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dc.contributor.advisorHugo, C. J.
dc.contributor.advisorSteyn, L.
dc.contributor.advisorJooste, P. J.
dc.contributor.authorBekker, Anneke
dc.date.accessioned2015-08-12T10:09:28Z
dc.date.available2015-08-12T10:09:28Z
dc.date.issued2011-11
dc.identifier.urihttp://hdl.handle.net/11660/823
dc.description.abstractEnglish: Chryseobacterium species have been reported to cause spoilage in food products such as fish, meat, poultry and dairy products. Some of these Chryseobacterium species can grow at temperatures below 7 °C which gives them the ability to grow and cause spoilage in milk kept at refrigerated temperatures. Protease and lipase enzymes produced by psychrotolerant species in milk are responsible for spoilage by the production of off-odours and –flavours. The aim of this study was to determine the growth and spoilage characteristics of Chryseobacterium species in milk and compare the results to those of Pseudomonas fluorescens which is regarded as the major organisms causing spoilage in milk. The specific growth rates and cardinal temperatures for C. joostei, C. bovis and Ps.fluorescens were determined by optical density measurements. Chryseobacterium joostei had the highest maximum specific growth rate followed by Ps. fluorescens and C. bovis. All three organisms were able to grow at 4 °C, but Ps. fluorescens showed the highest growth rate temperatures below 7 °C. All three organisms can thus be classified as psychrotolerant mesophiles due to the fact that growth was observed at 4 °C with optimum temperatures ranging between 25 and 30 °C. Arrhenius plots for the three species showed that C. joostei had the lowest activation energy followed by Ps. fluorescens and C. bovis. This means that C. joostei was the least sensitive to temperature changes that may take place while C. bovis was the most sensitive of the three tested organisms. The protease activity per mg protein for the three organisms was determined with the azocasein method. Chryseobacterium joostei showed the highest activity followed by C. bovis while Ps. fluorescens showed significantly lower activity than the Chryseobacterium species. All three species showed protease activity at 4 °C. Determination of the lipolytic activity of C. joostei and Ps. fluorescens were done by measuring the amount of FFAs present in fat-free and full cream milk incubated either at 4 or 25 °C. High levels of lipolysis were observed for all the inoculated samples. Although differences between the different sample treatments were observed, these differences were not significant enough to differentiate between the spoilage potential of C. joostei and Ps. fluorescens in the different milk samples. Secondary lipid oxidation of the two organisms was determined with the TBA method. Although inoculated milk samples demonstrated higher levels of oxidation compared to non-inoculated samples, there were no signigicant differences between any of the inoculated milk samples. Sensory analysis was done on the samples and C. joostei produced stronger odours than Ps. fluorescens. All the samples that were inoculated with C. joostei scored significantly higher spoilage scores than the control samples as well as the Ps. fluorescens samples. The odours described for the two organisms also showed distinct differences. In addition to the “smelly feet”, “blue cheese” and “agar” odours described for all the inoculated samples, C. joostei also produced “putrid” and “sour” odours while Ps. fluorescens produced odours described as “fruity”, “nutty” and “bitter”. The volatile compounds produced by C. joostei and Ps. fluorescens were identified with headspace SPME-GC/MS analysis. Ketones, alcohols and fatty acids were the main compounds produced. Ketones are responsible for the production of fruity and floral odours. Fatty acids produce sour odours, with isovaleric acid being responsible for the smelly feat odour. Alcohols do not usually contribute to the odour production in milk. The results could not be used to differentiate between the two organisms in the different milk samples.en_ZA
dc.description.abstractAfrikaans: Daar is al gerapporteer dat Chryseobacterium spesies bederf veroorsaak in verskeie voedselprodukte soos vis, vleis, hoender en suiwel produkte. Sommige van hierdie spesies kan by temperature laer as 7 °C groei, wat hulle in staat stel om bederf te veroorsaak in melk wat by yskas temperature gestoor word. Proteases en lipases wat deur psigrotolerante bakterieë geproduseer word is verantwoordelik vir bederf deur die vorming van afgeure en –reuke. Die doel van hierdie studie was om die groei en bederf eienskappe van Chryseobacterium spesies te bepaal en die resultate te vergelyk met dié van Pseudomonas fluorescens. Laasgenoemde is bekend as die hoof organisme wat bederf in melk veroorsaak. Die spesifieke groeitempo en kardinale temperature van C. joostei, C. bovis en Ps. fluorescens is deur optiese digtheid metings bepaal. Chryseobacterium joostei het die hoogste maksimum spesifieke groeitempo gehad, gevolg deur Ps. fluorescens en C. bovis. Al drie die organismes was in staat om by 4 °C te groei, maar Ps. fluorescens het die hoogste groeitempo gehad by temperature laer as 7 °C. Die organismes kan dus al drie geklassifiseer word as psigrotolerante mesofiele as gevolg van die feit dat groei by 4 °C plaasgevind het en optimum groei temperature tussen 25 en 30 °C was. Arrhenius grafieke vir die drie spesies het getoon dat C.joostei die laagste aktiveringsenergie het, gevolg deur Ps. fluorescens en C. bovis. Hierdie bevindinge dui daarop dat C. joostei minder sensitief is vir verandering in temperatuur, terwyl C. bovis die mees sensitiefste spesie was. Die protease aktiwiteit per mg proteïen vir die drie organismes is deur middel van die azocasein metode bepaal. Chryseobacterium joostei het die hoogste aktiwiteit gehad, gevolg deur C. bovis. Pseudomonas fluorescens het aansienlike laer aktiwiteit gehad. Al drie die species het by 4 °C steeds aktiwiteit getoon. Bepaling van die lipolitiese aktiwiteit van C. joostei en Ps. fluorescens is gedoen deur bepaling van die aantal vrye vetsure. Hoë vlakke van lipoliese is waargeneem vir al die geïnokuleerde monsters. Alhoewel verskille tussen die monsters waargeneem is, was hierdie verskille nie betekenisvol genoeg om te onderskei tussen die bederf potensiaal van C. joostei en Ps. fluorescens in die verskillende melk monsters nie. Sekondêre lipied oksidasie van die twee organismes is bepaal deur die TBA metode. Alhoewel die geïnokuleerde melk monsters hoër oksidasie vlakke getoon het in vergelyking die monsters wat nie geïnokuleer was nie, was daar geen beduidende verskille tussen enige van die geïnokuleerde monsters nie. Sensoriese analise is op die monsters gedoen en C. joostei het sterker reuke geproduseer as Ps. fluorescens. Al die monsters wat met C. joostei geïnokuleer was, het beduidend hoër bederf tellings getoon as die kontrole en Ps. fluorescens monsters. Die reuke wat beskryf is vir die twee organismes het ook beduidende verskille getoon. Bo en behalwe die “stink voete”, “bloukaas” en “agar” reuke wat vir al die monsters beskryf is, het C. joostei ook “vrot” en “suur” reuke geproduseer, terwyl Ps. fluorescens “vrugte”, “neut” en “bitter” reuke geproduseer het. Die vlugtige verbindings wat deur C. joostei en Ps. fluorescens geproduseer is, is geïdentifiseer deur middel van ‘headspace’ SPME-GC/MS analise. Ketone, alkohole en vetsure was die hoof verbindings wat geproduseer is. Ketone is gewoonlik verantwoordelik vir die vorming van vrugte en blomme geure, terwyl vetsure verantwoordelik is vir die suur reuke. Alkohole dra normaalweg nie by tot die reuk produksie in melk nie. Die resultate kan nie gebruik word om te onderskei tussen die twee organismes in die verskillende melk monsters nie.
dc.language.isoenen_ZA
dc.publisherUniversity of the Free Stateen_ZA
dc.subjectMilk -- Microbiologyen_ZA
dc.subjectFood spoilageen_ZA
dc.subjectBacterial growthen_ZA
dc.subjectProteolytic enzymesen_ZA
dc.subjectPseudomonas fluorescensen_ZA
dc.subjectDissertation (M.Sc. (Microbial, Biochemical and Food Biotechnology))--University of the Free State, 2011en_ZA
dc.titleGrowth and spoilage characteristics of Chryseobacterium species in milken_ZA
dc.typeDissertationen_ZA
dc.rights.holderUniversity of the Free Stateen_ZA


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