Dietary fibre and available carbohydrates in Finnish cereal products

Cereal products are the major source of most carbohydrates. They are the most important source of starch, and usually of dietary fibre. Certain bakery products contain considerable amounts of sugars, added as sucrose or syrups or as lactose from powdered milk. The functions of carbohydrates in foods and nutrition are various. Although chemically related, the carbohydrates are difficult to analyse simultaneously. Southgate (1969), Southgate et al. (1978), Englyst (1981), and Theander & Äman (1982) have developed methods that allow available carbohydrates and dietary fibre to be determined within a single analytical procedure. The method chosen in this study was the analytical scheme of Englyst (1981). The present study is part of a research project determining the carbohydrate composition of Finnish foods. The project, in turn, is part of a larger attempt to gather new and dependable data on Finnish foods and diet, of which the studies on mineral composition have been completed (Koivistoinen 1980, Varo 1981). The need for such data has become increasingly evident along with the sophistication of our daily lives: the information is required by nutritionists, dietitians and food inspectors, in the industry, and for medical research, to mention but a few.


Introduction
Cereal products are the major source of most carbohydrates.They are the most important source of starch, and usually of di- etary fibre.Certain bakery products contain considerable amounts of sugars, added as sucrose or syrups or as lactose from powdered milk.
The functions of carbohydrates in foods and nutrition are various.Although chem- ically related, the carbohydrates are difficult to analyse simultaneously.Southgate  (1969), Southgate et al. (1978), Englyst  (1981), and Theander & Äman (1982) have developed methods that allow available car- bohydrates and dietary fibre to be deter- mined within a single analytical procedure.The method chosen in this study was the analytical scheme of Englyst (1981).
The present study is part of a research pro- ject determining the carbohydrate composition of Finnish foods.The project, in turn, is part of a larger attempt to gather new and dependable data on Finnish foods and diet, of which the studies on mineral composition have been completed (Koivistoinen 1980,   Varo 1981).The need for such data has be- come increasingly evident along with the sop- histication of our daily lives: the information is required by nutritionists, dietitians and food inspectors, in the industry, and for medical research, to mention but a few.

Material and methods
The samples used in this study were col- lected for a previous study on the mineral element composition of Finnish foods (Koi-for 5 h (aliquot 1)and then with amyloglucosidase (16 h), after which it is separated by centrifugation into aliquot 2 and residue.The supernatants are analysed for free su- gars, starch and w.s.NCP.Free sugars (ali- quot 1), and free sugars and glucose from starch together (aliquot 2) are freeze-dried, formed into aldonitrilo acetates (Morrison 1975) and analysed by GLC.W.s. NCP are precipitated with 4 volumes of ethanol from aliquot 2, hydrolysed with 1 M H 2 S0 4 and analysed for neutral sugars as aldonitrilo acetates by GLC and for uronic acids colori- metrically after the carbazole reaction (Bitter & Muir 1962).The residue is sequen- tially hydrolysed with 1 M H 2 SG 4 and 72 % H 2 S0 4 , and analysed by GLC and colori- metry for w.i.s.NCP constituents, by colorimetry for cellulose (Roe 1955), and gravi- metrically for lignin.
The chromatography of the sugars was performed using an equimolar mixture of different sugars as an external standard, and inositol as an internal standard.
The overall analytical feasibility of the method was tested in two interlaboratory comparisons made during the present study (Theander 1981, Varo et ai.1983).Whole meal wheat flour, which was used as a stand- ard, was analysed several times during the study.As seen in Table 1, the variation in some fractions may be considerable.This may be due at least partly to the initial small sample size (200 mg).All samples were anal- ysed as six replicates, and the fractions with over 10 % variation were re-analysed.The analysis of starch tended to be especially problematic, and so it was also analysed on a macroscale from all samples using enzy- matic hydrolysis and colorimetry.Free su- gars and, less often, lignin also entailed re- checks. 1 X = mean, s = standard deviation, V% = coefficient of variation.
T a b l e C o n t e n t in 1. 01 1 .

Results and discussion
The available carbohydrates and fibre constituents of Finnish cereal products are given in Table 2.The results are largely con- sistent with those reported previously for ce- real foods (Paul & Southgate 1978, Souci   et al. 1981, Salo & Kotilainen 1970, Fro-lich & Asp 1981).
Free sugars.Cereal grains and flours are low in sugars, sucrose being the main one.Maltose was usually found only in trace amounts.Sugars other than those tabulated were sometimes detected (e.g. 4 % raffinose in wheat germ).Bakery products with added sucrose and leavened with yeast contained only little sucrose, but more fructose and glucose.Breads commonly contained 1 2 °?o maltose.Lactose was detected in breads with added milk or powdered milk.
Starch.The starch content of cereal products was generally in the expected range.The starch content was highest in polished rice and lowest in nuts.
Dietary fibre (DF).The fibre content of cereal products follows closely the extraction of flour used as a raw material.The bulk of the fibre constituents are in the bran frac- tion.Whole meal wheat flour contained about 10 % DF, whereas white flour contained 3.5 % and wheat bran c. 40 °Io.The fibre concentration of many bakery products was slightly higher than might be expected of their raw materials.This may indicate that bread making causes an increase in the amount of fibre especially while the crust is forming.However, not only lignin but other fibre fractions, too, were slightly increased.
Similar increments have been found in heat- treated potato (Varo et al. 1983, Varo et al.   1984).
W.i.s.NCP was generally the main DF fraction in cereal products.The present method shows that the concentrations of eel-C o n t e n t lulose and lignin were approximately the same in cereal foods.The concentration of w.s.NCP was fairly constant.As an exam- ple, whole meal wheat flour and white wheat flour contained equal amounts of this frac- tion.
Table 3 gives the relative neutral sugar and uronic acid compositions of w.s.NCP and  w.i.s.NCP of some flour and bread samples.The most variable is that of glucose, especially in the w.i.s.NCP fraction, suggesting that traces of starch may have been left in some of the w.i.s.NCP fractions.The relative amounts of other constituents remain fairly constant with increasing extraction.
Since the number of samples was limited to one per item, no information was obtain- ed in the variation within a single food com- modity.The main purpose of the study, to obtain average carbohydrate values for as many of the principal cereal foods as possible, was probably covered reasonably well considering the sampling procedure, which was planned to produce samples representing high volumes of production.
The analytical procedure chosen for the present study is too laborious for routine fibre determinations.The actual rate was only 2-4 samples/week/2 technicians.The need for rechecks of results was also undesirably high despite careful standardization of the procedures.One major problem was the difficulty of obtaining exactly repro- ducible fractionation of the small quantity of starting material.For instance, the gravimetric determination of a few milligrams of lignin necessarily caused high variation, which was greatly enhanced by small differences in fractionation.
In 1981 the consumption of cereals in Finland was 209 g/d/person, of which 128 g was wheat, 57 g rye and the rest equal amounts of barley, oats and rice (Agric.Econ.Res.Inst.1983).Nearly all the rye is consumed as whole grain products, whereas about 80 °/o of the wheat is used as refined flour (Salo- vaara 1979).About 70 % of all industrial bakery products are unsweetened rye and wheat bread, the remainder being sweetened products.Home baking, however, increases the share of sweetened products to at least 40 % of total bread consumption.It is es- timated that homebaked products account for about 13 % of total sugar consumption (Prättälä 1983).These findings, together with data on the detailed distribution of the production of bakery products (Salovaara  1979), and the present analytical data en- abled us to estimate roughly the average intake of carbohydrates from cereal products (Table 4).
Acknowledgement.This study has been supported by the Academy of Finland and the Finnish Sugar Company Ltd.
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

Table 4 .
Cereal products as sources of sugars, starch and dietary fibre in 1981 (energy level 10 MJ).