Erica Tirloni

Microbiological shelf life at different temperatures and fate of Listeria monocytogenes and Escherichia coli inoculated in unflavored and strawberry yogurts

Three different trials were performed on unflavored and strawberry yogurts produced in a small-scale dairy plant. In the first trial, the microbiological shelf life of the products was evaluated at 4, 8, and 20°C. At 4°C the product showed low total viable counts until the end of the trial (d 35=3.0±0.7 and 1.5±0.0 log cfu/g in unflavored and strawberry yogurt, respectively). The loads were lower in strawberry yogurt at 4°C compared with unflavored yogurt because of the antimicrobial activity exerted by potassium sorbate present in the fruit puree added. Yeasts were confirmed to be the specific spoilage agents of this product, reaching rapidly high loads with thermal abuse (5.9-7.4 log cfu/g at d 18). In the second trial, Escherichia coli and especially Listeria monocytogenes added at 2 concentrations (2 and 5 log cfu/g) showed a rapid decrease in both types thanks to the acidic conditions provided by the products, but L. monocytogenes was very resistant; its presence was always detected until the end of the period considered (d 68). In the third trial, no statistically significant differences were detected between wild and acid-adapted strains of L. monocytogenes added to the products, due to the quick adaptation that probably occurred after inoculation.

First Results of a Detection Sensor for the Monitoring of Laying Hens Reared in a Commercial Organic Egg Production Farm Based on the Use of Infrared Technology.

The development of a monitoring system to identify the presence of laying hens, in a closed room of a free-range commercial organic egg production farm, was the aim of this study. This monitoring system was based on the infrared (IR) technology and had, as final target, a possible reduction of atmospheric ammonia levels and bacterial load. Tests were carried out for three weeks and involved 7 ISA (Institut de Sélection Animale) brown laying hens. The first 5 days was used to set up the detection sensor, while the other 15 days were used to evaluate the accuracy of the resulting monitoring system, in terms of sensitivity and specificity. The setup procedure included the evaluation of different color background (CB) thresholds, used to discriminate the information contents of the thermographic images. At the end of this procedure, a CB threshold equal to an increase of 3 °C from the floor temperature was chosen, and a cutoff level of 196 colored pixels was identified as the threshold to use to classify a positive case. The results of field tests showed that the developed monitoring system reached a fine detection accuracy (sensitivity = 97.9% and specificity = 94.9%) and the IR technology proved to be a possible solution for the development of a detection sensor necessary to reach the scope of this study.

Former food products safety: microbiological quality and computer vision evaluation of packaging remnants contamination

ABSTRACT The use of alternative feed ingredients in farm animal’s diets can be an interesting choice from several standpoints, including safety. In this respect, this study investigated the safety features of selected former food products (FFPs) intended for animal nutrition produced in the framework of the IZS PLV 06/14 RC project by an FFP processing plant. Six FFP samples, both mash and pelleted, were analysed for the enumeration of total viable count (TVC) (ISO 4833), Enterobacteriaceae (ISO 21528-1), Escherichia coli (ISO 16649-1), coagulase-positive Staphylococci (CPS) (ISO 6888), presumptive Bacillus cereus and its spores (ISO 7932), sulphite-reducing Clostridia (ISO 7937), yeasts and moulds (ISO 21527-1), and the presence in 25 g of Salmonella spp. (ISO 6579). On the same samples, the presence of undesired ingredients, which can be identified as remnants of packaging materials, was evaluated by two different methods: stereomicroscopy according to published methods; and stereomicroscopy coupled with a computer vision system (IRIS Visual Analyzer VA400). All FFPs analysed were safe from a microbiological point of view. TVC was limited and Salmonella was always absent. When remnants of packaging materials were considered, the contamination level was below 0.08% (w/w). Of note, packaging remnants were found mainly from the 1-mm sieve mesh fractions. Finally, the innovative computer vision system demonstrated the possibility of rapid detection for the presence of packaging remnants in FFPs when combined with a stereomicroscope. In conclusion, the FFPs analysed in the present study can be considered safe, even though some improvements in FFP processing in the feeding plant can be useful in further reducing their microbial loads and impurity. Graphical Abstract

Influence of Skin Packaging on Raw Beef Quality: A Review

A detailed revision of several aspects related to the application of skin packaging to raw beef was considered. Skin packaging, a relatively new technique derived from vacuum packaging, was developed with the aim of retailing small portions of fresh meat, minced meat, or meat preparations. Above all, the influence of this typology of packaging on the microbial population of raw meat was studied, with particular attention to total viable count, aerobic spoilage bacteria, anaerobic bacteria, Enterobacteriaceae, Brochothrix thermosphacta, and lactic acid bacteria. Moreover, the effect on acidification by LAB was also deepened. As colour is the main characteristic influencing purchase decisions at the point of sale, the effect of skin packaging on this parameter was evaluated for raw meat but also for cooked meat. Tenderness, juiciness, and the ability to hold liquid of raw meat when packed in skin conditions were also considered. Furthermore, odour and flavour were considered as sensorial parameters possibly affected by skin packaging. Finally, acceptability by consumer was also investigated. In the studies considered, results showed that skin packaging is advantageous in terms of maintenance of meat quality and for prolonging shelf-life, improving the stability of the products.

American lobsters (Homarus americanus) not surviving during air transport: evaluation of microbial spoilage

Eighteen American lobsters (Homarus americanus), dead during air transport, were analysed in order to evaluate the microbial population of meat, gills and gut: no specific studies have ever been conducted so far on the microbiological quality of American lobsters’ meats in terms of spoilage microbiota. The meat samples showed very limited total viable counts, in almost all the cases below the level of 6 Log CFU/g, while higher loads were found, as expected, in gut and gills, the most probable source of contamination. These data could justify the possibility to commercialise these not-surviving subjects, without quality concerns for the consumers. Most of the isolates resulted to be clustered with type strains of Pseudoalteromonas spp. (43.1%) and Photobacterium spp. (24.1%), and in particular to species related to the natural marine environment. The distribution of the genera showed a marked inhomogeneity among the samples. The majority of the isolates identified resulted to possess proteolytic (69.3%) and lipolytic ability (75.5%), suggesting their potential spoilage ability. The maintanance of good hygienical practices, especially during the production of ready-to-eat lobsters-based products, and a proper storage could limit the possible replication of these microorganisms.

Predicting growth of Listeria monocytogenes in fresh ricotta

Challenge tests with eight brands of fresh ricotta showed rapid growth of Listeria monocytogenes and significant variability in physical-chemical characteristics. Thus, two cardinal parameters models were developed for the growth of L. monocytogenes in ricotta including, respectively, terms for temperature (Model 1) and temperature and pH (Model 2). Also an extensive, existing growth model including the effect of organic acids (Model 3) was product recalibrated to predict growth of L. monocytogenes in ricotta. Interestingly, a lack of anti-listerial effect of organic acids in ricotta was observed in this study. The range of applicability of Models 1 and 2 in ricotta (characterized by absence of competitive microbiota) included storage at temperatures from 4.1 to 20.6 °C, pH from 5.5 to 6.6, moisture contents from 72% to 82%, NaCl from 0.38% to 0.60%, concentrations of acetic acid from 579 to 1559 ppm in the water phase, citric acid from 14,774 to 46,116 ppm in the water phase, and lactic acid from 0 to 4146 ppm in the water phase. Comparing observed and predicted maximum specific growth rates of L. monocytogenes in ricotta showed a bias-factor significantly above 1, for existing models developed for broth and these models were thus fail-safe with predicted growth being faster than observed, while typically below 1 for models developed for other food types. The models developed in the present study showed bias-factors of 1.10, 1.06 and 0.78, respectively, for Model 1, 2, and 3. In particular, Model 1 and 2 developed and successfully validated could allow an easy determination of safe shelf-life of ricotta and facilitated the reformulation the product with the aim to increase shelf-life or safety.

Microbiological Evaluation of Carcasses of Wild Boar Hunted in a Hill Area of Northern Italy

This study evaluated the prevalence of potential pathogenic bacteria (mainly Campylobacter spp., but also Listeria monocytogenes and Salmonella) in wild boar (S us scrofa) and the hygiene of carcasses of wild boar hunted in a hill area of northern Italy during a hunting season (October to December). In total, 62 animals were submitted to microbiological analyses of the tonsils (detection of Listeria spp. and Listeria monocytogenes), caecal content (detection of Salmonella and Campylobacter spp.), mesenteric lymph glands (detection of Salmonella), and carcasses. In addition to analyzing pathogen prevalence and carcass hygiene of these animals, we performed an enumeration of total viable count (TVC), Enterobacteriaceae, Escherichia coli, coagulase-positive staphylococci, and spores of sulfite-reducing clostridia. Influencing factors considered were sex, weight, and age of the animals and environmental temperature on the day of hunting. A high prevalence was observed for L. monocytogenes in tonsils (35.3%) and for Campylobacter spp. in caecal content (51.8%), whereas Salmonella enterica strains (mainly serovar Thompson) were only occasionally isolated (7% in caecal content and 3.5% in lymph glands). The prevalence of L. monocytogenes was influenced by animal age and environmental temperature. Campylobacter spp. were the only pathogens detected on the carcasses (16.7%). Carcasses were characterized by low levels of contamination: TVC, 3.21 ± 0.80 log CFU/cm2, Enterobacteriaceae, 1.32 ± 0.89 log CFU/cm2; E. coli, 1.31 ± 0.93 log CFU/cm2; and occasional detection of low counts of staphylococci and clostridia. TVC was positively influenced only by high environmental temperature, and higher Enterobacteriaceae counts were detected on heavy male carcasses than on females. The results confirmed the potential role of wild boars as reservoirs for the most important foodborne pathogens. But a low carcass contamination level is achievable if hunters are properly trained about hygienic carcass management and slaughtering procedures.

Effect of dairy product environment on the growth of Bacillus cereus

pH is one of the most important parameters to manage bacterial replication in foodstuffs. In this study, the ability of 2 Bacillus cereus strains, 1 clinical human isolate (GPe2) and 1 isolate from a dairy product (D43), were investigated for in vitro growth at different pH values (from 3.5 to 7.5) at 2 temperatures (15 and 37°C), showing their ability to grow from 5.5 to 7.5 and from 5.0 to 7.5, respectively. The ability of spores of these 2 microorganisms to germinate in different typologies of dairy products (unflavored yogurt, Taleggio cheese, mascarpone cheese, and raw and pasteurized milk) was also investigated by inoculating the spores and maintaining the products at 15°C. No growth was observed in yogurt, likely due to the combined effect of low pH (<5) and the presence of natural microflora. An inhibitory action of the natural microflora on the growth of B. cereus was also hypothesized for Taleggio cheese and raw milk, as these substrates were characterized by a high natural lactic acid bacteria population and permissive pH values (5.8/6.8 in Taleggio cheese, >7 in raw milk). In pasteurized milk and mascarpone cheese, where pH was not restrictive for B. cereus growth and where no significant natural microflora was present, growth occurred rapidly up to loads close to 7 log cfu/g.

Evaluation of a loop-mediated isothermal amplification method for the detection of Listeria monocytogenes in dairy food

Objective of the present study was to test the performances of a loop-mediated isothermal amplification (LAMP)-based method for the detection of Listeria monocytogenes, with particular focus on the dairy products. The specificity of the method was evaluated on 42 different Listeria spp. strains from collections, food and environmental samples. 100% (32 of 32) of the L. monocytogenes strains were correctly recognised, and none of other 10 Listeria spp. strains was misidentified. The sensitivity was evaluated on four L. monocytogenes strains from different sources. The instrument was able to detect 10-400 CFU/mL. The ability to detect low initial numbers of L. monocytogenes (0.3-0.7 Log CFU/g) was also evaluated, in duplicate, in pasteurised milk (whole and skimmed) and dairy samples (fresh ricotta, crescenza, mascarpone, mozzarella, cottage cheese, cream cheese, taleggio, gorgonzola). The analysis was performed after 18, 24 and 48 h of incubation, and was coupled with the count of L. monocytogenes in the broth. Microbial loads were insufficient to achieve a positive result after 18 and 24 h in most of the samples; after 48 h, all the products, except taleggio and one gorgonzola sample, were identified as positive; the sensitivity of the method when applied to contaminated dairy foods was about 5 Log CFU/g. The LAMP method tested can be considered a very useful tool, as it is a costeffective and easy-functioning method. The preliminary data obtained should be confirmed with a validation process taking into account different food typologies.

Microbiological and chemico-physical shelf-life and panel test to evaluate acceptability of liver mortadella

This study aimed to evaluate the shelf life of sliced cooked liver mortadella packaged in MAP (70-85% N2, 15-30% CO2) and stored in refrigeration (4°C) or slight thermal abuse (8°C) for up to 49 days (declared best before date 45 days). The proximate composition, aw nitrites and NaCl content were determined at T0. Weekly, samples were submitted to microbiological [total viable count (TVC), lactic acid bacteria (LAB), Enterobacteriaceae, Escherichia coli, Pseudomonas spp., coagulase positive staphylococci, sulphite reducing clostridia, yeasts and moulds, Listeria monocytogenes and Salmonella spp.] and physicalchemical analyses [pH, colorimetric parameters, total volatile basic nitrogen (TVBN), thiobarbituric acid reactive substances (TBARs)], in parallel with consumer acceptability tests. The product characteristics (low salt and nitrites concentration, high aw and pH close to 6.5) were not efficient hurdles for microbial growth. No pathogens were detected in the samples; the initial TVC [5.4 Log colony forming unit (CFU)/g] increased rapidly, reaching values around 8 Log CFU/g at T14 for both the series, and was almost totally composed by LAB, leading to the acidification of the product (pH at T49=5.05 at 4°C and 5.24 at 8°C). The other microbiological parameters were below 2 Log CFU/g. The product showed a good protein and lipid stability (TVBN <33 N/100 g and TBARs <8 nmol/g at T49). The sensorial quality of liver mortadella was more affected by the storage time than by the temperature. An evident colour modification was detected after T35, when the product was also frequently rejected by the panellists, mainly due to odour. Thus, the shelf life of sliced cooked liver mortadella should be shortened below 30 days.