Browsing by Subject "elintarviketieteet"

Dynamics of raw milk associated bacteria during cold storage of raw milk and their antibiotic resistance was reviewed, with focus on psychrotrophic bacteria. This study aimed to investigate the significance of cold storage of raw milk on antibiotic-resistant bacterial population and analyse the antibiotic resistance of the Gram-negative antibiotic-resistant psychrotrophic bacteria isolated from the cold-stored raw milk samples. Twenty-four raw milk samples, six at a time, were obtained from lorries that collected milk from Finnish farms and were stored at 4°C/4 d, 6°C/3 d and 6°C/4 d. Antibiotics representing four classes of antibiotics (gentamicin, ceftazidime, levofloxacin and trimethoprim-sulfamethoxazole) were used to determine the antibiotic resistance of mesophilic and psychrotrophic bacteria during the storage period. A representative number of antibiotic-resistant Gram-negative isolates retrieved from the cold-stored raw milk samples were identified by the phenotypic API 20 NE system and a few isolates by the 16S rDNA gene sequencing. Some of the isolates were further evaluated for their antibiotic resistance by the ATB PSE 5 and HiComb system. The initial average mesophilic counts were found below 105 CFU/mL, suggesting that the raw milk samples were of good quality. However, the mesophilic and psychrotrophic population increased when stored at 4°C/4 d, 6°C/3 d and 6°C/4 d. Gentamicin- and levofloxacin-resistant bacteria increased moderately (P < 0.05) while there was a considerable rise (P < 0.05) of ceftazidime- and trimethoprim-sulfamethoxazole-resistant population during the cold storage. Of the 50.9 % (28) of resistant isolates (total 55) identified by API 20 NE, the majority were Sphingomonas paucimobilis (8), Pseudomonas putida (5), Sphingobacterium spiritivorum (3) and Acinetobacter baumanii (2). The analysis by ATB PSE 5 system suggested that 57.1% of the isolates (total 49) were multiresistant. This study showed that the dairy environment harbours multidrug-resistant Gramnegative psychrotrophic bacteria and the cold chain of raw milk storage amplifies the antibioticresistant psychrotrophic bacterial population.

The properties and evaluation methods of viili, the actions and interactions of viili starters in milk and bacteriophages of the viili starters were reviewed. The aim of the experimental study was to explore whether it was possible to make viili with single strain starters and combine them just before adding the starter to the milk. A new, second viili starter was made from the new strains. The success of the new starters was evaluated by sensory evaluation and by analysing the texture and chemical properties of viili. The starter strains were cultivated in a bioreactor, concentrated by a centrifuge and frozen at –75 °C. The starter strains were combined approx. 1 day before the viili production. The sensory evaluation of the viili was performed by groups of 3 to 6 persons. The texture (consistency, firmness and cohesiveness) of the viili and chemical analysis were made. The results of the sensory analysis were analysed statistically and new strain combinations were formulated based results. The viilis made by the traditional viili starter strains were evaluated by the triangle test (n = 10–11) and the second viili starter was evaluated by descriptive analysis (n = 8). The texture measurements and chemical analyses were also performed. The viili produced by the second starter was infected by the factory phage samples and the pH was measured. After infecting the viili with phage samples, the viili produced by second starter was acidified to pH 4.5 from 0 to 10 hours later compared to the viili without the phage sample. The viili produced by traditional starter did not acidify when the phage was added. The aroma producers did not grow properly in viili when the starter was made by single strains. The viilis made by the present viili starter strains were not distinguished by the triangle test which meant that the starters are possible to make from single strains. The viilis produced by the second viili starter differed from the viili made by traditional starter by appearance and texture characteristics. There was no difference in taste characteristics between the traditional and new starter.