Annalisa Serio

Characterization of the Enterobacteriaceae isolated from an artisanal Italian ewe's cheese (Pecorino Abruzzese)

Aims:  To evaluate some physiological characteristics of the Enterobacteriaceae isolated from Pecorino cheese.

Enterococcus populations in Pecorino Abruzzese cheese: biodiversity and safety aspects.

The presence of enterococci in Pecorino Abruzzese cheese during ripening was evaluated. Counts were high, especially in fully ripened summer batches. Seventy strains were isolated and identified based on phenotypical and genotypical features as Enterococcus faecium (48.5%), Enterococcus faecalis (40%), and Enterococcus durans (11.5%), with the first species predominant in spring batches and the second predominant in summer batches. High biodiversity was revealed by random amplification of polymorphic DNA and a PCR assay, suggesting the presence of autochthonous strains. E. faecium isolates were the most resistant to the tested antibiotics, especially to erythromycin, chloramphenicol, and penicillin, but all strains were susceptible to vancomycin, as confirmed by the absence of vanA and vanB genes. The presence of some virulence determinants was investigated, revealing the diffusion of aggregation substance (asal) and gelatinase (gelE) genes in 37.5% of E. faecalis strains. However, none of the isolates produced gelatinase in vitro, suggesting the presence of silent genes. The virulence genes were absent in E. durans. Among E. faecium strains, only Lab 41/1 possessed gelE and asal, whose presence previously has been reported only in E. faecalis. Decarboxylating activity was revealed for phenylalanine (27% of the strains) and tyrosine (96%) but not histidine. The presence of a tyrosine decarboxylase-encoding gene was observed for all strains. A comparison of these results with those of previous studies of clinical and food isolates indicates that enterococci from Pecorino Abruzzese cheese have low pathogenic potential.

Yeasts from Colombian Kumis as source of peptides with Angiotensin I converting enzyme (ACE) inhibitory activity in milk

This study investigated the possibility of using yeast strains in fermented milks to obtain products with high Angiotensin I-converting enzyme (ACE) inhibitory activity and low bitter taste. Ninety-three yeast strains isolated from Colombian Kumis in different geographic regions were molecularly identified, and their milk fermentation performances were determined. Molecular identification evidenced that Galactomyces geotrichum, Pichia kudriavzevii, Clavispora lusitaniae and Candida tropicalis, were the dominant species. Eighteen out of 93 strains produced fermented milk with ACE-inhibitory (ACEI) activity values ranging from 8.69 to 88.19%. Digestion of fermented milk samples by pepsin and pancreatin demonstrated an increase in ACEI activity, with C. lusitaniae KL4A as the best producer of ACEI peptides. Moreover, sensory analysis of the products containing the major ACE-inhibitory activity pointed out that P. kudriavzevii KL84A and Kluyveromyces marxianus KL26A could be selected as potential adjunct starter cultures in Kumis, since they made a considerable contribution to the ACE inhibitory activity and produced fermented milk without bitter taste. In this study we observed that Colombian Kumis can be an excellent vehicle for the isolation of yeasts with a potential to enhance bioactive peptides produced during milk fermentation.

Microbiological characteristics of kumis, a traditional fermented Colombian milk, with particular emphasis on enterococci population

Kumis is a traditional fermented cow milk produced and consumed in South West Colombia. The main objective of this research was to studied the enterococcal population, present in 13 kumis samples traditionally manufactured, for their role as beneficial organisms or opportunistic pathogens. The molecular identification of 72 isolates evidenced that Enterococcus faecalis and E. faecium were the dominant species. The genes gelE, esp, asa1, cyl and hyl, all associated with virulence factors in enterococci, were detected in 30 isolates, while 42 were free of virulence determinants. Skim milk media were fermented by all the different isolates and further tested for proteolysis (free NH(3) groups), Angiotensin-I Converting Enzyme (ACE) inhibitory activity and biogenic amines production. Nine E. faecalis and two E. faecium strains produced fermented milk with ACE-inhibitory activity values ranging from 39.7% to 84.35% .The digestion of fermented milk samples by pepsin and pancreatin evidenced an increase in ACE inhibitory activity, with E. faecalis KE09 as the best producer (IC50 = 14.25 μg ml(-1)). Moreover, the strains showed a very low tyrosine decarboxylase activity and did not produce histamine during 48 h fermentation in milk. This study underlines the that Colombian kumis is a good source of not virulent enterococci able to produce fermented milks with ACE-inhibitory activity.

Traditional Fermented Foods and Beverages from a Microbiological and Nutritional Perspective: The Colombian Heritage

Fermentation has been used for preserving foods for centuries prior to the invention of pasteurization and sterilization, and every culture has a variety of fermented products as part of its diet. This paper reviews the diversity of fermented foods and beverages from Latin America; these fermented products are produced by traditional methods that exploit mixed cultures of various nonpathogenic microorganisms. Fermented foods covered in this review include maize, cassava, palm sap, sugar cane juice, cocoa, and milk. We explore the history of some Colombian fermented foods and beverages, which are today part of the tradition of some ethnic groups, and evaluate their technology, microbiology, the presence of some nutritional factors, and safety concerns. To the best of our knowledge, this is the 1st systematic review on Colombian fermented beverages and foods, and we believe that it may contribute to valorize these products that are still part of the Latin America tradition.

Diversity of food-borne Bacillus volatile compounds and influence on fungal growth

To evaluate the antifungal activity of the volatile organic compounds (VOCs) produced by 75 different food‐borne Bacillus species against Aspergillus niger, Aspergillus flavus, Aspergillus parasiticus, Aspergillus clavatus, Fusarium oxysporum f. sp. lactucae and Moniliophthora perniciosa and to determine the VOCs responsible for the inhibition.

Control of household mycoflora in fermented sausages using phenolic fractions from olive mill wastewaters.

Biopreservation using polyphenols represents an alternative to chemical molecules for improving food safety. In this work, we evaluated the antifungal activity of polyphenols extracted from olive mill wastewater (OMWWP) to reduce or eliminate the growth of undesired fungi on the surface of dry fermented sausages. Antagonism against Penicillium expansum DSMZ 1282, Penicillium verrucosum DSMZ 12639, Penicillium nalgiovense MS01, Aspergillus ochraceus DSMZ 63304, Cladosporium cladosporioides MS12, and Eurotium amstelodami MS10 was evident at 1.25% OMWWP in vitro, whereas in situ application of 2.5% OMWWP strongly reduced undesired household fungal species such as C. cladosporioides, Penicillium aurantiogriseum, Penicillium commune, and Eurotium amstelodami, while a moderate antagonistic activity towards P. nalgiovense and Penicillium chrysogenum was observed at the same concentration. OMWWP at the concentrations used in this study demonstrated species-dependent antifungal activity by inhibiting both fungal growth and spore germination. Therefore, OMWWP can be regarded as a potential alternative to synthetic antifungal compounds to preserve the product from both oxidation and undesired fungi, without changing the sensory characteristics.

Volatile compounds produced in wine by Colombian wildSaccharomyces cerevisiae strains

Some tropicalSaccharomyces cerevisiae strains, isolated fromChampús, a traditional Colombian low alcoholic fermented beverage, were characterised in order to select yeasts for aroma improvement in wine. H2S production, volatile acidity, β-glucosidase activity, higher alcoholesters and terpenes production were evaluated in this study. These tropical strains were characterised by a considerable production of ethyl hexanoate, 2-phenylethanol, 2-phenylethyl acetate, and geraniol, detected by SPME-GC-MS. Odor activity values were calculated to analyse the effects of yeasts strains on wine aroma, resulting in six distinctive wine groups, as evidenced by discriminant analysis. These results suggest thatSaccharomyces strains isolated fromChampús can be an important source for new tropical yeast biotypes with potential winemaking applications, producing a wide range of aroma compounds.

Influence of incubation conditions on biofilm formation by Pseudomonas fluorescens isolated from dairy products and dairy manufacturing plants

In this study, biofilm formation of 64 Pseudomonas fluorescens strains isolated from milk, dairy products and dairy plants was compared. The strains were grown on Tryptic Soy Broth supplemented with 0.2% of glucose, on polystyrene microplates at 10 and 30°C for 48 h. In general, 57/64 P. fluorescens strains formed biofilm, although with great variability at both tested temperatures. Moreover, our results evidenced that the biofilm-forming ability of the strains was temperature- and strain-dependent. Interestingly, the ability of several isolates to form biofilms was associated with the low temperature after 48 h. Our findings evidenced that temperature was more important than incubation time for biofilm formation. Considering the origin of the strains, it is relevant to underline the importance of performing accurate cleaning and disinfection procedures on food processing surfaces.

Exploring the Bacterial Microbiota of Colombian Fermented Maize Dough “Masa Agria” (Maiz Añejo)

Masa Agria is a naturally fermented maize dough produced in Colombia, very common in the traditional gastronomy. In this study we used culture-dependent and RNA-based pyrosequencing to investigate the bacterial community structure of Masa Agria samples produced in the south west of Colombia. The mean value of cell density was 7.6 log CFU/g of presumptive lactic acid bacteria, 5.4 log cfu/g for presumptive acetic bacteria and 5.6 og CFU/g for yeasts. The abundance of these microorganisms is also responsible for the low pH (3.1–3.7) registered. Although the 16S rRNA pyrosequencing revealed that the analyzed samples were different in bacteria richness and diversity, the genera Lactobacillus, Weissella, and Acetobacter were predominant. In particular, the most common species were Lactobacillus plantarum and Acetobacter fabarum, followed by L. fermentum, L. vaccinostercus, and Pediococcus argentinicus. Several microorganisms of environmental origin, such as Dechloromonas and most of all Sphingobium spp., revealed in each sample, were detected, and also bacteria related to maize, such as Phytoplasma. In conclusion, our results elucidated for the first time the structures of the bacterial communities of Masa Agria samples obtained from different producers, identifying the specific dominant species and revealing a complete picture of the bacterial consortium in this specific niche. The selective pressure of tropical environments may favor microbial biodiversity characterized by a useful technological potential.