Vol. 68, Nr. 3, 2003—JOURNAL OF FOOD SCIENCE 1067 © 2003 Institute of Food Technologists Further reproduction prohibited without permission Sensory and Nutritive Qualities of Food JFS: Sensory and Nutritive Qualities of Food Development of a Quality Index Method to Evaluate Freshness in Mediterranean Hake ( Merluccius merluccius ) S. BAIXAS-NOGUERAS, S. BOVER-CID, T. VECIANA-NOGUÉS, M.L. NUNES, AND M.C. VIDAL-CAROU ABSTRACT: A Quality Index Method for the sensory assessment of freshness of Mediterranean hake was devel- oped and validated by sensory, chemical, and microbiological parameters. The Quality Index was the ratio between the overall sensory score obtained and the total achievable sensory score of the scheme and ranging 0 (fresh) to 1 (spoiled). This index increased significantly along the time of ice storage, allowing prediction of the remaining shelf life of hake. A value of 0.60 to 0.65 was estimated by statistical treatment as the rejection value, being concordant with sensory score of cooked hake, trimethylamine content, pH, as well as with legal regula- tions for mesophylic and enterobacteria counts. Keywords: Quality Index Method, hake, sensory analysis, trimethylamine, ice storage Introduction H AKE OF THE GENUS MERLUCCIUS HAS A WORLD-WIDE DISTRIBUTION and makes up a considerable proportion of the world catch of fish. The species caught in the Mediterranean sea is the European hake, Merluccius merluccius, which is particularly important for the fishing sector in Spain. In this country, fish is usually stored in box- es with ice during transport and commercialization. Characteristic sensory changes occur in the appearance, odor, taste, and texture of fish during deterioration, and thus, sensory methods are commonly used for quality assessment by inspection services and in the fishing industry. Sensory analysis has the ad- vantage of being rapid and simple. However, it shows a certain degree of subjectivity, which is only partially avoided by using an expert and extensively trained panel. Over the last 50 years a large number of sensory schemes have been developed for sensory analysis of raw fish. In Europe, the most commonly accepted meth- od is the EU scheme, introduced in 1976 and updated in 1996 (EEC 1996). This method includes 4 descriptive levels and grades the freshness of fish from E (extra), A (acceptable), and B (poor) to C (unacceptable for human consumption). This method is widely used for a variety of fish and has been satisfactorily correlated with chemical parameters, such as volatile amines (Pérez-Villarreal and Howgate 1987), microbial counts (Pastoriza and others 1998), and time of ice storage (Koutsoumanis and Nychas 1999). However, its suitability has been questioned because, in using general param- eters, it does not take into account particular differences among species. Alternative and more specific sensory methods, such as the so- called Quality Index Method (QIM), have been developed for var- ious species of raw fish. The QIM is based on detailed descriptors that are grouped into distinct characters within general attributes, such as general appearance, eyes, and gills. Unlike the traditional systems, the QIM descriptors should be precise, objective, indepen- dent, and primary rather than a cluster of terms (Luten and Martin- sdottir 1997). The QIM has been recognized as a fast and reliable approach to assess the freshness of fish (Botta 1995). The usefulness of this tool will be further improved when new schemes applicable for partic- ular fish species or products are developed (Dalgaard 2000). In fact, specific QIMs have been already designed for species such as cod (Larsen and others 1992; Warm and others 1998), sea bream (Huidobro and others 2000), and others (Botta 1995). Moreover, a QIM software (available on the “QIM Eurofish” Web site at http:// www.qim-eurofish.com) has been developed for anchovy, brill, cod (fresh and frozen), haddock, flounder, herring, hoki, plaice, redfish, saithe, salmon, sardines, sole, spotted trevalla, turbot, whiting, and 4 species of warm water fish from Australia (Dalgaard 2000). How- ever, despite limitations in the current European system (Sime- onidou and others 1998; Dalgaard 2000), to date no QIM has been described particularly for Mediterranean hake. Neither is the tra- ditional Torry scheme for lean fish appropriate to grade Mediterra- nean hake, since it is inconsistent with the results of both chemical and sensorial tests (Baixas-Nogueras and others 2002). In the framework of the European project CT3253, the aim of this work was to describe a QIM for the sensory assessment of raw Mediterranean hake. To develop and validate the proposed QIM, sensory, chemical (volatile amines and pH), and microbiological (total counts of mesophilic bacteria and enterobacteria) changes were monitored during ice storage. Chemical and microbiological parameters were used, together with complementary sensory anal- ysis of cooked fish, to establish a sensory Quality Index (QI) value as a limit of hake acceptability for human consumption. Material and Methods Samples Three treatments were performed in May (Treatment 1), July (Treatment 2), and December (Treatment 3) of the same year. Fresh and gutted hake (Merluccius merluccius var. mediterraneus) were purchased from the local Barcelona market and immediately trans- ported in ice to the laboratory. The samples had been caught the night before. To reduce variability factors that could hinder the interpretation of results, similar sized fish were chosen. Individuals had an average weight of approximately 350 g and average length of 35 to 40 cm, which correspond to the most usual size found in the local markets. They were stored in flaked ice (0 °C) in self-draining