Abstract
Food by-products can be used as natural and sustainable food ingredients. However, a modification is needed to improve the technofunctional properties according to the specific needs of designated applications. A lab-scale twin-screw extruder was used to process enzymatically treated apple pomace from commercial fruit juice production. To vary the range of the thermomechanical treatment, various screw speeds (200, 600, 1000 min−1), and screw configurations were applied to the raw material. Detailed chemical and functional analyses were performed to develop a comprehensive understanding of the impact of the extrusion processing on apple pomace composition and technofunctional properties as well as structures of individual polymers. Extrusion at moderate thermomechanical conditions increased the water absorption, swelling, and viscosity of the material. An increase in thermomechanical stress resulted in a higher water solubility index, but negatively affected the water absorption index, viscosity, and swelling. Scanning electron microscopy showed an extrusion-processing-related disruption of the cell wall. Dietary fiber analysis revealed an increase of soluble dietary fiber from 12.6 to 17.2 g/100 g dry matter at maximum thermo-mechanical treatment. Dietary fiber polysaccharide analysis demonstrated compositional changes, mainly in the insoluble dietary fiber fraction. In short, pectin polysaccharides seem to be susceptible to thermo-mechanical stress, especially arabinans as neutral side chains of rhamnogalacturonan I.
Highlights
Clarified apple juice is one of the most-consumed juices in the world
To characterize the thermomechanical stresses applied to the raw material, the specific mechanical energy input (SME) and the material temperature (TM) were monitored
This study investigates the functionalization of enzymatically treated apple pomace from commercial fruit juice production by extrusion processing
Summary
Clarified apple juice is one of the most-consumed juices in the world. Enzyme technology is often used to increase the juice yield and for juice clarification [1,2,3]. Apple pomace remains as major by-product of juice processing. As only a small portion is used for pectin extraction or as animal feed [4], tons of apple pomace are disposed of as waste [5]. There is no efficient method for the conversion of apple pomace into high-value products; apple pomace has very little to no economic value. There is a growing demand of consumers for healthy and sustainable foods [6,7]
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