Radiation Preservation: quick revision, 16 bites

Cold Sterilization: Killing Without Heat

Destroy microbes, skip the heat.

**Radiation** is the emission and propagation of energy through space or a material medium. In food preservation, **electromagnetic (EM) radiations** are used because of their destructive effect on microorganisms. When EM radiations kill microorganisms in food **without raising temperature**, the process is called **co…

Takeaway. Cold sterilization uses ionizing radiation to kill microbes without heat.

What Makes Radiation 'Ionizing'?

Energy high enough to strip electrons.

**Ionizing radiations** are those with a wavelength of **2000 Å or less**. They carry enough energy to cause the **ejection of an orbital electron** from an atom or molecule, leaving behind an ion. This ionization damages microbial cells and is the basis of cold sterilization.

Takeaway. Ionizing radiation (≤ 2000 Å) ionizes molecules and destroys microbes without heat.

EM Radiations Used in Food Preservation

Four radiations, four roles.

The electromagnetic radiations of importance in food preservation are **ultraviolet rays**, **X-rays**, **gamma rays**, and **microwaves**. Among these, the **ionizing radiations** — beta rays, gamma rays, and X-rays — are the ones that destroy microorganisms without raising temperature.

Takeaway. UV, X-rays, gamma rays and microwaves are the key EM radiations in food preservation.

UV Rays: Powerful but Skin-Deep

Great killer, poor penetrator.

**Ultraviolet (UV) rays** are powerful **bactericidal agents**. These non-ionizing radiations (< 450 nm) are absorbed by **proteins and nucleic acids**, causing photochemical changes and cell death. Death results from **lethal mutations in nucleic acid** that prevent transcription and DNA replication.

Takeaway. UV is a powerful surface sterilizer but penetrates only 0.1 mm.

Beta Rays vs Gamma Rays

Electrons versus nuclear emissions.

Takeaway. Gamma rays penetrate deeply and are cheap; beta rays have limited use.

Gamma Rays: The Deep Penetrator

From atomic waste to food safety.

**Gamma rays** are uncharged electromagnetic radiations emitted from the **excited nucleus** of radioactive elements such as **⁶⁰Cobalt** and **¹³⁷Cesium**. They are produced by the decay of radioactive isotopes and are the **cheapest** form of radiation for food preservation because source elements are available as by…

Takeaway. Gamma rays are cheap, deeply penetrating, and effective bactericidal agents.

X-Rays: Gamma's Twin

Made differently, behave the same.

**X-rays** are ionizing radiations produced by **bombarding a suitable metal target with high-velocity electrons**. In their behaviour, they are **like gamma rays** — both are ionizing and can destroy microorganisms. The key difference is their origin: X-rays are machine-generated, while gamma rays come from radioactiv…

Takeaway. X-rays are machine-generated and behave like gamma rays.

Radiation Dose Units: REP, RAD, GY

Three units, one goal.

Takeaway. REP, RAD and Gray measure radiation dose; 1 Gray = 100 rads.

Three Types of Radiation Processing

Three processes, three dose levels.

Takeaway. Radappertization, radicidation and radurization are the three radiation processes.

Radappertization: Radiation Sterilization

Sterile like heat, but cold.

**Radappertization** refers to the radiation process that brings about **destruction of microorganisms**. It is equivalent to the **commercial sterility** of heat-processed foods and is also called **radiation sterilization**. This process uses a radiation dose of **30–40 KGy** and ensures a sterile product.

Takeaway. Radappertization uses 30–40 KGy to achieve commercial sterility.

Don't Confuse the Three R's

Similar names, different doses.

Students often mix up **radappertization**, **radicidation** and **radurization**. Remember the hierarchy: **radappertization** is the strongest (sterilization, 30–40 KGy), **radicidation** targets pathogens, and **radurization** is the mildest, used to extend shelf life.

Takeaway. Radappertization > radicidation > radurization in dose and strength.

Exam Favourites from This Unit

Know these, score these.

Takeaway. Focus on cold sterilization, UV 260 nm, gamma sources, and dose conversions.

Safety Concerns with Radiation

Powerful tool, real hazards.

Takeaway. UV harms workers and fats; beta rays may induce radioactivity in food.

Remember the Dose Units

REP, RAD, GY — in order.

Think of the units as a **timeline of science**: **REP** (oldest, 83 ergs/g) → **RAD** (100 ergs/g) → **Gray** (newest, 100 rads = 1 J/kg). The numbers grow as the units modernize.

Takeaway. REP → RAD → Gray: older to newer, 83 → 100 ergs/g → 1 J/kg.

Why Fish Processors Care

Fresh fish, longer shelf life.

Fish spoils fast due to microbial growth. **Radiation preservation** offers a way to destroy microorganisms **without cooking the fish**, preserving its raw qualities. **Gamma rays** are especially useful because they penetrate up to **20 cm** — enough for typical fish fillets and packaging — and are cheaply available…

Takeaway. Gamma radiation preserves raw fish quality by killing microbes without heat.

Shorter Wavelength, Bigger Punch

Less length, more damage.

Generally, radiations of **shorter wavelength** are **more damaging to microorganisms** than long wavelengths. This is why ionizing radiations (≤ 2000 Å) are so effective — their short wavelength carries enough energy to eject electrons and destroy cells.

Takeaway. Shorter wavelength = more microbial damage.