Food Processing and Preservation Technologies
This domain tests how preservation steps inactivate or inhibit microorganisms and enzymes, and how process choice follows food pH, water activity, and packaging. Expect questions comparing pasteurization, commercial sterility, chilling, drying, high pressure, and irradiation.
Core rules
- Pasteurization reduces pathogens but does not produce a sterile product. HTST milk is typically 72°C for 15 seconds; LTLT is 63°C for 30 minutes. Refrigeration remains part of the hurdle.
- UHT processing, commonly 135–150°C for a few seconds, combined with aseptic packaging, yields a commercially sterile shelf-stable product. Commercial sterility means no viable organisms of public health concern and no spoilage under normal storage.
- Acid foods have pH 4.6 or below; low-acid foods require a scheduled retort process, typically 12D for C. botulinum. Acidified foods rely on pH control plus a pasteurization or hot-fill step.
- Freezing stops microbial growth but does not kill all cells; blanching inactivates enzymes before freezing. Drying lowers water activity; spray drying and freeze drying differ in heat exposure and product quality.
- High pressure processing inactivates vegetative cells but not bacterial spores. Irradiation is a cold process with defined doses for disinfestation, pathogen reduction, and shelf-life extension. Hurdle technology combines mild obstacles for stability.
Worked example
A salsa with equilibrium pH 4.2 and aw above 0.85 can be hot-filled and pasteurized rather than retorted, because the acid pH prevents C. botulinum growth. A low-acid soup at pH 6.0 in a sealed can requires a scheduled retort process sufficient for 12D reduction of C. botulinum spores. Changing the soup to a retort pouch changes heat-transfer assumptions, so the process must be revalidated.
Traps that cost marks
Calling pasteurized milk sterile. Assuming UHT alone is shelf-stable without aseptic packaging. Believing HPP kills spores or that freezing sterilizes food.