Tomislav Petrak

Occurrence of Vibrio spp. in sea fish, shrimps and bivalve molluscs harvested from Adriatic sea

Abstract One hundred and seventeen samples of sea fish (100), shrimps (10) and bivalve molluscs (7) were sampled at fish markets (100 samples) and hotels (17 samples) along the sea side in Croatia within the period from May to July 2000. The samples were tested for the presence of Vibrio spp. Vibrio spp. was isolated in 23 (19.65%) of total count of samples. The most frequently found were V. parahaemolyticus (9.40%), V. vulnificus (6.84%) and V. alginolyticus (3.42%). A significantly larger number of positive findings involved the samples collected at hotels (35.29%) as compared to those collected at fish markets (17.00%). The isolation was conducted by a conventional cultivation with the enrichment in alkaline peptone water and on TCBS Kobayashi agar (“Biolife”).

Characterization of traditional Istrian dry-cured ham by means of physical and chemical analyses and volatile compounds

The aroma-active compounds of Istrian dry-cured ham were investigated by using headspace-solid phase microextraction and gas chromatography-mass spectrometry (GC-MS). Samples of biceps femoris were also evaluated by measuring physical and chemical characteristics: moisture, protein, fat, ash and NaCl content, a(w) value; colour: L*, a*, b* and oxidation of fat: TBARS test. About 50 volatile compounds were identified and quantified which belonged to several classes of chemical: 5 alcohols, 8 aldehydes, 7 alkanes, 1 ketone, 2 esters, 9 monoterpenes and 15 sesquiterpenes. Except volatile compounds derived from lipolysis and proteolysis the most abundant constituents were terpenes (62.97; 41.43%) that originate from spices added in the salting phase of the production process.

Presence of Escherichia coli O157:H7 in ground beef and ground baby beef meat.

A total of 114 beef and baby beef samples were examined. The samples included ground baby beef, mixed ground baby beef and pork, and chopped and shaped meat. The samples were analyzed from 30 different grocery stores in Zagreb, Croatia. The object of this study was to evaluate the prevalence of Escherichia coli O157:H7 in the samples that can enhance the potential risk of outbreaks of hemorrhagic colitis and hemolytic uremic syndrome. The results in all tested samples of E. coli O157:H7 were negative. A single sample was positive in a latex agglutination test using antiserum to O157:H7. It was identified as Proteus vulgaris at the Pasteur Institute, Paris, France. This result correlates positively with cross-contamination with Yersinia enterocolitica 09, Brucella abortus, Salmonella type N, and Pseudomonas maltophila.

Determination of volatile compounds and quality parameters of traditional Istrian dry-cured ham.

The aim of this work was to determine the characteristics of Istrian dry-cured ham by instrumental methods and sensory analysis. The aroma-active compounds of Istrian dry-cured ham from 2010 and 2012 were investigated by using headspace-solid phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS). Samples of biceps femoris were also evaluated by measuring physical and chemical characteristics. 92 volatile aroma compounds of Istrian dry-cured ham were found. Volatile compounds belonged to several chemical groups: aldehydes (51.4; 51.3%), terpenes (16.5; 16.4%), alcohols (15.5; 13.2%), ketones (8.6; 7.4%), alkanes (3.8; 5.7%), esters (1.3; 1.6%), aromatic hydrocarbons (0.8; 3.9%) and acids (0.6; 0.9%). Principal component analysis (PCA) showed that fat content, tenderness and melting texture were positively correlated. Terpenes were strongly correlated with flavour of added spices. Sweet taste and the presence of esters were positively correlated as well as negative odour, raw meat flavour and water content.

A study of chemical profiles and appearance of white crystals in Istrian dry-cured ham: effect of desalting

Abstract In order to find out the effect on physical-chemical profile of Istrian dry-cured ham with particular regard to the appearance of white crystals in the muscles, raw salted legs were desalted by soaking the legs in cold water for 24 hours. The 20 raw hams taken from 10 slaughtered hogs (Swedish Landrace breed) and processed in the traditional Istrian manner were used. After salting and pressing, the raw hams were divided into two groups: 1) the 10 left legs of each hog were desalted (D); 2) the 10 right legs were not desalted (N). Following this, both groups of legs were subjected to continuous processing. Samples for chemical analysis and counting of white spots were taken from the 20 legs (10 N and 10 D) from 10 hogs, each weighing 12 to 15 kg. Chemical analysis of muscle tissue showed a highly significant difference (P<0.0001) in the salt quantity in the N (6.85%) and D (5.31%) dry-cured hams, as expected. Desalting affected the level of calcium which was higher (P=0.0124) in the D hams (0.27 g) than in the N hams (0.22 g). Desalting did not affect the free amino acid content, with the exception of methionine which was lower (P=0.0041) in D (0.14 g) than in N hams (0.17 g). Desalting affected the level of two free fatty acids as follows: heptadecanoic acid was higher (P=0.0203) in N (0.18%) than in D hams (0.24%) and DPA was higher (P=0.0373) in N (0.49%) than in D hams (0.39%). By counting the white precipitates, it was established that the regularity of appearance of the precipitate was noted on both the D and N hams, such that where there was no precipitate on the right N ham, nor was their any on the left D ham of the same hog. However, desalting only lead to a slight decrease in the appearance of precipitates (average of 0.7 points), but it is certain that desalting reduces the salt content in the legs, which affects some physical-chemical changes in the ham tissues during processing.

NUTRITIVE VALUE OF TROUT (ONCORHYNCHUS MYKISS) FARMED IN ADRIATIC SEA

Cilj ovog rada bio je određivanje kemijskog sastava fileta svježe i hladno dimljene kalifornijske pastrve (Oncorhynchus mykiss) uzgojene u Jadranskom moru mjerenjem udjela vode, masti, proteina, soli, pepela, sastava masnih kiselina s naglaskom na eikozapentaensku (EPA) i dokozaheksaensku (DHA) masnu kiselinu te fizikalnih karakteristika mjerenjem pH i određivanjem boje. Analize su izvrsene na homogeniziranom misicju nakon odvajanja kože i kostiju. Određivanje udjela vode, pepela, ukupne kolicine masti i proteina izvrseno je prema referentnim metodama AOAC (1995). Za određivanje sastava masnih kiselina pripremljeni su metilni esteri prema metodi HRN EN ISO 5509 (2004) te su analizirani plinskom kromatografijom prema metodi HRN EN ISO 5508 (1999). Rezultati su pokazali da je istražena svježa pastrva uzgojena u moru odlican izvor proteina (21, 21%) te da ima nesto niže vrijednosti udjela masti (5, 21%) i omega-3 masnih kiselina (12, 52 %) od rezultata drugih istraživanja. Proces hladnog dimljenja ne uzrokuje gubitke na udjelu masti i omega-3 masnih kiselina. Fileti svježe i dimljene kalifornijske pastrve uzgojene u Jadranskom moru mogu se smatrati namirnicama visoke prehrambene vrijednosti.