Effect of extrusion parameters on some properties of dietary fiber from lemon (Citrus aurantifolia Swingle) residues

Approximately 50% of the original whole fruit mass, after citrus processing for juice, consist of the peel, membranes and seeds. Citrus residues consist mainly of insoluble fiber (celluloses) and a small proportion of soluble fiber (hemicelluloses and pectin). For this reason, citrus residues could be considered as a potential high fiber ingredient that is used for food industry. In this study, lemon residues were extruded to modify and increase their soluble fiber fraction. Surface response methodology with six central points and six axial points was used to evaluate the changes in dietary fiber fractions in lemon residues. The independent variables studied were extrusion temperature (from 59.77 to 110.63°C), moisture content of the sample (from 33.18 to 66.82%) and screw speed (from 3.18 to 36.82). The extrusion process increased the soluble fiber from 38.60% in unprocessed lemon residues to 40.00 to 50.01% in extruded samples. The highest content of soluble fiber was 50.00% when operating conditions were high in temperature (100°C), low in moisture content (40%) and low in screw speed (10 rpm). The results of this study indicate that extrusion is a process that has the capability to transform insoluble fiber to soluble fiber in lemon residues.