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The discussions in the two previous chapters document the major need for rationalization and harmonization of methods of food analysis and energy conversion factors. The participants at the workshop recognized that this is no small task, but believe it is a task that can be accomplished gradually over a number of years, if scientists and regulatory authorities have the will and the willingness to work together to that end. The goal of this chapter is to start that process by summarizing and integrating the recommendations from the previous two chapters. For methods of food analysis, the recommendations are listed in order, from the most desirable approach based on current science to those approaches considered acceptable given current realities. For food energy conversion factors, the preferred factors are integrated into the recommendations, based on the analytical methods used. These factors are based on ME.


Preferred. Protein is best measured as the sum of individual amino acid residues (the molecular weight of each amino acid less the molecular weight of water). Amino acid analysis to determine protein should be mandatory in the following situations: 1) food used as the sole source of nourishment, such as infant formula; 2) foods and formulas designed specifically for special dietary conditions; and 3) foods that contain novel proteins. When protein is expressed as the sum of amino acids, an energy conversion factor of 17 kJ/g (4 kcal/g) should be used.

Acceptable. Until values for protein based on amino acid analyses are generally available, protein based on total nitrogen (N) by Kjeldahl (or comparable method) x a factor (AOAC, 2000) is acceptable. When protein is determined in this way, the general factor - 17 kJ (4 kcal/g) should be applied, unless the complete package of analyses specified by Merrill and Watt (1973) are used, in which case the specific factor is preferable.

4.2 FAT

Preferred. For energy purposes, fats should be analysed as fatty acids and expressed as triglycerides (FAO, 1998), as this approach excludes wax esters and the phosphate content of phospholipids, neither of which can be used for energy. For normal dietary fats, a factor of 37 kJ/g (9 kcal/g) should be used. With novel fats (such as salatrims and Olestra®), the content of non-digestible fat should not be included in the energy content of the food. In these instances, the conversion factor for the digestible portion of the fat is 37 kJ/g (9 kcal/g). This requires that a specific energy conversion factor be determined and used for these fats. For example, salatrims:[16] general family 22 kJ/g (5.2 kcal/g), Olestra® 0 kJ/g (0 kcal/g).

Acceptable. Although less desirable, a gravimetric method (AOAC, 2000), is acceptable for the measurement of normal dietary fats. When a gravimetric method is used, an energy conversion factor of 37 kJ/g (9 kcal/g) should be applied, unless the complete package of analyses specified by Merrill and Watt (1973) are used, in which case the specific factor is preferable.


Carbohydrate should be analysed in a way that allows determination of both available carbohydrate and dietary fibre.

Preferred - available carbohydrate. For purposes of energy evaluation, a standardized, direct analysis of available carbohydrate (by summation of individual carbohydrates) (FAO, 1998; Southgate, 1976) is preferable to an assessment of available carbohydrate by difference (total carbohydrate by difference minus dietary fibre). Direct analysis allows separation of individual mono- and disaccharides and starch, which is useful in determination of energy values. Direct analysis is considered the only acceptable method for analysis of carbohydrate in novel foods or in foods for which a reduced energy content claim is to be made. When carbohydrate is determined by direct analysis, it is expressed as the weight of the carbohydrate with a conversion factor of 17 kJ/g (4.0 kcal/g). When expressed as monosaccharide equivalents, a conversion factor of 16 kJ/g (3.75 kcal/g) should be used.

Acceptable - available carbohydrate. Assessment of available carbohydrate by difference (total carbohydrate by difference minus dietary fibre by Prosky or comparable method) is considered acceptable for purposes of energy evaluation of conventional foods. In these instances, an energy factor of 17 kJ/g (4 kcal/g) should be used.

Preferred - dietary fibre. The AOAC (2000) analysis - Prosky (985.29) or similar total dietary fibre method is preferred for analysis of dietary fibre in conventional foods, and an energy conversion factor of 8 kJ/g (2 kcal/g) should be used. When dealing with fibres or oligosaccharides that are specifically added to a food, an analytical method (Prosky or other) and an energy conversion factor specific for the fibre or oligosaccharide in questions should be used. For example, energy conversion factors range from 1.3 kJ/g (0.3 kcal/g) for maize bran fibre to 11 kJ/g (2.6 kcal/g) for fructo-oligosaccharides.

Acceptable - dietary fibre. At present, dietary fibre is determined by a number of methods yielding different results. The method used should be stated and the results of each method should be identified by INFOODS tagnames (Klensin et al., 1989). In food composition tables, the result should similarly be identified with the tagname. The energy factor to be applied to these results should be appropriate for the faction analysed. In the absence of a specific factor associated with the method, a value of 8 kJ/g (2 kcal/g) should be used.

A note about food labelling of carbohydrates. Having different energy conversion factors for carbohydrate determined by different methods is not ideal. Currently there is no way to label carbohydrate with a single value that describes the energy content accurately. As pointed out in Chapter 3, the same weight of different carbohydrates (monosaccharides, disaccharides and starch) yields different amounts of hydrous glucose, and thus different amounts of energy. Stated conversely, the amount (weight) of carbohydrate to yield a specific amount of energy differs depending on the form, owing to the water of hydration in different molecules.


Analytical methods for organic acids and polyols were not discussed, nor were recommendations made. The following general energy conversion factors are recommended for these substances: alcohol - 29 kJ/g (7 kcal/g), organic acids - 13 kJ/g (3 kcal/g), and polyols - 10 kJ/g (2.4 kcal/g). The recommendations reflect the EC directive (EC, 1990). Where one organic acid or polyol represents a substantial source of energy in a product, use of a more specific factor for that compound may be desirable.

[16] Salatrims: random short- and long-chain triacylglycerol molecules.

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