Low field nuclear magnetic resonance (LF-NMR) relaxometry in hake (Merluccius merluccius, L.) muscle after different freezing and storage conditions

• Published in: Food chemistry 2014-06, Vol.153, p.250-257
• Main Authors: Sánchez-Alonso, Isabel, Moreno, Pilar, Careche, Mercedes
• Format: Article
• Language: English
• Subjects: Accounting; Animals; Biological and medical sciences; Cold Temperature; Fish; Food Preservation - methods; Food Storage - methods; Food toxicology; Freezing; Frozen; Frozen storage; Gadiformes - physiology; Hake; Ice crystal; Low field NMR; Magnetic Resonance Spectroscopy; Marine; Medical sciences; Merluccius merluccius; Muscle; Muscle Relaxation; Muscle, Skeletal - chemistry; Muscle, Skeletal - physiology; Muscles; Nuclear magnetic resonance; Quality; Relaxation time; Seafood - analysis; Toxicology
• ISSN: 0308-8146; 1873-7072
• DOI: 10.1016/j.foodchem.2013.12.060

•LF NMR T2 relaxation is sensitive to different freezing and frozen storage conditions.•CONTIN analysis of T2 data of unfrozen muscle displayed a major band (T21) accounting for 90–92%.•Upon freezing, T21 became wider and an extra band appeared (120–360ms).•There was a clear temperature dependence of T2 profiles along storage. Low field NMR T2 transverse relaxation measurements were performed on muscle samples from sixty hake (Merluccius merluccius, L.). Fish fillets from hake stored in ice for 3 and 14days were subjected to different freezing methods (air blast, liquid nitrogen or walk-in freezer) and storage conditions (−20 and −10°C for 5days, 8 and 18weeks). Distribution analysis of T2 data of unfrozen muscle displayed a major band (T21), accounting for 90–92% of the total signal, with a relaxation time centred at 47–60ms and a broad band with protons of higher mobility between 300 and 800ms, accounting for 3–5% of the signal. Upon freezing, T21 became wider and an extra band appeared within the range 120–360ms. Whereas no changes were detected at −20°C, the T21 time constant decreased during frozen storage at −10°C in a similar way for all three freezing methods. The relative abundance of T21 declined with storage time but differences were found as a function of freezing. Results are discussed in the light of morphological alterations and protein denaturation, and it is concluded that LF NMR relaxometry is sensitive to different freezing and frozen storage conditions which can have important implications for the quality of fish muscle.