Effect of usage Urtica dioica L. on microbiological properties of sucuk, a Turkish dry-fermented sausage

The effect of dried-ground Urtica dioica L. on microbiological characteristics of Turkish dry-fermented sausage (sucuk) were investigated. Dried-ground Urtica dioica L. was added to sucuk batters by the rate of 0%, 1%, 3% and 5%, and microbiological analysis were made on the 0, 3, 7, 10 and 14 days of ripening period.

According to the results, both the level of Urtica dioica L. and ripening time had a significant effects on the total aerobic mesophylic bacteria, lactic acid bacteria, Micrococcus/Staphylococcus, yeast-mould and Enterobacteriaceae counts (p<0.01). It was determined that the interactions ripening time × the levels of Urtica dioica L. had a significant effects on the counts of total aerobic mesophylic bacteria, lactic acid bacteria, Micrococcus/Staphylococcus, yeast-mould and Enterobacteriaceae (p<0.01). Enterobacteriaceae count were also found to be under the detectable level (<100 cfu/g) in sucuks (in day 14 of ripening) containing 3% and 5% Urtica dioica L.     

Molecular grouping and pathogenic analysis of Listeria monocytogenes of clinical and food origin

The phylogenesis and pathogenesis of ten Chinese Listeria monocytogenes isolates of clinical (n = 2) and food (n = 8) origin have been investigated in this study. The 597 bp nucleotide sequence at 3′ terminal of actA gene of these L. monocytogenes isolates were amplified and sequenced. Compared with those of published sequences of the corresponding region within the same gene, the phylogenetic tree was constructed using MEGA2.1 software. It was shown that one clinical strain 1579 and food strains YZ5, YZ7, YZ8 belong to lineage I, while the other clinical strain 1191, and food strains YZ1, YZ2, YZ3, YZ4, YZ6 belong to lineage II. The virulence of these strains based on experimental infection model of SPF chick embryos were determined, and compared between L. monocytogenes isolates of two lineages and their hemolytic activity was assessed according to the development of zones of hemolysis around the colonies. Isolates of lineage I showed high virulence while isolates of lineage II (except clinical isolates 1191) exhibited low virulence, since 100% mortality rate and relative short time to death for embryos were observed for strains of lineage I, while 20–30% mortality rate and long time to death for embryos were observed for isolates of lineage II. Hyper-virulent isolate 1579, YZ8 and lower-virulent isolates YZ2, YZ3, YZ4 and YZ6 show strong hemolytic activity while hyper-virulent isolate 1191, YZ5, YZ7 and lower-virulent isolate YZ1 show weak hemolytic activity. The discrepancy between virulence and hemolytic activity indicates that L. monocytogenes hemolytic activity is not directly proportional to their virulence and thus it can not be used as a reliable criteria for assessment of the virulence of L. monocytogenes.     

Survival and growth of Listeria monocytogenes on sausage formulated with inoculated and stored rework product

To assess the effect of including contaminated rework on survival and growth of Listeria monocytogenes, two sausage formulations (one American, Bologna sausage; and one Bulgarian, Stranja sausage) were inoculated with the pathogen and stored for 4 days at 10 °C plus 15 h at 30 °C. After storage, both rework types were included (at 20% and 40%) in corresponding fresh sausage emulsions and heated to 68, 70 and 71.7 °C; fresh Bologna and Stranja emulsions served as controls and were inoculated with 24 h broth cultures of the same 10-strain mixture of L. monocytogenes and thermally treated to the same temperatures. The results showed that heating to 68 and 70 °C inactivated 3–4 log CFU/g of the initial concentration of L. monocytogenes cells (>7 log CFU/g), while heat treatment to 71.7 °C in the center of experimental samples reduced counts by 6 log CFU/g. Survival of L. monocytogenes in samples heated to 68 and 70 °C was higher in controls. Control samples of Stranja emulsion heated to 71.7 °C allowed higher growth (P < 0.05) during storage (5 days at 10 °C) as compared to other control and experimental rework samples. The Stranja emulsion had a higher fat content (20.2%) compared to the Bologna emulsion (11%). This study provides evidence about the possible danger when potentially contaminated rework is stored and then introduced into fresh product formulations.     

Quality deterioration of phane, the edible caterpillar of an emperor moth Imbrasia belina

The cause for the deterioration of quality in phane, the edible larva of the emperor moth, Imbrasia belina (Westwood) was investigated. Samples were subjected to bacteriological and mycological analyses. In addition insect pests which affect storage life of the product were also assessed. 70% of the bacterial isolates associated with phane were proteolytic and 75% were either chitinolytic, lipolytic or both. Most isolates were sporeformers. But, other Gram-positive and negative isolates were also present in significant numbers. The most frequent fungal isolates were species of Aspergillus, Penicillium, Fusarium, Cladosporium and phycomycetes. Some of the fungal isolates are known to be mycotoxin producers. The insect which were associated with phane were Dermestes maculatus, Sitophilus zeamais, Corcyra cephalonica, Tribolium confusum, Tribolium casteneum, Oryzaephilus surinamensis, Bracon hebetor, Anisopteromalus cavandrae, and Stathmopoda species. Mites were also found infesting stored phane. The postharvest deterioration of phane appeared to be a concerted effort by the bacteria, moulds and insects.     

Identification of moulds from the Taleggio cheese environment by the use of DNA barcodes

The aim of this work was to characterize the mould populations of the Taleggio PDO cheese surface by a combination of culture dependent and independent techniques. DNA samples were extracted: (i) from isolates derived from brine and cheeses at various ripening midpoints, (ii) directly from the surface of commercial cheeses made in different dairies. DNA was examined by PCR at various loci (DNA barcodes). Amplified regions were both ribosomal (ITS1, ITS2 and the D1/D2 region of the 26S rRNA gene) and non-ribosomal (portions of the β-tubulin and EF1α genes). The mould community appeared to be dominated by a species that alone represents 87% of the sequences obtained using the β-tubulin barcode, and is 99% homologous to Penicillium commune. It has been obtained, always identical, from brine, from cheeses at the various ripening midpoints, and from all the commercial cheeses. It presumably represents a new variant of P. commune typical of Taleggio. Three isolates were identified as belonging to three different species of the genus Cladosporium: Cladosporiumoxysporum and two potential new species, detected on the basis of their β-tubulin sequences. Finally, 2 isolates were identified as Aureobasidium pullulans and Eutypella scoparia. This is the first characterization of the mould species for this important Italian PDO cheese production, and is one of the first reports of molecular characterization by means of DNA barcodes on mould DNA directly extracted from cheese without culturing.     

Effect of nisin on the storage of sous vide processed Korean seasoned beef

Seasoned beef called Jangzorim in Korea is produced by boiling in soy sauce, and is a popular food in Korea. The aim of this study is to evaluate the microbial safety and physical qualities of sous vide processed seasoned beef, and the effect of nisin during storage. Sous vide processed packages with or without nisin (100 IU or 500 IU) were stored at 4 °C or 25 °C for 60 days, and samples measured for quality at regular intervals throughout this storage period. In the case of 25 °C storage, the number of mesophilic microorganisms in seasoned beef packages without nisin increased markedly, but with nisin there was no observed increase. Psychrotrophic microorganisms, anaerobic microorganisms, and B. cereus cells showed similar trends, although C. perfringens was not detected in all samples. At 25 °C storage, changes in the cutting force of packages containing nisin showed no significant change, packages without nisin decreased markedly. The colour of packages without nisin showed a drastic decrease in lightness (‘L’) while no changes were observed in packages with nisin.     

High hydrostatic pressure treatment applied to model cheeses made from cow’s milk inoculated with Staphylococcus aureus

Pasteurized milk was inoculated with two strains of Staphylococcus aureus (CECT4013 or ATCC13565) and used to elaborate soft-curd cheeses with approximately 7.5-log CFU/g of S. aureus. Cheeses were submitted to 10 min high hydrostatic pressure (HHP) treatments of 300, 400 or 500 MPa at 5 °C or 20 °C. Staphylococcus enterotoxin (SE) was evaluated in cheeses containing ATCC13565. Counts of S. aureus were measured after HHP treatment (day 1) and after 2, 15 and 30 days ripening at 8 °C. Inactivation increased with pressure and storage time, but was similar for both treatment temperatures. Maximum S. aureus reductions were achieved after 30 days ripening for samples treated at 500 MPa and 5 °C: 6.0 ± 0.1 and 4.7 ± 0.5-log CFU/g for CECT4013 and ATCC13565, respectively. However, SE was detected in all cheese samples containing ATCC13565 before and after HHP and after 30 days ripening.     

Evolution of Listeria monocytogenes populations during the ripening of naturally contaminated raw ewe’s milk cheese

The aim of this work was to study, in loco, the evolution of Listeria monocytogenes populations, during ripening (7, 42, 60 and 120 days) of naturally contaminated raw ewe’s milk cheese. Two batches of cheese consisting of 20 or 16 cheeses were obtained from two farmstead cheesemakers, respectively. A significant increase in numbers of L. monocytogenes was observed for both batches, from 7 to 42 days of ripening. These results suggest that this type of cheese has potential to support the survival of L. monocytogenes, while stressing the importance of cheese contamination in the dairies by resident strains.     

Occurrence of pathogenic bacteria in raw milk, cultured pasteurised milk and naturally soured milk produced at small-scale dairies in Zimbabwe

The presence of selected pathogenic bacteria in raw milk (RM), cultured pasteurised milk (CPM), and naturally soured raw milk (NSRM) sold at three small-scale dairies in Zimbabwe was determined. Mean levels of Escherichia coli in RM, CPM and NSRM were 4.5, 7.1 and 7.8 log₁₀ CFU ml⁻¹, respectively. Enterotoxigenic E. coli (ETEC), producing heat-stable enterotoxin (ST1) was found in 16 of the samples. Presumptive Staphylococcus aureus was identified in 7 of 12 RM, 15 of 27 CPM and 20 of 21 NSRM samples at mean levels of 5.2, 7.3 and 7.8 log₁₀ CFU ml⁻¹, respectively. Klebsiella pneumonia spp., Enterobacter cloacae, Proteus mirabilis, Hafnia alvei, Citrobacter spp., Serratia marcescens and Aeromonas hydrophilia were found in 27 samples. The high number of S. aureus, E. coli, identification of ETEC-ST1 and the other pathogenic microorganisms found in pasteurised and unpasteurised milk products represent a health hazard to the consumers and emphasises the need for improved hygiene practice at all levels in the dairy.     

Microbiological characteristics of cake prepared from rice flour and sticky rice flour

Microbiological, chemical and sensory changes in MiGao (a traditional Chinese steamed cake) were studied during five days of storage at 25 °C. Microorganisms examined for were: Enterobactericeae, lactic acid bacteria, Gram-positive, catalase-positive cocci, Staphylococcus aureus, Bacillus strains, yeasts and moulds, and pH and moisture content were also analyzed. Total plate counts in the products under study in the third day of storage were in the range <10³ CFU/g and the shelf-life of the product was estimated to be only two or three days by the panelists. During the first two days, Gram-positive bacteria were dominant, mainly represented by Staphylococcus epidermidis. Bacillus strains occurred by the third day, reaching a maximum level of 1 × 10⁶ CFU/g after five days of storage. No Enterobactericeae or Lactic acid bacteria were detected in the processed products throughout the storage period. All the isolated strains from the mannitol salt agar belonged to the genus Staphylococcus. The predominant species were S. epidermidis and S. aureus. Most Bacillus strains, isolated from the tryptone soya agar, belonged to the species Bacillus brevis. The count of yeasts and moulds increased slowly but remained low throughout the storage period.     

Characteristics of Bacillus cereus isolates from legume-based Indian fermented foods

An antibiogram of 48 strains of Bacillus cereus isolated from 6 different kinds of legume-based Indian fermented foods (amriti, dhokla, dosa, idli, papad and wadi) was generated against 18 different antibiotics that are commonly used against foodborne diseases, mainly gastroenteritis. Each of the isolates was found to be resistant against at least nine different antibiotics. Production of extracellular enzymes, namely protease, lipase and amylase by 33%, 27% and 46%, respectively, of the isolates indicates their potentiality for food spoilage. In brain–heart infusion broth supplemented with glucose, the D_100 °C-values for the tested 12 strains ranged from 3.0 to 9.2 min. In nutrient broth, the minimum and maximum pHs permitting growth of B. cereus were 5.3 and 11.6, respectively. The minimum inhibitory concentrations of sodium chloride, benzoic acid and sorbic acid for the growth of the isolates were 65–85 mg ml⁻¹, 400–700 μg ml⁻¹ (pH 5.0–4.2) and 500–600 μg ml⁻¹ (pH 5.0–4.8), respectively. Of the tested 10 strains, eight were resistant to 300 μg nisin ml⁻¹ (pH 5.0). While studying the combined effect of selected hurdles on the growth of an isolate, the judicious combination considered was 20 mg sodium chloride, 300 μg benzoic acid and 25 μg nisin ml⁻¹ at pH 5.6. The whole-cell protein fingerprinting (WCPF) analysis using SDS–PAGE revealed a high level of diversity among the isolates. At 60% similarity level, the WCPF profiles could be grouped into four major clusters which were divided into 34 subclusters. Most of the subclusters were source-wise homogeneous.     

Antifungal effect of poly(lactic acid) films containing thymol and R-(-)-carvone against anthracnose pathogens isolated from avocado and citrus

Biodegradable antifungal films were developed to be used for controlling postharvest anthracnose pathogens. Two antifungal compounds, thymol and R-(-)-carvone, were incorporated into poly(lactic acid) (PLA)-based polymer at 10, 15 and 20% (w/w). Antifungal activity of the pure compounds and the antifungal films against Colletotrichum gloeosporioides isolated from avocado and citrus was evaluated at 12 and 25 °C using vapor diffusion assays. The results indicated that the colony diameter was affected by the vapor concentration of the antifungal compounds in the headspace. At 12 °C, 20% thymol showed complete growth reduction of avocado isolate, while at 25 °C, 15 and 20% thymol showed complete growth reduction of both avocado and citrus isolates. The PLA films incorporated with 15% R-(-)-carvone and 20% thymol were the most effective at 12 °C in suppressing the mycelial growth of the avocado and citrus C. gloeosporioides isolates, respectively, whereas the film incorporated with 20% thymol had the highest antifungal activity against both anthracnose isolates at 25 °C. The inhibitory effect of the antifungal films against anthracnose isolates was correlated to the vapor concentration of the antifungal compounds remaining in the headspace of the Petri dish. Antifungal packaging films can potentially be used to control postharvest pathogens of fresh produce.     

Elimination of Yersinia enterocolitica on carrots (Daucus carota L.) by using household sanitisers

In this study, the effects of lemon juice, the mixture of lemon juice–vinegar (1:1) and lemon dressing against Yersinia enterocolitica on carrot were investigated. Carrots inoculated with Y. enterocolitica cells (approximately 10⁶ cfu/ml) were treated with 100%, 75% and 50% lemon juice, a mixture of lemon juice–vinegar, and lemon dressing for 0, 15, 30 and 60 min. Enumeration of Y. enterocolitica populations on CIN agar beside TSA agar by using two methods as then performed. One hundred percent lemon juice was the most effective agent used, completely inhibiting viable cells of Y. enterocolitica on carrot after 15 min exposure. Although no growth was observed on carrots treated with 100% lemon juice for 15 min, there was no statistical difference between the antibacterial effects of 100% lemon juice, 75% lemon juice, the mixture of lemon juice–vinegar and lemon dressing whilst the effect of 50% lemon juice was statistically different from those solutions (P < 0.05) and its definite inhibitive activity was seen after 60 min treatment.     

Microbiological,biochemical and sensory characteristics of artisanal and industrial Manchego cheeses

Manchego cheese production may be artisanal or industrial, according to whether the cheeses are manufactured with raw or pasteurised ewe’s milk. This work was designed in order to study the predominant microflora in artisanal and industrial Appellation of Origin Manchego cheeses and its influence on the biochemical characteristics and the gustative profile of the cheeses at 60 days of ripening (just the moment that the cheeses can be marketed). Only two biotypes of the same species of Lactococcus lactis subsp. lactis were found in the industrial cheeses, while in the artisanal cheeses the microflora was much more heterogeneous. At 60 days of ripening, the artisanal cheeses accounted for higher values of pH, salt content, total nitrogen and nitrogen fractions than the industrial cheeses. Besides, the artisanal cheeses obtained higher scores for most of the gustative attributes evaluated than the industrial cheeses. This could be due to the more complex enzymatic system of the artisanal cheeses compared to the industrial ones, that could perform stronger biochemical changes in the cheeses made with raw milk.     

Biogenic amine content and aromatic profile of Salama da sugo,a typical cooked fermented sausage produced in Emilia Romagna Region (Italy)

Salama da sugo is a fermented sausage from Ferrara tradition, subjected to a long ripening period (4–6 months). It can be consumed after cooking, served with its sugo, i.e. the liquid extracted by cooking process. Besides to pork meat and fat, also NaCl, curing salts, sugar, spices and almost 15% of red wine are added. The aim of this research was the microbial and aromatic profile characterization of Salama da sugo during ripening. The product was sampled in order to study chemico-physical parameters, microbial population composition (Enterobacteriaceae, lactobacilli, enterococci, micrococci and staphylococci, including coagulase positive, fungi, total mesophilic bacteria), biogenic amine content and aromatic profile. The results showed that this traditional product was characterized by a complex aroma.Moreover, the biogenic amine concentration was low (less than 200 mg/kg for tyramine, about 50 mg/kg for cadaverine and putrescine while histamine was below the detection limit).     

Microbiological safety and quality of commercial sufu – a Chinese fermented soybean food

In this study, the microbiological safety and quality of commercial sufu were investigated. Twenty-three samples of three different types of sufu were obtained, mainly in China and some in The Netherlands. Chemical parameters analysed included moisture, pH, free amino N, NaCl, ethanol, sucrose, glucose, and fructose. Concentrations of NaCl, ethanol, glucose and fructose varied from 6.2%, 0.5%, 0% and 0% to 14.8%, 6.3%, 6.2% and 4.8%, respectively. Microbiological analyses were done for total count of mesophilic aerobic bacteria (TMAB), bacterial endospores, total count of halotolerant bacteria at 10% (THB10) and at 17.5% NaCl (THB17.5), lactic acid bacteria (LAB), fungi, Enterobacteriaceae, and the following pathogens: Bacillus cereus, Clostridium perfringens, Staphylococcus aureus and Listeria monocytogenes. High levels (>10⁵ CFU/g) of TMAB and bacterial endospores were found in most samples, and 85% of TMAB was identified as Gram-positive. Considerable levels (10⁵ and 10⁷ CFU/g) of LAB were detected in two samples of white sufu, and isolates of LAB were identified as most probably Lb. casei. One-third of the samples contained less then 10³ CFU/g B. cereus, but three samples had over 10⁵ CFU/g indicating potential hazard to consumers. All samples had less than 10³ CFU/g C. perfringens, except sample R11 (10⁵ CFU/g). S. aureus could not be detected in any of the samples tested since the competitive microflora (usually bacilli) disturbed typical features on the selective medium used; however S. aureus enterotoxin A was detected in some of the white and grey sufu samples. Fungi, Enterobacteriaceae, and L. monocytogenes were not detected in any of the samples. Based on these results, a microbiological guideline for safe commercial sufu is proposed.     

Inhibition of food poisoning and pathogenic bacteria by Lactobacillus plantarum strain 2.9 isolated from ben saalga, both in a culture medium and in food

The bacteriocinogenic strain Lactobacillus plantarum 2.9 isolated from the traditional pearl millet-based African fermented food ben saalga was tested for inhibition of food poisoning and pathogenic bacteria in MRS broth and in a malted millet flour slurry. In MRS broth, strain 2.9 completely eliminated Bacillus cereus, Escherichia coli O157:H7 and Salmonella enterica cells within 48 h incubation at 22–30 °C. A much lower inhibition was observed at 15 °C. The inhibitory effect of strain 2.9 on the above-mentioned target bacteria was corroborated in the malted millet flour slurry, reducing viable cell counts below detection levels after 8 h storage for B. cereus or after 24 h for S. enterica and 48 h for E. coli. An Enterobacter aerogenes strain was only moderately inhibited in the slurry. Results from the present study suggest that strain 2.9 could be used as starter culture to improve the microbiological safety of fermented ben saalga.     

Effect of the length of salting time on the proteolytic changes in dry-cured lacón during ripening and on the sensory characteristics of the final product

The effects of the length of salting time (0.75, 1 or 1.25 days/kg) on the proteolytic changes that take place during ripening of dry-cured lacón (a traditional meat product made in NW Spain) and on the sensory characteristics of the final product were investigated.The rate of proteolysis decreased as the length of salting time was increased. The salting time did not affect the free amino acid profile, which appears to indicate that the same enzymatic activities occurred during ripening of all batches of lacón, and that the length of salting time modulated these activities.Longer salting times resulted in a more intense yellow colour of the fat, a more intense red colour of the meat and harder meat, as well as more rancid odour, and more intense salty, cured and rancid taste of the dry-cured lacón pieces. Regarding the global evaluation, the tasters preferred the pieces that had been salted for an intermediate length of time (1 day/kg).     

Survival of Campylobacter jejuni on vacuum or carbon dioxide packaged primal beef cuts stored at −1.5 °C

The ability of two Campylobacter jejuni strains (MOO3, a cattle isolate, and MOO8, a sheep isolate) to survive on chilled, preservatively packaged primal beef cuts was examined. Each of the strains was inoculated separately (10⁵ cfu g⁻¹) onto 500 g beef steaks, packaged under vacuum or 100% carbon dioxide, and stored, with uninoculated controls, for 41 days at −1.5 °C. Bacterial numbers were determined at 0, 1, 3, 6, 13, 20, 27, 34 and 41 days by dilution, plating on both Columbia Sheep Blood Agar and Campylobacter Blood-Free Selective Agar and incubation at 42 °C for 48 h under microaerophilic conditions. In addition, an aerobic count on all samples was determined by dilution, plating on Plate Count Agar and incubation at 25 °C for 72 h. No significant changes in numbers of the C. jejuni strains or aerobic bacteria occurred during storage at −1.5 °C on steaks packaged under either vacuum or carbon dioxide. The ability of these pathogens to survive standard preservative packaging conditions is different from that reported in the literature and therefore a cause for concern. Strict hygienic practice or the implementation of decontamination technologies are recommended as mechanisms to assure safety of meat with respect to this pathogen.     

An evaluation of the effect of storage and processing temperatures on the microbiological status of sous vide extended shelf-life products

The microbiological and organoleptic quality of selected sous vide products was monitored over a storage period of up to five weeks at 3°C and 8°C, respectively. Sous vide products stored at the recommended temperature of 3°C showed negligible microbial growth and were found to be organoleptically acceptable throughout the storage period. Total plate counts at the end of the fourth week of storage were in the range <10–7×10³ CFU/g for all 19 products under study. Listeria monocytogenes, Salmonella, Clostridium perfringens, Bacillus cereus and Enterobacteriaceae were not detected in any of the processed samples. At 8°C, under temperature abuse conditions, while some products had acceptable microbial levels of 10²–10⁴ CFU/g after three weeks, others such as chicken chasseur had counts above 10⁶ CFU/g by the second week of storage. Lactic acid bacteria and Pseudomonas species were dominant in the microbial flora of spoilt samples and B. cereus (>3×10⁴ CFU/g) was isolated from spoilt chicken chasseur samples in the fourth week of storage at 8°C. Critical factors affecting sous vide product safety are discussed.