Effect of defrosting on quantity of volatile amines in stored sardines and herring used for tuna fattening

Abstract

Institute of Oceanography and Fisheries, Split, CroatiaSummaryStudied were the quantities of volatile amines, total volatilebases nitrogen (TVB-N) and trimethylamine nitrogen (TMA-N) in stored sardines (Sardina pilchardus) and herring (Clupeaharengus) over a 24-h period after defrosting. At the beginningof the experiment analyses showed TVB-N quantities in theflesh of both species to be higher than the FAO-recommendedlimit. TMA-N concentrations exceeded the acceptance limit6 h after defrosting in herring samples and after 12 h insardines. During the entire experiment TMA-N and TVB-Nconcentrations in sardines were above the tolerance limit. Thedefrosting method usually applied in tuna farms is unsuitablefor maintenance of a high quality food supply. Low qualitybaitfish can cause reduced weight gain as well as induce healthproblems and mortality in farmed tuna (Thunnus thynnus)populations.IntroductionDemands for quality tuna fish (Thunnus thynnus) in theJapanese and European markets have increased significantlyover the past decade. To meet these demands Croatianaquaculture companies have expanded cage farming of tuna(Katavic´ et al., 2003a,b; Ottolenghi et al., 2004); this produc-tion expansion requires large quantities of small blue fish,sardines and herring, for tuna fattening. Exclusively for thisreason, frozen blocks of herring are being imported from northEuropean countries for storage in farming companies at)18 C. Depending on the storage time, significant changes inquality and freshness (Nielsen et al., 1994) take place, which inturn affect the resulting quality of the farmed tuna. Feedingwith low quality baitfish can cause serious health problems andeventual mortality in farmed populations (Anon, 2005; Ruiz-Capillas and Moral, 2005; Mladineo et al., 2006). The baitfishspoilage rate depends on several factors such as species, fatcontent, size, shape and season, fishing method, and fishmanipulation after catch which includes the freezing procedureand storage time (Lima dos Santos et al., 1981; Gram et al.,1987; Ababouch et al., 1996). Fish muscles undergo a series ofchanges immediately after catch and during storage underconventional (chilled) conditions, resulting in gradual deteri-oration and loss of quality. These changes have been assessedusing nucleotides, ATP and breakdown compounds, biogenicamines and volatile amines: total volatile base (TVB) andtrimethylamine (TMA) (Hebard et al., 1982; Gill, 1992; Huss,1995; Ruiz-Capillas and Moral, 2005). Concentrations ofvolatile amines (TVB and TMA) increase during frozenstorage, causing loss of freshness and the beginning of spoilagedue to enzymatic and ⁄ or microbiological activities. The initialquantity of trimethylamine and total volatile base depends onmany factors, including fish handling before freezing; thus thelimits for some economically important species have alreadybeen ascertained. According to the FAO (Huss, 1995), formost frozen stored fish the acceptance limit of TMA-N is10–15 mg ⁄ 100 g. The concentration for sardines is5–10 mg ⁄ 100 g, and 10–15 mg ⁄ 100 g for herring (Huss,1995; Ababouch et al., 1996). Also according to the FAO(Huss, 1995; Ababouch et al., 1996), the TVB-N limit in fish is30–35 mg ⁄ 100 g: 25–35 mg ⁄ 100 g for sardines and30–35 mg ⁄ 100 g for herring. Despite the commercial impor-tance of tuna farming, studies on the non-quality feed influencein the farming process have not as yet been investigated.Due to the lack of scientific information on the defrostingeffects in changes of quality in fish food used for tunafattening, the changes in TVB-N and TMA-N concentrationsin sardine and herring over a 24-h defrosting period wereanalyzed. The objective of this study was to examine thequantity of volatile amines: total volatile base nitrogen (TVB-N) and trimethylamine nitrogen (TMA-N) in sardine andherring flesh over a 24-h period after defrosting.Material and methodsThe species used in this study were sardines (Sardina pilchar-dus) caught in the Adriatic Sea and held on ice untilindividually frozen and stored at )18 C for 10 days beforethe experiment, and herring (Clupea harengus) imported fromDenmark in frozen blocks and stored at )18 C for 9 months.Before the analyses, fish were thawed under seawater showersand held at room temperature (22 ± 1 C) until sampling time.Changes in concentrations of total volatile base nitrogen(TVB-N) and trimethylamine nitrogen (TMA-N) were deter-mined every 3 h during the first 24 h after thawing. Allanalyses were done in triplicate.Fish fillets were cut into pieces no larger than 4 mm. Fishextracts were prepared by homogenizing 100 g of the fishsample with an addition of 5% (v ⁄ v) trichloroacetic acid(TCA) in a laboratory homogenizer for 1 min at high speed.The homogenate was centrifuged at 4500 g for 10 min and thesupernatant liquid then filtered through a Whatman No.1 filterpaper to remove all tissue and fat particles. Concentrations oftotal volatile base nitrogen (TVB-N) and trimethylaminenitrogen (TMA-N) were determined by semi-micro steamdistillation method and expressed in mg ⁄ 100 g, according tothe Analytical Methods Committee (1979).Mean values, standard error, and the Box & Whisker plotfor the mean value comparison were analyzed with