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Effects of pH and the gel state on the mechanical properties, moisture contents, and glass transition temperatures of whey protein films
RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, SIK – Institutet för livsmedel och bioteknik.ORCID iD: 0000-0003-0310-4465
RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Sveriges tekniska forskningsinstitut, SIK – Institutet för livsmedel och bioteknik.
1999 (English)In: Journal of Agricultural and Food Chemistry, ISSN 0021-8561, E-ISSN 1520-5118, Vol. 47, no 5, p. 1878-1886Article in journal (Refereed) Published
Abstract [en]

The mechanical properties, moisture contents (MC), and glass transition temperature (T(g)) of whey protein isolate (WPI) films were studied at various pH values using sorbitol (S) as a plasticizer. The films were cast from heated aqueous solutions and dried in a climate chamber at 23 °C and 50% relative humidity (RH) for 16 h. The critical gel concentrations (c(g)) for the cooled aqueous solutions were found to be 11.7, 12.1, and 11.3% (w/w) WPI for pH 7, 8, and 9, respectively. The cooling rate influenced the c(g), in that a lower amount of WPI was needed for gelation when a slower cooling rate was applied. Both cooling rates used in this study showed a maximum in the c(g) at pH 8. The influence of the polymer network on the film properties was elucidated by varying the concentration of WPI over and under the c(g). Strain at break (?(b)) showed a maximum at the c(g) for all pH values, thus implying that the most favorable structure regarding the ability of the films to stretch is formed at this concentration. Young's modulus (E) and stress at break (?(b)) showed a maximum at c(g) for pH 7 and 8. The MC and ?(b) increased when pH increased from 7 to 9, whereas T(g) decreased. Hence, T(g) values were -17, -18, and -21 °C for pH 7, 8, and 9, respectively. E and ?(b) decreased and ?(b) and thickness increased when the surrounding RH increased. The thickness of the WPI films also increased with the concentration of WPI.

Place, publisher, year, edition, pages
1999. Vol. 47, no 5, p. 1878-1886
Keywords [en]
Food Engineering
Keywords [sv]
Livsmedelsteknik
National Category
Food Science
Identifiers
URN: urn:nbn:se:ri:diva-8794DOI: 10.1021/jf981115dPubMedID: 10552465OAI: oai:DiVA.org:ri-8794DiVA, id: diva2:966667
Available from: 2016-09-08 Created: 2016-09-08 Last updated: 2018-08-20Bibliographically approved

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Stading, Mats

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