Dipartimento di Scienze Medico-Veterinarie Corso di Laurea Magistrale a ciclo unico in Medicina Veterinaria METODO DI RILEVAMENTO DELLA FRESCHEZZA E VITALITA’ NEGLI ESEMPLARI DI OSTRICA CONCAVA (Crassostrea gigas) PACIFIC OYSTER (Crassostrea gigas) FRESHNESS AND VITALITY EVALUATING METHOD Relatore: Prof.ssa Silvia Bonardi Correlatore: Prof. Renato Maria Malandra Laureando: Paolucci Cesare Anno accademico 2018-2019 Sommario Abstract .................................................................................................................................. 3 Introduzione ........................................................................................................................... 5 Classificazione tassonomica delle ostriche ........................................................................ 9 Famiglia Ostreidae: caratteri distintivi ........................................................................ 10 Caratteristiche fisiche esterne degli esemplari appartenenti alla Famiglia delle Ostreidae: .................................................................................................................. 10 Identificazione di Crassostrea gigas ......................................................................... 11 Denominazione di Crassostrea gigas in diverse lingue.................................................... 13 Storia di Crassostrea gigas .............................................................................................. 13 Anatomia di Crassostrea gigas ........................................................................................ 15 Denominazioni anatomiche dei molluschi bivalvi ....................................................... 15 Composizione e crescita della conchiglia .................................................................... 15 Parti molli ..................................................................................................................... 16 1. I mantelli ........................................................................................................... 16 2. La cavità del mantello ....................................................................................... 18 3. Gli organi della cavità del mantello .................................................................. 18 Habitat e biologia ............................................................................................................. 27 Sistemi di produzione ...................................................................................................... 32 Fasi e tipologie di ciclo di produzione ............................................................................. 32 Fornitura del seme ........................................................................................................ 32 Riproduttori .................................................................................................................. 33 Coltura larvale e post-larvale ....................................................................................... 34 Incubatoio ..................................................................................................................... 36 Tecniche di crescita-affinaggio .................................................................................... 37 Coltura di fondo (on-bottom culture) ........................................................................... 37 Coltura sollevata dal fondo (off-bottom culture) .......................................................... 37 Coltura sospesa ............................................................................................................. 40 1 Coltura galleggiante ..................................................................................................... 43 Indurimento .................................................................................................................. 43 Tecniche di raccolta ......................................................................................................... 44 Manipolazione e lavorazione ........................................................................................... 44 Principali presentazioni commerciali .............................................................................. 46 Nazioni maggiormente coinvolte nella produzione di prodotti ittici ed ostriche ............ 48 Costi di produzione .......................................................................................................... 51 Problemi principali .......................................................................................................... 52 Pratiche di acquacoltura sostenibili ................................................................................. 54 Malattie e misure di controllo .......................................................................................... 55 Situazione legislativa europea ......................................................................................... 56 Obiettivo della tesi ........................................................................................................... 57 Materiali e metodi ............................................................................................................... 59 Risultati ............................................................................................................................... 71 Dati riguardanti la perdita di massa ................................................................................. 71 Dati riguardanti la registrazione del Sound Score ........................................................... 76 Dati relativi all’intensità sonora (dB) .............................................................................. 81 Rapporto tra i valori di Sound Score e l’intensità sonora ................................................ 86 Osservazioni sulla mortalità degli esemplari ................................................................... 90 Relazioni tra Sound Score, valori di intensità sonora (dB) e vitalità nei campioni ......... 91 Discussione e conclusioni ................................................................................................... 93 Considerazioni riguardanti la perdita di massa................................................................ 93 Considerazioni riguardanti le caratteristiche del suono ................................................... 96 Considerazioni riguardanti la vitalità dei campioni e conclusioni ................................ 101 Riferimenti bibliografici e sitografici ................................................................................ 103 Indice delle figure .............................................................................................................. 107 Indice delle tabelle ............................................................................................................ 113 2 Abstract In this study the physical attributes of 73 Pacific cupped oysters (Crassostrea gigas) exemplars were studied in order to lay the foundation for the development of a freshness and vitality estimating method and to refine the expiration date assignment: furthermore, three different ranges of temperature were tested, in order to ascertain the one that best preserved the hallmarks of a live and fresh mollusk, since there is currently not a specified one by any European regulations. The Pacific cupped oyster was the selected species because of its global distribution and its consumption: moreover, the final product is often eaten raw, possibly setting up important hazards for human health. The specimens were received at the Milan Fish Market on the 26/05/2019. They were collected directly from the shellfish purification tanks: 30 the 30/05/2019 while the remaining 43 the 26/05/2019. Both of the assortments were divided into three main groups, according to the respective range of preservation temperature: the first was stored at 8,5°C on average (6°C-11°C), the second between 6°C and 8°C (7°C on average) and the last within 1,5°C and 2,3°C. Four exemplars for the first two groups and five for the last were maintained with the right (flat) valve facing downwards. The mass of each animal was recorded daily, as well as the mean sound intensity (dB) generated by three percussions on the shell of the oysters and the mean Sound Score (assigned depending on the tone perceived by the operator) created by two of the impacts. The exemplars studied may have been too few to provide statistically significant results, but they always displayed a definite and steady mass loss, opposite to the continuous increase of the sound intensity and the Sound Score, particularly noticeable in deceased specimens, whereas the vitality seemed to be more retained by the oysters that lost the most limited volume of intravalvular liquid, echoed by a lower level reached by the sound parameters measured. The most excellent results in freshness and liveliness occurred by preserving the oysters within 6°C and 8°C, and with the right valve facing upwards. Forthcoming researches may regard the development of an automatic detector of dead oysters or freshness evaluator, suitable in self-inspection procedures. 3 4 Introduzione Le ostriche, ed in particolare l’ostrica concava del Pacifico (Crassostrea gigas), la quale sarà il centro focale di questa trattazione, sono consumate a livello europeo (Figura 1 e Figura 2) e mondiale (Figura 3 e Figura 4). Rappresentano un alimento nutritivo (Tabella 1), presentato