Elsevier

LWT

Volume 92, June 2018, Pages 258-264
LWT

Smart technique for accurate monitoring of ATP content in frozen fish fillets using fluorescence fingerprint

https://doi.org/10.1016/j.lwt.2018.02.026Get rights and content

Highlights

  • ATP content in frozen fish fillets was predicted by fluorescence fingerprints (FFs).

  • Actual variation of ATP content was estimated by HPLC over 48 h of ice storage.

  • Four partial least squares (PLS) models were developed to predict ATP contents.

  • The most important combinations of excitation-emission wavelengths were obtained.

  • FF could be a smart tool for determining the market price of frozen fish based on ATP.

Abstract

The aim of the present study was to develop a fast and nondestructive method based on fluorescence fingerprints (FFs) to predict the ATP content in frozen fish meat frozen at early stages after death using fillets of horse mackerel (Trachurus japonicus) as a model. Fifty-six fish were sacrificed instantly, stored in ice for different periods (0–48 h), and then filleted and frozen. The fluorescence fingerprints of the frozen fillet samples were acquired using fluorescence spectrophotometer with fiber probe installed inside a freezer. Subsequently, the ATP-related compounds of the same samples were determined using HPLC. Finally, four different models based on partial least squares (PLS) were developed to predict ATP contents from HPLC and the FFs data. The best PLS model with a correlation coefficient (R2) of 0.88 and root mean square error estimated by cross validation (RMSECV) of 0.97 μmol/g was obtained when the most important combinations of excitation-emission wavelengths were used for prediction. This methodology offers a simple and rapid approach to detect the ATP contents in frozen fish nondestructively without thawing the sample during the assessment that could be applied during any stage of fish marketing, facilitating quality control activities and the determination of fishery market price.

Introduction

In the fish muscle, a series of chemical and autolytic changes that involve enzymes occur during post-mortem metabolism, for instance, adenosine 5′-triphosphate (ATP) is sequentially hydrolyzed to breakdown products and phosphate (Hong, Regenstein & Luo, 2017). Because the degradation of ATP indicates changes in the fish meat in terms of freshness and quality, deep freezing (≤−30 °C) is a method of long-term preservation, which is useful to the fishing industry, for keeping the original quality as well as the ATP content unchanged (Burgaard & Jørgensen, 2010). Frozen fish with high ATP content exhibit a high tolerance to protein denaturation and muscle discoloration during frozen storage (Inohara, Kimura, & Yuan, 2013). Moreover, fish (such as Atlantic salmon, cod, and mackerel) that are frozen in the pre-rigor stage retain good quality with high ATP content, and better color and meat texture than the fish, which are frozen in the post-rigor stage (Skjervold et al., 2001, Einen et al., 2002, Cappeln and Jessen, 2001, Fukuda et al., 1984).

In commercial tuna fishing, different types of fish (dead and alive) are often hauled onto the deck after day long fishing using long lines, and most fish are immediately frozen at ultra-low temperatures (−60 °C) in the ship (Inohara et al., 2013). Some species are stored in ice for several hours/days on a fishing vessel and then frozen, upon arrival at the landing center. This makes it difficult to distinguish dead catch and alive catch in the frozen state, with respect to quality, by the naked eye. In the fish markets of Japan, the price of frozen tuna is empirically determined based on the color and degree of shrinkage of the caudal region after rapid thawing, since high shrinkage (thaw-rigor) indicates the presence of high ATP levels, and it appears that these fish are frozen in the pre-rigor stage, which increases the market prices (Okazaki, 2009). Furthermore, the rapid thawing of ATP-replete frozen fish may cause muscle contraction, which reduces the quality of the fish (Peters et al., 1968, Einen et al., 2002). Consideration on the treatment methods such as thawing conditions suitable to the fish materials will be paid depending on their ATP content. Thus, real-time measurement of ATP levels is strongly desired from the viewpoint of fishery-related industries and food distribution.

However, conventional chemical methods for determining ATP concentration or changes in ATP levels are more complex because of space and time limitations and the destructive nature of the technique. Thus, the development of a simple, rapid, reliable, non-invasive, and selective method for the detection of ATP without thawing the sample is challenging. Although there are some fast and destructive methods utilizing paper strips and luminescence for the detection of ATP (Drew and Leeuwenburgh, 2003, Hattula and Wallin, 1996), these methods are not suitable for the accurate monitoring of ATP levels in frozen fish meat because ATP breakdown begins immediately after thawing.

Techniques based on fluorescence spectroscopy appear to fulfill the requirements imposed by the fisheries sector for providing critical information on quality during the different stages of food production and in regulatory affairs.The method of the fluorescence fingerprints (FFs), which is also called excitation-emission matrix (EEM), is based on repeated records of emission signals for multiple numbers of excitation wavelengths. The technique has been demonstrated in specific pieces of work for the prediction of the freshness of frozen fish (ElMasry et al., 2015, ElMasry et al., 2016), detection of microbial spoilage (Oto et al., 2013, Yoshimura et al., 2014), and estimation of the levels of various constituents (Dufour et al., 2003, Engelen et al., 2007).

A few previous studies using fluorescence spectroscopy have examined the freshness of frozen horse mackerel samples, which were previously stored in a refrigerator at 4 °C until 12 days based on several indices of freshness (K, K1, P, G, H-values) (ElMasry et al., 2015, ElMasry et al., 2016). However, the implicated fluorescent compounds (such as ATP-related compounds), which were related to the indices of freshness, could not be specified and the fish bodies in which ATP was almost depleted, were treated. Therefore, the present study was aimed at specifically examining the ATP content in horse mackerel fillet (as a model) to know the early post-mortem quality of frozen fish by using a fast and nondestructive method of detection based on fluorescence spectroscopy and multivariate analyses. This is the first study to investigate the use of a fluorescence spectroscopy technique for detecting ATP contents in frozen fish at a very early post-mortem stage.

Section snippets

Samples

Assuming the frozen fish meat with different storage period after death and different ATP content, the samples of horse mackerel (Trachurus japonicus) (20.07 ± 0.53 cm and 132.60 ± 9.81 g of average body length and weight, respectively) were used in this study as a model sample. Alive fish were transported to the laboratory from the fish store (Tokyo, Japan). Fifty-six fish were sacrificed instantly by spinal cord destruction and stored in ice for different periods (0, 0.5, 1, 1.5, 2, 3, 4, 5,

FF spectra of frozen fillet samples

Fig. 2 shows FFs of the fillet samples with different ice storage time from 0 to 48 h. The most intense fluorescent peak was located at excitation (λEx) 290 nm, and emission (λEm) 330 nm. This fluorescence might be generated by combination of aromatic amino acids such as tryptophan and tyrosine residues of protein and ATP. The same peak was observed in the previous studies (Dufour et al., 2003, ElMasry et al., 2015). Moreover, a weaker peak was also observed at Ex. 380 and Em. 450, which was

Conclusion

This study was conducted to utilize fluorescence fingerprints of frozen fish fillets to build different PLS models for predicting ATP content as an indicator to evaluate the original quality of fillets in an early stage after death without thawing. After some preprocessing operations applied to the fluorescence fingerprint data, the predictive models were built with several variable selection methods. The best-resulting model was established by only six discrete wavelength pairs identified from

Acknowledgments

Authors would like to significantly acknowledge the financial support by Science and Technology Research Promotion Program for Agriculture, Forestry, Fisheries and Food Industry 25054C. Also, the Grant-in-Aid for Scientific Research (JSPS No. 26.03391) provided by the Japan Society for the Promotion of Science is highly appreciated.

References (31)

  • M.G. Burgaard et al.

    Effect of temperature on quality-related changes in cod (Gadus morhua) during short- and long-term frozen storage

    Journal of Aquatic Food Product Technology

    (2010)
  • C.Y. Chang et al.

    Fluorescence intrinsic characterization of excitation-emission matrix using multi-dimensional ensemble empirical mode decomposition

    International Journal of Molecular Sciences

    (2013)
  • B. Drew et al.

    Method for measuring ATP production in isolated mitochondria: ATP production in brain and liver mitochondria fo Fischer-344 rats with age and caloric restriction

    American Journal of Physiology - Regulatory, Integrative and Comparative Physiology

    (2003)
  • S. Ehira et al.

    Determination of fish freshness using K value and comments on some other biochemical changes in relation to freshness

  • Y. Fukuda et al.

    Effect of freshness of chub mackerel on the freeze-denaturation of myofibrillar protein

    Bulletin of the Japanese Society of Scientific Fisheries

    (1984)
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    Mario Shibata and Gamal ElMasry contributed equally to this work.

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