Preservation Methods and Packaging Technology
This domain connects a preservation hurdle with a package: canning, freezing, drying, irradiation, chemical preservatives, fermentation, vacuum, modified atmosphere packaging (MAP), aseptic and active packaging. Expect shelf-life and safety reasoning.
Core rules and concepts
- Low-acid canned foods (pH above 4.6) need a pressure retort process; high-acid foods can be hot-filled or pasteurized.
- Freezing at -18°C stops microbial growth but not enzyme activity; blanch vegetables before freezing.
- Drying must bring water activity below about 0.6, and the package must be a moisture barrier.
- Irradiation is a cold preservation method; it does not make food radioactive, and dose limits and labelling rules apply.
- Vacuum packaging removes oxygen but can favour anaerobic pathogens. MAP uses CO2, N2 and O2 blends; aseptic packaging pairs UHT with sterile filling.
- Active packaging includes oxygen scavengers and moisture absorbers; intelligent packaging includes time-temperature indicators.
Worked example
Fresh-cut salad respires and browns. Use 2-5% O2, 5-10% CO2, N2 balance, and keep at 0-4°C. Too little O2, below about 1%, risks anaerobic pathogens and off-flavours; too much CO2 damages tissue. MAP buys shelf life only when raw material hygiene and cold chain are already good.
Traps that cost marks
- Vacuum packing does not control Clostridium botulinum.
- MAP cannot rescue poor raw material or a broken cold chain.
- Irradiation is not a substitute for hygiene.
- Low-acid canned foods cannot be safely processed in boiling water at home.
- A oxygen scavenger is not a substitute for correct sealing.