Effect of selected substances on the properties of frozen myofibril preparation obtained from mechanically recovered poultry meat

The experimental material was a myofibrillar preparation obtained from mechanically recovered poultry meat by the washing and separation of fat and connective tissues. Changes occurring during frozen storage were investigated in the preparation without and with the addition of the following substances: 2 g/kg carrageen, 2.5 g/kg sodium tripolyphosphate (TPP) mixture and 80 g/kg polydextrose, and 3 g/kg enzymatic preparation (ACTIVA WM) containing microbial transglutaminase (MTG). Samples with the addition of MTG were pre-incubated at the temperature of 7 ± 1 °C for 1, 3, 5, 24 h. All samples were stored at the temperature of approx. −23 °C for 2, 30, 60, 90 days. The smallest change in protein solubility was observed in samples with added TPP and polydextrose. Along with the extension of pre-incubation time of samples containing the enzyme a gradual decrease was found in the amount of soluble protein. Also the results of the investigations obtained using the DSC technique showed the most advantageous protective effect, i.e., causing the smallest decrease in enthalpy values of samples during freezer storage, in case of the addition of TPP and polydextrose mixture. Analysis of thermal drip volume from gels showed that carrageen was the most advantageous addition to the myofibrillar preparation. Moreover, a gradual increase was observed in the volume of thermal drip along with the extension of pre-incubation time of the protein isolate with enzymatic preparation. Results of gel texture testing indicated that the most advantageous effect on gel quality was found for ACTIVA applied in 3 and 5 h pre-incubation with the myofibrils. Assuming that among the analyzed properties the most important were thermal drip and gel texture, 3 g/kg MTG at pre-incubation time of 3 h was considered the most advantageous additive.     

Analysis of texture and dynamics of water binding in enzymatically modified myofibrillar preparation obtained from washed mechanically recovered poultry meat

Experiments were conducted on a myofibrillar preparation, obtained from washed mechanically recovered poultry meat. An enzymatic preparation containing microbial transglutaminase (MTG) was added to samples of the myofibril isolate. The binding of water contained in the protein preparation with added MTG was assessed using low field nuclear magnetic resonance (NMR). Moreover, texture was analyzed in myofibril samples with the addition of transglutaminase pre-incubated for 0.5, 1.5, 3, 4.5 and 6 h. All measurements were taken at 7 ± 0.2 °C. Samples with added transglutaminase exhibited improved mechanical failure strength and better water binding capacity. The most dynamic increase of texture parameter values was observed in the interval from 1.5 to 3 h pre-incubation of the preparation with the added enzyme. Based on NMR (T ₁) testing it was established that the highest amount of water was bound by protein in the period from approximately 1 to 1.5 h pre-incubation. After that time free water content in the sample was again found to increase. This means that water was displaced from the system as a result of protein–protein interactions dominating over protein–water interactions. The above suggests that the enzymatic modification of the protein preparation contributed to the intensification of cross-linking between proteins in the preparation.     

Studies on thermal treatment of hake Part 1. Effects of thermal treatment and frozen storage on the content of SH groups and rheologic properties of hake flesh

Effects of frozen storage (3–8 months at –28° C) and heating temperatures (40, 60, 80, 100, 120 and 130° C) on SH groups content and minced meat hardness of the Pacific hake (Merluccius productus) were studied. Of the two factors under study, temperature effects proved dominating, both on the SH dynamics and on hardness. The duration of frozen storage did not influence the maximum content of SH groups: it affected only the location of the peak of the thiol groups contents temperature curve. Additionally, a high correlation between the SH content and hardness was found as a function of heating temperature; the correlation, however, became weaker with frozen storage time.     

Effect of preheating temperature on the microstructure of walleye pollack surimi gels under the inhibition of the polymerisation and degradation of myosin heavy chain

BACKGROUND: The physical attribute of heat‐induced gel texture is highly dependent on the microstructure of the gel. In this study the microstructures of walleye pollack surimi gels preheated at various temperatures with and without inhibitors (ethylenediamine‐N,N,N′,N′‐tetraacetic acid, iodoacetamide and leupeptin) were observed with a natural scanning electron microscope. RESULTS: Without inhibitors, gels preheated at 30 °C showed a fine and uniform network structure together with the highest polymerisation of myosin heavy chain (MHC) and the highest gel strength. At 60 °C, gels exhibited a broken, disrupted and loose cluster‐like structure together with the highest degradation of MHC and the lowest gel strength. Under the inhibition of polymerisation and degradation of MHC a fine network was observed up to 40 °C during preheating. However, after a second step of heating at 80 °C the microstructures were disrupted and resembled each other regardless of the preheating temperature. CONCLUSION: Heat‐induced gel formation is related to the polymerisation and degradation of MHC and the microstructure of the gel during preheating. Gelation occurred during setting even under the inhibitory condition, and the formation of covalent bonding by transglutaminase is not essential to the formation of a three‐dimensional network during setting but is essential to the gel strength enhancement effect of setting by subsequent heating at 80 °C. Copyright © 2010 Society of Chemical Industry     

High pressure-induced tapioca starch gels: physico-chemical characterization and stability

Gelatinization of tapioca starch (25% dry basis) was induced by high hydrostatic pressure processing (HPP) at 600 MPa under different time and temperature regimes (30 °C for 10, 20 and 30 min; 50 °C for 10 min; 80 °C for 10 min). Textural, thermal and structural properties of the gels were studied and their stability was evaluated after 28 days of refrigerated (4 °C) and frozen (−18 °C) storage. Thermally induced gels (90 ± 1 °C, 20 min, gel-T) were used as controls. HPP resulted in the formation of harder gels than thermal processing (more significantly at lower processing temperatures) partially preserving the granular structure of the native starch. Longer HPP treatments caused only a slight decrease in hardness that was significant only at longer processing times (30 min). DSC thermograms of high pressure-induced samples showed a more asymmetrical ice-melting peak than that of thermally induced gels. Asymmetry of the peak of HP treated samples was more pronounced in samples processed at lower than at higher temperature. A different starch–water and/or starch/starch interaction may be hypothesized. During storage, all samples became stiffer and the amylopectin recrystallization increased, more extensively in thermally induced than in HPP samples where a stronger starch–starch and/or starch/water interactions may have hindered the recrystallization process.     

Continuous Gel Formation by HTST Extrusion-Cooking: Soy Proteins

The continuous production of gels of high moisture content is carried out by extrusion-cooking, with a residence time of 30-100 sec, using soy protein isolate as a model ingredient. The hot viscous extrudate can be collected in a mold, and gels upon cooling. The best texture characteristics are obtained with protein and water concentrations of 18 and 80% (wet basis), respectively, and extrusion temperatures of 150-160°C. The effects of acidification, addition of NaCl, CaCl₂ or sucrose on gel texture are investigated. Extrusion-prepared soy gels melt reversibly upon further heating (120°C) and withstand frozen storage. Their texture and micro-structure are compared to those of soy gels prepared by conventional batch heating at 100-120°C.     

Interaction of Myosin-Albumin and Myosin-Fibrinogen to Form Protein Gels

Myosin, fibrinogen, albumin, myosin-fibrinogen and myosin-albumin gels were formed by heating in pH 6.0 phosphate buffer at two heating rates. Gel strength was measured with an annular pump and soluble protein was determined. Myosin and fibrinogen interacted to form a gel which was stronger than the sum of the gel strengths for the two individual proteins. The strength of myosin-fibrinogen gels formed at 50°C was not affected by heating method; however, the strength of gels developed between 55°C and 70°C was related to heating method. Myosin and albumin did not interact to form a gel matrix until 80°C where sufficient thermal alteration of albumin had occurred.     

Thermal and rheological properties of hydrogels prepared with retrograded waxy rice starch powders

Waxy rice starch dispersed in water (50% solids) was gelatinized by heating the dispersion at 121°C for 20 min, and retrograded by storing the paste at 4°C for 2 days. The starch gel was then freeze-dried and ground into powders. The retrograded starch powders were hydrated at 20–30% solid concentration at different temperatures (4 and 23°C), and then thermal and rheological properties were analyzed using the hydrogels. The gel hydrated at 4°C had an onset temperature of melting at 34.9°C, which was approximately 10°C lower than that observed for the gel hydrated at 23°C. The enthalpy value was greater for the gel hydrated at 4°C (14.2 J/g) than the gel hydrated at 23°C (8.8 J/g). The yield stress and consistency of the hydrogels were proportional to the solid concentration. The hydrogel prepared with 30% retrograded starch powders at 4°C displayed a thick creamy texture with retrograded starch crystals that could melt at a temperature range of 35–51°C. The thermal and rheological properties of the hydrogels exhibited the possibility for the retrograded starch powders to be used as fat mimetic in foods.     

Effect of selected commercial substances with cryoprotective activity on the quality of mechanically recovered,washed and frozen stored poultry meat

Investigations were conducted on mechanically recovered poultry meat (MRPM) and on protein preparation obtained from MRPM by washing it first with 1% water solution of sodium chloride and with water afterwards. The raw materials were frozen at the temperature of –23°C. The effect of added stabilizers on the quality of gels produced from fresh raw materials, and after freezing and frozen storage was assessed. The following additives were used: 1% pork hydrolizate (Pork Stock( 0.5% Cremodan containing carrageens, and 1.5% bovine blood plasma (AMP 600N). Freezing and frozen storage caused a significant reduction of functional properties of MRPM and its protein preparation. None of the examined additives protected simultaneously all the investigated functional properties of the frozen samples. The amount of thermal drip, the gel texture and the amount of protein transition heat were determined by scanning differential calorimetry. The lowest thermal drip in gels obtained from frozen‐stored samples was observed when bovine blood plasma was used as a stabilizer. On the other hand, the most advantageous protective effect on the proteins of the frozen MRPM and on the preparation, determined by mechanical strain resistance of the gels, was found with 1% pork hydrolizate added. The results of thermodynamic investigations of proteins revealed that the best protective effect on the frozen preparation was observed with 1.5% blood plasma added. No protective activity of added Cremodan on proteins of the frozen protein preparation was noted.     

Trypsin Treatment to Improve Freeze Texturization of Minced Bream

Mild trypsin proteolysis (enzyme concentration 0.05% at 15°C, pH 7.4; mixing 30 min at 20 rpm) of bream mince improved mince susceptibility to freeze texturization. Formation of porous-fibrous texture of heat-set, freeze-texturized minces was associated with strong fragmentation of myosin heavy chain (MHC), decrease in extractability of myofibrillar protein and increased insoluble protein and thermal drip. Some deamidation of protein was also observed. We concluded that limited trypsin proteolysis accelerated transglutaminase mediated cross-linking of protein by acyl transfer reactions. Protein polymerization through plastein reactions and intermolecular hydrophobic interaction probably also occurred.     

Principal component analysis to study the effect of temperature fluctuations during storage of frozen potato

 The effects of temperature fluctuation ranges, number of fluctuations carried out, and packaging during frozen storage on the texture of potato tissue in terms of compression, shear, and tension rheological parameters were assessed through data generated according to a factorial design using principal component analysis (PCA). Five ranges of fluctuation (–24  °C to –18  °C, –18  °C to –12  °C, –12  °C to –6  °C, –24  °C to –12  °C and –18  °C to –6  °C) applied 2, 4, 8, 16, 24, and up to 32 times on unpacked and pre-packed frozen potatoes, were considered. The controls were unpacked and prepacked frozen tissues thawed immediately without undergoing any fluctuation. In addition, several geometrical, technological, and chemical parameters were determined. PCA showed that maximum shear force, F_s was the best rheological parameter for differentiation of the structural damage and softening occurring in the tissue at each treatment, which was closely related to its duration, TT _d . PCA did not permit complete discrimination between the five fluctuation ranges, but it clearly separated samples subjected to –18  °C/–6   °C from those subjected to –24  °C/–18  °C. Frozen samples undergoing up to four fluctuations formed a separate cluster from those undergoing a higher number. Analysis also clearly separated unpacked from pre-packed samples in response to slower freezing rates reached in the latter. Received: 17 December 1999     

Quality changes during storage of sous vide cooked green beans (Phaseolus vulgaris)

 The acceptability and quality of sous vide cooked green beans (Phaseolus vulgaris) were investigated during chilled storage. A suitable heating procedure was established whereby 2.0-kg packages were heat processed at 90°C for 25 min, corresponding to an average pasteurization value, PV_70,10, of 14 min. During storage for up to 25 days at 3°C drip loss, pH, colour (Minolta L ^* a ^* b ^*), texture (Instron) and microbiological stability were examined and sensory characteristics evaluated by a trained sensory panel. No marked changes in texture, drip loss, pH or microbiological counts were observed but a change of colour from green to olive green was observed by both objective and sensory analyses. This detrimental change in colour, which had begun during the first week, was the limiting factor for shelf-life during storage. Subsequent reheating, however, resulted in further colour changes which partially obscured the initial differences observed during the storage period. Storage for more than 1 week resulted in undesirable quality changes in the odour and flavour of the green beans. Therefore, a maximum shelf-life of 8 days at 3°C was recommended. Inoculation trials showed that psychrotrophic Bacillus cereus were able to germinate and grow to levels of 10⁷ g^–1 in the packages at abuse temperatures (7°C and 17°C), whereafter numbers declined. Received: 21 April 1997     

Gel Characteristics—Waterbinding Properties of Blood Plasma Gels and Methodological Aspects on the Waterbinding of Gel Systems

A methodological study on the waterbinding properties of protein gels was made, where two tests were evaluated. Only one of them, the “net test,” was found useful for work on protein gels. The moisture loss of blood plasma gels was then studied as a function of heating temperature, heating time, pH, protein concentration, and sodium chloride concentration. It was finally demonstrated that a change in the gel structure may affect waterbinding and texture characteristics differently, and these properties should therefore be treated separately when evaluating protein gels. It was, e.g., shown that blood plasma gels became firmer with increasing heating temperature from 72 – 92°C, whereas the waterbinding properties became poorer at temperatures above 77°C and had an optimum at 75 – 77°C.     

The effects of particle size, connective tissue and cooking regime upon properties of washed mechanically recovered broiler meat

Mechanically recovered meat (MRM) from broilers was washed with water, with or without prior chopping and with or without sieving to remove connective tissue. The resultant protein extract was mixed with salt and cooked in a one-step (directly to 80°C) or two-step (to 55°C and then to 80°C) cooking regime, to form gels. Washing broiler MRM gave stronger gels with lower cooking loss and expressible moisture than unwashed broiler MRM. These washed gels were also lighter in colour and less red. The best products were produced when some of the collagen had been removed by sieving, but not if the samples had Wrst been chopped, even though the total protein and dry matter contents were also reduced. A two-step cooking procedure enhanced gel strength. Evidence of a more porous, but dense, structure of washed broiler MRM subjected to a two-step cooking treatment was given by scanning electron microscopy and these differences could be related to the changes in gel strength and water holding.     

Probing thermal behaviour of microbial transglutaminase with fluorescence and in silico methods

BACKGROUND: Knowledge of transglutaminase behaviour at thermal treatment allows efficient applications in food processing. The heat‐induced conformational changes of microbial transglutaminase were studied by fluorescence spectroscopy and a molecular modelling approach. RESULTS: The experimental results indicate the unfolding of transglutaminase in a single‐phase reaction, at temperatures over 60 °C. The incidence of conformational changes is also supported by the increase of both intrinsic and 1‐anilino‐8‐naphthalene sulfonate fluorescence intensity with temperature. Changes in the secondary and tertiary structure of transglutaminase were outlined after running molecular dynamics simulations at temperatures ranging from 25 °C to 80 °C. CONCLUSION: The motif's particularities varied with the temperature, suggesting structural rearrangements of the protein, mainly in helices. The largest deviation from the structure equilibrated at 25 °C was observed at 80 °C. © 2012 Society of Chemical Industry     

Rheological and microstructural changes in gels made from high and low quality sardine mince with added egg white during frozen storage

 This paper examines the influence of freezing temperature (–40°C or –18°C) and frozen storage temperature (–18°C or –12°C) on gels made from two different sardine minces (M1, high functional quality; M2, low functional quality), with the addition of egg white as a gel enhancing ingredient. To characterize the washed mince, proximate analyses and protein functionality were determined. Freezing at either –40°C or –18°C caused no drastic changes in gel structure. Throughout the course of frozen storage of all samples, a decrease in the water holding capacity (WHC) was detected, along with an increase in the amount of protein soluble in 8 M urea. At 90 days the gels frozen at –40°C exhibited numerous ice micro-crystals; however, they did not affect the external appearance of the gel and had hardly any effect on gel strength, shear strength, hardness, cohesiveness or elasticity. On the other hand, at 90 days the gels frozen at –18°C and stored at either temperature exhibited large, macroscopically visible ice crystals. In these samples, gel strength and shear strength increased while hardness decreased. No definite changes attributable to mince quality were detected during frozen storage. Received: 23 June 1997     

Changes in ginsenosides and antioxidant activity of Korean ginseng (Panax ginseng C.A. Meyer) with Heating Temperature and Pressure

This study was carried out to investigate the changes of ginsenoside compositions and antioxidant activity of fresh ginseng induced by thermal processing at different temperatures (25, 100, 121, and 150°C), pressure (0.1, 10, 20, and 30 MPa), and soaking solvents (water and ethanol). The levels of ginsenosides were similar trend with the pressure of 0.1–30 MPa, while there were significantly differences in heated ginseng with heating temperature and soaking solvent. When water and ethanol was used, the ginsenoside compositions significantly changed at 100 and 121°C, respectively, and it was rapidly decreased at 150°C. After heating, the level of 3 ginsenosides (Re, Rf, and Rg1) decreased and that of 5 other ginsenosides [Rb1, Rb2, Rb3, Rc, and Rg2(S)] increased up to 121°C compare to raw ginseng. Ginsenoside F2, F4, Rg2(R), Rk3, Rh4, Rg3(S), Rg3(R), Rk1, and Rg5, which was absent in raw ginseng, was detected in heated ginseng. Especially, ginsenoside Rg3(S), Rg3(R), Rk1, and Rg5 were remarkably produced after thermal processing. After heating, the phenolic compounds (1.43–11.62 mg/g), 50% inhibition concentration (IC₅₀) value (1.48–3.11 mg/g), and ABTS radical scavenging activity (0.66–9.09 mg AA eq/g) of heated ginseng were increased.     

Effect of Heating Rate on Thermally Formed Myosin, Fibrinogen and Albumin Gels

Myosin, fibrinogen and albumin gels were formed by heating in pH 6.0 phosphate buffer at three heating rates. Turbidity (A_660nm) and solubility were monitored along with gel strength, as measured with an annular pump. Myosin and fibrinogen suspensions became turbid and solubility decreased as temperatures preceding the development of gel strength. Linearly increasing heating rates of 12°C/hr and 50°C/hr produced the strongest myosin and fibrinogen gels at 70°C, whereas albumin gels formed at 95°C by heating at 12°C/hr or constant heating for 20 min did not differ in strength.     

Rapid (microwave) heating rate effects on texture,fat/water holding,and microstructure of cooked comminuted meat batters

Comminuted and gelled, fat-containing meat products such as frankfurters and luncheon meats are commercially processed by heating relatively slowly (for up to 2 h or more) to an endpoint of about 70 °C prior to cooling. This study compared such a slow, ramp heating regime (0.5 °C/min), terminated at 70 °C, to rapid, square-wave cooking (one step: rapid 100 °C/min heating to 70 °C endpoint, plus isothermal holding prior to cooling, or two-step: rapid heating to 50 °C, holding, then rapid heating to 70 °C plus holding prior to cooling) on meat batter gel properties (fracture and small strain rheology, microstructure, cook loss, and expressible water). The results indicated that a rapid cooking process, with its inherent advantages of reduced process time, lower equipment footprint, and more efficient use of energy, can produce a product nearly equivalent in textural properties and cook yield to one processed by traditional smokehouse cooking when the cook value of the processes is similar and an intermediate (near 50 °C) holding step is included (two-step rapid heating). One-step rapid heating negatively affected gel structural homogeneity and water/fat holding properties of fat-containing gels.     

Structural and rheological properties of amaranth protein concentrate gels obtained by different processes

The heat-induced gelation of amaranth protein concentrates (APCs) by three processes was studied. The first was the conventional process for isolating protein (standard process-st), the second included an acid washing step prior to protein extraction (acid washing process-aw) and the third included heating (50 °C) during the alkaline extraction step (heat process-ht). The dispersions (12%, w/v) were heated to 55–90 °C and assessed by rheological measurements made under small deformations, whereas the gels obtained by heating at 70, 80 or 90 °C/30 min were subjected to uniaxial compression measurements (TPA and mechanical properties). The rheological parameters associated with the network structure, elasticity modulus (E) and storage modulus (G′), increased with increasing gelation temperature. For the APCst and APCht gels, protein aggregation occurred in two steps, whereas for APCaw, gelation occurred in a single step. The APCht gels showed the highest fracturability, hardness and adhesiveness, followed by the APCst and APCaw gels (p < 0.05). Similar results were obtained for the mechanical properties at fracture. Increasing the heat treatment temperature from 80 to 90 °C resulted in a more structured matrix with greater water-holding capacity as compared to gels obtained at 70 °C, and these properties were influenced by the extraction processes used to obtain the APCs. Heat extraction (APCht) improved the gelation and water-holding properties, whereas the acid treatment had the opposite effect.