Masters Degrees (Food Science)

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Browsing Masters Degrees (Food Science) by Subject "Alicyclobacillus"

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    Evaluation of the distribution and accumulation of species of Alicyclobacillus in the fruit concentrate processing environment
    (Stellenbosch : University of Stellenbosch, 2011-03) Steyn, Catharina Elizabeth; Witthuhn, R. C.; Cameron, M.; University of Stellenbosch. Faculty of AgriSciences. Dept. of Food Science.
    ENGLISH ABSTRACT: Alicyclobacillus species are thermo-acidophilic bacteria that produce highly resistant endospores able to survive the processing temperatures of fruit concentrate manufacturing, including evaporation and conventional pasteurisation (86 ° - 96 °C for ± 2 min). Alicyclobacillus endospores retain their viability in juice concentrates which, under favourable conditions, could germinate and multiply to numbers high enough to cause spoilage and product deterioration through the production of chemical taint compounds. This thesis reports on the distribution of Alicyclobacillus in the fruit concentrate processing environment and the effect of current manufacturing practices on the accumulation of Alicyclobacillus in fruit concentrates. These practices include the recirculation (recycling) of flume water as a means of water conservation, as well as continuous process running times when facilities operate at full capacity. This thesis also reports on the effect of fruit variety and skin type on the occurrence of Alicyclobacillus in fruit concentrates. Alicyclobacillus was monitored at nine processing stages of fruit concentrate manufacturing during the functioning of either a recirculating or a one-pass (not recirculated) flume water system. Significantly higher Alicyclobacillus levels were recovered in fruit mash, single strength juice, concentrate and the final pasteurised product (± 30 °Brix) during the functioning of a re circulating flume system, compared to when a one-pass flume system was functional (P < 0.05). Irrespective of the flume system, high Alicyclobacillus levels were recovered from the concentrate and condensate water (a by-product of juice concentration) from the evaporator, which makes this a point of concern during concentrate manufacturing. Manufacturing practices such as the recirculation of flume water and the recovery of condensate water for fruit washing purposes pose a potential risk of Alicyclobacillus contamination and accumulation in fruit concentrates and the processing environment. The effect of continuous process running times on Alicyclobacillus was monitored in a facility that was operating at full capacity. Sampling occurred every 12 h at four processing stages, during a processing tempo of 1.8 - 2.0 t h-1 for 108 h. Vegetative cells increased significantly (P < 0.05) in single strength juice and condensate water after 84 h of processing, with 3.15 and 3.85 log10 cfu mL-1 recovered, respectively. Similar accumulation patterns of vegetative cells were observed in concentrate and the final pasteurised product. Endospores in single strength juice, concentrate and the final product were also the highest after 84 h of processing with 1.32, 1.59 and 1.64 log10 cfu mL-1, respectively. When fruit concentrate manufacturing facilities process at full capacity, a restriction in the continuous process running time to under 84 h in between CIP procedures, along with good manufacturing practices, can minimise Alicyclobacillus accumulation in fruit concentrates. The effect of fruit skin type, specifically hairy-skinned stone fruits (peach and apricot) and smooth-skinned pome fruits (apple and pear) on the occurrence of Alicyclobacillus in concentrates were examined. Apple concentrate samples had the highest occurrence (average %) of vegetative Alicyclobacillus cells (50%), followed by apricot (40%), peach (15%) and pear (10%) concentrates. The occurrence of Alicyclobacillus endospores in fruit concentrate samples were also the highest in apple (50%), followed by pear (25%), apricot (20%), and peach (10%) concentrates. The occurrence of Alicyclobacillus vegetative cells and endospores did not differ significantly (P > 0.05) between concentrates from hairy-skin and smooth-skin fruit varieties. Thus it was concluded that fruit washing steps prior to processing was more critical for the control of Alicyclobacillus than the type of fruit skin being processed.
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    Growth and guaiacol production of species of Alicyclobacillus isolated from the South African fruit processing environment
    (Stellenbosch : University of Stellenbosch, 2009-12) Smit, Yvette; Witthuhn, R. C.; Venter, P.; Le Roux, Y.; University of Stellenbosch. Faculty of Agrisciences. Dept. of Food Science.
    ENGLISH ABSTRACT: Bacteria belonging to the genus Alicyclobacillus are thermo-acidophilic spore-formers that are able to spoil acidic food and beverage products through the production of guaiacol and other taint compounds, which causes a medicinal off-flavour and/or odour in the products. This thesis reports on the comparison of methods used for the isolation of species of Alicyclobacillus, as well as the growth behaviour and guaiacol production of different strains isolated from the South African fruit processing environment. Two methods for guaiacol detection were also evaluated and compared. Three isolation methods frequently used by South African fruit processors were compared with regards to their ability to isolate a strain of A. acidoterrestris from diluted peach juice concentrate. Method 1, the International Federation of Fruit Juice Producers (IFU) Method No. 12, makes use of spread plating onto Bacillus acidoterrestris (BAT) agar plates; Method 2 involves pour plating using acidified potato dextrose agar (PDA); and Method 3 makes use of membrane filtration and incubation of the membrane on K agar. The IFU Method No. 12 was the most effective method for the isolation of A. acidoterrestris, with a recovery of 75.97%. These results support the use of the IFU Method No. 12 as a standard international method for the isolation and detection of species of Alicyclobacillus. Seven strains of Alicyclobacillus, including the type strains A. acidoterrestris DSM 3922T and A. acidocaldarius DSM 446T and five strains isolated from a South African fruit processing plant, A. acidoterrestris FB2, FB14, FB32, FB38 and A. acidocaldarius FB19, were analysed based on their growth characteristics and guaiacol production under optimum conditions. Strains were inoculated into BAT medium at pH 4.00, supplemented with 100 mg.L-1 vanillin, and incubated at 45°C for 7 d. All the strains had similar growth patterns, with cell concentrations increasing rapidly from 0-24 h, followed by a stabilisation around maximum cell concentrations of 105-107 cfu.mL-1. Cell concentrations after heat shock, measured as an indication of spore formation, increased to maximum values of 105-107 cfu.mL-1, indicating an increase in spores as the cell density and competition for resources increased. All the strains were able to produce guaiacol in detectable concentrations [as measured by the peroxidase enzyme colourimetric assay (PECA)], and, therefore, possess the potential to cause product spoilage. Bacteria belonging to the genus Alicyclobacillus are thermo-acidophilic spore-formers that are able to spoil acidic food and beverage products through the production of guaiacol and other taint compounds, which causes a medicinal off-flavour and/or odour in the products. This thesis reports on the comparison of methods used for the isolation of species of Alicyclobacillus, as well as the growth behaviour and guaiacol production of different strains isolated from the South African fruit processing environment. Two methods for guaiacol detection were also evaluated and compared. Three isolation methods frequently used by South African fruit processors were compared with regards to their ability to isolate a strain of A. acidoterrestris from diluted peach juice concentrate. Method 1, the International Federation of Fruit Juice Producers (IFU) Method No. 12, makes use of spread plating onto Bacillus acidoterrestris (BAT) agar plates; Method 2 involves pour plating using acidified potato dextrose agar (PDA); and Method 3 makes use of membrane filtration and incubation of the membrane on K agar. The IFU Method No. 12 was the most effective method for the isolation of A. acidoterrestris, with a recovery of 75.97%. These results support the use of the IFU Method No. 12 as a standard international method for the isolation and detection of species of Alicyclobacillus. Seven strains of Alicyclobacillus, including the type strains A. acidoterrestris DSM 3922T and A. acidocaldarius DSM 446T and five strains isolated from a South African fruit processing plant, A. acidoterrestris FB2, FB14, FB32, FB38 and A. acidocaldarius FB19, were analysed based on their growth characteristics and guaiacol production under optimum conditions. Strains were inoculated into BAT medium at pH 4.00, supplemented with 100 mg.L-1 vanillin, and incubated at 45°C for 7 d. All the strains had similar growth patterns, with cell concentrations increasing rapidly from 0-24 h, followed by a stabilisation around maximum cell concentrations of 105-107 cfu.mL-1. Cell concentrations after heat shock, measured as an indication of spore formation, increased to maximum values of 105-107 cfu.mL-1, indicating an increase in spores as the cell density and competition for resources increased. All the strains were able to produce guaiacol in detectable concentrations [as measured by the peroxidase enzyme colourimetric assay (PECA)], and, therefore, possess the potential to cause product spoilage. iv The influence of temperature on the growth and guaiacol production of the Alicyclobacillus strains was also investigated and two guaiacol detection methods, the PECA and headspace gas-chromatography mass-spectrometry (HS GC-MS), were compared with regards to their ability to detect guaiacol. The strains were incubated at 25°C and 45°C for 6 d and samples analysed every 24 h. Growth of the A. acidoterrestris strains was slower at 25°C, and maximum cell concentrations were lower than at 45°C. A decrease in cell concentrations was observed in the A. acidocaldarius strains at 25°C, as this temperature is below their growth temperature range. All the strains were able to produce guaiacol at 45°C, with guaiacol only being detected once a cell concentration of 104-105 cfu.mL-1 had been reached. The maximum guaiacol concentrations detected at 45°C in the samples containing A. acidoterrestris were significantly higher than those detected in the A. acidocaldarius samples. At 25°C there was a longer lag phase before guaiacol was detected in the A. acidoterrestris samples, while no guaiacol was detected in the samples containing A. acidocaldarius. Because guaiacol is produced at ambient temperatures, cooling of products is recommended to control spoilage by A. acidoterrestris. The sensitivity of the two guaiacol detection methods also differed significantly and, therefore, the PECA is recommended for presence/absence detection of guaiacol, while HS GCMS is recommended where accurate quantification of guaiacol is required. Alicyclobacillus acidoterrestris FB2 was investigated for its ability to grow and produce guaiacol in white grape juice supplemented with vanillin at different concentrations. Alicyclobacillus acidoterrestris FB2 was inoculated into white grape juice concentrate diluted 1:10 with distilled water containing 0-500 mg.L-1 vanillin and incubated at 45°C for 6 d. Similar growth patterns were observed in all the samples, except in the sample containing 500 mg.L-1 vanillin, which had a longer lag phase of growth. Guaiacol concentrations, detected using the PECA, increased as the vanillin concentration increased, with the exception of the sample containing 500 mg.L-1 vanillin, where less guaiacol was detected than in the sample containing 250 mg.L-1 vanillin, due to growth inhibition caused by the higher vanillin concentration. A number of conditions need to be favourable for detectable guaiacol production to occur and it could, therefore, be possible to minimise or prevent guaiacol production by controlling or eliminating some of these factors. Good manufacturing practices should be employed in order to minimise contamination and, therefore, spoilage, by Alicyclobacillus species.