Thesis (MScVoedselwet)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Red meat has a limited shelf-life at refrigerated temperatures, where spoilage is mainly
due to the proliferation of bacteria, yeast and moulds, acquired during the dressing
process. In addition, almost a fifth of food-borne disease outbreaks, caused by microorganisms
such as Escherichia coli 0157:H7, Listeria monocytogenes and
Staphylococcus aureus are associated with red meat. To improve the microbiological
quality of red meat, systems such as HACCP, GHP and GMP are currently practiced;
however, these practices are not able to extend the shelf-life of these products. At
present suitable food-grade preservatives are recommended, but the use of some of
these preservatives is increasingly being questioned with regard to their impact on
human health. Additionally, food service customers demand high quality products that
have a relatively long shelf-life, but still prefer the appearance of minimally processed
food. All these factors challenge the food manufacturing industry to consider more
natural means of preservation.
Antimicrobial metabolites of food grade bacteria, especially lactic acid bacteria,
are attracting increasing attention as food preservatives. Bacteriocins are antimicrobial
peptides (3 to 10 kDa) with variable activity spectra, mode of action, molecular weight,
genetic origin and biochemical properties that are bacteriostatic or bactericidal to
bacteria closely related and bacteria confined within the same ecological niche.
Micro-organisms were isolated from beef, lamb and pork, obtained from four
commercial retailers. The number of viable cells three days after the sell-by date at 4ºC
ranged from 80 cfu.g-1 to 1.4 × 108 cfu.g-1. Fifty-three percent were Gram-negative
bacteria, 35% Gram-positive and 12% yeast. The microbial population of the meat was
greatly influenced by the origin, i.e. the retailer. Bacteriocins produced by Enterococcus
faecalis BFE 1071, Lactobacillus curvatus DF 38, Lb. plantarum 423, Lb. casei LHS, Lb.
salivarius 241 and Pediococcus pentosaceus ATCC 43201 were screened for activity
against bacteria isolated from the different meat samples. Sixteen to 21% of the
isolates, identified as members of Klebsiella, Shigella, Staphylococcus, Lactobacillus,
Lactococcus, Leuconostoc, Enterococcus, Pediococcus, Streptococcus and Bacillus
were sensitive to the bacteriocins.
Curvacin DF 38, plantaricin 423 and caseicin LHS (2.35 to 3.4 kDa) had the
broadest activity range and inhibited species of Lactobacillus, Pediococcus,
Enterococcus, Listeria, Bacillus, Clostridium and Propionibacterium. The bacteriocins
remained stable at 121ºC for 20 min, in buffers with a pH ranging from 2 to 10 and in
NaCl concentrations of between 0.1 and 10% (m/v). Like most peptides, they were sensitive to proteolytic enzymes. Curvacin DF 38 is sensitive to amylase, suggesting
that the bacteriocin might be glycosylated.
To assess the efficiency of curvacin DF 38, plantaricin 423 and caseicin LHS as
meat preservatives, they were partially purified by ammonium sulphate precipitation and
separation in a Sep Pak C18 cartridge. The shelf-life of pork may be extended by up to
two days. Meat samples treated with bacteriocins were darker than the control
(untreated) sample. Descriptive sensory evaluation by a seven-member panel indicated
that there were significant differences (P ≤ 0.05) regarding the aroma, sustained
juiciness, first bite and metallic taste attributes of the control and the 4 day-treated
samples. The control and 2 day-treated samples and the 2 day- and 4 day treated
samples did not differ significantly regarding these attributes. There were no significant
differences regarding the initial juiciness, residue and pork flavour attributes.
Concluded from the results obtained in this study, bacteriocins produced by Lb.
curvatus DF 38, Lb. plantarum 423 and Lb. casei LHS effectively extended the shelf-life
of pork loins by up to 2 d at refrigerated temperatures with no drastic changes on
sensory characteristics. In edition, the stability of these bacteriocins broadens their
application as preservatives in many foods. / AFRIKAANSE OPSOMMING: Die rakleeftyd van rooivleis by yskastemperature is beperk, waar bederf hoofsaaklik
deur die vermenigvuldiging van bakterieë, giste en swamme veroorsaak word. Die
meeste van hierdie kontaminante is afkomstig van die slagtingsproses. Byna ’n vyfde
van alle uitbrake van voedselvergiftigings wat deur organismes soos Escherichia coli
0157:H7, Listeria monocytogenes en Staphylococcus aureus veroorsaak word, word
met rooivleis geassosieër. Die praktyke HACCP, GMP en GHP word tans toegepas om
die mikrobiologies kwaliteit van vleis te handhaaf, maar is egter nie voldoende om die
rakleeftyd van rooivleis the verleng nie. Die preserveermiddels wat huidiglik aanbeveel
word vir dié doel, word toenemend bevraagteken aangaande die invloed daarvan op die
menslike gesondheid. Hierby is daar ’n aanvraag na hoë kwaliteit, ongeprosesseerde
produkte met ’n verlengde rakleeftyd. Gevolglik word die voedsel vervaardigings
industries aangemoedig om meer natuurlike vorms van preservering the oorweeg.
Die aandag word tans op die anti-mikrobiese metaboliete van voedselgraad
microbes, veral melksuurbakterieë, gevestig. Bakteriosiene is anti-mikrobiese peptiede
(3 tot 10 kDa) met verskeie aktiwiteitsspektra, werkswyse, molekulêre massa, genetiese
oorsprong en biochemiese eienskappe. Bakteriosiene is meestal bakterie-dodend of -
staties teen taksonomies naby geleë organismes en organismes vanuit dieselfde
ekologiese nis.
Mikroörganismes is geïsoleer vanuit bees-, skaap- en varkvleis, verkry vanaf vier
supermarkte. Die aantal lewensvatbare selle per gram (cfu.g-1) het drie dae na die
“verkoop”-datum by 4ºC vanaf 80 cfu.g-1 tot 1.4 × 108 cfu.g-1 gevarieër. Drie en vyftig
persent van die isolate is as Gram-negatief, 35% as Gram-positief en 12% as giste
geïdentifiseer. Die sensitiwiteit van hierdie isolate teen bakteriosiene wat deur
Enterococcus faecalis BFE 1071, Lactobacillus curvatus DF 38, Lb. plantarum 423, Lb.
casei LHS, Lb. salivarius 241 en Pediococcus pentosaceus ATCC 43201 geproduseer
is, is vervolgens getoets. Tussen 16% en 21% van die isolate was sensitief teen die
bacteriosiene en is onder andere as Klebsiella, Shigella, Staphylococcus, Lactobacillus,
Lactococcus, Leuconostoc, Enterococcus, Pediococcus, Streptococcus en Bacillus
geïdentifiseer.
Die bakteriosiene met die wydste aktiwiteitsspektrum, naamlik, curvacin DF 38,
plantaricin 423 en caseicin LHS is verder ondersoek. Hierdie antimikrobiese peptiede
(2.35 tot 3.4 kDa) toon aktiwiteit teen spesies van Lactobacillus, Pediococcus,
Enterococcus, Listeria, Bacillus, Clostridium and Propionibacterium. Die bakteriosiene
is stabiel by 121ºC vir 20 min, in buffers met ‘n pH-reeks van tussen 2 en 10 en soutkonsentrasies vanaf 0.1% tot 10%. Soos die geval by meeste peptiede is hierdie
bakteriosiene sensitief vir proteolitiese ensieme. Curvacin DF 38 is ook sensitief vir
amylase, wat daarop dui dat hierdie bakteriosien moontlik geglikosileer is.
Die effektiwiteit van curvacin DF 38, plantaricin 423 en caseicin LHS as
preserveermiddel in voedselsisteme is getoets deur dit te suiwer (ammonium sulfaat
presipitasie en Sep Pak C18 kolom) en op vark lendestukke aan te wend. Mikrobiese
analise het bewys dat die rakleeftyd van vark met sowat 2 dae verleng kan word.
Volgens die vleiskleurevaluering was die bakteriosien behandelde vark donkerder as die
kontrole. Die aroma-, sappigheid-, tekstuur- en metaalgeur-eienskappe van die kontrole
en die 4-dag behandelde monster het volgens ‘n opgeleide sensoriese paneel
betekenisvol verskil (P ≤ 0.05). Die kontrole en die 2-dag behandelde en die 2-dag
behandelde en die 4-dag behandelde monsters het nie betekenisvol verskil nie. Daar
was geen betekenisvolle verskil aangaande die aanvanklike sappigheid-, residu- en
varkgeur-eienskappe nie. Hierdie sensoriese eienskappe is belangrik ten opsigte van
die verbruiker se aanvaarding van die produk.
Vervolgens kan uit hierdie resultate afgelei word dat die bakteriosiene wat deur
Lb. curvatus DF 38, Lb. plantarum 423 en Lb. casei LHS geproduseer word voldoende
is om die rakleeftyd van vark lendestuk by 4ºC met 2 dae te verleng met min of geen
effek op die sensoriese persepsie van die vleis. Hierdie bakteriosiene is ook stabiel
onder verskeie kondisies wat die toepassing as preserveermiddel aansienlik verbreed.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/16371 |
| Date | 12 1900 |
| Creators | Kohrs, Gertruida Ansia |
| Contributors | Dicks, L.M.T., Hoffman, L.C., Britz, T.J., University of Stellenbosch. Faculty of Agrisciences. Dept. of Food Science. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | vii, 125 leaves : ill. |
| Rights | University of Stellenbosch |
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