Numbers Of Psychrotrophic Bacteria Research Articles

Psychrotrophic Bacteria and Yeast Populations in Turkish White and Tulum Cheeses

In this study, pH and microbiological (psychrotrophic bacteria and yeast) properties of White and Tulum cheeses were investigated. According to the results of our study, the lowest pH value identified was 4.42, and the highest pH was 5.84 in the cheese samples. Psychrotrophic bacteria counts ranged from 4.15 to 6.21 log CFU/g for White cheese and 4.02 to 6.15 log CFU/g for Tulum cheese. Psychrotrophic yeast counts ranged from 2.98 to 7.58 log CFU/g for White cheese and 2.99 to 6.77 log CFU/g for Tulum cheese. The highest values of psychrotrophic yeast were detected in the Tulum cheese samples. As a result, it was determined that the numbers of psychrotrophic bacteria and yeast were high in both Tulum and White cheese samples. These high numbers of psychrotrophic microorganisms during cheese storage in the refrigerator may increase even further and reduce shelf life. To extend the shelf life of these cheeses, it is recommended to ensure hygienic handling practices and explore the use of natural preservatives or modified atmosphere packaging.

Psychrotrophic Bacteria and Yeast Populations in Turkish White and Tulum Cheeses

In this study, pH and microbiological (psychrotrophic bacteria and yeast) properties of White and Tulum cheeses were investigated. According to the results of our study, the lowest pH value identified was 4.42, and the highest pH was 5.84 in the cheese samples. Psychrotrophic bacteria counts ranged from 4.15 to 6.21 log CFU/g for White cheese and 4.02 to 6.15 log CFU/g for Tulum cheese. Psychrotrophic yeast counts ranged from 2.98 to 7.58 log CFU/g for White cheese and 2.99 to 6.77 log CFU/g for Tulum cheese. The highest values of psychrotrophic yeast were detected in the Tulum cheese samples. As a result, it was determined that the numbers of psychrotrophic bacteria and yeast were high in both Tulum and White cheese samples. These high numbers of psychrotrophic microorganisms during cheese storage in the refrigerator may increase even further and reduce shelf life. To extend the shelf life of these cheeses, it is recommended to ensure hygienic handling practices and explore the use of natural preservatives or modified atmosphere packaging.

Carboxymethyl cellulose-based multifunctional film combined with zinc oxide nanoparticles and grape seed extract for the preservation of high-fat meat products

CMC-based functional films incorporated with grape seed extract (GSE, 5 wt% of CMC) and zinc oxide nanoparticles (ZnONPs, 1, 2, and 3 wt% of CMC) were fabricated via the solution casting method. The addition of GSE provided an excellent antioxidant activity to the CMC-based films, exhibiting nearly 95% and 25% scavenging activity against ABTS and DPPH oxidative free radicals. It also gave the film 100% UV protection. On the other hand, the addition of ZnONPs increased the mechanical and water vapor barrier properties with potent antibacterial activity against foodborne pathogens, E. coli, and L. monocytogenes. High-fat beef was packaged in the CMC-based film and stored refrigerated for 15 days to investigate quality changes. The number of psychrotrophic bacteria in the meat wrapped with CMC/ZnO3%/GSE film was 5.9 Log CFU/g, within the acceptable range. In addition, the film virtually prevented lipid oxidation in the meat when refrigerated, reducing it by 88%. Therefore, the CMC/ZnO3%/GSE film can be used as a sustainable material in active packaging applications of high-fat meat products such as beef.

Characterization of the indigenous microflora in raw and pasteurized buffalo milk during storage at refrigeration temperature by high-throughput sequencing

The effect of refrigeration on bacterial communities within raw and pasteurized buffalo milk was studied using high-throughput sequencing. High-quality samples of raw buffalo milk were obtained from 3 dairy farms in the Guangxi province in southern China. Five liters of each milk sample were pasteurized (72°C; 15 s); and both raw and pasteurized milks were stored at refrigeration temperature (1–4°C) for various times with their microbial communities characterized using the Illumina Miseq platform (Novogene, Beijing, China). Results showed that both raw and pasteurized milks contained a diverse microbial population and that the populations changed over time during storage. In raw buffalo milk, Lactococcus and Streptococcus dominated the population within the first 24h; however, when stored for up to 72h the dominant bacteria were members of the Pseudomonas and Acinetobacter genera, totaling more than 60% of the community. In pasteurized buffalo milk, the microbial population shifted from a Lactococcus-dominated community (7d), to one containing more than 84% Paenibacillus by 21d of storage. To increase the shelf-life of buffalo milk and its products, raw milk needs to be refrigerated immediately after milking and throughout transport, and should be monitored for the presence of Paenibacillus. Results from this study suggest pasteurization should be performed within 24h of raw milk collection, when the number of psychrotrophic bacteria are low; however, as Paenibacillus spores are resistant to pasteurization, additional antimicrobial treatments may be required to extend shelf-life. The findings from this study are expected to aid in improving the quality and safety of raw and pasteurized buffalo milk.

Microflora of farm and hunted pheasants in relation to biogenic amines production

The aim of the study was to compare, within 3-week cold storage, the content of eight biogenic amines (BA) and the development of microflora in different parts of bodies (breast and thigh muscles and liver) of farm pheasants and pheasants hunted in the wild. Killed and untreated bodies of pheasants were stored hanging in an air-conditioned chamber at a cold temperature (5 ± 1 °C). The pheasant bodies were subjected to microbiological analysis and identification of isolated microorganisms whose decarboxylase activity was detected. The production of biogenic amines and polyamines was determined by means of HPLC after pre-column derivatisation with dansylchloride. The total number of microorganisms in all parts of the pheasant bodies as well as the number of psychrotrophic bacteria, enterobacteria and lactic acid bacteria was increasing during storage (P < 0.05). A total of 127 strains of bacteria from the pheasant bodies were isolated and identified. Production of at least one biogenic amine was found in vitro in 107 isolates. Three strains were found to produce four biogenic amines—histamine, tyramine, putrescine and cadaverine. Production of phenylethylamine, tryptamine, spermidine and spermine in the isolated bacteria was not detected. Within all the biogenic amines detected in the analysed samples of pheasant bodies, the lowest concentration was found in histamine and the highest one in tyramine and cadaverine. The amount of BA detected in the individual parts of pheasant bodies was increasing during the storage period. The total amounts of seven biogenic amines (histamine, tyramine, putrescine, cadaverine, phenylethylamine, spermidine and spermine) in the individual parts of pheasant bodies were ranging between 9 and 708 mg/kg.

Effects of high-pressure processing on the quality of chopped raw octopus

This study evaluated the effects of high-pressure treatment on microbial growth and production of off-flavor compounds in raw octopus during 16 days of refrigerated storage. Chopped raw octopus samples were treated at 150, 300, 450, and 600 MPa for 6 min using high-pressure laboratory food processing equipment. The number of psychrotrophic bacteria on day 16 was reduced by 0.1, 0.5, 1.3, and 2.8 CFU/g after pressure treatment at 150, 300, 450, and 600 MPa, respectively, as compared with control group. The amounts of trimethylamine (TMA) and dimethylamine (DMA) produced in the chopped raw octopus treated at 600 MPa was significantly reduced by 42.5% and 62.2%, respectively, as compared to the levels in the control. The production of biogenic amines (BAs) increased up to 1.82 mg/g in the control after 12 days of refrigerated storage, while the BA levels in the 450 MPa- and 600 MPa-treated octopus were 1.40 and 1.35 mg/g, respectively. Thus, high-pressure treatment effectively inhibited microbial growth and suppressed the formation of off-flavor compounds in raw octopus. High-pressure treatment is a promising alternative technology for extending the shelf life of raw octopus.

Application of high pressure processing for extending the shelf-life of sliced raw squid

This study was designed to evaluate the effect of high pressure processing (HPP) on the microbiological safety and quality of sliced raw squid during refrigerated storage. The sliced and vacuum-packed raw squid samples were treated at 200, 300, and 400 MPa for 20 min by using a custom-made high pressure processor. The numbers of psychrotrophic bacteria in the sliced raw squids treated at 200, 300, and 400 MPa were reduced by 0.5, 2.5, and >4.7 log CFU/g, respectively. The amounts of trimethylamine (TMA) produced in the sliced raw squids were reduced by 20, 33, and 51% at 200, 300, and 400 MPa, respectively, as compared to the control. The amount of total biogenic amines (BAs) in the control significantly increased up to 1.70 mg/g after 10 days of refrigerated storage, while that in the 400 MPa-treated squid sample gradually increased up to 1.33 mg/g. The autolytic activity values in the control, 200, 300, and 400 MPa-treated squid samples were 4.70, 2.28, 2.18, and 1.55 nkat/g, respectively, after 20 days of refrigerated storage. The HPP effectively retarded the microbial growth, TMA formation, autolytic activity in the sliced raw squids. Therefore, the HPP could be used as an effective processing tool for improving microbiological safety and quality of seafood.

Microbial Growth on Broiler Carcasses Stored at Different Temperatures After Air- or Water-Chilling

Poultry meat has a high risk of contamination during its processing. Storage temperature, type of packaging, and types and numbers of psychrotrophic bacteria are the major factors determining the spoilage of poultry meat. Before packaging, poultry carcasses are chilled by air or water currents in commercial slaughterhouses. The packaging material and methods are other factors influencing the spoilage of poultry meat. Although unpackaged carcasses had lower production costs, they were found to contain high numbers of microorganisms. The unpackaged carcasses are often not recommended for food safety and public health risks. The present study examines the growth of some spoilage microorganisms on unpackaged carcasses and on broiler carcasses packaged in polyethylene bags or synthetic plates. The carcasses examined in this study were collected from the slaughterhouses of the Bolu region of Turkey. All carcasses were subjected to an air or water chilling process in the slaughterhouse and then stored at 0, 4, or 7 degrees C for 14 d. Samples were taken on d 0, 4, 8, 10, and 14 of storage and analyzed for total bacterial count, and for Pseudomonas spp., Enterobacteriaceae, yeasts, and molds. The carcasses packaged in synthetic plates or polyethylene bags and kept at 0 degrees C were microbiologically safer and had longer shelf life, so they are found to be the most reliable for consuming. The shelf life of broiler carcasses could be further increased by improving hygiene and sanitation procedures at the slaughterhouse.

Potential applications of high pressure homogenisation in processing of liquid milk

Studies of the potential of high pressure homogenisation (HPH) for the combined pasteurisation/ homogenisation of raw bovine milk were undertaken. Raw milk was preheated to 45 degrees C and HPH-treated at 150, 200 or 250 MPa; milk outlet temperature at these pressures were 67, 76.8 and 83.6 degrees C, respectively, with a holding time of approximately 20 s. Raw and commercially pasteurized and homogenized (CPH) milk samples were analysed as controls. Fat globules in HPH samples were approximately half the size of those in CPH samples, although differences were not significant (P>0.05). beta-Lactoglobulin was denatured at pressures > or =150MPa, although little denaturation of alpha-lactalbumin was observed. Numbers of psychrotrophic bacteria in raw milk were reduced by 2.73 log cycles by HPH at 150 MPa and were uncountable following HPH at 200 or 250 MPa. Mesophilic bacterial counts were reduced by 1.30, 1.83 and 3.06 log cycles by HPH at 150, 200 or 250 MPa, respectively. No viable Staphylococcus aureus nor coliform cells remained in any HPH milk samples. HPH did not affect the colour of milk and HPH samples did not cream during refrigerated storage. The activities of plasmin, alkaline phosphatase and lactoperoxidase in milk were all greatly reduced by HPH. Pseudomonas fluorescens, inoculated into milk (approximately 10(6) cfu/ml), was reduced to undetectable levels by HPH at 200MPa (milk inlet temperature, approximately 10 degrees C); however, Ps. fluorescens proteinase was quite resistant to HPH under such conditions. Overall, owing to the significant increase in temperature and the possibility of varying the holding time, there may be potential applications for HPH as a novel liquid milk processing technique, combining many advantages of conventional homogenization and pasteurization of milk in a single process.

Microbiological properties of labneh (concentrated yoghurt) stored without vegetable oil at room or refrigeration temperatures

Labnehs (concentrated yoghurts) were made from cow or goat milk (and produced directly from either yoghurt or strained yoghurt) and stored without submersion in vegetable oil at either room or refrigeration temperatures. The results showed that total aerobic mesophilic bacterial counts decreased during storage at both temperatures. Yeast and mould counts, however, increased especially in the samples stored at room temperature due to increased acidity during storage. The number of aerobic spore-forming bacteria decreased, although it was high at the beginning of storage. The number of psychrotrophic bacteria significantly decreased after 60 days in the samples stored at refrigeration temperature and to a smaller degree decreased in the samples stored at room temperature. The statistical analysis showed that the variety of milks and draining of the yoghurts and their interactions had no effect on the growth/survival of total aerobic mesophilic bacteria and psychrotrophic bacteria (P>0.05). However, storage time had a significant effect on the growth of aerobic mesophilic bacteria and aerobic spore-forming bacteria (P<0.01) and yeast, mould and psychrotrophic bacterial counts (P<0.05). No coliform bacteria and Escherichia coli were detected in any sample. The labnehs were consumable for a short period of time, if stored at room temperature and for 180 day, if stored at refrigeration temperature.

Microbial and sensory quality of commercial fresh processed red lettuce throughout the production chain and shelf life

Red pigmented ‘Lollo Rosso’ lettuce was processed under usual and controlled conditions in an industrial plant. At different steps of the production chain (reception, shredding, washing, draining, rinsing, centrifugation, and packaging), microbial counts were evaluated. Following industrial practices, processed lettuce was packaged at 5 °C in sealed polypropylene (PP) bags with an initial atmosphere containing 3 kPa O 2 and 5 kPa CO 2. The numbers of psychrotrophic bacteria, coliform and lactic acid bacteria (LAB) were influenced by all the studied steps of the production chain of the fresh processed ‘Lollo Rosso’ lettuce. Shredding, rinsing and centrifugation in particular increased bacterial counts. During a storage period of 7 days at 5 °C, sensory attributes (general appearance, texture, aroma, translucency, initial and persistent off-odors, leaves superficial browning, leaves edges browning, and decay) as well as microbial counts (psychrotrophic and mesophilic bacteria, coliforms and lactic acid bacteria) were monitored. Due to high microbial counts and off-odors evaluation, a shelf life shorter than 7 days should be considered for fresh processed ‘Lollo Rosso’ lettuce.

Effects of evisceration and storage temperature on changes in meat quality of traditional farm‐fresh Turkeys

Abstract 1. Conditions affecting the keeping quality of traditional farm‐fresh turkeys were investigated. 2. Storage of uneviscerated Wrolstad turkeys at 4 °C for 10 days caused no statistically significant changes in meat flavour or texture. 3. During further storage at —2 °C, however, there was a slight but significant change in flavour, which became more marked with time in birds which had been eviscerated after the initial period at 4 °C. 4. Both eviscerated and uneviscerated birds became slightly tougher during storage. 5. Initial holding at 4 °C increased the numbers of psychrotrophic bacteria on the skin by about 103 but subsequent changes at — 2 °C were slight for uneviscerated birds. 6. Eviscerated carcases had higher counts than uneviscerated birds after storage at — 2 °C and, although ‘off’ odours were not detected, spoilage appeared to be imminent at the end of the 20‐d period.

Microbiological Contamination and Primal Cut Yields of Skinned and Scalded Pork Carcasses

ABSTRACTMicrobiological contamination was determined in core samples from the surface of the ham, shoulder, belly and back of skinned and scalded pork carcasses. Aerobic plate counts of mesophilic organisms indicated that ham and shoulder areas of scalded carcasses had higher bacterial numbers than skinned carcasses. Contamination on the back of the carcass was similar for skinned and scalded carcasses, while skinned carcass bellies had slightly higher counts than did scalded bellies. Numbers of psychrotrophic bacteria were negligible in all cases. Weights of primal cuts were compared in skinned and scalded carcasses by alternately skinning one side of each of 23 pork carcasses, while the other side was left skin‐on. Belly, picnic shoulder and ham yields were less for skinned sides, while the loin and Boston shoulder were not affected.

Psychrotrophic Bacteria in Prerigor Ground Pork

ABSTRACTThe numbers of psychrotrophic bacteria in prerigor ground pork were slightly greater than in postrigor ground pork throughout an 11‐day storage period at 2°C. Freezing both types of samples and subsequent thawing before storage at 2°C reduced the initial psychrotrophic counts but the freezing effects did not persist beyond 8 days of storage. Differences in psychrotrophic counts between prerigor and postrigor ground pork were not sufficiently great in any comparison to limit the use of prerigor grinding of pork.

Inactivation of Heat Resistant Proteases in Normal Ultra-high Temperature Sterilized Skim Milk by a Low Temperature Treatment

Heat-resistant proteases produced by psychrotrophic bacteria in raw milk survive ultra-high temperature sterilization and cause development of bitter flavor and gelation in sterile skim milk. However, these proteases undergo a unique inactivation at low processing temperatures. A low temperature inactivation treatment of 55C for 1h has been proposed as a feasible means to inactivate these heat-resistant proteases in sterile skim milk. The effectiveness of the low temperature inactivation treatment for proteases in normal skim milk was investigated with pilot plant sterilization equipment. All but one of the milk samples tested met Grade A Standards, and all contained heat-resistant protease, although protease activity did not appear to be correlated with the Standard Plate Count, numbers of psychrotrophic bacteria, or numbers of proteolytic-psychrotrophic bacteria in raw milk. Inactivation of heat-resistant proteases in normal ultra-high temperature sterilized skim milk averaged 87 to 90%. No enzyme reactivation was observed in milk samples stored up to 300 days. Milk that did not receive treatment showed signs of gelation and whey separation after 3 mo at room temperature. There was no evidence of gelation in low temperature inactivated sterile skim milk, and the storage time required to produce bitter flavor increased an estimated ten fold. Treatment did not affect deleteriously the flavor or quality of the sterilized milk.