Page 66 - FoodFocusThailand No.231 June 2025

STRONG QC & QA

2. Filtration Sampling
Here, air is drawn through a membrane filter made
of materials such as cellulose acetate, polycarbonate,
or gelatin. The filter traps particles and microorganisms,
which are then either cultured or analyzed via molecular
methods.
Advantages:
• Highly sensitive, especially for low microbial
concentrations
• Can be paired with downstream testing, such as PCR
(to detect microbial DNA) or ATP testing (to check for organic
contamination)
• Ideal for dry or enclosed environments
Limitations:
• More complex and requires additional handling
• Risk of sample desiccation, which can affect microbial
recovery
• Results depend heavily on lab processing techniques
3. Impingement Sampling
This method captures airborne particles by bubbling air
through a liquid medium (such as sterile water or buffer
solution). As air passes through the liquid, microorganisms
Advantages: and particles are trapped and suspended.
• Easy to implement, even without specialized training Advantages:
• Inexpensive and ideal for trend analysis over time • Gentle on microorganisms, preserving their viability
• Useful for routine surveillance in low- to medium-risk zones • Allows immediate culturing or chemical analysis from
Limitations: the liquid
• Results are semi-quantitative (colonies per plate per hour) • Useful for sampling both biological and chemical
and don’t account for air volume. contaminants
• Susceptible to external factors such as air turbulence or Limitations:
room activity • Requires specialized glassware (impingers) and lab
• Limited sensitivity in detecting low-level or fast-moving setup
contaminants • Liquid can evaporate during longer sampling sessions
While passive sampling gives a general snapshot of • Less convenient for routine use due to equipment size
microbial load, it may miss transient spikes in contamination and handling needs
or airborne particles that remain suspended rather than settling. Active sampling is especially valuable in zones where
Active Sampling: Precision and Control contamination must be tightly controlled, such as packaging
Active air sampling draws air through a device at a controlled areas for sterile or allergen-free products. While impaction
rate, capturing airborne contaminants directly onto a collection and filtration are the most commonly used active
medium. This provides quantitative results, usually expressed methods, impingement is particularly useful in environments
as CFU/m³. where preserving delicate microorganisms is important
There are three main active sampling methods used in the or when testing requires a liquid sample for further
food industry: impaction, filtration, and impingement. Each analysis.
offers different advantages depending on the environment, the
type of contaminants being monitored, and the sensitivity New Frontier: ATP Testing for Air Monitoring
required. Traditionally used for surface hygiene assessments,
1. Impaction Sampling adenosine triphosphate (ATP) testing is now being explored
In this method, air is pulled through a sampler and forced onto for air monitoring. ATP is a molecule found in all living
a solid surface—typically an agar plate. Devices like slit-to-agar, organisms, and its presence indicates organic contamination—
sieve samplers, or centrifugal impactors are commonly used. whether microbial or non-microbial (like food residue or
Advantages: biofilms). In air monitoring, ATP can be measured in two
• Offers accurate, repeatable, and volume-based data ways:
• Suitable for validating cleanrooms and high-hygiene zones • After filtration: Air is pulled through a filter, which is
• Enables mapping of contamination sources and hotspots then swabbed and tested using a luminometer.
Limitations: • HVAC swabbing: Key components of heating,
• Requires calibrated equipment and trained operators ventilation, and air conditioning systems are swabbed to
• Costlier than passive sampling detect bio-load buildup in ducts or filters.
• Some microorganisms may be damaged by the impaction
force, affecting viability

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