Browsing by Subject "mikrobiologinen"

Sort by: Order: Results:

Now showing items 1-2 of 2
  • Lehtonen, Heidi (Helsingin yliopisto, 2018)
    Vitamin B12 is a water-soluble molecule with a complex structure. In the active form to humans B12 has to have 5,6-dimethylbenzimidazole as a lower ligand. B12 is synthesised only by certain bacteria and natural sources in the human diet are restricted mainly to foods of animal origin. The exact structure of B12 and vitamin activity, the supply from different diets and absorption in the body were discussed in the literature part of this thesis. Also B12 determination methods and B12 levels in foods of animal origin were discussed. Usually vitamin B12 contents in foods have been obtained with a microbiological method (MBA). Currently it has been of concern that MBA may overestimate results because test organism in the MBA method reacts also to compounds similar to B12. The aim of the experimental part of this thesis was to investigate content of vitamin B12 in foods of animal origin. Further, two determination methods, MBA and ultra-high performance liquid chromatography (UHPLC), were compared with each other. The aim was also to examine the effect of different extraction methods on the yield of vitamin B12. The samples chosen to this study were beef, pork meat, chicken meat, beef and pork liver, rainbow trout, Baltic herring, egg, skim milk, yogurt and Edam and Emmental cheese. Also two insects, cricket and mealworm, were chosen to this study. The extraction tests showed that it was not possible to use one extraction method to all samples. Extraction with pepsin improved the yield of vitamin B12 in rainbow trout, egg yolk, beef and milk whereas pancreatin improved the yield in cheeses and Baltic herring. As expected B12 content was the highest in livers of beef and pork. Also beef, Baltic herring and cheeses had high concentrations of B12. Chicken meat contained the lowest concentration of B12. Comparison between the MBA and the UHPLC method proved that with MBA the vitamin B12 concentrations were much higher than with UHPLC. B12 concentrations with UHPLC were 7–64% lower in meat and fish samples. Milk products and egg yolk had 20–67% lower B12 concentrations with UHPLC and insects had 71–81% lower concentrations. MBA method is sensitive and has low reagent costs but in the future UHPLC method should be chosen for B12 analysis because it can separate the active B12 form from the inactive forms.
  • Männistö, Irina (Helsingin yliopisto, 2018)
    High pressure processing (HPP) is a cold pasteurisation method, in which the products are generally processed at 300–800 MPa for a few minutes. Processing generally happens below 45 °C, so the treatment preserves the nutritional and sensory properties of the products. The literature review discussed high pressure processing as a food processing method and studied its effects on food. The focus was on the effects on microbes, enzymes, structure and chemical properties of dairy and vegetable products. The aim of the experimental research was to study the effects of high pressure processing on the microbiological and sensorial shelf life of blueberry puree, raw milk and roasted cheese. The objective was also to examine the shelf life of the products that can be achieved when using high pressure processing. Blueberry puree was analyzed for microbiological quality, pH, color and sensory properties during storage of 2 months. Raw milk and roasted cheese was analyzed for microbiological and sensory quality. Roasted cheese was also analyzed for total solids content. The raw milk was stored for 1 month and the roasted cheese for 3 months. The microbiological quality of high pressure processed raw milk remained good about two weeks. The sensory quality remained good for about 9 days. After three weeks, the high pressure processed raw milk reached the same microbiological level than reference sample on day 1. No difference occurred in color and pH between the high pressure processed blueberry puree samples and the reference samples during the storage. High pressure processed blueberry puree remained microbiologically high quality 8 weeks, while the reference puree was good only for 2 weeks. All blueberry purees remained sensorically good for 8 weeks. The shelf life of the roasted cheese after high pressure processing was approximately 1 month: reference samples remained good for 2 weeks. Mini roasted cheese remained microbiologically good for up to 3 months while the sensory quality declined after 2 months. High pressure processing significantly increases the microbiological shelf life of the product. Enterobacteriaceae, yeasts and molds are effectively inactivated by high pressure processing. Pseudomonas bacteria, which can produce pressure resistant enzymes like lipases, are more resistant to high pressure.