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Article

Modification of Apple Pomace by Extrusion Processing: Studies on the Composition, Polymer Structures, and Functional Properties

1
Institute of Process Engineering in Life Sciences, Chair of Food Process Engineering, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany
2
Institute of Applied Biosciences, Department of Food Chemistry and Phytochemistry, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany
*
Author to whom correspondence should be addressed.
Foods 2020, 9(10), 1385; https://doi.org/10.3390/foods9101385
Received: 1 September 2020 / Revised: 21 September 2020 / Accepted: 23 September 2020 / Published: 1 October 2020
By-products of fruit and vegetable processing are an inexpensive and sustainable source of dietary fiber, potentially offering valuable functional properties such as water binding and thickening. Due to these favorable properties, they can be utilized to reformulate widely-consumed foods, e.g., bakery products or beverages. In this study, apple pomace was used as a model system to study whether extrusion technology affects food by-product functionality and thus has the potential to broaden the application of by-products in foods. The effect of the process parameters and the extent of thermo-mechanical treatment on the structural and functional properties of apple pomace were analyzed after extrusion trials using various screw speeds, water contents, and barrel temperatures. Compared to the raw material, apple pomace extruded at Tbarrel = 100 °C, n = 700 min−1 and mH2O = 17% showed an increased water solubility up to 33%. The water absorption increased from 5 to 19 Pa·s and the paste viscosity from 5 to 339 Pa·s by extrusion processing. Analyses of dietary fiber contents and fiber polysaccharide structures revealed that thermo-mechanical stress (n = 700 min−1, mH2O = 22%) increased the content of soluble dietary fiber from 12.5 to 16.7 g/100 g dry matter, and that the harshest conditions even enabled the formation of low-molecular-weight dietary fiber. Arabinans (as neutral rhamnogalacturonan I side chains) appeared to be most sensitive to thermo-mechanical stress, whereas xylans (i.e., a group of minor polysaccharides) were an example of a more stable fiber polysaccharide. Also, the degree of methylation of the pectic polysaccharides was strongly reduced from 50% to 15% when thermo-mechanical stress was applied. Imaging and pore size analysis showed that extrusion processing could disrupt the rigid cell wall macromolecular structure. View Full-Text
Keywords: upcycling; valorization; by-products; dietary fiber; plant cell wall; non-starch polysaccharides; rheology upcycling; valorization; by-products; dietary fiber; plant cell wall; non-starch polysaccharides; rheology
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MDPI and ACS Style

Schmid, V.; Trabert, A.; Schäfer, J.; Bunzel, M.; Karbstein, H.P.; Emin, M.A. Modification of Apple Pomace by Extrusion Processing: Studies on the Composition, Polymer Structures, and Functional Properties. Foods 2020, 9, 1385. https://doi.org/10.3390/foods9101385

AMA Style

Schmid V, Trabert A, Schäfer J, Bunzel M, Karbstein HP, Emin MA. Modification of Apple Pomace by Extrusion Processing: Studies on the Composition, Polymer Structures, and Functional Properties. Foods. 2020; 9(10):1385. https://doi.org/10.3390/foods9101385

Chicago/Turabian Style

Schmid, Vera, Antje Trabert, Judith Schäfer, Mirko Bunzel, Heike P. Karbstein, and M. A. Emin 2020. "Modification of Apple Pomace by Extrusion Processing: Studies on the Composition, Polymer Structures, and Functional Properties" Foods 9, no. 10: 1385. https://doi.org/10.3390/foods9101385

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