acronym synonymous with decimal reduction time ($D$ value).

Primary technological objectives of blanching:

• Blanching sets bright natural chloroplast pigments and protects delicate volatile flavors by preventing enzymatic browning.
• Blanching expels trapped intercellular respiratory gases ($CO_2$, $O_2$), reducing internal can corrosion and can strain during thermal processing.
• Blanching softens tissue but does not deliberately reduce piece dimensions (cutting, chopping, and slicing perform size reduction).
• Blanching thermally denatures quality-degrading enzymes (polyphenol oxidase, peroxidase, catalase, and lipoxygenase).