A comparison of the effects of storage of raw milk at 2°C and 6°C on the yield and quality of Cheddar cheese

The advantages of storing raw milk, which is to be used for Cheddar cheese manufacture, at 2°C rather than at 6°C was examined. Storage of milk at the lower temperature effectively reduced the level of psychrotroph growth, and after 4 days the psychrotroph counts in samples stored at 2°C were 100-fold lower than those found in samples stored at 6°C. There was no advantage in terms of cheese yield in storing milks at the lower temperature, but an overall improvement in cheese quality was noted in samples produced from milk stored at 2°C.     

Metabolomes of the psychrotolerant bacterium Listeria monocytogenes 10403S grown at 37 °C and 8 °C

Listeria monocytogenes is a food-borne pathogen with the ability to grow at refrigeration temperatures. Knowledge of the mechanisms involved in low temperature growth is incomplete and here we report the results of a metabolomics investigation of this. The small molecule contents of L. monocytogenes 10403S grown at 37 °C and 8 °C were compared by gas chromatography/mass spectrometry (GC/MS). Over 500 peaks were detected in both 37 °C and 8 °C-grown cells, and 103 were identified. Of the identified metabolites, the concentrations of 56 metabolites were increased (P < 0.05), while the concentrations of 8 metabolites were decreased at low temperature. Metabolites increasing in concentration at 8 °C included amino acids, sugars, organic acids, urea cycle intermediates, polyamines, and different compatible solutes. A principal component analysis (PCA) was used to visualize and compare the matrix containing the data in 6 samples, and this clearly identified the 37 °C and 8 °C metabolomes as different. The results indicated that an increase in solute concentrations in the cytoplasm was associated with low temperature adaptation, which may be a response to chill stress with the effect of lowering the freezing point of intracellular water and decreasing ice crystal formation.     

Effect of prolonged heat treatment from 48 °C to 63 °C on toughness, cooking loss and color of pork

The effect of low temperature long time (LTLT) heat treatment at 48 °C, 53 °C, 58 °C, and 63 °C for T(c) (time to reach a core temperature equal to the water bath), T(c)+5h holding time, and T(c)+17h holding time was studied in Longissimus dorsi and Semitendinosus muscles from slaughter pigs and sows. Meat toughness (Warner-Bratzler Shear Force), cooking loss and color (Minolta L*a*b*-values) was measured and in the cooking loss the amount of heat-soluble collagen and activity of cathepsin B+L was determined. Decreasing shear force and increasing cooking loss during LTLT treatment was observed between 53 °C and 58 °C. Furthermore, increasing temperature from 53 °C to 58 °C and increasing time from T(c) to T(c)+17h increased the solubility of collagen. Residual activity of cathepsin B+L in LTLT treated pork was mainly affected by temperature, showing the highest activity at 58 °C and 63 °C.     

Spores of Bacillus cereus strain KBAB4 produced at 10 °C and 30 °C display variations in their properties

Spores of the psychrotrophic Bacillus cereus KBAB4 strain were produced at 10 °C and 30 °C in fermentors. Spores produced at 30 °C were more resistant to wet heat at 85 °C, 1 % glutaraldehyde, 5 % hydrogen peroxide, 1 M NaOH and pulsed light at fluences between 0.5 and 1.75 J cm⁻² and to a lesser extent to monochromatic UV-C at 254 nm. No difference in resistance to 0.25 mM formaldehyde, 1 M nitrous acid and 0.025 g l⁻¹ calcium hypochlorite was observed. Spores produced at 10 °C germinated more efficiently with 10 mM and 100 mM l-alanine than spores produced at 30 °C, while no difference in germination was observed with inosine. Dipicolinic acid (DPA) content in the spore was significantly higher for spores prepared at 30 °C. Composition of certain fatty acids varied significantly between spores produced at 10 °C and 30 °C.     

Liberation of actin from actomyosin in meats heated to 65°C

This study investigated whether actin liberation from myofibrils occurs during the heating of various muscles, as well as squid mantle muscle at temperatures, such as 60°C, employed for vacuum cooking of meats. Actin liberation was demonstrated in scallop striated adductor muscle, but not in beef, pork, or chicken, using the detection method previously employed with squid muscle, in which liberated actin was detected with SDS-PAGE, in the supernatant obtained by centrifugation of the homogenate of heated muscle in 0.2M KCl at a neutral pH. However, actin liberation was demonstrated in beef, pork and chicken by a new detection method, in which heated muscle was homogenized in 0.6M KCl or NaCl at a slightly alkaline pH and maintained at 4°C for 16h with stirring, after which the homogenate was diluted three times with water and centrifuged to obtain the supernatant containing the liberated actin. This new method indicated that actin liberation in beef, pork, and chicken was marked by heating at 65°C, but scarcely induced at 80°C. Thus, the liberation of actin from myofibrils may contribute to the greater tenderness of vacuum-cooked meat (meat heated at a low temperature for long time), as compared with meat prepared by cooking at a higher temperature.     

Detection of specific spoilage bacteria from fish stored at low (0°C) and high (20°C) temperatures

The spoilage potential of 309 bacterial strains isolated from fish spoiled at 0 and 20°C was investigated. Gram-negative, non-fermentative, motile rods tentatively identified as Alteromonas were the major spoilage organisms at 0°C. These bacteria were also found at 20°C, but a large number of Gram-negative, fermentative, motile rods belonging to the Vibrionaceae were also identifieas spoilage organisms at this temperature. Most of the Vibrionaceae did, however, not produce hydrogen sulphide from thio-sulphate but only from the sulphur containing amino acid, L-cysteine. A specific count of fish spoilage organisms at both low and high temperatures could therefore be obtained directly on an Iron Agar containing thiosulphate and cysteine where bacteria capable of forming H₂S from either source of sulphur would appear as black colonies.     

The viabilities of cells in cultures of Escherichia coli growing with formation of filaments at 6 °C

Cold adapted, exponential phase cells of three strains of Escherichia coli were incubated at 6 °C for 10 days. Cells in all cultures grew by elongation, with formation of filaments to different extents, but with generally only small changes in the numbers of colony forming units (cfu). At later incubation times some cells of all lengths were identified as dead by LIVE/DEAD staining, with cell wall damage being apparent in some cells stained as dead but not in cells stained as live. When samples of cultures were incubated at 37 °C for 2h, the numbers of cfu of two strains (ATCC 11775 and ATCC 23739) increased similarly and were not affected by the time of prior exposure to 6 °C. When incubated at 37 °C, the numbers of cfu of the other strain (8WT) increased less after incubation at 6 °C for 1, 2 or 3 days than when transferred to 37 °C from 15 °C. After>3 days at 6 °C numbers of strain 8WT were reduced after incubation at 37 °C for 2h. The findings show that in cultures of E. coli elongating at 6 °C, elongating cells and filaments do not divide; and cells of all lengths lose viability at similar rates. Also, the findings indicate that substantial fractions of cells in cultures elongating at refrigerator temperatures are inactivated by an abrupt change of temperature to 37°C.     

Effects of combining of smoking and marinating on the shelf life of anchovy stored at 4°C

The quality of smoked and marinated anchovy was investigated in terms of sensory, chemical [total volatile basic nitrogen (TVB-N), thiobarbituric acid (TBA), peroxide value (PV), fatty acids, free fatty acids (FFA), and pH] and microbiological parameters (total aerobic count (TVC), coliform, Escherichia coli, Salmonella, Staphylococcus aureus) during 7 months of storage. The results of sensory analyses showed that the total appearance, odor-taste, and texture scores decreased gradually during storage period. The results of the chemical analyses also correlated well with the sensory analyses apart from TVBN value. TBA significantly increased (p<0.05) from 1.9 to 4.25 MA/kg after the storage of 6 month. Peroxide value (POV) showed significant fluctuations (p<0.05) during the storage period. Initial TVC of 3.8 log CFU/g increased to 6.2 log CFU/g at the end of storage period. According to results obtained from sensory, chemical, and microbiological analyses, shelf life of this product was about 6 month.     

Quality changes of ready-to-eat ginseng chicken porridge during storage at 25°C

Ready-to-eat (RTE) ginseng chicken porridge was heated in a retort with an F-value of 4.0 after being packaged in a gas-tight plastic tray (PP/EVOH/PP) with top film (PET/PA/CPP). Various quality changes were investigated during the storage for 28weeks at 25°C. Over the storage period, microorganisms were not detected above 1.0 log cfu/cm(2) (detection limit). The viscosity increased sharply from 775 to 2025cp for initial 4weeks and increased steadily until 16weeks, with a slight reduction thereafter. During the 28weeks of storage, the ratio of residual oxygen and pH decreased from 10.8% and 6.49 to 5.7% and 6.05, while retrogradation degree increased from 0% to 55.9%. Hunter L(?), b(?), and ΔE values increased until 20weeks and remained for the rest of storage. Based on sensory, microbiological and physicochemical evaluations, the RTE ginseng chicken porridge could be marketable for at least 24weeks at 25°C.     

Dielectric and thermophysical properties of meat batters over a temperature range of 5-85 °C

Dielectric (dielectric constant (ε(')) and loss factor (ε″)) and thermal (heat capacity (c), thermal conductivity (k) and thermal diffusivity (α))) properties of two meat batters (pork luncheon roll (PLR) and white pudding (WP)) were measured between 5 and 85 °C. Radio frequency (RF) and microwave (MW) ε″ values varied across 5-85 °C (P<0.05). MW ε(') and ε″ values for WP tended to peak at 45 °C and decrease thereafter, whereas for PLR, ε(') and ε″ peaked at 65 °C which appeared to match potato starch gelatinisation within this product. WP and PLR had significantly higher c values at 25 °C, which corresponded to the MP of pork fat. For PLR, an additional c peak was noted at 65 °C, which appeared to correspond to potato starch gelatinisation. At 85 °C, k values were higher (P<0.05) than at 5, 25 and 45 °C but were not higher than values at 65 °C. α values increased with temperature (P<0.05).     

The effect of cooling rate on beef tenderness: The significance of pH at 7 °C

To study the effects of cooling regime on beef tenderness, seven commercial beef slaughterhouses with different cooling regimes were selected to obtain different carcass cooling rates. The pH values and temperatures of 8 M. longissimus dorsi (LD) and M. semimembranosus (SM) muscles from each slaughterhouse were monitored for 30 h. The muscles of the monitored carcasses were excised and vacuum packed for Allo-Kramer shear force (SF) determinations. Samples were kept at 3-4 °C for 5 or 21 d. The slaughterhouses were grouped by their average pH values of the muscles, prevailing at the moment when the temperature of the muscles reached 7 °C. The pH groups for LD were (i) low (5.52-5.63), (ii) medium (5.84-5.97) and (iii) high (6.16-6.17). The highest shear forces were in group (iii), being the toughest: 155-152 N/g, and the lowest in group (i) (the most tender): 108-116 N/g, respectively. The regression equation or the shear force was SF=-295.4+73.0?(pH at 7 °C); (R(2)=87%). There was no significant correlation between the cooling rate and tenderness in SM, indicating that it is difficult to control the tenderness of all muscles using the same cooling regime. The ageing effect was more marked and the variation in the shear forces smaller in the slaughterhouses generating carcasses with low pH values at 7 °C than in those generating high ones. It was concluded that a low cooling rate, or more specifically, the temperature/pH at the onset of rigor mortis, is important for beef tenderness. The pH of LD must fall to values below 5.7 before/when the temperature reaches 7 °C.     

Some structural properties of ovalbumin heated at 80°C in the dry state

Dry heating of ovalbumin at 80°C improved the gel properties, including the gel strengthening and transparency upon the subsequent heating for gelation [Matsudomi, N., Ishimura, Y., & Kato, A., (1991). Improvement of gelling properties of ovalbumin by heating in dry state. Agricultural and Biological Chemistry, 55, 879–881.]. Some structural properties of the dry-heated ovalbumin responsible for such gel properties were studied. The electrophoretic patterns revealed the formation of ovalbumin polymer through hydrophobic and disulfide protein-protein interaction during heating in the dry state. The slight changes in circular dichroism spectrum and surface hydrophobicity indicated mild conformational changes in ovalbumin molecules. Differential scanning calorimetry themograms showed that enthalpy of denaturation of ovalbumin was markedly decreased with an increase of dry-heating time. The deamidation of ovalbumin was found to occur during the dry-heating process, and the degree of deamidation reached 10% after dry heating at 80°C for 7 days. It was assumed that the partially unfolded and deamidated ovalbumin produced by the dry heating forms specific soluble aggregates during subsequent heating for gelation, resulting in the formation of an ordered gel matrix.     

Kinematic Viscosity of Aqueous Solutions of Ethanol and Glucose in the Range of Temperatures from 20 to 45°C

The purpose of this investigation was to determine, using a capillary viscosimeter, kinematic viscosity data of aqueous solutions of ethanol and glucose, at several temperatures (from 20 up to 45ºC) and concentrations. Glucose solubility strongly depended on ethanol concentration allowing the kinematic viscosity study (from 5% up to 45% w/w ethanol concentration with variable glucose concentrations as a function of its solubility). Kinematic viscosity modelling with solution concentration and temperature simultaneously, based on previous models for respective binary systems, was successfully carried out. The estimated values by this model give low average deviations (2.62%) from the experimental data. Glucose solubility (at 25ºC) in alcohol solutions and index of refraction (at 20ºC) of ternary solutions were also determined and empirical models are proposed in order to evaluate both physical properties with high (R² > 0.993 and >?0.991, respectively) accuracy.     

Effects of curdlan on the texture and structure of Alaska pollock surimi gels treated at 120°C

The effects of curdlan (2%, 3% and 4%) on the gel properties of Alaska surimi using high-temperature treatment were examined in this study. Curdlan treatment improved the gel strength of surimi in a concentration-dependent manner. Based on the results of dynamic rheology and differential scanning calorimetry (DSC), curdlan promoted the stability of proteins in the gel. Moreover, curdlan facilitated the interaction between gel proteins and actomyosin, thereby preventing the aggregation and denaturation of protein and increased the thermal transition temperature. The results of scanning electron microscopy showed that the addition of curdlan induced the formation of a more ordered and denser gel matrix and the fibrils in the three-dimensional network became more delicate. Therefore, surimi samples with curdlan may hold more moisture and exhibit improved transfer of free water to bound water, leading to a higher water-holding capacity (WHC).     

Characterization of starter-free Queso Fresco made with sodium-potassium salt blends over 12 weeks of 4°C storage

Development of reduced-sodium cheese to meet the demands of consumers concerned about sodium levels in their diet is challenging when a high-moisture, higher pH, fresh cheese, such as Queso Fresco (QF), depends on its NaCl salt content to obtain its signature flavor and quality traits. This study evaluated the effects of different Na-K salt blends on the compositional, sensorial, microbial, functional, and rheological properties of QF stored for up to 12 wk at 4°C. Queso Fresco curd from each vat was divided into 6 portions and salted with different blends of NaCl-KCl (Na-K, %): 0.75-0.75, 1.0-0.5, 1.0-1.0, 1.0-1.3, 1.0-1.5, and 2.0-0 (control). Within this narrow salt range (1.5 to 2.5% total salt), the moisture, protein, fat, and lactose levels; water activity; pH; and the textural and rheological properties were not affected by salt treatment or aging. The total salt, sodium, potassium, and ash contents reflected the different Na-K ratios added to the QF. Total aerobic microbial count, overall proteolysis, the release of casein phosphopeptides, and the level of volatile compounds were affected by aging but not by the salt treatment. Only the 1.0-1.3 and 1.0-1.5 Na-K cheeses had sensory saltiness scores similar to that of the 2.0-0 Na-K control QF. Loss of free serum from the cheese matrix increased steadily over the 12 wk, with higher losses found in QF containing 1.5% total salt compared with the higher Na-K blends. In conclusion, KCl substitution is a viable means for reduction of sodium in QF resulting in only minor differences in the quality traits, and levels of 1.0-1.3 and 1.0-1.5 Na-K are recommended to match the saltiness intensity of the 2.0-0 Na-K control. The findings from this study will aid cheese producers in creating reduced-sodium QF for health-conscious consumers.     

Effect of a 10-day ageing at 30°C on the texture of dry-cured hams processed at temperatures up to 18°C in relation to raw meat pH and salting time

The aim of this study was to investigate the effect of a 10-day ageing at 30 ± 2 °C on the texture of dry-cured hams processed at temperatures up to 18 ± 2 °C for 12 months in relation with raw ham pH and salting time. Three pH groups (semimembranosus muscle at 24 h post-mortem: Low pH < 5.7, Medium pH = 5.7  pH  5.9, and High pH > 5.9), three salting times (6 d, 10 d and 14 d) and two ageing temperatures (18 °C and 30 °C) were investigated. Physicochemical characteristics, instrumental and sensory texture and product sliceability were evaluated on biceps femoris and semimembranosus muscles. Hams with pH_SM24 < 5.7 should be avoided in order to reduce the incidence of texture problems in dry-cured ham elaboration. Texture problems are especially important in hams with a reduced salt content that are mechanically sliced (not frozen). A 10-day ageing at 30 °C could be useful for reducing the soft texture problems in dry-cured hams processed at temperatures up to 18 °C for 12 months without affecting the product flavour.     

Effect of muscle restraint on sheep meat tenderness with rigor mortis at 18°C

The effect on shear force of skeletal restraint and removing muscles from lamb m. longissimus thoracis et lumborum (LT) immediately after slaughter and electrical stimulation was undertaken at a rigor temperature of 18°C (n=15). The temperature of 18°C was achieved through chilling of electrically stimulated sheep carcasses in air at 12°C, air flow 1-1.5 ms(-2). In other groups, the muscle was removed at 2.5 h post-mortem and either wrapped or left non-wrapped before being placed back on the carcass to follow carcass cooling regimes. Following rigor mortis, the meat was aged for 0, 16, 40 and 65 h at 15°C and frozen. For the non-stimulated samples, the meat was aged for 0, 12, 36 and 60 h before being frozen. The frozen meat was cooked to 75°C in an 85°C water bath and shear force values obtained from a 1 × 1 cm cross-section. Commencement of ageing was considered to take place at rigor mortis and this was taken as zero aged meat. There were no significant differences in the rate of tenderisation and initial shear force for all treatments. The 23% cook loss was similar for all wrapped and non-wrapped situations and the values decreased slightly with longer ageing durations. Wrapping was shown to mimic meat left intact on the carcass, as it prevented significant prerigor shortening. Such techniques allows muscles to be removed and placed in a controlled temperature environment to enable precise studies of ageing processes.     

Influence of low dose irradiation on the quality of fresh buffalo meat stored at 0-3°C

The effect of low dose irradiation on the microbiological, chemical and sensory qualities of fresh buffalo meat stored at 0-3°C was studied. Meat slices packed in polyethylene bags subjected to 2·5 kGy dose had a shelf-life of 4 weeks with acceptable sensory score, low total volatile basic nitrogen values and remarkable improvement in microbiological quality. Irradiated meat was completely free of Pseudomonas spp. and Enterobacteriaceae throughout storage. In contrast, the unirradiated control meat spoiled within 2 weeks.     

Design of a combined process for the inactivation of Salmonella Enteritidis in liquid whole egg at 55°C

This paper is an evaluation of the lethal effectiveness of a successive application of pulsed electric fields (PEFs) and heat treatment in liquid whole egg (LWE) in the presence of different additives on the population of Salmonella serovar Enteritidis. Synergistic reductions of the Salmonella Enteritidis population were observed when LWE samples containing additives were treated with PEF (25 kV/cm; 100 and 200 kJ/kg), heat (55 °C), or PEF followed by heat. The presence of additives, such as 10 mM EDTA or 2% triethyl citrate, increased the PEF lethality 1 log?? cycle and generated around 1.5 log?? cycles of cell damage, resulting in the reduction of undamaged cells of 4.4 and 3.1 log?? cycles, respectively. The application of PEF followed by heat treatment significantly (p < 0.05) reduced D(55 oC) from 3.9 ± 0.2 min in LWE to 1.40 ± 0.06 min or 0.24 ± 0.02 min in the presence of 10 mM EDTA or 2% triethyl citrate, respectively. A PEF treatment of 25 kV/cm and 200 kJ/kg followed by a heat treatment of 55 °C and 2 min reduced more than 8 log?? cycles of the population of Salmonella Enteritidis in LWE combined with 2% triethyl citrate, with a minimal impact on its protein soluble content. The heat sensitizing effect of PEF treatments in the presence of 2% triethyl citrate on the Salmonella population could enable LWE producers to reduce the temperature or processing time of thermal treatments (current standards are 60 °C for 3.5 min in the United States), increasing the level of Salmonella inactivation and retaining the quality of non-treated LWE.     

Effect of low temperatures (-18 to +5°C) on the texture of beef lean

The textural properties of beef over the temperature range −18 to +5 °C were measured using Warner Bratzler (WB) and tensile techniques. In addition, the effects of rapid radio frequency (RF) tempering and slower conventional air tempering on texture were compared. Temperature showed a significant effect (P < 0.05) on WB and tensile shear force, with higher values obtained at temperatures on or below −5 °C. Work to fracture values showed two peaks at −15 and −3 °C. Sample thickness and muscle fibre direction were also important factors affecting shear force, with samples cut across fibres showing higher values. Tempering method showed no effect (P ? 0.05) on the textural properties measured. In light of the rapid nature of RF tempering, these findings will be of interest to the meat industry.