Effects of edible coatings based on ultrasound-treated whey proteins in quality attributes of frozen Atlantic salmon (Salmo salar) Laura Rodriguez-Turienzo, Angel Cobos, Olga Diaz ⁎ Área de Tecnología de Alimentos. Departamento de Química Analítica, Nutrición y Bromatología. Facultad de Ciencias. Universidad de Santiago de Compostela. 27002 Lugo, Spain abstract article info Article history: Received 28 July 2011 Accepted 8 December 2011 Editor Proof Receive Date 7 February 2012 Keywords: Edible coatings Ultrasound Fish Yields Colour Lipid oxidation The effects of ultrasound-treated whey protein coatings on frozen Atlantic salmon quality parameters were evaluated. The experiment was performed using an ultrasonic bath at a frequency of 35 kHz and three son- ication times (1, 15 and 60 min). The yield, the thaw yield, the drip loss in thawing, the drip loss after chilled storage and the cooking loss of fish samples were not influenced by the ultrasound treatment of coatings when compared to fish samples with untreated whey protein coatings. Decreases in yield, drip loss in thawing and drip loss after chilled storage were observed in samples from whey proteins sonicated 60 min in relation to those sonicated 15 min. The ultrasound treatment of whey proteins did not modify the colour of frozen and thawed fillets but increased L* and whiteness of cooked samples in comparison with untreated whey protein coated samples. All whey protein coatings decreased the lipid oxidation of fish fillets. However, the ultrasound treatment of coatings significantly delayed the lipid oxidation of salmon pieces in comparison with those coated with untreated proteins. The sensory properties of salmon samples were not negatively affected by these coat- ings. Industrial relevance: Freezing is a very usual method of fish preservation; some changes during frozen storage that decrease product quality can occur, such as lipid oxidation. The results obtained in this investigation show that ultrasound applied to whey protein coatings could be useful for the reduction of the lipid oxidation of frozen salmon. These treated coatings could be a good alternative to conventional packaging and, at least, they could partially substitute plastic packaging. The edible coatings can contribute to reduce the plastic pack- aging residues of frozen seafood industry and the environmental contamination. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction Freezing is a good method of fish preservation that allows for a prolonged shelf life with minor changes in fish quality if certain pre- cautions are taken. However, some undesirable modifications can occur, such as protein denaturation, weight loss, freeze burning and lipid oxidation. Some of these alterative changes can be prevented by means of the use of appropriate packaging. In this sense, edible coatings are a good alternative; they are coated directly onto the food, can prevent water loss and lipid changes. They are biodegrad- able and environment-friendly materials that could reduce the use of plastic packaging. Several compounds can be applied as edible coatings for frozen fish; among them, proteins (caseins, whey, soy and egg proteins) form coatings which are able to delay lipid oxida- tion and to decrease moisture losses of this product (Hirasa, 1991; Rodriguez-Turienzo et al., 2011; Sathivel, 2005; Stuchell & Krochta, 1995). When some of these proteins (whey, soy and egg proteins) are used for edible package formation, a thermal treatment is included in the solution preparation, in order to denature them and produce films of adequate strength and permeability. The thermal treatment is also usually applied to the protein solutions for frozen fish coatings, even though they never form a solid film. However, some denaturation can be useful in certain proteins, such as whey proteins, due to the changes in their structure that probably expose some antioxidant amino acid groups (Elias, McClements, & Decker, 2005). Instead of heat treatment, other methods that change protein structure have been proposed for edible film preparation. Increased applications in food industry have been found for high-intensity ultra- sound (20–100 kHz, 10–1000 Wcm -2 ) due to their capacity to induce physical and chemical changes in foods. They are used in the extraction of enzymes and proteins, induction of oxidation/reduction reactions, emulsification, meat tenderization, sterilisation, etc. (Marcuzzo, Perssini, Debeaufort, & Sensidoni, 2010). Cavitation (formation and vio- lent collapse of bubbles) is the main process responsible for the effects of ultrasound on food components, although other mechanical, physical and chemical effects are detected, such as heating, shear stress, turbu- lence and generation of radicals (Chandrapala, Zisu, Palmer, Kentish, & Ashokkumar, 2011; Villamiel & de Jong, 2000). The fact that ultrasound (US) induces changes in the secondary and tertiary structures of proteins, with the disruption of intramolecular Innovative Food Science and Emerging Technologies 14 (2012) 92–98 ⁎ Corresponding author. Tel.: + 34 982 824124; fax: + 34 982 285872. E-mail address: olga.diaz.rubio@usc.es (O. Diaz). 1466-8564/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.ifset.2011.12.003 Contents lists available at SciVerse ScienceDirect Innovative Food Science and Emerging Technologies journal homepage: www.elsevier.com/locate/ifset