Enzymatic Method for Determination of (1→3)(1→4)-Beta-D-glucans in Grains and Cereals: Collaborative Study

The McCleary enzymatic assay for mixed linkage (1→3)(1→4)-beta-D-glucans has been modified to apply to oat and barley fractions and ready-to-eat (RTE) cereals. The proposed method involves lower sample concentrations; stirring the samples; a longer, warmer lichenase digestion; and longer beta-glucosidase digestion. These changes result in higher recovery of beta-glucan. This modification expands on the American Association of Cereal Chemists (AACC) Method 32-22 by the addition of a desugaring procedure, which is necessary for RTE cereals. Results from collaborative studies sponsored by AACC and AOAC demonstrate good precision for an enzymatic assay. The average relative standard deviation for reproducibility (RSDR, a measure of inter laboratory variation) for 20 oat, barley, and cereal samples was 9.7%. The average RSD for repeatability (RSDr, intralaboratory variation) was 5.0%. The enzymatic method has been adopted first action by AOAC International for determination of beta-glucans in oat and barley fractions, and ready-to-eat cereals.

Determination of carbohydrates in soluble coffee by anion-exchange chromatography with pulsed amperometric detection: interlaboratory study

A collaborative study was conducted to validate a liquid chromatographic (LC) method to determine the free and total (after acid hydrolysis) carbohydrate profile of soluble coffee. Carbohydrates were separated on a pellicular anion-exchange column using pure water as mobile phase, and were detected by pulsed amperometry. Eleven collaborators were sent 6 test samples of commercial soluble coffee for duplicate analysis. They were also sent a practice sample with known levels of free and total carbohydrates and material for preparation of all standard solutions. The reproducibility relative standard deviations (RSDR) were 9.9-59.5% for mannitol, 35.6-72.6% for fucose, 4.9-21.1% for arabinose, 4.1-13.0% for galactose, 6.1-24.3% for glucose, 10.0-41.6% for sucrose, 20.2-37.7% for xylose, 10.6-40.0% for mannose, 15.5-71.7% for fructose, and 17.8-97.9% for ribose. Precision in the determination of free and total carbohydrates was very similar. The average repeatability RSDr and RSDR values were 4.5 and 14.3%, respectively, for carbohydrate levels above 0.3%. The precision of the technique was considered good, regardless of the usual peak integration problems always encountered in LC, the low levels of free carbohydrates, the hydrolysis step, and the relative lack of experience of most participating laboratories. The method allows good and reproducible separation of all major carbohydrates found in soluble coffee and is, therefore, suitable for routine analysis.

Determination of free and total carbohydrate profile in soluble coffee

A liquid chromatographic (LC) method was evaluated for the determination of free and total carbohydrates in soluble coffee. Samples are solubilized in water for free carbohydrates or hydrolyzed with 1.00N hydrochloric acid for total carbohydrates. An aliquot of the sample solution is analyzed on a pellicular anion-exchange polystyrene-divinylbenzene column using pure water as the mobile phase. Carbohydrates are quantitated by a pulsed amperometric detector. All major carbohydrates found in soluble coffee are determined in a single run. The technique allowed the detection of fraudulent addition of coffee husks or parchments as well as cereals or caramelized sugar for the 63 commercial products analyzed. High levels of free mannitol, free fructose, free glucose, sucrose, total glucose, and total xylose are a good indication of adulteration. Data were compared with those obtained from separate enzymatic determinations and from a different LC procedure. A close agreement among the methods was observed. However, the original method was superior in precision and was the only procedure that enabled the quantitation of all major carbohydrates. The technique is, therefore, a very powerful tool for routine analysis and for purity assessment of soluble coffee.

Adulteration of soluble coffee with coffee husks and parchments

Commercial soluble coffee can be adulterated with coffee husks or parchments. Xylose is a good tracer for this type of mispractice. The analysis of total xylose in a wide selection of green beans and the assessment of its fate during processing allowed the derivation of a maximum total xylose limit of 0.40%, above which a soluble coffee should be considered as adulterated. Out of the 700 commercial soluble coffees analyzed, 81 exhibited a total xylose level above this limit. Of the samples with total xylose level lower than the limit, 99% displayed concentrations in free mannitol and total glucose below 0.30 and 2.10%, respectively.

Determination of acesulfam-K in foods

A liquid chromatographic method was evaluated for the determination of the intense sweetener acesulfam-K in tabletop sweetener, candy, soft drink, fruit juice, fruit nectar, yogurt, cream, custard, chocolate, and biscuit commercial preparations. Samples are extracted or simply diluted with water and filtered. Complex matrixes need a clarification step with Carrez solutions. An aliquot of the extract is analyzed on a reversed-phase mu Bondapak C18 column using 0.0125M KH2PO4 (pH 3.5)-acetonitrile (90 + 10) as mobile phase. Detection is performed by UV absorbance at 220 nm. Recoveries ranged from 95.2 to 106.8%. With one exception, all analyzed values were within +/- 15% of the declared levels. The repeatabilities and the repeatability coefficients of variation were, respectively, 0.37 mg/100 g and 0.98% for products containing less than 40 mg/100 g acesulfam-K and 2.43 mg/100 g and 1.29% for other products. The same procedure also allowed detection of many food additives or natural constituents, such as other intense sweeteners, organic acids, and alkaloids, in a single run without interfering with acesulfam-K. The method is simple, rapid, precise, and sensitive; therefore, it is suitable for routine analyses.

Determination of aspartame and its major decomposition products in foods

A liquid chromatographic procedure already evaluated in a preceding study for the analysis of acesulfam-K is also suitable for the determination of the intense sweetener aspartame in tabletop sweetener, candy, fruit beverage, fruit pulp, soft drink, yogurt, cream, cheese, and chocolate preparations. The method also allows the determination of aspartame's major decomposition products: diketopiperazine, aspartyl-phenylalanine, and phenylalanine. Samples are extracted or diluted with water and filtered. Complex matrixes are centrifuged or clarified with Carrez solutions. An aliquot of the extract is analyzed on a reversed-phase muBondapak C18 column using 0.0125M KH2PO4 (pH 3.5)-acetonitrile ([85 + 15] or [98 + 2]) as mobile phase. Detection is performed by UV absorbance at 214 nm. Recoveries ranged from 96.1 to 105.0%. Decomposition of the sweetener was observed in most food samples. However, the total aspartame values (measured aspartame + breakdown products) were within -10% and +5% of the declared levels. The repeatabilities and the repeatability coefficients of variation were, respectively, 1.00 mg/100 g and 1.34% for products containing less than 45 mg/100 g aspartame and 4.11 mg/100 g and 0.91% for other products. The technique is precise and sensitive. It enables the detection of many food additives or natural constituents, such as other intense sweeteners, organic acids, and alkaloids, in the same run without interfering with aspartame or its decomposition products. The method is consequently suitable for quality control or monitoring.