Influence of muscle type on rheological properties of porcine myofibrillar protein during heat-induced gelation

The gelation characteristics of myofibrillar proteins are indicative of meat product texture. Defining the performance of myofibrillar proteins during gelation is beneficial in maintaining quality and developing processed meat products and processes. This study investigates the impact of pH on viscoelastic properties of porcine myofibrillar proteins prepared from different muscles (semimembranosus (SM), longissimus dorsi (LD) and psoas major (PM)) during heat-induced gelation. Dynamic rheological properties were measured while heating at 1 °C/min from 20 to 85 °C, followed by a holding phase at 85 °C for 3 min and a cooling phase from 85 to 5 °C at a rate of 5 °C/min. Storage modulus (G′, the elastic response of the gelling material) increased as gel formation occurred, but decreased after reaching the temperature of myosin denaturation (52 °C) until approximately 60 °C when the gel strength increased again. This resulted in a peak and depression in the thermogram. Following 60 °C, the treatments maintained observed trends in gel strength, showing SM myofibrils produced the strongest gels. Myofibrillar protein from SM and PM formed stronger gels at pH 6.0 than at pH 6.5. Differences may be attributed to subtle variations in their protein profile related to muscle type or postmortem metabolism. Significant correlations were determined between G′ at 57, 72, 85 and 5 °C, indicating that changes affecting gel strength took effect prior to 57 °C. Muscle type was found to influence water-holding capacity to a greater degree than pH.     

Surface functional properties of blood plasma protein fractions

The solubility, foaming and emulsifying properties of porcine blood plasma and its main protein fractions (serum, globulins and albumin) were investigated at pH 4.5, 6.0 and 7.5 in order to clarify the contribution of each fraction and encourage the optimisation of plasma-derived products. Soluble protein contents above 85% were obtained in all samples. Plasma, serum and albumin showed good foaming capacities, reasonably similar at different pH conditions, although the highest foam stability corresponded to both albumin and plasma at pH 4.5 and 6.0. All protein fractions showed good emulsifying activities, but the stability of the formed emulsions decreased with acidification, being emulsions of albumin and globulins at pH 7.5 the most stable ones. In addition, the interaction indexes calculated to investigate protein–protein interactions revealed synergistic interactions between albumin and globulins when in co-occurrence in their foaming capacity at pH 6.0 and 7.5, and in the stability of emulsions at pH 4.5 and 6.0, but slightly negative effects in the solubility of the mixture, and a great decrease in the stability of emulsions at pH 7.5. On the other hand, the elimination of fibrinogen improved the stability of emulsions and foams at acidic conditions.     

Functional properties of isolated porcine blood proteins

The isolated proteins contained in the blood from slaughterhouses could be recovered and used to improve the functional and nutritional properties of food products. In this work some functional properties, namely solubility, emulsifying capacity, gelling and foaming capacity have been tested for different protein fractions of porcine blood. The blood proteins studied were globins (α, β and γ), albumin and fibrinogen and the whole plasma from the plasmatic fraction, and haemoglobin and globin obtained from the haemoglobin by a chemical method from the cellular fraction. The effect of pH and protein concentration on functional properties was determined. Results indicate that blood proteins present good functional properties specially solubility, gellation and emulsifying capacities that could make blood protein useful as food additives in the formulation of food products.     

Effect of peanut protein isolate on functional properties of chicken salt-soluble proteins from breast and thigh muscles during heat-induced gelation

In this study, we investigated the impact of peanut protein isolate (PPI) on the functional properties of chicken salt-soluble protein (SSP) prepared from breast and thigh muscles during heat-induced gelation. The addition of PPI increased the water-holding capacity, gel strength and elasticity of heat-induced chicken SSP mixed gel. Breast and thigh SSP had the best gel properties at the addition of 2.5% and 3.5% PPI, respectively. Rheology indicated that thigh SSP showed higher storage modulus (G') than breast SSP. Differential scanning calorimetry showed that the addition of PPI changed transition temperatures (Tmax) and enthalpy of denaturation (ΔH) of chicken SSP. Scanning electron microscopy indicated that the PPI-treated SSP gels had more compact ultrastructures than controls. The results suggested that PPI may be a potential protein additive for improve the characteristics of SSP gelations.     

Improvement of gelling properties of porcine blood plasma using microbial transglutaminase

The effect of microbial transglutaminase (MTGase) on the texture and water-holding capacity (WHC) of heat-induced gels prepared from porcine blood plasma at pH 5.5 was investigated. Different concentrations of commercial MTGase were added to plasma and incubated for several times under specific conditions of temperature and pH. From the results obtained, it can be postulated that enzymatic treatment enhances textural properties and WHC of plasma gels at pH 5.5, especially when incubated with 3% of the commercial product for 3 h at 30 °C and pH 7. This treatment increased by 0.4 N the hardness of gels and reduced by 3% the water released after gel centrifugation with respect to the control samples. SDS–PAGE confirmed that cross-linking took place when MTGase was added to plasma solutions. However, the results suggest that the sole addition of MTGase was not effective enough to improve the gelling properties of plasma proteins under acidic conditions.     

Study of the denaturation/aggregation behaviour of whole porcine plasma and its protein fractions during heating under acidic pH by variable-temperature FTIR spectroscopy

Variable-temperature (VT) Fourier transform infrared (FTIR) spectroscopy was employed to examine changes in secondary structure of whole plasma proteins as well as of plasma protein fractions (serum, serum albumin and globulins) upon heating at pH 4.5 and to establish their kinetics of thermally induced protein aggregation through formation of non-native intermolecular beta-sheets. A detailed analysis of the amide I′ band in the VT-FTIR spectra indicated that plasma proteins were more thermally sensitive at pH 4.5 than at pH 7.5 both when found as mixtures and in monomolecular systems, with the thermal aggregation being strongly enhanced under acidic conditions, particularly in the case of serum albumin. Comparison of the spectral changes of plasma and serum (fibrinogen-depleted plasma) during heating indicated that fibrinogen has no role in protein aggregation under acidic conditions, in contrast to findings at pH 7.5. Considering the particular characteristics of the different plasma proteins, the strong predominance of positive charges in the plasma as a whole at pH 4.5 along with the effects of these pH conditions on the conformation of fibrinogen could be suggested as the main factors responsible for the lack of a contribution by fibrinogen to protein aggregation. Moreover, 2D correlation spectroscopy indicated that the sequence of structural changes occurring during heating was practically identical among the different protein fractions examined and completely different from that established at pH 7.5, with the native beta-sheets being now more heat-sensitive than the alpha-helical structures and with protein aggregation through the formation of intermolecular beta-sheets beginning after native beta-sheets started to unfold.     

Characteristics and antioxidative activity of Maillard reaction products from a porcine plasma protein–glucose model system as influenced by pH

Maillard reaction products (MRPs) were prepared by heating the solution containing 2% porcine plasma protein (PPP) and 2% glucose adjusted to various pHs (8, 9, 10, 11 and 12) at 100 °C for different times (0, 2, 4, 6 and 8 h). The pH of all MRPs markedly decreased within 2 h of heating time. Browning and intermediate products, as monitored by absorbance at 420 nm and absorbance at 294 nm, sharply increased within 2 h (P < 0.05). Thereafter, slight increases were observed up to 8 h. Fluorescence intensity (Ex 347 and Em 415 nm) sharply increased within the first 2 h with a subsequent decrease when heating time increased (P < 0.05). Increases in browning and formation of intermediate products were concomitant with the decreases in free amino group and reducing sugar contents. Among all MRPs tested, those derived from the PPP–glucose system at pH 12 rendered the highest browning and intermediate products. However, no differences in reducing power or DPPH radical-scavenging activity of MRPs with initial pH ranges of 10–12 were noticeable. Electrophoretic study revealed that cross-linked proteins with high molecular weight were formed in the PPP–glucose model system to a greater extent at pHs 8 and 9, than at pHs 10–12. Nevertheless, heating times had no pronounced effect on protein pattern of glycated proteins.     

Scale-up of the process to obtain functional ingredients based in plasma protein concentrates from porcine blood

The feasibility of a scaled-up process to obtain two protein concentrates from porcine blood plasma, i.e. serum and albumin, for use as functional food ingredients was assessed. The process consisted of fractionating plasma proteins by salting out, concentrating and purifying fractions by means of membrane technology, and subsequently dehydrating through spray-drying. The fractionation process allowed a good isolation of the desired proteins, which were then concentrated and desalted in a tangential flow filtration (TFF) process combining ultra and diafiltration. Purification, pre-concentration and dehydration were successfully achieved. The functional properties of dehydrated serum and albumin were determined. As compared to the same hemoderivatives obtained by a lab-scale production system, serum maintained the gelling properties; albumin exhibited similar foaming properties; and both serum and albumin concentrates showed slightly improved emulsifying properties.     

Antioxidant activity and functional properties of porcine plasma protein hydrolysate as influenced by the degree of hydrolysis

Antioxidant activity and functional properties of porcine blood plasma protein hydrolysates (PPH) prepared with Alcalase at 6.2%, 12.7% and 17.6% of degree of hydrolysis (DH) were investigated. The PPH showed stronger radical-scavenging ability and possessed stronger Cu²⁺-chelation ability and a reducing power compared to non-hydrolysed plasma protein (P < 0.05). The antioxidant activity of PPH, indicated by thiobarbituric acid-reactive substance (TBARS) values in a liposome-oxidising system, increased with increasing DH (P < 0.05). The Alcalase hydrolysis increased protein solubility from its original 68.46–81.79% (non-hydrolysed) to 82.95–94.94% (hydrolysed) over a broad pH range (3.0–8.0). However, hydrolysis decreased surface hydrophobicity and suppressed emulsifying and foaming capacity of the plasma protein. To identify antioxidant peptide, PPH was subjected to ultrafiltration, ion-exchange chromatography and reverse-phase high performance liquid chromatography (RP-HPLC), and the amino acid sequences of isolated peptides were determined by liquid chromatography/tendem mass spectrometry (LC–MS/MS). The peptide with the strongest antioxidant activity had the amino acid sequence of His-Asn-Gly-Asn. The results indicated that PPH could be used as a novel antioxidant but may be of limited utility as an emulsifying or foaming agent.     

Heat-induced denaturation/aggregation of porcine plasma and its fractions studied by FTIR spectroscopy

The aim of the present work is the in depth study of the protein aggregation mechanisms of whole porcine plasma and its fractions (serum, albumin and globulins) during heating using FTIR spectroscopy. Also, 2D correlation spectroscopy (2D COS) was used to establish the sequence of events during heat-induced gelation for all fractions. The results indicate that serum albumin quickly aggregates from 70 °C through non-native intramolecular β-sheets while globulins show lower susceptibility to protein aggregation. When found together, the aggregation pattern strongly depends on the composition of the protein mixture. That makes the great difference between plasma (serum albumin + globulins + fibrinogen) and serum (serum albumin + globulins) behavior, with the aggregation degree at the end of the thermal process being enhanced in the presence of fibrinogen - and achieving a similar level to that of serum albumin - while minimized in its absence. Attending on the low content of fibrinogen in plasma, our results suggest a great fibrinogen ability to alter the thermal serum albumin and globulins behavior by modifying the negative interactions established between them when no more proteins are found in the media. Moreover, it is noteworthy the slow plasma aggregation pattern at the beginning of the thermal process relative to serum albumin, this way allowing a higher protein unfolding. This could be related to the high heat-induced gel properties of plasma. Also, 2D COS indicates that the sequence of events is very similar for the all analyzed samples, with α-helix being more thermo-labile than native β-sheet structure.     

Determination of androstenone levels in porcine plasma by LC-MS/MS

Androstenone (5α-androst-16-en-3-one) is a major component in boar taint. Here, a liquid chromatography-tandem mass spectrometry method was developed to analyse androstenone in porcine plasma to facilitate studies of its transport from pig testes to adipose tissues. The method used androstanone (5α-andro-stan-3-one) as internal standard, Oasis® MCX solid-phase extraction, C18 reversed-phase column, and API 5000 Triple Quadrupole mass spectrometry with positive electrospray ionisation interface operating in the multiple reaction monitoring mode. Incubation of the plasma samples with β-glucuronidase/arylsulfatase revealed an increase in androstenone yield indicating the presence of a conjugated form of its 3-enol isomer. With this method the limit of detection (LOD) was 1.0 ng and the limit of quantification (LOQ) was 3.3 ng per mL of plasma. In conclusion, the presented method is sensitive and reproducible and thus suitable for accurate quantification of androstenone levels in a small volume of porcine plasma.     

Effectiveness of high pressure processing on the hygienic and technological quality of porcine plasma from biopreserved blood

The effects of a high hydrostatic pressure (HHP) treatment (450MPa, 15min at 20°C) on both the microbiological quality and the functional properties of plasma from biopreserved porcine blood were evaluated. Blood was inoculated with Enterococcus raffinosus-PS99 (10(7)ufcmL(-1)) and stored at 5°C. After 72-h storage, bacterial counts in inoculated samples decreased by 52, 70, 81 and more than 99% for coliforms, Pseudomonas spp, hemolytic and proteolytic bacteria, respectively. Counts of these bacterial groups were undetectable in the final product after pressurization, whereas total lactic acid bacteria were detected at levels up to 10(2)ufcmL(-1). Gelling, foaming and emulsifying properties of the plasma proteins were not noticeably affected by HHP. The results show that it is possible to obtain high-quality and microbiologically stable blood derivatives as functional ingredients, by combining biopreservation and HHP.     

Color improvement by titanium dioxide and its effect on gelation and texture of proteins recovered from whole fish using isoelectric solubilization/precipitation

Whiteness is a critical attribute for restructured fish products such as surimi seafood. However, the whiteness of gels made from proteins recovered from fish processing by-products or whole fish using isoelectric solubilization/precipitation is poor. The by-products and whole fish contain bones, scales, skin, etc. that affect gel color. Therefore, whiteness needs to be improved if marketable products are to be developed from recovered proteins. The objectives of this study were to determine effects of titanium dioxide (TiO₂) on: (1) color; (2) texture; and (3) viscoelasticity (G′) of gels made from isolated carp proteins and Alaska pollock surimi. Carp proteins were recovered with isoelectric solubilization/precipitation. TiO₂ was added to carp proteins at 0-0.5 g/100 g. TiO₂ was not added to surimi. Due to much higher (P < 0.05) yellowness (b^∗) and lower (P < 0.05) lightness (L^∗), the whiteness of carp gels without TiO₂ was lower (P < 0.05) than surimi gels. TiO₂ at ≥ 0.2 g/100 g resulted in better (P < 0.05) whiteness of carp gels than surimi gels without chalky and artificially white appearance. TiO₂ did not affect texture or viscoelasticity. This research demonstrates that whiteness of restructured fish products based on proteins recovered from whole fish via isoelectric solubilization/precipitation can be similar to the whiteness of surimi seafood.     

Functional and quality characteristics of the red blood cell fraction from biopreserved porcine blood as influenced by high pressure processing

The effects of high hydrostatic pressure (HHP) processing, at 400 MPa for 15 min at 20 °C, on the microbiological and functional characteristics of the red blood cell (RBC) fraction obtained from porcine blood, previously preserved by means of lactic acid bacteria (LAB) was studied. Biopreservation was achieved by incubation of inulin-enriched blood inoculated with a LAB strain (Enterococcus raffinosus PS99) for 72 h at 5 °C. Results showed that incubation of blood with added E. raffinosus followed by HHP treatment reduced the levels of contaminant coliforms, proteolytic, hemolytic bacteria, and Pseudomonas spp. on RCB. Color parameters, protein solubility, foaming and emulsifying properties, as well as texture and water holding capacity of heat-induced gels from RBC were not seriously damaged by the combined treatments. This is a new approach to process and preserve animal blood fractions for the development of functional and/or nutritional food ingredients with added value.     

Heat-induced gel formation of plasma proteins: New insights by FTIR 2D correlation spectroscopy

Generalized 2D correlation spectroscopy (COS) has been applied to FTIR spectra of porcine plasma proteins to elucidate the sequence of events leading to pH- and/or thermal-induced protein unfolding and aggregation. Changes in the amide I′ region of the infrared spectra (in the pH range between 7.5 and 4.5, at 0.5 pH intervals) at 30 °C were especially evident as the pH approached the pI of serum albumin (4.8), with the globulin fraction in the plasma proteins undergoing denaturation prior to serum albumin. The effect of increasing temperature (from 30 to 90 °C, in increments of 5 °C) on the secondary structure of the plasma proteins at pHs in the range of 7.5–6.0 revealed that a decrease in alpha-helical structures is taken place previously to diminish native beta-sheets. So, the overall results of this study demonstrate that serum albumin and the globulin fraction differ in their sensitivity to pH and temperature.     

Heat-induced gelation of whey protein at high pH studied by combined UV spectroscopy and refractive index measurement after size exclusion chromatography and by in-situ dynamic light scattering

Summary The interactions between β-lactoglobulin and α-lactalbumin involved in gelation at 67.5 °C at high pH and low salt concentration were studied by size exclusion chromatography, followed by UV and refractive index measurements, and by in-situ dynamic light scattering. This was achieved by choosing whey protein samples with different proportions of the two proteins. The ratio of absorbance at 280 nm to the refractive index was used to demonstrate that α-lactalbumin was incorporated in aggregates and gels and drastically changed the properties of the gel, making them much more turbid than the transparent gels formed by β-lactoglobulin alone at the same pH and ionic strength. At a ratio of 1:2 for α-lactalbumin relative to β-lactoglobulin in the samples, the gel consisted of a 1:1 mixture of the two proteins. The aggregates present after 10 min of heating at 67.5 °C had molar mass of about 6.10⁶ g/mol and a radius of gyration of about 40 nm. After gel formation the field autocorrelation function could be described as a power law over many decades of lag time for all samples, demonstrating selfsimilarity of the gel structure. The only exception to this was for the gel with high content of α-lactalbumin which showed an oscillatory behaviour of the autocorrelation function. Significant amounts of glycosylated caseino-macro-peptide were observed in many of the samples at the position of β-lactoglobulin. However it did not affect gelation as it remains in solution.     

Characteristics of pressurised pork meat batters as affected by addition of plasma proteins,apple fibre and potato starch

Pork meat (low‐fat) batters were prepared without and with the addition of three non‐meat ingredients: (blood) plasma proteins, (dietary) apple fibre and potato starch. The batters were processed by cooking‐alone (70 °C) and by high‐pressure/temperature combination (400 MPa/70 °C). Protein denaturation and starch gelatinisation through the different processings were followed by differential scanning calorimetry. Batter characteristics such as water holding (weight loss) and different texture parameters (texture profile analysis) were used as quality criteria for comparisons among different formulations and processes. Plasma proteins and apple fibre behaved as inert fillers in both kinds of processed batters. Potato starch effects depended on processing conditions to the extent that these influenced the degree of gelatinisation. In pressurised batters (pressure and heating in sequence), regular preservation effects against subsequent thermal denaturation of proteins were observed. Differential scanning calorimetry revealed that starch was also pressure‐preserved from subsequent thermal gelatinisation, which was confirmed by scanning electron microscopy. The presence of native‐like proteins and ungelatinised starch produced cumulative softening effects in pressurised batters. © 2000 Society of Chemical Industry     

Preservation of porcine blood quality by means of lactic acid bacteria

The capacity of 12 lactic acid bacteria (LAB) strains to preserve porcine blood during storage was evaluated. A general ability of LAB to prevent blood's hemolysis and to maintain the functional properties of plasma was observed. Two strains, PS99 (Enterococcus raffinosus) and TA43 (Lactobacillus reuteri), were selected for studies at 5°C according to their antibacterial activity in blood stored at 15°C. After 144h at 5°C, lower counts of coliforms, Pseudomonas spp., proteolytic and hemolytic bacteria were obtained in blood containing either PS99 or TA43 as compared to the non-inoculated blood. When inulin (2%) was added to blood, higher inhibition values were obtained and Enterococcus raffinosus (PS99) showed the best abilities for blood preservation. On the basis of these results it seems worthwhile to supplement blood with inulin and to inoculate it with an active LAB strain to avoid undesirable changes during chill storage, especially useful to prevent the effects of a cold-chain breakdown.     

Gelation properties of previously cooked minced meat from Jonah crab (Cancer borealis) as affected by washing treatment and salt concentration

The influence of washing treatment (dewatered only, one wash, and three washes) and sodium chloride (NaCl) concentration (0%, 2%, and 4%) on the gelation properties of crab mince was investigated. This previously cooked muscle mince is a low-value by-product of the crab processing industry, considered to have little or no functional properties. Crab mince gels were produced and tested for water-holding capacity (WHC), gel strength, colour, and electrophoretic profile. Wash treatment and NaCl concentration significantly affected gelation. Washed samples exhibited significantly higher WHC than dewatered samples. The 4% NaCl treatment decreased WHC compared to lower NaCl levels. Multiple washing steps increased the force to gel deformation. Wash treatment and NaCl concentration also affected the colour of gels. Based on these results, cooked crab meat mince treated with three washes and 0% NaCl resulted in the strongest gels with the best water-holding capacity, which can be used in the development of value-added products.     

Protein co-precipitates from milk and blood plasma: Preparation and investigation of some functional properties

Various processing methods were investigated for the production of milk and porcine blood plasma co-precipitates. Factors considered included pH and temperature treatments as well as the ratio of milk to plasma proteins in mixtures of the raw materials. The recovery of protein in precipitates was measured and the following method was selected accordingly for further studies: pH adjustment of skim milk and blood plasma mixtures to pH 9.5, heating to 70° C, readjustment of pH to 9.5, holding for 3 min, cooling to 68°C, pH adjustment to 3–5, holding for 5 min, cooling to ambient temperature and final pH adjustment to 4.7. Two co-precipitates (70/30 M/P and 30/70 M/P) were prepared from a 70:30 and a 30:70 mixture of skim milk (M) and blood plasma (P). Some of the functional properties of these preparations were measured and compared with those of total milk protein (TMP) and blood plasma precipitate (P) prepared by the same procedure as well as acid-precipitated casein. The protein contents of preparations freeze-dried at pH 7.0 varied between 91.5 and 92.3% and those freeze-dried at pH 4.7 varied between 93.1 and 96.0%. The solubility profile and emulsifying capacity of the 70/30 M/P compared favourably with those of caseinate and TMP. The solubilities of 30/70 M/P and 100% P were, however, poor. The viscosity of solutions of 70/30 M/P was considerably higher than those of caseinate and TMP solutions. Water adsorption isotherms of protein preparations were constructed and are presented in graphical form. Precipitates freeze-dried at pH 7.0 adsorbed more moisture than the same preparations freeze-dried at pH 4.7. These differences were especially evident a water activities >0.8.