Solubility and viscosity of herring (Clupea harengus) proteins as affected by freezing and frozen storage

ABSTRACT:  The aim of this work was to evaluate the effects of freezing and frozen storage at –24 °C on the quality of Icelandic herring fillets, focusing on protein solubility and viscosity at pH 2.7 and 11 used for pH-aided protein isolation. The evaluation of quality was based on chemical analyses, protein degradation measurements, and changes in protein solubility and viscosity at pH 2.7 and 11 after up to 6-mo frozen storage of the herring fillets. Lipid oxidation measured as TBARS values increased significantly during the frozen storage ( P < 0.05). Protein solubility at pH 2.7 decreased during frozen storage for 6 mo, where the solubility was about 10% lower after 6-mo frozen storage compared to the beginning ( P < 0.05). At pH 11, the solubility became approximately 15% lower after 6-mo frozen storage compared to initial solubility ( P < 0.05). Viscosity, measured at pH 2.7, increased after 3 mo of frozen storage ( P < 0.05). At pH 11, the viscosity increased significantly after 1-wk frozen storage, compared to fresh herring fillets, but did not increase significantly with further storage ( P < 0.05). Changes found in solubility and viscosity indicated protein degradation due to freezing and frozen storage. SDS-PAGE analysis did not reveal any protein cross-linking or aggregation formation, either with frozen storage or due to exposure to low pH.     

RHEOLOGICAL AND SENSORY QUALITY OF READY-TO-BAKE CHAPATTI DURING FROZEN STORAGE

The effect of prolonged frozen storage at − 18C, on the textural and sensory properties of ready-to-bake frozen chapatti (R-BFC) was evaluated. The R-BFC samples were prepared from normal- (control) and microwave-treated (18% moisture content for 80 s) wheat grains. Results showed that the extensibility of dough and maximum load for resistance increased gradually in both the samples during frozen storage; however, the increase was lesser in the treated ones. Chapattis prepared from both R-BFC samples exhibited higher hardness, cohesiveness, chewiness and lower springiness values during frozen storage. Microwave-treated R-BFC samples were rated as better retained in color, texture and overall acceptability scores as compared with control, up to 6 months of storage at − 18C. Thiamin and riboflavin contents were monitored during frozen storage and a loss of 12.0–14.5% in thiamin and 4–6% in riboflavin after 6 months of frozen storage was recorded.

PRACTICAL APPLICATIONS

During frozen storage, various physical, rheological and sensory changes occur in the food products, which determine the consumer's acceptability. The results of this study will help to establish quality of the frozen chapattis with respect to texture, color and aroma which will meet the consumer's acceptance. The protocol for the storage of frozen chapattis will help the industry to deliver the product of optimum quality.     

CONTRACTIBILITY OF MUSCLE FIBRES AS A POSSIBLE AID TO JUDGING TEXTURAL CHANGES IN FROZEN MEATS AND FISH

Abstract Following addition of ATP, the contractibility of muscle fibres in suspension (obtained by muscle homogenization) changes during frozen storage of the muscle. These changes were detected by turbidity measurements. In beef, there were no significant changes up to 6 months storage at— 8°C or lower. Considerable loss in contractibility occurred in chicken white muscle. Losses were rapid in cod and carp muscle, contractibility being completely lost in one month at— 3°C. The method is proposed as one criterion for judging textural changes in lean fish during frozen storage.     

EFFECT OF SEASONAL VARIATIONS ON PROTEIN FUNCTIONAL PROPERTIES OF FISH DURING FROZEN STORAGE

Influence of seasonal variation (February, July and October), time elapsed before freezing, and type of processing of the muscle on several functional properties (protein solubility, emulsifying capacity, and viscosity) in two species of fish with differing seasonal behavior (hake and sardine) were studied. Correlations between the changes in these functional properties during frozen storage were established. Although proximate analyses of the hake muscle were similar throughout the year, significant differences were observed in viscosity and protein solubility during storage between lots of fish caught in different seasons. Changes in the functional properties were less evident in sardine, which undergoes wide seasonal variations. The larger differences in the functional proprities of hake muscle, depending on season, were related to differences in the dimethylamine content after the fifth month of frozen storage. High correlations were established between functional properties in fish caught in the same or different seasons. Any of the three functional properties studied can be used as a suitable index of the quality of frozen fish, irrespective of the different conditions studied.     

Probiotic culture survival and implications in fermented frozen yogurt characteristics

Low-fat ice cream mix was fermented with probiotic-supplemented and traditional starter culture systems and evaluated for culture survival, composition, and sensory characteristics of frozen product. Fermentations were stopped when the titratable acidity reached 0.15% greater than the initial titratable acidity (end point 1) or when the pH reached 5.6 (end point 2). Mix was frozen and stored for 11 wk at -20 degrees C. The traditional yogurt culture system contained the strains Streptococcus salivarius ssp. thermophilus and Lactobacillus delbrueckii ssp. bulgaricus. The probiotic-supplemented system contained the traditional cultures as well as Bifidobacterium longum and Lactobacillus acidophilus. We compared recovery of Bifodobacterium by three methods, a repair-detection system with roll-tubes and plates on modified bifid glucose medium and plates with maltose + galactose reinforced clostridial medium. Culture bacteria in both systems did not decrease in the yogurt during frozen storage. The roll-tube method with modified bifid glucose agar and repair detection system provided at least one-half log10 cfu/ml higher recovery of B. longum compared with recoveries using modified bifid glucose agar or maltose + galactose reinforced clostridial agar on petri plates. No change in concentrations of lactose or protein for products fermented with either culture system occurred during storage. Acid flavor was more intense when product was fermented to pH 5.6, but yogurt flavor was not intensified. The presence of probiotic bacteria in the supplemented system seemed to cause no differences in protein and lactose concentration and sensory characteristics.     

Untersuchung über Änderungen von Fleischproteinen während der Gefrierlagerung

Investigation of changes in meat proteins during frozen storage. The effect of freezing and frozen storage on proteins was investigated in case of pork L. dorsi muscle. After fresh pork was sliced (1 cm thickness), wrapped and frozen (2 different velocities) samples were taken (control, 48 h-, 2, 4 and 6 month-frozen storage) and changes in proteins investigated by DSC and SDS-PAGE. DSC-thermograms show 4 peaks corresponding to myosin (peak 1) and actin (peak 4). Peak 2 reflects the sarcoplasmic proteins and connective tissue contribution. Peak 3 is not defined. When measuring the enthalpies of the DSC-thermograms, it can be observed that the enthalpy ascribed to myosin decreases during frozen storage, while the enthalpy corresponding to actin is not affected. At the beginning of our experiments SDS-PAGE was supposed to be a proper method for the investigation of protein denaturation. Our results show no significant changes in the electropherograms during the whole period of frozen storage.     

EFFECT OF SPLEEN IN RESTRUCTURED BEEF

Boneless beef chucks were converted to restructured beef steaks and formulated with 1% NaCl and 0.25% sodium tripolyphosphate (STP). Experimental treatments included (1) control-frozen, (2) control-5 days storage at 0°C, (3) 1% spleen pulp-frozen and (4) 1% spleen pulp-5 days storage at 0°C. Treatments 2 and 4 were evaluated only after storage for 5 days; whereas, treatments 1 and 3 were studied at 5 and 70 days. Spleen pulp enhanced (P<0.05) color development during frozen storage for a short period but offered no (P>0.05) contribution to color preservation during prolonged storage. Visual color and overall appearance were affected more by storage time and conditions than by the addition of spleen pulp. Spleen pulp had no effect (P>0.05) on product cohesiveness, texture, tenderness and flavor of frozen restructured beef steaks but improved the tenderness of unfrozen samples.     

QUALITY CHARACTERISTICS OF TURKEY BOLOGNA FORMULATED WITH CARRAGEENAN, STARCH, MILK AND SOY PROTEIN

A low-fat (12%) high-added water (27%) bologna was formulated with mechanically deboned turkey meat (MDTM) and either carrageenan (0.5%), milk protein (2%), isolated soy protein (2%), or starch (2%). Cooking loss, purge loss during storage, cooked product bind, sensory characteristics, and batter viscosity were evaluated. Starch added late in the chopping process was the most effective in reducing cooking loss as well as decreasing (P < 0.05) purge loss during storage (both refrigerated and frozen storage). Cooked product hardness was increased (P < 0.05) by all test ingredients, except starch and kappa carrageenan added late in the chopping process. Kappa carrageenan incorporated before chopping significantly (P < 0.05) increased cooked product bind. Overall acceptability (sensory analysis) scores were higher (P < 0.05) when milk protein, isolated soy protein and starch were added during chopping, compared to their addition prior to chopping. However, this order of addition effect was not observed for either of the carrageenan treatments.     

The effect of frozen storage on the functional properties of the muscle of volador (Illex coindetii)

Functional properties of muscle proteins of volador (Illex coindetii) were evaluated during frozen storage and classified according to gender and anatomical part of the animal. Solubility of protein in 5% NaCl, in all lots, showed a significant increase in the initial months and then a decrease. This solubility was generally greater in the mantles than in the arms. The viscosity was initially very high and fell rapidly, and there were no significant differences between the lots. This initial viscosity was greater in the arm lots than in the mantle ones. Likewise, extracts of the muscle of the arms also had the greatest initial emulsifying capacity values (P⩽0.05). Soluble collagen, in an acid medium-exhibited a similar trend in all lots, throughout frozen storage. At the early stages of storage, soluble collagen remained stable or increased slightly, and then tended to become insoluble. The lowest solubilities were for the muscles of the arms. Myofibrillar protein and collagen solubilities, as well as emulsifying capacities were effective for detecting molecular changes in the proteins during frozen storage and results showed that, the volador mantles were more suited to frozen storage than the arms.     

The effect of frozen storage of mackerel (Scomber scombrus) on its quality when hot-smoked

Whole mackerel (Scomber scombrus) were frozen using a horizontal plate freezer, wrapped in plastic bags and frozen stored at - 20°C. At suitable intervals (11, 22 and 33 weeks) the fish were removed from the cold store and subsequently hot smoked (in gutted from) using an AFOS-Torry Mini Kiln. All smoked mackerel samples, despite their different previous histories, were assessed by the panellists as moderately acceptable products in- terms of their texture and flavour, even after 33 weeks frozen storage prior to smoking. Protein denaturation, as related to salt-soluble protein, was influenced by the frozen storage history (24% drop after 33 weeks frozen storage) and seemed to be affected by the free amino acids formed during frozen storage. After smoking the denaturation was extensive (above 80%) in all mackerel samples. Lipid oxidation was quite extensive (PV 108 meq kg^?1) in the 22 and 33 weeks frozen stored mackerel samples. However, no rancid flavour in the latter smoked mackerel samples was detected by taste panellists. A 58% increase in free amino acids during frozen storage was observed. Extensive losses of 74% in available lysine were observed in the 22 and 33 weeks frozen stored mackerel samples after smoking which could be due to aminocarbonyl reactions with the products of lipid oxidation. A 40% loss of thiamine was observed in the 33 weeks frozen stored samples after smoking. The histamine contents did not exceed 94 mg kg^?1 and would not be expected to cause symptoms of scombrotoxin poisoning.     

竹荚鱼冻藏过程中肌肉品质与蛋白质理化性质的变化及其相关性分析

为探究竹荚鱼冻藏期间的新鲜度品质变化规律,本文以色泽、电导率、冰晶大小及形态、质构、K值、TBA值、拉曼光谱、总蛋白二级结构、肌原纤维蛋白巯基含量和Ca2+-ATPase活性等为指标,研究了真空包装（VP）和空气包装（AP）的竹荚鱼在?18 ℃冻藏90 d内的肌肉品质和肌肉蛋白质理化性质的变化。结果显示,随着冻藏时间的延长,VP、AP两组鱼肉样品的K值、L*值、白度值、TBA值均逐渐升高,其中K值冻藏90 d后分别增加了65.83%和66.44%;同时鱼肉中冰晶孔隙逐渐增大,a*值、b*值、硬度、咀嚼度、回复性则逐渐下降,内聚性和电导率呈现先升高后降低趋势。蛋白质理化测定结果显示,冻藏过程中,α-螺旋百分含量由63.28%分别降低到43.70%、41.91%,β-折叠、β-转角、无规则卷曲百分含量逐渐升高,肌原纤维蛋白的总巯基、活性巯基含量逐渐降低,Ca2+-ATPase活性分别下降了63.58%和72.52%。空气、真空两种包装方式对竹荚鱼冻藏期间的肌肉品质影响不大,对蛋白质生化特性有一定影响且真空包装略优于空气包装。由相关性分析可知,两组鱼肉样品的K值、色泽、TBA值、巯基含量、Ca2+-ATPase活性、总蛋白二级结构百分含量与冻藏时间之间、两两之间均显著相关（P<0.05）或极显著相关（P<0.01）,可作为评价竹荚鱼冻藏过程中品质变化的有效指标。研究结果可为深入探究竹荚鱼的品质变化机理和生产实践中的货架期预测提供理论参考。     

CHANGES IN PROXIMATE COMPOSITION OF THORNBACK RAY (RAJA CLAVATA, L. 1758) SURIMI DURING WASHING AND FROZEN STORAGE

The effects of frozen storage of surimi produced from thornback ray and the washing of mince on the chemical composition were investigated. The crude ash content which was initially found as 1.38% in raw thornback ray decreased approximately 12 and 80% after the first and second washing, respectively. After the third washing, crude ash content increased to 207% of the amount in the second washing because of addition of salt to the last washing water. The crude protein content of mince also decreased approximately to 28 and 20% after the first and second washing, respectively. After the third washing, the decrease in the lipid levels was approximately 30%. At the end of 6 months of frozen storage at − 23.8  ±  2C, dry matter, crude ash and crude protein contents increased in a greater ratio in surimi containing 4% sorbitol, 4% sucrose and 0.3% Na-tripolyphosphate than surimi prepared with 8% sorbitol and 0.3% Na-tripolyphosphate.

PRACTICAL APPLICATIONS

In the present study, the effects of frozen storage of surimi produced from thornback ray and the washing of mince on the chemical composition were investigated. Washing procedure significantly decreased crude ash, crude protein and crude fat content of mince. There were significant differences in moisture, crude ash, and crude protein contents during the 6 months storage period of frozen surimi obtained by using different cryoprotectant mixtures. The folding test scores were highest in fresh surimi and during the first two months of storage. Thornback ray can be used for the production of surimi.     

Effect of caffeic acid on haemoglobin‐mediated lipid and protein oxidation in washed cod mince during ice and frozen storage

BACKGROUND: Little is known about the relation between haemoglobin (Hb)‐mediated lipid and protein oxidation in muscle foods and how these two reactions can be inhibited by naturally occurring antioxidants. This study was aimed at evaluating (1) lipid oxidation and protein oxidation induced by 20 µmol L^?1 Hb during chilled and frozen storage of washed cod mince and (2) the efficiency of 10–1000 ppm (0.063–6.3 mmol L^?1) caffeic acid in preventing these reactions. RESULTS: Addition of 20 µmol L^?1 Hb increased peroxide value (PV), rancid odour, protein carbonylation, protein insolubilisation, redness loss and α‐tocopherol loss in ice‐stored washed cod mince. Since both lipid and protein oxidation developed at the same time, it was not possible to conclude which reaction initiated the other. All studied reactions were efficiently inhibited by ≥ 50 ppm caffeic acid, which could be a result of α‐tocopherol regeneration, general radical scavenging, reduced formation of oxidised Hb forms and/or conformational changes in Hb structure. During frozen storage the only clear effect of Hb was increased PV, and here caffeic acid was less efficient as an antioxidant. CONCLUSION: Hb‐induced lipid and protein oxidation occurred quickly in ice‐stored washed cod mince, and the two reactions could not be separated in time. During frozen storage, Hb caused only limited lipid oxidation. Caffeic acid (≥50 ppm) was an efficient antioxidant during ice storage. Copyright © 2010 Society of Chemical Industry     

Effect of pre-freezing icing duration on quality changes in frozen Nile perch (Lates niloticus)

Deterioration of fish during frozen storage entails change in texture, loss of protein functionality, lipid hydrolysis as well as biochemical changes. These changes were monitored in Nile perch frozen after 3, 6, 9, 12, 24, 48 and 72 h on ice, with the aim of establishing the effect of pre-freezing icing on deterioration of fish during frozen storage. During the icing duration, the expressible moisture (EM) was found to reduce while protein solubility (PS), thiobarbituric acid (TBA), trimethylamine (TMA), hypoxanthine (Hx), and free fatty acids (FFA) concentration increased. During frozen storage, PS decreased while EM was found to increase. Hx, TBA and FFA increased, while texture was found to deteriorate. TMA remained constant during frozen storage. The extent of texture deterioration was correlated negatively to PS and positively to EM. It was concluded that holding fish on ice for about 9 h deterred the negative changes that occur during frozen storage.     

GEL-FORMING ABILITY OF COMMON CARP FISH (CYPRINUS CARPIO) MEAT: EFFECT OF FREEZING AND FROZEN STORAGE

Effect of freezing and frozen storage on gel‐forming ability of muscle from fresh water fish, common carp (Cyprinus carpio), was investigated. Fresh carp meat had good gel‐forming ability as revealed by large strain test (gel strength of 1027 g·cm) and dynamic viscoelastic behavior. Freezing and frozen storage at ?18C for 180 days significantly (P < 0.01) reduced the gel‐forming ability of common carp meat. Reduction in protein solubility and calcium‐activated adenosinetriphosphatase enzyme activity of common carp meat during frozen storage was also significant (P < 0.05). Structural change of proteins during frozen storage was evident from reduced viscosity and gel filtration profile. Higher drip loss and reduction in gel‐forming ability of carp meat is attributed to denaturation of proteins during frozen storage.     

Use of Cryoprotectants to Stabilize Functional Properties of Prerigor Salted Beef During Frozen Storage

Changes in functional properties (gelforming ability, water-holding capacity, and protein solubility) of salted prerigor beef and postrigor beef were measured over 6 months frozen storage at ?28°C, as affected by addition of 5.6% cryoprotectants [Polydextrose® or a mixture (1:1) of sucrose and sorbitol]. Addition of NaCl to comminuted muscle prior to freezing accelerated destabilization of muscle proteins with respect to functional properties. This effect was reduced by cryoprotectants; most effectively by sucrose/sorbitol and only slightly less effectively by polydextrose. As evidenced by the parameters investigated, quality of prerigor salted muscle treated with cryoprotectants and stored 6 months was approximately equal to that of untreated postrigor meat prior to freezing.     

Evaluation of various infused cryoprotective ingredients for their freeze-thaw stabilizing and texture improving properties in frozen red hake muscle

ABSTRACT:  Various cryoprotective ingredients were evaluated for their freeze–thaw stabilizing and texture improving properties during 6-mo frozen storage when red hake ( Urophycis chuss ) fillets were injected with sorbitol–sodium tripolyphosphate (STPP) (40% to 60% : 3%), 1.5% alginate, or 0.75% alginate with soy protein isolate (SPI)–sorbitol–STPP (5% to 10% : 40% : 3%). Injection of 10% SPI, 1.5% alginate, or 0.75% alginate–5% SPI effectively improved water binding and retarded the freeze-induced texture changes when drip and cooking loss, centrifugal expressible moisture, protein extractability, SDS-PAGE profile, and Instron and sensory texture were assessed. The sorbitol and STPP combination was not as effective as alginate and SPI. Freeze-susceptible whitefish can be injected with proper cryoprotective ingredients for improved frozen storability.     

海藻酸丙二醇酯对全麦冷冻面团冻藏稳定性和烘焙特性的影响

本文研究了海藻酸丙二醇酯（Propylene glycol alginate,PGA）对全麦冷冻面团冻藏期间稳定性的影响,并探究了冷冻面团烘焙面包品质的变化。将0.3%的PGA加入全麦面团,通过测定冷冻面团冻藏1、2、3、4和5周后发酵特性、流变特性、蛋白质二级结构、微观结构以及面包的比容、质构特性、内部纹理结构和老化程度等,研究冷冻面团冻藏期间的稳定性。结果表明,随着冻藏时间的延长,添加PGA的冷冻面团在冻藏5周后具有较好的保水性,其发酵特性及流变特性相对于对照组均有所改善。冻藏5周后,对照组与PGA组其面包比容分别下降了19.872%和14.153%;面包硬度分别升高了64.186%和36.386%;气孔表面积分率分别下降了3.497%和2.300%;老化焓值分别上升了65.142%和42.416%。添加PGA能延缓冷冻面团冻藏期间β-折叠含量的上升和β-转角相对含量的下降。电镜扫描图（SEM）显示,随着冻藏时间的延长,PGA组的冷冻面团孔洞数目相比对照组明显减少且大小均匀,面筋网络结构完整性和连续性提高。研究结果表明PGA可以有效地延缓冷冻面团在冻藏期间的品质劣变,维持冷冻面团的稳定性并提高面包的烘焙特性。     

Protein Structural Changes During Preparation and Storage of Surimi

The changes in protein structure associated with the preparation and frozen storage of surimi were investigated. Raw surimi was prepared by repeatedly washing Alaska pollock flesh with chilled water. The product was either slowly frozen or underwent rapid freezing using liquid air; in either case it was then subjected to frozen storage at ‐20 °C for 24 mo. Fourier transform infrared/attenuated total reflectance (FTIR/ATR) spectroscopy showed that during preparation of surimi, the a‐helix content increased with increased number of washing cycles. Differential scanning calorimetry (DSC) revealed a shift in the thermal transition of actin to a higher temperature during surimi preparation. Electrophoresis, FTIR/ATR spectroscopy, and DSC results revealed a loss of myofibrillar proteins from surimi after 3 washing cycles, suggesting that 3 washing cycles were adequate to prepare surimi. Sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE) showed relatively minor changes in protein subunit structure with some loss of the myosin light chains (MLC); myosin heavy chain (MHC), actin, and tropomyosin were found to be relatively stable. Native‐PAGE showed no major changes in surimi after 24 mo storage at ‐20 °C. FTIR/ ATR spectroscopy indicated a significant decrease in a‐helix relative to p‐sheet structure in surimi after 2 y of storage at ‐20 °C. The loss of α‐helical content was more significant in slowly frozen surimi compared with rapid‐frozen surimi samples. DSC results revealed a shift in the thermal transition of actin to lower temperatures during frozen storage of surimi.     

Cryoprotective effects of trehalose and sodium lactate on tilapia (Sarotherodon nilotica) surimi during frozen storage

The cryoprotective effects of trehalose and sodium lactate at level of 8% (w/w) in tilapia surimi were studied in comparison with a conventional cryoprotectant (sucrose/sorbitol, 1:1) during extended storage at −18 °C for up to 24 weeks. All present cryoprotectants retarded the protein changes as evidenced by the lowered decrease in salt extractable protein (SEP), Ca²⁺-ATPase activity, total sulfhydryl content as well as the impeded increase in disulfide bond content and surface hydrophobicity. The gel-forming ability of frozen surimi was more retained with addition of cryoprotectants. Among all cryoprotectants used, trehalose exhibited the greatest protective effect on protein denaturation as shown by the effectiveness in maintaining Ca²⁺-ATPase activity and protein solubility. Additionally, the greatest breaking force and deformation were obtained in surimi added with 8% trehalose throughout the frozen storage up to 24 weeks. Sodium lactate showed a similar cryoprotective effect to sucrose/sorbitol blend. Therefore, trehalose and sodium lactate appeared to be promising alternative cryoprotectants for surimi owing to their low sweetness and caloric value.