Multivariate factor analysis of Girgentana goat milk composition

The interpretation of the several variables that contribute to defining milk quality is difficult due to the high degree of correlation among them. In this case, one of the best methods of statistical processing is factor analysis, which belongs to the multivariate groups; for our study this particular statistical approach was employed. A total of 1485 individual goat milk samples from 117 Girgentana goats, were collected fortnightly from January to July, and analysed for physical and chemical composition, and clotting properties. Milk pH and tritable acidity were within the normal range for fresh goat milk. Morning milk yield resulted 704 ± 323 g with 3.93 ± 1.23% and 3.48±0.38% for fat and protein percentages, respectively. The milk urea content was 43.70 ± 8.28 mg/dl. The clotting ability of Girgentana milk was quite good, with a renneting time equal to 16.96 ± 3.08 minutes, a rate of curd formation of 2.01 ± 1.63 minutes and a curd firmness of 25.08 ± 7.67 millimetres. Factor analysis was performed by applying axis orthogonal rotation (rotation type VARIMAX); the analysis grouped the milk components into three latent or common factors. The first, which explained 51.2% of the total covariance, was defined as “slow milks”, because it was linked to r and pH. The second latent factor, which explained 36.2% of the total covariance, was defined as “milk yield”, because it is positively correlated to the morning milk yield and to the urea content, whilst negatively correlated to the fat percentage. The third latent factor, which explained 12.6% of the total covariance, was defined as “curd firmness,” because it is linked to protein percentage, a30 and titatrable acidity. With the aim of evaluating the influence of environmental effects (stage of kidding, parity and type of kidding), factor scores were analysed with the mixed linear model. Results showed significant effects of the season of kidding and parity on common factors, while no differences were found between goats with one or more kids. The multivariate factor analysis technique was effective in describing the quality of Girgentana milk with a low number of new latent variables. These new variables have been useful in the study of the effect of some technical factors such as parity and season of kidding on the quantitative and qualitative aspects of milk production in this goat breed

Analysis of microbiological variation in PDO Vastedda della valle del Belìce cheese during the storage period

The PDO “Vastedda della valle del Belìce” is a Sicilian pasta filata sheep cheese, made from raw milk without starter addition. It is a small round cheese without rind, weighing about 500-700 g. It is cheese is marketed also out of Sicily to allow its marketing and to prolong its shelf-life. The aim of this work was to evaluate the variation of microbiological parameters during the shelf-life period. Then 162 Vastedda cheeses from 18 cheese-making processes in 7 farms have been analysed at different times of storage at 4°C (0, 15, 30, 45, 60, 75, 90, 105, 120 days). Coliforms and E. coli were detected into 7/18 cheese-making processes and their count decreased during the storage period. Enterococci were more resistant to high temperature achieved during the stretching and their were rather stable during storage period (105 cfu/g). The concentration of total Bacterial Count and Mesophilic Lactococci were around 107 cfu/g, while the concentration of Thermophilic Lactococci was higher (108 cfu/g) probably due to the stretching at 90°C. In conclusion, this study shows the good sanitary conditions of cheeses. Overall, the lactic flora was kept alive and vital at high concentration (> 107 cfu/g) until 120 days of storage

Cellule somatiche in latte ovino: analisi e applicazione delle curve ROC

Negli ovini da latte le mastiti costituiscono una delle principali cause di perdite economiche per la ridotta produzione e soprattutto per la scarsa qualità tecnologica del latte. Diversi studi hanno dimostrato che il contenuto in cellule somatiche (SCC) del latte può essere impiegato sia come metodo diagnostico sia come criterio di selezione nei programmi di miglioramento genetico per la resistenza alle mastiti. Obiettivo di questo lavoro è stato applicare la metodologia delle Receiver Operating Characteristics curves (ROC) per valutare la capacità diagnostica del SCC nel discriminare le mammelle infette da quelle sane e per individuare un valore soglia discriminante in ovini da latte. In totale sono stati analizzati 14.072 campioni di latte individuale da 720 pecore di razza Valle del Belice in 5 allevamenti. L’isolamento e l’identificazione batterica sono stati effettuati tramite semina di 10 μl di latte su Agar Sangue incubato a 37°C per 24 - 48h in aerofilia e, se necessario, in microaerofilia e la determinazione delle SCC mediante citometria di flusso. In base al risultato dell’esame batteriologico sono stati identificati 9 gruppi. La media aritmetica del SCS per i test negativi e positivi è risultata rispettivamente di 5.17 ± 0.008 e 5.80 ± 0.010, la media geometrica del SCC per i test negativi e positivi è risultata rispettivamente di 146.96 x 103 e 630.85 x 103 cells/ml. Complessivamente sono risultati positivi all’esame batteriologico 6207 campioni con una prevalenza pari al 44,1%. L’AUC è risultata pari a 0.73 ± 0.004 (P 0.0001). Il POO è risultato essere >427x103 cells/ml, in corrispondenza di tale punto la sensibilità è pari al 59,2% mentre la specificità si attesta all’80,9%. In corrispondenza di tale valore il 71% dei soggetti positivi ed il 72% dei soggetti negativi sono classificati correttamente. L’approccio di tipo non parametrico per la stima delle ROC ha dimostrato che il SCC può essere validamente utilizzato per discriminare gli animali infetti da quelli sani. Tuttavia ulteriori studi si ritengono necessari per una più precisa valutazione economica dei costi delle mastiti in considerazione del fatto che il POO sulle ROC tende a spostarsi verso valori con più alta Se e più bassa Sp man mano che i costi dei falsi positivi si riducono rispetto a quelli dei falsi negativi o quando aumenta il valore della prevalenza

Cellule somatiche ed isolamento di agenti mastidogeni in ovini di razza Valle del Belice

Il conteggio delle cellule somatiche nel latte ovino si è dimostrato un valido strumento per la determinazione dello stato sanitario della mammella. Oggetto del presente studio è stato valutare eventuali relazioni fra il contenuto in cellule somatiche (SCC) e le infezioni mammarie (IMI) negli ovini. L’indagine è stata condotta nel periodo 2006-2012 su n.14072 campioni di latte individuale. In base al tenore i campioni sono state inseriti in 4 classi: 300.000; da 301.000 a 500.000; da 501.000 a 1.000.000 e ≥1.001.000 cellule/ml. Per l’isolamento colturale sono stati seminati 10 μl di latte su piastre di Agar Sangue incubate per 24-48 h a 37 °C in aerofilia e, se necessario, in microaerofilia. Sono stati distinti 10 gruppi: nessun isolamento, isolamento di stafilococchi coagulasi positivi (S. aureus, S. intermedius e S. hyicus), stafilococchi coagulasi negativi (CNS), streptococchi patogeni (S. agalactiae, S. dysgalactiae e S. uberis), altri streptococchi o enterococchi (S. acidominimus,S. canis, S. viridans, S. mitis, S. mitior ed E. faecalis), Corynebacterium, Mannheimia haemolithyca, Bacillus spp, altri germi (Proteus spp., E.coli e Pseudomonas spp.) ed associazione di CNS ed altri streptococchi. Per ogni gruppo è stata calcolata la media geometrica del SCC. Il 44% dei campioni analizzati mostrava positività all’esame microbiologico con percentuali crescenti in funzione della classe di SCC d’appartenenza. Si riportano i microrganismi isolati e le relative prevalenze: CNS 80%, stafilococchi coagulasi positivi 11,76% di cui 677 S. aureus (10,9%), 43 S. intermedius (0,69%) e 10 S. hyicus (0,16%), Streptococcus spp. 3,09%, streptococchi patogeni 2,64%, M. haemolytica 0.63%, Corynebacterium 0,18%, Pseudomonas 0,10%, Bacillus 0,68%, E. coli 0,06% e Proteus 0,34%. La media geometrica del SCC mostra differenze statisticamente significative fra i vari gruppi di batteri. Nell’allevamento ovino gli CNS si confermano i principali agenti di mastite subclinica con tendenza alla cronicizzazione pertanto ulteriori approfondimenti sono necessari per indagare il loro ruolo patogenetic

Animal rennets as sources of dairy lactic acid bacteria

The microbial composition of artisan and industrial animal rennet pastes was studied by using both culture-dependent and -independent approaches. Pyrosequencing targeting the 16S rRNA gene allowed to identify 361 operational taxonomic units (OTUs) to the genus/species level. Among lactic acid bacteria (LAB), Streptococcus thermophilus and some lactobacilli, mainly Lactobacillus crispatus and Lactobacillus reuteri, were the most abundant species, with differences among the samples. Twelve groups of microorganisms were targeted by viable plate counts revealing a dominance of mesophilic cocci. All rennets were able to acidify ultrahigh-temperature-processed (UHT) milk as shown by pH and total titratable acidity (TTA). Presumptive LAB isolated at the highest dilutions of acidified milks were phenotypically characterized, grouped, differentiated at the strain level by randomly amplified polymorphic DNA (RAPD)-PCR analysis, and subjected to 16S rRNA gene sequencing. Only 18 strains were clearly identified at the species level, as Enterococcus casseliflavus, Enterococcus faecium, Enterococcus faecalis, Enterococcus lactis, Lactobacillus delbrueckii, and Streptococcus thermophilus, while the other strains, all belonging to the genus Enterococcus, could not be allotted into any previously described species. The phylogenetic analysis showed that these strains might represent different unknown species. All strains were evaluated for their dairy technological performances. All isolates produced diacetyl, and 10 of them produced a rapid pH drop in milk, but only 3 isolates were also autolytic. This work showed that animal rennet pastes can be sources of LAB, mainly enterococci, that might contribute to the microbial diversity associated with dairy productions

Microbial activation of wooden vats used for traditional cheese production and evolution of the neoformed biofilms

Three Lactococcus lactis subsp. cremoris strains were used to develop ad hoc biofilms on the surfaces of virgin wooden vats used for cheese production. Two vats (TZ) were tested under controlled conditions (pilot plant), and two vats (TA) were tested under uncontrolled conditions (industrial plant). In each plant, one vat (TA1 and TZ1) was used for the control, traditional production of PDO Vastedda della Valle del Belìce (Vastedda) cheese, and one (TA2 and TZ2) was used for experimental production performed after lactococcal biofilm activation and the daily addition of a natural whey starter culture (NWSC). Microbiological and scanning electron microscopy analyses showed differences in terms of microbial levels and composition of the neoformed biofilms. The levels of the microbial groups investigated during cheese production showed significant differences between the control trials and between the control and experimental trials, but the differences were not particularly marked between the TA2 and TZ2 productions, which showed the largest numbers of mesophilic lactic acid bacterium (LAB) cocci. LAB populations were characterized phenotypically and genotypically, and 44 dominant strains belonging to 10 species were identified. Direct comparison of the polymorphic profiles of the LAB collected during cheese making showed that the addition of the NWSC reduced their biodiversity. Sensory evaluation showed that the microbial activation of the wooden vats with the multistrain Lactococcus culture generated cheeses with sensory attributes comparable to those of commercial cheese. Thus, neoformed biofilms enable a reduction of microbial variability and stabilize the sensorial attributes of Vastedda cheese