Alternatively, inline measurement involve in-situ test probes that continuously measure disinfectant levels and provide real-time feedback enabling dosing to be adjusted.

The technologically advanced inline monitoring systems are more desirable as they cause the least disruption to the processing operation and enable sophisticated plant automation. Sensors for pH, temperature, turbidity, chlorine, etc. are widely used in the food and beverage industry for monitoring disinfectant levels and wash water properties.

However, the poultry industry poses several unique challenges for inline monitoring systems.

• The high organic load of the plant causes rapid fouling of the test probes. This reduces the efficiency of the probe and requires the probe to be cleaned, at a frequency that is impractical.
• Poultry processing often involves disinfectants being applied at dozens of unique points. Placing an inline dose measurement probe at each of these steps would be inefficient, in terms of both cost and operational complexity.
• Inline systems need to be calibrated often to ensure accurate measurements.

Given the limitations involved, including the need for frequent calibration of a large number of probes, makes using inline monitoring systems impractical for poultry processing.

When it comes to the poultry industry, offline monitoring techniques are the most feasible, least effort intensive methods. There are several methods to conduct tests offline and in the example of monitoring peracetic acid, the best methods are HPLC or two-stage titration.

High Performance Liquid Chromatography (HPLC) is a laboratory-based test method that involves running a test sample through a chromatography column under highly controlled conditions. The column physically separates all of the chemicals in the sample so that we can isolate and measure just the peracetic acid component. When performed by a trained operator, it is a highly accurate process, which is not impacted by other interfering chemicals or disinfectant by-products.

Although treated as the gold standard in test methodologies, HPLC has several drawbacks. It is an expensive and complex process that requires employing highly skilled personnel. Also, it is a slow process. From collecting the sample to running the test and obtaining the results, it can take anywhere between several hours to days depending on whether the test is conducted on-site or is sent to a third-party laboratory, which is clearly not practical for onsite dosing control.

The second laboratory based test for PAA is a double (two-stage) titration that in the first step removes hydrogen peroxide from the sample before analysing the PAA in the second step. Hydrogen peroxide interferes in all PAA titrations that utilise potassium iodide so removing it from the sample is necessary for an accurate result.

There are two main chemistries that can be used to remove the hydrogen peroxide: potassium permanganate or cerium with ferroin. A two-stage titration can require careful sample temperature control and skilled analysts, as over titration of the first stage can cause significant issues with the PAA measurement in the second stage.

Due to the limitations with HPLC and two-stage titration, poultry plants rely on quick field test methods to test the levels of disinfectants.

Visual colorimetric tests are the easiest and simplest way of estimating the level of disinfectant in wash water and chillers. The simple test method does not require the operator to complete extended or in-depth training prior to carrying out the test, and a result can be produced in minutes.

The two most commonly used colorimetric tests used in the food and beverage industry are the DPD (N,N-diethyl-p-phenylenediamine) method with a comparator and the test strips method.

In the DPD method, a buffer and indicator are added to a test sample and the colour change is observed. The colour is then compared to a range of standard colours pre-established on the basis of the concentration of the test chemical.

Similarly, with the test strips method, a pre-fabricated test strip is dipped in a test sample. The change in the strip colour is an indicator of the concentration of the test chemical.

Although visual colorimetric test methods offer low-cost testing on-site they have several drawbacks:

• Dependence on ambient light: To be able to accurately assess the colour of the solution, proper ambient lighting is necessary. Depending on how dark or bright it is, the visual interpretation is subject to change.
• Open to interpretation: Different team members may interpret colours differently, causing a variation in the results.
• Reagents add complexity: The use of reagent tablets, powders and solutions adds unnecessary complexity to the process.
• Need for dilution:The measurement range of DPD and other colorimetric indicators is extremely limited, often requiring sample dilutions that add additional time, complexity and error.

The limitations of visual testing can be overcome by using photometers or reflectometers. Photometry relies on light transmission to detect colour changes in a sample and reflectometers detect colour change on the surface of a test strip. Both test methods then display the reading on a screen.

Despite these advantages, photometric and reflectometric readings are prone to interference from other chemicals and oxidizers, extreme sample pH and the time it takes to get the sample into the device. Additionally, as photometers rely on light transmission anything that alters the passage of light through the sample can reduce the accuracy of the results. This means photometers are not suitable for highly coloured or turbid samples – even a scratch on the test tube can alter the results.

Drop count tests are mini, simplified titration kits that require several reagents to be added to the sample in a step by step process. Reagents need to be added slowly and in a specific order, using a dropper to ensure accurate readings.

Like with laboratory titrations, the drop count tests still require a skilled operator to carry out the titration for the most accurate results. The kits are susceptible to manual errors, such as using the wrong titrant, or inadequate swirling. Mistakes can also be made during the calculation process.

When monitoring PAA, drop count kits do not effectively handle interference from hydrogen peroxide. Some kits make no attempt to correct for hydrogen peroxide at all, while other kits intentionally catalyse the reaction with hydrogen peroxide. Kits that attempt to include the hydrogen peroxide reaction incorrectly assume that in ‘real’ contaminated samples the ratio of PAA to hydrogen peroxide is the same as in the bulk chemical, adding additional error.

Finally, and potentially the biggest limitation for the poultry industry, drop count kits for PAA commonly come in two variants:

• Low range kits that utilise between a 5 and 15 ppm-per-drop calibration and are rated for samples up to around 500-600 ppm.
• High range kits that utilise between an 80 and 300 ppm-per-drop calibration and are rated for samples up to several thousand ppm.

The high ppm-per-drop calibration of the high range kits makes them unsuitable for dosing control, meaning many plants rely on the low or regular range drop count kits even for samples that are above 600 ppm. Without dilution, these kits will significantly under-report the concentration of PAA due to insufficient addition of reaction chemicals like buffers and potassium iodide. In these circumstances results, will often ‘plateau’ even with increasing PAA concentration. This can cause costly overdosing to go undetected for long periods of time.

To find out why our Kemio technology performs better than drop count in poultry processing read our article.