14 May / June 2016
Direct Mono- and Disaccharide Determinations in Foods and Beverages
by Jeffrey S. Rohrer*, Sachin Patil, J. R. Thayer, Hua Yang Thermo Fisher Scientific, 1214 Oakmead Parkway, Sunnyvale, CA 94085 *- To whom correspondence should be addressed.
The mono- and disaccharide contents of coffee, sports drinks, fruit juices, and honey were determined by high-performance anion-exchange chromatography with pulsed amperometric detection (HPAE-PAD). The determination of free and total carbohydrates in coffee required less than ten minutes per injection. The low abundance small carbohydrates in honey were well resolved from the high concentrations of fructose and glucose (~35% each) using a recently introduced anion-exchange column with 4 µm resin particles.
Introduction:
Carbohydrates, especially mono- and disaccharides, are key ingredients of many foods and beverage products. The mono- and disaccharides often account for much of the product’s caloric content as well as its sweetness, texture, and taste. Also, mono-and disaccharides are often a large percentage of the carbohydrate content that must be labelled in the United States [1] and many other countries. In addition, determination of the mono- and disaccharide content of food and beverage products is important for quality control and can indicate product adulteration and/or mislabelling. For example, the content of individual carbohydrates is indicative of a honey’s origin and therefore a carbohydrate analysis can determine if the labelled origin is accurate. Honey from some countries is more valued than honey from others and those from lower priced origins have been fraudulently labelled as honey from a more highly valued origin. There are examples of products being adulterated with a sugar not typically present in the product to correct for a product defi ciency such as a lack of sweetness. One such example is a recent report showing the carbohydrate content of pear juice from growing regions worldwide to be used for authentication, to reveal adulteration with lower cost sweeteners, and to determine if other juices, such as apple juice, have been adulterated with pear juice [2].
While there are numerous methods for carbohydrate analysis, over the last 30 years HPAE-PAD has become a
standard technique for carbohydrate determinations of foods and beverages [3]. HPAE-PAD separates carbohydrates by converting them to oxyanions at high pH. These oxyanions are separated on a high- performance anion- exchange column, and are then detected by their oxidation at high pH on a gold working electrode with only a few percent of the carbohydrate oxidised for detection. Pulsed amperometric detection is sensitive and requires no analyte derivatisation. The carbohydrates are separated with a sodium or potassium hydroxide mobile phase (eluent). If desired, the potassium hydroxide eluent can be generated from deionised water by the instrument. This eluent generation precludes the analyst from having to prepare the eluent, eliminates eluent preparation errors, and enhances instrument to instrument and lab to lab method transfer. Some of the high-performance anion-exchange columns used for HPAE-PAD have recently been produced in formats containing 4 µm resin particles. This allows higher resolution carbohydrate separations with increased
Figure 1. Separation of nine common sugars analysed on the CarboPac SA10- 4µm column (4 x 250 mm) with its guard (4 x 50 mm) with the conditions used for instant coffee analysis described in the Experimental section. Peaks:1) mannitol 2) fucose 3) sucrose 4) arabinose 5) galactose 6) glucose 7) xylose 8) mannose 9) fructose.
sample throughput. Newer chromatography systems for HPAE-PAD were designed to use columns with 4 µm resin particles together with electrolytic eluent generation for the determination of carbohydrates using hydroxide eluents.
In this article, three HPAE-PAD food and beverage applications are shown where the analytes of interest are monosaccharides, disaccharides, and other small carbohydrates. In less than ten minutes, the important carbohydrates in instant coffee were determined accurately, with a signifi cant reduction in the analysis time required compared to the AOAC method [4]. The second application shows how the sucrose, glucose, and fructose contents
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56
