Optimization of the extrusion process for preparation of soluble dietary fiber-enriched calamondin pomace and its influence on the properties of bread

Calamondin pomace is a by-product obtained after calamondin juice extraction. The effects of extrusion variables on the soluble dietary fiber (SDF) of calamondin pomace were investigated by response surface methodology. Bread samples with different contents of extruded calamondin pomace (ECP) additive were produced and their textural and sensory properties evaluated. The optimal conditions for the extrusion of calamondin pomace were found to be a barrel temperature of 129 degrees C, feed moisture of 16%, and a screw speed of 298 rpm. The results revealed that extrusion increased the SDF of the calamondin pomace because the redistribution of insoluble dietary fiber formed SDF. A monosaccharide profile indicated that total dietary fiber in calamondin pomace processed by extrusion contained a high content of uronic acid and arabinose and a low amount of glucose, suggesting the presence of pectic polysaccharide and trace amounts of cellulose and hemicellulose. Increasing the ECP content decreased the specific volume and altered the textural properties, such as the hardness, gumminess and chewiness of the bread, and the bread became darker and redder in appearance. Sensory evaluation indicated that bread with 5% ECP content had good overall acceptability. Thus, extrusion of calamondin pomace can effectively increase the SDF content and resulting ECP can be used to produce SDF-enriched breads with sensory acceptability.