# Low-field NMR measured on four gadoid fish species

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## Introduction

Water content of fish muscle and water holding capacity are important quality parameters influencing the texture, juiciness and overall impression of the fish product. Therefore, it is relevant to predict the water content and the water holding capacity by a fast non-destructive method, such as low-field NMR. However, a practical problem is that only a minor fraction of the fish can be analyzed. This gives a sampling variation when the sample measured is not representative of the whole fish. These data contains low-field NMR measurements taken at several positions within each fish. This enables an investigation of the influence of the sampling variation on the predictions of the reference parameters.

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## Reference

Andersen, C.M., Bro, R. and Brockhoff, P. Effect of sampling errors using replicated measurements. Submitted for publication

Andersen, C.M. and Bro, R. Quantification and handling of sampling errors in instrumental measurements: A case study. Submitted for publication

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## Get the Data (Matlab)

The data are available in a MATLAB format (fish). The data file contains the NMR decays in four matrices (cod, whiting, saithe and haddock). The different fish of each species are indicated by numbers in the vectors “cod_no”, “whiting_no”, “saithe_no” and “haddock_no”. The water content and the water holding capacities are found in the vectors “water” and “whc”. Row 1 to 12 contain data for whiting, row 13 to 24 contain data for haddock, row 25 to 36 contain data for saithe and row 37 to 51 contain data for cod.

If you use the data we would appreciate that you report the results to us as a courtesy of the work involved in producing and preparing the data. Also you may want to refer to the data by referring to

Andersen, C.M., Bro, R. and Brockhoff, P. Effect of sampling errors using replicated measurements. Submitted for publication

Andersen, C.M. and Bro, R. Quantification and handling of sampling errors in instrumental measurements: A case study. Submitted for publication

## Data Description

Samples: Fish of four species were analyzed; including 12 whiting, 12 haddock, 12 saithe and 15 cod. NMR relaxations were measured at 18 points spread throughout the whole fish.

NMR measurements: The measurements were performed on a Maran Benchtop Pulsed NMR analyzer operating at 23.2 MHz and equipped with an 18 mm variable temperature probe head. The receiver delay was set to 6 s. Transverse relaxations were measured using the CPMG sequence. For each measurement eight scans were performed with 1024 echoes and tau at 500 ms. Only even echoes were recorded of which only every second were used. This gives 256 echoes for each sample. All measurements were performed at 4°C. The fish were introduced into the NMR probe by placing samples of 2-4 g into glass tubes that matched the inner diameter of the 18 mm NMR sample tubes.

Water content: The water content was determined on exactly the same samples as were used for the NMR measurements, after the NMR relaxations were measured. The fish samples were kept in the small glass tubes and dried overnight at 110°C. They were weighed before and after drying. The water content is given as the average of all measurements of each fish.

Water holding capacity: The water holding capacity was determined on approximately 2 g of minced fillet. The samples were weighed, placed in plastic tubes with a special filter bottom (pore size 0.1 mm), centrifuged (1500g, 10°C, 5 min) and weighed again. Each analysis was made in quadruplicate. Water holding capacity is defined as the amount of water left in the mince after centrifugation relative to the dry matter content.