Identification of the contaminating psychrotrophic bacteria in refrigerated bulked raw milk and the assessment of their deteriorating potential

This work aimed to characterize, identify, and determine the deteriorating potential of the contaminating psychrotrophic bacteria in refrigerated raw milk. Samples were submitted to serial dilutions and plated in specific culture media to form a bacterial culture collection. The isolates were characterized for their morphology and biochemical characteristics. The deteriorating potential of the isolates was determined according to the proteolytic, lipolytic and lecithinase activities at 4.0 ºC, 6.5 ºC, and 25.0 ºC. The results obtained for deterioration potential were assessed by the multivariate statistical method and by the principal components analysis (PCA). A total of 159 isolates were characterized, and of these, 46 strongly proteolytic Gram-negative isolates were selected for identification using the API 20 NE kit. The predominant bacteria were Gram-negative and oxidase and catalase positive, with a predominance of bacteria of the genus Pseudomonas. Using PCA, it was shown that the bacteria with the greatest deterioration potential were lecithinase producers, and that, in the autumn, proteolytic bacteria predominated at 4.0 ºC. Of the 46 isolates identified, more than 80% belonged to the species Pseudomonas fluorescens. Thus, attention should be given to the importance of implementing microbial contamination prevention measures in the bulking process, since, even under refrigeration, psychrotrophic bacteria multiply and produce enzymes that deteriorate lipids and proteins, with consequent quality losses of the milk and its derivatives, yield losses in the production of dairy products, and economic losses.

Microbiological quality assessment of fresh tilapia marketed in the Federal District and of the ice used for its conservation

Tilapia (Oreochromis niloticus) is the most cultivated and consumed freshwater fish in Brazil. The present study aimed to evaluate the microbiological quality of ice and fresh tilapia samples commercialized in the Federal District. Tilapia samples were tested for counts of mesophilic and psychrotrophic bacteria, determination of total and thermotolerant coliforms, Staphylococcus aureus counts and presence of Salmonella. Ice samples were analyzed for determination of total coliforms and thermotolerant coliforms and presence of Escherichia coli. Of the 20 samples of fresh tilapia analyzed, ten samples (50%) presented Salmonella (genetically confirmed through the presence of the invA gene) and, therefore, were unfit for consumption. S. aureus was found in 11 samples (55%), and one sample of fillet presented S. aureus counts (3.15 CFU/g) above the limit allowed by Brazilian legislation (3 log CFU/g). S. aureus colonies were confirmed by detection of CoA gene in molecular analysis. Of the 14 ice samples analyzed, 12 samples (85.7%) were unfit for use in fish conservation due to the presence of total coliforms and 9 ice samples (64.3%) were also contaminated with thermotolerant coliforms. E. coli was isolated from 6 ice samples (42.9%) and confirmed in the molecular analysis through the amplification of the MalB gene. In conclusion, the high contamination of tilapia samples with Salmonella and of the ice used for its conservation with coliforms and E. coli indicates the need for better hygienic practices in the tilapia production chain, to increase its quality and microbiological safety.

Avaliação do uso de ozônio em temperaturas de leite cru refrigerado na contagem de psicrotróficos

A qualidade do leite cru está associada às boas práticas de ordenha proveniente de rebanhos sadios e com refrigeração obrigatória do leite cru na granja leiteira entre 4 e 7° C, podendo chegar até, no máximo, 9° C durante a coleta final (BRASIL 2018). Embora a refrigeração seja eficaz para aumentar a vida útil do leite cru, a manutenção das baixas temperaturas favorece a multiplicação de bactérias psicrotróficas, que produzem proteases e lipases termorresistentes, que permanecendo ativas mesmo após a pasteurização, podem afetar negativamente, tanto o próprio leite, quanto seus derivados (RIBEIRO et al., 2018). Visando reduzir a contagem de microrganismos psicrotróficos no leite cru, o presente trabalho avaliou a eficácia da aplicação de ozônio, considerado um bactericida verde por não ser poluente e não deixar resíduos no alimento, diretamente no tanque de resfriamento. As amostras de leite cru foram obtidas de um rebanho saudável e recolhidas diretamente do tanque de resfriamento da propriedade e armazenadas em frascos estéreis com volume de 6 litros sob refrigeração (4 e 9° C). A aplicação do ozônio seguiu delineamento fatorial com variáveis independentes sendo as temperaturas do leite (4 e 9° C) e os tempos de exposição ao ozônio (5 e 15 minutos) utilizando Gerador de Ozônio N202F Bivolt 500mg/h O³ Disinfector - Diluka Power. Foram retiradas amostras antes e após a ozonização. As amostras foram então armazenadas por 48 horas sob refrigeração (4° C) para permitir a proliferação da flora psicrotrófica. O teor de psicrotróficos e a contagem bacteriana total das amostras e do grupo controle foram avaliados em meio ágar bacteriológico PCA por 10 dias a 7° C e a 36° C por 24 horas, respectivamente. A aplicação de ozônio foi eficaz em reduzir a contagem de microrganismos psicrotróficos no tempo de 5 minutos a 4° C, esse resultado é extremamente satisfatório, visto que, a temperatura de aplicação é a mesma aplicada aos tanques de refrigeração nas propriedades, o que permitiria, facilmente, a aplicação nas próprias fazendas. Agradecimentos Agradecemos à equipe do Serviço de Orientação à Alimentação Pública da FMVZ-Unesp e ao proprietário da fazenda por disponilibizar o material utilizado na pesquisa. Referências BRASIL. Ministério da Agricultura, Pecuária e Abastecimento. Instrução normativa nº 76, de 26 de novembro de 2018. Regulamentos Técnicos que fixam a identidade e as características de qualidade que devem apresentar o leite cru refrigerado, o leite pasteurizado e o leite pasteurizado tipo A. Diário Oficial da União, Brasília, 2018. RIBEIRO JÚNIOR, J. C.et al. The main spoilage1 related psychrotrophic bacteria in refrigerated raw milk. Journal of dairy science, v. 101, n. 1, p. 75-83, 2018. PALAVRAS-CHAVE: Microbiologia dos alimentos, Qualidade do leite, Tecnologia verde

Effect of modified atmosphere packaging and vacuum packaging on quality characteristics of lamb meat

The aim of the study was to evaluate the effect of vacuum packaging and modified atmosphere packaging (80 % N2 + 20 % CO2) on the microbial and physicochemical parameters of lamb meat and the sensory properties of cooked meat. Musculus longissimus thoracis et lumborum samples were examined at 10 d intervals (0, 10, 20 and 30 d) during storage at 4 ∘C. There was no significant effect of the packaging method and storage time used on cooking loss, natural drip loss, lightness, yellowness, and intensity of taste and aroma. An interaction between storage time, packaging method, and mesophilic aerobic bacteria and coliform counts was observed. Storage time significantly affected the number of aerobic psychrotrophic bacteria, redness, pH (P≤0.001), shear force value (P=0.006), and the desirability of aroma (P<0.026) and taste (P<0.01). During the storage time, an increase in red saturation from 11.92 to 13.33 and pH value from 5.69 to 5.80 was recorded. Moreover, the storage method affected sensory properties. Vacuum-packed meat was characterized by higher scores in juiciness, tenderness and taste desirability in comparison to MAP. The obtained results suggest that both packaging methods allow for maintaining high-quality lamb meat during a long period of storage under refrigeration conditions.

Physicochemical and Microbial Quality of Prepackaged Shrimp Processed by a Scaled-Up Microwave-Assisted Induction Heating Technology

A second generation and scaled-up equipment, named Aligo-2TM (microwave-assisted induction heating, MAIH) with a sample capacity of approximately 1.0 L was designed and invented by Bottle Top Machinery Co., Ltd., Taiwan. Pre-packaged raw shrimps were heated in a scaled-up system using heating temperatures of 130 °C and 90 °C for 80 to 150 s, and the physicochemical and microbial qualities were evaluated. The total plate count, psychrotrophic bacteria count, and coliform levels decreased as heating time increased, whereas the cooking loss, color (L*, a*, and W) value, and texture increased. When shrimps were heated for the longest time of 120 s at 130 °C or 150 s at 90 °C, they displayed obvious overcooked, shrunken, and dry appearance. To obtain samples that showed a red color, cooked well, and had no microbial count, better heating conditions for the processing of pre-packaged shrimps via the MAIH scale-up system were 130 °C for 100 s or 90 °C for 130 s. This novel and scaled-up MAIH equipment provides shrimp to be cooked after being packed, thereof avoiding the post-contamination problem.

The influence of modified atmosphere packaging on shelf life of ćevapčići

The aim of this study was to determine the microbiological, sensory and chemical changes of modified atmosphere packaged ćevapčići in a gas mixture consisting of 70% O2 and 30% CO2. Packaged ćevapčići were stored for 10 days at 3ºC. Microbiological examination comprised determination of pathogenic microorganisms (Salmonella spp., coagulase positive staphylococci, Escherichia coli and Listeria monocytogenes) as well as indicators of hygiene and spoilage (total viable count, psychrotrophic bacteria, Enterobacteriaceae, lactic acid bacteria and Brochothrix thermosphacta). Using quantitative-descriptive test with grading scales from one to five, sensory properties of ćevapčići were assessed (color and odor in raw condition and odor, texture and taste after roasting) on the 1st, 4th, 6th, 8th and 10th days of storage. Regarding the chemical parameters, every day during the storage, pH was examined and on 4th and 8th days, acid value and peroxide number were established. On the basis of the results obtained and the recommended total viable count, which should not be higher than 7 log cfu/g, and taking into consideration sensory properties, we can conclude that ćevapčići packed in the modified atmosphere containing 70 % O2 and 30% CO2 had a shelf life of seven days.

Effect of a Novel Microwave-Assisted Induction Heating (MAIH) Technology on the Quality of Prepackaged Asian Hard Clam (Meretrix lusoria)

The microwave-assisted induction heating (MAIH) method—an emerging thermal technique—was studied to heat the prepackaged raw hard clam (Meretrix lusoria). The cooking effects on microbial and physiochemical qualities of clam were investigated. After the heating of the clam meat samples, the aerobic plate count (APC), psychrotrophic bacteria count (PBC), and total volatile basic nitrogen (TVBN) levels decreased with increasing heating time, but the shucking ratio, area shrinkage, and texture (hardness, cohesiveness, and chewiness) increased. In addition, the L* (lightness) and W (whiteness) of the clam meat samples increased significantly at the beginning of the heating period, whereas they decreased significantly with extended heating time. However, a* (redness) had the opposite trend. This study found that when clams were heated for more than 120 s at 130 °C or 150 s at 90 °C, they displayed obvious shrinking and a yellow-brown appearance, indicating that they are overcooked. After heating by MAIH for at least 110 s at 130 °C or 130 s at 90 °C, the samples were cooked well and gains a completely shucking, along with no microbial count detected. Therefore, the results indicated that the optimum heating conditions for prepackaged hard clams subjected to an MAIH machine were 130 °C for 110 s or 90 °C for 130 s.

Bacterial community shift and effects of the inclusion of a mixed psychrotrophic bacteria strain for sewage treatment in constructed wetland in winter seasons

The mechanism of wastewater treatment based on psychrophilic strains to improve the denitrification efficiency of constructed wetlands at low temperatures has already become a new hotspot. In this study, three mixed psychrophilic strains (Psychrobacter TM-1, Sphingobacterium TM-2 and Pseudomonas TM-3) with high capacity of denitrification were added into a vertical-flow constructed wetlands (CWs), and the effect of the mixed strains on CWs sewage treatment was evaluated. The removal efficiency of chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), total nitrogen (TN) and total phosphorus (TP) was quantified to establish the degradation kinetic model and determine the best dosage of the mixed strains. The effect mechanism of the mixed strains on indigenous microbial community and the change of sewage treatment performance in low temperature constructed wetlands was clarified by high-throughput sequencing technology. The results showed that the mixed strains can effectively remove the organic pollutants (nitrogen and phosphorus) and the optimum dosage of the mixed strain was 2.5%,with average removal rates of 1.52, 2.12, 2.07 and 1.29 times than those of the control. Meanwhile, the dominant strains in the CWs were Proteobacteria (31.23–44.34%), Chloroflexi (12.04–19.05%), Actinobacteria (10.6-20.62%), Acidobacteria (8.23–11.65%), Firmicutes (2.23–15.95%) and Bacteroidetes (4.01–18.9%). These findings provide a basis for the removal of pollutants in constructed wetlands at low temperature.

Improving the Storability of Cod Fish-Burgers According to the Zero-Waste Approach

This research explored the potential of the zero-waste concept in relation to the storability of fresh food products. In particular, the prickly pear (Opuntia ficus-indica) peel (usually perceived as a by-product) and the pulp were dehydrated, reduced in powder, and used as food additives to slow down the growth of the main spoilage microorganisms of fresh cod fish burgers. The proportion between peel and pulp powder was such as to respect the zero-waste concept. The antibacterial activity of the peel and pulp in proper proportion was first assessed by means of an in vitro test against target microorganisms. Then, the active powder was added at three concentrations (i.e., 2.5 g, 7.5 g, and 12.5 g) to cod fish burgers to assess its effectiveness in slowing down the microbial and sensory quality decay of burgers stored at 4 °C. The results from the in vitro test showed that both the peel and pulp were effective in delaying microbial growth. The subsequent storability test substantially confirmed the in vitro test results. In fact, a significant reduction in growth rate of the main fish spoilage microorganisms (i.e., Pseudomonas spp., psychrotrophic bacteria, and psychrotolerant and heat-labile aerobic bacteria) was observed during 16 days of refrigerated storage. As expected, the antimicrobial effectiveness of powder increased as its concentration increased. Surprisingly, its addition did not affect the sensory quality of fish. Moreover, it was proven that this active powder can improve the fish sensory quality during the storage period.

Effect of High-Pressure Processing on Physico-Chemical, Microbiological and Sensory Traits in Fresh Fish Fillets (Salmo salar and Pleuronectes platessa)

High-pressure (HP) treatment could lead to several advantages when applied to fish and seafood since it would affect the extension of the shelf life of this highly perishable food. In this regard, this study aimed to evaluate the effect of high-pressure treatment (500 MPa for 2 min at a temperature of 4 °C) on changes in quality on two different kinds of fresh fish fillets (Salmo salar and Pleuronectes platessa). Specifically, physico-chemical (VOCs, untargeted metabolomics spectra, pH and color), microbiological (Enterobacteriaceae, Pseudomonas spp., mesophilic and psychrotrophic bacteria) and sensory traits were evaluated at different days of refrigerated storage. From the results obtained, it is possible to state that the high pressure significantly (p ≤ 0.05) reduced microbial growth for each investigated microorganism. Regarding the colorimetric coordinates, no remarkable effects on a* and b* indices were found, while a significant effect (p = 0.01) was observed on the colorimetric index L*, making the HP-treated samples lighter than their respective controls. The sensory analysis showed that for the odor attribute, the HP treatment seems to have had a stabilizing action during shelf-life. Moreover, the treated samples obtained a better score than the respective controls (p ≤ 0.05). With regards to texture and appearance attributes, the treatment seems to have had a significant (p ≤ 0.05) effect, making the treated samples more compact and opaque than controls, therefore resulting in the loss of the characteristics of raw fish for the treated samples. Moreover, from a chemical point of view, HP treatment prevents the development of volatile sulfides and delays the formation of histamine (p ≤ 0.05). Very interestingly, the metabolomic approach revealed novel dipeptide markers for the HP procedure.