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Analytical Trends in Measuring Food Quality
by John Szpylka, PhD
As the tools of analytical measurement continue to get more sensitive, more specific, and faster, the industries using these tools must keep up with the changes. New methods of testing for food quality continue to be developed alongside improving traditional methods of analysis. All of these advancements set new standards and protocols on how the quality of foods and of their ingredients is defined and monitored. Understanding some of the general trends is needed to plan for what lies ahead.
Use of liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) has grown rapidly in the field of food testing. LC-MS/MS is being utilized more in food company quality and R&D divisions as a flexible alternative to traditional methods due to its high sensitivity and faster throughput.
An excellent overview on the use of LC-MS/MS to monitor for food contamination was published in the February/March 2011 issue of Food Quality1 where Andre Schreiber and Art Sims highlighted the advantages of LC-MS/MS technology. Since that publication, those advantages have been further leveraged for the analysis of food nutrients.
Analytical methods which use LC-MS/MS are being rapidly developed due to the technique’s high sensitivity, selectivity, accuracy, and increased availability of isotopic standards. An additional advantage is the reduced amount of clean-up required because of the mass spectrometer’s high specificity. As the resolution of and software for MS detectors increase and improve, the ability of the MS detector to “filter out” potential interferences is taken advantage of by the new methods.
AOAC International has recently adopted LC-MS/MS methods for the analysis of vitamin D (AOAC 2011.11, 2011.12, 2011.13, 2012.11). Each of these methods takes advantage of the points highlighted above alongside the additional advantage of LC-MS/MS simultaneously using MS/MS to confirm the identity of the vitamins being tested. After a vitamin’s parent ion is identified, two daughter ions are created by fragmenting the parent ion, and these daughters are used to confirm the identity of the vitamin. The daughter ion levels are also used to quantify both vitamin D2 and vitamin D3.
LC-MS/MS analysis of certain vitamins is complicated for vitamins which are bioactive in several forms, with some of those forms typically in low concentrations. The recently adopted method, AOAC 2011.062 for the measurement of total folates (vitamin B9) does quantify six forms of vitamin B9 including the common fortifying form of folic acid3. Research is underway to measure other vitamins present is various bioactive forms. The common approaches include converting the different forms into one form (i.e., saponification converting the multiple forms of vitamin A into the retinol form, and conversion of multiple forms of vitamin B12 into cyanocobalamin).
UPLC and UHPLC Technology
Ultra Performance Liquid Chromatography (UPLC) and its equivalent Ultra High Performance Chromatography (UHPLC) are recently developed companions to traditional high performance liquid chromatography (HPLC). UPLC and UHPLC can separate compounds in less time than HPLC while using less solvent. This is due to the development of columns containing uniform, smaller particle sizes (in the 1.7 µm scale) which increase the column’s theoretical plates, thus improving peak separation efficiency (better peak resolution). The time needed for peak separation is therefore decreased. To use these columns, higher pressures are needed to push mobile phase through the bed of smaller particle-sized stationary phase.
When this technology first appeared, a somewhat limited number of columns were available. As the efficiency and reliability of this technology was recognized, the number of columns has increased dramatically. Use of this technology is becoming more common.
Advances in Methods
In the world of pesticides testing, the QuEChERS extraction is becoming more prevalent. The acronym of Quick Easy Cheap Effective Rugged Safe highlights desired method attributes by the laboratory, by the customers, and by management who sets financial budgets.
Early pesticide methods were targeted for specific pesticides. A welcome development was the development of methods which extract and quantify a broader scope of pesticides. One common example was the Luke extraction with rapid extraction followed by pesticide detection using a number of chromatographic systems with specific detectors. Confirmation of detected pesticides was performed by subsequent analysis using a mass spectrometer detector. This approach is being used less often, however, it is still available due to its versatility in testing for some matrix types.
The QuEChERS method is a streamlined version of extracting pesticides combined with GC-MS/MS and LC-MS/MS separation and quantification. This approach is very common today. The original method was developed in 2001/2002 by Michelango Anastassiades while at USDA in the laboratory of Steve Lehotay4 and has since been standardized as AOAC 2007.01. This method has been demonstrated to reliably test for more than 300 pesticides in fruits, vegetables, and most grains. The scope of pesticides covered by the method can be expanded as needed.
When analyzing foods and ingredients outside the original scope, an “on-the-fly” method validation is performed. For example, if a laboratory is testing eggplant for the first time, the sample is analyzed alongside a spiked eggplant sample (matrix-match standards). Acceptable recovery of the spiked amounts demonstrates and documents the method’s applicability for testing eggplant by the laboratory.
The QuEChERS method is a streamlined version of extracting pesticides combined with GC-MS/MS and LC-MS/MS separation and quantification.
Improvements in Sensory Analysis
At one point in my career, I was a quality engineer for a yogurt company. On my first day at this new position, my boss told me to taste every type of product we make, including every product style, every flavor, and samples from all our production locations. I became quite the yogurt-tasting connoisseur, which was the intent of this exercise.
The more someone understands their products, the faster quality issues can be identified. More and more companies are asking production site personnel to taste finished products. Fully trained Sensory Panels are also becoming more common at production sites. Members of these panels receive training to calibrate their tasting of the foods with focus on identified key characteristics. For example, if a product’s creaminess is recognized as a critical attribute, a commercially available product (i.e., a baby food) can be used to “remind” panel members what the desired creaminess level is.
Encapsulation of nutrients to improve stability can challenge analytical methods. Traditional extraction techniques may need to be improved for use on these new ingredient forms, both on the base ingredients and on finished products. Some encapsulating agent(s) require more dedicated dispersal to safely liberate the protected nutrient. Some approaches include enzymatic digestion of the encapsulating agents (i.e., proteins, fats, starches), use of alternate solvents to break the encapsulation, adjusted heat treatments, sonication of the sample in the extraction solution, and more aggressive agitation.
The food industry has benefited greatly from the constant improvement of the tools and processes to monitor food quality. This does require keeping abreast of what is occurring in the supporting area of analytical testing, but in the long run will result in better quality and safer foods.
Dr. Szpylka is the director of chemistry NA, Silliker Laboratories, a Merieux NutriSciences Co. He can be reached at firstname.lastname@example.org.
- Schreiber, A., Sims, A., “Advances in LC/MS for Food Safety Testing: New Liquid Chromatography/Mass Spec Technologies Make a Difference in the Lab,” Food Quality, Feb/March 2011.
- AOAC International Official Methods of Analysis.
- Szpylka, J., DeVries, J., Cheney, A., House, S., Determination of Total Folates in Infant Formula and Adult Nutritionals by Trienzyme Extraction and UPLC-MS/MS Quantitation, J. AOAC Int, 95(6), 1547-1554, (2012).
- Anastassiades, M., Lehotay, S. J., Stajnbaher, D., Schenck, F.J., Fast and Easy Multiresidue Method Employing Acetonitrile Extraction/Partitioning and “Dispersive Solid-Phase Extraction” for the Determination of Pesticide Residues in Produce, JAOAC Int, 86(2), 412-31, (2003).