Sofia Cosentino

In‐vitro antimicrobial activity and chemical composition of Sardinian Thymus essential oils

Essential oils and their components are becoming increasingly popular as naturally occurring antimicrobial agents. In this work the chemical composition and the antimicrobial properties of Thymus essential oils and of their main components were determined. Three essential oils obtained from different species of Thymus growing wild in Sardinia and a commercial sample of Thymus capitatus oil were analysed. The essential oil components were identified by GC/MS analysis. The antimicrobial activity of the oils and components was determined against a panel of standard reference strains and multiple strains of food‐derived spoilage and pathogenic bacteria, using a broth microdilution method. The GC/MS analysis showed that the major constituents of the oils were monoterpene hydrocarbons and phenolic monoterpenes, but the concentration of these compounds varied greatly among the oils examined. The results of the antimicrobial assay showed that essential oils extracted from Sardinian Thymus species have an antimicrobial activity comparable to the one observed in other thyme oils. It seems also confirmed that the antimicrobial properties of thyme essential oils are mainly related to their high phenolic content. Among the single compounds tested carvacrol and thymol turned out to be the most efficient against both reference strains and food‐derived bacteria. The results of this study confirmed the possibility of using thyme essential oils or some of their components in food systems to prevent the growth of foodborne bacteria and extend the shelf‐life of processed foods.

Yeasts associated with Sardinian ewe's dairy products

In the present work, the occurrence of yeasts in different types of typical Sardinian ewes cheeses (32 samples of pecorino, 32 of caciotta, 40 of feta, 56 of ricotta) was determined. For the strains isolated the following properties were studied: proteolytic and lipolytic activities, the ability to grow at different temperatures, different concentrations of salt, and to assimilate and/or ferment compounds like lactate, citrate, lactose, glucose, galactose, lactic acid. Of 160 samples analysed, 76.2% yielded growth of yeasts. Yeast counts showed a certain variability among the samples. The highest levels were observed in caciotta and feta cheeses. A total of 281 strains belonging to 16 genera and 25 species were identified. In general, Debaryomyces hansenii was the dominant species, representing 28.8% of the total isolates. Other frequently appearing species were Geotrichum candidum, Kluyveromyces lactis and K. marxianus. Other genera encountered were Pichia, Candida, Dekkera, Yarrowia and Rhodotorula. With regard to the biochemical and technological properties of the yeasts, only K. lactis, K. marxianus and Dek. anomala assimilated and fermented lactose, whereas the majority of the species assimilated lactic acid. The assimilation of citrate was a characteristic of D. hansenii, R. rubra and Y. lipolytica. On the whole, the yeasts were weakly proteolytic while lipolytic activity was present in several species. A high percentage of strains showed a certain tolerance to low temperatures while only some strains of D. hansenii and K. lactis were able to grow at a 10% NaCl concentration.

Incidence and biochemical characteristics of Bacillus flora in Sardinian dairy products

This study was planned to assess the frequency and level of Bacillus spp. contamination in Sardinian dairy products and to evaluate some food-spoilage-related characteristics of the strains isolated. Of the 378 dairy products tested, 265 (70%) were found to contain Bacillus spp. The overall level of contamination ranged from less than 10 cfu per ml or gram up to a maximum of 1200 cfu. A total of 483 strains, belonging to 14 species, have been isolated from the 265 positive samples. The most frequently isolated psychotropic species were B. cereus (18.6% of total isolates), B. coagulans and B. mycoides. B. subtilis, B. licheniformis and B. pumilis were the most common mesophilic strains and B. stearotermophilus was the dominant thermophilic species. Most strains showed strong enzymatic activity, as indicated by the high percentage of isolates capable of hydrolysing casein, gelatin, starch and liquids. As regards possible health hazards. 72% of the B. cereus strains tested showed evidence of toxin production using a reversed passive latex agglutination assay.

Composition and Antimicrobial Properties of Sardinian Juniperus Essential Oils against Foodborne Pathogens and Spoilage Microorganisms

In this work, the chemical compositions and antimicrobial properties of Juniperus essential oils and of their main components were determined. Five berry essential oils obtained from different species of Juniperus growing wild in Sardinia were analyzed. The components of the essential oils were identified by gas chromatography-mass spectrometry (GC-MS) analysis. The antimicrobial activities of the oils and their components against food spoilage and pathogenic microorganisms were determined by a broth microdilution method. The GC-MS analysis showed a certain variability in the concentrations of the main constituents of the oils. Alpha-pinene was largely predominant in the oils of the species J. phoenicea subsp. turbinata and J. oxycedrus. Alpha-pinene and myrcene constituted the bulk (67.56%) of the essential oil of J. communis. Significant quantitative differences were observed for myrcene, delta-3-carene, and D-germacrene. The results of the antimicrobial assay show that the oils of J. communis and J. oxycedrus failed to inhibit any of the microorganisms at the highest concentrations tested (MLC > or = 900 microg/ml), while the oils extracted from J. turbinata specimens were active against fungi, particularly against a strain of Aspergillus flavus (an aflatoxin B1 producer). Of the single compounds tested, delta-3-carene was found to possess the broadest spectrum of activity and appeared to contribute significantly to the antifungal activity observed for J. turbinata oils. This activity may be helpful in the prevention of aflatoxin contamination for many foods.

A NMR metabolomics study of the ripening process of the Fiore Sardo cheese produced with autochthonous adjunct cultures

Fiore Sardo (FS) is a traditional Italian raw ewes milk cheese carrying a Protected Designation of Origin (PDO). This study investigated the kinetics of FS cheese ripening by physicochemical parameters, microbial counting, and NMR metabolomics using aqueous extracts. Four Fiore Sardo cheeses, manufactured from milk with deliberately added autochthonous lactic acid bacteria (LAB) or commercial starters were studied during a period of 90days of ripening. Major differences in the metabolic profiles were observed amongst the samples as a function of the adjunct culture utilised. (1)H NMR metabolomics in combination with multivariate data analysis was able to classify cheese samples on the basis of their maturation age and the type of added cultures. These findings lay the metabolic basis for the authentication of Fiore Sardo cheese produced in compliance with PDO specifications which allow the use of only native LAB cultures.

Comparison between fungal airspore concentration at two different sites in the South of Sardinia

Abstract The occurrence of airborne fungi at an urban coastal site was compared with that at a rural inland site in the South of Sardinia. Spore concentrations at the two sites differed markedly with lower concentrations at the urban site but the spore types found were similar. The general trend of the fungal airspores was also very similar at both sites as a result of the similar climatic conditions. Mould spore concentrations were greatest in late spring (May-June) and autumn (October-November) with a decrease during summer months at both sites sampled. Cladosporium was the most common spore type identified followed by Basidiomycetes, Alternaria, Fusarium. These taxa are well known as allergens. It is recommended that further aeromycological surveys should be performed in different areas to determine the clinical importance of fungi as allergens in Sardinia.

Characterization of yeast population and molecular fingerprinting of Candida zeylanoides isolated from goat's milk collected in Sardinia

The occurrence of yeast microflora in raw goats milk collected from 62 dairy farms located in different areas of Sardinia was evaluated. Candida zeylanoides was the most frequently occurring species followed by different Basidiomycetous species. In the strains isolated some biochemical characteristics of technological interest were investigated and a predominance of lipolytic yeast species was found. We employed a simple method of DNA extraction that in a minimal time and with low-cost provided a high quality of DNA for RAPD analysis of 32 isolates of C. zeylanoides. The primers M13 and CDU were used and at 40% of similarity, two distinct clusters were observed. The presence of C. krissii species was supposed but further molecular studies are needed to exclude the presence of an as-yet-undescribed species.

Yeast populations in Sardinian feta cheese

In this study, the yeast populations in feta cheese from two different Sardinian dairies were examined. Samples of good quality feta (32) and samples of feta with a slimy surface defect (10) were examined from Dairy A. Similar, samples of good quality feta (23), feta with slimy surface defects (14) and samples with swelling defects (6) were examined from Dairy B. Kluyveromyces lactis was the dominating species in feta from Dairy A (95.2% of samples) followed by Debaryomyces hansenii (76.2%), Dekkera anomala (28.6%) and Dek. bruxellensis (19%). D. hansenii was dominant in samples from Dairy B (93%), followed by K. lactis (23.3%), Geotrichum candidum (23.3%) and Dek. anomala (18.6%). No significant difference was observed between the occurrence of yeast species in feta of good quality and in feta with slimy surface defects, thus confirming that slimy production is not associated with yeast contaminations. The swelling of samples observed in Dairy B seems to be caused by Dek. anomala. In fact, this strong fermenting species was present in all swelled samples in numbers exceeding 10(6) CFU g(-1), while it was isolated in very low concentration in only 5.4% of good samples.

Preliminary Evaluation of Probiotic Properties of Lactobacillus Strains Isolated from Sardinian Dairy Products

Twenty-three Lactobacillus strains of dairy origin were evaluated for some functional properties relevant to their use as probiotics. A preliminary subtractive screening based on the abilities to inhibit the growth of microbial pathogens and hydrolyze conjugated bile salts was applied, and six strains were selected for further characterization including survival under gastrointestinal environmental conditions, adhesion to gut epithelial tissue, enzymatic activity, and some safety properties. All selected strains maintained elevated cell numbers under conditions simulating passage through the human gastrointestinal tract, well comparable to the values obtained for the probiotic strain Lactobacillus rhamnosus GG, and were able to adhere to Caco-2 cells to various extents (from 3 to 20%). All strains exhibited high aminopeptidase, and absent or very low proteolytic and strong β-galactosidase activities; none was found to be haemolytic or to produce biogenic amines and all were susceptible to tetracycline, chloramphenicol, erythromycin, ampicillin, and amoxicillin/clavulanic acid. Our results indicate that the Lactobacillus strains analyzed could be considered appropriate probiotic candidates, due to resistance to GIT simulated conditions, antimicrobial activity, adhesion to Caco-2 cell-line, and absence of undesirable properties. They could be used as adjunct cultures for contributing to the quality and health related functional properties of dairy products.

Metabolomics and microbiological profile of Italian mozzarella cheese produced with buffalo and cow milk

Italian buffalo mozzarella (BM) cheese metabolite profile and microbial communities were characterised and compared to cow mozzarella (CM). Polar metabolite profiles were studied by gas-chromatography mass-spectrometry (GC-MS) and results elaborated by multivariate analysis (MVA). BM produced using natural whey starter cultures (NWS) exhibited a higher microbial diversity with less psychrotrophic bacteria. BM samples were higher in threonine, serine, valine, and lower in orotic acid and urea. CM produced with commercial starters (CMS) had the highest count of Streptococcus thermophilus and higher levels of galactose and phenylalanine. CM obtained by direct acidification (CMA) had lower microbial counts and higher levels of urea and sugars. Orotic acid was the only metabolite linked to milk animal origin. Results indicated that this metabolite pool well reflects the different production protocols and microbial complexity of these dairy products. This approach can help to protect the designation of origin of Italian buffalo mozzarella.