Influence of sodium pyrophosphate on thermal inactivation of Listeria monocytogenes in pork slurry and ground pork

The thermal inactivation (55–62·5°C) of Listeria monocytogenes in pork slurry and ground pork that contained 0, 0·25 or 0·5% sodium pyrophosphate (SPP) was evaluated. Surviving cells were enumerated on Modified Oxford Medium. Decimal reduction (D)-values in pork slurry control (0% SPP) were 8·15, 2·57, 0·99, and 0·18 min, at 55, 57·5, 60 and 62·5°C, respectively; D-values in ground pork ranged from 15·72 min at 55°C to 0·83 min at 62·5°C. D-values in pork slurry that contained 0·25% SPP (w/v) were 4·75, 1·72, and 0·4 min, at 55, 57·5, and 60°C respectively; the values in ground pork ranged from 16·97 at 55°C to 0·80 min at 62·5°C. At 62·5°C,L. monocytogenes in slurry that contained SPP were killed too rapidly to allow determination of the D-value. Addition of 0·5% SPP further decreased (P<0·05) the heat resistance of L. monocytogenes in pork slurry but not in ground pork. The z-values in slurry ranged from 4·63 to 5·47°C whereas higher z-values (5·25 to 5·77°C) were obtained in ground pork. Degradation of SPP to orthophosphates in ground pork was two or three times greater than in pork slurry. Possible reasons for failure of SPP to reduce the thermal resistance of L. monocytogenes in ground pork are discussed.     

Changes in Microflora and Other Characteristics of Vacuum-packaged Pork Loins irradiated at 3.0 kGy

Effects of 3.0-kGy irradiation on microflora and other attributes of fresh, vacuum-packaged pork loins were examined during storage (2–4°C, 98 days) and mishandling (24–25°C, 24 and 48 hr). Shelf life of pork chops from irradiated loins was determined at 5°C. Irradiated loins kept at 2–4°C tested negative for Salmonella spp., Campylobacter spp., Clostridium perfringens and Staphylococcus aureus. Yersinia spp. was detected in pork chops held at 5°C; this organism, C. perfringens and Aeromonas spp. were present in abused samples. In two irradiated samples Listeria monocytogenes was found. Irradiation reduced aerobic, anaerobic and Aeromonas spp. counts; lactobacilli were least affected. Chemical spoilage began after 91 days at 2–4°C. With irradiation, TBA values were unaffected but Hunter a color values increased.     

Quality changes and storage life of common carp (Cyprinus carpio) at various storage temperatures

The shelf life and freshness changes in pond-grown common carp (Cyprinus carpio L) during storage at 0–2°C, 5–6°C and room temperature (26–29°C) were investigated by sensory, microbiological, physical and chemical analyses. The effect of gutting on the shelf life during storage at 0–2°C was examined. Iodine/starch and potassium sorbate were examined for their effects on shelf life of whole fish stored at 0–2°C and 5–6°C. Sensory results indicated that the whole fish had a maximum shelf life of 24 to 25 days at 0– 2°C. The life of the fish to the point beyond which it would be unsuitable for sale (commercial shelf life) was 17 days at 0–2°C. Storage at 5–6°C shortened shelf life 2- to 2.5-fold. At room temperature (26–29°C), spoilage was evident after 13 h. Gutting the carp shortened its storage potential at 0–2°C. Iodine treatment of this species stored at 0–2°C and at 5–6°C did not extend shelf life. The maximum shelf life of sorbate-treated fish at 0–2°C and 5–6°C was extended by 1–2 days, commercial shelf life by 3–4 days. Total volatile basic nitrogen, pH and penetrometer analyses were not reliable indicators of changes in freshness during shelf life. Thiobarbituric acid values were not useful as rancid odours or flavours were not detected during storage.     

Evaluations of Warmed-over Flavor during Chill Storage of Cooked Broiler Breast, Thigh and Skin by Chemical, Instrumental and Sensory Methods

Broiler breast, thigh and skin were cooked to 80°C, stored at 2°C for up to 5 days, and evaluated by chemical, gas chromatographic (GC) and sensory methods. Water and fat content of cooked meat did not change during storage. Thiobarbituric acid (TBA) values and levels of major headspace volatiles increased throughout storage time. Intensities of cardboard, warmed-over, rancid/painty, and overall off-flavor characteristics increased. Skin showed the least changes. Breast and thigh meat differed in GC profiles but were similar in sensory scores after 1 day and in TBA values after 2 days of storage. Both TBA and headspace GC measurements are associated with the off-flavor development.     

Effect of Sodium Erythorbate on Residual Nitrite, pH and Bacterial Growth in Liver Sausage Formulated with Different Levels of Mechanically Separated Pork

Some microbiological, chemical, and physical characteristics of liver sausage formulated with 0, 25, 50, and 75% mechanically separated pork (MSP), 156 ppm sodium nitrite and 0 or 550 ppm sodium erythorbate were studied during refrigerated storage (5°C, 6 days) and subsequent elevated-temperature holding (20–24°C, 48 hr). Growth of inoculated Clostridium sporogenes was inhibited by 156 ppm nitrite in all sausages even after 48 hr at 20–24°C, regardless of MSP level. Growth of aerobic mesophiles and facultative anaerobes at 20–24°C was also inhibited in sausage formulated with 156 ppm nitrite and 550 ppm erythorbate. Erythorbate addition and increased MSP levels resulted in higher Hunter a color values. Residual nitrite, pH values, and total iron content of liver sausage increased with increasing MSP content.     

Storage Stability of Intermediate Moisture Mullet Roe

A storage stability study was performed on intermediate moisture roe (a_w= 0.84, salt content = 4%). Samples were stored at various temperatures for up to 1 month. Microbial analyses indicated that bacteria could grow from 5–25°C. Fungi grew at 15° and 25°C while their growth was inhibited at 5°C; however, a lag phase was detected at 15°C. TBA values increased linearly during storage. Microbial analyses, chemical determination of rancidity and sensory evaluations showed that the product was still acceptable after 30 days storage at 5°, 15° or 25°C.     

Effects of refrigeration and oxygen on the coffee brew composition

The aim of this work was to monitor the changes both in the composition and in some sensory parameters of Colombian Arabica coffee brews stored at room and refrigeration temperatures, with and without oxygen. Some nonvolatile compounds related to the taste of coffee brews were determined, in an attempt to study possible relationships between chemical and sensory changes. Storage time hardly affects the amounts of chlorogenic, caffeic and ferulic acids, reported to have some beneficial health effects, mainly due to their antioxidant activities. In contrast, pH decreases in all the coffee brews along the time, mainly in that stored at 25 °C with oxygen. The appearance of sourness and other non typical coffee tastes (rancid taste, aftertaste) and an increase in astringency leads to establish a shelf-life of 10 days for coffee brews stored at 25 °C with oxygen, 15 days for coffee brews stored at 4 °C with oxygen and at 25 °C without oxygen, and 20 days for coffee brews stored at 4 °C without oxygen. The behaviour of 5-caffeoylquinic acid, caffeic acid and 4-vinylguaiacol throughout time was different from other studies conducted at higher temperatures to accelerate the staling, what reveals that stability studies of coffee brews should be made in real time and temperature. Part of this paper was presented at the 21st ASIC Colloquium, Montpellier, 2006.     

Sodium Lactate Effects on Shelf-Life, Sensory, and Physical Characteristics of Fresh Pork Sausage

The objective of our study was to evaluate the effects of various levels (0%, 1%, 2%, 3%) of sodium lactate on selected physical, sensory, and microbiological characteristics of fresh pork sausage stored at 4°C for 28 days. Samples containing 0% and 1% SL reached 10⁸ CFU/g after 10 days refrigerated storage. Addition of 2% or 3% SL to fresh pork sausage delayed microbial deterioration, pH decline, and development of sour- and off-flavors 7 days at 4°C. Samples containing 2% SL did not reach total plate counts of 10⁸ CFU/g until 24 days storage. SL appeared to protect red color, and to “enhance” pork-and salty-flavors in sausage. TBA, L-, a-, and b-values were unaffected by SL level.     

Effects of Fat and NaCl/Phosphate Levels on the Chemical and Sensory Properties of Pork Patties

Ground pork shoulders were combined with 50/50 pork trimmings to achieve fat levels of 20.0, 23.3, 26.6, and 30.0%. Salt/phosphate (NaCl/PO₄) combinations of 0/0, 1/0, 1/0.25 and 2%/0.5% were blended with each fat level. Each treatment combination was stored at 3°C for 7 days in air-permeable film (AP), 21 days in vacuum pouches (VP) and at ?23°C for 90 days in double-wrapped (DW) freezer paper. Fat level did not affect pH, expressed moisture (EM), peroxide value (PV), 2-thiobarbituric acid (TBA) values or cooking losses. Patties with 30.0% fat were jucier and required less energy to compress. A combination of 1%NaCl/0.25%PC₄ reduced cooking losses, enhanced sensory properties and moderated the oxidation effects of NaCl up to 60 days of frozen storage. The NaCl treatment accelerated lipid oxidation most during all storage conditions while the control remained the least oxidized.     

Gamma-Irradiation of Frozen Kiwifruit Pulp

Frozen (–18°C) de-seeded kiwifruit pulp (Actinidia deliciosa) was irradiated at a dose of 100 krad and stored at -18°C. Irradiation resulted in a 2.11 log₁₀ reduction in aerobic plate count (APC) with bacteria being most susceptible. Molds were less susceptible than yeasts. Assessments carried out over 6 months storage showed no significant differences in physical, chemical and sensory properties between irradiated and nonirradiated pulps. The microbial populations of the pulps decreased in parallel throughout the storage period. Frozen storage without irradiation resulted in a 3 log₁₀ reduction in APC over the 6 months period, a 38% reduction in ascorbic acid, and a slight loss of color. Three days frozen storage (– 18°C) following irradiation resulted in an APC only 0.89 log₁₀ higher than 6 months frozen storage (- 18°C) without irradiation with potential savings in energy and holding times which could have economic benefits.     

Effect of Low Dose Irradiation of Pork Loins on the Microflora, Sensory Characteristics and Fat Stability

The effects of low dose (100 krad) irradiation on microflora, sensory characteristics, and development of oxidative rancidity of vacuum packaged pork loins was investigated after irradiation and during low temperature (4°C) storage up to 21 days. Irradiation reduced numbers of mesophiles, psychrotrophs, anaerobic bacteria (P<0.01), and staphylococci (P<0.05), with the effect on mesophiles and psychrotrophic spoilage organisms the greatest. Effect of irradiation on sensory characteristics of pork loin was minimal with no detectable differences between irradiated and nonirradiated pork after 14 days of storage. Irradiation of pork did not affect cooking loss or thiobarbituric acid values.     

Effect of ionizing radiation on quality characteristics of vacuum-packaged normal,pale–soft–exudative,and dark–firm–dry pork

Normal, pale–soft–exudative (PSE), and dark–firm–dry (DFD) pork Longissimus dorsi muscles were vacuum-packaged, irradiated at 0, 2.5 or 4.5 kGy, and stored at 4 °C for 10 days. The pH, color and lipid oxidation of pork were determined at 0, 5 and 10 days of storage. Volatile production from pork loins was determined at Day 0 and Day 10, and sensory characteristics at Day 7 of storage. Irradiation increased the redness of vacuum-packaged normal, PSE and DFD pork. However, the 2-thiobarbituric acid reactive substances (TBARS) values of three types of pork were not influenced by irradiation and storage time. Irradiation increased the production of sulfur (S)-containing volatile compounds, such as mercaptomethane, dimethyl sulfide, carbon disulfide, methyl thioacetate, and dimethyl disulfide, as well as total volatiles in all three types of pork. Normal pork produced higher levels of total and S-containing volatile compounds than the PSE and DFD pork did. The volatiles produced by irradiation were retained in the vacuum packaging bag during storage. Although the odor preference for the three meat types of pork was not different, the panelists could distinguish irradiated meat from the non-irradiated. Industrial relevance: Several US meat companies have already started test-marketing irradiated meat products. Irradiation and the subsequent storage of pork improved the color of PSE and DFD pork, and showed generally similar effects on the production of volatiles, except that there appeared to be a lower level of S-volatiles in the PSE than in the other two samples. This indicated that irradiation can increase the utilization of low-quality pork (PSE and DFD). DFD pork, in particular, which has shorter shelf-life than the others, could benefit the most from irradiation because the shelf-life of DFD meat can be extended significantly by both the methods of vacuum packaging and irradiation.     

Effect of packaging atmosphere and pH on the virulence and growth ofYersinia enterocoliticaon pork stored at 4°C

Growth and virulence of pathogenicYersinia enterocoliticawere investigated on high (pH>6.0) and normal (pH<5.8) pH pork packaged in modified atmospheres and stored at 4°C. Modified atmospheres used in the study were vacuum packaging and saturated CO₂. Pork was packaged in a high gas barrier packaging film and examined over a 30-day period. Phenotypic characteristics were used to detect the presence of the virulence plasmid ofY. enterocoliticaafter exposure to the pork packaging and storage regimen. Phenotypic characteristics ofY. enterocoliticaisolates from pork loin stored at 4°C for 30 days that were studied included Congo red uptake, calcium dependence and autoagglutination in methyl red Voges–Proskauer broth and tissue culture medium. Numbers ofY. enterocoliticaon the lean surface of high pH pork slices increased approximately 2.7logcfucm⁻²when vacuum packaged and stored at 4°C for 30 days. Storage of inoculated normal pH pork in 100% CO₂resulted inY. enterocoliticaremaining in the lag phase over the storage period. Virulence ofY. enterocoliticawas maintained in 25 to 35% of isolates following storage for 30 days at 4°C in vacuum- and CO₂-packaged meats and was not affected by pH of the pork loin.     

Isolation of Yersinia enterocolitica from ready-to-eat foods and pork by a simple two step procedure

Out of 119 ready-to-eat food samples and pork processed for isolation of Yersinia enterocolitica, 15 samples (12·6%) were positive for the presence of Y. enterocolitica by a two step procedure in a modified trypticase soy broth containing 0·25% yeast extract, 0·2% bile salts and 4 μg ml^-1 Irgasan at pH 7·6 and upon incubating at 10°C and 22°C for 6 days. Only five samples (4·2%) were positive by cold enrichment in trypticase soy broth containing 0·2% yeast extract, incubated at 4°C for 14 days. Four strains of Y. enterocolitica and one strain of Y. intermedia were isolated from pork samples processed by cold enrichment. Out of 15 strains of Y. enterocolitica isolated from pork (four strains) and ready-to-eat food samples (10 strains) by two step procedure only three strains belonged to pathogenic serotype O:3 and which were isolated only from pork samples. Overall recovery of Y. enterocolitica was much better by the two step procedure as compared to cold enrichment (P < 0·05).     

Development of Meat Snack Dips: Chemical, Physical, Microbiological and Sensory Characteristics

Snack dips containing 50% ham, 26% bacon or 28% pepperoni in combination with sour cream, unflavored yogurt and tofu were developed. The developmental phases of the study were discussed in relation to ingredient and meat flavor selection, formulation and sensory evaluation. Microbiological, chemical and physical analyses of the new products indicated that the meat-containing snack dips were stable and safe under storage conditions simulating wholesale (3 wk 2-4°C), retail (10 days, 5°C, household (10 days, 8-10°C) and longer-than-normal temperature abuse (12 and 24 hr, 24-25°C).     

Evaluation of Freshness in Determination of Volatile Organic Compounds Released from Pork by HS-SPME-GC-MS

Freshness is an important parameter for evaluating the quality of pork, which has strong correlation with the characteristic volatile organic compounds (VOCs) in meat. In this study, the pork was stored at a refrigerator, and the VOCs were determined by using headspace solid-phase microextraction–gas chromatography–mass spectrometry (HS-SPME-GC-MS). The results of HS-SPME-GC-MS measurements were compared to total viable counts, total volatile basic nitrogen, and pH value to determine possible volatile spoilage markers. The pork was stored in a refrigerator up to 5 days at 4 °C and 466 days at ?18 °C. The pork became stale at 4 °C when the 2,3-butanedione, 3-methyl butyraldehyde, 3-methyl-1-butanol, and acetoin increased to 26.44, 13.72, 71.56, and 340.48 μg/L, respectively. These substances can be seen as characteristic compounds of stale pork. The VOCs such as ethyl acetate, ethyl propionate, ethyl butyrate, and ethyl hexanoate had negative correlation (P?<?0.05) with the pork freshness, which can be potentially considered as characteristic compounds of fresh pork. Therefore, the selected VOCs can be used as indicators for evaluation of pork freshness, and VOCs could be potentially applied in the development of intelligent refrigerators and refrigerated storehouse.     

Production and Regeneration of Principal Volatiles in Apples Stored in Modified Atmospheres and Air

In a series of exploratory experiments, storage of McIntosh apples (Malus domestica Borkh.) in modified atmospheres (MA) (5% CO₂+ 3% O₂ at 2.8°C) suppressed the development of headspace ethanol and acetaldehyde from that in apples stored in air at 0°C (RA). Acetaldehyde, ethanol, ethyl butyrate and hexanal production from intact fruit was further suppressed when the apples were stored in 1.5% CO₂+ 1.5% O₂ or 1.5% CO₂+ 1.0% O₂ at 2.8°C. Placement of fruit in RA following MA storage initially regenerated ethyl butyrate and hexanal in preference to ethanol and acetaldehyde. However storage of fruit in 1.5% CO₂+ 1.0% O₂ for 320 days completely suppressed the principal headspace volatiles and blocked their subsequent regeneration in RA.     

Modified Atmosphere Packaging to Maintain Direct-Set Cottage Cheese Quality

Direct-set cottage cheese packaged in barrier containers was flushed with 100% CO₂ 75% CO₂:25% N₂, 100% N_2, or air, and stored at 4°C for 28 days. Quality was assessed by sensory, microbiological, and chemical tests. No change was observed in headspace gas composition during storage. Psychrotrophic and lactic acid bacteria counts increased for air-treated samples, but counts for cottage cheese packaged under modified atmospheres remained unchanged. Product discoloration was not observed. Acidity increased over storage life, but lactic acid did not contribute towards increased acidity. Sensory characteristics of cottage cheese packaged under modified atmospheres remained satisfactory after 28 days, with 100% CO₂ best.     

Identification of Microbial Isolates from Vacuum-Packaged Ground Pork Irradiated at 1 kGy

Bacterial cultures from irradiated (1 kGy) and nonirradiated, vacuum-packaged ground pork held at 5°C were isolated and characterized over a 12-day storage period. The initial flora of the meat was composed mostly of Pseudomonas sp. and Enterobacter sp. Although the microflora of nonirradiated samples gradually shifted from Gram-negative to Gram-positive microorganisms, 76% of the isolates were characterized as Gram-negative at the onset of spoilage (9 days at 5°C). In contrast, the irradiated ground pork microflora was mainly Gram-positive (66%) shortly after irradiation and increased to 97% after 9 days at 5°C. A total of 720 isolates were identified to genus.     

Storage Study of a Gas-Packaged Bakery Product

English style crumpets were packaged in the atmosphere of CO₂ and N₂ (3:2) and stored at 20°, 22°, 24° and 30°C. In all cases, package volume and headspace CO₂ concentration decreased during the first week of storage. At 30°C, the volume started to increase after 12 days due to production of CO₂ and other metabolites by microorganisms. At 24°C, the volume did not start to increase until after 25 days, while at 22° and 20°C it remained stable or gradually decreasing. Aerobic plate counts and metabolites were higher in the product stored at 30°C for 19 days than those stored at 20°C for 1 month. Product pH after 1 month at 20°C was lower (5.9) than that at 30°C for 19 days (6.5) due, essentially, to the absorption of CO₂.