Functional and compositional changes of orange peel fiber thermally-treated in a twin extruder

The use of fruit and vegetable by-products from the food industry may stimulate the generation of novel ingredients with unique functional properties due to the high content of dietary fiber (DF). Extrusion has proved to efficiently modify the composition of DF's from cereal brans, and consequently their functionality. However, the use of this technology to treat fruit wastes has not been completely explored. The aim of this investigation was to evaluate the effects of the extrusion conditions on the DF composition of orange peel fiber-concentrate (OPFC). A three factorial Box-Behnken design including as variables the barrel temperature (70, 115, 160 degrees C), the screw speed (100, 150, 200 rpm) and moisture content (24, 41, 58% wb) was conducted to study changes in the DF profile in terms of soluble and insoluble fractions (SDF and IDF) and functionality properties (solubility, swelling and water/oil holding capacity: SOL, SC, WHC, and OHC, respectively). The SDF content increased in all extruded samples from 6.4 observed in the untreated sample to values up to 23.8 (g.100 g(-1) db) in samples extruded at 41% moisture, 160 degrees C, and 200 rpm. Consequently, all extrusion treatments reduced IDF of OPFC. The statistically constant value of the total dietary fiber (TDF) and the linear correlation (R boolean AND 2 = 0.93) between the reduction of IDF and the increment of SDF demonstrated the solubilization of IDF during the thermo extrusion process. Positive correlations between the SDF/IDF ratio and WHC, SOL, and SC were found. Extrusion modifies the DF composition of orange peel increasing SDF at expenses of IDF resulting in materials with innovative properties for the production of high quality and nutritious food products.