Lipid and protein structure analysis of frankfurters formulated with olive oil-in-water emulsion as animal fat replacer

Lipid and protein structural characteristics of frankfurter formulated with olive oil-in-water emulsion stabilized with soy protein isolate (SPI) as pork backfat replacer were investigated using Fourier transform infrared spectroscopy (FT-IR). Proximate composition and textural properties were also evaluated. Different frankfurters were reformulated: F/PF with pork backfat, F/SPI with oil-in-water emulsion stabilized with SPI and F/SPI + SC + MTG with emulsion stabilized with a combination of SPI, sodium caseinate (SC) and microbial transglutaminase (MTG). Replacement of pork backfat with these emulsions produced an increase (P < 0.05) of hardness, springiness, cohesiveness and chewiness but a reduction (P < 0.05) of adhesiveness. F/SPI and F/SPI + SC + MTG frankfurters showed the lowest (P < 0.05) half-bandwidth in the 2922 cm⁻¹ band, which could be related to lipid chains were more ordered than in F/PF. Modifications in the amide I band profile revealed a higher concentration of aggregated intermolecular β-sheets in F/SPI + SC + MTG samples. Lipid and protein structural characteristics could be associated with specific textural properties of healthier frankfurters.     

Olive oil-in-water emulsions stabilized with caseinate: Elucidation of protein–lipid interactions by infrared spectroscopy

This paper reports a FT-IR study for probing lipid and protein structural changes and their interactions in various oil-in-water emulsions. Two different emulsions were prepared using sodium caseinate, as stabilizer system, without and with microbial transglutaminase (MTG), denominated E/SC and E/SC + MTG respectively. Proximate composition, fat and water binding properties and textural characteristics were also evaluated in the emulsions. Penetration force and gel strength values were used to distinguish different (P < 0.05) textural behaviours depending on the formulation of emulsifying system. E/SC + MTG emulsion showed gel textural behaviour while E/SC lack of this property. The spectral results showed frequency upshifting of the amide I band in going from protein stabilizer systems isolate (the solution used as reference) to their corresponding emulsions, what is attributable to greater protein structural order upon emulsion formation. Enzymatic action of MTG in the sodium caseinate stabilizing system induces structural changes, in terms of lipid chain disorder or lipid–protein interactions and protein secondary modifications, which may reflect the formation of a gel structure in the emulsion. These results could help to choose the stabilizing system that is most suitable and effective for its use in the formulation of food products.     

Raman spectroscopic study of the effects of microbial transglutaminase on heat-induced gelation of pork myofibrillar proteins and its relationship with textural characteristics

The effects of microbial transglutaminase (MTG) on heat-induced gelation of pork myofibrillar proteins (PMP) structural changes, textural properties were studied by Raman spectroscopy and texture profile analysis (TPA), respectively. And the relationships between the structural changes and textural characteristics were estimated by principal component analysis (PCA). Changes in the Raman spectra were interpreted as the occurrence of secondary structural changes in myofibrillar proteins with MTG added. Modifications in the amide I (1600-1700 cm^− 1) regions indicated a significant (p < 0.05) decrease in ??-helix content, accompanied by a significant (p < 0.05) increase in ??-sheets, ??-turns and random coil content due to the addition of the enzyme. Obvious texture property changes were also determined by TPA. All these changes showed a strong, irreversible heat-induced gel formed due to the addition of MTG. The application of a dimensionality reducing technique such as PCA proved to be useful to determine the most influential properties of heat-induced gel. Significant (p < 0.05) correlations were found between these structural changes and the textural characteristics (hardness) in PMP system with the addition of MTG by PCA. The hardness was related positively to fraction of ??-sheet, ??-turns and random coil, and negatively to normalized intensity of 760 cm^− 1 and fraction of ??-helix. The samples are closely grouped in a cluster defined by level of MTG.     

Effect of non-meat proteins on hydration and textural properties of pork meat gels enhanced with microbial transglutaminase

The combined effect of incorporation of four non-muscle proteins, NMP (blood plasma, BP; sodium caseinate, SC; soy protein isolate, SPI; gelatin, G) at 2 g/100 g levels on hydration and textural characteristics of pork gels processed without or with 0.6 g/100 g microbial transglutaminase preparation (MTG) was investigated. Addition of SC and BP most favourably affected hydration properties and thermal stability, yielding lower cooking loss and expressible moisture for pork gels. Interactions between NMP and MTG were observed. Improvement of gel strength by addition of transglutaminase was observed for treatments containing SC and BP but not G nor soy isolate. Of the four proteins tested SC was found to be a superior substrate for MTG in enhancing textural properties of a gelled meat system. None of the tested ingredients was able to yield gel cohesiveness equivalent to the control containing 8% muscle proteins. Results of this study indicate a potential for using MTG to improve or modify the functional and textural properties of investigated food proteins (SC and BP in particular) in comminuted meat products.     

Antioxidant and emulsifying properties of potato protein hydrolysate in soybean oil-in-water emulsions

The efficacy of a previously developed antioxidative potato protein hydrolysate (PPH) for the stabilisation of oil droplets and inhibition of lipid oxidation in soybean oil-in-water (O/W) emulsions was investigated. Emulsions (10% lipid, pH 7.0) with PPH-coated oil droplets were less stable than those produced with Tween 20 (P < 0.05). However, the presence of PPH, whether added before or after homogenisation with Tween 20, retarded emulsion oxidation, showing reduced formation of peroxides up to 53.4% and malonaldehyde-equivalent substances up to 70.8% after 7-d storage at 37 °C (P < 0.05), when compared with PPH-free emulsions. In the emulsions stabilised by PPH + Tween 20, 8–15% of PPH was distributed at the interface. Adjustment of the pH from 3 to 7 markedly increased ζ-potential of such emulsions (P < 0.05). Inhibition of lipid oxidation by PPH in soybean O/W emulsions can be attributed to both chemical and physical (shielding) actions.     

Physicochemical characterisation and oxidative stability of fish oil and fish oil–extra virgin olive oil microencapsulated by sugar beet pectin

Spray-dried microcapsules were prepared at 25% and 50% w/w oil load from sugar beet pectin-stabilised emulsions (pH 3) containing fish oil, and a blend of fish oil and with extra virgin olive oil (1:1 w/w). Microencapsulation efficiencies were high (≥90%). However, deterioration in microcapsule wall integrity and an increase in oil droplet size were observed during storage (25 °C, 0–3 months). Lipid oxidation increased with both increased oil load (P < 0.05) and storage duration (P < 0.05), but was independent of oil composition (P > 0.05). These results suggest that sugar beet pectin functions poorly as a wall material and its residual metal ions exacerbate omega-3 oxidation, despite the presence of endogenous antioxidants found in extra virgin olive oil. Interestingly, under accelerated storage conditions (OxiPres® at 80 °C, 0.5 bar oxygen pressure), microcapsules containing the oil blend showed the best oxidative stability (P < 0.05), irrespective of oil load. A possible explanation for the superior oxidative stability of the microencapsulated oil blend at high storage temperature is discussed.     

Microbial transglutaminase and caseinate as cold set binders: Influence of meat species and chilling storage

The effect of microbial transglutaminase/sodium caseinate (MTG/C) systems on meat batter characteristics (water binding and textural properties of raw and cooked products) was studied in the presence of NaCl (1.5 g/100 g) and sodium tripolyphosphate (0.5 g/100 g), and storage time (96 h at 3 °C) for three meat species (pork, chicken, lamb). Samples prepared from pork and lamb with only MTG/C (no salts) had the highest cooking loss (CL) values, about 23 and 29 g/100 g, respectively; for chicken, the CL was less than 13 g/100 g. Hardness (Hd) and chewiness (Cw) generally tended to be higher in cooked samples containing MTG/C than in samples containing only salts. Products combining salts and MTG/C had higher (P<0.05) Hd and Cw. The efficiency of the MTG/C system as a texture conditioner of cooked products varied with the meat source.     

Stabilization of acidic soy protein-based dispersions and emulsions by soy soluble polysaccharides

Soy soluble polysaccharides (SSPS) are shown to prevent destabilization of soy protein isolate (SPI) dispersions and SPI-based oil-in-water (O/W) emulsions under acidic conditions. Addition of SSPS above a critical concentration (0.25 wt%) increased the stability of 0.50 wt% SPI dispersions against aggregation and phase separation under conditions where SPI would normally precipitate (near its isoelectric point). Though SSPS neutralized SPI surface charge via electrostatic interaction, there was increased stability against aggregation due to steric repulsion. At acidic pH, addition of 1 wt% NaCl electrostatically screened protein–polysaccharide complexation which led to SPI precipitation and sedimentation. However, the order of salt addition had a significant impact on charge screening, with salt added before pH adjustment reducing SPI–SSPS complexation whereas it had less effect when added afterwards. Salt penetration efficacy diminished with decreasing pH. O/W emulsions (5 wt% oil) prepared with 0.50 wt% SPI destabilized at pH 4–5 due to protein aggregation, but addition of ≥0.25 wt% SSPS improved emulsion stability by inhibiting protein–protein interactions thus limiting increases in oil droplet diameter over time. Overall, both dispersion and emulsion stability greatly depended on pH, ionic strength and SSPS concentration. These results demonstrated that SSPS could effectively stabilize acidic SPI dispersions and that SPI–SSPS interactions may be used as a tool to improve the kinetic stability of SPI-based O/W emulsions.     

Low-fat frankfurters formulated with a healthier lipid combination as functional ingredient: microstructure, lipid oxidation, nitrite content, microbiological changes and biogenic amine formation

Oil (healthier lipid combination of olive, linseed and fish oils)-in-water emulsions stabilized with different protein systems (prepared with sodium caseinate (SC), soy protein isolate (SPI), and microbial transglutaminase (MTG)) were used as pork backfat replacers in low-fat frankfurters. Microstructure, lipid oxidation, nitrite content, microbiological changes and biogenic amine formation of frankfurters were analyzed and found to be affected by the type of oil-in-water emulsion and by chilling storage (2° C, 41 days). Although the lipid oxidation levels attained were low, replacement of animal fat by healthier oil combinations in frankfurter formulation did promote a slight increase in lipid oxidation. Residual nitrite was affected (P < 0.05) by formulation and storage. Only 51-61% of the added nitrite was detectable in the product after processing and 17-46% at the end of storage. The microbial population was low in all formulations during chilling storage. Spermine was the most abundant amine (19-20 mg/kg), but similar in level to all samples.     

The use of microbial transglutaminase and soy protein isolate to enhance retention of capsaicin in capsaicin-enriched layered noodles

Specialty layered noodles (LN) were prepared by sandwiching a capsaicin-enriched dough (CED) between two gastro-resistant dough layers made up of wheat flour, soy protein isolate (SPI) and microbial transglutaminase (MTG) at 0.5 (0.5MTG LN), 1.0 (1.0MTG LN) and 1.5 (1.5MYG LN) g/100 g of wheat-SPI flour. The textural, tensile and structural breakdown properties, capsaicin retention, microstructures and the sensory characteristics of cooked LN were evaluated. Compared to other LN, 1.5MTG LN exhibited the highest textural and tensile parameters, highest capsaicin retention, densest structure and was the most difficult to breakdown. The sensory quality of all LN was acceptable, even though it was the Control LN (prepared without SPI and MTG) that scored the highest acceptability. In general, increasing the level of MTG in the sandwiching dough layers of MTG LN reduced the release of capsaicin in simulated mouth, gastric and intestinal conditions, and these results could be due to increased protein cross-linking.     

Influence of pH and CaCl2 on the stability of dilute whey protein stabilized emulsions

The influence of pH and CaCl₂ on the physical stability of dilute oil-in-water emulsions stabilized by whey protein isolate has been studied. The particle size, zeta potential and creaming stability of 0.05 wt% soy bean oil-in-water emulsions (d ≈ 0.53 μm) were measured with varying pH (3 to 7) and CaCl₂ concentration (0 to 20 μM). In the absence of CaCl₂ extensive droplet aggregation occurred around the isoelectric point of the whey proteins (4 < pH < 6) because of their low electrical charge, which led to creaming instability. Droplet aggregation occurred at higher pH when CaCl₂ was added to the emulsions. The minimum concentration of CaCl₂ required to promote aggregation increased as the pH increased. Aggregation was induced in the presence of CaCl₂ probably because of the reduction in electrostatic repulsion between droplets, caused by binding of counter ions to droplet surfaces and electrostatic screening effects.     

Improvement of physicochemical stabilities of emulsions containing oil droplets coated by non-globular protein-beet pectin complex membranes

The potential of beet pectin for improving the physical and chemical stabilities of emulsions containing silk fibroin coated droplets was investigated. Five wt.% corn oil-in-water emulsions containing fibroin-coated droplets (0.5 wt.% fibroin) and anionic pectin (0.05 wt.%) were prepared at pH 7. The pH of these emulsions was then adjusted to pH 4, so that the anionic pectin molecules electrostatically deposited to the fibroin-coated droplets. The influence of pH (3 to 7) and sodium chloride concentrations (0 to 500 mM) on the properties of primary (0 wt.% pectin) and secondary (0.05 wt.% pectin) emulsions was studied. Pectin was deposited to the droplet surfaces at pH 3, 4, and 5, but not at pH 6 and 7. In addition, secondary emulsions were stable up to higher ionic strengths (< 500 mM) than primary emulsions (< 200 mM). The addition of beet pectin also prolonged the lag phase of lipid oxidation in the emulsions as determined by the formation of lipid hydroperoxides and headspace hexanal. The controlled electrostatic deposition method utilized in this study could be used to extend the range of application of silk fibroin in the industry.     

Real-time measurement of oxygen transport across an oil-water emulsion interface

A method for real-time, in situ measurement of oxygen transport across oil-in-water emulsion interface was developed. This method is based on reversible fluorescence quenching of tris ruthenium (II) bis (hexafluorophosphate) complex dye encapsulated in the oil phase of an emulsion upon interaction with oxygen. Oxygen transport across the oil-water interface for four different emulsions (whey protein isolate (WPI), sodium-dodecyl sulphate (SDS), cross-linked WPI and SDS-chitosan emulsions) was measured and effective diffusion coefficients were calculated. Results show that cross-linking of WPI did not alter the oxygen transport rate (p > 0.01), while addition of a chitosan layer to the SDS emulsion significantly reduced the oxygen transport rate (p < 0.01). An increase in temperature from 25 to 40 °C reduced the oxygen transport rate in WPI and cross-linked WPI emulsions (p < 0.01). Effective diffusion coefficient values for transport of oxygen based on fluorescence data were 0.14-1.15 × 10⁻¹² cm²/s for the tested emulsions. Regardless of relatively low effective diffusion coefficients, the selected emulsions exhibited poor barrier properties in limiting oxygen transport across an emulsion interface. In summary, this rapid method is sensitive to detect changes in rate of oxygen transport due to changes in temperature and chemical composition of emulsion interface. This method can be used to screen and evaluate the barrier properties of encapsulation matrices leading to rational design of encapsulated structures.     

β-Conglycinin and glycinin soybean protein emulsions treated by combined temperature–high-pressure treatment

Most studies on functionality of soybean proteins have been made with total protein isolates, with the drawback to limit the knowledge of phenomena due to the important complexity of protein composition. In this study we have tried to better understand the behavior of soy emulsions by using their two partially purified fractions: β-conglycinin (7S) and glycinin (11S). Furthermore, we have assessed the combined effect of temperature (20–60 °C) and high pressure (0.1–600 MPa) on physicochemical, microstructural and rheological properties of oil-in-water emulsions prepared with 7S or 11S proteins at 7% (w/v). Our results show that 7S and 11S emulsions behaved differently under the combined treatments and that 7S protein was responsible for the global properties of soybean emulsions, whereas 11S proteins exerted a negligible effect. From 400 MPa and at 60 °C, we have noticed for 7S emulsions an increase of flocculation and gelation, largely confirmed by confocal microscopy due to aggregation between adsorbed and aqueous 7S proteins. Globally we have evidenced that temperature reinforces the effect of high pressure and that the threshold to obtain some changes is 400 MPa. The very different behavior of 7S and 11S proteins in emulsions under treatments could help to orientate their commercial use as function of planed treatments.     

Freeze-thaw stability of oil-in-water emulsions prepared with native and thermally-denatured soybean isolates

Freeze-thaw stability of oil-in-water emulsions prepared with native or thermally-denatured soy isolates (NSI and DSI, respectively) as the sole emulsifier and sunflower oil (? = 0.25) has been examined at various protein concentrations (0.5, 1.0 and 2.0% w/v), comparatively with sodium caseinate (SC). The freeze-thaw stability was assessed by measurements of particle size, oiling off and gravitational separation after isothermal storage at −20 °C for 24 h and further thawing. The oil phase remained in liquid state and the amount of ice formed was similar (>97%) whatever the sample type and protein concentration. At 0.5%, NSI and DSI emulsions where highly unstable, exhibiting a coagulated cream layer with appreciable oiling off (>25%), whereas those prepared with SC were more stable, due to their initial lower flocculation degree (FD %) and particle size. For all emulsions, the increase of protein concentration (0.5–2.0% w/v) improves the freeze-thaw stability as a consequence of a decrease of initial FD %. At 2.0%, where is enough protein to cover the interface, a lower coalescence stability of NSI emulsion respect to those prepared with NSI was observed after freeze-thawing. This result can be attributed to the high tendency to aggregation of native soy globulins at subzero temperatures. Notwithstanding this, unlike the SC emulsions, the formation of new flocs in soy isolates-stabilized emulsions during freeze-thawing cannot be totally controlled.     

Carcass and meat quality characteristics and fatty acid composition of tissues from Pietrain-crossed barrows and gilts fed an elevated monounsaturated fat diet

Fifty-one (Landrace∗Large White)∗Pietrain barrows and gilts were used to compare the effect of a diet rich in oleic acid (HO) by feeding a by-product of the olive industry (Greedy-Grass OLIVA®: 1.4% growing, 3.8% finishing) or a grain and soy diet (CONTROL) on carcass characteristics, meat quality and fatty acid profile of intramuscular and subcutaneous fat. Gilts had leaner (P < 0.05) carcasses with lower fat percentage in major primal cuts, and less (P < 0.05) saturated fat compared with barrows with no interaction (P > 0.05) between dietary treatment and gender. Source of dietary fat had no effect (P > 0.05) on primal cut yields, composition of major primal cuts, or carcass and meat quality characteristics. Intramuscular fat from HO fed pigs had higher (P < 0.05) percentage of saturated (SFA) and monounsaturated (MUFA) fatty acids, and lower (P < 0.05) polyunsaturated fatty acids (PUFA) and n-6:n-3 ratio compared with CONTROL animals (37.4% vs. 36.8%, 44.7% vs. 40.1%, 17.9% vs. 23.2%, and 18.9 vs. 21.8 ratio, respectively). Subcutaneous fat from pigs fed HO had greater (P < 0.05) MUFA percentage, lower (P < 0.05) SFA and PUFA percentage, and lower (P < 0.05) n-6:n-3 ratio than pigs fed CONTROL diet (51.4% vs. 48.0%, 30.5% vs. 32.9%, 18.1% vs. 20.1%, and 9.83 vs. 11.3 ratio, respectively). Intramuscular fat had higher proportion of SFA and lower of MUFA showing a higher degree of tissue saturation compared with subcutaneous fat. Feeding Greedy-Grass increased MUFA and decreased PUFA proportions in fat depots reducing the risk of production of carcasses that are soft and oily which result in lower technological and processing quality.     

Gelation properties of myofibrillar/pea protein mixtures induced by transglutaminase crosslinking

Gelation properties of mixtures of myofibrillar protein isolate (MPI)/pea protein isolate (PPI) were studied using a dynamic oscillatory rheometer and a texture analyzer to evaluate PPI as a possible meat product additive. The inclusion of microbial transglutaminase (MTG) increased the gel strength of MPI/PPI mixture (3% + 1%) more than it did for MPI (3%), but less than a 3% MPI, 1% soy protein isolate combination. The direct evidence of interaction between muscle and pea proteins in the form of new sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) bands was not found; however, the improvement in gel strength or gel peak force for the MPI/PPI mixture (3% + 1%) with inclusion of MTG suggested that some ? (γ-glutamyl) lysine (G-L) crosslinking occurred between muscle and pea proteins. It likely that pea protein acted as a non-gelling component and interspersed throughout the primary MPI gel network and the addition of MTG promoted partial crosslinking of MPI. Consequently, MTG is useful in improving gelation properties of heat-induced MPI/PPI gel.     

Complexation of curcumin with soy protein isolate and its implications on solubility and stability of curcumin

Curcumin, a natural polyphenolic food colourant, suffers a low bioavailability because of its low solubility and instability in aqueous solutions. Our study demonstrates that the food derived soy protein isolate (SPI) can form a complex with the curcumin. Fluorescence spectroscopy of the SPI–curcumin complex revealed that the complex is formed through hydrophobic interactions. Moreover, curcumin molecules quench the intrinsic fluorescence of SPI upon binding. Upon complexation, curcumin showed increased water solubility. Stability studies by UV spectroscopy showed that >80% of the curcumin was stable in the SPI–curcumin complex when dissolved in water, simulated gastric and intestinal fluids for 12 h, which would provide sufficient time for intestinal absorption. SPI–curcumin complex exhibits enhanced antioxidant activity and is capable of forming foam and emulsion, indicating its possible utilisation in food product formulation. This study suggests that SPI, being an edible protein, could be used as a material to encapsulate water-insoluble bioactive compounds in functional foods.     

Rheological and baking characteristics of batter and bread prepared from pregelatinised cassava starch and sorghum and modified using microbial transglutaminase

The effect of different concentrations (0, 0.5, 1 and 1.5 U/g) of microbial transglutaminase (MTG) on the creep-recovery properties of gluten-free batter prepared from pregelatinised cassava starch, sorghum and egg white was investigated. The test conducted in the rheometer had an instant loading of 80 Pa for 60 s and recovery of 0 Pa for 140 s. Increasing MTG concentration decreased the batters’ resistance to deformation and compliances but increased zero shear viscosity and elastic recovery. Changes in batter rheological properties were insignificant (P > 0.05) at MTG concentrations beyond 0.5 U/g. Crumb properties of gluten-free bread baked from the batter revealed that increasing MTG concentration increased (P < 0.05) crumb firmness and chewiness, whereas increasing incubation time decreased (P < 0.05) crumb cohesiveness, chewiness and resilience. There were no significant interaction effects (P > 0.05) between enzyme concentration and incubation time.     

Heat-induced changes in oil-in-water emulsions stabilized with soy protein isolate

The physicochemical properties of soy proteins stabilized oil-in-water emulsions were studied after heating at two different temperatures, 75 and 95 °C. The effect of changing the order of the process (heating the solution before emulsification, or heating the emulsion) was also studied. The heating temperatures were chosen as they are known to selectively cause denaturation of the two major proteins present in the soy protein isolate: β-conglycinin and glycinin. The thermal transitions observed for soy proteins adsorbed at the interface were different from those measured in protein solutions, suggesting that some changes occur in the structure of the soy proteins upon adsorption on the oil droplet. Heating induces aggregation of the oil droplets, as shown by an increase of the particle size and the bulk viscosity of the emulsions, with a more prominent effect after heating at 95 °C. Transmission electron microscopy observations clearly demonstrate that heating induces the formation of large protein aggregates at the interface. In addition, the composition of the protein present at the interface changes depending on the order of heating and homogenization. While heating the solutions before emulsification results in all the protein subunits to be present at the interface in an aggregated form, when heating is applied after emulsification, a portion of the α and the α′ subunit of β-conglycinin as well as the acidic subunits of glycinin remain unadsorbed.