Food Safety Focus (209th Issue, December 2023) – Article 2

Food Test and Analysis - How to Ensure Accuracy?

Reported by Dr. Kenny WONG, Chemist,
Food Research Laboratory, Centre for Food Safety

Globalisation of the food industry is a result of modern logistics. This mobility has powered international food trade and led to the import of a vast variety of foods into Hong Kong from different places. To guarantee food safety, food testing plays an important role, as it can identify the potential health hazards and determine the content of particular chemicals in food.  The accuracy of the test results is definitely crucial in protecting both people's health and the reputation of food suppliers. While erroneous measurement of contaminants and their quantity can endanger people's health, incorrect measurements and false positive results can cause unnecessary panic.  Hence, all food testing organization should maintain a good quality system to ensure rigorous, robust and reliable food testing results.

What is Quality System in Food Testing? 

A quality system refers to the organisational resources, processes and procedures to implement quality management, which involve two main aspects – Quality Assurance (QA) and Quality Control (QC).  The relationship among quality system, QA and QC can be outline as in Figure 3.

Figure 3: Relationship among Quality System, Quality Assurance and Quality Control

QA is to prevent quality issues and ensure the integrity of the testing service. If accredited by an accreditation body, it can certify that the quality management system set up by the testing organization is capable of producing precise and trustworthy measurements in compliance with the general guidance of ISO 17025.  For example, in Hong Kong, the Hong Kong Accreditation Service (HKAS) is the third party accreditation organization, which lay out the specific requirements based on ISO 17025 and helps to assess and grant the certificate of Hong Kong Laboratory Accreditation Scheme (HOKLAS) to the local testing organisations. 

QC is a measuring process to provide assurance that all testing results are accurate and reliable.  In this regard, internationally recognized bodies and authorities such as CODEX, AOAC, IUPAC and ISO have published relevant guidelines and standards regarding method validation, quality controls and the competence of testing organizations.

Potential Errors in Food Testing 

1. Pre-analytical Stage
   

   Before analysis, mishandling of food samples may affect the measurement results; these errors include sample mix-up, mislabeling, inappropriate sampling methods and improper storage or transportation. This may cause contamination, analysis of the wrong samples and sample degradation, which leads to false results.

   To minimize pre-analytical errors, one should:

   • Adhere strictly the established standard operating procedures.
   • Label clearly the samples with date of collection, sources and tests to be done.
   • Store and transport the samples in appropriate containers and keep them at the recommended temperature.
2. Analytical Stage
   

   In the analytical stage, errors can arise during the process of testing.  This could be due to the use of inappropriate methods with low extraction efficiency and recovery, the wrong analytical conditions (e.g. incorrect temperature), the use of unsuitable equipment, etc. 

   For example, when analysing inorganic arsenic, the use of inappropriate extraction solution with lower extraction efficiency may underestimate the actual amount of inorganic arsenic in the sample.  When testing for aspartame in candies, the use of an unsuitable detector, such as refractive index detector instead of photodiode array detector, will affect the specific detection of aspartame and the actual amount of aspartame may be overestimated. The inappropriate analytical condition like the adoption of too high a temperature for the extraction of pesticide residues in food during the analytical stage may underestimate the actual amount of pesticides in the sample.  It is because some types of pesticides can degrade easily at high temperature.

   These errors can be minimised by:

   • Using validated and accredited methods to analyse a particular chemical as appropriate.
   • Following strictly the QC measures required in the validated testing methods.
   • Maintain all laboratory equipment in good condition and with proper calibrations.
3. Post-analytical Stage
   

   The post-analytical errors mainly focus on data-treatment process, which include incorrect recording, calculations and interpretation of results. For example, using wrong equations, outdated worksheets etc. could lead to false results. 

   To minimise these types of errors:

   • Ensure that only well-trained personnel interpret and record results.
   • Update the worksheets and/or equations frequently and protect them from unintended changes.

   Accreditation and quality system are essential components for supporting accurate testings and measurements. Therefore, using analytical laboratories that are accredited for the required tests is recommended.