Enzymatic modification of selected functional properties of myofibril preparation obtained from mechanically recovered poultry meat

The effect of addition of 3 g/L of commercially available transglutaminase preparation to protein extracts obtained from mechanically recovered poultry meat was studied. The content of free thiol groups (–SH), thermal drip and gel texture were determined. After pre-incubation at 7–8 °C for 1, 3, 5 and 24 h, the samples were subjected to one-step heating at 50, 60, 70 and 80 °C and two-step heating at 50/80, 55/80 and 60/80 °C. The addition of preparation and the extension of pre-incubation time led to decrease of free -SH groups content. After heating, the number of thiol groups decreased, the texture was improved, but thermal drip from gels increased. The amount of –SH groups in gel extracts subjected to one-step heating decreased with simultaneous increase of mechanical strength of gels. Protein gels subjected to two-step heating exhibited higher firmness than gels subjected to one-step heating. Thus, the 3 g/L addition of transglutaminase preparation in combination with one-step thermal processing at 70 °C and pre-incubation for 3 h contributed to improvement of texture properties of model gels and low thermal drip.     

Enzymatic modification of protein preparation obtained from water-washed mechanically recovered poultry meat

Studies were conducted on a protein preparation obtained from washed mechanically recovered poultry meat (MRPM). The effect of addition of 3 g/kg microbial transglutaminase (MTG) to poultry meat protein was evaluated in terms of texture changes by dynamic mechanical analysis (DMA) and nuclear magnetic resonance (NMR) to determine water content in the preparation and its effect on protein. Samples with the addition of MTG were pre-incubated at 5–6 °C for 1.5, 3, 4.5, 6, 7.5, 9 and 24 h. The largest changes for both texture parameters and rheological properties were observed in the interval of approx. 4–7 h incubation. The protein preparation with the enzyme added had significantly higher values of the moduli of elasticity (G₁) and losses (G₂) in comparison to the control system. Samples with the addition of MTG also showed a higher water-binding capacity. From the NMR studies it was found that the greatest amount of water was bound by protein in the period of approx. 2.5–5 h incubation. After that time an increase was found in the amount of free water in the sample, which suggests that it was displaced from the system by stronger protein–protein bonds.     

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.     

Modification of functional quality of raw myofibril preparation obtained from water-washed mechanically recovered chicken meat

The aim of this study was to evaluate the effect of enzymatic modification of poultry myofibril preparation on its selected functional properties, that is, solubility of proteins, polymerisation rates of myosin and actin, thermodynamic properties and texture. The myofibril preparation (MP) from mechanically recovered chicken meat, produced by washing and separation of fat and connective tissue, was subjected to the action of the transglutaminase preparation added at 0.3 % for a period ranging from 0.5 to 24 h at a temperature of 6–7 °C. The highest dynamics of a reduction in protein solubility was observed up to 3 h of incubation. A reduction in solubility influenced the electrophoretic pattern of proteins. A significant decrease was found for the intensity of the myosin band in successive modification periods. The addition of the enzyme also influenced a reduction in enthalpy for proteins of the tested system, occurring most dynamically up to 3 h of incubation. The most distinct changes characterising a high increase in all the texture parameters of MP were found in the initial period of enzymatic modification, that is, up to 4.5 h.     

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.     

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.     

Optimization of conditions for myofibril preparation from mechanically recovered chicken meat

The influence of various conditions affecting the isolation of a myofibrillar preparation (MP) from chicken mechanically recovered meat (MRM), i.e. the time of additional chopping in a bowel chopper, washing time, the number of washings, and the water to MRM ratio, on the recovery of dry matter and myofibrillar protein, and fat content in the preparation was investigated. The following particular steps were determined to be the most desirable parameters: chopping MRM for 10 minutes, washing time of 15 minutes, 3 (or 2) consecutive washings, 3:1 water to MRM ratio (v/w). Under these conditions a significant decrease of fat content (93% on average) was found in comparison to the content in MRM. The removal of fat, sarcoplasmic protein and connective tissue increased the concentration of myofibrillar protein. The number of aqueous washings of MRM had the biggest influence on the protein and fat content in the concentrate. Electrophoretic analysis (SDS-PAGE) of protein in the preparation obtained under optimal conditions showed that myosin heavy chains (MHC) and actin constituted approximately 50% of all the proteins in the preparation.     

Influence of the addition of mechanically recovered meat on the physico-chemical properties of meat model blends

The physico-chemical properties of meat model blends (basic composition: fresh lean pork, pork back fat, 2% NaCl, water with ice), with added mechanically recovered pork (MRM), were studied. Fresh MRM was added at levels of 10% and 20% substitution of meat protein with or without further substitution by 10% sodium caseinate or soya isolate. The addition of MRM to meat blends caused an increase in the pH, the water-holding capacity, the viscosity, the dominant wavelength and colour purity. No effects on emulsifying capacity were observed but thermal cooking losses and lightness of colour were reduced. The addition of blends of MRM and soya isolate or sodium caseinate caused lower values of the investigated features than those observed when only MRM was used.     

鸽肉酶解液水解工艺优化及其体外抗氧化性研究

以乳鸽胸脯肉为原料,利用风味蛋白酶、碱性蛋白酶、菠萝蛋白酶和木瓜蛋白酶对其进行水解,以水解度为指标,利用单因素实验和正交实验对酶解工艺进行了优化,并以抗坏血酸为对照,以还原能力、DPPH自由基清除能力、超氧阴离子自由基清除能力、羟自由基清除能力为指标分析了酶解液的体外抗氧化能力。结果表明,最佳水解工艺为:风味蛋白酶600 U/g(原料),水解温度55 ℃,pH7. 0,在此条件下水解2.5 h,水解度达到28.69%±0.29%;水解得到的鸽肉酶解液具有一定的还原能力,对DPPH自由基、超氧阴离子自由基、羟自由基均具有很好的清除作用。     

Effect of addition of cryoprotectants on the mechanical properties, colour and sensory attributes of fresh and frozen/thawed mashed potatoes

Cryoprotectants such as hydrocolloids (amidated low-methoxyl (ALM) and high methoxyl (HM) pectins), kappa- and iota-carrageenans (k-C and i-C), xanthan gum (XG)) and dairy proteins [whey protein (WP), sodium caseinate (SC)] were added to mashed potatoes to investigate ways of improving the effects of freezing and thawing. It was found that each hydrocolloid and protein, depending on concentration, affected the mechanical properties [instrumental textural profile analysis (ITPA), cone penetration (CP) test], the total colour difference (ΔE*) with respect to fresh control (FC) and the sensory attributes of fresh (F) and frozen/thawed (F/T) mashed potatoes in a different way. In the F/T samples, adding 5 and 8 g kg⁻¹ ALM, 3, 5 and 8 g kg⁻¹ k-C, 1.5, 3, 5 and 8 g kg⁻¹ i-C and 1.5, 5 and 15 g kg⁻¹ WP significantly increased ITPA consistency. Also, adding 2.5 and 5 g kg⁻¹ XG significantly increased ITPA consistency of the F/T product. In both F and F/T samples, k-C provided the highest ITPA consistency and also high CP average force evidencing a stronger synergistic effect in κ-C/denatured milk protein systems, although the excessive thickening and stickiness provided was judged undesirable by the panellists. Adding 8 g kg⁻¹ HM pectin had a disruptive effect on the mashed potatoes and decreased both ITPA consistency and CP average force. In all cases, freezing and thawing reinforced the gel structure of the products as compared to F and FC counterparts. The ΔE* values were higher in F samples containing ALM and HM pectins. Dairy proteins affected the taste and odour of the mashed potatoes and were judged unacceptable in the sensory analysis. Samples containing 0.5 and 1.5 g kg⁻¹ added XG were preferred organoleptically due to the creamy mouthfeel it produced. ITPA consistency correlated well with sensory texture attributes.     

The preparation of an oligochitosan‐glycosylated and cross‐linked caseinate obtained by a microbial transglutaminase and its functional properties

A glycosylated and cross‐linked caseinate (GCC) with glucosamine amount of 4.74 g/kg protein was generated from caseinate and oligochitosan by a microbial transglutaminase. The applied temperature, pH and molar ratio of acyl donor/acceptor were 37 °C, 7.5 and 1:3, respectively; while caseinate concentration, transglutaminase addition and reaction time selected from single‐factor trials were 50 g/L, 10 kU/kg protein and 3 h, respectively. Electrophoretic analysis revealed the cross‐linking and glycosylation of caseinate. Compared with caseinate, GCC showed improved solubility in pH 4–11, higher digestibility in vitro and water binding capacity, about 3‐fold, but lower surface hydrophobicity and oil binding capacity (34%).     

Effect of reducing agents on physicochemical properties and gel-forming ability of surimi produced from frozen fish

Effects of different reducing agents (cysteine, ascorbic acid and sodium bisulfite) at various levels on physicochemical properties of protein, transglutaminase activity and gel properties of surimi produced from frozen croaker, lizardfish, threadfin bream and bigeye snapper were studied. Addition of cysteine resulted in the highest increase in the breaking force and the deformation of surimi gels, compared with other reducing agents. The optimum levels of cysteine were 0.05, 0.1, 0.05 and 0.1% (w/w) for surimi from frozen croaker, lizardfish, threadfin bream and bigeye snapper, respectively. Surimi from frozen croaker with cysteine added showed a similar breaking force and deformation to that produced from fresh fish. With addition of cysteine, an increase in sulfhydryl content with a concomitant decrease in disulfide bond content was generally observed. Ca²⁺ ATPase activity also increased, indicating the renaturation of the myosin molecule. T_max of peak 1 (myosin peak) of all surimi sols in the presence of cysteine was shifted to higher temperature. The increased transglutaminase activity was observed with addition of cysteine. Therefore, reducing agents, especially cysteine, recovered the denatured muscle proteins and activated the transglutaminase in the muscle, leading to the increased gel-forming ability of surimi produced from frozen fish.     

Antioxidant and functional properties of gelatin hydrolysates obtained from skin of sole and squid

Antioxidant and functional properties were evaluated for gelatin hydrolysates obtained from sole and squid skin gelatin by Alcalase, with a degree of hydrolysis of ∼35% and ∼50%, respectively. Both hydrolysates mainly consisted of peptides below 6.5 kDa, together with peptidic material from around 16 to 6.5 kDa. Moreover, the squid hydrolysate showed a peptide band of around 26 kDa. Antioxidant properties of both gelatins were highly increased by hydrolysis, especially ABTS and metal chelating abilities. The squid hydrolysate showed the highest antioxidant capacity by FRAP, ABTS and metal chelating assays in spite of the lower content in hydrophobic amino acids. Both gelatin hydrolysates had a good solubility (over 95%). The emulsifying activity index (EAI) decreased with increasing concentration. Conversely, the foam expansion increased with increasing concentration. However, both foam and emulsion stabilities were not apparently affected by the concentration of hydrolysate. In the case of the sole hydrolysate, which showed a lower degree Pro and Lys hydroxylation, foam stability was very poor, and 50% of foam expansion was lost after 5 min at all concentrations.     

Effect of acid- and alkaline-aided extractions on functional and rheological properties of proteins recovered from mechanically separated turkey meat (MSTM)

Functional and rheological characteristics of acid- and alkali-extracted proteins from mechanically separated turkey meat (MSTM) have been investigated. Extractions were carried out at 4 pH values (2.5, 3.5, 10.5, and 11.5). The study demonstrated that alkali and acid extractions resulted in significant (P < 0.0001) decreases of cooking and water loss compared to raw MSTM; however, the cooking loss was found to be similar (P = 0.5699) among the different protein isolates. Proteins extracted at pH 10.5 showed the lowest (P = 0.0249) water loss. Emulsion and foaming properties were found to be slightly higher in alkali-extracted proteins compared to those for acid extractions. The myofibrillar protein fraction showed better ability to form and stabilize emulsions compared to sarcoplasmic proteins. Myofibrillar proteins also showed better foam expansion; however, foam volume stability was similar for both myofibrillar and sarcoplasmic protein fractions. Textural characteristics (hardness, chewiness, springiness, and cohesiveness) of recovered proteins were found to be unaffected (P > 0.05) by different extraction pH. The protein extracted at pH 3.5 formed a highly viscoelastic gel network as evidenced by storage modulus (G') values, whereas the gel formed from proteins extracted at pH 10.5 was found to be the weakest. The work also revealed that acid treatments were more effective for removal of total heme pigments from MSTM. Color characteristics of protein isolates were markedly improved compared to the initial material and tended to be better when subjected to acid extractions. PRACTICAL APPLICATION: Mechanically separated meat is one of the cheapest sources of protein obtained by grinding meat and bones together and forcing the mixture through a perforated drum. The use of mechanically separated turkey meat (MSTM) for the production of further processed poultry products is limited due to its undesirable color and textural properties. Recovery of proteins from MSTM using pH shifting process will help the poultry processors to get better returns and also create opportunity to produce functional food ingredients.     

Assessing the quality of mechanically and manually recovered chicken meat

The biochemical composition and histological characteristics of meat recovered mechanically by the auger/sieve (a/s) and the hollow drum/belt (hd/b) principles from two different chicken carcass parts were compared with meat recovered manually. The quality of meat recovered mechanically by the hollow drum/belt principle was equal to or higher than the quality of manually recovered meat. The degradation of muscle structure was highest in the meat recovered by the a/s principle and lowest in the manually recovered meat. For the biochemical measurements with the exception of collagen, determinations of a single sample were sufficient to achieve a repeatability of 0.9, whereas for the histological measurements at least 8 samples were necessary. It is suggested that a quality-grading scale based on biochemical composition and level of degradation of muscle fibre structure should be established for all types of minced meat regardless of whether the meat is obtained by mechanical or manual procedures and that legislation concerning the use of MRM should be based on such a scale.     

Proteomic approach for the detection of chicken mechanically recovered meat

Mechanically recovered meat is cheaper than raw meat and thus has been incorporated into many meat-derived products. EU regulations exclude mechanically recovered meat from the definition of meat; as a consequence analytical procedures are needed to differentiate it from hand-deboned meat. The present pilot study has utilized a proteomic approach to find potential markers for the detection of chicken mechanically recovered meat. Intact proteins were extracted from raw meat and then analyzed with OFF-GEL electrophoresis followed by SDS-PAGE and identification of potential markers by nano-LC-MS/MS. It was shown that it is possible to extract, separate and identify key proteins from processed meat material. Potential chicken mechanically recovered meat markers--hemoglobin subunits and those similar to myosin-binding protein C were also identified.     

Production of high quality gels from sea bass: Effect of MTGase and dietary fibre

The effects of MTGase (5 g/kg, w/w) and dietary fibre (inner pea fibre, 40 g/kg, w/w, carrageenan, 10 g/kg, w/w, carrageenan + konjac flour, 10 + 10 g/kg, w/w) on heat-induced gels from sea bass (Dicentrarchus labrax) trimmings were studied. MTGase incorporation had a positive effect on texture: gel strength and force at rupture increased. MTGase reduced protein solubility, meaning greater protein aggregation, according to electropherograms. Pea fibre had no positive effects: texture was quite similar to that of the control products and WHC was reduced. Carrageenan addition had no deleterious effect upon the texture of the gels and made them harder and springier. Force at rupture (even without MTGase) and WHC were greatly improved. Combination of carrageenan and konjac further enhanced these effects. For those gels without MTGase, protein solubility in urea and urea + DTT was reduced by both fibres, suggesting a reduction of hydrogen bonding between proteins.     

The effects of transglutaminase on the functional properties of the myofibrillar protein concentrate obtained from beef heart

The aim of the present study was to evaluate the effect of bacterial transglutaminase on the functional properties of the myofibrillar protein concentrate from beef heart. The degrees of hydration and aggregation and emulsifying properties were studied. The degree of polymerization of the myofibrillar proteins depended on the enzyme concentration and setting time; the best results in terms of functional properties were obtained with 0.3 g transglutaminase/100 g protein with 60 min setting at 35 °C. This investigation confirms that transglutaminase may be used for the production of myofibrillar protein aggregates with enhanced functional properties.     

Thermophysical properties of processed meat and poultry products

Thermophysical properties of various meat and poultry emulsions were evaluated at four temperatures (20, 40, 60 and 80 °C). Thermal conductivities (0.26–0.48 W m⁻¹ K⁻¹) increased linearly with temperature between 20 and 60 °C. Between 60 and 80 °C, it remained constant for most products except bologna. Curves for thermal conductivity as a function of temperature could be roughly grouped into two different categories: products containing meat particles and those containing meat emulsions. The application of various models was investigated for thermal conductivity prediction. It was found that a three phase structural based Kirscher model had the potential for predicting thermal conductivities with acceptable accuracy. Densities decreased slightly as a function of temperature from 20 to 40 °C. A transition phase was observed from 40 to 60 °C, which was followed by a decrease from 60 to 80 °C. There was a decrease of about 50 kg m⁻³ between the density of a raw product at room temperature (at maximum 1070 kg m⁻³) and the product heated to 80 °C (at minimum 970 kg m⁻³), due to the gelation or setting of the structure. After a transition period from 10 to 30 °C, the heat capacity increased linearly from 30 to 80 °C, and ranged from 2850 to 3380 J kg⁻¹ °C⁻¹, respectively. Densities and heat capacities were strongly influenced by the carbohydrate content (i.e. as the carbohydrate content increased the density decreased). The salt content adversely affected thermal conductivity and thermal diffusivity values. However, these parameters increased with moisture content.