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Coatings 2018, 8(2), 58; https://doi.org/10.3390/coatings8020058

Mechanical and Barrier Properties of Potato Protein Isolate-Based Films

1
TUM School of Life Sciences Weihenstephan, Technical University of Munich, 85354 Freising, Germany
2
Fraunhofer Institute for Process Engineering and Packaging IVV, 85354 Freising, Germany
*
Author to whom correspondence should be addressed.
Received: 18 December 2017 / Revised: 19 January 2018 / Accepted: 30 January 2018 / Published: 5 February 2018
(This article belongs to the Special Issue Edible Films and Coatings)
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Abstract

Potato protein isolate (PPI) was studied as a source for bio-based polymer films. The objective of this study was the determination of the packaging-relevant properties, including the mechanical properties and barrier performance, of casted potato protein films. Furthermore, the films were analyzed for cross-linking properties depending on the plasticizer concentration, and compared with whey protein isolate (WPI)-based films. Swelling tests and water sorption isotherm measurements were performed to determine the degree of swelling, the degree of cross-linking, and the cross-linking density using the Flory–Rehner approach. The effects of different plasticizer types and contents on compatibility with potato protein were studied. Glycerol was the most compatible plasticizer, as it was the only plasticizer providing flexible standalone films in the investigated concentration range after three weeks of storage. Results indicated that increasing glycerol content led to decreasing cross-linking, which correlated in an inversely proportional manner to the swelling behavior. A correlation between cross-linking and functional properties was also reflected in mechanical and barrier characterization. An increasing number of cross-links resulted in higher tensile strength and Young’s modulus, whereas elongation was unexpectedly not affected. Similarly, barrier performance was significantly improved with increasing cross-linking. The overall superior functional properties of whey protein-based films were mainly ascribed to their higher percentage of cross-links. This was primarily attributed to a lower total cysteine content of PPI (1.6 g/16 g·N) compared to WPI (2.8 g/16 g·N), and the significant lower solubility of potato protein isolate in water at pH 7.0 (48.1%), which was half that of whey protein isolate (96%). Comparing on an identical glycerol level (66.7% (w/w protein)), the performance of potato protein isolate was about 80% that of whey protein isolate regarding cross-linking, as well as mechanical and barrier properties. View Full-Text
Keywords: potato protein isolate; whey protein isolate; plasticizer; cross-linking; oxygen barrier; mechanical performance potato protein isolate; whey protein isolate; plasticizer; cross-linking; oxygen barrier; mechanical performance
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Schäfer, D.; Reinelt, M.; Stäbler, A.; Schmid, M. Mechanical and Barrier Properties of Potato Protein Isolate-Based Films. Coatings 2018, 8, 58.

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