Nutritional value through the eyes of an analyst

The nutrition declaration is an important element of the labeling of foodstuffs. Consumers very often use it to select foodstuffs before buying them, which reflects the growing interest in proper nutrition and a healthy lifestyle. The obligation to provide this information results from the provisions of food law, and the principles of nutrition labeling are set out in Regulation (EU) No. 1169/2011 of the European Parliament and of the Council of 25 October 2011 on the provision of food information to consumers, amending the Regulations of the European Parliament and (EC) No 1924/2006 and (EC) No 1925/2006 and repealing Commission Directive 87/250/EEC, Council Directive 90/496/EEC, Commission Directive 1999/10/EC, Directive 2000/13/EC of the European Parliament and Council, Commission Directives 2002/67/EC and 2008/5/EC and Commission Regulation (EC) No. 608/2004 (as amended). This regulation clearly regulates the requirements regarding the content as well as the manner of providing information on the label. All this is intended to enable you to make informed choices and avoid unfair competition among food producers. These regulations oblige entities that place foodstuffs on the market to include this information, but do not impose the source of information on the content of individual nutrients. The manufacturer can obtain this data in practice from three sources: from tables of nutritional values available in databases (different in different countries), own calculations from technological recipes and from laboratory tests. The first two methods, although acceptable as sources of nutritional information, do not provide accurate information about a particular food. The same raw material used for food production may have different content of individual ingredients depending on the origin, method of cultivation or breeding, and even on the season in which it was obtained. The content of nutrients calculated in this way indicates their theoretical, not the actual amount, which may mislead consumers.

So what is nutritional value?

 It is information on how many nutrients are in a given product and how much a given product provides energy expressed in kcal and kJ. For people on a "reducing diet", this is practically the most important information, and its exact value is extremely important. Pursuant to the Regulation, the nutritional value of the product must include information on how much the product provides: energy, fat and saturated fatty acids, carbohydrates and sugars, protein, and salt. These contents should refer to the form of the product in which it is available for sale (e.g. instant). In addition, there may also be information on the content of: monounsaturated fatty acids, polyunsaturated fatty acids, polyhydric alcohols, starch, fibre, as well as vitamins and minerals present in amounts in accordance with the Annex to the Regulation.

The first component of the nutritional value is the energy value, which can be determined in several ways. One of the main methods is the measurement using a bomb calorimeter. This determination consists in burning the sample in an oxygen atmosphere, and then measuring the amount of heat released during combustion.Another method, also indicated in Regulation (EU) No 1169/2011 of the European Parliament and of the Council, is the calculation of energy using conversion factors. This calculation consists in summing up the calculated energy provided by individual nutrients, whose energy in turn is calculated by multiplying the amounts of a given ingredient by the appropriate factors for them.

Determining the amount of individual nutrients by analytical methods and calculating the energy value based on them provides the greatest guarantee that the values given in this way reflect the actual nutritional value of the product.

At the WESSLING Polska Food Analysis Laboratory, we analyze food in terms of the main nutrients. There are many ways to mark them. In order to determine the content of individual ingredients in a given product in the most accurate way, the research methodology for a given matrix should be properly selected.

For the correct calculation of the energy value, it is necessary to enter the total fat content. For this purpose, prior to extraction, prior sample preparation by hydrolysis is required. In practice, this means boiling the test sample in hydrochloric acid for a certain time, then, after rinsing and drying, the fat is extracted with petroleum ether and marked by weight.

Another nutrient is fatty acids. The full spectrum of fatty acids is determined by gas chromatography coupled with a flame ionization detector (GC-FID). The chromatographic separation is preceded by the esterification of triacylglycerols present in the fat to fatty acid methyl esters. The fatty acid methyl esters quantified in this analysis are then converted to fatty acids and the results are given per 100 g of the test sample. To calculate the fatty acid content, it is necessary to know the fat content.

Protein content is the only nutrient for which the EU Regulation No. 1169/2011 indicates a reference research technique - the Kjeldahl method. This method consists in determining the content of total nitrogen in the tested sample. The food sample is mineralized in a concentrated sulfuric acid environment, followed by a distillation process. The last stage of the analysis is titration with standard hydrochloric or sulfuric acid of distilled nitrogen, the amount of which is calculated on the basis of the amount of milliliters of acid used for titration. The average nitrogen content in protein of various origins is about 16%, so for the purposes of protein conversion, the conversion factor is 6.25 (100:16 = 6.25). In various foodstuffs, protein differs both in qualitative and quantitative composition, and thus in nitrogen content. For this reason, the exact protein content is determined using different conversion factors for different types of food. Nevertheless, for the purpose of nutrition labelling, the legislator indicated the aforementioned factor of 6.25, regardless of the type of food.

Another component of the nutritional value are carbohydrates, which, according to the definition contained in the regulation, are: "all carbohydrates that are subject to metabolic processes in the human body, including polyhydric alcohols". This means that the carbohydrates that are indicated in the mandatory nutrition declaration are assimilable carbohydrates, and thus it is necessary to know the fiber content, which, interestingly, is not required on the label. Available carbohydrates are calculated by subtracting protein, fat, water, ash and fiber content from 100% of the sample weight.

The water content in the Food Analysis Laboratory is determined by weight. The test consists in drying the sample in the time and temperature specified by the standards, during which water is removed from it, which allows you to determine its amount after weighing the remaining "dry mass" of the sample. The method is simple, but in some matrices it also requires taking into account the loss of other volatile substances, such as e.g. essential oils (in spices), which evaporate together with water.

The ash in the sample is a measure of the mineral content. In the WESSLING Polska Laboratory, it is determined by burning the sample at high temperature (usually around 550 °C) and gravimetric determination. In addition to the minerals remaining after the sample has been burned, the ash also includes various types of impurities, such as sand, glass or residues of the chemicals used.

The water and ash content is not indicated on the label, but it is necessary to determine them to calculate the content of available carbohydrates.

Although the ash itself is not required on the label, one of its components - salt must be placed on it. The analysis of the salt content consists in the mineralization of the sample, and then in the determination of sodium using the technique of atomic emission spectroscopy with induction plasma excitation (ICP-OES). This technique is used to determine most elements in various types of samples. For nutritional labeling purposes, the salt content is calculated by converting from the previously labeled sodium content and multiplying it by a factor of 2,5. The conversion factor given reflects the sodium content of a salt molecule (sodium chloride: NaCl).

An interesting component of nutritional value is fiber. It is a component of plant origin that is not digested or absorbed in the human digestive tract. Unfortunately, there is no one universal method for the determination of fiber in food due to the variety of fractions included in it. The method used in WESSLING Polska consists in digesting the sample with three enzymes, and then precipitating the fiber with ethanol. The protein and ash content of the digestate should then be determined and included in the calculation of total dietary fibre.

Sugars and polyhydric alcohols are part of assimilable carbohydrates. At WESSLING Polska, we use two methods of sugar determination. The first of them is the Luff Schoorl method, which uses the reducing properties of simple sugars. This is a titration method that only determines sugars. To determine the total sugar content, complex sugar molecules must first be broken down into simple sugars by acidic hydrolysis.

The second method for the determination of sugars is the technique of high-performance liquid chromatography with the RID detector (HPLC-RID). The advantage of this method is greater accuracy and the ability to quantify the content of individual sugars present in the product. The test consists in extraction of the sample with hot water, followed by chromatographic analysis. The content of individual sugars and/or polyhydric alcohols is calculated on the basis of a calibration curve.

It should be remembered that when calculating the energy value, the content of assimilable carbohydrates should be reduced by the amount of polyhydric alcohols. Otherwise, the energy value will be falsified, as they provide less energy per unit than carbohydrates.

If the product contains ingredients such as salatrims (reduced calorie triglycerides), organic acids and alcohol, they should also be labeled and their amount included in the calculation of the energy value in accordance with the conversion factors provided in the regulations.

Justyna Do Huu

Konrad Wasinkiewicz


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