Projects / Programmes
Tailor-made starter cultures for production of traditional cheeses
| Code |
Science |
Field |
Subfield |
| 4.02.00 |
Biotechnical sciences |
Animal production |
|
| Code |
Science |
Field |
| T430 |
Technological sciences |
Food and drink technology |
| T490 |
Technological sciences |
Biotechnology |
traditional cheeses, starter cultures, antimicrobial activity, safety, bioactive peptides, nutritional value
Researchers (9)
Organisations (1)
Abstract
Production of traditional dairy products presents an important part of Slovenian cheese production and therefore deserves adequate attention and protection. Beside a need to protect and preserve typical products, microbiological safety of traditional cheeses is also of great concern especially because most of such products are produced from raw milk. Among possible alternatives for thermal treatment which would negatively affect the natural microflora important for development of typical organoleptic properties, is introduction of selected lactic acid bacteria (LAB) with activity against pathogenic or spoilage bacteria, such as Staphylococcus aureus and Listeria monocytogenes but do not influence species involved in ripening. The proposed project will be focused mainly on : screening for and selection of competitive natural microbial flora present in four slovenian traditional cheeses, evaluation of technological properties of selected strains and/or consortium of strains exhibiting strong antagonistic activities against L. monocytogenes and S. aureus, constitution/construction of “tailor made” starter cultures and their testing/evaluating on pilot plant level and in real cheese production. In the first stage, a new set of tools for evaluation of anti-microbial activity directly in cheese such as qualitative and quantitative analysis of bacteriocins in situ in cheese during the ripening, by analysis of bacteriocin gene expression with RT-PCR and direct detection of antimicrobial activity (DDAA) in cheese extracts by flow cytometric method will be introduced. Than we intend to select competitive natural microflora from traditional cheeses and determine new “tailor made” starter cultures. In the last stage, testing of new starter cultures on pilot plant level and in real cheese production is intended. Changes in starter culture combinations which will positively affect the safety quality traditional cheeses but also the nature and quantity of bio-active peptides present in cheese are expected.
Significance for science
The most important contribution to advancement of science are the methods we developed end optimized during our work on this project. The most innovative of it would be the methods for direct extraction of DNA, RNA and bioactive peptides from cheese matrix. All of these methods were optimized to be applicable in other dairy products and with additional optimization it could be used for extraction from non-dairy food or even complex media other than food. Concrete results that would be also scientifically important are the ones indicating that there are bioactive peptides and structural genes for bacteriocins of lactic acid bacteria present in the cheeses. Although there have been many reports on raw milk cheeses as source of bacteriocin producing lactic acid bacteria (LAB) our research group was the first one describing the actual diversity of bacteriocinogenic LAB. In a single cheese sample we could find structural genes for up to nine bacteriocins and following results showed that most of the bacteriocinogenic strains could be found also in microbial consortia cultivated on different selective agar media.
Additional studies revealed that all tested cheese consortia had an obvious effect on the growth of pathogenic bacteria S. aureus and consequently possibly also on the enterotoxin production in-situ. Although acid formation is known to be an important factor for S. aureus survival, in our study it was found to be only a minor factor of inhibition. As mentioned, in cheese consortia from Tolminc cheese we detected a number of bacteriocin genes that, if expressed, could play an important role in inhibition. The expression of bacteriocin genes were demonstrated in challenge test with nisin producer. But, inhibition of S. aureus could be also a mater of one single bacteriocin like enterocin P whose genes were detected in cheese consortia from different cheeses.
However, we also established that most of the strains that are carrying gene determinants for bacteriocins do not have competitive advantage in isolated cheese consortia cultivated in lab conditions. On the other hand the strains that did have competitive advantage in microbial population were often related to unacceptable technological defects in final product which was observed in challenge tests. Results of inhibitions of pathogenic bacteria L. monocytogenes and S. aureus showed that mechanisms behind the inhibition do not necessarily involve only action of bacteriocins, acids or any other inhibitory substances. These mechanisms that probably involve competition for nutrients are really interesting field for continuing research of microbial interactions.
Significance for the country
The major advancement we would like to expose is again the methods that were developed and which will help in continuing research on traditional food products. During our work we determined the entire composition of three traditional cheeses (Tolminc, Bovški ovčji in Kraški ovčji). Representatives of microflora and technologically interesting strains from these cheeses were characterized and stored in our microbial collection. This is very important for protection of these traditional products since the microflora together with technological procedure and quality of entering milk determines the quality of end product. Data on microbial composition and its growth dynamics will be a good supplement to description of technological procedure and sensory characteristics found in documentation needed for protection of traditional products. Selected strains that exhibit suitable protective and technological properties were used to develop starter culture. This starter culture was tested in pilot scale cheese making as well as in real cheese production. Working on this project contributed a lot to achieving goals that were set by Council Regulation on the protection of geographical indications and designations of origin for agricultural products and foodstuffs (EEC No. 2081/92) and Council Regulation on certificates of specific character for agricultural products and foodstuffs (EEC No. 2082/92). Furthermore, the innovations in the production of traditional cheeses have been involved and educational material including the guide for the production of good quality Tolminc has been prepared and distributed among Tolminc cheese producers.
Most important scientific results
Annual report
2008,
final report,
complete report on dLib.si
Most important socioeconomically and culturally relevant results
Annual report
2008,
final report,
complete report on dLib.si
