15 An emerging powerful technique: NMR applications on quality assessments of fish and related products
Somer Bekiroglu
15.1 Introduction
Nuclear magnetic resonance (NMR) spectroscopy provides ease, versatility, and power that has lead to advancements within the life sciences. However, concerning the degree of employment of NMR spectroscopy as a technique in applied sciences and particularly in food science, it is imperative to state that the possibilities have not been exploited to their full extent compared to the ones exploited ubiquitously within chemical and structural analyses areas. NMR spectroscopy in food science is generally used for studies such as the analysis of solid fat content (fat containing products), moisture content (margarine, starches, and rice etc.), component analysis (milk), moisture and fat content (general food products, e.g. milk powders), oil composition (oils), moisture and oil content (emulsions and flour), droplet size distributions (emulsions), moisture and solid distributions (suspensions and gels), freezing process research (solids and liquids), and extent of cooking/hydrolysis (ready-to-eat/cooked food) . Therefore, it is not difficult to foresee that fish and related products are no exceptions for the upcoming extensive use of NMR techniques. Many different fish and fish product characteristics that can be attained by NMR spectroscopy range from fingerprinting analysis of marker compounds for authenticity studies [2] to the non-destructive analysis of whole fish for quality control efforts . In general, NMR spectroscopy is typically non-destructive and sometimes non-invasive technique that gives varied information about molecular structures, as well as temporal and dynamic molecular properties, in terms of spectra of various dimensions. With a coarse simplification, it can be depicted as measuring the resonance response of nuclei to applied electromagnetic radiation usually with radiowave frequency (RF), provided that the nuclei possess non-zero spin quantum numbers (e.g. 1 H, 13 C, 23 Na, 31 P, etc.) and are placed in a constant magnetic field (B 0 ). These signals carry important structural information about the sensed local environment within the molecule studied. The resonances (the state of emission of radiation absorbed as RF) fade out as time goes by, following two major relaxation pathways, spin-lattice relaxation T 1 and spinspin relaxation T 2 . Usually structures of molecules are studied in a solution environment. However, solid-state NMR and magnetic resonance imaging (MRI) methods allow one to study heterogeneous systems of intact samples such as cells or even tissues, and whole