Deterioration of Fresh-Water Whitefish Muscle During Frozen Storage at −10°C

SUMMARY— Organoleptic and chemical deterioration of freshwater whitefish muscle frozen at −10°C for periods up to 16 weeks was assessed. As frozen storage of muscle progressed, the toughness and rancidity of baked muscle increased. The solubility of the myofibrillar protein fraction, "actomyosin," dropped from about 72 to 22% over the 16 week storage period of whitefish muscle. No change in the solubility of sarcoplasmic protein in frozen stored muscle was observed. However, with polyacrylamide disc electrophoresis, two new sarcoplasmic protein bands were detected after 16 weeks of storage. With storage of frozen muscle, water-binding capacity diminished. Although the total lipid and cholesterol contents of muscle remained constant throughout frozen storage, the phospholipid content decreased as the free fatty acid content increased. Oxidative deterioration of lipid in frozen muscle was estimated.     

Effect of Mixing and Moisture Modification on Toughening and Dimethylamine Formation in Alaska Pollock Mince during Frozen Storage at −10°C

Alaska pollock minces having reduced, normal and elevated levels of moisture were stored at - 10°C for 2 and 4 wk to determine how toughening was influenced by different amounts of ice in the frozen tissue. Minces containing reduced or elevated amounts of ice exhibited greater toughening than that observed in control minces. Also, some minces received an extra mixing step prior to freezing and this resulted in less toughening during storage, perhaps due to oxygen incorporated and partial inhibition of the enzyme system that converts trimethylamine oxide to dimethylamine and formaldehyde. However, among moisture-modified minces that received the same mixing treatment, development of toughening did not relate in any consistent manner with the development of dimethylamine.     

Chemical Deterioration of Frozen Bovine Muscle at −4° C

SUMMARY— During an 8-week storage period of bovine muscle at −4°C, the total extractable protein content dropped from 91 to 51%. This decline, accompanied by a decrease in water-binding capacity of muscle, was primarily caused by the insolubilization of both sarcoplasmic proteins and actomyosin. The increase in the free fatty acid content from about 1.6 to 9.1% over the 8-week period may be attributed to phospholipid hydrolysis. The TBA number rose progressively throughout the entire storage period while the peroxide value increased to a maximum in 2 weeks of storage and then decreased to a constant value of 7.     

Chilled (5°C) and Frozen (−18°C) Storage Stability of the Purple-Hinge Rock Scallop, Hinnites multirugosus Gale

Purple-hinge rock scallops (Hinnites multirugosus), native to northeast Pacific Coast waters and under evaluation for commercial aquaculture, were harvested wild and analyzed for storage stability. Over 2 wk of chilled storage at 5°C or 5 months of frozen storage at ?18°C, scallops showed no appreciable lipid oxidation, proteolytic change, and ammonia development. Hypoxanthine fluctuated throughout fresh storage. Bacterial numbers were unchanged at ?18°C but sharply increased during the second week at 5°C. Odor of raw scallops deteriorated somewhat at week 2 of chilled storage and month 4 of frozen storage. However, when cooked, scallops showed no significant differences for most sensory characteristics or for acceptability. Cooking losses were variable. Textural shear parameters changed with weight and frozen storage.     

冻藏对肌原纤维蛋白结构特性与功能特性的影响

冷冻贮藏是肉类食品重要的贮藏方法,但在冻藏会引起肉类食品中的主要蛋白一肌原纤维蛋结构发生变化,引起蛋白质发生变性,从而影响其功能特性,降低肉类制品的品质。论述了肌原纤维蛋白的冷冻变性机理,并对冷冻贮藏期间肌原纤维蛋白结构与功能特性的变化进行论述。     

Quality changes in frozen whole and gutted anchovies during storage at −18°C

Fresh samples of whole and gutted anchovies were blast frozen at −35°C and stored at −18°C. The quality of the samples was examined as organoleptic, microbiological and chemical changes during the storage period. Gutting had no significant effect on the quality of the final product. Sensory quality was good for up to 90 days of storage. No increase in microbial activity was detected, but some oxidative and hydrolytic deterioration of fats were observed. The final product was still edible after 180 days.     

Behaviour of the mechanically separated flesh of some common fish species of the Mexican shrimp by-catch during storage at −20°C

Deboned minces prepared from fish species predominant in the Mexican shrimp by-catch were examined with respect to their stability during storage for 10 months at –20°C. Reductions in the extractability of salt-soluble proteins occurred to varying levels in all samples, particularly in the initial storage phase. These changes were shown to influence the textural characteristics of the minces, albeit to a minimal extent. Considerable variability in the colour of minces from different species was observed and a washing procedure which effectively removes dark pigments is described. In general, the acceptability of the products was maintained throughout the storage period. It is thus concluded that deboning and the freezing of the resultant minces could offer a potential means of processing currently wasted by-catch fish into human food.     

Characterization of aroma changes in human milk during storage at −19 °C

Breastfeeding is believed to impart major beneficial effects on babies, due to various human-specific components. Compatibility of family and profession, however, often necessitates the pumping of breast milk and its storage under diverse conditions, either in a refrigerator, freezer or for brief periods at room temperature. The present study investigates the formation of a characteristic fish-like and metallic off-odour during the conventional storage of human milk that does not develop during cow milk storage, and elucidates the molecular factors for these specific aroma changes. Odorants in fresh and stored human milk containing the specific fishy-metallic off-odour were characterized by means of gas chromatography–olfactometry and identified based on their mass spectrometric data and specific chromatographic and sensory characteristics.     

Moisture Sorption Isotherms of Dried Apricot, Fig and Raisin at 20 °C and 36°C

Isotherms were found to be of type I, typical of high sugar foods. Study on temperature dependence of isotherms showed that above water activities of 0.6, moisture content was higher at higher temperature. This was explained by endothermic dissolution of sugar at high water activities. Iglesias and Chirife, Halsey, BET and GAB equations were tested to fit the data. Monolayer moisture contents for the three foods were determined from BET and GAB equations. In both models, monolayer moisture was found to decrease with increasing temperature. Isosteric heat of sorption data from the isotherms at two temperatures, revealed that strength of interactions between water vapor and adsorbent increased with moisture content.     

Cryoprotective Effects of Some Materials on Cod-Surimi Proteins during Frozen Storage

Freeze-induced protein denaturation of cod surimi was studied as affected by carbohydrates (sucrose and glucose syrup at 8% w/w), polyols, (sorbitol and glycerol at 8% w/w), protein hydrolysates (fish protein and casein hydrolysates at 4% w/w), hydrocolloids (pectin-1% w/w, sodium alginate, lambda- and iota-carrageenan-0.5% w/w) and combinations of the above, (sucrose/sorbitol 1:1 mixture at 8% w/w, or combined with protein hydrolysates at 4% w/w). Salt extract-able protein (SEP) and heat induced denaturation by differential by differential scanning calorimetry (DSC) were used to monitor protein changes in surimi stored 16 wk at -20°C. The best cryoprotection effect was achieved from sorbitol, glucose syrup (DE = 60), sucrose and sucrose/sorbitol 1:1 w/w mixture at 8% w/w in surimi. Correlations between certain DSC parameters and SEP were high.     

Development of flavour defects in pasteurized double cream during storage at 6°C and at 10°C

A total viable count in excess of 1× 10⁷ cfu/ml is required before organoleptic defects can be detected in pasteurized double cream, although defects were shown to be the results of non-bacterial sources in creams from one creamery in the survey. Proteolysis was associated mainly with the presence of Bacillus spp. and resulted in the detection of a bitter flavour in the creams.     

Microbial, Compositional, and Other Quality Characteristics of Pecan Kernels Stored at −20°C for Twenty-five Years

Sensory, microbial, and compositional characteristics of pecans hermetically sealed in cans and stored at ?20°C for 25 yr were compared to those of pecans harvested in 1986 and stored at ?20°C for 10 mo. Total aerobic and yeast/mold populations were 10²?10³ CFU/g in stored and 1986 crop nuts. Peroxides were not detected, and no difference in iodine values and free fatty acid contents were observed between 25-yr-old and 1986 crop nuts. Although subjective analyses revealed that texture changed during storage, other sensory quality characteristics (color, flavor, appearance) were not different from pecans harvested in 1986. It is concluded that low temperature (?20°C) storage will maintain quality of pecans packaged in hermetically sealed under ambient air in containers for up to 25 yr.     

Sensory Evaluation of Lamb After Growth of Yeasts at −5°C

Cryptococcus laurentii var laurentii was inoculated at various densities onto lamb loins, which were then frozen and stored at 5°C for 10 wk. During storage, yeast numbers increased by two log cycles. Loin samples that included yeast-bearing surfaces were prepared for evaluation by a trained taste panel. No foreign flavors associated with high yeast numbers could be discriminated by the panel.     

Amino acid composition of whole mackerel (Scomber scombrus) stored anaerobically at 20°C and at 2°C

Total amino acid composition of whole mackerel ( Scomber scombrus ) and of milt and roe from mackerel stored at different conditions were studied. During storage at low temperature, no obvious changes were found. When stored at high temperature (20°C), the contents of several of the amino acids decreased, and phenylethylamine, tyramine, putrescine, histamine and cadaverine were formed the formation of cadaverine was higher than the loss of lysine.     

Cryoprotective Effects of Lactitol, Palatinit and Polydextrose® on Cod Surimi Proteins during Frozen Storage

The cryoprotective effects of lactitol dihydrate, Polydextrose® and Palatinit (Isomalt) at 8% w/w in codsurimi were compared to an industrial control containing a sucrose/sorbitol 1:1 mixture and a control without additive. Surimi was stored at ?20°C for 12 wk and examined for freeze-induced protein changes every 2 wk by salt extractable protein and differential scanning calorimetry analyses: Palatinit®, lactitol and Polydextrose® stabilized surimi proteins equally well as did the sucrose/sorbitol mixture. Salt extractable protein and myosin peak enthalpy for surimi were maintained at the same level as the industrial control. Confirming earlier results, initial T_max-myosin yielded information regarding surimi protein stability over extended periods of frozen storage.     

冻结速率对凡纳滨对虾虾仁贮藏特性的影响

本文以凡纳滨对虾（Penaeusvannamei）虾仁为原料,分别采用-80℃和．20℃两种冻结条件对虾仁进行冻结处理,分析冷冻速率对凡纳滨对虾虾仁贮藏过程中理化、鲜度及色泽特性的影响,明确冻结速率对虾仁解冻后的质量变化特征的影响规律。总体来讲,冻藏过程中虾仁质量变化趋势基本一致,随着冻藏时间的延长,虾肉解冻损失率增加,鲜度降低,pH呈下降后上升的趋势,TVB-N值上升,产品的亮度指标L＊升高。冻结速率对虾仁的贮藏特性影响差异显著,冻藏6d后冻结速率对虾仁解冻损失率、鲜度指标影响出现分化,-80℃速冻处理可明显改善虾仁的解冻失水,保证虾仁鲜度。20d后,pH值、TVB-N值变L‘值变化情况也表明-80℃速冻在一定程度上可以减轻虾仁贮藏过程中的质量劣化程度。     

Influence of Postmortem Changes in Bovine Muscle on the Water-Holding Capacity of Beef. Postmortem Storage of Muscle at 20°C

Rigor mortis occurs in bovine neck muscles as soon as pH 5.9 and an ATP level of about 1 μMol/g are reached. At 20°C muscle contraction does not occur before the onset of rigor. Postmortem changes in water-holding capacity (WHC) were followed by measuring the cooking loss of unsalted and salted (2% NaCl) muscle homogenates prepared after storage of the intact muscle tissue at 20°C for different periods postmortem. At tissue pH above 5.9 addition of salt causes a strong increase of WHC of muscle homogenates. There is a small decrease of WHC of both unsalted and salted homogenates during the prerigor phase which is apparently caused by the postmortem fall of pH. Rigor mortis does not influence the WHC of unsalted muscle homogenates but causes a strong decrease of WHC of salted homogenates. The reason for this difference is discussed. No more than one-third of the total postmortem decrease of WHC and protein solubility in salted muscle homogenates was attributed to the fall of pH, so at least two-thirds were due to the development of rigor.     

Sensory Analysis of Dairy Products irradiated with Cobalt-60 at −78°C

Sensory evaluations by healthy individuals were conducted on cobalt-60 irradiated retail dairy products which were to be incorporated into the low microbial diets of immunosuppressed patients. Irradiation (40 kGy at -78°C) caused little change in product color or texture, but generally there was a decrease in overall acceptability and an increase in off-flavor and aftertaste. Modified atmosphere packaging (nitrogen, helium, or air) or antioxidant addition (ascorbyl palmitate or a combination of butylated hydroxyanisole and butylated hydroxytoluene) prior to irradiation were effective in preserving specific sensory attributes, which in some cases resulted in improved overall acceptability (helium packed peppermint ice cream; ascorbyl palmitate treated strawberry yogurt bars) when compared to untreated irradiated products.     

Effect of Oxidation on the Emulsifying Properties of Myofibrillar Proteins

The aim of this work was to investigate the effect of chemical oxidation on the emulsifying properties of myofibrillar proteins. Myofibrillar proteins were oxidized by a hydroxyl radical generating system (Fenton reaction). Structural changes of oxidized or non-oxidized myofibrillar proteins were determined using surface hydrophobicity (H₀) and Fourier transform infrared (FTIR) spectroscopy. The results suggested that H₀ increased (p?<?0.05) after treatment with oxidizing agent. Result from FTIR suggested that protein aggregation occurred and there was an increase in β-sheet structure accompanied by a decrease in turns, alpha helix, and random structures with the increase of oxidizing agent. Changes in zeta potential of the test emulsions suggested that protein oxidation could alter the electric charge of myofibrillar proteins. The analysis of the emulsions showed that protein oxidation had a negative effect on the emulsifying properties of myofibrillar proteins due to changes in electric charge, surface active properties, and protein molecular flexibility.