Low-field NMR instrumentation offers a user-friendly and cost-effective means for assessment of water and oil droplet size measurements in food emulsions. Examples are given of major food application areas, and these are supported with validation data in terms of precision and equivalence to other methods. The NMR method gives the same results as other techniques, such as microscopy, laser diffraction and electric sensing, but with similar or better precision. NMR distinguishes itself by a simple and non-perturbing sample preparation procedure (in addition to the aforementioned advantages). For reliable results, the NMR parameters should be properly chosen and adjusted. A survey is given of experimental NMR parameters than can have an impact on the performance of water and oil droplet size determination. Copyright 2002 John Wiley & Sons, Ltd. KEYWORDS: NMR;1 H NMR; droplets; emulsion; foods; laser diffraction; microscopy INTRODUCTIONIn food research, the pressure to bring products faster to the market has become stronger, and the systems under investigation are becoming ever more complex both in structure and in chemical composition. 1 NMR spectroscopy has become an indispensable technique that can relate meso-and microstructural parameters to consumer-related features, such as shelf-life and mouthfeel.2 However, NMR is still considered an expert technique, whereas the rapid pace of product development requires understanding and/or control of food structures at the laboratory bench/kitchen table or manufacturing plant. In recent decades, low-cost and easy-to-handle benchtop NMR systems 3 have been developed which can determine phase-compositional 4 and microstructural 5 parameters of food materials. These systems operate at low field, typically 0.47 T (20 MHz for 1 H), and this poses intrinsic limitations on sensitivity and resolution. Nevertheless, these systems have gained a considerable position in food industry laboratories, with applications ranging from research and development to process and product control.The classical NMR application in the microstructural domain is the assessment of water droplet size distributions in food emulsions.6 -8 These methods are being used to explain and predict physical and microbiological stability of water-in-oil food emulsions, 9 such as margarines and low-calorie spreads. A more recent development is the assessment of oil droplet size distributions in oil-in-water systems.10 These systems also are fairly abundant as Ł Correspondence to: J. P. M. van Duynhoven, Unilever R&D Vlaardingen, Olivier van Noortlaan 120, 3133 AT Vlaardingen, The Netherlands. E-mail: john-van.duynhoven@unilever.com mayonnaises, cheese, dressings, spreads, etc. 11 Both the water and oil droplet size distribution measurements are based on the restricted diffusion of the liquid inside a droplet, a phenomenon that can be described analytically. The droplet size determination by low-field NMR has several significant advantages over other, and perhaps more obvious, methods. A summary of the typical ch...
The results of a collaborative study by 38 laboratories were analyzed statistically to calculate the precision of a novel capillary gas-liquid chromatography (GLC) method for the determination of low levels of trans fatty acids (TFA) in edible oils. The participants came from 17 countries, mainly European, and were spread evenly between Unilever companies and external laboratories. All participants used the same GLC method, including a temperature optimization step, which is suitable for the determination of a large range of TFA levels in refined oils and fats and for the determination of total saturated fatty acid, cis mono-and cis-cis methylene-interrupted polyunsaturated fatty acid isomers. For TFA levels down to 0.5%, the collaborative study yielded values for R within that ranged from 0.08 to 0.13% (absolute values) and for R between from 0.2 to 0.4%, depending on the isomer distribution in a particular edible oil. The proposed GLC method allows reliable TFA analysis at low levels that is suitable for monitoring oil processing practices and intake control. JAOCS 75, 483-488 (1998). FIG. 1. Representative bar graph of the accepted data for one batch of soybean oil [target trans fatty acid (TFA) level 0.90%]. For each of the 38 participants, the blind duplicate results are given in adjacent bars.
The quality grade of an olive oil is attributed on the basis of a number of chemical and physical parameters, and, in accordance with EC rules, additionally by the sensory evaluation by a taste panel. Evaluation of the statistics of the method of the Conseil Olticole International (COI) as reported by Albi and Gutierrez (J Sci Food Agric 54 (1991) 255-267) revealed a number of limitations and weaknesses. An alternative test has therefore been developed. Oils are first tasted by a small panel which decides on acceptance, rejection or further sensory evaluation by a larger panel. The alternative conceptually simpler nonparametric three-point scoring system developed removes some drawbacks of the CSIC method. The method was applied to the panel results published by Albi and Gutierrez and the results of both methods were compared.
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