Browsing by Author "Reijonen, Mirva"

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Adenovirusvektorit syöpähoidossa
(2012) Reijonen, Mirva
Kemian tekniikan korkeakoulu | Bachelor's thesis
Occurrence of Alicyclobacillus bacteria in beverage ingredients and control with plant extracts
(2016-04-12) Reijonen, Mirva
Kemian tekniikan korkeakoulu | Master's thesis
Consumer demands of more natural and healthy products have directed the beverage industry to minimise the usage of synthetic additives and thermal processing and to increase the content of real juices and new functional ingredients in beverages. This trend can be expected to increase product spoilage rate unless new preservatives and methods are used. Thermoacidophilic, endospore-forming bacteria belonging to the genus Alicyclobacillus are a spoilage threat to beverage industry due their ability to survive through pasteurization process and cause smoky and medicinal off-flavours and tastes in ambient stored fruit juices and juice drinks. The aim of this master’s thesis was to find a new potential plant based antimicrobial agent against Alicyclobacillus acidoterrestris to inhibit the outgrowth of Alicyclobacillus spores in fruit juice. 12 phenolic extracts were studied against A. acidoterrestris spores. Statistical modelling was ap-plied for evaluating combined effects between antimicrobial plant extracts, recipe factors and storage temperature. Fluorescence staining together with microscopy or fluorometry was used in mode of action studies. The occurrence of alicyclobacilli in juices and beverage ingredients was also studied by using the International federation of fruit juice producer standard method No 12. In addition, a new differential growth medium was evaluated for detecting guaiacol producing spoilage strains. Selective medium could not reliably separate the guaiacol producing strains from non-guaiacol producing strains. Bacteria isolated from ingredients and beverages were identified to belong to Alicyclobacillus acidocaldarius, Alicyclobacillus acidoterrestris and Alicyclobacillus sendaiensis species. A guaiacol-producing A. acidoterrestris strain was found in the sweetener, indicating that that sweeteners could act as possible carriers of Alicyclobacillus into products. During the inspection process of beverage ingredients it was suspected that current methods may not be sufficient for detecting alicyclobacilli positive samples reliably. Instructions of how to pretreat different ingredient groups would be needed. Since it is possible that Alicyclobacillus spores may pass the inspection process unnoticed, the control methods during the beverage production and in the final product are urgently called for. Both bitter hop residue and birch leaf extract proved to be effective for inhibiting the growth of A. acidoterrestris in apple juice and trypticase soy broth in 100 mg/l – 500 mg/l concentrations at 45 °C for seven days. Although effective, the organoleptic properties may prevent the usage of the bitter hops extract since the odour is characteristic to hops. Around 130 mg/l of birch leaf extract was found to be effective for inhibiting the growth of A. acidoterrestris E1733 for 30 days in apple juice at 32-42°C. In addition, antimicrobial activity of birch leaves were found to be insensitive to variations of growth conditions and storing in the freezer for 24 months. However, since birch leaves have only food supplementary status, the EU novel food status for the extract may apply. Thus, the chemical composition of birch leaf extract and possible toxicological and antinutritive effects should be next evaluated.