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 °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.

In vitro hypoglycemic, cholesterol-lowering and fermentation capacities of fiber-rich orange pomace as affected by extrusion.

Our previous study suggested that extrusion can enhance the soluble dietary fiber (SDF) and improve the physicochemical properties of fiber-rich orange pomace (OP). The aim of this study was to determine the predictive indices for the hypoglycemic, hypocholesterolemic, and fermentation capacities of extruded orange pomace (EOP) with several in vitro assays. The results revealed that EOP could effectively retard glucose diffusion and inhibit α-amylase activity relative to OP. Moreover, EOP had the binding capacities of cholesterol micelles and bile acids. During the in vitro fermentation of EOP, a high content of short chain fatty acid was produced. Scanning electron microscope images showed a more porous and irregular shaped structure of the EOP, which may influence physiological activities, relative to OP. The morphological alterations in the EOP were caused by mechanical shear. Thus, EOP has potential to become a functional food additive for glycemic control and the attenuation of blood cholesterol.

The effect of extrusion processing on the physiochemical properties of extruded orange pomace.

Soluble dietary fibre (SDF) is considered the most effective fraction of dietary fibre (DF) for human health. In this study, extrusion technology was applied to enhance the SDF obtained from orange pomace, a byproduct of juice extraction containing a high level of DF. The pomace was processed in a single-screw extruder at various barrel temperatures (X1; 115-135 °C), feed moistures (X2; 10-18 g/100g), and screw speeds (X3; 230-350 rpm). Based on response surface methodology, the optimum extrusion conditions, which produced a maximum SDF value of 30.36%, were as follows: barrel temperature, 129 °C; feed moisture, 15%; and screw speed, 299 rpm. Compared with unextruded pomace, SDF fraction in extrudate had a higher level of uronic acid. Furthermore, the extrusion process improved the physicochemical properties of extrudate, increasing the water-holding capacity, swelling, water solubility index, and cation-exchange capacity and decreasing the oil-holding capacity.