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THE USE AND CONTROL OF MICROORGANISMS TO IMPROVE THE QUALITY OF FOOD
Get PDFIn this present PhD thesis were examined and evaluated different methods for improving the quality of various food products.
The first work involved the study of antibacterial properties of the extract of the leaves of the plant Cocculus orbiculatus, against several serotypes of Listeria monocytogenes. The study of the composition of the extract showed the presence of 26 different compounds, thirteen of which have been extracted by hydro distillation and thirteen compounds by extraction with ethanol. Preliminary, also, the identification of the plant was carried out using molecular techniques. The results showed a bacteriostatic effect of the extract against the target organism under examination.
The work presented in the second chapter, is part of a research project on “Qualification of pig genetic resources aimed at enhancement of production for the Protected Designation of Origin of the dry-cured ham San Daniele Friuli (D.O.P. Prosciutto di San Daniele Friuli), the Protected Designation of Origin of the Gran Padano pig (D.O.P. Gran Suino Padano), and to the Protected Geographical Indication (I.G.P. Sauris) of fresh meat and sausages obtained and recognized with the brand AQUA of Friuli Venezia Giulia”. It follows the chain of the pig from birth to slaughter. In particular, it was evaluated the impact of different pig breed on the final quality of the meat, using the same system of breeding and feeding. The breeds tested were Goland and Duroc per Large White mother. The evaluation was made by taking into account both, the meat (M. longissimus dorsi muscle) and San Daniele dry-cured ham, which is one of the transformed products. The results showed that there are no differences in the chemical-physical and microbiological characteristics of the meat as such, nor significant differences of physico-chemical characteristics of the dry-cured ham.
The third work involved the use of starter cultures of L. curvatus and L. sakei to improve the shelf-life of cooked ham, sliced and packaged under modified atmosphere packaging (MAP). The use of bioprotective cultures influenced the flavour, odour and colour stability of the sliced cooked ham. In addition, the growth of indigenous lactic acid bacteria was inhibited, preventing the formation of the white superficial slime and consequently extending the shelf-life of the product up to 30 days.
The fourth part of this thesis deals with the use of ozone for the decontamination of the equipment and tools used in food chain. Results obtained showed a great variability, depending on both, the type of the tested microorganisms (more or less-resistant, vegetative cells or spores) and the method used to deliver the ozone (wet and dry). As a result, an ozone concentration of 2 or 4 ppm allowed to obtain a reduction from 1 to 5 logs of the target microorganisms.
The last part of this work involved a mix of bioprotective cultures, which were Lactobacillus carnosus/Lactobacillus sakei + Staphylococcus xylosus, Lactococcus lactis subsp. lactis/Lactobacillus sakei + Staphylococcus xylosus, also in different ratio, for the improvement of the shelf-life of hamburger packed under modified atmosphere (MAP) and stored at 4 ± 2 °C. Data showed that inoculated cultures extended the hamburgers shelf-life by limiting the ammoniacal molecules production, the development of spoilage and pathogenic microorganisms, in particular Brochothrix thermosphacta, and avoiding the formation of the white slime on the surface of the hamburgers
Biocontrol of ochratoxigenic moulds (Aspergillus ochraceus and Penicillium nordicum) by Debaryomyces hansenii and Saccharomycopsis fibuligera during speck production
Get PDFSpeck is a meat product obtained from the deboned leg of pork that is salted, smoked and seasoned for four to six months. During speck seasoning, Eurotium rubrum and Penicillium solitum grow on the surface and collaborate with other moulds and tissue enzymes to produce the typical aroma. Both of these strains usually predominate over other moulds. However, moulds producing ochratoxins, such as Aspergillus ochraceus and Penicillium nordicum, can also co-grow on speck and produce ochratoxin A (OTA). Consequently, speck could represent a potential health risk for consumers. Because A. ochraceus and P. nordicum could represent a problem for artisanal speck production, the aim of this study was to inhibit these mould strains using Debaryomyces hansenii and Saccharomycopsis fibuligera. Six D. hansenii and six S. fibuligera strains were tested in vitro to inhibit A. ochraceus and P. nordicum. The D. hansenii DIAL 1 and S. fibuligera DIAL 3 strains demonstrated the highest inhibitory activity and were selected for in vivo tests. The strains were co-inoculated on fresh meat cuts for speck production with both of the OTA-producing moulds prior to drying and seasoning. At the end of seasoning (six months), OTA was not detected in the speck treated with both yeast strains. Because the yeasts did not adversely affect the speck odour or flavour, the strains are proposed as starters for the inhibition of ochratoxigenic moulds
A case of spoilage in wurstel sold in an Italian supermarket
No full textIn the current study, the shelf-life and the spoilage of Italian wurstel sold in a local supermarket was investigated. The analysis included identifying the causative microorganisms and the variations in physical-chemical parameters (pH, aW, lactic acid, and ammonia). The spoilage consisted of a white surface coating or slime that appeared after the thirtieth day of storage. The cause of the spoilage was the uncontrolled growth of thermoduric heterofermentative lactic acid bacteria (LAB) that occurred during storage. The LAB, including Leuconostocs and Brochothrix thermosphacta organisms, can survived the pasteurisation process. Due to the deacidifying action of B.thermosphacta and the production of ammonia, there was no evidence of off-odour or off-flavour and no change in pH. Furthermore, no loss of the vacuum seal was observed in the spoiled wurstel
Come migliorare la qualità del prosciutto cotto affettato confezionato in atmosfera modificata. Impiego di Lactococcus lactis ssp. lactis come coltura bioprotettiva.
No full textImpiego di colture bioprotettive per migliorare la qualità igienico-sanitaria e sensoriale di hamburger
No full textThe use of mix of Lactobacillus carnosus/Lactobacillus sakei + Staphylococcus xilosus, Lactococcus lactis
ssp. lactis/Lactobacillus sakei + Staphylococcus xilosus, Lactobacillus carnosus/Lactobacillus sakei + Staphylococcus
xilosus, can permit to extend the shelf-life of hamburger packaged in MAP and storaged at
a 4 ± 2 °C. The bioprotective coltures have influenced the flavour and the odour of the hamburger.
Moreover they have limited the growth of B.thermosphacta and of Pseudomonas spp. and consequently
no white slime is observed on the hamburger and a low concentration of total volatile nitrogen
(TVN). The shelf-life of the products added with starter is extended to 9 days
Isolamento da colture autoctone, caratterizzazione ed utilizzo di Lactobacillus rhamnosus nella produzione di yogurt
No full textL’impiego di colture lattiche probiotiche è largamente diffuso nei prodotti fermentati (in primis, lo yogurt) e numerose sono le specie lattiche probiotiche utilizzate sottoforma di starter commerciali, tra cui il Lactobacillus rhamnosus. Tuttavia, la possibilità di individuare tali microrganismi anche in colture autoctone, ossia isolate da prodotti di zone geografiche ben definite, è un fattore che, per lo stretto legame con il territorio, conferisce valore aggiunto al prodotto in cui vengono impiegate. Per questo motivo lo scopo del presente lavoro è stata la ricerca e caratterizzazione di ceppi appartenenti alla specie L. rhamnosus in lattoinnesto di un formaggio friulano, il "Fagagna". Tale formaggio è prodotto da latte non pastorizzato e senza l'aggiunta di starter commerciali. I batteri lattici isolati ed identificati, utilizzando metodi molecolari, appartenevano alle specie L. delbrueckii, L. thermophylus, L. rhamnosus, L. fermentum, Streptococcus macedonicus, Enterococcus faecalis e Leuconostoc pseudomesenteroides. I ceppi di L. rhamnosus isolati sono stati caratterizzati per la resistenza al pH, la crescita a diverse temperature, la capacità proteolitica, la capacità di produrre ammine biogene, l'antibiotico resistenza e dal punto di vista molecolare (RAPD, Rep-PCR). Dopo aver valutato i risultati della caratterizzazione, un ceppo di L. rhamnosus (104 ufc/ml) è stato scelto ed utilizzato per la produzione di uno yogurt potenzialmente probiotico accanto alle colture starter tradizionali (Lactobacillus bulgaricus e Streptococcus thermophylus) (109 ufc/ml). Il prodotto ottenuto è stato monitorato nel tempo (0, 10, 20 giorni) e, rispetto al controllo prodotto senza l'aggiunta di L. rhamnosus, gli andamenti nel tempo di L. bulgaricus e Str. thermophylus sono risultati simili, attestandosi a valori di circa 108 ufc/ml. L. rhamnosus è stato capace di crescere e portarsi a valori comparabili a quelli delle altre due specie, concentrazioni che ha mantenuto fino quasi al termine del periodo considerato, dove è stato rilevato alla concentrazione di 107 ufc/ml
Alterazione nei wurstel durante la conservazione.
No full textIt has been studied the spoilage of some italian wurstel, sold in local supermarket. The study included
the identification of the causative microorganisms and the variation of physical-chemical parameters
(pH, Aw, lactic acid, ammonia). The spoilage consisted of a white surface coating or slime, which appeared
later than the thirtieth day of storage. The case was due to an uncontrolled development, during
the storage, of thermoduric heterofermentative LAB, survived the pasteurization, such as Leuconostoc
spp. and B. thermosphacta. There was no evidence of off-odor or off-flavor and no pH changing, due
to deacidifying action of B. thermosphacta and the production of ammonia. It was not also observed in
frankfurters altered any loss of vacuum
Use of bio-protective cultures to improve the shelf-life and the sensorial characteristics of commercial hamburgers
Get PDFThe use of mixtures of bio-protective cultures, like Lactobacillus sakei subsp. carnosus/L sakei + Staphylococcus xylosus (1/1 ratio), Lactococcus lactis spp. lactis/L sakei + S. xylosus (1/1 ratio), and L sakei subsp. carnosus/L. sakei + S. xylosus (1/2 ratio), inoculated in beef hamburger packaged in modified atmosphere and stored at 4 +/- 2 degrees C, determined a better microbiological and chemical-physical quality of the products. In particular, they inhibited the growth of Brochothrix thermosphacta resulting in no white slime on the products as well as they determined a low concentration of total volatile basic nitrogen (TVB-N). Moreover, the bio-protective cultures influenced the flavour and the odour of the hamburgers. For this reason, the shelf life of the products added with starter cultures could be extended up to 12 day
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