The oxidative stability of lard at −20°C: Evidence for a synergistic prooxidant effect of copper and curing salts

In connection with an interest in the problem of rancidity development in cold-stored cured meat products (particularly bacon), the effect of certain trace components and permitted food additives on the oxidative stability of model systems containing lard was examined. Lard, to which additions of various single additives or combination of additives had been made, was stored for periods of up to 16 weeks at ?20°C. Samples were removed during this time to assess the extent of their oxidation by chemical analysis (peroxide value determination) and sensory evaluation (odour). The additives studied included water, sodium chloride, sodium nitrate, sodium nitrite and copper (as palmitate, acetate and sulphate). It was observed that there was progressive oxidative deterioration of the lard with noticeable rancidity developing after 8 to 16 weeks' storage at ?20°C when water, sodium chloride, sodium nitrate, sodium nitrite and copper were present in combination.     

Thermal Gelation of Previously Cooked Minced Meat from Jonah Crab (Cancer borealis)

ABSTRACT:  Crab processing typically involves picking meat from whole cooked product. Remaining meat can be recovered as mince and potentially processed into value-added products. This study focused on gelation of commercially processed crab mince. Objectives of the research were to determine the effects of cryoprotectants, freezing, and various heat treatments on gel formation of washed mince from previously cooked crab. Previously frozen minced meat from thermally processed Jonah crab was washed to remove soluble components. Four different treatments were applied to the washed mince: (1) freezing with cryoprotectants, (2) freezing with no cryoprotectants, (3) no freezing with cryoprotectants, and (4) no freezing with no cryoprotectants. Unwashed mince was used as a control treatment. Sodium chloride (2.5%) was mixed into the mince prior to stuffing into sausage casings and heating at 35 °C/30 min, 90 °C/30 min, or 35 °C/30 min followed by 90 °C/30 min. Gels were tested for proximate composition, color, water-holding capacity, and gel strength. All mince samples formed gels except for the unwashed control. Gels with no cryoprotectants had 10% to 20% greater water holding capacity, lower L* values, and greater gel strength than those with cryoprotectants. Freezing of washed mince resulted in lower water-holding capacity of gels and higher a* values. A 2-stage heating treatment resulted in gels with the greatest gel strength, whereas gels cooked at 35 °C had the greatest distance to fracture. Results indicate that protein gels can be formed using previously cooked crab meat, which may be useful in the development of value-added products.     

Effect of Salt, Tripolyphosphate and Tertiary Butylhydroquinone on Myoglobin-Lipid Oxidation Indicators in Freeze-Dried Meats

The previously developed myoglobin oxidation indicators were used to detect the effect of curing agents, sodium chloride and sodium tripolyphosphate (TPP), and also the antioxidant effect of mono tertiary butylhydroquinone (TBHQ) on the oxidation of restructured freeze-dried beef upon storage. Fresh, choice-grade deboned chuck with 15% fat was flaked and treated with salt, TPP, and TBHQ, freeze-dried and stored in the presence of air at 37°C. Upon storage, beef samples were reconstituted and a meat extract was obtained. Myoglobin in-solubilization (measured spectrophotometrically at the isobestic point at 525 nm) and oxidation (measurement of a peak intensity of met-myoglobin at 630 nm) in stored samples were determined. Antioxidant-containing samples showed the least myoglobin insolubilization and myoglobin oxidation as compared to control beef (with no additives) and beef treated with salt and TPP.     

γ-聚谷氨酸对鸡肉糜凝胶特性的影响

以鸡胸肉为原料,制备鸡肉糜凝胶,研究不同添加量的γ-聚谷氨酸(γ-polyglutamic acid,γ-PGA)在不同Na Cl添加量条件下对鸡肉糜凝胶特性的影响。研究结果表明:单独添加0.9‰的γ-PGA可以显著降低鸡肉糜凝胶蒸煮损失率,提高凝胶强度和保水性,明显改善凝胶的硬度、弹性、内聚性和咀嚼性,对鸡肉糜凝胶白度值影响较小。在一定Na Cl添加量条件下,γ-PGA对鸡肉糜凝胶特性的改善作用更为明显,且在Na Cl添加量为3.0%、γ-PGA添加量为0.6‰时,鸡肉糜凝胶蒸煮损失率最小,保水性、凝胶强度、硬度、弹性、内聚性和咀嚼性都达到最大值;在Na Cl添加量为3.0%、γ-PGA添加量为1.2‰时鸡肉糜凝胶白度值最小。流变学曲线变化表明,γ-PGA能够提高凝胶的形成能力。通过十二烷基硫酸钠-聚丙烯酰胺凝胶电泳研究发现,γ-PGA与蛋白质分子间有一定的交联作用。     

STORAGE DETERIORATION OF FREEZE-DRIED AVOCADO PUREE AND GUACAMOLE

SUMMARY— The effect of storage temperature, time and atmosphere on the chemical and organo-leptic characteristics of freeze-dried avocado puree and guacamole was studied using Waldin, Lula and Booth-8 varieties of avocado. Oxidation rates were slower at 21°C than at 38°% storage and nitrogen atmospheres reduced the peroxide formation. Significant differences existed in oxidation rates between avocado varieties and also between guacamole and avocado puree in some instances. A logarithmic relationship was found between peroxide values and storage time in air. Guacamole made with Lula avocados was unacceptable after 3 weeks of storage in air at 38°C. Samples stored in nitrogen at 38°C ware unacceptable at the end of 7 weeks. Samples stored in air at 21°Cwere acceptable after 12 weeks and those stored in nitrogen at 2l°C after 15 weeks. A commercial BHA antioxidant reduced the oxidation rate of Lula puree but did not increase shelf life in air storage at 38°C. Peroxide values were of no use in predicting acceptability, since organoleptic deterioration could occur without any peroxide increase.     

Viscoelasticity of Frozen/Thawed Egg Yolk as Affected by Salts, Sucrose and Glycerol

Based on dynamic rheological measurements, sucrose, glycerol and magnesium chloride (MgCl₂) prevented egg yolk gelation at concentrations of 2% and higher. These additives showed improved cryoprotectant effects as their concentrations were increased. Sodium chloride (NaCl) at higher than 2% also prevented gelation but at 10%, it caused a considerable increase in viscosity of unfrozen yolk. Calcium chloride (CaCl₂) showed an opposite effect, promoting protein coagulation before freezing. Samples with 2% CaCl₂ gelled completely after 36h at -24°C. Before freezing, potassium chloride (KCl) in the range 2–10% had an effect similar to that of NaCl. However, after freezing its effect changed. Yolk with 2% KCl, frozen 36h at -24°C, showed very elastic behavior.     

Rheological and Microstructural Properties of Porcine Myofibrillar Protein–Lipid Emulsion Composite Gels

ABSTRACT:  The objective of the study was to investigate the role of emulsified fat (lard) and oil (peanut oil) in the rheology and microstructure of porcine myofibrillar protein (MP) gels. Heat-induced composite gels were prepared from 2% MP with 0% to 15% pre-emulsified lipids at 0.6 M NaCl, pH 6.2. Dynamic rheological testing upon temperature sweeping (20 to 80 °C at 2 °C/min) showed substantial increases in G ' (an elastic modulus) of MP sols/gels with the addition of emulsions. Gel hardness was markedly enhanced ( P < 0.05) by incorporating ≥10% emulsions, and the composite gel with 15% lard was 33% more rigid ( P < 0.05) than that with 15% peanut oil. Incorporation of both emulsions at 10% or higher levels improved the water holding capacity of the gels by 28% to 44% ( P < 0.05). Light microscopy revealed a compact gel structure filled with protein-coated fat/oil globules that interacted with the protein matrix via disulfide bonds. The results indicated that both physical and chemical forces contributed to the enhancements in the rheology, moisture retention, and lipid stabilization in the MP–emulsion composite gels.     

Improvement of Gelling Properties of Lizardfish Mince as Influenced by Microbial Transglutaminase and Fish Freshness

ABSTRACT:  The effects of microbial transglutaminase (MTGase) at different levels (0 to 0.8 units/g sample) on the properties of gels from lizardfish ( Saurida undosquamis ) mince set at 25 °C for 2 h or 40 °C for 30 min prior to heating at 90 °C for 20 min were studied. Breaking force and deformation of gels increased with increasing MTGase amount added ( P < 0.05). At the same MTGase level used, gels with the prior setting at 40 °C for 30 min showed a higher breaking force compared with those subjected to prior setting at 25 °C for 2 h ( P < 0.05). Sodium dodecyl sulfate-polyacrylamide gel electrophoretic study revealed that myosin heavy chain (MHC) underwent polymerization to a higher extent in the presence of MTGase. Regardless of setting condition, microstructure of gel added with MTGase was finer with a smaller void compared with that of gel without MTGase. Therefore, setting temperature affected the property of gels added with MTGase. Gel properties of mince obtained from lizardfish stored in ice for different times (0 to 10 d) with and without MTGase at a level 0.6 units/g were determined. Irrespective of MTGase addition, breaking force and deformation of all gels decreased as the storage time of lizardfish increased ( P < 0.05). The addition of MTGase was able to increase both breaking force and deformation of the resulting gel produced from lizardfish kept in ice for all storage times used. Therefore, both freshness and MTGase addition had the direct impact on gel properties of lizardfish mince.     

Influence of Lipid Composition on the Water and Fat Exudation and Gel Strength of Meat Batters

Blends of lard with eight separate fats or oils (70:30 w/w) were prepared and used as the fat component of meat batters. After cooking, the batters were analyzed for water and fat exudation and gel strength. None differed significantly from the control of 100% lard. Positive correlation coefficients, however, were significant between percent monounsaturated triglycerides and water exudation, polyunsaturated triglycerides and fat exudation and saturated triglycerides and gel strength. Addition of lecithin, cholesterol or methyl palmitate to the lard increased fat exudation and decreased gel strength. Sodium laurate had the opposite effect whether added to the lard or to the aqueous phase.     

Effect of Ice Storage on the Physicochemical and Dynamic Viscoelastic Properties of Ribbonfish (Trichiurus spp) Meat

ABSTRACT: Changes in physicochemical and dynamic viscoelastic properties of ribbonfish ( Trichiurus spp) meat during different periods of ice storage were investigated. The differential scanning calorimetry profile of fresh ribbonfish meat revealed transitions at 33.17 °C, 48.85 °C, and 60.96 °C, indicating denaturation temperature of different protein fractions. The effect of cornstarch or tapioca starch at 9% level on the viscoelastic properties of ribbonfish meat stored in ice for different periods was also evaluated. Total volatile basic nitrogen (TVBN) increased significantly ( P < 0.05) during ice storage for 24 d. However, the myosin heavy chain concentration was unaltered during the ice storage period, as revealed by sodium dodecyl sulphate-polyacrylamide gel electrophore-sis (SDS-PAGE) pattern. A significant ( P < 0.05) decrease in protein solubility (in phosphate buffer 50 m M , pH 7.5, containing 1 M NaCl), calcium-activated adenosine triphosphatase (ATPase) activity, and an increase in reduced viscosity at a protein concentration of 5 mg/mL was observed after 10 d of ice storage indicating protein denaturation and aggregation. The addition of tapioca and cornstarch enhanced storage modulus values of fresh ribbonfish meat. The gelatinization temperature of tapioca starch solution was found to be in the range of 60 °C to 65 °C and for cornstarch 67 °C to 70 °C, as revealed by the differential scanning calorimetry (DSC) profile and dynamic rheological testing. The viscoelastic properties of ribbonfish meat was altered significantly ( P < 0.05), both due to the addition of starch and ice storage period as revealed by frequency sweep of prepared gels.     

Mechanisms of gelation of sardine proteins: influence of thermal processing and of various additives on the texture and protein solubility of kamaboko gels

Surimi prepared from freshly caught sardines was mixed with NaCl and other additives and used to prepare kamaboko gels. Protein-protein interactions involved in the setting (at 4 or 37°C) and/or the cooking (at 90°C) gelation steps were investigated (i) by assessment of kamaboko texture as a result of the type and concentration of additive added; (ii) by partial solubilization of kamaboko gels in buffers containing mercaptoethanol, sodium dodecyl sulphate (SDS) and/or urea, followed by determination of the soluble protein constituents by polyacrylamide gel electrophoresis. Cooked gels of high elasticity and of varying rigidity and gel strength were obtained in the 73–80% water range. Adequate gel texture required a NaCl content of 1.7–3.5% and a pH range of 6.4–8.4. Low concentrations of reducing agents (mercaptoethanol, dithiothreitol, cysteine) or of divalent cations (Ca²⁺, Mg²⁺) improved the texture of gels obtained by setting at 37°C with and without subsequent cooking at 90°C. On the other hand, the addition of N -ethyl maleimide or of ethylene diamine tetra-acetate led to texture deterioration after cooking. These data demonstrate the involvement of disulphide bonds and of electrostatic interactions in surimi gelation. Gel solubilization experiments indicate that the aggregation of myosin heavy chains through various types of protein-protein interactions may be responsible for the elastic gel network formed during setting at 37°C (30 min) or 4°C (24h). Strengthening of the gel network after cooking appears to be due to additional disulphide and hydrophobic interactions.     

Combined Effect of High Hydrostatic Pressure and Lysine or Cystine Addition in Low-Grade Surimi Gelation with Low Salt Content

The aim of this study was to reduce the sodium chloride (NaCl) level in surimi-based products by adding lysine or cystine in combination with high hydrostatic pressure (HHP). For experiments, Alaska pollock surimi was used to prepare gels in a factorial design (3?×?3?×?2) using three additive levels (no additive, lysine, and cystine), three NaCl levels (0, 0.3, and 3 %), and two HHP levels (0 and 300 MPa/10 min/10 °C). After blending, the pastes, consisting of surimi, additives, and different levels of salt, were stuffed into casings, high pressure treated, and stored at 5 °C for 24 h (suwari gel). Subsequently, samples were heated at 90 °C for 30 min (kamaboko-type gel). To assess the degree of protein denaturation prior to gelation at 90 °C, suwari gels were analyzed by differential scanning calorimetry to determine myosin denaturation enthalpy. Kamaboko-type gels were characterized by lightness properties, water binding capacity, and mechanical properties (by puncture test). Results showed that the pressure treatment at 300 MPa and/or the addition of lysine or cystine (0 and 0.1 %) to low-sodium-chloride samples (0 and 0.3 %) resulted in gels with similar quality characteristics to those with the regular 3 % sodium chloride addition, most likely due to the protein unfolding induced by both HHP treatment and the additives used.     

RELATIONSHIPS BETWEEN BINDING QUALITY OF MEAT AND MYOFIBRILLAR PROTEINS V. Effect of 'Setting' and Pyrophosphate on Rheological Properties of Heated Minced-Meat Gel

‘Setting’ was observed in minced hen meat stored with 3.5% wt/wt added NaCl. When gels were made from the ‘set’ sol the breaking energy was greatly increased and the relaxation modulus was characterized by a wide ‘quasi-equilibrium’ region. The effect of added pyrophosphate on the rheological properties of the gel prepared at pH 6.0 from ground ‘set’ sol was very similar to that previously observed for ATP in gels prepared at pH 6.0 from ‘unset’ sols. When pyrophosphate or ATP were added at pH 7.0 to the ‘unset’ minced meat sol, the strain at the breaking point and the ratio of the equilibrium to the instantaneous modulus of the heated gel were increased. A comparison with previous results from a model system suggests that pyrophosphate brings about a change in gel structure by dissociating ‘myosin B’ into myosin A and F-actin.     

Reducing sodium intake from meat products

Sodium intake exceeds the nutritional recommendations in many industrialized countries. Excessive intake of sodium has been linked to hypertension and consequently to increased risk of stroke and premature death from cardiovascular diseases. The main source of sodium in the diet is sodium chloride. It has been established that the consumption of more than 6g NaCl/day/person is associated with an age-increase in blood pressure. Therefore, it has been recommended that the total amount of dietary salt should be maintained at about 5-6g/day. Genetically salt susceptible individuals and hypertensives would particularly benefit from low-sodium diets, the salt content of which should range between 1 and 3g/day. In industrialized countries, meat products and meat meals at home and in catering comprise one of the major sources of sodium, in the form of sodium chloride. Sodium chloride affects the flavour, texture and shelf life of meat products. The salt intake derived from meat dishes can be lowered by, whenever possible, adding the salt, not during preparation, but at the table. In most cases, salt contents of over 2% can be markedly lowered without substantial sensory deterioration or technological problems causing economical losses. Salt contents down to 1.4% NaCl in cooked sausages and 1.75% in lean meat products are enough to produce a heat stable gel with acceptable perceived saltiness as well as firmness, water-binding and fat retention. A particular problem with low-salt meat products is, however, that not only the perceived saltiness, but also the intensity of the characteristic flavour decreases. Increased meat protein content (i.e. lean meat content) in meat products reduces perceived saltiness. The required salt content for acceptable gel strength depends on the formulation of the product. When phosphates are added or the fat content is high, lower salt additions provide a more stable gel than in non-phosphate and in low-fat products. Small differences in salt content at the 2% level do not have marked effects on shelf life of the products. By using salt mixtures, usually NaCl/KCl, the intake of sodium (NaCl) can be further reduced.     

Determination of the presence of antioxidants deriving from sage and oregano extracts added to animal fat by means of assessment of the radical scavenging capacity by photochemiluminescence analysis

Herbs and their extracts with antioxidant capacity could be used directly as stabilisers of fat and indirectly as feed additives, in order to improve quality and shelf-life of meat and fat-containing food. In this work a sensitive analytical method is proposed for determination of the antioxidant activity measured by photochemiluminescence (PCL) in lard stabilised with extracts of sage (Salvia officinalis L.) or oreganum (Origanum vulgare L.). A prior step of purification of fat samples is required, in order to separate and concentrate the phenolics from lipidic substances. The method was validated by determination of recovery rate and repeatability. In addition fat samples originating from pigs fed with feed additives of Salviae folium or Origani herba were analysed to investigate the supposed antioxidative effects, that could increase the shelf-life of meat products. In contrast with lard mixed with extracts of sage or oregano, back fat samples originating from pigs fed with feed additives of the same herbs didn't show a higher antioxidant activity than the control group. On the one hand it seems possible to keep perishable fat-containing food longer by an addition of an extract of sage or oregano due to their antioxidative properties, on the other hand administration of feed additives of dried herbs to pigs had no effect on quality and shelf-life of fat obtained from these animals.     

Characteristics of Bovine Plasma Gels as Affected by pH Sodium Chloride, and Sodium Tripolyphosphate

A model system, which simulated the pH, sodium chloride (NaCl), and alkaline phosphate (STP) levels of typical processed meat products, was used to determine the effect of NaCl, STP and pH on firmness and percent cooked yield of bovine plasma gels. Bovine plasma gel firmness increased with increasing plasma pH, whereas percent cooked yield was not affected. In contrast, when the pH, of the plasma solutions, was adjusted to a constant 5.6 to simulate the pH and buffering of meat, percent cooked yield was affected; gel firmness was not affected. With increased levels of NaCl and STP, the percent cooked plasma gel yield increased.     

鸭腿减盐滚揉腌制过程中的传质动力学

用减盐（30% KCl＋70% NaCl）和氯化钠食盐（即普通食盐,NaCl质量分数≥99.1%）分别腌制肉鸭鸭腿,测定滚揉腌制过程中鸭腿肉总质量、水分质量分数、食盐质量分数变化情况,获得鸭腿肉在不同食盐腌制时的传质动力学数据,并进行十二烷基硫酸钠-聚丙烯酰胺凝胶电泳实验,研究不同食盐滚揉腌制过程对鸭腿肉蛋白质的影响。结果显示：氯化钠腌制和减盐腌制中鸭腿肉的总质量变化量（ΔMt0）、水分质量分数变化量（ΔMtw）以及盐分含量变化量（ΔMts）均与腌制时间的平方根（t0.5）呈现出较好的相关性,而且前4 h ΔMt0、ΔMtw以及ΔMts增长较快;氯化钠腌制和减盐腌制的有效扩散系数De分别为4.432×10－8 m2/s和4.462×10－8 m2/s,相差较小;十二烷基硫酸钠-聚丙烯酰胺凝胶电泳图谱显示两种腌制方法肌原纤维蛋白都在不断降解。综上,减盐腌制和氯化钠腌制相比,对传质速率并无明显影响。     

Phosphates and antioxidants as cryoprotectants in meat batters

The gelation and rheological properties of minced beef frozen and stored at -18°C for 6 months without additives, with salt (1·5% NaCl), tripolyphosphate (TPP 0·5%), sodium acid pyrophosphate (SAPP 0·5%) and an antioxidant mix (BHA + BHT, 200 ppm) were studied. The relationships between shear rate and shear stress for the different treatments were nonlinear and resembled the Bingham pseudoplastic behaviour. Continuous evaluation of the modulus of rigidity (G) during cooking (0·5°C/min) revealed higher G values for the unfrozen phosphate treatments. Salt addition resulted in significantly lower G values of the stored meat compared to the control. Antioxidant addition retarded some of these effects. Among the phosphates, TPP was the best in maintaining the same G values as the control. Water-holding capacity (after salt addition) was increased after phosphate addition in the unfrozen meat and did not change after storage. The control, NaCl and antioxidant treatments showed an increase in WHC during storage.     

发酵豆粕中异黄酮热稳定抗氧化性的研究

为开发利用发酵豆粕中异黄酮(FSMI)天然食品抗氧化剂,采用烘箱贮藏法,以过氧化值为指标,研究了高温(120℃)下FSMI对猪油和菜籽油的抗氧化作用.结果表明:在高温下,FSMI具有良好的抗氧化稳定性,并且随着FSMI添加量的增加,其抗氧化作用显著增强;对猪油和菜籽油的抗氧化效果优于同浓度的SMI(从豆粕中提取的异黄酮)、茶多酚和BHT;并对由金属离子(Cu2+、Fe2+)引起的促氧化作用有明显的抑制效应.     

Gelling Properties of Atlantic Croaker Surimi Processed by Acid or Alkaline Solubilization

ABSTRACT: Textural properties of gels from Atlantic croaker surimi recovered by isoelectric precipitation, following acid (AC) or alkaline (AL) solubilization, were compared with that of conventionally washed (CW) surimi. Gel strengths were in the order of AL > AC > CW, with higher gel strength and deformability induced by microbial transglutaminase addition. None of the surimi treatments evidenced endogenous TGase activity. Salt (2% NaCl) addition had variable effects. Proteolysis was evident by sodium dodecyl sulfate-polyacrylamide gel electrophoresis in gels from all treatments when preincubated at 30 °C or 40 °C.