Enhancing food quality with high quality sample prep

18-Dec-2014 - Last updated on 18-Dec-2014 at 10:28 GMT

QuEChERS was developed to extract pesticide residues from a range of fruit and vegetable matrices

The globalization of the food chain has led to an increasing focus on food safety and as a result, food manufacturers are facing increasingly stringent regulatory requirements.

In addition, the increasing use of pesticides in modern agriculture has raised concerns over the impact these compounds could have on human health.

Another area that is receiving a growing amount of attention is the danger associated with the intake of mycotoxins from contaminated food and feed.

It has been estimated that a quarter of the world’s crops are affected by mould or fungal growth, which means that the presence of mycotoxins in the food chain can be highly significant.

Essential development of analytical techniques

The development of analytical techniques for enhanced analysis of food, from fruit and vegetables to meat and dairy products, has been essential.

These ensure that food manufacturers can comply with regulatory requirements, prevent contamination of the supply chain and keep up with the demand for high-quality products.

Traditional sample preparation techniques for pesticide analysis for food had a number of limitations, including being time consuming and requiring large quantities of solvents that are costly and can contaminate the sample.

QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) was developed to be a simple, effective and affordable way to extract pesticide residues from a range of fruit and vegetable matrices.

Reliable food safety testing begins with reliable and consistent sample preparation. As analytical instrumentation becomes faster, more selective and increasingly sensitive, the sample preparation needs to keep pace.

Dangers of mycotoxins in the food chain

Mycotoxins are secondary fungal metabolites typically produced by fungi growing on grains and fruit during shipment or storage. Because mycotoxins are small, heat-stable molecules that can permeate the host, cleaning or heating foods may remove the fungi but leave the mycotoxins unaffected.

Some mycotoxins, such as aflatoxins, are carcinogenic, with well-documented toxic effects on humans and animals. Ingestion of high levels of mycotoxins can cause acute or chronic disease and repeated exposure to low-level mycotoxins can affect growth and development and cause immunosuppression.

Since the discovery of aflatoxins in the 1960s, regulations have been established worldwide to protect consumers from harmful effects. For example, the European Union legislation regarding mycotoxins determination includes specific maximum levels for certain mycotoxins in individual foodstuffs.

While low levels of mycotoxins in foods do not pose a food safety risk, their presence above these regulatory acceptable levels can be harmful. Both European and US governmental agencies require the results of mycotoxin analysis to be reported to ensure they do not exceed acceptable levels.

The challenges of sample preparation

If done correctly, sample preparation ensures sample integrity and removes contaminants that may otherwise interfere with analysis. However, analysts face a number of considerations on a daily basis when ensuring food quality and safety. Are my results reliable? Are they reproducible? Will I stay within my budget and meet my deadline? Finding the most appropriate sample preparation technique poses similar challenges, including:

Sample integrity
False positives and negatives in trace-level analysis due to impurities and matrix effects
Lengthy and time consuming method development of a new sample prep method
Repeating analytical runs because of inconsistent results

Inconsistency between techniques used by different analysts, variable extractions and adjusting sample prep methods for large or dirty samples are notoriously inefficient. It is important to determine the technique that will best help achieve the desired results quickly and consistently.

Matching the sample preparation approach to the challenge can require some thought, and there are many procedures to choose from, from ‘dilute and shoot’ to solid phase extraction (SPE).

SPE for analysis of mycotoxins

LC/MS/MS has become the method of choice for detecting and confirming these toxic compounds. Traditional sample preparation for mycotoxin analysis typically involves extraction with acetonitrile/water and clean up via charcoal-alumina columns. Another technique uses immunoaffinity columns (IAC).

While these columns provide highly selective extractions with high recoveries, separate IAC columns are required for each toxin, which adds additional costs to the analysis. To overcome the limitations of existing sample preparation methods, extraction and clean-up methods can now be used for the simultaneous determination of several mycotoxins with high recoveries by minimizing the matrix effects.

When high selectivity and sensitivity are required, SPE removes the widest set of matrix interferences and produces cleaner samples. This technique is very specific and so extracts the target compounds while leaving little or no matrix behind.

Agilent Bond Elut Mycotoxin optimizes mycotoxin sample prep. This solid phase extraction sorbent cleans up food extracts for improved trichothecene and zearalenone analysis. The method is effective because the toxin analytes pass through the cartridge while the food matrix components are retained.

Sample preparation for pesticide analysis

Recognized as the official Association of Analytical Communities (AOAC) and European method for pesticide analysis, QuEChERS involves three easy steps:

Extract - An extraction step based on partitioning via salting-out extraction, involving an equilibrium between an aqueous and organic layer
Clean - A dispersive solid phase extraction step that involves further clean-up using various combinations of salts and porous sorbents to remove interfering substances
Analyze - Detection of compounds typically using GC/MS or LC/MS, or both

Pesticides can enter the food chain in a multitude of ways and it is essential that potential contaminants in food be monitored effectively to ensure they are at or below regulatory levels.

As other food types containing pesticide residues have come under scrutiny, the QuEChERS technique has come into play as a solution for pesticide analysis not only for fruits and vegetables but also for non-traditional matrices including chicken, rice and cooking oil.

Analytical chemists have a common saying; “Analytical methods are like toothbrushes, everybody uses their own”. While QuEChERS is not the holy grail of sample preparation, it is easy to see why it is an increasingly popular option for pesticide analysis for applications beyond fruit and vegetables.

Today’s consumers demand foods and beverages that are safe, high quality and nutritious. The analysis undertaken by food laboratories lays the foundation for meeting this consumer demand and this starts with sample preparation. Consistent quality provides consistent results.