Shelf Life of Vacuum- or Nitrogen-Packed Pastrami: Effects of Packaging Atmospheres, Temperature and Duration of Storage on Microflora Changes

Numbers of lactobacilli, psychrotrophs and anaerobes in either vacuum- or nitrogen-packed pastrami increased significantly as storage temperature was increased above -4°C or duration extended beyond 7 days at 0, 3 and 7°C. Few significant differences observed in their numbers were attributed to types of packaging but numbers of yeasts and molds decreased significantly in nitrogen-packed samples, particularly at 7°C. Growth of coliforms to log 4.5 per gram occurred at 7°C in both packaging treatments. The initial psychrotrophs consisted of Brochothrix (51–54%), Lactobacillus (40–42%) and Pseudomonas spp. (6.6–9.0%) but Lactobacillus spp. represented 80–92% at 49 days.     

Effect of Tumbling and Tumbling Temperature on Total Aerobic Plate Counts (Incubated at 25°C) and Quality of Boneless, Cured Hams

The effects of intermittent tumbling (up to 18 hr) and processing temperature (25°C or 3°C) on internal temperature and exudate total aerobic plate counts incubated at 25°C (ATPC) in boneless, cured hams were determined. The design used 80 hams in five replicates involving four treatment groups (tumbled at 25°C tumbled at 0°C, control held at 25°C and control held at 0°C). The significant (P < 0.01) tumbling effect on the rise in internal ham temperature occurred after 3 hr, but only accounted for a difference of 1.26°C-1.32°C, independent of processing temperature. While tumbling significantly improved the cooked yield by 3.45%, processing at 25°C rather than at 0°C resulted in a significant (P<0.05) yield reduction of 2.15% after 9 hr of processing. The exudate ATPC was significantly (P<0.01) reduced after 18 hr of tumbling.     

Effect of Nitrogen Flushing on the Production of Proteinase by Psychrotrophic Bacteria in Raw Milk

Raw milk was flushed with 100 ml N₂ min ^-1 during storage at 4°C. Microflora (total psychrotrophs, proteolytic psychrotrophs, lactic acid bacteria) in nitrogen-flushed milk exhibited a longer lag phase and slower growth rates than those in milk stored aerobically at 4°C. Although proteolytic psychrotrophs grew in nitrogen-flushed milk, proteinases could not be detected in these milk samples. Proteinase assays and electrophoresis showed extensive proteolytic activity and hydrolysis of β-casein in control milk but no detectable casein degradation in nitrogen-flushed milk, even after storage for 18 days at 4°C. This study shows the potential of controlled atmosphere storage of raw milk for inhibition of the accumulation of proteolytic enzymes from psychrotrophic bacteria.     

Changes in appearance and natural microflora on iceberg lettuce treated in warm,chlorinated water and then stored at refrigeration temperature

The objective of this study was to determine the effect of warm, chlorinated water on the survival and subsequent growth of naturally occurring microorganisms and visual quality of fresh-cut iceberg lettuce. After dipping cut lettuce leaves in water containing 20 mg l⁻¹free chlorine for 90 s at 50°C, samples were stored at 5 or 15°C for up to 18 or 7 days, respectively. Populations of aerobic mesophiles, psychrotrophs, Enterobacteriaceae, lactic acid bacteria, and yeasts and molds were determined. The visual appearance and development of brown discoloration were monitored. Treatment of lettuce in warm (50°C) chlorinated water delayed browning of lettuce. Shelf life of lettuce stored at 5°C, as determined by subjective evaluation of color and general appearance, was about 5 days longer than that of lettuce stored at 15°C. Treatment in warm (50°) water, with or without 20 mg l⁻¹chlorine, and in chlorinated water at 20°C significantly (α= 0·05) reduced the initial population of mesophilic aerobic microflora by 1·73–1·96 log₁₀cfu g⁻¹. Populations increased, regardless of treatment, as storage time at 5°C and 15°C increased. The same trends were observed in populations of psychrotrophs and Enterobacteriaceae. Yeast populations increased slightly in lettuce stored at 5°C but were consistently about 3 logs lower than mesophilic aerobes. Populations of molds and lactic acid bacteria were less than 2 log₁₀cfu g⁻¹throughout storage at 5 or 15°C. Results suggest that heat (50°C) treatment may have delayed browning and reduced initial populations of some groups of micro-organisms naturally occurring on iceberg lettuce, but enhanced microbial growth during subsequent storage.     

Effects of Potassium Sorbate, Sodium Acetate, Phosphates and Sodium Chloride Alone or in Combination on Shelf Life of Vacuum-Packaged Pork Chops

Microbiological and some physical and chemical effects of treating pork chop surfaces with sodium acid pyrophosphate, a commercial phosphate blend, potassium sorbate and phosphate/sorbate/sodium acetate solutions, with or without sodium chloride, before packaging were studied in pork chops vacuum-packaged and stored at 2–4°C for 10 weeks. All treatments containing potassium sorbate reduced (P<0.05) counts of mesophiles, psychrotrophs, EnterobacteriaCeae, facultative anaerobes, and lactobacilli. Treatment of chops with 10% phosphates/ 10% potassium sorbate solutions improved pork color and decreased purge. Potassium sorbate alone reduced microbial counts more than it did when combined with phosphates, but chops were darker and had more exudate (P<0.05). Combined use of 10% phosphates/10% potassium sorbate extended shelf life in vacuum-packaged fresh pork chops to 10 weeks at 2–4°C compared with 4 weeks for untreated pork and protected meat color.     

Low-dose Gamma Irradiation and Refrigerated FStorage in vacua Affect Microbial Flora of Fresh Pork

Vacuum-packaged ground fresh pork samples absorbed gamma radiation doses of 0. 0.57. 1.91. 3.76. 5.52. or 7.25 kGv at 2°C. Samolcs were analyzed after 1, 7, 14, 21, 28,‘or 35 days itorage at 2°C’for presence and number of aerobic and anaerobic mesophiles and endospore formers, and aerobic psychrotrophs. Conventional plate counts did not detect surviving microflora in any sample that received an absorbed dose of 1.91 kGy or higher, even after refrigerated storage for up to 35 days. The microflora in the control were predominantly Gram-positive for the first 21 days; however, Serratia predominated at 28 and 35 days. Staphylococcus, Micrococcus, and yeast species predominated in samples that received 0.57 kGy.     

Effect of Tumbling and Tumbling Temperature on Surface and Subsurface Contamination of Lactobacillus Plantarum and Residual Nitrite in Cured Pork Shoulder

The effect of intermittent tumbling (up to 18 hr) was compared to a nontumbled treatment at processing temperatures of 3°C and 23°C on tissue surface inoculated with Lactobacillus plantarum. The surface and subsurface number of L. plantarum and the residual nitrite in boneless cured pork shoulder were determined. The L. pluntarum levels were significantly increased (P < 0.05) by tumbling, increased by time (linear, P < 0.01) and by sample location with levels de creasing from nontumbled exudate to surface samples to internal samples. Residual nitrite in cured pork shoulder tumbled intermittently for 18 hr at 23°C was significantly lower (P < 0.01) than in nontumbled tissue. Nitrite level interactions for tumbling time × temperature were highly significant (P < 0.01).     

Quality of chilled ready-to-bake pizza stored in air and under modified atmospheres: Microbiological and sensory attributes

Modified atmosphere packaging (MAP) studies on microbiological and sensory analysis were conducted to extend the shelf life of ready-to-bake pizza stored at 7±1°C. The gas combinations used were: atm1: air (control), atm2: CO₂ (100%), atm3: N₂ (100%), atm4: 50% CO₂/50% N₂. Total plate count (TPC), yeasts/molds (Y/M), coliforms, lactic acid bacteria (LAB), psychrotrophs, and anaerobic spore formers were estimated at time intervals of 0, 5, 10, 15, and 20 days. TPC and LAB of pizza samples (atm1) reached 7.10 and 8.14 log CFU/g after 10 days of storage, respectively. Coliforms, psychrotrophs, and Y/M were significantly higher (p<0.05) for pizza samples stored in atm1 than other storage conditions of MAP. Finally, counts of anaerobic spore formers were low (<3 log CFU/g) irrespective of the packaging conditions throughout the entire storage period. It was concluded that among the 4 atmospheres examined, atm2 (100% CO₂) was the best, followed by atm4>atm3>atm1 respectively, in descending order. MAP conditions under this study may extend shelf life of pizza to considerable amount of time.     

Effects of temperature and storage duration on the microflora, physicochemical and sensory changes of vacuum- or nitrogen-packed pork

A comparative study of vacuum packaging alone or vacuum followed by nitrogen back-flushing of fresh pork stored at -4, 0, 3 and 7°C for 49 days showed that pork stored at -4°C generally exhibited small changes in microbial numbers, pH, exudate, appearance and off-odour. Samples stored above 0°C could not be kept beyond 14-28 days without obvious changes, regardless of package atmospheres. Storage life was inversely related to temperature. The initial psychrotrophs consisted primarily of Pseudomonas spp. but these organisms diminished as Lactobacillus spp. multiplied in both atmospheres. Few significant differences in numbers of fecal coliforms were found between treatments, although the numbers tended to increase in samples stored at 7°C. Nitrogen packaging did not reduce exudate losses as compared with vacuum packaging.     

Evaluation of Changes in Listeria monocytogenes Populations on Frankfurters at Different Stages from Manufacturing to Consumption

ABSTRACT: This study evaluated the fate of inoculated Listeria monocytogenes on frankfurters stored under conditions simulating those that may be encountered between manufacturing and consumption. Frankfurters with or without 1.5% potassium lactate and 0.1% sodium diacetate (PL/SD) were inoculated (1.8 ± 0.1 log CFU/cm²) with a 10‐strain composite of L. monocytogenes, vacuum‐packaged, and stored under conditions simulating predistribution storage (24 h, 4 °C), temperature abuse during transportation (7 h, 7 °C followed by 7 h, 12 °C), and storage before purchase (60 d, 4 °C; SBP). At 0, 20, 40, and 60 d of SBP, samples were exposed to conditions simulating delivery from stores to homes or food establishments (3 h, 23 °C), and then opened or held vacuum‐packaged at 4 or 7 °C for 14 d (SHF). Pathogen counts remained relatively constant on frankfurters with PL/SD regardless of product age and storage conditions; however, they increased on product without antimicrobials. In vacuum‐packaged samples, during SHF at 4 °C, the pathogen grew faster (P < 0.05) on older product (20 d of SBP) compared to product that was fresh (0 d of SBP); a similar trend was observed in opened packages. At 7 °C, the fastest growth (0.35 ± 0.02 log CFU/cm²/d) was observed on fresh product in opened packages; in vacuum‐packages, growth rates on fresh and aged products were similar. By day 40 of SBP the pathogen reached high numbers and increased slowly or remained unchanged during SHF. This information may be valuable in L. monocytogenes risk assessments and in development of guidelines for storage of frankfurters between package opening and product consumption.     

Sodium Lactate Affects Shelf Life And Consumer Acceptance Of Fresh Catfish (Icfalurus nebulosus, marmoratus) Fillets Under Simulated Retail Conditions

Fresh Ictulurus nebulosus, marmoratus (Speckled Bullhead catfish) fillets were tumbled under vacuum (172.32 kPa for 15 min) with either 0.1, or 2% sodium lactate solutions %(w/w) adjusted to pH 5.50, and stored at 1.11 1°C for 8 days. Shelf life of fillets treated with 2% sodium lactate was extended from 4 to 7 days. Aerobic plate counts and TBA values were lower (P < 0.05) for fillets treated with 2% sodium lactate, compared to controls. Total and fecal coliforms, psychrotrophs, pH, water activity, proximate composition and fatty acid profiles were not affected by sodium lactate. Cooking yields and sodium content were higher for fillets treated with sodium lactate compared to controls.     

Microbiological and Sensory Changes in Minced Beef Treated with Potassium Lactate and Sodium Diacetate during Refrigerated Storage

The effect of potassium lactate and sodium diacetate on the microbiological changes and sensory properties of vacuum-packaged minced beef was investigated. The meat samples both with a preservative (in the amounts 0.65% and 1.3%) and without were stored at temperatures of 0–1°C and 5–6°C. The influence of storage time on changes in total bacteria count (TBC), lactic acid bacteria (LAB), Brochothrix thermosphacta, and the microbes of the Enterobacteriaceae family was investigated, as well as changes in pH and sensory quality. It was found that the addition of the preservative to the minced meat caused a significant extension (p < 0.05) of the lag phase and an inhibition of microbial growth rate, depending on temperature, storage time, and its concentration. The antibacterial effect was significantly higher (p < 0.05) at a temperature of 0–1°C than at 5–6°C and most susceptible to it were the bacteria belonging to the Enterobacteriaceae. The study results showed that the minced beef containing the preservative which had been vacuum stored at 0–1°C, presented a better sensory quality and had a shelf-life of about 6 days longer, in relation to the quality and shelf-life of the control samples. For each of the refrigeration storage temperatures however, there was no statistically significant change (p < 0.05) in the pH for the various storage periods and preservative quantities present.     

The tentative recognition of psychrotrophic Gram-negative bacteria in 48 h by their surface growth at 10°C

Employing 153 species and strains of Gram-negative bacteria representing 20 genera, 79 produced visible growth on brain heart infusion agar (BHIA) at 7°C in 10 days and thus conformed to the definition of psychrotrophs. All but 5 of the 79 (93.7%) grew on BHIA plates at 10°C in 2 days. At 12°C, 13 psychrotrophs did not grow in 24 h while in 2 days 28 nonpsychrotrophs grew. Surface plating for colony enumeration generally required 3 days, and pour plating 4 days for countable colonies. It is suggested that those bacteria that grow rapidly at 7°C but not at 40°C be designated stenopsychrotrophs while those that can grow at 40°C or above and generally more slowly at 7°C be designated eurypsychrotrophs. The use of 10°C for 2 days may be used to make a rapid and tentative designation of Gram-negative psychrotrophs when turbid broth cultures are streaked on BHIA plates.     

Impact of high-pressure processing on microbial shelf-life and protein stability of refrigerated soymilk

The effects of pressure (400, 500 and 600 MPa), dwell time (1 and 5 min) and temperature (25 and 75 °C) on microbial quality and protein stability of soymilk during 28 days of storage (4 °C) were evaluated under aerobic and anaerobic conditions. After processing and during storage, there were significant differences in total bacterial count (TBC), numbers of psychrotrophs (PSY) and Enterobacteriaceae (ENT), and protein stability between untreated (control) and pressurized samples (P < 0.05). Pressure applied at an initial temperature of 75 °C resulted in a greater suppression in growth of PSY compared to TBC. No ENT was detected in pressurized samples throughout the storage period tested. Dwell time had no significant effect on log reduction of TBC at 25 or 75 °C (P > 0.05). Pressure at 400 MPa (5 min), 500 and 600 MPa (1 and 5 min) produced 100% sub-lethal injury in surviving bacterial populations irrespective of temperature. After 28 days of refrigerated storage, both aerobic and anaerobic pressurized samples had better or similar stability as the control on day one of storage. Soymilk control samples were spoiled after 7 days whereas pressurization increased soymilk shelf-life by at least 2 weeks. Pressure (600 MPa) at 75 °C for 1 min not only significantly reduced initial microbial populations and increased the microbial shelf-life but also extended the protein stability of soymilk (P < 0.05).     

EFFECT OF PRESSING ON MOISTURE LOSS AND SENSORY PROPERTIES OF BEEF

Paired halves of top round (Semimembranosus and Adductor muscles) sub-primals were removed from each of ten, USDA Choice, approximately 272 kg steers, freezer wrapped, frozen, and stored at -24° C for approximately 1 month. Following freeze-tempering, each primal was divided longitudinally with one half being pressed at 344 Newtons/cm² to a specified shape in a Bettcher Model 70 Press, while the other half served as nonpressed control. Moisture loss and sensory properties were determined for 2.54 cm thick steaks. No significant differences were found in juiciness, flavor or Kramer shear values between pressed and non-pressed top round steaks, however, sensory tenderness scores were lower (P < 0.05) for steaks that were pressed than for those that were not pressed. Holding steaks at 2° C for 0, 1, 2, or 3 days did not significantly alter Kramer shear or sensory panel evaluations. Cooking loss, drip loss and total loss were not affected by pressing. Drip loss was lower (P < 0.05) and cooking loss was higher (P < 0.05) for steaks held one day at 2° C than for steaks held 2 or 3 days at 2° C. When drip loss and cooking loss were combined (total loss) there was no difference among the four storage times. Drip loss following portion cutting could result in a problem in fresh merchandising of freeze-tempered cuts.     

Synergistic Effect of Sodium Chlorite and Edible Coating on Quality Maintenance of Minimally Processed Citrus grandis under Passive and Active MAP

Edible coating has been an innovation within the bioactive packaging concept. The comparative analysis upon the effect of edible coating, sodium chlorite (SC) and their combined application on quality maintenance of minimally processed pomelo (Citrus grandis) fruits during storage at 4 °C was conducted. Results showed that the combination of edible coating and SC dipping delayed the microbial development whereas the sole coating or dipping treatment was less efficient. The synergetic application of edible coating and SC treatment under modified atmosphere packaging (MAP, 10% O₂, 10% CO₂) was able to maintain the total soluble solids level and ascorbic acid content, while reduce the weight loss as well as development of mesophiles and psychrotrophs. Nonetheless, the N, O‐carboxymethyl chitosan solely coated samples showed significantly higher level of weight loss during storage with comparison to the untreated sample. Furthermore, the combined application of edible coating and SC dipping under active MAP best maintained the sensory quality of minimally processed pomelo fruit during storage.     

Gas‐producing and spoilage potential of Enterobacteriaceae and lactic acid bacteria isolated from chilled vacuum‐packaged beef

This study aimed to enumerate and identify lactic acid bacteria and Enterobacteriaceae from spoiled and nonspoiled chilled vacuum‐packaged beef and determine their potential to cause blown pack spoilage. These microbial groups were also enumerated in nonspoiled samples and detected in abattoir samples. The potential of isolates to cause ‘blown pack’ spoilage of vacuum‐packaged beef stored at chilled temperature (4 °C) and abuse temperature (15 °C) was investigated. Populations of lactic acid bacteria in exudate of spoiled and nonspoiled samples were not significantly different (P > 0.05), whereas the number of lactic acid bacteria on the surface was significantly higher (P < 0.05) in spoiled samples as compared to nonspoiled samples. The population of Enterobacteriaceae species in exudate and on the surface of samples were significantly higher (P < 0.05) in spoiled packs in comparison with nonspoiled packs. Results of the deterioration potential showed that ‘blown pack’ spoilage was noticeable after 7 days at 15 °C and after 6 weeks at 4 °C for samples inoculated with Hafnia alvei.     

Biochemical and Nutritional Changes in Corn (Zea mays) during Storage at Three Temperatures

Two cultivars of corn (Zea mays), yellow and white were stored at 0°, 20° and 55°C for 7 months as whole grains and flours at 13-14% moisture. The changes in the soluble sugars and titratable acidity of the grains at 55°C and the titratable acidity of yellow corn grains stored at 0° and 20°C were significant (P < 0.05). Changes also occurred in the moisture content of all the samples and browning in the grains at 55°C (P < 0.05). The decrease in the Hunter L-values was greater in the grains than in the flour (P < 0.05). There were no significant differences in the pH, free amino nitrogen and protein digestibility (P > 0.05).     

Original article: Gel properties of red tilapia surimi: effects of setting condition,fish freshness and frozen storage

This study aimed to determine effects of setting condition, fish freshness and storage time of frozen surimi on properties of red tilapia surimi gel. To investigate the effect of setting condition, a combination of eight setting temperatures (35–70 °C) and four setting times (30–120 min) was used. Maximum breaking force, deformation and gel strength were obtained after the gel had been set at 40 °C for 90 or 120 min. Setting at 65 °C resulted in the lowest obtained gel strength, because of proteolytic degradation of myosin heavy chain. Increasing storage time of raw fish material in ice caused a significant decrease in gel strength of the resultant surimi gel (P < 0.05). Gels produced from surimi kept in frozen storage for up to 9 months also exhibited reduced gel strength, with a concomitant increase in the expressible drip, with increasing storage time (P < 0.05).     

Shelf-Life of Pasteurized Fluid Milk as Affected by Age of Raw Milk

Increasing raw milk storage time prior to pasteurization may affect product shelf-life. Raw milk was stored at 4.5°C for 0, 2, 4, and 6 days prior to pasteurizing. Milk samples from each pasteurized lot were analyzed after continuous storage at 4.5°C for 0, 4, 8, 12, 16, and 20 days. Both raw and pasteurized samples were analyzed for coliforms, psychrotrophs, and total bacteria counts. Flavor scores were also determined. No correlations were significant between raw or pasteurized samples and total bacteria or coliform counts. Related were flavor score and days held raw, shelf-life of the resulting pasteurized product, and interaction of days held raw and shelf-life of the pasteurized product. Psychrotrophic counts and age of the raw milk were correlated. From correlations of flavor scores with shelf-life of the milk, a predictive equation was: Flavor score = 8.00 – .88 R – .11 P – .0015 P² – .009 R P, where R is days held raw and P is shelf-life of the pasteurized product.