Natural microflora of sheep meat during processing of kastradina, a Croatian dry-cured meat product

Sastav prirodne mikroflore svakog tradicijskog proizvoda je specifičan i ima važnu ulogu u razvoju tipičnih senzorskih svojstava ovih proizvoda. Autohtona mikroflora je dobro prilagođena okolini u kojoj raste i procesima proizvodnje te je dominantna nad ostalom mikroflorom. Ona utječe na osnovnu, prirodnu i pridodanu kvalitetu kao i na samu sigurnost hrane. Kako u literaturi nema pouzdanih podataka o prirodnoj mikroflori tradicijskog hrvatskog suhomesnatog ovčjeg proizvoda, kaštradine, cilj ovog rada je bio izolirati i identificirati prirodnu mikrofloru kaštradine u različitim fazama proizvodnje te utvrditi utjecaj tehnoloških postupaka na mikrobnu populaciju u različitim fazama proizvodnje. Istraživanjem je bilo obuhvaćeno 40 trupova ovaca pasmine travnička pramenka. Nakon 24-satnog hlađenja trupovi su rasječeni na polovice, a sa svake polovice je odvojen but s potkoljenicom i plećka sa podlakticom. Preostali dio se naziva „kora“. Primijenjene su dvije varijante soljenja mesa: soljenje solju te soljenje smjesom soli i prirodnih začina. Unutar svake skupine bile su dvije podskupine: dio uzoraka uziman je 14. dan, odnosno neposredno nakon završetka faze dimljenja, odnosno sušenja, a dio je bio na zrenju još deset dana, za utvrditi utjecaj produljenog zrenja na sastav mikroflore kaštradine. Iz rezultata određivanja mikrobiološke čistoće pribora ovčjih trupova razvidno je da je higijena objekta za klanje bila zadovoljavajuća, a hladni ovčji trupovi bili su u potpunosti zdravstveno ispravni. Uzorci su uzimani prvog, sedmog te u jednoj podskupini četrnaestog, a u drugoj dvadeset i četvrtog dana tehnološkog procesa proizvodnje kaštradine. Istraživane su slijedeće skupine mikroorganizama: ukupne aerobne mezofilne bakterije, bakterije mliječne kiseline, enterokoki, mikrokoki, kvasci i plijesni, S. aureus, enterobakterije, koliformi, E. coli, Salmonella spp., Listeria spp. i sulfitreducirajuće klostridije. Istraživani uzorci kaštradine, bez obzira na tehnologiju proizvodnje i duljinu zrenja bili su zdravstveno ispravni. Broj aerobnih mezofilnih bakterija, bakterija mliječne kiseline i enterokoka je bio maksimalan nakon faze soljenja, s izuzetkom mikrokoka kojih je najviše identificirano u zreloj kaštradini produljenog zrenja soljenoj čistom soli. Tijekom faze dimljenja i zrenja broj navedenih skupina mikroorganizama bio je znatno manji. Promjena broja kvasaca i plijesni je bila varijabilna, odnosno njihov broj se zrenjem povećavao u tehnološkom procesu soljenja s kraćim zrenjem i tehnologije soljenja smjesom soli i začina s produljenim zrenjem. Nasuprot navedenom, faza soljenja negativno je utjecala na broj S. aureus, enterobakterija i koliforma s izuzetkom broja koliforma nakon faze soljenja u tehnologiji soljenja smjesom soli i začina s produljenim zrenjem što se može objasniti naknadnom kontaminacijom. Iz rezultata je razvidno kako dodani začini negativno utječu na prosječni broj ukupnih aerobnih mezofilnih bakterija i koliforma u zreloj kaštradini. Nasuprot tome, dodatak začina pozitivno utječe na prosječni broj kvasaca i plijesni u uzorcima nakon faze soljenja. Produljeno zrenje kod tehnologije soljenja čistom soli ima pozitivan učinak na prosječni broj bakterija mliječne kiseline i mikrokoka. Nasuprot tome, produljeno zrenje kod tehnologije soljenja smjesom soli i začina ima negativan utjecaj na prosječni broj enterokoka. Dominantnu mikrofloru zrele kaštradine čine kvasci i plijesni s iznimkom kaštradine proizvedene tehnologijom soljenja s produljenim zrenjem u kojoj dominantnu mikrofloru čine mikrokoki.Sheep rearing in Croatia is a traditional branch of livestock farming and farmers quite often have no means of disposing of the ewes and rems worn-out with age and infirmity. Dry-cured mutton produced in Dalmatia region is well-known under the local term kastradina. Kastradina is being produced from mutton, which, in most of the cases, is either the meat of old ewes or wethers. Traditional dry-cured meat products (pork, beef or mutton) represent an important part of the cultural and gastronomic heritage of numerous countries worldwide. In the literature there are neither available data regarding the dominant microflora of kastradina nor the type of microorganisms appearing during the whole technological process of production. Microorganisms gain access into the meat from the environment, from equipment and from handlers during processing affecting the microbiological status of the product. They also inhibit the growth of undesirable microorganisms by decreasing the pH and competing for the nutrients. But while pathogenic microorganisms would affect the safety, spoilage microorganisms would limit the shelf life of the meat product. Thus, an understanding of the microbial profile of drycured meat is vital. The aim of this study was to explore how the technological process of production affects the microbiological quality and natural microflora of kastradina. In this study, we used 40 sheep carcasses of Travnik Pramenka for the production of kastradina. Sheep slaughtering was done in a certified slaughterhouse. After the slaughter carcasses were put in refrigerators for the period of 24 hours at the temperature of +4 °C and after that cut in halves. Each half was dissected in such a way that legs with hind shanks were dissected from the sirloin/loin and flank/paunch. Also, fore shanks were dissected from the neck, ribs and breast. The remaining third part of the half is called “kora”. The parts of the carcass dissected in this way were submitted to processing which included the following phases: salting, smoking and ripening. In the process of salting applied in two variants: 1. salting with sea salt and the 2. curing mixture of sea salt and ground spices - garlic (Allium sativum), laurel (Laurus nobilis) and rosemary (Rosmarinus officinalis). The left half carcases were salted with variant 1, and the right half carcases variant 2. In order to determine the growth curve of the microorganisms during the technological process, meat sampling was conducted for three times, on the 1st (raw meat), 7th (after salting phase) and 14th (dry product) day. The following groups of bacteria were determined on selective media by using classical microbiological methods of isolation: aerobic mesophyll bacteria, lactic acid bacteria, Enterococcus, Micrococcocaceae, sulphite-reducing clostridia, Salmonella spp., Enterobacteriaceae, Escherichia coli, Staphylococcus aureus, yeast, and mould, and Listeria spp. All the statistical analyses have been conducted by using the software package SPSS version 17.0.0 (SPSS Inc., Chicago, IL, USA). The data were statistically processed by using the Tukey's honest significance test and the dominant population of microorganisms during specific phases of production was determined. The results obtained indicated that the dominant microflora of kastradina, regardless of the technological process, consists yeasts and molds (4.13 to 4.38 log CFU /g), followed by lactic acid bacteria (from 3.87 to 4.39 log CFU/g ) and micrococci (3,87 to 5,04 log CFU/g). The exception was production technology with salting pure salt with prolonged ripening during which micrococci become dominant microflora, followed by yeasts and molds and lactic acid bacteria. Total aerobic mesophilic bacteria, LAB and Enterococcus reached maximum counts at the end of the salting phase. During the drying/ripening phase their counts decreased. Ripening time had a significant influence on growing of the bacteria belonging to the genus Micrococcus (in technological process of salting). Their number was constantly increased. S. aureus decrease during the whole process and there are absent at the end of maturation. The technological process of producing kastradina had a negative effect on the number of Enterobacteriaceae and coliforms, too. Pathogenic microorganisms (Escherichia coli, Listeria spp., Salmonella spp., sulphite-reducing clostridia) weren’t detected in any of the samples. Salting phase has a positive effect on the number of total aerobic mesophilic bacteria, lactic acid bacteria, enterococci, micrococci, yeasts and molds. Ripening had a negative impact on the total aerobic mesophilic bacteria, lactic acid bacteria, enterococci, S. aureus, enterobacteria and coliforms. The number of yeasts and molds increases during the technological process of salting with pure salt with shorter ripening time and technological process of salting with a mixture of salt and spices with longer ripening time. The results obtained indicated that the added spices negative impact on the average number of total aerobic mesophilic bacteria and coliforms. In contrast, the addition of spices has a positive effect on the average number of yeasts and molds in the samples after the salting phase Prolonged ripening time technology with salting pure salt has a positive effect on the average number of lactic acid bacteria and micrococcus. In contrast, prolonged ripening time technology with salting mixture of salt and spices have a negative impact on the average number of enterococci