Effects of phosphate treatment on quality of red shrimp (Pleoticus muelleri) processed with cryomechanical freezing

This paper presents a study combining the use of cryomechanical freezing and phosphate. Red shrimp (Pleoticus muelleri) were treated with sodium tripolyphosphate at 5 g/100 mL and a phosphate blend at 5 g/100 mL. Treated shrimp were partially frozen in liquid nitrogen (−86 °C) and finish in blast tunnel (−30 °C) before glazing with water. Frozen shrimp were held for 15 days at −25 °C before analysis. Drip loss on thawing and after cooking process was evaluated and sensory attributes were analyzed using acceptance tests. Results indicated that dipping shrimp in phosphates solutions can be used to prevent large cooking-related yield losses. Sensory analysis showed that shrimp treated with phosphate retain sensory attributes, contributing to major preference and acceptance of panellists. Cryomechanical freezing combined with phosphate treatment offers a simple and economical solution to increase freezing capacity, improve water retention and, consequently, improve product quality.     

Experimental study on the freezing characteristics of four kinds of vegetables

Mushroom, green cauliflower, navy bean and pea pod are four kinds of favored vegetables. Their freezing characteristics are studied in this paper. For fresh samples, the moisture contents of mushroom, navy bean, pea pod and green cauliflower were 88.7±4.9, 92.9±0.4, 87.7±1.0 and 89.7±0.9 g/100 g, respectively. After pre-treating, cooling curve method and differential scanning calorimetry (DSC) were employed to measure the end-points of freezing and glass transition temperatures. The initial freezing points varied from −0.1 to −2.7 °C. The end-points of freezing were all below −20.0 °C. The partial glass transition temperatures varied from −50.3 to −76.1 °C. With a cryomicroscope, the sizes of ice crystals in frozen vegetable saps were found to decrease from 26 to 3 μm when the freezing rates increased from 1.0 to 10.0 °C/min.     

Freezing of potato tissue pre-treated by pulsed electric fields

The effects of pulsed electric fields (PEF) pre-treatment on the freezing, freeze-drying and rehydration behavior of potato were studied. Potato samples (26 mm diameter, 10 mm high) were treated by PEF (400 V/cm) for various durations between 10⁻⁴ and 0.3 s. The degree of tissue damage was quantified by the change in electrical conductivity. PEF treated and untreated samples were either frozen in an air-blast freezer with air at −35 °C and 2 m/s velocity or freeze-dried at 0 °C and 0.04 mbar pressure and then rehydrated in water at 25 °C. The freezing times for PEF pre-treated samples reduced as the PEF-induced tissue damage increased. Scanning electron microscope images of the air-blast frozen and then freeze-dried samples showed increased deformation of cells and larger intercellular spaces (frozen samples only) for the PEF pre-treated samples. However, PEF pre-treatment improved the rate of freeze-drying and improved the quality and rehydration of the samples.     

Effects of freezing and frozen storage conditions on the rheological properties of different formulations of non-yeasted wheat and gluten-free bread dough

Empirical and fundamental rheological measurements were made on fresh and frozen dough to study the effects of freezing and frozen storage conditions. Frozen dough was stored at two different temperatures, −18 °C and −30 °C, and for 1, 7 and 28 days. Four dough formulations were tested: a standard wheat dough, a fibre-enriched wheat dough, a standard gluten-free dough and a gluten-free dough containing amaranth flour. No yeast was used in any formulation. The wheat dough is more affected by freezing and by the first days of storage whereas the gluten-free dough is more affected by a longer storage time. A storage temperature of −30 °C alters dough rheological properties more than a storage temperature of −18 °C. The addition of dietary fibres to the wheat dough increases its resistance to freezing and frozen storage. The addition of amaranth flour to gluten-free dough also increases its resistance to freezing but decreases its resistance to storage conditions.     

Effect of high-pressure versus conventional thawing on color, drip loss and texture of Atlantic salmon frozen by different methods

Atlantic salmon (Salmo salar) samples were frozen by conventional air freezing, plate freezing and liquid nitrogen (LN) freezing, and subjected to different thawing treatments: water immersion thawing (WIT) (4°C and 20°C) and high-pressure thawing (HPT) at 100, 150 and 200 MPa with water (containing 2 g oil/100 g) as pressure medium at 20°C. Temperature and phase change behavior of fish samples were monitored during freezing and thawing. The phase change point of frozen salmon was lowered to −14°C, −19°C and −25°C for the HPT processes at 100, 150 and 200 MPa, respectively. These phase change temperatures were lower than for pure ice at the same pressures possibly due to the presence of solutes in salmon. The HPT times were 22.6±1.4, 18.1±1.4 and 17.0±1.3 min at 100, 150 and 200 MPa, respectively, as compared with 26.6±2.1 and 94.3±3.4 min for the WIT process at 20°C and 4°C, respectively. Employing pressures above 150 MPa caused noticeable color changes in salmon during the HPT process and the product texture was significantly modified during HPT at 200 MPa. Different freezing rates prior to thawing resulted in differences in drip loss in salmon samples, but they did not induce specific color and texture changes. A significant (P<0.05) reduction of drip loss by the HPT process was observed only for the LN frozen samples in which mechanical cracking occurred and much of the drip appeared after WIT process. Drip loss formed during pressure thawing seems to be a complicated process, for which further studies are needed.     

Effects of freezing temperature and duration of frozen storage on lipid and protein oxidation in chicken meat

This study examined the effects of freezing temperature and duration of frozen storage on lipid and protein oxidation in chicken leg and breast meat. The meat was frozen at three different temperatures (−7, −12 and −18 °C) and then stored at −18 °C for up to 6 months. A significant effect of frozen storage duration on lipid oxidation was detected in leg and breast meat, whereas freezing temperature had no significant effect. In leg meat, freezing at −7 °C had a significant impact on protein oxidation, measured as the increase in carbonyl groups and the decrease in total sulphydryl groups, after 3 months of frozen storage. Lipid and protein oxidation appeared to occur simultaneously in chicken meat during frozen storage and was more intense in leg meat than in breast meat.     

Combined effects of freezing rate, storage temperature and time on bread dough and baking properties

This study compares the effects of freezing temperature and rate as well as storage temperature and time on the quality of frozen dough. Yeasted bread dough was frozen using four freezing rates (19-69 °C/h), then stored at −10, −20, −30, or −35 °C for up to 180 days. Dough strength diminished with longer storage time and higher storage temperatures. Cryo-SEM showed that dough stored at −30 and −35 °C had the least damaged gluten network. NMR studies showed that more rapidly frozen dough, and that stored at lower temperatures had lower transverse relaxation (T₂) times (9-10 ms). However, dough stored at −20 °C displayed the highest yeast activity among samples. Bread loaf volume decreased with storage time, and bread made from dough stored at −20 °C showed the highest loaf volume. Breads produced from −30 and −35 °C stored dough displayed less change in the texture profile during storage as well as less change in T₂ values. Response surface analysis showed that optimal properties occurred at freezing rates of around 19-41 °C/h and storage temperatures of −15 to −20 °C.     

Effects of freezing rates on starch retrogradation and textural properties of cooked rice during storage

The effects of freezing rates and storage temperatures on starch retrogradation and textural properties of cooked rice were evaluated. Cooked rice was frozen with different freezing rates and then stored at 4 °C for 14 days or −18 °C for up to 7 months. Starch retrogradation enthalpy (ΔH_r) of cooked rice was determined by a differential scanning calorimetry, and textural properties were determined by a texture analyser. The results showed that the ΔH_r and hardness values had a negative correlation with freezing rate, however, a positive correlation was found between adhesiveness and freezing rate. On the other hand, the advantages (lower hardness and higher adhesiveness, less starch retrogradaton) of cooked rice gained by rapid freezing, were lost quickly in the first 3 days of storage at 4 °C. However, rapid freezing combined with −18 °C frozen storage can effectively retard starch retrogradation and maintain the textural properties of cooked rice for at least 7 months. Therefore, high quality cooked rice can be produced by combined rapid freezing with frozen storage.     

The initial freezing point temperature of beef rises with the rise in pH: A short communication

This study tested the hypothesis that the initial freezing point temperature of meat is affected by pH. Sixty four bovine M. longissimus thoracis et lumborum were classified into two ultimate pH groups: low (< 5.8) and high pH (> 6.2) and their cooling and freezing point temperatures were determined. The initial freezing temperatures for beef ranged from − 0.9 to − 1.5 °C (? = 0.6 °C) with the higher and lower temperatures associated with high and low ultimate pH respectively. There was a significant correlation (r = + 0.73, P < 0.01) between beef pH and freezing point temperature in the present study. The outcome of this study has implications for the meat industry where evidence of freezing (ice formation) in a shipment as a result of high pH meat could result in a container load of valuable chilled product being downgraded to a lower value frozen product.     

Dehydrofreezing of pineapple

Dehydrofreezing technique involves one step of partial dehydration before freezing, in order to diminish the tissue damage by removing part of water from vegetable tissue prior to freezing. The objective of the present study was to evaluate the effect of osmotic dehydration and hot air-drying, applied previous to the freezing process, on the end quality of pineapple slices. Quality loss was quantified through drip loss, ascorbic acid content and mechanical properties changes of tissue. Freezing was carried out in a conventional air-blast tunnel at −31.5 ± 2 °C. Mechanical properties of fresh and dehydrated fruit, with and without the later process of freezing, were evaluated through compression tests. Ascorbic acid content was quantified by liquid chromatography. Osmotic dehydration and hot air-drying have the beneficial effect of reducing the time necessary for pineapple samples freezing. The freezing–thawing process affects the values of pineapple samples mechanical properties. Ascorbic acid losses were somewhat greater during the osmotic dehydration than with air dehydration.     

Influence of freezing rate variation on the microstructure and physicochemical properties of food emulsions

The freezing rate used in industrial applications may vary for a number of reasons, such as changes in food mass, food composition, and freezing equipment operation. In this study, we evaluated the influence of freezing rates on the microstructure, stability and physicochemical properties of model emulsion-based sauces. Slow freezing (−0.015 °C/min) resulted in a larger mean particle size than fast freezing (−0.11 °C/min), which was attributed to increased fat droplet flocculation and coalescence. The influence of various additives (salt, sugar, gums) on the properties of the sauces was also investigated. The addition of 200 mmol/L NaCl promoted droplet flocculation and phase separation whereas 150 mmol/L sucrose inhibited droplet flocculation and phase separation, and inhibited ice crystal growth. The addition of 0.2% xanthan gum promoted flocculation, but inhibited phase separation and ice crystal growth. Our results are interpreted in terms of the influence of the additives on the phase behavior of water, and the colloidal interactions between the fat droplets. This study provides valuable information about the major factors, i.e., salt and sugar, and influence on the stability of emulsion-based products to freeze–thaw abuses, which has important implications for the development of high quality frozen meals.     

Impact of frozen storage on polyacetylene content, texture and colour in carrots disks

This study investigated the effect of freezing method (slow or blast freezing) with or without blanching during storage at −20 °C on the levels of three polyacetylenes, falcarinol (FaOH), falcarindiol (FaDOH), falcarindiol-3-acetate (FaDOAc) in carrot disks. The quality of the carrot disks was also assessed using instrumental texture and colour measurements. Blast frozen carrot disks retained higher amounts of polyacetylenes compared to their slow frozen counterparts. Whilst the levels of retention of total polyacetylenes was higher in unblanched than blanched disks prior to freezing there was a sharp decrease in the levels of polyacetylenes in unblanched frozen carrots during the storage period for 60 days at −20 °C. FaDOH was observed to be the most susceptible to degradation during frozen storage of unblanched carrot disks, followed by FaOH and FaDOAc. The changes in the level of polyacetylenes during storage were adequately described by using Weibull model. The texture and colour were also found to decrease during frozen storage compared to fresh carrots.     

Detection of frozen-thawed salmon (Salmo salar) by a rapid low-cost method

The aim of this study was to evaluate a rapid low-cost system based on impedance spectroscopy as an alternative method to differentiate between fresh and frozen-thawed salmon. Samples of fresh salmon and others submitted to freezing at −18 °C or to 2 freezing cycles, kept in frozen storage for different times, were analysed. In general, no significant differences in moisture, total volatile basic nitrogen, pH, texture parameters, K₁ value, or microbial counts between the different samples were observed. This revealed that the freezing process, storage time or number of freezing cycles did not affect the physico-chemical parameters of fish samples, except for water holding capacity, which was significantly lower in all frozen samples compared with fresh salmon. The results showed that impedance spectroscopy was unable to differentiate between different storage times under frozen conditions; however, this technique could be a useful tool to detect fish submitted to freezing process.     

Effect of freezing method and frozen storage duration on lamb sensory quality

This study assessed the effect of three freezing methods with three frozen storage durations (1, 3, and 6 months) on the sensory quality of lamb. Methods were: air blast freezer, freezing tunnel + air blast freezer, and nitrogen chamber + air blast freezer. Meat was frozen after 48 h of ageing (0-4 °C). Fresh meat (72 h ageing at 2-4 °C) was used as control. Sensory analyses (trained panel and consumer tests) were performed on loin chops (Longissimus lumborum) after 24 h of thawing. Results from the trained panel test showed that freezing (method and/or storage duration) had no significant effect. Consumers found that freezing affected sensory quality. Cluster analysis for overall acceptability divided the population into four classes with different preference patterns, and none of them showed a significant preference for fresh meat. The small differences between fresh and thawed meat shown in this study should not give consumers concerns about buying frozen meat or consuming thawed meat.     

Evaluation of green tea extract as a glazing material for shrimp frozen by cryogenic freezing

Solutions of green tea (Camellia sinensis) extract (GTE) in distilled water were evaluated as a glazing material for shrimp frozen by cryogenic freezing. Total of 2%, 3%, and/or 5% GTE solutions (2GTE, 3GTE, 5GTE) were used for glazing. Distilled water glazed (GDW) and nonglazed shrimp (NG) served as controls. The GTE was characterized by measuring color, pH, (o) Brix, total phenols, and % antiradical activity. Individual catechins were identified by HPLC. The freezing time, freezing rate, and energy removal rate for freezing shrimp by cryogenic freezing process were estimated. The frozen shrimp samples were stored in a freezer at -21 °C for 180 d. Samples were analyzed for pH, moisture content, glazing yield, thaw yield, color, cutting force, and thiobarbituric acid reactive substances (TBARS) after 1, 30, 90, and 180 d. The HPLC analysis of GTE revealed the presence of catechins and their isomers and the total polyphenol content was 148.10 ± 2.49 g/L. The freezing time (min) and energy removal rate (J/s) were 48.67 ± 2.3 and 836.67 ± 78.95, respectively. Glazed samples had higher moisture content compared to NG shrimp after 180 d storage. GTE was effective in controlling the lipid oxidation in shrimp. Glazing with GTE affected a* and b* color values, but had no significant effect on the L* values of shrimp.     

Effect of freezing conditions and storage on ice crystal and drip volume in turbot (Scophthalmus maximus): Evaluation of pressure shift freezing vs. air-blast freezing

Turbot fillets were frozen either by pressure shift freezing (PSF, 140 MPa, −14°C) or by air-blast freezing (ABF), and then stored at −20°C for 75 days. Smaller and more regular intracellular ice crystals were observed in fillets frozen by PSF compared with air-blast frozen ones. Ice crystals area in PSF samples was approximately 10 times smaller than that of ABF samples, on average. The PSF process reduced thawing drip compared with air-blast freezing. Conversely to this classical freezing process, the storage time did not adversely influence the thawing drip of PSF samples. In addition, PSF appeared to reduce cooking drip after 45 days of storage at −20°C. Differential scanning calorimetry analysis showed a significant reduction of the total enthalpy of denaturation for the pressure shift frozen samples compared to fresh and conventional frozen samples. Besides, a new melting transition appeared on the thermogram of PSF samples at approximately +40°C.     

Effect of cold storage on vitamins C and E and fatty acids in human milk

Vitamins C and E and fatty acid levels in human milk were determined when fresh, after refrigeration at 4 °C for 96 h, and after freezing at −20 °C or −80 °C for 12 months. Total vitamin C content at 4 °C (6 h), −20 °C (8 months) and −80 °C (12 months) was significantly decreased. Vitamin E levels did not change at either refrigeration temperature (under 24 h) or at freezing or ultrafreezing temperatures. Our analysis revealed that fatty acids are not affected by cold storage. In conclusion, we recommend a change in milk storage practices; specifically, it should be stored up to 3 h in a refrigerator, up to 5 months in a freezer or up to 8 months in an ultrafreezer (−80 °C). Alternatively, vitamin C supplementation may be considered. In addition, we propose vitamin C as a marker for human milk stability.     

Minimizing texture loss of frozen strawberries: effect of infusion with pectinmethylesterase and calcium combined with different freezing conditions and effect of subsequent storage/thawing conditions

Vacuum infusion (VI), freezing, frozen storage and thawing conditions were optimized in order to minimize the texture loss of frozen strawberries. Slow freezing caused severe loss in textural quality of the strawberries. This quality loss could not be prevented by the application of VI prior to slow freezing, or by the application of rapid, cryogenic or high-pressure shift freezing conditions on non-infused fruits. A remarkable texture improvement was noticed when infusion of pectinmethylesterase (PME) and calcium was combined with rapid or cryogenic freezing. The highly beneficial effect of PME/Ca-infusion followed by HPSF on the hardness retention of frozen strawberries was ascribed to the combined effect of the infused PME (53% reduction in degree of esterification (DE) of the strawberry pectin) and the high degree of supercooling during HPSF. During frozen storage, textural quality of PME/Ca-infused high-pressure frozen strawberries was maintained at temperatures below −8 °C, whereas the texture of PME/Ca-infused strawberries frozen under cryogenic freezing conditions was only preserved at temperatures below −18 °C. Thawing at room temperature seemed to be an appropriate method to thaw strawberries. Fast thawing by high-pressure induced thawing (HPIT) did not prevent textural quality loss of frozenstrawberries.     

Freezing time prediction for partially dried papaya puree with infinite cylinder geometry

Dehydrofreezing which is the drying of foods to intermediate moisture content and subsequent freezing has the advantages of lowering the transportation costs due to reduced weight and improved texture. The available empirical equations for freezing time prediction and the experimental data on thermo-physical properties are for fresh produce. Some of these empirical equations were used to predict the freezing times of papaya puree infinite cylinders with initial moisture contents ∼52% to ∼91%. The accuracies of these methods to predict the freezing times for final center temperatures of −10 °C and −18 °C were discussed. The most accurate methods for fresh and partially dries papaya puree were suggested.