Dietary fiber content and composition of vegetables determined by two methods of analysis

Abstract

Forty-one samples representing different forms of 12 types of vegetables were analyzed for dietary fiber content using the Association of Official Analytical Chemists method and for fiber content and composition using the Uppsala method. Mean fiber content measured by the former method was 2.1 +/- 0.9 g/100 g and by the latter method, 1.8 +/- 0.8 g/100 g. The mean soluble fiber concentration determined by the Uppsala method was 15% of total vegetable fiber. Insoluble fiber contained more neutral sugars than uronic acid; soluble vegetable fiber was a mixture of uronic acid and polysaccharides containing galactose and arabinose. Cooking either had no effect or increased the proportion of total fiber extracted as soluble fiber. Some vegetables that are frequently treated as similar foods in nutritional studies (e.g., potatoes and cooked greens) contained different amounts of fiber. The results indicate that for some vegetables the source, preparation method, variety, and analytical method should be considered when daily intakes of total dietary fiber or fiber components are calculated.