DETERMINATION OF DIETARY FIBRE – THE INFLUENCE OF MILLING FRACTION AND MIXING PROCESS

Dietary fibre is an important constituent of a healthy diet, composed of non-digestible carbohydrates and lignin. Over the last decades dietary fibre has gained importance for human nutrition, due to its beneficial effects on health. In addition to classical enzyme-gravimetric methods, new methods for the determination of total, insoluble and soluble dietary fibres in foods have recently been developed, but have not yet been fully implemented for use. For the purpose of creating food composition databases and for food labelling, the classical AOAC 985.29 and 991.43 methods are still widely used. The methods are enzyme-gravimetric and therefore sensitive to enzyme kinetics. The aim of the study was to investigate the effect of milling fraction and mixing of the sample on dietary fibre content determined with the AOAC method 991.43. The results showed that milling fraction significantly influences the content of dietary fibre, especially in unprocessed or slightly processed cereals, the mixing acts synergistically with milling. According to the results it is proposed to mill the sample between 200 and 500 μm. For accurate determination of dietary fibre content, it is necessary to prepare the sample correctly, since the AOAC 991.43 method is, despite its robustness, sensitive during the sample preparation step.