Histological discrimination of fresh and frozen/thawed fish meat: European hake (Merluccius merluccius) as a possible model for white meat fish species

Abstract

The present study aimed at setting up a standard operating histological procedure to discriminate fresh from frozen-thawed fish products of the species Merluccius merluccius (European hake). A preliminary histological analysis of fresh M. merluccius muscle was performed to select the sampling site and highlight possible timedependent tissue alterations during shelf-life. To set a suitable operational grid for discriminating the freezing process, morphological and morphometrical parameters were assessed on 90 muscle tissue samples collected from 30 fresh, 30 experimentally frozen at-20°C and 30 Individual Quick Frozen (IQF) specimens of M. merluccius. Structural score, presence of freezing vacuoles, a number of vacuoles per field higher than 1.12 and the presence of interstitial seroproteinaceous material, which had achieved statistical significance in group comparisons were chosen as freezing markers. Accuracy and repeatability, assessed on the analysis of two independent operators (on-training and expert), showed high analytical specificity and sensitivity and a concordant diagnostic performance regardless the operators expertise. The grid was finally validated by a single blind test on 30 additional M. merluccius commercial products and allowed the allocation of all the samples to fresh or frozen status without inconclusive results. The method could be profitably applied against fraudulent adulteration practices.

Development of An Algorithm for Identifying the Thermal State of Meat and Fish Raw Materials

“…4. The histological preparation of muscle tissue defrosted poultry The above information allows us to consider these criteria as identification and to differentiate the thermal state of meat and fish raw materials, which is consistent with the results of studies of other authors [4,9]. Table -I Analyzing the obtained values, it was found that the number of thickenings of myofibrils in defrosted products was 5.55, which is 259% more than in chilled products; the number of voids inside the muscle fibers and between them -2.67, by 256.78%, more than in chilled raw materials; the number of muscle fiber breaks in defrosted meat and fish was 41.24, which exceeds this value in chilled products by 15.3 times.…”

“…1, 2 (Fig. 3, 4), while in similar preparations made from chilled products, similar morphological changes were encountered in isolated cases or were not found in the material [2,4]. 4.…”

Emerging Techniques for Differentiation of Fresh and Frozen–Thawed Seafoods: Highlighting the Potential of Spectroscopic Techniques

“…Histological differentiation between fresh and frozen–thawed fish and fishery products has been reported in several research studies [ 12 , 13 , 14 ]. These techniques are based upon the investigation of changes in the structure and microstructure of seafoods, occurring during freezing and frozen storage, which is followed by using these changes to distinguish between fresh and frozen–thawed products.…”

“…Later, similar approaches were applied to discriminate between fresh and frozen–thawed products of marinated anchovy ( Engraulis encrasicolus ) fillets [ 69 ] and smoked salmon [ 13 ]. Recently, four histological parameters were proposed in order to discriminate fresh from frozen–thawed European hake ( Merluccius merluccius ) [ 12 ].…”

“…To detect and avoid such fraud, different analytical methods and approaches of analysis have been investigated and developed. These include microscopy and scanning electron microscopy [ 12 , 13 , 14 ], enzymatic and electrophoretic methods [ 15 , 16 , 17 , 18 , 19 ], and other physicochemical measurements (e.g., protein and lipid oxidation, volatile compounds, water-holding capacity, etc.) [ 20 , 21 , 22 , 23 ].…”