The effect of pH, temperature and heating time on inulin chemical stability

Background. Inulin is a storage carbohydrate found in many plants especially in chicory root, Jerusalem artichoke and dahlia tuber. It is a prebiotic with many functional proper-ties. In earlier research concerning chemical stability of inulin, the effect of pH on rheological properties of inulin gels was mainly analysed. In these studies, the effect of time, temperature and pH on inulin chemical stability was not analysed profoundly espe-cially considering the inulin concentrations unable to form gel structure. Thus, the aim of this work was to study the effect of the above mentioned factors on inulin chemical stabil-ity in water solution. Material and methods. 5 % (w/w) inulin solutions at pH 1-12 were heated at 20, 40, 60, 80 and 100°C for 5-60 min. After the neutralisation the content of reducing sugar was analysed according to Miller’s method (1959) with 3,5-dinitrosalicylic acid. Results. The conducted studies showed that inulin chemical stability at pH 4 decreased with an increase of heating time and temperature. In a neutral and basic environment inu-lin was chemically stable regardless of heating time and temperature. Conclusions. Inulin application in food systems may be limited in acidic products espe-cially when heated above 60°C during the production process. However, in products at pH ≥ 5, the degradation of this fructan does not occur even at thermal processing. Key words: inulin, hydrolysis, temperature, pH