The influence of cooking technique on dietary fibre of boiled potato

Samples of twenty-five different cultivars of potatoes were prepared and examined after cooking by boiling and by pressure cooking, peeled and ‘in the jacket’ in a factorial design to study the effect of cooking on dietary fibre fractions of potatoes. Raw samples were prepared as control. The samples were analysed for acid detergent fibre (ADF) and lignin by published procedures. Filtration problems were encountered with the published procedure for neutral detergent fibre (NDF) giving rise to lack of reproducibility. Reproducibility was restored by introducing a short incubation of the sample with α-amylase enzyme (Bacillus subtilis) prior to the normal detergent digestion. The lignin content of all samples was < 0.25% on a dry matter basis. Both ADF and NDF increased on cooking but boiled samples did not differ from pressure cooked samples. Cooking ‘in the jacket’ gave higher ADF values than peeled samples but the effect was not observed for NDF values. Cultivar differences were significant for both ADF and NDF values but as the samples were all from a single season's crop in a single field a definitive ranking is not possible.