Journal of the Science of Food and Agriculture, Oct 28, 2014
Background: Pig rennet is traditionally used in Pecorino di Farindola cheese. Different Pecorino ... more Background: Pig rennet is traditionally used in Pecorino di Farindola cheese. Different Pecorino cheeses, obtained using calf, kid and pig rennet, were compared in terms of fatty acids, volatile molecules profiles, texture, and sensory properties during ripening. Results: The rennet influenced the fatty acid composition of cheeses although palmitic, myristic and oleic acids were always predominant. The analysis of volatiles by GC/MS/SPME showed that Pecorino from calf rennet, at the end of ripening, was the least 'evolved' in terms of volatiles profile. The GC/MS/SPME analysis revealed that cheeses from calf rennet showed the slowest accumulation of free fatty acids over ripening time. Volatiles data permitted to differentiate cheese samples ripened from 30 to 180 days according to the rennet used. The textural analysis differentiated the cheeses made with pig and calf rennet from those made with kid one, which resulted less hard and more elastic. Sensory analysis differentiated the cheeses on the basis of rennet type and cheeses made with pig rennet showed the lowest elasticity, bitter taste, fruity and hay flavour intensity. Conclusions: Pig rennet is fundamental to determine the quality parameters of Pecorino di Farindola cheese and could be used to impair peculiar quality features to ewes' cheeses.
Sono riportati in letteratura molti lavori riguardanti la presenza di ceppi di S. cerevisiae in f... more Sono riportati in letteratura molti lavori riguardanti la presenza di ceppi di S. cerevisiae in formaggi freschi e semi-stagionati. Pochi sono invece gli studi riguardanti le fermentazioni e le cinetiche di crescita. Lo scopo di questo lavoro \ue8 stato quello di studiare l\u2019interazione tra Saccharomyces cerevisiae e Streptococcus thermophylus e/o Lactobacillus delbrueckii subsp. bulgaricus, inoculati in co-cultura, utilizzando siero come mezzo di sviluppo, seguendo la dinamica di produzione di CO2 e la cinetica di sviluppo. Il confronto tra le dinamiche di crescita del lievito e dei batteri lattici, inoculati da soli o insieme hanno evidenziato che la crescita di S.cerevisiae \ue8 stimolata dalla presenza di Str. thermophylus and Lb. delbrueckii subsp. bulgaricus
Effects of the diameter on physicochemical, microbiological and volatile profile in dry fermented... more Effects of the diameter on physicochemical, microbiological and volatile profile in dry fermented sausages produced with two different starter cultures, Food Bioscience,
In this study, PCR-based procedures were developed to detect the occurrence and quantify the expr... more In this study, PCR-based procedures were developed to detect the occurrence and quantify the expression of the tyrosine decarboxylase gene (tdc) in gram-positive bacteria associated with fermented foods. Consensus primers were used in conventional and reverse transcription PCR to analyze a collection of 87 pure cultures of lactic acid bacteria and staphylococci. All enterococci, Staphylococcus epidermidis, Lactobacillus brevis, Lactobacillus curvatus, and Lactobacillus fermentum strains and1of 10 Staphylococcus xylosus strains produced amplification products with the primers DEC5 and DEC3 in accordance with results of the screening plate method and with previously reported result obtained with high-performance liquid chromatography. No amplicons were obtained for tyramine-negative strains, confirming the high specificity of these new primers. A novel quantitative real-time PCR assay was successfully applied to quantify tdc and its transcript in pure cultures and in meat and meat pro...
The main aim of this work was to evaluate, at pilot scale in an industrial environment, the effec... more The main aim of this work was to evaluate, at pilot scale in an industrial environment, the effects of the biocontrol agent Lactococcus lactis CBM21 and thyme essential oil compared to chlorine, used in the washing step of fresh-cut lamb's lettuce, on the microbiota and its changes in relation to the time of storage. The modification of the microbial population was studied through pyrosequencing in addition to the traditional plate counts. In addition, the volatile molecule and sensory profiles were evaluated during the storage. The results showed no significant differences in terms of total aerobic mesophilic cell loads in relation to the washing solution adopted. However, the pyrosequencing data permitted to identify the genera and species able to dominate the spoilage associations over storage in relation to the treatment applied. Also, the analyses of the volatile molecule profiles of the samples during storage allowed the identification of specific molecules as markers of t...
ABSTRACT In this study the thermal resistance of seven strains of staphylococci was studied. Thre... more ABSTRACT In this study the thermal resistance of seven strains of staphylococci was studied. Three of them (two Staphylococcus epidermidis and one Staphylococcus lugdunensis) were isolated from pasteurized tofu, while one Staphylococcus aureus from fermented sausages. Also the corresponding type strains were tested. Their heat resistance was assessed at 80 °C also in relation to different growth conditions (high NaCl concentrations and low pH). Moreover, the effect of two terpenes (carvacrol and citral) on their survival during thermal treatment was assessed. All the strains were able to survive a 20 min thermal treatment and showed a similar behavior, i.e. an inactivation of about 6 log units in the first 2–4 min of treatment, followed by constant survivor counts (2–4 log CFU/ml). The pre-culture of staphylococci under stressing conditions (high NaCl concentration and low pH) increased the susceptibility to thermal treatment in three strains isolated from food matrices. The addition of carvacrol and citral during thermal treatment influenced the number of survived cells at the end of the treatment. This new insight in the thermal resistance of staphylococci needs to be better investigated, in order to study proper strategies to control their occurrence and behavior in real food systems.
The aim of this study was to evaluate the competitive effects of three bacteriocin producing stra... more The aim of this study was to evaluate the competitive effects of three bacteriocin producing strains of Lactococcus lactis subsp. lactis against two aminobiogenic lactic acid bacteria, i.e. the tyramine producing strain Enterococcus faecalis EF37 and the histamine producing strain Streptococcus thermophilus PRI60, inoculated at different initial concentrations (from 2 to 6 log cfu/ml). The results showed that the three L. lactis subsp. lactis strains were able to produce bacteriocins: in particular, L. lactis subsp. lactis VR84 and EG46 produced, respectively, nisin Z and lacticin 481, while for the strains CG27 the bacteriocin has not been yet identified, even if its peptidic nature has been demonstrated. The co-culture of E. faecalis EF37 in combination with lactococci significantly reduced the growth potential of this aminobiogenic strain, both in terms of growth rate and maximum cell concentration, depending on the initial inoculum level of E. faecalis. Tyramine accumulation was strongly reduced when E. faecalis EF37 was inoculated at 2 log cfu/ml and, to a lesser extent, at 3 log cfu/ml, as a result of a lower cell load of the aminobiogenic strain. All the lactococci were more efficient in inhibiting streptococci in comparison with E. faecalis EF37; in particular, L. lactis subsp. lactis VR84 induced the death of S. thermophilus PRI60 and allowed the detection of histamine traces only at higher streptococci inoculum levels (5-6 log cfu/ml). The other two lactococcal strains did not show a lethal action against S. thermophilus PRI60, but were able to reduce its growth extent and histamine accumulation, even if L. lactis subsp. lactis EG46 was less effective when the initial streptococci concentration was 5 and 6 log cfu/ml. This preliminary study has clarified some aspects regarding the ratio between bacteriocinogenic strains and aminobiogenic strains with respect to the possibility to accumulate BA and has also showed that different bacteriocins can have different effects on BA production on the same strain. This knowledge is essentially aimed to use bacteriocinogenic lactococci as a predictable strategy against aminobiogenic bacteria present in cheese or other fermented foods.
Journal of the science of food and agriculture, 2014
Pig rennet is traditionally used in Pecorino di Farindola cheese. In this study, different Pecori... more Pig rennet is traditionally used in Pecorino di Farindola cheese. In this study, different Pecorino cheeses obtained using calf, kid and pig rennets were compared in terms of fatty acids, volatile molecule profile, texture and sensory properties during ripening. The rennet type influenced the fatty acid composition of cheeses, though palmitic, myristic and oleic acids were always predominant. The analysis of volatiles by SPME-GC/MS showed that Pecorino from calf rennet, at the end of ripening, was the least 'evolved' in terms of volatile profile. SPME-GC/MS analysis revealed that cheeses from calf rennet showed the slowest accumulation of free fatty acids over ripening time. Volatile data permitted the differentiation of cheese samples ripened from 30 to 180 days according to the rennet used. Texture analysis differentiated cheeses made with pig and calf rennet from those made with kid rennet, which were less hard and more elastic than the former. Also sensory analysis diffe...
Aims: To characterize the lactobacilli community of 20 sourdoughs using a novel polyphasic approa... more Aims: To characterize the lactobacilli community of 20 sourdoughs using a novel polyphasic approach. Methods and Results: A polyphasic approach, consisting of a two-step multiplex polymerase chain reaction (PCR) system, 16S rRNA gene sequence analysis and physiological features, was applied to identify 127 isolates, representing about 37% of the presumptive lactobacilli collected from sourdough samples. Multiplex PCR successfully identified 111 isolates, while 16S rRNA gene sequencing was applied for the other 16 isolates, two of which could not be associated with any previously described lactic acid bacteria (LAB) species. Strain diversity was evaluated by phenotypic and random amplified polymorphic DNA-PCR analysis. Molecular detection of Lactobacillus group species was also performed on total DNA extracted from the doughs. Conclusions: Abruzzo region sourdough lactobacilli biodiversity, reflected in both Lactobacillus species composition and strain polymorphism, is similar to that of other Italian regions and is a source of novel LAB species. Significance and Impact of the Study: Within culture-independent methods, multiplex PCR is a rapid tool to study the lactobacilli population of sourdoughs.
Journal of the Science of Food and Agriculture, Oct 28, 2014
Background: Pig rennet is traditionally used in Pecorino di Farindola cheese. Different Pecorino ... more Background: Pig rennet is traditionally used in Pecorino di Farindola cheese. Different Pecorino cheeses, obtained using calf, kid and pig rennet, were compared in terms of fatty acids, volatile molecules profiles, texture, and sensory properties during ripening. Results: The rennet influenced the fatty acid composition of cheeses although palmitic, myristic and oleic acids were always predominant. The analysis of volatiles by GC/MS/SPME showed that Pecorino from calf rennet, at the end of ripening, was the least 'evolved' in terms of volatiles profile. The GC/MS/SPME analysis revealed that cheeses from calf rennet showed the slowest accumulation of free fatty acids over ripening time. Volatiles data permitted to differentiate cheese samples ripened from 30 to 180 days according to the rennet used. The textural analysis differentiated the cheeses made with pig and calf rennet from those made with kid one, which resulted less hard and more elastic. Sensory analysis differentiated the cheeses on the basis of rennet type and cheeses made with pig rennet showed the lowest elasticity, bitter taste, fruity and hay flavour intensity. Conclusions: Pig rennet is fundamental to determine the quality parameters of Pecorino di Farindola cheese and could be used to impair peculiar quality features to ewes' cheeses.
Sono riportati in letteratura molti lavori riguardanti la presenza di ceppi di S. cerevisiae in f... more Sono riportati in letteratura molti lavori riguardanti la presenza di ceppi di S. cerevisiae in formaggi freschi e semi-stagionati. Pochi sono invece gli studi riguardanti le fermentazioni e le cinetiche di crescita. Lo scopo di questo lavoro \ue8 stato quello di studiare l\u2019interazione tra Saccharomyces cerevisiae e Streptococcus thermophylus e/o Lactobacillus delbrueckii subsp. bulgaricus, inoculati in co-cultura, utilizzando siero come mezzo di sviluppo, seguendo la dinamica di produzione di CO2 e la cinetica di sviluppo. Il confronto tra le dinamiche di crescita del lievito e dei batteri lattici, inoculati da soli o insieme hanno evidenziato che la crescita di S.cerevisiae \ue8 stimolata dalla presenza di Str. thermophylus and Lb. delbrueckii subsp. bulgaricus
Effects of the diameter on physicochemical, microbiological and volatile profile in dry fermented... more Effects of the diameter on physicochemical, microbiological and volatile profile in dry fermented sausages produced with two different starter cultures, Food Bioscience,
In this study, PCR-based procedures were developed to detect the occurrence and quantify the expr... more In this study, PCR-based procedures were developed to detect the occurrence and quantify the expression of the tyrosine decarboxylase gene (tdc) in gram-positive bacteria associated with fermented foods. Consensus primers were used in conventional and reverse transcription PCR to analyze a collection of 87 pure cultures of lactic acid bacteria and staphylococci. All enterococci, Staphylococcus epidermidis, Lactobacillus brevis, Lactobacillus curvatus, and Lactobacillus fermentum strains and1of 10 Staphylococcus xylosus strains produced amplification products with the primers DEC5 and DEC3 in accordance with results of the screening plate method and with previously reported result obtained with high-performance liquid chromatography. No amplicons were obtained for tyramine-negative strains, confirming the high specificity of these new primers. A novel quantitative real-time PCR assay was successfully applied to quantify tdc and its transcript in pure cultures and in meat and meat pro...
The main aim of this work was to evaluate, at pilot scale in an industrial environment, the effec... more The main aim of this work was to evaluate, at pilot scale in an industrial environment, the effects of the biocontrol agent Lactococcus lactis CBM21 and thyme essential oil compared to chlorine, used in the washing step of fresh-cut lamb's lettuce, on the microbiota and its changes in relation to the time of storage. The modification of the microbial population was studied through pyrosequencing in addition to the traditional plate counts. In addition, the volatile molecule and sensory profiles were evaluated during the storage. The results showed no significant differences in terms of total aerobic mesophilic cell loads in relation to the washing solution adopted. However, the pyrosequencing data permitted to identify the genera and species able to dominate the spoilage associations over storage in relation to the treatment applied. Also, the analyses of the volatile molecule profiles of the samples during storage allowed the identification of specific molecules as markers of t...
ABSTRACT In this study the thermal resistance of seven strains of staphylococci was studied. Thre... more ABSTRACT In this study the thermal resistance of seven strains of staphylococci was studied. Three of them (two Staphylococcus epidermidis and one Staphylococcus lugdunensis) were isolated from pasteurized tofu, while one Staphylococcus aureus from fermented sausages. Also the corresponding type strains were tested. Their heat resistance was assessed at 80 °C also in relation to different growth conditions (high NaCl concentrations and low pH). Moreover, the effect of two terpenes (carvacrol and citral) on their survival during thermal treatment was assessed. All the strains were able to survive a 20 min thermal treatment and showed a similar behavior, i.e. an inactivation of about 6 log units in the first 2–4 min of treatment, followed by constant survivor counts (2–4 log CFU/ml). The pre-culture of staphylococci under stressing conditions (high NaCl concentration and low pH) increased the susceptibility to thermal treatment in three strains isolated from food matrices. The addition of carvacrol and citral during thermal treatment influenced the number of survived cells at the end of the treatment. This new insight in the thermal resistance of staphylococci needs to be better investigated, in order to study proper strategies to control their occurrence and behavior in real food systems.
The aim of this study was to evaluate the competitive effects of three bacteriocin producing stra... more The aim of this study was to evaluate the competitive effects of three bacteriocin producing strains of Lactococcus lactis subsp. lactis against two aminobiogenic lactic acid bacteria, i.e. the tyramine producing strain Enterococcus faecalis EF37 and the histamine producing strain Streptococcus thermophilus PRI60, inoculated at different initial concentrations (from 2 to 6 log cfu/ml). The results showed that the three L. lactis subsp. lactis strains were able to produce bacteriocins: in particular, L. lactis subsp. lactis VR84 and EG46 produced, respectively, nisin Z and lacticin 481, while for the strains CG27 the bacteriocin has not been yet identified, even if its peptidic nature has been demonstrated. The co-culture of E. faecalis EF37 in combination with lactococci significantly reduced the growth potential of this aminobiogenic strain, both in terms of growth rate and maximum cell concentration, depending on the initial inoculum level of E. faecalis. Tyramine accumulation was strongly reduced when E. faecalis EF37 was inoculated at 2 log cfu/ml and, to a lesser extent, at 3 log cfu/ml, as a result of a lower cell load of the aminobiogenic strain. All the lactococci were more efficient in inhibiting streptococci in comparison with E. faecalis EF37; in particular, L. lactis subsp. lactis VR84 induced the death of S. thermophilus PRI60 and allowed the detection of histamine traces only at higher streptococci inoculum levels (5-6 log cfu/ml). The other two lactococcal strains did not show a lethal action against S. thermophilus PRI60, but were able to reduce its growth extent and histamine accumulation, even if L. lactis subsp. lactis EG46 was less effective when the initial streptococci concentration was 5 and 6 log cfu/ml. This preliminary study has clarified some aspects regarding the ratio between bacteriocinogenic strains and aminobiogenic strains with respect to the possibility to accumulate BA and has also showed that different bacteriocins can have different effects on BA production on the same strain. This knowledge is essentially aimed to use bacteriocinogenic lactococci as a predictable strategy against aminobiogenic bacteria present in cheese or other fermented foods.
Journal of the science of food and agriculture, 2014
Pig rennet is traditionally used in Pecorino di Farindola cheese. In this study, different Pecori... more Pig rennet is traditionally used in Pecorino di Farindola cheese. In this study, different Pecorino cheeses obtained using calf, kid and pig rennets were compared in terms of fatty acids, volatile molecule profile, texture and sensory properties during ripening. The rennet type influenced the fatty acid composition of cheeses, though palmitic, myristic and oleic acids were always predominant. The analysis of volatiles by SPME-GC/MS showed that Pecorino from calf rennet, at the end of ripening, was the least 'evolved' in terms of volatile profile. SPME-GC/MS analysis revealed that cheeses from calf rennet showed the slowest accumulation of free fatty acids over ripening time. Volatile data permitted the differentiation of cheese samples ripened from 30 to 180 days according to the rennet used. Texture analysis differentiated cheeses made with pig and calf rennet from those made with kid rennet, which were less hard and more elastic than the former. Also sensory analysis diffe...
Aims: To characterize the lactobacilli community of 20 sourdoughs using a novel polyphasic approa... more Aims: To characterize the lactobacilli community of 20 sourdoughs using a novel polyphasic approach. Methods and Results: A polyphasic approach, consisting of a two-step multiplex polymerase chain reaction (PCR) system, 16S rRNA gene sequence analysis and physiological features, was applied to identify 127 isolates, representing about 37% of the presumptive lactobacilli collected from sourdough samples. Multiplex PCR successfully identified 111 isolates, while 16S rRNA gene sequencing was applied for the other 16 isolates, two of which could not be associated with any previously described lactic acid bacteria (LAB) species. Strain diversity was evaluated by phenotypic and random amplified polymorphic DNA-PCR analysis. Molecular detection of Lactobacillus group species was also performed on total DNA extracted from the doughs. Conclusions: Abruzzo region sourdough lactobacilli biodiversity, reflected in both Lactobacillus species composition and strain polymorphism, is similar to that of other Italian regions and is a source of novel LAB species. Significance and Impact of the Study: Within culture-independent methods, multiplex PCR is a rapid tool to study the lactobacilli population of sourdoughs.
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