Elena Torrieri

Changes in the Spoilage-Related Microbiota of Beef during Refrigerated Storage under Different Packaging Conditions

ABSTRACT The microbial spoilage of beef was monitored during storage at 5°C under three different conditions of modified-atmosphere packaging (MAP): (i) air (MAP1), (ii) 60% O2 and 40% CO2 (MAP2), and (iii) 20% O2 and 40% CO2 (MAP3). Pseudomonas, Enterobacteriaceae, Brochothrix thermosphacta, and lactic acid bacteria were monitored by viable counts and PCR-denaturing gradient gel electrophoresis (DGGE) analysis during 14 days of storage. Moreover, headspace gas composition, weight loss, and beef color change were also determined at each sampling time. Overall, MAP2 was shown to have the best protective effect, keeping the microbial loads and color change to acceptable levels in the first 7 days of refrigerated storage. The microbial colonies from the plate counts of each microbial group were identified by PCR-DGGE of the variable V6-V8 region of the 16S rRNA gene. Thirteen different genera and at least 17 different species were identified after sequencing of DGGE fragments that showed a wide diversity of spoilage-related bacteria taking turns during beef storage in the function of the packaging conditions. The countable species for each spoilage-related microbial group were different according to packaging conditions and times of storage. In fact, the DGGE profiles displayed significant changes during time and depending on the initial atmosphere used. The spoilage occurred between 7 and 14 days of storage, and the microbial species found in the spoiled meat varied according to the packaging conditions. Rahnella aquatilis, Rahnella spp., Pseudomonas spp., and Carnobacterium divergens were identified as acting during beef storage in air (MAP1). Pseudomonas spp. and Lactobacillus sakei were found in beef stored under MAP conditions with high oxygen content (MAP2), while Rahnella spp. and L. sakei were the main species found during storage using MAP3. The identification of the spoilage-related microbiota by molecular methods can help in the effective establishment of storage conditions for fresh meat.

Polyphasic Screening, Homopolysaccharide Composition, and Viscoelastic Behavior of Wheat Sourdough from a Leuconostoc lactis and Lactobacillus curvatus Exopolysaccharide-Producing Starter Culture

ABSTRACT After isolation from different doughs and sourdoughs, 177 strains of lactic acid bacteria were screened at the phenotypic level for exopolysaccharide production on media containing different carbohydrate sources. Two exopolysaccharide-producing lactic acid bacteria (Lactobacillus curvatus 69B2 and Leuconostoc lactis 95A) were selected through quantitative analysis on solid media containing sucrose and yeast extract. The PCR detection of homopolysaccharide (gtf and lev) and heteropolysaccharide (epsA, epsB, epsD and epsE, and epsEFG) genes showed different distributions within species and strains of the lactic acid bacteria studied. Moreover, in some strains both homopolysaccharide and heteropolysaccharide genes were detected. Proton nuclear magnetic resonance spectra suggest that Lactobacillus curvatus 69B2 and Leuconostoc lactis 95A produced the same exopolysaccharide, which was constituted by a single repeating glucopyranosyl unit linked by an α-(1→6) glycosidic bond in a dextran-type carbohydrate. Microbial growth, acidification, and viscoelastic properties of sourdoughs obtained by exopolysaccharide-producing and nonproducing lactic acid bacterial strains were evaluated. Sourdough obtained after 15 h at 30°C with exopolysaccharide-producing lactic acid bacteria reached higher total titratable acidity as well as elastic and dissipative modulus curves with respect to the starter not producing exopolysaccharide, but they showed similar levels of pH and microbial growth. On increasing the fermentation time, no difference in the viscoelastic properties of exopolysaccharide-producing and nonproducing samples was observed. This study suggests that dextran-producing Leuconostoc lactis 95A and Lactobacillus curvatus 69B2 can be employed to prepare sourdough, and this would be particularly useful to improve the quality of baked goods while avoiding the use of commercially available hydrocolloids as texturizing additives.

A combination of modified atmosphere and antimicrobial packaging to extend the shelf-life of beefsteaks stored at chill temperature.

An antimicrobial polyethylene (PE) film was obtained by coating a nisin-based antimicrobial solution. PE sheets were coated on both sides and were used for the packaging of beefsteaks to be stored in air or modified atmosphere packaging (MAP, 60% O₂-40% CO₂). Microbial populations, species diversity, headspace volatile organic compounds, colour and sensory properties were monitored after 0, 1, 7 and 12 days of storage at 4 °C. The viable counts showed that there was an effect of MAP and antimicrobial film on the development of all the spoilage associated microbial populations. Carnobacterium spp., Brochothrix thermosphacta, Pseudomonas fragi and Rhanella aquatilis were found in most of the samples. C. maltaromaticum was identified in MRS bulk cells from samples stored in air as well as MAP. Quantitative data of headspace-SPME-GC/MS analysis showed that during storage the production of volatile organic compounds (VOCs) was affected by the use of the treated film and the MAP storage. Compounds such as phenylethylalcohol, nonanal, decanal and ethylbutanoate were produced only from 7 to 12 day of storage and only in the samples stored in air. In agreement with the microbiological and VOCs data, the meat stored in active packaging scored the best rankings in the sensory evaluation. Principal component analysis of microbial, sensory and instrumental data showed that beefsteaks stored with the combination of MAP and active packaging for 12 days at 4 °C differed from the other samples that were more associated to high microbial loads, VOCs concentration and meat off odour perception. In conclusion, the antimicrobial sheets in combination with MAP storage at 4 °C were effective for the storage of beefsteaks by retarding the growth of spoilage bacteria, determining lower concentration of VOCs and keeping acceptable levels of colour and other sensory parameters for more than 10 days.

Antimicrobial packaging to retard the growth of spoilage bacteria and to reduce the release of volatile metabolites in meat stored under vacuum at 1°C.

A nisin-EDTA solution was used for activation of the internal surface of plastic bags that were used to store beef chops at 1°C after vacuum packaging. The aim of the work was to evaluate the effect of the antimicrobial packaging on beef during storage. Volatile compounds and microbial populations were monitored after 0, 9, 20, 36, and 46 days of storage. The active packaging retarded the growth of lactic acid bacteria. Brochothrix thermosphacta was unable to grow for the whole storage time in treated samples, while the levels of Carnobacterium spp. in treated samples were below the detection limit for the first 9 days and reached loads below 5 Log CFU/cm(2) after 46 days. On the other hand, Enterobacteriaceae and Pseudomonas spp. were not affected by the use of the antimicrobial packaging and grew in all of the samples, with final populations of about 4 Log CFU/cm(2). Carnobacterium divergens was identified by PCR-denaturing gradient gel electrophoresis analysis of DNA extracted from beef after 36 days of storage. During beef storage, alcohols, aldehydes, ketones, and carboxylic acids were detected in the headspace of beef samples by solid-phase microextraction-gas chromatography-mass spectrometry analysis. The microbial metabolic activity was affected by the use of the antimicrobial film from the beginning up to 36 days with a maximum in the differences of volatile metabolites in samples analyzed at 20 days. The volatiles were also determined by electronic nose, allowing differentiation based on the time of storage and not on the type of packaging. The active packaging reduces the loads of spoilage microbial populations and the release of metabolites in the headspace of beef with a probable positive impact on meat quality.

Mathematical Modelling of Modified Atmosphere Package: An Engineering Approach to Design Packaging Systems for Fresh-Cut Produce

Consumer demand for freshness and for convenience food has led to the evolution and increased production of fresh-cut fruits and vegetables. Moreover, this may represent a way to increase the consumption of fresh fruits and vegetables and therefore be a benefit for the crops-sector economy. Because the increase in convenience for the consumer has a detrimental effect on product quality, attention must be focused on extending shelf-life while maintaining quality. Modified atmosphere packaging (MAP) is a packaging technology that, by making qualitative or quantitative changes to the atmosphere composition around the product, can improve product preservation. However, MAP must be carefully designed, as a poorly designed system may be ineffective or even shorten product shelf-life. Thus, whereas in the past a trial-and-error approach to packaging of food was predominant, nowadays the need has emerged for an engineering approach to properly design a package to improve product shelf-life. Therefore, to ensure an appropriate gas composition during the product’s shelf-life, a model should take into account all the variables that play a critical role, such as product respiration and its mass; packaging material and its geometry; and environmental conditions such as temperature, relative humidity, and gas composition.

Shelf Life Prediction of Fresh Italian Pork Sausage Modified Atmosphere Packed

The shelf life of fresh Italian pork sausages packed in modified atmosphere was studied. Samples were packed using different levels of oxygen (high and low) with different levels of carbon dioxide (high-low) in the atmospheres headspace and were stored at 4 °C for 9 days. Microbial, physiochemical and sensory parameters were analyzed during storage. A consumer test was performed to determine the critical acceptability levels. Sensory data were mathematically modelled to estimate product shelf life. A first-order kinetic model and a Weibull-type model aptly described, respectively, the changes in fresh pork sausage odor and color over storage time. These models may be used to predict the sensory shelf life of fresh pork sausage. Results showed that 20% O2 and 70% CO2 extend fresh pork sausage shelf life to 9 days at 4 °C. The microbial quality of the samples at the critical sensory level of acceptability was within the range of microbial acceptability.