CURRENT STATUS AND FUTURE TRENDS IN MICROBIOLOGICAL METHODOLOGY

W. KNEIFEL^a)
a) Department of Dairy Research & Bacteriology, Agricultural University, Gregor Mendel-Str. 33, A-1180 Vienna, Austria

Review paper
Language: English

ABSTRACT
For quite a long time, the microbiological examination of dairy products has been regarded as an area being dominated mainly by traditional or partly even historical methods. Even today classical methods, e.g. culture techniques, play an important role. However, scientific knowledge about pathogenic and spoilage microorganisms as well as about general food quality has increased considerably and led to a radical change and rearrangement of the microbiological laboratory during the last decade. Thus, today the microbiological examination of foods is based on a broad array of old and new methods which are complementary to each other. Necessarily, the microbiological examination of dairy products is directed towards two main goals: the detection and enumeration of pathogenic and spoilage microorganisms; and the enumeration of typical microorganisms, for instance as a potential measure representing the high quality of a fermented product. In this lecture, a survey is given on various microbiological methods including the following items: modern and classical methods, rapidity and automation, fluorogenic or chromogenic substrates, bioluminiscence and impedance techniques, immunological and molecular-biological methods.

THE STUDY OF THE PRESENCE OF THE BACTERIA Bacillus cereus IN MILK AND DAIRY PRODUCTS

Karmen GODIČ-TORKAR^a)
a) Univ. of Ljubljana, Biotechnical Fac., Zootechnical Dept., Groblje 3, SI-1230 Domžale, Slovenia

Original scientific paper
Language: Slovene

ABSTRACT
The presence of aerobic sporeformer bacteria Bacillus cereus in milk and dairy products was established. For strain isolation and identification we used PEMBA selective medium, MPN technique, the microscope examination for the presence of spores and lipid globules, determination of hemolytic activity and mobility in solid medium and degradation of glucose in anaerobic conditions. From December to June 141 samples of pasteurized milk with 1.6, 3.2 and 3.6% milk fat, pasteurized sweet cream, curd, pudding, ice cream, milk powder, sterile milk with 1.6 and 3.2% milk fat and sterile cream were analysed. Bacillus cereus was present in 46.8% of samples and in 38.3% of samples pasteurized again. The milk powder was contaminated 100%, there were 64.0% positive samples of pasteurized sweet cream, 62.5% positive samples of curd and ice cream, 35.0 to 50.0% of pasteurized milk and 44.4% positive samples of pudding. The strains of the bacteria Bacillus cereus were also appeared in 15.0% of sterile milk and sterile sweet cream. In the average the largest number of these microorganisms was found in pudding (55.4 CFU/ml), while in pasteurized milk there were only 0.08 to 0.33 CFU/ml. The seasonal oscillations with two peaks in December to January and in May to June were characteristic. The correlation between the presence of Bacillus cereus, total bacterial count, the number of psychrotrophs and sporeformer bacteria in samples were not found.

DETECTION OF BACTERIOPHAGES IN WHEY AND CHARACTERIZATION OF PHAGES Lactococcus lactis fMB18 AND fMB20

Irena ROGELJ^a), Andreja MIKLIČ, Petra ANDREJKA
^a) Univ. of Ljubljana, Biotechnical Fac., Zootechnical Dept., Groblje 3, SI-1230 Domžale, Slovenia

Original scientific paper
Language: Slovene

ABSTRACT
Methods for phage monitoring were studied. Spot test, indicator test and turbidity test were tested with bacteriophage fCHL92 and host cell Lactococcus lactis CAa120. Indicator test and turbidity test were performed in microtitre plates. Two different phages (fMB18 and fMB20) were isolated from whey obtained from Slovenian dairy. The host strain of phage fMB18 is Lactococcus lactis subsp. lactis MB18 and host strain of phage fMB20 is Lactococcus lactis subsp. cremoris MB20. Latent period, burst size and percentage of adsorption were determined. Morphological characteristics of bacteriophages were studied by transmission microscopy. Burst size of phage fMB18 is 82.7, and of fMB20 37.6. Latent period about 35 min for fMB18 and 33 min for fMB20 were determined. Phage fMB18 is prolate headed (43x55 nm) and has a 95 nm long tail. Phage fMB20 possess an isometric head (51x50 nm) and a fairly long tail (134 nm).

COMPARISON OF UREA CONTENT IN MILK DETERMINED WITH TWO DIFFERENT METHODS

Marija KLOPČIČ^a), Vanja PENCA-HABJAN, J. POGAČAR
^a) Univ. of Ljubljana, Biotechnical Fac., Zootechnical Dept., Groblje 3, SI-1230 Domžale, Slovenia

Original scientific paper
Language: Slovene

ABSTRACT
In the period of nine months; from April to the end of December, the bulk milk samples from 11 farms in Gorenjska region were taken once a week to analyse and to determine the urea content in milk. Each time two parallel samples were analysed in two different laboratories and by two different methods. During our research, 368 sample pairs were analysed. In laboratory A the urea content was determined photometrically on COBAS-MIRA, and in laboratory B the enzymatic method was used - Boehringer-Mannheim test combination. The urea content in milk was statistically higher in laboratory A than in laboratory B, where the calculated correlation between measurements of both labs proved high (r=0.75) and statistically significantly different from zero. Also the calculated regression coefficients proved statistically significant. The determination coefficient in our case was 56.3 %.

ANALYTICAL QUALITY ASSURANCE IN DAIRY LABORATORIES

Slavica GOLC-TEGER^a)
a) Univ. of Ljubljana, Biotechnical Fac., Zootechnical Dept., Groblje 3, SI-1230 Domžale, Slovenia

Review paper
Language: Slovene

ABSTRACT
With the advent of the Single European Market and the mutual recognition of the quality of products, the need for analytical Quality Assurance in laboratories has become greater demand. The laboratory accreditation, using validated and standardized methods, the maximum repeatability (r) of the laboratory, the participating in proficiency testing assume a far greater importance. The article expose the analytical Quality Assurance in dairy laboratories: organisation of proficiency testing schemes as a part of European Network of dairy reference laboratories.

STANDARDS FOR MILK AND MILK PRODUCTS

Mira KOS-ZUPANC^a)
a) Ministrstvo za znanost in tehnologijo, USM, Kotnikova 6, SI-1000 Ljubljana, Slovenia

Review paper
Language: Slovene

ABSTRACT
Slovenian technical committe USM TC KŽP Agriculture food products is working within the scope of activities of Standards and metrology institute of Slovenia. It deals international technical committe ISO TC 34 Agriculture food products. Slovenian working group WG 5 deals international subcommitte SC 5 Milk and milk products. On the one hand our aim in this article is to make an overview of the international standards dealing with milk and milk products, meaning of standards by using in chemical analytical laboratories and on the other hand is to make an overview of present work in our working group.

SHELF-LIFE AS A CONDITION FOR MILK PRODUCT QUALITY

Jasmina LUKAČ-HAVRANEK^a), Mirza HADŽIOSMANOVIĆ
^a) Sveučilište u Zagrebu, Agronomski fakultet, Svetošimunska 25, 41000 Zagreb, Hrvatska

Review paper
Language: English

ABSTRACT
In the complete determination of milk and milk products quality, durability or shelf-life one of the elements that influence quality of the products. The quality is not a matter of choice, but because of whole number of economical reasons and European regulations, it’s a condition for survival on the market. It should be insisted on the objective possibilities of some milk products shelf-life, according to their nature and possibility of storage through maximal permitted time in which there will be no undesirable changes in milk that are usually caused by microbiological and physical and chemical factors. In that sense, durability is a consequence of all phases of production process: collecting, processing and utilization of milk, including the distribution and selling of milk products and their storage in stores under the adequate control. The quality should be seen in accordance to their maximal satisfaction of consumers' requests and improvement of producer’s material indicators. Modern concepts of management, control and observation (TQM; QSA; GMP; LISA; HACCP) in concordance to International Standardization Organization regulations (ISO: 9000, 9011, etc.) have the most important role in reaching the adequate durability.

MILCHPRÜFRING BAYERN e.V. – RAW MILK QUALITY CONTROL IN BAVARIA

C. BAUMGARTNER^a)
a) Milchprüfring Bayern e.V., Herzog-Heinrich-Straße 5, 80336 München, Deutschland

Professional paper
Language: English

ABSTRACT
In Bavaria 79.000 dairy farmers with 1.600.000 cows produce some 7 million tons of raw milk per year. The "Milchprüfring Bayern e.V." performs quality control of raw milk according to German and Bavarian law. This paper provides information about its organisation, obligations and duties. The "Milchprüfring" is a privately initiated organisation of the Bavarian dairy farmers and dairy industry with members out of each group. Budgets are 50% publicly financed, 25% come from the Bavarian dairy fonds and from fees for sample processing, respectively. The "Milchprüfring" runs 4 central labs, equipped with most modern automates for milk analysis. About 200 persons of laboratory and technical staff are performing 10 million investigations for fat, protein, lactose, bacteria, somatic cells, freezing-point and inhibitors. Additionaly 10 million samples per year are investigated for fat, protein, lactose, somatic cells and urea due to performance testing of cows. Automation of all the investigation process from sampling to handling and mailing of results and tight collaboration with scientific instituts make sure, that quality of analysis is constantly high. External technical staff supports states’ veterinary services by visiting farms and controlling conditions according to the hygiene guideline 92/46 EEC, which was set to german law with the "Milchverordnung" of May, 3rd 1995.

RHEOLOGICAL PROPERTIES OF YOGHURT

M. BARUT^a), G. TORRIANO, M. ŽUMER
^a) BIA d.o.o., Teslova 30, SI-1000 Ljubljana, Slovenia

Original scientific paper
Language: English

ABSTRACT
Shear stress transients at six different constant shear rates, ranging from 30 to 300 s^-1 and three selected temperatures (4, 12 and 20 °C) were measured as a function of the shearing time for a whole-milk and a low-fat yoghurt. A Couette-type rotational rheometer was used. The transients showed a highly time-dependent rheological behaviour for both yoghurts and were described with a stretched exponential equation. A characteristic time t_c and a structural parameter L for the structural break-down magnitude were defined to compare the behaviours of two yoghurts under different conditions. The data base so obtained was then used to construct a mathematical model for describing the irreversible degradation of yoghurt under shear based on the phenomenological approach of Cheng and Evans. From the results it could be concluded that the whole-milk yoghurt had a dense structure which was, however, more easily broken down by shear forces in comparison with the less developed but more resistant structure of the low-fat yoghurt.

AROMA PROFILES AND SENSORY EVALUATION OF YOGHURT DURING STORAGE

Mirjana HRUŠKAR^a), Nada VAHČIĆ, Milana RITZ
^a) Prehrambeno-biotehnološki fakultet, 41000 Zagreb, Pierottijeva 6, Hrvatska

Original scientific paper
Language: English

ABSTRACT
It is known that more than 100 chemical compounds have been isolated from yoghurt and related milk products but only a few (acetaldehyde, ethanol, aceton, diacetyl and butanon-2) have a high impact on the desired product flavour. The concentration of these typical flavour compounds changed during storage depending on duration and temperature in depot. In this article six commercial brands of plain yoghurt were stored within 10 days on two diferent temperatures and every two days changes in acetaldehyde, diacetyl and ethanol were established. At the same time sensory evaluation was carried out. Acetaldehyde and ethanol concentration was determined by aldehyde dehydrogenase and alcohol dehydrogenase method. Diacetyl was measured by a modification of the Hill’s colorimetric method. Sensory analysis was conducted by a five member panel, using a scoring system with weighted factors in the 20-point scale. Expert panel ratings were regressed against the concentations of aroma compounds for both temperature levels and linear relationship among them were determined. The most pronounced relationship expressed as correlation coefficients (r) between expert panel ratings and concentrations of individual compounds was observed with ethanol (r = –0.999) in yoghurt sample stored at +4 °C. Coefficients of correlation were generally high (from –0.722 to –0.999) and consequently very accurately predicting equations were obtained by regression analysis.

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