Dietary fibre and available carbohydrates in Finnish vegetables and fruits

Abstract. The dietary fibre and available carbohydrate contents of vegetables, fruits and berries commonly consumed in Finland were analysed using the Englyst total carbohydrate method. The tables give the composition of 73 fresh and processed vegetables and fruits. The estimated average daily intakes of carbohydrates received from this category of foods were: total soluble sugars 23.7 g, starch 30.6 g and dietary fibre 7.2 g (energy level 10 MJ).


Introduction
Vegetables and fruits are the main sources of dietary fibre after cereal products.A con- siderable portion of vegetable and fruit fibre is water soluble.Consequently, its physical properties are different from those of cereal fibre; its waterbinding capacity is especially high (Eastwood 1983).Some fruit and berry products contain added sugar, but on the whole, natural sugars occur in greater amounts in this category of foods.The starch content is generally low, except in potato, which is one of the main sources of starch in Finland.In the present study the dietary fibre and available carbohydrates in the vegetable foods commonly consumed in Finland were analysed in an attempt to establish in detail the carbo- hydrate composition of Finnish foods (Varo  et ai.1984).The foods were analysed ac- cording to the method of Englyst (1981).

Material and methods
The sample material, 2-4 subsamples (1.5 -2 kg each) per item, was bought from local retail shops.Subsamples were washed and cut as in common household practice into edible portions, which were then united as one sample proper.Part of this was freeze- dried and homogenized in a blender.Only one sample per item was analysed.This is a T a b l e

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2 .L i g n i n g 1. 9 2. 2 4. 9 0. 7  reflection of the complexity of the analytical procedure, which allowed only a very limited number of samples to be analysed within the context of the present study.
The analytical scheme used was that de- veloped by Englyst(l9Bl) and slightly mod- ified by Laine et ai.(1981).The method has been described in detail in the preceding pa- per (VARoet al. 1984).The standard sample was the same as in the cereal study.For com- parison, the total dietary fibre of some vegetables and fruits was also analysed with the enzymatic-gravimetric method of Asp et al.  (1983).This showed that the results obtained with the present method were 10-15 % lower than those obtained with the enzymaticgravimetric analysis in this category of foods (Varo 1984).
The results of the water-soluble non-cellulosic polysaccharide (w.s.NCP) fraction tended to be the most variable, and the whole fraction was therefore completely re-analysed on a sample 10 times bigger using gravimetric determination of filtered and dried precipitate.Free sugars and, less often, lignin caused re- checks.
C o n t e n t

Results and discussion
The results of the present study are given in Table 1.Free sugars, starch and the main components of dietary fibre are tabulated.By and large, the results are consistent with findings from earlier carbohydrate studies (Salo 1967, Paul & Southgate 1979, Eng-  lyst 1981, Souci et al. 1981).
Sugars.Most vegetables, fruits and berries contain considerable amounts of natural sugars.Usually the three sugars glucose, fruc- tose and sucrose are present, fructose often being the most abundant.Sorbitol may be present, too (Souci et al. 1981), but it was not measured in the present study.Canned fruits, jams and marmalades contain appre- ciable added sugar.
Starch.The amount of starch, if present, is usually quite low.Its concentration is dis- tinctly highest in potato and banana.Some vegetables contain fructosanes (Salo 1967).
In this study they were detected in onion.In the present analytical scheme these carbo- hydrates were cohydrolysed with starch.Dietary fibre.The fibre content of vege- tables and fruits is high in relation to their energy content.It was highest in some berries with seeds, which increase the lignin fraction in particular.The water-soluble fraction was usually quite large.The sugar and uronic acid composition of w.s.NCP and w.i.s.NCP of some vegetables and fruits is given in Table 2. Uronic acids were the main con- stituents of the w.s.NCP fraction; the composition of w.i.s.NCP was more variable and included large amounts of galactose, pentoses and uronic acids.
According to statistics (Anon. 1981,Agric.Econ.Res.Inst.1983), the average consumption of vegetables in 1981 was 116 g/d and that of fruits 239 g/d.The average consump- tion of potato was 162 g/d.The vegetables with the highest consumption are cucumber, tomato, cabbage and carrots, their share being over 60 % of the total.Citrus fruits, apples and banana are the principal fruits, their share being nearly 70 % of total fruit consumption.The most common processed products are various juices, especially orange juice.The estimate of the daily intakes of sugars and fibre given in Table 3 is based on these statistics.The estimated fibre intake from cereals was 11.6 g/d (VARoet al. 1984).Thus, the total fibre intake is 19 g/d.This is well within the range of other estimates of the average fibre intake in Finland (Laakkonen & Haaramo 1983).It was also calculated that added sugar accounts for about 20 °/o of the total intake of soluble sugars received from this category of foods.
Table 3.The estimated average intake (g/d) of dietary fibre and available carbohydrates derived from vegetables and fruits (energy level 10 MJ k -c u p ( L a c t a r i u s t r i v i a l i s ) r a t e s F r e e s u g a r d u c t A b b r e v i a t i o n s : -c e l l u l o s i c p o l y s a c c h a r i d e s ).