Effect of enzymatic treatment and concentration method on chemical, rheological, microstructure and thermal properties of prickly pear syrup

Abstract The present work aimed to study the influence of prickly pear pulp treatment with enzymes as well as the concentration method on some quality characteristics of elaborated syrups. Liquefaction of prickly pear pulp was optimized using pectinase and cellulase. The effect of hydrolytic enzymes concentrations (0–20 U) and incubation times (20–300 min) on soluble solids yield (SSY) of juice was studied. Results showed that treatment with 5 U cellulase and 20 U pectinase for 150 min at 50 °C gave the highest SSY value (89.15 g TSS/100 g). This combination was used to prepare prickly pear syrups after concentration at 60 °C under vacuum (SE-60) or with a hot plate at 100 °C (SE-100). Chemical, rheological, thermal and microstructural properties of the elaborated products were investigated, and compared with two control samples (SC-60 and SC-100) obtained without enzymatic treatment. Determination of rheological behavior showed that all samples behave as Newtonian fluids. Determination of activation energy (Ea) revealed higher values for enzymatic treated samples indicating more sensibility to temperature. Analysis of thermal profile of elaborated syrups showed absence of crystallization and glass transition reflecting a stability of all products. Microscopic observations revealed fewer crystals for treated syrups, demonstrating a better stability by increase in reducing sugars, which limit crystallization.