Analytical methods and laboratory choice for food composition, an introduction

Transcription

1 Analytical methods and laboratory choice for food composition, an introduction Paul Hulshof, Global challenges Research Fund Foodomp workshop, Pretoria, 5-9 Feb, 2018

2 General Reasons for analyzing food constituents in general are diverse: Government regulations and recommendations Standards Nutritional labeling Authenticity Food inspection and grading Food safety Quality control Characterization of raw materials Monitoring of food properties during processing Characterization of final product Research and development Food composition databases

3 General Primary objective in analysis for food composition databases: Provide users with compositional information on nutrients Nutrient values must represent nutritional value of foods

4 Measures to ensure a laboratory produces reliable results

5 Laboratory data quality Precision Accuracy Data Quality Challenge for labs because: Food is a very complex & variable matrix holding many different nutrients in different concentration! Large choice in analytical procedures 5

6 AOAC procedures for fatty acids (Milk products and infant formula) (fatty acids) (Fat, Total, Saturated, and Unsaturated in Foods) (fatty acids) (Fat, Total, Saturated, Unsaturated, and Monounsaturated in Cereal Products) (fatty acids (Total trans fatty acid isomers in margarines) (fatty acids) (Oils and Fats/Oils) (fatty acids) (Meat and Meat Products/Meat) (fat) (Foods/Oils and Fats) (fat) (Total trans fatty acid isomers in margarines) (fatty acids) (Hydrogenated vegetable oils and animal fats) (fatty acids) (Erucic Acid in oils and fats) (fatty acids) (Eggs and Egg Products/Eggs) (fatty acids) (Foods/Oils and Fats) (total fatty acids) (Oils/Crude and Refined Oil) (free fa) (Foods/Oils and Fats) (fatty acids aggregated) (Foods/Oils and Fats) (fatty acids aggregated) (Oils and Fats/Partially Hydrogenated Fats) (fatty acids aggregated)

7 Example

8 What makes vitamin analysis so challenging?

9 Which method / laboratory to choose?

10 Whatever method is chosen: obtaing reliable data requires that a laboratory Uses validated methods of analysis Uses internal quality control procedures Participation in proficiency tests Becomes accredited to international standard e.g ISO/IEC (IUPAC, 2002)

11 From primary sample to analytical portion sampling Synonyms Analytical sample Analytical portion Test portion

12 General steps in the analytical process Take analytical portion Treatment of food matrix (extraction, destruction, saponification, etc) Optional: treatment to remove interfering components or concentration step (e.g. by SPE) Instrumental measurement / separation of components Detection confirmation of identity quantification Quality control Report of results in proper modes of expression

13 Choice of analytical methods Method selection 1-considerations Method chosen for analysis of nutrients should reflect information required by FCDB users: this may differ from that of other data users such as those regulating food composition or quality control of food production. Total nitrogen versus protein by Lowry versus total protein by sum of amino acid residues Total dietary fiber (Prosky fiber), versus AOAC , versus Englyst fiber versus crude fiber Total carotene versus individual provitamin A carotenoids for assessing Retinol Activity Equivalents

14 Choice of analytical methods Obtaining reliable nutrient data: Requires careful work of analyst working under Quality Assurance scheme Choice of appropriate method Not prerogative of analyst alone; technical and scientific staff need knowledge of underlying principles Availability of methods differ for nutrients: good, adequate, not adequate for all foods, lacking (see Table 6.1 GreenGate)

15 Choice of analytical methods Adequacy of methods Nutrient Good Adequate Not adequate for certain foods Moisture Moisture Lacking Nitrogeneous constituents Total nitrogen, amino acids Protein, non-protein nitrogen Lipid constituents Fatty acids Cholesterol, phospholipids, trans fatty acids, individual triacylglycerols some isomeric fatty acids Carbohydrates and dietary fibre Individual sugars, starch, non-starch polysaccharides Total dietary fibre, individual non starch polysaccharides, resistant starch lignin Inorganic constituents Sodium, potassium, calcium, phosphorus, iron, copper, zinc, boron, chloride Selenium, manganese, fluorine Chromium, haem iron, cobalt, molybdenum Vitamins Thiamin, riboflavin, niacin Vit C, retinol, carotenoids, vit E, vit D, Vit B6, total folate, biotin, panthotenic acid, vit B12 Carotenoid isomers, vitamin K Some folate isomers Source: Greenfield and Southgate, 2003

16 Choice of analytical methods (do not confuse adequacy of method availability with adequacy of performance)

17 Interlaboratory studies measure laboratory data quality Collaborative study Well-defined materials Experienced laboratories Well-defined method Proficiency study Well-defined materials Approved methods Certification study Well-defined materials Experienced laboratories Validated methods, different principles Precision method Precision laboratories True value 17

18 Choice of analytical methods Method selection 2 - considerations Methods used often depend on resources available: Labor costs versus instrument cost Sophisticated methods (requiring expensive instruments) not necessarily always better than non-sophisticated methods (labor intensive) Strategy: concentrate on limited number of methods (specialization) and cooperate with others (you cannot be excellent in all methods); invest in regional capacity building!

19 Choice of analytical methods Method selection 3 - considerations Preference should be given to methods: For which reliability* has been established in inter-laboratory collaborative studies Recommended or adopted by international organizations (AOAC, ISO, CEN, AOCS, ) Applicable to range of food types and matrices Practical: speed, cost, technical skills required, safe in laboratory For which the validity has been demonstrated in the environment of the laboratory *Reliability: reflects degree of satisfaction with the performance of a method in relation to applicability, specificity, accuracy, precision, detectability, sensitivity and robustness (attributes of methods)

20 Choice of analytical methods Source: Eurachem guide 1998: a laboratory guide to method validation

21 Choice of analytical methods Which attributes of a method should be validated? Eurachem* identifies the following method attributes: Limit of detection Limit of quantification Recovery Confirmation of identity Linearity Accuracy Precision (repeatability, reproducibility) Ruggedness/robustness * Source: Eurachem guide 1998: a laboratory guide to method validation

22 Analytical requirements and related method performance characteristics Analytical requirement elements When quantitative answer is required Is analyte present in more than one form, are you interested in extractable, free or total analyte? What are the analytes of interest and the likely levels present (%, ppm, ppb) Related attribute Limit of detection, limit of quantification Confirmation of identity, recovery Linearity What are the likely interferences to the analytes? Is method performance stable when small but deliberate variations are introduced? Selectivity/specificity Robustness/ruggedness How accurate and precise must answer be? What degree of uncertainty is allowed and how is it to be expressed Accuracy/trueness, repeatability precision, reproducibility precision

23 Reference to official methods ISO methods AOAC methods Codex standard/methods CEN methods spx

24 CEN standards

25 Choice of analytical methods If you are using outdated methods you are risking the analytical integrity of your laboratory AOAC international

26 Choice of analytical methods When are analytical methods outdated? Not easy to say in general Dependent on the impact of developing techniques: Gravimetric methods, colorimetric and microbiological methods are likely to become outdated In favor of chromatographic methods (ion-exchange, GC-MS, LC-MS/MS), spectroscopic methods (flame photometry, atomic absorption, ICP-MS/AES), immunological methods

27 Example for vitamins

28 Men Material Methods Machine Manipulation Assuring the quality of lab data

29 Essential: Third party assessment Essential elements in laboratory quality assurance: Use of validated analytical methods Participation in laboratory proficiency testing schemes Analysis of (certified) reference materials Accreditation involving auditing

30 Choice of analytical methods (Summary) Nutritional relevance Does it measure the constituents the user needs? Quality assurance Chosen method Fully documented Officially accepted Validated in collaborative trials Validated in environment of laboratory

31 In search of / understanding methods of analysis: WIKI pages

32 E-learning