Assessment of freshness and freeze-thawing of sea bream fillets (Sparus aurata) by a cytosolic enzyme: Lactate dehydrogenase Mamadou Diop a,g , Denis Watier b,c,d,e,f , Pierre-Yves Masson b , Amadou Diouf g , Rachid Amara a , Thierry Grard b,c,d,e,f,⇑,1 , Philippe Lencel b,c,d,e,f,1 a Univ. Littoral Côte d’Opale, CNRS, Univ. Lille, UMR 8187, LOG, Laboratoire d’Océanologie et de Géosciences, 32 Avenue Foch, Wimereux, France b Univ. Littoral Côte d’Opale, USC ANSES, EA 7394 – ICV – Institut Charles Viollette, F-62200 Boulogne sur Mer, France c Univ. Lille, F-59000 Lille, France d Univ. Artois, F-62000 Arras, France e INRA, France f ISA, F-59000 Lille, France g Université Cheikh Anta DIOP de Dakar, Laboratoire de Toxicologie et d’Hydrologie, BP 5005 Dakar, Senegal article info Article history: Received 28 July 2015 Received in revised form 23 February 2016 Accepted 29 April 2016 Available online 30 April 2016 Chemical compounds used in this article: L-glutamine (PubChem CID 5961) Penicillin (PubChem CID 5904) Streptomycin (PubChem CID 19649) Disodium phosphate (PubChem CID 24203) Monosodium phosphate (PubChem CID 23672064) Sodium chloride (PubChem CID 5234) Hydrochloric acid (PubChem CID 313) Iodonitrotetrazolium chloride (PubChem CID 64957) Keywords: Lactate dehydrogenase Autolysis Sea bream (Sparus aurata) Fish cell lines SAF-1 Frozen-thawed Fish freshness abstract The evaluation of freshness and freeze-thawing of fish fillets was carried out by assessment of autolysis of cells using a cytosolic enzyme lactate dehydrogenase. Autolysis plays an important role in spoilage of fish and postmortem changes in fish tissue are due to the breakdown of the cellular structures and release of cytoplasmic contents. The outflow of a cytosolic enzyme, lactate dehydrogenase, was studied in sea bream fillets and the Sparus aurata fibroblasts (SAF-1) cell-line during an 8 day storage period at +4 °C. A significant increase of lactate dehydrogenase release was observed, especially after 5 days of storage. The ratio between the free and the total lactate dehydrogenase activity is a promising predictive marker to measure the quality of fresh fish fillets. The effect of freeze-thawing on cytosolic lactate dehydrogenase and lysosomal a-D-glucosidase activities was also tested. Despite the protecting effect of the tissue com- pared to the cell-line, a loss of lactate dehydrogenase activity, but not of a-D-glucosidase, was observed. In conclusion, lactate dehydrogenase may be used as a marker to both assess freshness of fish and distin- guish between fresh and frozen-thawed fish fillets. Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction Freshness is a key factor determining the quality of fish for human consumption. The alterations in fish tissues begin rapidly post-mortem and proceed through biochemical, physicochemical and microbial mechanisms (Ahmed, Donkor, Street, & Vasiljevic, 2015; Ocaño-Higuera et al., 2011). They depend considerably on species, age at the time of capture, slaughter methods, methods and temperature of storage (Álvarez, García García, Garrido, & http://dx.doi.org/10.1016/j.foodchem.2016.04.136 0308-8146/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: Univ. Littoral Côte d’Opale, USC ANSES, EA 7394 – ICV – Institut Charles Viollette, F-62200 Boulogne sur Mer, France. E-mail addresses: mamedou82@yahoo.fr (M. Diop), denis.watier@univ-littoral.fr (D. Watier), pierreyves.masson@gmail.com (P.-Y. Masson), amdiouf@refer.sn (A. Diouf), rachid.amara@univ-littoral.fr (R. Amara), thierry.grard@univ-littoral.fr (T. Grard), philippe.lencel@univ-littoral.fr (P. Lencel). 1 T. Grard and P. Lencel share co-authorship of this article. Food Chemistry 210 (2016) 428–434 Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem