Estimation of available energy of dietary fibres by indirect calorimetry in rats.

BACKGROUND: Knowledge of energetic availability of dietary fibres is important for human nutrition. But up to now results are often different and depend on the methods used. Estimation of metabolisable energy of dietary fibres (mainly by balance technique) is a time-consuming procedure and needs special technical effort. AIM OF THE STUDY: Validation of the experimental design for short-term studies by using indirect calorimetry with feeding below maintenance requirement to evaluate the energetic availability of dietary fibres and their influence on absorption velocity of carbohydrates (CHO). METHODS: Energy expenditure and CHO oxidation (including short-chain fatty acids as fermentation products) were estimated in Wistar rats over 23 h after being fed a basal diet for the first day (300 KJ/kg0.75, 20% protein, 3% fat, 77% CHO) followed by supplementation with either microcrystalline cellulose, the soluble rye fibre arabinoxylan, apple pectin, amylomaize starch (with 48% of resistant starch) or gelatinised wheat starch (200 KJ/kg0.75 each) as control for the following days. Energetic availability was determined by comparing the increase of CHO oxidation after addition of gelatinised wheat starch with that of the dietary fibres tested. RESULTS: In comparison to wheat starch (100%), the following energetic availability of the dietary fibres was found: microcrystalline cellulose 14%, arabinoxylan 33%, pectin 39%, amylomaize starch 62%. The time-course of CHO oxidation indicated that microcrystalline cellulose enhances, whereas the soluble rye fibre slows down the velocity of CHO absorption due to the different consistency of the intestinal contents modified by the kind and properties of the used dietary fibres. After intake of arabinoxylan or pectin, CHO oxidation remained at a higher level during the experimental period elucidating an increased activity of fermentation to short-chain fatty acids. CONCLUSIONS: Short-term experiments in rats using indirect calorimetry are a suitable method for comparative estimation of the energetic availability of dietary fibres. Results are partly in agreement with values estimated by long-term in vivo methods.

[Alpha-amylase inhibitors and soluble dietary fiber in rye: partial purification and effect on postprandial glycemia]. / alpha-Amylase-Inhibitoren und lösliche Ballaststoffe aus Roggen: Partielle Reinigung und Einfluss auf die postprandiale Glykämie.

The protein inhibitor of the alpha-amylase (D-type) and the soluble arabinoxylan of rye (Var. Clou) were isolated from flour and bran, respectively. The isolation of the alpha-amylase inhibitor involves the extraction of rye flour in aqueous CaCl2-solution (2 x 10(-3) M containing the hemicellulase preparation Veron HE (2 g/100 g flour), dialysis and lyophilization (preparation I) and further fractionation with ammonsulfate, using the fraction 20-50% for isolation (preparation II). The arabinoxylan isolation is carried out using extraction of rye bran in 80% ethanol (80 degrees C), centrifugation, aqueous extraction of the sediment, dialysis and lyophilization (preparation I). The further purification using the precipitate of the fraction 20-50% leads to preparation II. The alpha-amylase inhibitor preparation II and the arabinoxylan preparation II were applied in a diet containing wheat starch and casein and fed to diabetic and healthy rats (Levis and Wistar). The postprandial increase of glucose was determined. It was detected that the postprandial increase of glucose is influenced neither by the alpha-amylase inhibitor nor by the soluble arabinoxylan in comparison to the control experiments. However, the alpha-amylase inhibitor of wheat significantly decreases the postprandial increase of glucose. The application of a test meal with alpha-amylase inhibitor of rye to health and diabetic of type-II-volunteers showed no variation of the blood glucose values. The reduction of the increase of glucose by the soluble beta-glucan of oat cannot be confirmed for the soluble arabinoxylan of rye. We conclude that the effect of the alpha-amylase inhibitor as well as the soluble pentosan or glucan has to be examined for each cereal species.

[Synthesis and properties of carrier-fixed enzymes. VII. Linking of glucoamylase to dialdehyde cellulose, carboxymethylcellulose hydrazide and carboxymethylcellulose azide]. / Synthese und Eigenschaften trägerfixierten Enzyme. VII. Fixierung von Glukoamylase an Dialdehydzellulose. Karboxymethylzellulosehydrazid und Karboxymethylzelluloseazid.

Glucoamylase (alpha-1,4-glucan glucohydrolase, EC 3.2.1.3) has been covalently linked to dialdehyde cellulose resulting in an immobilized enzyme containing 0.98% protein and an activity of 4.5 mg of the native enzyme per g of matrix, i.e. 46% relative activity. The complex lost its activity in continuous and batch hydrolysis of starch at 55 degrees C down to a limit of 18% of its original value. In contrast, the activity of the complex did not change when working at a temperature of 25 degrees C. Glucoamylase-carboxymethylcellulose complexes synthesized via carboxymethylcellulose hydrazide and azide, in contrast to MAEDA und SUZUKI [1], showed only an activity of 1 mg of the native enzyme per g of matrix. We did not succeed in coupling periodate-oxidized glucoamylase to carboxymethylcellulose hydrazide because the enzyme used lost nearly all of its activity already during periodate oxidation.