F. W. SCOTT ANDR. MONGEAU
Food Directorate, Nutrition Research Division, Banting Research Centre, Ottawa, Ontario, Canada
P. WOOD
Centre for Food and Animal Research, Agriculture and Agri-Food Canada, Ottawa, Ontario, Canada
INTRODUCTION
The Canadian Nutrition Recommendations published in 1990 by Health Canada refer to the benefits of diets high in complex carbohydrates, defined essentially as starches. For the purposes of food labeling claims in Canada the term “complex carbohydrates” is permitted and has been taken to mean only starch which is the term used on the nutrition label itself. In other jurisdictions, the term “complex carbohydrates” has been taken to mean either starches or starches plus dietary fiber. Thus, the term is a source of confusion, is difficult to define in a manner that can be verified analytically and has little scientific meaning for many scien-tists and lay people alike (1, 2). There is a need to simplify and more clearly define in chemical terms what is meant by the advice to consume foods high in complex carbohydrates. It is time to re-think the use of this chemically undefined 35
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term and we suggest that “complex carbohydrate” be replaced by the terms starch and dietary fiber.
MEASUREMENT AND IDENTIFICATION OF CARBOHYDRATES
As the physiological effects of different polysaccharides become better under-stood it is appropriate to bring improved definition and precision to the area of food carbohydrates. This message is important when one considers that as re-cently as 1992 carbohydrate was still measured “by difference” in USDA Hand-book 8, a practice subject to error because it includes minor non-carbohydrate components and is subject to cumulative analytical error derived from the analy-ses for protein, fat, moisture and ash. The FDA does not permit the term complex carbohydrate but requires the term “other carbohydrate” which is defined as the amount of carbohydrates remaining after subtraction of dietary fiber, sugars and sugar alcohols from total carbohydrates (3). This introduces another ill-defined and confusing term and continues to avoid mentioning by name the chemically well-defined term starch.
STARCH
We feel that a more useful and practical solution at present is to use the terms starch and dietary fiber separately. An appropriate definition of starch follows:
“Starch is a large polymer of glucose consisting of glucose units formed into unbranched amylose chains composed of alpha-1,4 linked glucose residues and highly branched amylopectin with alpha-1,4 and alpha-1,6 bonds.” There are sev-eral methods to measure starch (4–9). There are commercially available kits to measure starch based on converting it to soluble fragments with minimal produc-tion of glucose followed by quantitative hydrolysis by amyloglucosidase (4).
(This kit can also provide an estimation of enzyme-“resistant” starch). In the method for total starch, starch is solubilized with DMSO or the sample is cooked in buffer with a thermostable alpha-amylase. Complete breakdown to dextrins is carried out by subsequent treatment with the de-branching enzyme pullulanase in combination with alpha-amylase to minimize the amount of free glucose formed by continued action of alpha-amylase. Quantitative hydrolysis of the re-sulting maltotrioses and maltoses, (which are not substrates for the bacterial alpha-amylase) to glucose is carried out with amyloglucosidase and glucose is measured using a standard enzyme/color reaction with samples read in a spectro-photometer. Unlike the term “complex carbohydrates”, starch is a more defined chemical entity and can be measured by several methods.
Suggested Alternatives 37
DIETARY FIBER
Dietary fiber is essentially dietary non-starch polysaccharides and cell wall-associated components such as lignin. The report of the Canadian Expert Com-mittee (10) strongly emphasized that dietary fiber excludes polymers formed during food processing or preparation and that the labeling of dietary fiber content in a food has value only because certain physiological benefits are expected of fiber.
To consider dietary fiber as complex carbohydrates also ignores the fact that the non-carbohydrate components participate in maintaining the botanical (plant cell wall) structure of dietary fiber and the structure of the food. The botani-cal structure and particle size may account for a significant proportion of the beneficial effects of dietary fiber on postprandial blood glucose response and intestinal function (11).
PHYSIOLOGICAL EFFECTS AND LABELING
The approach we suggest here focuses on two groups of components that can be analyzed using available methods.
The ingestion of starches can have a variety of effects depending on the plant source, cooking conditions and the individual’s digestive tract. These varia-tions result from interacvaria-tions in both the upper gastrointestinal tract and in the colon and are not necessarily a consequence of chemical differences that are easily identified. Evidence that small amounts of “resistant starch” may have effects on gastrointestinal function and metabolism is important but this is just one aspect of a spectrum of effects originating from the same chemical entity.
Information on these effects is not yet sufficient to include recommendations with respect to different starches and should not be of concern for the purpose of food labeling at this time.
Because high carbohydrate diets containing foods high in starches and di-etary fiber can have beneficial health effects, the most useful and practical posi-tion at present for the purposes of labeling is to identify starches and dietary fiber separately. This approach to simplifying the definitions, analytical and labeling issues would facilitate healthy food choices by the consumer.
Products enriched in non-native or novel fiber sources also have a place in the market and may have benefit for particular segments of the population.
Thus, the only justification for enriching foods in these materials should be the clear demonstration of beneficial physiological effects and not simply the artifi-cial inflation of total carbohydrate and dietary fiber values.
REFERENCES
1. Asp, N.-G. (1994) Nutritional classification and analysis of food carbohydrates. Am J. Clin. Nutr. 59 (Suppl), 679S–681S.
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2. Johnson, I. T., and Southgate, D.A.T. (1994) Dietary fibre and related substances.
in Dietary fibre and related substances. Chapman and Hall, London. 132 pp.
3. Anonymous (1993) Discussion on other carbohydrates. Federal Register 58, 2177.
4. Total starch procedure TSA 9/92 (1993) Megazyme Australia, 2/11 Ponderosa Pa-rade, Warriewood, (Sydney), NSW 2102, Australia (Fax: 612-979-8272).
5. Moreels, E. (1987) Measurement of the starch content of commercial starches. Starch 39, 414–416.
6. Mitchell, G. A. (1990) Methods of starch analysis. Starch 42, 131–134.
7. Henry, R. J., Balkeney, A. B., and Lance, R.C.M. (1990) Enzymatic determination of starch in samples with high sugar content. Starch 42, 468–470.
8. Batey, I.L. (1982) Starch analysis using thermostable alpha-amylases. Starch 34, 125–128.
9. Baur, M.C., and Alexander, R. J. (1979) Enzymatic procedure for determination of starch in cereal products. Cereal Chem. 56, 364–366.
10. Health and Welfare Canada (1985) Report of the Expert Advisory Committee on Dietary Fibre, National Health and Welfare Canada, Ottawa, Ontario.
11. Mongeau, R., Scott, F. W., and Brassard, R. (1997) Definition and analysis of dietary fiber. In Complex carbohydrates: Definition, analysis, and applications. Marcel Dek-ker, New York.