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Modification of Apple Pomace by Extrusion Processing: Studies on the Composition, Polymer Structures, and Functional
Vera Schmid1, Antje Trabert2, Judith Schäfer2
1Institute of Process Engineering in Life Sciences, Chair of Food Process Engineering, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany.
Foods (Basel, Switzerland)
|October 6, 2020
Summary
Extrusion processing enhances the functionality of apple pomace, a fruit processing by-product. This technology improves dietary fiber properties, increasing water solubility and viscosity for broader food applications.
Area of Science:
- Food Science and Technology
- Biomaterials Engineering
- Sustainable Food Systems
Background:
- Fruit and vegetable processing by-products are abundant, low-cost sources of dietary fiber.
- These by-products possess functional properties like water binding and thickening, suitable for food reformulation.
- Extrusion technology offers potential for modifying and enhancing the functionality of food by-products.
Purpose of the Study:
- To investigate the impact of extrusion technology on the structural and functional properties of apple pomace.
- To determine how extrusion process parameters influence the modification of dietary fiber in apple pomace.
- To assess the potential of extrusion to broaden the application of fruit processing by-products in food products.
Main Methods:
- Apple pomace was subjected to extrusion trials with varying screw speeds, water contents, and barrel temperatures.
- Structural and functional properties, including water solubility, water absorption, paste viscosity, and dietary fiber content/structure, were analyzed.
- Pectic polysaccharide degree of methylation and cell wall macromolecular structure were examined using imaging and pore size analysis.
Main Results:
- Extrusion at 100 °C, 700 min⁻¹, and 17% water content significantly increased water solubility (up to 33%) and paste viscosity (from 5 to 339 Pa·s).
- Thermo-mechanical stress (700 min⁻¹, 22% water) increased soluble dietary fiber from 12.5 to 16.7 g/100 g dry matter, forming low-molecular-weight fiber.
- Extrusion disrupted the cell wall structure, reduced pectic polysaccharide methylation (50% to 15%), and showed differential effects on arabinans and xylans.
Conclusions:
- Extrusion processing effectively modifies the functional properties of apple pomace by altering its dietary fiber composition and structure.
- Optimized extrusion parameters can enhance water-binding and thickening capacities, making apple pomace a more versatile food ingredient.
- This study demonstrates the potential of extrusion technology to valorize fruit by-products, contributing to sustainable food systems.
