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Browsing by Subject "spoilage"

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  • Lehto, Jenni (University of HelsinkiHelsingin yliopistoHelsingfors universitet, 2009)
    The quality of easily spoiling minced meat is regularly inspected by food control authorities. The quality of minced meat near the sell-by date has often been found to be poorer than could be wished for. In previous studies psychrotrophic lactic acid bacteria have been found to be significant spoilage bacteria in modified atmosphere packed meat but the spoilage bacteria of minced meat have not been studied. An industrial manufacturer delivered 20 packages of modified atmosphere packed minced meat which were studied on the sell-by day (±1 day). The concentrations of lactic acid bacteria and enterobacteria in the minced meat samples were quantified on MRS agar and VRBG agar respectively. The appearance and smell of raw minced meat was judged organoleptically. 349 lactic acid bacteria isolates were identified using ribotyping based on numerical analysis. The DNA of the lactic acid bacteria was isolated and digested with the restriction enzyme HindIII. The DNA fragments were separated by agarose gel electrophoresis and transferred to a nylon membrane where the fragments were hybridized with a labelled probe. Thus the ribopatterns of the isolates could be visualised on the membrane. The ribopatterns were compared with corresponding patterns in the research group's database which comprises the ribopatterns of over 7000 strains. Identification of the isolates is based on the locations of type strains in the clusters created in the numerical analysis according to similarity of ribotypes. The lactic acid bacteria counts in the minced meat samples were 1,1 × 107 – 4,9 × 108 cfu/g (on average 1,9 × 108 cfu/g). Enterobacterial counts were 9,0 × 102 – 9,0 × 104 cfu/g (on average 1,4 × 104 cfu/g). Observations in the sensory evaluation included grayness and off-odours of varying strength. The off-odours were described as rancid and buttery. The most common species of lactic acic bacteria were identified to be Leuconostoc gasicomitatum (58 % of lactic acid bacteria isolates) and Leuconostoc gelidum (20 %). Other species were Carnobacterium divergens (10 %), Carnobacterium maltaromaticum (4 %), Lactococcus spp. (3 %), Leuconostoc mesenteroides (2 %), Lactobacillus algidus (1 %), Lactobacillus sakei (1 %), and Leuconostoc carnosum (1 %). In addition to these, 15 isolates were identified as Brochothrix thermospacta which appeared to grow on MRS along with lactic acid bacteria. Lactic acid bacteria, especially L. gasicomitatum and L. gelidum, were recognised as the spoilage bacteria of industrially manufactured, modified atmosphere packed minced meat. These organisms have been shown to grow on modified atmosphere packed meat during cold storage and to be connected with the formation of sour and buttery off-odours. L. gasicomitatum and L. gelidum are not part of the natural microbiota of slaughter animals and therefore the significance of the production environment as their source should be examined.