Original article Assessment of protein changes in farmed giant catfish (Pangasianodon gigas) muscles during refrigerated storage Saroat Rawdkuen, 1 * Akkasit Jongjareonrak, 2 Suttirug Phatcharat 3 & Soottawat Benjakul 3 1 Food Technology Program, School of Agro-Industry, Mae Fah Luang University, Muang, Chiangrai, 57100, Thailand 2 Nutraceutical and Functional Food Research and Development Center, Faculty of Agro-Industry, Prince of Songkla University, Hat Yai, Songkhla, 90112 Thailand 3 Department of Food Technology, Faculty of Agro-Industry, Prince of Songkla University, Hat Yai, Songkhla, 90112 Thailand (Received 29 August 2009; Accepted in revised form 10 February 2010) Summary Farmed giant catﬁsh (Pangasianodon gigas) muscles (dorsal and ventral sites) were stored in a refrigerator (at 4 °C) for 14 days to determine the eﬀect of refrigerated storage on biochemical and physical changes. The analyses were carried out at 0, 2, 4, 7, 10 and 14 days of storage. At day 14, Ca 2+ -ATPase activity markedly decreased when compared to its value at day 1 (>90%), while a small decrease was observed for surface hydrophobicity and reactive sulfhydryls content. Total volatile basic nitrogen and trichloroacetic-soluble peptide content gradually increased when the storage period was extended. The myosin heavy chain decreased slightly on SDS-PAGE for both meat cuts with increased storage time. Expressible drip and cooking loss were highest during the ﬁrst day of storage and slightly decreased with storage time. Instrumental hardness was signiﬁcantly higher in the ventral compared to the dorsal muscle, while the toughness was the highest at the second day of storage. The muscle bundles with scanning electron microscopy were less attached, resulting in the observed big gaps over increasing storage time. Results indicated that changes of proteins have detrimental eﬀects on the quality attributes of farmed giant catﬁsh muscles during refrigerated storage, particularly physical and biochemical properties. Keywords Farmed giant catﬁsh, muscle sites, protein changes, refrigerated storage. Introduction Immediately after death, several biochemical and enzy- matic changes are triggered in ﬁsh muscle. This is especially the case if improperly handled. Among post- harvest changes, the degradation of ﬁsh muscle caused by endogenous proteases is a primary cause of quality loss during cold storage or post-harvest handling (Haard, 1994). The ﬁsh muscle degradation as well as microbial induced activity cause the loss of nutritive value, acceptability and protein functionality. In gen- eral, the functional properties of ﬁsh myoﬁbrillar proteins are important for determining and predicting the ﬁnal quality of ﬁshery products (Roura & Crupkin, 1995). The most important factor for increasing shelf life is the product temperature, since ﬁsh are much more perishable than other muscle foods, the temperature is even more important. Chilling is a means of preserving ﬁsh before processing or consumption. When ﬁsh is stored at low temperature, both enzymatic and chemical reactions are slowed down. Biochemical and physico- chemical changes have been widely used as measurable parameters for determining muscle food spoilage (Ben- jakul et al., 1997; Rawdkuen et al., 2008). Myoﬁbrillar ATPase activities, trimethylamine, total volatile bases and individual nucleotides have been used to monitor post-mortem changes during iced or frozen storage. Autolytic degradation products have also been used as indices for ﬁsh proteins deterioration. Texture, water loss and muscle microstructure can also be used to predict the ﬁsh freshness (Torrissen et al., 2000). The giant catﬁsh (Pangasianodon gigas) is the world’s largest freshwater catﬁsh. It grows to about 3 m in length and to a weight of more than 300 kg. Recently, giant catﬁsh have been successfully farmed in artiﬁcial ponds in Chiang Rai Province in the northern part of Thailand. The farmed giant catﬁsh are signiﬁcantly smaller (25–30 kg) than that normally found in natural habitats (>150 kg). Giant catﬁsh are in high consumer demand due to their quality attributes such as texture, colour and nutritive values. It has become an econom- ically important cultured freshwater ﬁsh in Thailand. *Correspondent: Fax: +66 5391 6739; e-mail: saroat@mfu.ac.th International Journal of Food Science and Technology 2010, 45, 985–994 985 doi:10.1111/j.1365-2621.2010.02217.x Ó 2010 The Authors. Journal compilation Ó 2010 Institute of Food Science and Technology