Variations in Major Nutrients and Minerals Due to Standardized Preparation for Dishes and Raw Ingredients: 1. Losses and Gains in Preparation

When analyzing food for nutrient contents variation in the results arise for a number of reasons. Sources of such variations are purchase of ingredients, preparation to ready dishes, and analytical determination. The corresponding uncertainty in the reported values implies problems when interpreting data from nutrition surveys and epidemiological studies. The aim of the present study was to reveal representative levels, with uncertainties, for major nutrients and minerals, both for prepared dishes and for corresponding ingredients before cooking, and to investigate some sources of variation. Losses and gains in nutrients when preparing dishes were also of interest. Ingredients for 10 different typical Swedish dishes were bought on two occasions and were prepared in a standardized manner on four occasions. Analyses of moisture, ash, nitrogen, fat, calcium, phosphorus, iron, sodium, and potassium were performed. Due to low reliability if presenting results for each dish separately, the concept of an “average dish,” a summing of all dishes together, was used. For the different analytes the uncertainties in the average dish, in relative standard deviation (RSD), were 2–4%, except for fat (about 6%) and for iron (about 9%). The separated variations (ANOVA) due to determination were 2–4% RSD and those due to preparation were about three times larger, 6–10%. The variations due to preparation were only slightly larger for the ready dish (assembling + cooking) than for the ingredients (only assembling). The factors for recalculating the amounts of nutrients in raw ingredients to an average dish were close to unity, except for iron where the factor was 1.2.