The effect of sub-zero temperatures on different lifestages of Lasioderma serricorne (F.) and Ephestia elutella (Hübner)

The effect of sub-zero temperatures on different lifestages of Lasioderma serricorne and Ephestia elutella was investigated as a means of disinfesting stored tobacco. Eggs, unacclimated cocoons and acclimated cocoons of L. serricorne were exposed to −10 °C, −15 °C and −20 °C in insulated boxes. There was no adult emergence from eggs or unacclimated cocoons following exposure to the respective temperatures for 4 h, 2 h and 1 h. With acclimated cocoons there was no adult emergence after 2 h at −15 °C and 1 h at −20 °C, but at −10 °C, there was adult emergence after 8, 12 and 24 h exposures.In field-scale experiments, cold acclimated fourth-instar larvae of L. serricorne were inserted into cases of leaf tobacco and boxes of finished product, put into commercial freezers and exposed to minimum temperatures of −10 °C, −18 °C or −25 °C. Critical temperatures were measured at the core of the commodity. No adults emerged from the commodity when exposed to at least −18 °C for periods ranging between 3.75 h and 39.25 h or when exposed to at least −25 °C for between 2.4 h and 3.7 h. At a minimum of −10 °C, 3 live adults emerged after 24 h exposure.With E. elutella, diapausing larvae were inserted into small scale tobacco bales and exposed to −10 °C, −13 °C, −15 °C or −20 °C. No emergence of adults and no larval survival was achieved after 21 d, 3 d and 2 h exposure at −10 °C, −15 °C and −20 °C respectively. At −13 °C, there was no adult emergence after 2 and 5 d exposure, but live larvae remained after 24 weeks incubation at 25 °C.Minimum conditions of −18 °C for 24 h and −25 °C for 4 h are recommended for the control of L. serricorne and −20 °C for 24 h for the control of E. elutella in stored tobacco (to fit with operational logistics).     

Freezer Burn of Animal Tissue. 7. Temperature Influence on Development of Freezer Burn in Liver and Muscle Tissue

SUMMARY: Various treatments found previously to affect the development of freezer burn at −10°C (Kaess et al. 1962a, 1967a,b) were applied to slices of beef liver and muscle stored at −20°C. While the general pattern of the development of freezer burn was similar to that obtained at −10°C, evaporative weight losses needed to produce a definite intensity of burn were significantly lower at −20°C. Although less freezer burn developed in low fat livers than in high fat livers at −10°C, fat content had no influence at −20°C. The layer of condensed cells at the evaporating surfaces was thinner at −20°C than at −10°C. Immersion of the tissues in solutions of glycerol or sodium chloride before freezing was effective in controlling freezer burn except with muscle slices cut across the fibers. In similar experiments carried out at −4°C desiccation of the tissue always resulted in the formation of the characteristic condensed layer at the surface but no ireezer burn developed.     

Effect of Brining, Modified Atmosphere Packaging, and Superchilling on the Shelf Life of Cod (Gadus morhua) Loins

ABSTRACT:  The aim of these experiments was to evaluate the effect of brining, modified atmosphere packaging (MAP), and superchilling on the quality changes of cod loins as measured by microbial, sensory, and chemical analysis. Unbrined and brined (2.5 ± 1.0% NaCl) cod loins were kept in styrofoam boxes (air) and under modified atmosphere (MA, CO₂/O₂/N₂: 50/5/45) at 0, −2, and −3.6 °C. Samples were examined over a 4-wk period. Total viable psychrotrophic counts and counts of H₂S-producing bacteria reached higher numbers in the air-packed brined fish at −2 and −3.6 °C than in comparable unbrined groups, being significantly different ( P  < 0.05) at the lower temperature. However, lower counts of these bacteria were obtained in the brined MAP fish than in comparable unbrined fish. Counts of  Photobacterium phosphoreum  increased most rapidly in air- and MA-packed loins kept at 0 °C. Lower counts were found at superchilled temperatures. According to sensory analysis the shelf life of unbrined air-packed loins was about 11 d at 0 °C and 14 to 15 d at −2 °C. The shelf life of MA-packed unbrined loins was about 14 to 15 d at 0 °C but 21 d at −2 °C. Thus, synergism of combined superchilling (−2 °C) and MA led to a considerable shelf life increase for unbrined loins despite the fact that processing and packaging took place 4 to 5 d post-catch. The shelf life of air-packed brined loins at −2 °C was 12 to 15 d but only 13 d under MA. The same synergistic effect did therefore not apply to brined loins as with unbrined ones.     

Super Chilling Enhances Preservation of the Freshness of Salted Egg Yolk During Long-Term Storage

ABSTRACT:  Pasteurized egg yolk with 10% (w/w) salt was stored at 5, –5, –15, –20, and –30 °C for 1 to 6 mo, respectively. Changes in generation of volatiles of the stored samples (5 and −5 °C for 6 mo) were analyzed by SPME-GC-MS. Emulsifying properties of egg yolk stored at −5, −15, −20, and −30 °C for 1 mo, respectively, were also evaluated by measurement of emulsion particle diameters in model emulsions prepared with the yolk samples. In addition, structural changes in low-density lipoprotein (LDL) in the egg yolks dependent on storage conditions for 6 mo were evaluated by ³¹P–NMR. Volatile compounds such as hexanal, 2-methylbutanal, and 3-methylbutanal increased in egg yolk during storage at 5 °C; however, volatile compounds hardly increased in any samples stored at −5 °C (super chilling). The mean emulsion particle diameter in super chilled egg yolk was significantly smaller than that in egg yolk stored at the other lower temperatures. In addition, the results of ³¹P–NMR evaluation suggested that prevention of structural changes of LDL resulted in maintenance of emulsifying properties of egg yolk. Thus, these results indicate that super chilling is an effective means of preserving salted egg yolk during long-term storage.     

Influence of immersion freezing in NaCl solutions and of frozen storage on the viscoelastic behavior of mozzarella cheese

ABSTRACT:  The freezing of Mozzarella cheese by immersion in NaCl solutions may be an innovative procedure for the dairy industry because it combines conveniently salting and freezing processes. In this work, the influence of this type of freezing method and of the frozen storage of samples on the viscoelastic behavior of Mozzarella cheese was studied. Slabs (2 × 10 × 10 cm³) were immersed in 23% w/w NaCl solutions (control samples: 4 °C, 90 min; frozen samples: −15 °C, 180 min). Half of the frozen samples were immediately thawed at 4 °C . The other half was stored at −20 °C for 2 mo and then was thawed at 4 °C (frozen-stored samples). Samples were stored at 4 °C and assayed at 1, 7, 14, 20, 27, 34, and 41 d. Rheological tests were carried out in oscillatory mode (parallel-plate geometry, diameter: 20 mm, gap: 1 mm, frequency: 1 Hz). Strain sweeps were run (0.001 ≤γ₀≤ 0.1) at 20, 40, and 60 °C, and temperature sweeps were run from 20 to 65 °C (1.33 °C/min, γ₀= 0.005). Similar crossover temperatures were observed after 20 d of ripening. The influence of temperature on complex viscosity was studied by an Arrhenius-type equation. Activation energy values of 15.9 ± 0.4, 14.1 ± 0.5, and 13.8 ± 0.6 kcal/mol were obtained at 41 d for control, frozen, and frozen-stored samples, respectively. Although the immersion freezing of Mozzarella cheese affects some of the studied parameters, the differences observed between frozen and frozen-stored samples with control samples were small. Therefore, it was considered that the immersion freezing might be useful for the manufacture and commercialization of Mozzarella cheese.     

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.     

Comparison of Viability and Heat Resistance of Clostridium sporogenes Stored at Different Temperatures

ABSTRACT:  The objective of this study was to determine the influence of storage temperature on the viability and heat resistance of Clostridium sporogenes spores. Spore suspension containing both spores and vegetative cells was divided into 3 groups to be stored at different temperatures of −20 (freezing), 4 (refrigerating), and 25 °C (ambient temperature). Samples stored for different times within the 2 mo were tested for viability by comparison of colony counts on plates and for heat resistance by determining D values at 121 °C. No significant differences were found in the viability of vegetative cells during the storage period, regardless of storage temperatures tested, while the viability of the spores stored for more than 4 wk was significantly higher at 4 °C than at −20 °C. The heat resistance of spores stored at 4 °C for more than 4 wk was remarkably higher than that at 25 °C, but similar to that at −20 °C throughout the storage period. Consequently, it turned out that a refrigerating temperature of 4 °C is satisfactory for storage of C. sporogenes spores in maintaining viability and heat resistance. This study suggests that storage temperature influences the viability and heat resistance of C. sporogenes spores.     

THERMAL CONDUCTIVITY OF CHICKEN MEAT AT TEMPERATURES BETWEEN −75 AND 20°C

Effects of temperature and time postmortem on the thermal conductivity of white and dark chicken meat were studied using a line heat source thermal conductivity probe to measure thermal conductivity. The effect of time postmortem was determined at body temperature and 20° C by leaving probes in whole birds for periods of 1–2 days; time postmortem had no significant effect. The effect of temperature was studied at temperatures of 20, 10, 0, −10, −20, −40 and −75°C using cylindrically shaped samples 3/4 in. in diam × 11/2 in. long. 48 samples were used from 24 7-lb cockerels. Three thermal conductivity measurements were made on each sample at each temperature level. The effect of temperature was similar to that reported in the literature for other meats. The following equations may be used to express the results obtained for white meat: k(Watt/m-°C) = 0.476 + 0.00060T(°C) (0–20°C) and k(Watt/m-°C) = 1.07 − 0149T − 1.04 × 10⁻⁴T²(−75 to −10°C). Similar expressions were obtained for dark meat.     

Influence of Pretreatment Conditions on the Texture and Cell Wall Components of Carrots During Thermal Processing

ABSTRACT: Diced carrots ( Daucus carota var. Nerac) were subjected to different pretreatment conditions. The pretreated carrots were subsequently thermally processed in an oil bath (100°C) and in a static retort (equivalent processes [F_oΔ 6 min] at 115°C, 120°C, and 125°C). Changes in texture were analyzed as well as changes in the degree of methylation (DM) of pectin. From all the pretreatment conditions tested, high-pressure pretreated carrots (400 MPa, 60°C for 15 min) exhibited the highest resistance to texture loss. The textural properties were significantly improved when calcium infusion was combined with low-temperature blanching condition (60°C for 40 min). A significant reduction in the DM of carrot pectin was observed for all pretreatment conditions that resulted in a reduced texture loss after thermal processing. A strong negative correlation (r ≥−0.90) exists between the changes in the degree of methylation of carrot pectin and the observed changes in texture.     

Influence of osmodehydrofreezing with different sugars on the quality of frozen rambutan

The objective of this research was to study the effect of osmotic pretreatment with different sugars on the quality of frozen rambutan. Rambutan pieces were osmotically dehydrated in 50% sucrose, trehalose and maltitol solutions. The amount of water loss and solid gain during osmotic dehydration were determined. The increase of water loss and solid gain were not significantly different among the syrups ( P  > 0.05). For osmodehydrofreezing, the fruit pieces were immersed for 1 h before freezing at −40 °C with an untreated sample used for comparison. The physical and chemical properties of samples stored at −18 °C for 3, 60 and 120 days were studied. Pretreatment with sucrose received the highest scores in terms of taste, texture and acceptability. The glass transition temperature values of treated samples, especially those treated with trehalose, increased significantly compared to the untreated sample, but they were all much lower than the storage temperature of −18 °C. All of the experimental samples were in a rubbery state, and therefore the glass transition concept could not be used to predict quality.     

Growth of the psychrotrophic pathogens Aeromonas hydrophila, Listeria monocytogenes and Yersinia enterocolitica on smoked blue cod (Parapercis colias) packed under vacuum or carbon dioxide

Commercially prepared smoked blue cod ( Parapercis colias ) was divided into 25-g subsamples which either served as uninoculated controls or were inoculated with a two-strain cocktail of one of the psychrotrophic pathogens Aeromonas hydrophila, Listeria monocytogenes or Yersinia enterocolitica. The inoculated and control subsamples were then either vacuum or carbon dioxide packed prior to storage at 3°C or −1.5°C. After various periods of storage, triplicate samples from both packaging treatments for the three pathogens and the corresponding uninoculated controls were removed and subjected to microbiological analysis. None of the three pathogens was found as a natural contaminant of the commercial product. In vacuum-packs all three psychrotrophic pathogens were able to grow during storage at 3°C. Reduction of the storage temperature to − 1.5°C retarded but did not prevent pathogen proliferation. Under carbon dioxide, only A. hydrophila was able to grow at 3°C and then only after a 21-day lag period. None of the psychrotrophic pathogens was able to grow under carbon dioxide at − 1.5°C. With the possible exception of A. hydrophila , pathogen numbers did not decline in carbon dioxide packs during 155 days storage at − 1.5°C. It is concluded that provided gross contamination with psychrotrophic pathogens prior to packaging does not occur, a 100% carbon dioxide controlled atmosphere can be used to extend the product life of smoked blue cod during storage at or below 0°C without compromising its safety in respect to growth of A. hydrophila, L monocytogenes or Y. enterocolitica.     

Effects of freezing and thawing processes on the quality of Atlantic salmon (Salmo salar) fillets

ABSTRACT:  High-pressure processing is finding a growing interest in the food industry. Among the advantages of this emerging process is the ability to favorably freeze and thaw food. This study aims at comparing the effect of different freezing and thawing processes on the quality of Atlantic salmon fillets. Atlantic salmon ( Salmo salar ) samples were frozen by Pressure-Shift Freezing (PSF, 200 MPa, −18 °C) and Air-Blast Freezing (ABF, −30 °C, 4 m/s). Samples were stored 1 mo at −20 °C and then subjected to different thawing treatments: Air-Blast Thawing (ABT, 4 °C, 4 m/s), Immersion Thawing (IMT, 20 °C), and Pressure-Assisted Thawing (PAT, 200 MPa, 20 °C). Changes in texture, color, and drip loss were investigated. The toughness of the PSF samples was higher than that of the ABF sample. The modification of color was more important during high-pressure process than during the conventional process. The PSF process reduced thawing drip compared with ABF. The presence of small ice crystals in the pressure-shift frozen sample is probably the major reason leading to the reduced drip volumes. The freezing process was generally much more influent on quality parameters than the thawing process. These results show the interaction between freezing and thawing processes on selected quality parameters.     

HISTOLOGICAL AND PHYSICAL CHANGES IN CARROTS AS AFFECTED BY BLANCHING, COOKING, FREEZING, FREEZE DRYING AND COMPRESSION

SUMMARY— The effect of processing variables on the cell structure and physical characteristics of carrots were determined. The phloem portion of fresh carrots was subjected to one of the following treatments: blanching; cooking for 10 min; freezing at 0°F, −30°F or −320°F; freeze drying, compressing after freeze drying at approximately 1500 psi. Carrots at each treatment were tested for: (1) texture by means of the Ailo-Kramer Shear Press; (2) water holding capacity by centrifuging at 500, 1000, 1500, 2000 and 2500 rpm; (3) histological changes by microscope observation of the tissue structure. Results indicate that among all treatments, freezing temperature is the most critical factor affecting the cell structure of the carrots. Freezing at 0°F or −30°F results in considerable disruption of the cellular structure, whereas it was minimal at −320°F. Carrots frozen at −320°F showed firmer texture as well as higher water holding capacity than the rest. Significant correlation coefficient was established between the shear press values and percent weight loss measured by centrifugation. This suggests that the latter may be used as an objective test for measuring textural changes in processed carrots and perhaps other foods.     

Influence of Bacterial Cellulose (nata) on the Physicochemical and Sensory Properties of Frankfurter

The physicochemical and sensory characteristics of pork frankfurters containing different levels (10% to 30%) of bacterial cellulose (nata) were evaluated. Emulsion stability of the raw meat batter decreased with the addition of nata. For nata‐added treatments, increasing levels of nata in frankfurters resulted in decreased textural hardness and shear values. Sensory results indicated that N10 and N20 had significantly higher firmness scores than N30 and control. However, juiciness score did not differ for all treatments. Incorporation of nata at lower levels (10% to 20%) did not have detrimental effects on the physicochemical, textural, sensory, and microbiological properties of regular‐fat frankfurters. Addition of a higher level (30%) of nata essentially produced comparable sensory properties to the control, but lower levels of nata in frankfurters yielded higher sensory firmness and instrumental hardness values. Based on the composite results, manufacture of regular‐fat frankfurter containing 10% to 20% high‐fiber nata resulted in product quality comparable to the control.     

Formulation and shelf-life of a bottled pawpaw juice beverage

A simple procedure was developed for production of bottled pawpaw beverage juice by peeling and macerating peeled tissue in 25% water, straining through a 0.8-mm sieve, adjustment of juice pH with citric acid and flavour adjustment with sucrose. Fresh juice was optimized for acceptability at pH 3.9 and 10% (w/w) sucrose. Heating for 6 min at 72.2°C was required to achieve commercial pasteurization. Samples of juice were prepared with no preservative, and containing sodium benzoate (125mg/100ml), sodium metabisulphite (50mg/100ml) and sodium metabisulphite/sodium benzoate combination (25mg and 60mg/100ml) for trials in which acceptability, pH, specific gravity, brix, total acidity, vitamin C and biomass concentrations were measured over 90 weeks storage at 10°C and 30.2°C. Sodium benzoate alone extended the shelf-life at 30°C up to 80 weeks but the other preservatives were not effective after 20 weeks. The control juice was already deteriorating by 10 weeks at 30°C. At 10°C all preserved samples were stable up to 80 weeks, although the control deteriorated rapidly after 20 weeks.     

Frozen storage life of the Bolivian fish, sabalo (Prochilodus platensis)

A supply of the Bolivian fish sabalo, Prochilodus platensis , was stored at -15° and −30°C. Samples were taken at intervals for analysis and taste panel assessment. No significant change was observed in 20 months at either temperature in the pH or in the percentage of protein soluble in 5% sodium chloride. The fish remained acceptable to the taste panel throughout. Thus the storage life of the species is shown to be in excess of 20 months at both −15° and −30°C.     

The thermal stability of Quorn™ pieces

Summary Quorn pieces were heat-treated at 90 °C, 100 °C and at various F values (equivalent time in minutes at a reference temperature of 121.1 °C) for 6.2–24 min and at different pHs (4.5–6.0). The heat-treated Quorn product was assessed for texture using a Voledkevich probe cell, weight change, and the sensory properties of tenderness, juiciness and overall acceptability. The processed and unprocessed Quorn pieces were examined by electron microscopy. Temperature and pH were found to influence sensory tenderness but not instrumental texture. pH also influenced water absorption. However, in general Quorn pieces were found to be stable to heat processing at 90 °C, 100 °C and 120 °C.     

Freezing tilapia by airblast and liquid nitrogen – freezing point and freezing rate

Processing data was obtained for the freezing of tilapia meat. The initial freezing point of tilapia meat was measured by differential scanning calorimetry (DSC), and also by measuring the centre temperatures of meat chunks during cooling. the freezing point was −1.03°C by DSC, and between −0.81 and −0.90°C by the cooling method, determined at the point where the standard deviation of the mean temperature was close to zero, i.e. a minimum.
Tilapia chunks, 0.95 to 1.45 cm thick, were frozen in an airblast freezer at −7, −20 and −36°C, and in a liquid nitrogen freezer at −87 and −128°C.
Freezing rate, defined as the half thickness of a meat chunk divided by the time for the centre temperature to decrease from 0 to −5°C, was 0.09 cmh⁻¹ at −7°C. At freezing temperatures of −20, −36, −87 and −128°C, the rates were respectively 4, 19, 158 and 331 times faster than that at −7°C, and correlated with freezing temperature ( r = 0.99) regardless of the freezing method.     

Colour and texture changes during sterilization of packed ripe olives

There were no temperature- or time-dependent significant changes in colour or iron content of two cultivars of bottled ripe olives during heat sterilization at temperatures between 117 and 129°C. the addition of calcium had no effect on the activation parameters of texture, although the olives were always firmer when the cation was added. the z-values for the texture of ripe olives were found to be around 20°C and the average activation energy was 138 kJ/mol.     

Morphological changes in tilapia muscle following freezing by airblast and liquid nitrogen methods

The cross-section spacing between the muscle fibre bundles of fresh tilapia chunks was ≈3.06 μm. After freezing by airblast at −20 and −36°C, and by liquid nitrogen at −87 and −128°C at freezing rates of 0.25, 1.53, 9.74 and 19.4 cm h⁻¹, respectively, the spacing increased to 3.21–7.69 μm, which was 5 to 151% greater than that in the fresh samples. The spacing further increased with storage time. Liquid nitrogen freezing resulted in smaller increases in spacing than airblast freezing. On freezing at constant temperatures of −20 to −128°C followed by storage at −20°C for 1 month, the extracellular spacings were 7.38–13.8 μm, and increased to 22.16–29.38 μm after 2 months. After storage at −20°C or −40°C for 6 months, the muscle fibre bundles showed fragmentation in both the airblast and the liquid nitrogen frozen tilapia chunks. The integrity of muscle structure was maintained better with liquid nitrogen freezing than with airblast freezing. All the differences resulting from freezing methods or freezing rates disappeared upon prolonged frozen storage at −20°C or −40°C. The correlations between the freezing temperature and extracellular spacing, and the activation energy (E_a) was calculated. The time required for freezing-temperature-induced differences in crystal growth, or in the extracellular spacing of muscle fibre bundles to disappear when E_a= 0 can be considered as the high-ultrastructural quality shelf-life, which is predicted to be 2.7 months at −20°C for tilapia frozen with liquid nitrogen.