Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references (leaves 77-86). Also available on the Internet.

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 101-116). Also available on the World Wide Web.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 75-84).

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.

Thesis (MSc Food Sc)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: Maas is a traditional fermented milk drink of the indigenous people of Southern Africa and can thus be used to uplift the nutritional status of the South African population, especially for the lower income groups. Furthermore, the problem of lactose intolerance among the Black population can also be addressed by the consumption of Maas. The objective of this study was to screen mesophylic lactic acid bacterial strains (25 in total) from the University of Stellenbosch Food Science Culture Collection for suitable metabolite production and then to produce traditional Maas with a starter culture combination that produces a distinctive acid and traditional flavour. The representative 25 single lactic acid starter strains were identified as Lactococcus lactis subsp. leetis biovar diacetylactis (12 strains), L. leetis subsp. leetis (four strains) and L. leetis subsp. cremoris (nine strains). These strains were inoculated into pasteurised full cream milk and activated for 8 h at 22°C. Pasteurised full cream milk was then inoculated with each of the activated starter strains, incubated at 22°C for 16 h and assessed for acid production abilities (pH = 4.6) under controlled time-temperature conditions. The results of this study showed that nine of the single strains, L. lactis subsp. leetis biovar diacetylactis (S1, S2, S3 and S5), L. teetis subsp. lactis (S13, S15 and S16) and two L. leetis subsp. cremoris strains (S17 and S22), produced sufficient acid, rendering them suitable for the use as starters in the production of traditional Maas. A pH range of 4.3 - 5.1 was reached by the nine single strains after 16 h at 22°C. Two-strain starter combinations were then formed by combining the most suitable single L. leetis subsp. leetis biovar diacetylactis, L. lactis subsp. lactis and L. lactis subsp. cremoris strains, respectively. From the data, it was concluded that acceptable Maas could be produced with four two-strain combinations (S3S 17, S3S22, S5S17 and S5S22). This selection was again based on suitable acid and metabolite production, as well as on sensory evaluation of the final product. These four two-strain combinations produced sufficient acid to reach a pH in the 4.6 - 4.8 range, and showed a high metabolite concentration for the most suitable compounds and formed a thick, smooth and creamy body texture after 16 h at 22°C. Three-strain combinations formed between the two-strain starter combinations and L. leetis subsp. teetis strains (813, 815 and 816), were also evaluated. With these combinations a lack of a pronounced Maas flavour was found. Thus, it was decided to add aroma producing strains of the species Leuconostoc mesenteroides subsp. dextranicum (strain L1) and L. mesenteroides subsp. citrovorum (strain L2) to the three-strain combinations. Four culture combinations (A, B, C and D) were then formed by combining the selected Leuconostoc strains (L1 and L2) with the most suitable Lactococcus strains (83,817,813 and 822). These combinations produced sufficient acid to reach the pH 4.5 - 4.6 range after 14 h at 22°C. Acetaldehyde was the major flavour metabolite formed in the Maas made with these four combinations, with concentrations ranging between 26.6 - 89.3 mg.l ̄ ¹, while other flavour metabolites (ethanol, acetone, diacetyl and 2-butanone) were present at lower concentrations. It was found that three of the four culture combinations (A, C and D) were characterised by a superior, but delicate flavour and a typical characteristic Maas body texture. Fruit flavoured Maas was subsequently prepared with the three most suitable culture combinations (A, C and D) using 11 flavours and a sensory evaluation performed. The statistically evaluated data showed that the appearance, smoothness, flavour intensity, sweetness and overall acceptability were influenced by the type of fruit flavour and the culture combination. Fruit flavour 4 (banana) was the most preferred flavour. The sensory panellists also indicated that the culture combination C gave the best overall acceptability over a three week study period. Data on the shelf-life study of natural unflavoured Maas, prepared with the three culture combinations (A, C and D), showed that the Maas still had an acceptable appearance, taste and good microbiological quality after 15 d at refrigerated temperatures. / AFRIKAANSE OPSOMMING: Maas is 'n tradisionele gefermenteerde melkdrankie onder die inheemse bevolking van Suid-Afrika en kan gebruik word om die voedingstatus van die Suid-Afrikaanse bevolking te verhoog, veral vir die laer inkomste groepe. Bowendien, kan die probleem van laktose intoleransie onder die Swart gemeenskap ook aangespreek word deur die verbruik van Maas. Die doel van hierdie studie was om enkelstam mesofiliese melksuur bakterieë (25 in totaal) van die Universiteit van Stellenbosch Voedselwetenskap Kultuur Versameling te ondersoek vir geskikte metaboliet produksie en tradisionele Maas met 'n kenmerkende suurheid en tradisionele geur met 'n geskikte kultuur kombinasie te produseer. Die toonaangewende 25 enkelstamme is Lactococcus lactis subsp. leetis biovar diacetylactis (12 stamme), L. lactis subsp. lactis (vier stamme) en L. lactis subsp. cremoris (nege stamme). Hierdie stamme was in gepasteuriseerde volroom melk geïnokuleer en geaktiveer vir 8 h teen 22°C. 'n Inokulum van die onderskeie geaktiveerde stamme is hierna in gepasteuriseerde volroom melk geplaas, vir 16 h teen 22°C geïnkubeer en hul vermoë om suur te produseer (pH = 4.6) onder beheerde tyd-temperatuur kondisies is bepaal. Die resultaat van die studie het aangedui dat nege enkelstamme, naamlik L. leetis subsp. lactis biovar diacetylactis (S1, S2, S3 en S5), L. lactis subsp. leetis (S13, S15 en S16) en twee L. leetis subsp. cremoris (S 17 en S22), geskikte suurheidsvlakke vir die produksie van Maas bereik het. 'n pH vlak van 4.3 - 5.1 is na 16 h teen 22°C deur hierdie nege enkelstamme bereik. Twee-stam kombinasies is onderskeidelik gevorm tussen die geskikte enkel L. lactis subsp lactis biovar diacetylactis, L. lactis subsp. lactis en L. lactis subsp. cremoris stamme. Die gevolgtrekking gemaak uit die data, is dat aanvaarbare Maas voorberei kan word met vier van die twee-stam kombinasies (S3S17, S3S22, S5S17 en S5S22) op grond van suurvorming, metaboliet produksie en sensoriese evaluasie. Hierdie vier kombinasies het genoegsame suur geproduseer om 'n pH vlak van 4.6 - 4.8 bereik, hoë metaboliet konsentrasies geproduseer en 'n dik, gladde en romerige tekstuur aangeneem na 16 h teen 22°C. Drie-stam kombinasies is gevorm tussen die onderskeie twee-stam kombinasies en L. lactis subsp. lactis stamme (813,815 en 816) en ook geëvalueer. Die tekort aan 'n skerp Maas geur in die drie-stam kombinasies het daartoe gelei dat Leuconostoc mesenteroides subsp. dextranicum (stam L1) en L. mesenteroides subsp. citrovorum (stam L2) bygevoeg is. Vier kultuur kombinasies (A, B, C en D) is gevorm deur die geselekteerde Leuconostoc stamme (L1 en L2) te kombineer met die mees gepaste Lactococcus stamme (83, 817, 813 en 822). Hierdie kombinasies het genoegsame suur geproduseer wat 'n pH vlak van 4.5 - 4.6 na 14 h teen 22°C bereik het. In die Maas wat met bovermelde kombinasies gemaak is, was die asetaldehied die mees geproduseerde geur metaboliet teen konsentrasies van 26.6 - 89.3 mg.l ̄ ¹. Ander geur metaboliete (etanol, asetoon, diasetiel, 2-butanoon) is in laer konsentrasies geproduseer. Daar is gevind dat drie uit die vier kultuur kombinasies (A, C en D) 'n superieur, delikate geur wat 'n tipies karakteristiek van die Maas gehad het. Vrugte gegeurde Maas geproduseer met die drie kultuur kombinasies (A, C en D) deur 11 geursels te gebruik, is sensories geëvalueer. Die statistiese geëvalueerde data het getoon dat die voorkoms, gladheid, geur intensiteit, soetheid en die algehele aanvaarbaarheid beïnvloed is deur die tipe vrugte geursels en die kultuur kombinasies. Die vrugte geursel 4 (piesang) het voorkeur geniet. Die sensoriese paneellede het ook aangedui dat kultuur kombinasie C die algehele mees aanvaarbare Maas geproduseer het oor die studie periode van drie weke. Data van die rakleeftyd van die natuurlike ongegeurde Maas wat geproduseer is met die drie kultuur kombinasies (A, C en D) het aangedui dat die Maas na 15 d by yskas temperatuur steeds 'n aanvaarbare voorkoms, smaak en goeie mikrobiologiese kwaliteit gehad het.

Thesis (MScAgric.)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: Changes in the bacterial population throughout the malting process of two barley cultivars, i.e. Clipper (local cultivar) and Prisma (imported cultivar), malted at Southern Associated Maltsters (SAM), Caledon, South Africa, were studied. Samples were taken from four individual runs of each cultivar at ten different stages, i.e. dry barley before steep, water from the first steep water-stand, barley after draining the first steep, water from the second steep water-stand, barley from the second steep water-stand, barley after draining of the second steep, barley from the first, second and third days of germination in the germination vessels (GV), and malt after kilning. Emphasis was placed on the taxonomy and composition of the lactic acid bacteria (LAB) isolated from the ten different phases. The LAB were identified to species level by using numerical analysis of total soluble cell protein patterns, RAPD-PCR banding patterns and 16S rRNA sequencing. The Gram-negative bacteria were identified to genus level by using the API 20E system and included Citrobacter spp., Enterobacter spp., Pantoea spp., Proteus spp., Seratia spp., Kluyvera spp., Klebsiella spp., Vibrio spp. and Escherichia coli. The number of viable bacteria throughout the malting process of the two cultivars did not differ significantly, although the LAB counts in the barley before steep and on the kilned malt were higher in Prisma than in Clipper. Leuconostoc argentinum, Leuconostoc laetis and Weissella confusa were the most predominant in both cultivars. A few strains of Weissella paramesenteroides, Lactobacillus casei, Lactococcus laetis and Lactobacillus rhamnosus were also isolated. Lb. casei and Lb. rhamnosus were not isolated from the Prisma cultivar, whilst W paramesenteroides and Le. laetis were absent in the Clipper cultivar. Kilned malt of the Clipper cultivar contained predominantly Le. argentinum, whereas the Prisma cultivar contained mainly Le. lactis. The effect of these bacteria on the fermenting ability of the brewer's yeast Saccharomyces cerevisiae SAB 05, was also studied. Fermentations were conducted in wort prepared from Clipper and Prisma malt. Yeast in combination with the different bacteria were used in the fermentation studies. Wort with only yeast was used as control. Emphasis was placed on the effect the bacteria has on the gravity, pH, yeast- and bacterial- counts and the different volatile aroma compounds produced throughout the fermentations. The presence of LAB and Gram-negative bacteria had no effect on the yeast to reduce the gravity of the fermenting wort, whilst the LAB caused a decrease in the pH of the fermentations in both Clipper and Prisma wort. The cell numbers of the Gram-negative bacteria decreased throughout the fermentations, whilst the LAB cell numbers remained constant. Comparisons could be drawn between the volatile aroma compounds produced in the control fermentation and fermentations with yeast and Gram-negative bacteria, yeast and Lactobacillus spp. and yeast and Weissella spp. Leuconostoc spp. had a much greater influence on the aromatic composition of fermented malt, with much more clear variations between Prisma and Clipper. No major differences were recorded in the aroma profiles of Prisma and Clipper malt fermented in the presence and absence of Lactococcus spp. The Gram-negative bacteria had no significant effect on the volatile aroma compounds produced by the yeast, whilst the LAB had a definite effect on aroma composition in both cultivars. The levels of four of the five principle aroma compounds, present in beer, were in the acceptable concentration range on the fmal day of fermentation. The compounds with the highest concentrations were iso-amyl alcohol, acetic acid and acetoin, with acetic acid being present in the highest concentration in all the fermentations. / AFRIKAANSE OPSOMMING: Veranderinge in die bakteriese populasie van die gars kultivars, Clipper (plaaslik) en Prisma (ingevoer), vermout by Southern Associated Maltsters (SAM), Caledon, Suid Afrika, is ondersoek. Monsters is van vier individuele lopies van elke kultivar en tydens tien verskillende fases van die vermoutingsproses geneem. Die tien verskillende stadia het die volgende ingesluit: Droë gars voor benatting, water van die eerste benattingsfase, gars nadat water van die eerste benattingsfase gedreineer is, water van die tweede benattingsfase, gars van die tweede benattingsfase, gars na die dreinering van water in die tweede benattings fase, gars na die eerste, tweede en derde dag van ontkieming binne die ontkiemingstenke, en mout na droging. Klem is geplaas op die taksonomie en samestelling van melksuurbakterieë (MSB) wat tydens die tien verskillende fases geïsoleer is. Die MSB is tot spesievlak geïdentifiseer deur gebruik te maak van numeriese analise van totale oplosbare selproteïen bandpatrone, RAPD-PKR bandpatrone en 16S rRNA volgorde-bepaling. Gram-negatiewe bakterieë is tot op genusvlak geïdentifiseer deur gebruik te maak van die API 20E toetssisteem. Spesies van die genera Citrobacter, Enterobacter, Pantoea, Proteus, Seratia, Kluyvera, Klebsiella, Vibrio asook Escherichia coli is geïdentifiseer. Tydens die vermoutingsproses van die twee kultivars is geen beduidende verskille in die lewensvatbare bakterietellings gevind nie, alhoewel die MSB-tellings in die gars voor benatting en mout na droging in Prisma hoër was as in Clipper. Leuconostoc argentinum, Leuconostoc laetis en Weissella confusa het die meeste voorgekom in beide kultivars. Kleiner hoeveelhede van Weissella paramesenteroides, Lactobacillus casei, Lactococcus laetis en Lactobacillus rhamnosus is ook geïsoleer. Lb. casei en Lb. rhamnosus het nie in die Prisma-kultivar voorgekom nie, terwyl W paramesenteroides en Le. laetis nie in die Clipper-kultivar teenwoordig was nie. Le. argentinum het meestal in die gedroogde mout van die Clipper-kultivar voorgekom, terwyl Le. laetis meestal in die Prisma-kultivar waargeneem is. Die effek van hierdie bakterieë op die fermentasievermoë van die brouersgis Saccharomyces cerevisiae SAB 05 is ook bestudeer. Die fermentasies is in Clipper- en Prisma- wort gedoen. Vir die fermentasiestudies is gis in kombinasie met verskillende bakterieë gebruik. Wort met slegs gis het as kontrole gedien. Klem is geplaas op die effek van die bakterieë op die digtheid, pH, gis- en bakterietellings en die verskillende vlugtige komponente wat tydens die fermentasies geproduseer is. Die teenwoordigheid van MSB en Gram-negatiewe bakterieë het geen effek gehad op die vermoë van die gis om die digtheid van die gefermenteerde wort te verlaag nie. Die MSB het wel 'n verlaging van die pH in beide Clipper- en Prisma- wort teweeggebring. Tydens die fermentasie het die Gramnegatiewe bakterietellings verminder, terwyl die MSB-tellings konstant gebly het. 'n Verband is gevind tussen vlugtige komponente geproduseer in die kontrole-fermentasie en fermentasies met gis en Gram-negatiewe bakterieë, gis en Lactobacillus spp. en gis en Weissella spp. Leuconostoc spp. het groter veskille in die samestelling van die gefermenteerde wort teweeg gebring met duidelike verskille tussen Clipper en Prisma. Die teenwoordigheid van Lactococcus spp. het nie groot verskille in die samestelling van die gefermenteerde wort getoon nie. Op die laaste dag van die fermentasies was die vlakke van vier uit die vyfbelangrikste vlugtige aroma komponente wat in bier voorkom in die kontrole fermentasies in aanvaarbare konsentrasies teenwoordig. Die Gramnegatiewe bakterieë het geen beduidende invloed gehad op die vlugtige aroma komponente wat deur die gis geproduseer is nie, terwyl die MSB 'n besliste effek in die aroma-samestelling van beide die kultivars gehad het. Die komponente met die hoogste konsentrasies was, isoamiel-alkohol, asynsuur en asetoin. Asynsuur was in al die fermentasies in die hoogste konsentrasie teenwoordig.

Thesis (MSc)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: The presence and growth of lactic acid bacteria (LAB) in wine and their influence on wine quality has received much attention in recent years. Lactic acid bacteria are responsible for conducting malolactic fermentation (MLF) in wine. The benefits associated with malolactic fermentation in terms of deacidification of wine and the contribution to wine flavour and complexity have also recently been the topic of research. It is impossible to describe malolactic fermentation as distinctly desirable or undesirable in terms of its influence on the final quality of wine. The benefits and disadvantages are dependent upon viticultural region, grape variety, wine composition, winemaking techniques and the style and objectives of the winemaker. Brandy production is a multi-stage process in which base wine production, distillation technique and wood maturation all have a large influence on the final chemical profile and organoleptic quality of the brandy. The volatile composition of the base wine, which basically undergoes a concentration process during the subsequent double distillation phase, is critical in determining the aroma and flavour quality of the final brandy product. Thus, the brandy is only as good as the base wine it is distilled from. The aims of this study were to determine the effect of lactic acid bacteria and spontaneous malolactic fermentation on the quality of brandy base wine and the resulting distillate, and to determine which LAB species had been responsible for the occurrence of spontaneous MLF. This study showed that LAB are present at high numbers and are able to conduct spontaneous MLF of brandy base wines. It was shown that the incidence of spontaneous MLF varied from year to year. In 1998, 50% of the commercially produced base wines had undergone partial MLF prior to distillation. In 1999 and 2000 respectively, 34% and 45% of the commercial base wines had undergone partial MLF prior to distillation. The occurrence of spontaneous MLF had an influence on the chemical composition and the sensory quality of the base wine and distillate. There was an increase in the concentrations of ethyl lactate, acetic acid and diethyl succinate in samples that had undergone MLF. There was also a decrease in the concentrations of esters, such as iso-amyl acetate, ethyl acetate, ethyl caproate, hexyl acetate and 2-phenethyl acetate in these same samples. Sensory evaluation of the base wines and distillates demonstrated that samples that had undergone MLF differed significantly from samples that had not undergone MLF. It was also shown that distillates that had not undergone MLF had a slightly better aroma profile than those that had. Sweet aromas, like chocolate and caramel, as well as negative aromas, like chemical or solvent, were more prominent in brandy distillates that had undergone MLF. Herbaceous and fruity aromas were more intense in distillates not having undergone MLF. Fifty-four strains, all Gram-positive and catalase negative, were isolated at different stages of brandy production. Seven strains were isolated from the grape juice, 15 strains were isolated from the base wine, 20 strains were isolated during MLF and 12 strains were isolated from the base wine after MLF had been completed. Based on C02 production from glucose and gluconate, 17 strains were classified as facultatively heterofermentative and 37 strains as obligately heterofermentative. Fifteen of the 37 obligately heterofermentative strains were rod-shaped and were regarded as lactobacilli. The remaining 22 strains were oval or cocci-bacilli shaped. The isolates were identified to species level by using numerical analysis of the total soluble cell protein patterns, 16S rRNAsequencing and polymerase chain reaction (PCR) with species-specific primers. The facultative heterofermentative lactobacilli were identified as Lactobacillus paracasei and Lactobacillus p/antarum. The fifteen obligately heterofermentative lactobacilli were identified as members of the species Lactobacillus brevis, Lactobacillus verrniforme, Lactobacillus buchneri and Lactobacillus hi/gardii. The 22 obligate heterofermentative isolates, with a coccoid morphology, could be grouped into two clusters and were identified as Oenococcus oeni. O. oeni was the species responsible for the occurrence of spontaneous MLF in most of the commercial base wines. Lb. brevis, Lb. hi/gardii and Lb. paracasei were also isolated from commercial base wines that had undergone spontaneous MLF. In nine out of 14 experimental base wine samples that had undergone spontaneous MLF, O. oeni was again the predominant species. Lb. brevis, Lb. hi/gardii and Lb. paracasei were identified in the remaining experimental base wine samples. This is the first report of the presence of Lb. perecese! and Lb. vermiforme in brandy base wine. It was shown that the occurrence of spontaneous MLF had a negative effect on the quality of brandy base wine, but that was shown to be due to the different species and strains performing MLF. In the non-preferred distillate samples, Lactobacillus spp. had performed MLF or had developed after or during MLF. / AFRIKAANSE OPSOMMING: Die teenwoordigheid en die vermoë van melksuurbakterieë (MSB) om in wyn te groei, is 'n onderwerp wat al heelwat nagevors is. Melksuurbakterieë is verantwoordelik vir die uitvoering van appelmelksuurgisting (AMG) in wyn. Die voordele verbonde aan appelmelksuurgisting, ten opsigte van die verlaging van die totale suurinhoud en die bydrae tot die verbeterde geur en kompleksiteit van die wyn, is ook al goed bestudeer. Wat die invloed op die finale wynkwaliteit betref, is dit byna onmoontlik om AMG as uitsluitlik gewens óf ongewens te beskou. Die voordele en nadele van AMG is afhanklik van verskeie faktore, nl. wingerdkundige streek, druifkultivar, wynsamestelling, wynmaakpraktyke, asook die styl en doelwitte van die wynmaker. Die produksie van brandewyn is 'n multistapproses waarin die bereidingsmetode van die basiswyn, die distillasietegniek en houtveroudering 'n groot invloed op die finale kwaliteit en chemiese samestelling van die brandewyn het. Die vlugtige verbindings van die basiswyn, wat tydens die dubbele distillasieproses gekonsentreer word, is van wesenlike belang in die bepaling van die aroma en geur van die finale brandewynproduk. Brandewyn is dus inderdaad net so goed soos die basiswyn waarvan dit gestook is. Die doelwitte van hierdie studie was om te bepaal wat die invloed van MSB en die voorkoms van spontane AMG op die kwaliteit van die basiswyn en die distillaat is, asook om die MSB wat vir die voorkoms van spontane AMG verantwoordelik was, te identifiseer. Hierdie studie het bewys dat MSB in hoë getalle teenwoordig was en dat dit in staat is om die spontane AMG van basiswyne uit te voer. Daar is bewys dat die voorkoms van spontaneAMG moontlik van jaar tot jaar kan verskil. In 1998 het 50%, in 1999 het 34% en in 2000 45% van die kommersieel-geproduseerde basiswyn gedeeltelike AMG spontaan voor distillasie ondergaan. Daar is ook gevind dat spontane AMG 'n invloed op die chemiese samestelling en sensoriese kwaliteit van die basiswyn en die distillaat gehad het. Daar was 'n toename in die konsentrasies van etiellaktaat, asynsuur en diëtielsuksinaat in monsters wat spontane AMG ondergaan het. In dieselfde monsters was daar ook 'n afname in die konsentrasies van iso-amielasetaat, etielasetaat, etielkaproaat, heksielasetaat en 2-fenielasetaat. Sensoriese evaluering van die basiswyne en distillate het getoon dat daar betekenisvolle verskille was tussen die monsters wat AMG ondergaan het en dié wat nie AMG ondergaan het nie. Daar is bewys dat die distillate wat nie AMG ondergaan het nie, 'n beter aromaprofiel gehad het as dié wat AMG ondergaan het. Soet geure, soos sjokolade en karamel, en negatiewe geure, soos "chemies" en "oplosmiddel", was prominent in distillate wat AMG ondergaan het. Kruidagtige en vrugtige geure was meer intensief in distillate wat nie AMG ondergaan het nie. Vier-en-vyftig bakteriese rasse, almal Gram-positief en katalase-negatief, is gedurende die verskillende stadia van brandewynproduksie geïsoleer. Sewe rasse is uit druiwesap, 15 rasse gedurende die alkoholiese fermentasie, 20 rasse gedurende AMG en 12 rasse na voltooiing van AMG geïsoleer. Op die basis van koolstofdioksied (C02)-produksie vanaf glukose en glukonaat is 17 rasse as fakultatief heterofermentatief en 37 rasse as obligaat heterofermentatief geklassifiseer. Vyftien van die 37 obligaat-heterofermentatiewe rasse was staafvormig en is as lactobacilli geïdentifiseer. Die oorblywende 22 het ovaal of kokkus-bacillusvormige selmorfologie getoon. Identifikasie tot op spesievlak is gedoen deur van numeriese analise van die totale oplosbare selproteïenprofiele, 16S-rRNAvolgordebepalings en spesie-spesifieke inleiers vir die polimerasekettingreaksie (PKR) gebruik te maak. Die fakultatief-heterofermentatiewe rasse is as Lactobacillus paracasei en Lactobacillus p/antarum geklassifiseer. Die 15 obligaat heterofermentatiewe stafies is as Lactobacillus brevis, Lactobacillus buchneri, Lactobacillus hi/gardii en Lactobacillus vermiforme geïdentifiseer. Die 22 ovaal, obligaat heterofermentatiewe isolate kon in twee groepe ingedeel word en is as Oenococcus oeni geïdentifiseer. Daar is bevind dat O. oeni-isolate vir die voorkoms van spontane AMG in die meeste van die kommersiêle basiswyne verantwoordelik was. Lb. brevis, Lb. hi/gardii en Lb. paracasei is ook uit kommersiêle basiswyne wat spontane AMG ondergaan het, geïsoleer. In nege uit 14 van die eksperimentele basiswyne wat spontane AMG ondergaan het, was O. oeni die dominante spesie. In die oorblywende eksperimentele wyne is Lb. brevis, Lb. hi/gardii en Lb. paracasei aangetref. Hierdie is die eerste vermelding van die teenwoordigheid van Lb. paracasei and Lb. vermiforrne in brandewynbasiswyn. Daar is gevind dat die voorkoms van spontane AMG "n negatiewe invloed op brandewynkwaliteit het, maar dit is as gevolg van die verskeidenheid van MSB-spesies en rasse wat voorkom. In die distillate wat deur die proepaneel afgekeur is, het Lactobacillus spesies die AMG deurgevoer, of het dit tydens of na AMG ontwikkel.

Made available in DSpace on 2015-04-17T14:49:37Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 735178 bytes, checksum: 968afb8a739940705597ba86834ec161 (MD5) Previous issue date: 2014-03-10 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Lactic acid bacteria can produce bacteriocins and have been explored for applications as natural preservatives in foods. Bacteriocins are peptides and proteins with antimicrobial activity and can inhibit the growth of pathogenic bacteria such as Listeria monocytogenes and other spoilage microorganisms. L. monocytogenes can be present in many types of food due to its ability to survive in a wide temperature range, and causes listeriosis by ingestion of contaminated food. This study aimed at the isolation and identification of lactic acid bacteria (LAB) with bacteriocinogenic potential, the characterization of the cell-free supernatants (CFS) regarding: the antimicrobial activity; the spectrum of action; thermal stability and at different pHs; resistance to chemicals and NaCl concentrations; the mode of action of the bacteriocins produced; the adsorption capacity to the target cells in different temperatures, pH and concentrations of chemicals and NaCl; perform the molecular identification of the LAB. Three strains (LS1, LS2 and LS3) bacteriocinogenic of raw goat's milk with anti-listeria activity were isolated. In particular Lactococcus lactis (LS2), which produced bacteriostatic, active bacteriocin at low pH and 4 ° C to 80 ° C, which can be an alternative for the control of Listeria in fermented dairy products. / Bactérias láticas podem produzir bacteriocinas e têm sido exploradas em aplicações como conservadores naturais nos alimentos. Bacteriocinas são peptídeos e proteínas com atividade antimicrobiana e podem inibir a multiplicação de bactérias patogênicas como Listeria monocytogenes e micro-organismos deterioradores. L. monocytogenes pode estar presente em diversos tipos de alimentos, devido à sua capacidade de sobreviver em ampla faixa de temperatura e causar a listeriose através da ingestão de alimentos contaminados. Este estudo objetivou o isolamento e identificação de bactérias láticas (BAL) com potencial anti-Listeria de leite de cabra cru, a caracterização dos sobrenadantes livres de células (SLC) quanto: à atividade antimicrobiana; ao espectro de ação; à estabilidade térmica e em diferentes valores de pH; à resistência a agentes químicos e a diferentes concentrações de NaCl; ao modo de ação; à capacidade de adsorção à listeria em diferentes condições de temperatura, pH e na presença de agentes químicos. Também visou realizar a identificação molecular dos isolados a fim de aplicar as BAL ou as bacteriocinas por elas produzidas como estratégia de bioconservação de alimentos. Foram isoladas três culturas (LS1, LS2 e LS3) bacteriocinogênicas de leite de cabra cru com atividade anti-listeria. Em particular Lactococcus lactis (LS2), que produziu bacteriocina bacteriostática, ativa em pH baixo e em temperatura de 4 °C a 80 °C, que pode ser uma alternativa para o controle de listeria em produtos lácteos fermentados.

De nombreux problèmes ont été identifiés lors des tentatives d’incorporation de protéines végétales dans nos aliments. En particulier, les faux goûts, le goût et la texture ont été mis en évidence comme de véritables obstacles à l’acceptabilité des produits végétaux par les consommateurs. Le consommateur lui-même est aussi un déterminant important en ce qui concerne le terme « acceptabilité ». Donc, dans le but de développer un nouveau produit fermenté à base de protéines de pois deux volets ont été étudié : le produit et le consommateur. Afin de comprendre la physico-chimie et l’acceptabilité de produits fermentés à base de protéines de pois, plusieurs facteurs ont été étudiés dans des étapes successives tels que la culture, les allégations positives sur la santé et l’environnement, les cocktails de souches lactiques et les procédés de préparation. Dès les premiers tests sensoriels, il était clair qu’il ne serait pas facile de convaincre les consommateurs de consommer des produits fermentés à base de pois : les consommateurs français n’acceptent pas les produits même à une faible concentration de pois (10 %). Ni la familiarité pour un produit proche de nos produits étudiés, ni l’encouragement des consommateurs à accepter ce type d’aliment en passant des messages positifs sur les protéines végétales n’étaient assez efficaces. Ainsi, une deuxième série d’études a été réalisée afin d’optimiser les propriétés rhéologiques et organoleptiques de ces produits. La meilleure combinaison, 1- cocktail bactérien (S. thermophilus + Lb. bulgaricus) 2- matière première (globuline de pois isolée dans notre laboratoire) 3- paramètres de préparation (mélange des deux laits avant le traitement thermique à 90 °C) a été sélectionnée afin d’optimiser les produits fermentés en ce qui concerne l’acidité, la fermeté, les profils volatils et peptidiques. Enfin, du point de vue sensoriel, une légère amélioration de l’acceptabilité a été remarquée. 20 % de protéines de pois a donné un produit accepté par la plupart des consommateurs, et 40 % de protéines de pois a été évaluée positivement par certains consommateurs et négativement par d'autres. / Many problems have been identified following the attempts to incorporate vegetal proteins in our food. In particular, off-flavor, taste or texture have been highlighted as real barriers to the acceptability of plant products by consumers. The consumer himself is also an important determinant regarding the term "acceptability." So, in order to develop a new fermented product based on pea, two issues were studied: the product and the consumer. To understand the physico-chemical properties and the acceptability of pea protein-based fermented products, several factors have been investigated in successive stages such as culture, positive health and environmental claims, lactic acid bacteria strains and preparation processes. From the first sensory tests, it was clear that it will not be easy to convince consumers to buy the pea-based fermented product: French consumers did not accept products even in a lower concentration of pea (10%). Neither the familiarity to close products nor encouraging consumers to accept this type of food by transmitting positive messages about vegetal protein were efficient enough. Thus, a second series of studies was carried out in order to optimize the rheologic and organoleptic properties of these products. Best combination of 1- starter culture (S. thermophilus + Lb. bulgaricus) 2- raw material (pea globulin isolated in our laboratory) 3- preparation parameters (mixing both milk before heat treatment at 90 ° C) were selected to optimize the fermented products in terms of volatile compounds and peptide profiles, acidity and firmness. Finally, from the sensory point of view, a slight improvement in the acceptability was noticed. 20% of pea protein gave a product accepted by most of the consumers, and 40% of pea protein was assessed positively by some consumers and negatively by others

Resumo: O presente trabalho apresenta um estudo de produção de ácido lático a partir de Lactobacillus rhamnosus imobilizado por aprisionamento em alginato de cálcio, com a utilização de soro de queijo como fonte de carbono alternativa à glicose encontrada tradicionalmente no meio MRS para bactérias láticas. A imobilização foi efetiva com 2 % de alginato, tendo eficiência de 99,99 %, e taxa de saída de células de 0,25 %, utilizando MRS como meio de cultivo. Estudou-se também o uso de fontes alternativas de nitrogênio como água de maceração de milho, Pro-Floo®, autolisado de levedura e sulfato de amônio. Os melhores resultados de produção e rendimento foram obtidos a partir da utilização de soro de queijo com as fontes de nitrogênio do MRS (extrato de levedura, peptona e extrato de carne), chegando a um rendimento (Yp/s) de 0,83, com produtividade de 0,90 g.L-1.h-1, seguido do cultivo com água de maceração de milho (AMM) e Pro-Floo®, com Yp/s de 0,72 e 0,57 respectivamente. No cultivo com água de maceração de milho a produção de ácido lático atingiu 119,04 g/L em 48 h. Com células livres, o melhor resultado de rendimento foi 0,73 quando de utilizou água de maceração de milho, com produtividade de 2,25 g.L-1.h-1 e produção de ácido lático de 107,89 g/L. Foram realizados dois ensaios utilizando uma modificação no alginato com ácido palmítico, para melhoria na viabilidade das células imobilizadas. Houve melhora no Yp/s quando se utilizou a alginato modificado com ácido palmítico passando de 0,72 para 0,79 no cultivo com AMM e de 0,57 para 0,67 quando se utilizou Pro-Floo®. Outro cultivo foi conduzido em reator de leito empacotado com imobilização em alginato recoberto de polietilenoimina, utilizando meio MRS. No reator pode-se observar a produção contínua de ácido lático até 72 horas com rendimento de 0,88 em 4 horas de cultivo atingindo uma concentração de 11,79 g/L de ácido lático. / Abstract: This work presents a study of lactic acid production by Lactobacillus rhamnosus immobilized by entrapment technique in calcium alginate, using whey as alternative carbon source, avoiding glucose use in the traditional MRS medium for lactic acid bacteria. Cell immobilization was effective using 2% of alginate, with efficiency of 99.99% and rate of cell release of 0.25 %. Alternative nitrogen sources like corn steep liquor (CSL), Pro-Floo®, autolyzed yeast and ammonium sulfate was also studied. The higher values of production and yield (Yp/s) were obtained in the cultivation with whey and the MRS nitrogen sources (yeast extract, peptone and meat extract), reaching an Yp/s of 0.83, and productivity of 0.90 g.L-1.h-1, followed by the cultivation with corn steep liquor and Pro-Floo®, with Yp/s of 0.72 and 0.57 respectively. With corn steep liquor, the lactic acid production reached 119.04 g/L in 48 h. In the culture with free cells the yield was 0.73 with corn steep liquor in 48 h, the productivity was 2.25 g.L-1.h-1 and production 107.89 g/L. Two experiments were done with a palmitolation of alginate to improve of immobilized cell viability. Increase in yield was obtained when palmitolation was employed; the yield increased from 0.72 to 0.79 in the cultivation using corn steep liquor, and from 0.57 to 0.67 when Pro-Floo® was used an alternative nitrogen source. Another experiment was realized in a packed-bed continuous reactor, with polyethyleneimine coated alginate beads, using MRS as culture medium. It was observed continuous lactic acid production until 72 h, with a yield of 0.88 in 4 hours reaching a lactic acid concentration of 11.79 g/L. / Orientador: Jonas Contiero / Coorientador: Cristina Jacques Bolner de Lima / Banca: Rubens Monti / Banca: Eliana Setsuko Kamimura / Mestre