Effect of a 10-day ageing at 30 °C on the texture of dry-cured hams processed at temperatures up to 18 °C in relation to raw meat pH and salting time

The aim of this study was to investigate the effect of a 10-day ageing at 30 ± 2 °C on the texture of dry-cured hams processed at temperatures up to 18 ± 2 °C for 12 months in relation with raw ham pH and salting time. Three pH groups (semimembranosus muscle at 24 h post-mortem: Low pH < 5.7, Medium pH = 5.7 ⩽ pH ⩽ 5.9, and High pH > 5.9), three salting times (6 d, 10 d and 14 d) and two ageing temperatures (18 °C and 30 °C) were investigated. Physicochemical characteristics, instrumental and sensory texture and product sliceability were evaluated on biceps femoris and semimembranosus muscles. Hams with pH_SM24 < 5.7 should be avoided in order to reduce the incidence of texture problems in dry-cured ham elaboration. Texture problems are especially important in hams with a reduced salt content that are mechanically sliced (not frozen). A 10-day ageing at 30 °C could be useful for reducing the soft texture problems in dry-cured hams processed at temperatures up to 18 °C for 12 months without affecting the product flavour.     

Coating papers with soy protein isolates as inclusion matrix of carvacrol

Antimicrobial papers were prepared by coating paper with soy protein isolate (SPI) solution as inclusion matrix of carvacrol, an antimicrobial agent. Addition of carvacrol (30% w/w of SPI) to SPI solution (10% w/v) prepared at 25 °C induced soy protein aggregates and viscosity decrease. Heat treatment (50, 70, 90 °C) of SPI solutions and carvacrol addition improved homogeneity reduced particles size and increased viscosity of solutions. The aggregated structure of SPI in the presence of carvacrol at 25 °C may play the role of a trapping structure leading to low carvacrol losses during coating and drying process of paper (9.6% against 37% after heat treatment at 90 °C) and to lower release rates specially the first three days (0.04 g/m²/day and 0.31 g/m²/day when SPI coating solutions were prepared at 25 and 90 °C, respectively). Regardless of the heat treatments received by the SPI solutions, residual carvacrol quantities in the coated papers after 50 days ranged between 0.6 and 0.7 g/m².     

Quercetagetin loaded in soy protein isolate–κ-carrageenan complex: Fabrication mechanism and protective effect

In the present study, the potential of soy protein isolate (SPI)–κ-carrageenan (κ-CG) complex as a protective carrier for quercetagetin was investigated at different pH values (pH 2.3 and 6.5). The particle size of the ternary aggregates was slightly increased at pH 2.3, yet dramatically decreased at pH 6.5 with increasing quercetagetin concentration. Moreover, the negative ζ-potential of the ternary aggregates was increased significantly (p < 0.05) at pH 6.5. The addition of quercetagetin to the SPI–κ-CG complex could highly quench the intrinsic fluorescence of SPI. Circular dichroism spectra further suggested that the bound quercetagetin could induce the rise of β-sheet and β-turn contents at the cost of α-helix and unordered coil fractions of SPI. In addition, quercetagetin could increase the viscoelasticity of the ternary aggregates at both pH. Furthermore, the SPI–κ-CG complex was found to be superior to single SPI or κ-CG in terms of improving light stability and radical scavenging ability of quercetagetin.     

Lactoferrin-based nanoparticles as a vehicle for iron in food applications – Development and release profile

This study aims at developing and characterizing bovine lactoferrin (bLf) nanoparticles as an iron carrier. bLf nanoparticles were characterized in terms of size, polydispersity index (PdI), electric charge (ζ-potential), morphology, structure and stability over time. Subsequently, iron release experiments were performed at different pH values (2.0 and 7.0) at 37 °C, in order to understand the release mechanism. bLf (0.2%, w/v) nanoparticles were successfully produced by thermal gelation (75 °C for 20 min). bLf nanoparticles with 35 mM FeCl₃ showed an iron binding efficiency value of approximately 20%. The nanoparticles were stable (i.e. no significant variation of size and PdI of the nanoparticles) for 76 days at 4 °C and showed to be stable between 4 and 60 °C and pH 2 and 11. Release experiments at pH 2 showed that iron release could be described by the linear superposition model (explained by Fick and relaxation phenomenon). On the contrary, the release mechanism at pH 7 cannot be described by either Fick or polymer relaxation behaviour. In general, results suggested that bLf nanoparticles could be used as an iron delivery system for future food applications.     

Cheese made from instant infusion pasteurized milk: Rennet coagulation,cheese composition,texture and ripening

Milk subjected to instant infusion pasteurization (IIP) at 72 °C, 100 °C and 120 °C (holding time 0.2 s) exhibited increased rennet coagulation time and decreased curd firming rate for increasing heat treatment temperature, when compared with raw or high temperature short time pasteurized (HTST) milk. However, addition of 4.5 mm or 9.0 mm of calcium restored the impaired rennet coagulation ability. Open texture cheeses produced from IIP milk (100 °C and 120 °C) contained significantly more moisture, had lower pH and shorter texture than similar cheese from IIP at 72 °C and HTST pasteurized milk. Cheese ripening was also affected by heat treatment, and different patterns of casein breakdown and peptide formation resulted from cheeses made from milk treated to IIP at 100 °C and 120 °C compared with cheeses made using IIP at 72 °C or HTST.     

Softness in dry-cured porcine biceps femoris muscles in relation to meat quality characteristics and processing conditions

The aim of the study was to quantify the effect of meat quality characteristics and some processing conditions on the softness of dry-cured biceps femoris (BF) muscles. The BF muscles were dissected from forty hams and classified according to their pH_BF into three groups: LpH (pH < 5.66), MpH (5.66 ⩽ pH ⩽ 6.00) and HpH (pH > 6.00). BF muscles within each pH_BF group were distributed into three different Salting levels (1%, 2% or 4% of added NaCl). Muscles were salted, vacuum-packed and stored at 3 °C for 30 days. The post-salting BF muscles were classified into two intramuscular fat (IMF) levels: Low (IMF < 4%) and High (IMF ⩾ 4%). Thereafter, the muscles were divided into two pieces and dried at two of the three different Drying levels (1.5, 2 and 2.5 g H₂O/g desalted dry matter). Then, each piece was divided into two samples that were packed in N₂ and stored at 5 °C or 30 °C for 1 month. Stress Relaxation was used to evaluate texture. Dry-cured BF muscles with initial pH > 6.0, with IMF > 4% or with added NaCl levels less than 2% were more prone to show soft texture. Softness in dry-cured muscles can be reduced by applying an ageing temperature of 30 °C for 30 days, despite increasing proteolysis. The softness reduction by ageing at 30 °C compared with 5 °C is expected to be higher when applied to drier samples, which show a smaller increase in proteolysis.     

Aqueous fractionation yields chemically stable lupin protein isolates

The chemical stability of lupin protein isolates (LPIs) obtained through aqueous fractionation (AF, i.e. fractionation without the use of an organic solvent) at 4 °C or 20 °C was assessed. AF of lupin seeds results in LPIs containing 2 wt.% oil. This oil is composed of mono- and poly-unsaturated fatty acids and the isolate may thus be prone to lipid and protein oxidation. Lipid and protein oxidation marker values of LPIs obtained at 4 °C and at 20 °C were below the acceptability limit for edible vegetable oils and meat tissue protein; the level of lipid oxidation markers was lower at 20 °C than at 4 °C. The fibre-rich pellet and the protein-rich supernatant obtained after AF also had lower levels of oxidation markers at 20 °C than at 4 °C. This is probably the result of a higher solubility of oxygen in water at lower temperature, which could promote lipid oxidation. The differences between fractions can be explained by the differences in their composition; the fibre-rich pellet contains polysaccharides that potentially have an anti-oxidative effect, while the protein-rich supernatant is rich in sulphur-rich proteins that may scavenge metal ions and free radicals from the aqueous phase. Additionally, the differences in solubility of metal ions and metal-chelating properties of protein at pH 4.5 and pH 7.0 explain the higher level of oxidation in the LPI at pH 4.5 compared with the LPI at pH 7.0. The application of a heat treatment to reduce oxidation decreased the protein and oil recovery values, and increased oxidation values above the acceptability limit. Therefore, AF at 20 °C is the most suitable process to obtain chemically stable LPIs.     

Dynamics of gelation,textural and microstructural properties of gelatin gels in the presence of casein glycomacropeptide

The aim of this work was to study the interaction between gelatin and casein glycomacropeptide (CMP) in the dynamic of gelation and the textural and microstructural properties of the mixed gels. Size particle, dynamic of gelation and textural and microstructural properties of CMP, gelatin and CMP-gelatin systems at pH 3.5 and pH 6.5 were determined. Size particle of gelatin increased by decreasing temperature from 35 °C to 5 °C, while no differences were observed in the size particle of CMP. At pH 6.5 the critical gelling concentration of gelatin was 1.5% and CMP did not gel, but the behavior of mixed systems was similar to gelatin. The more relevant result was observed at pH 3.5 since at concentrations in which CMP and gelatin did not gel on its own, the mixed systems gelled suggesting a synergistic effect.     

The influence of lactoperoxidase,heat and low pH on survival of acid-adapted and non-adapted Escherichia coli O157:H7 in goat milk

In hot climates where quality of milk is difficult to control, a lactoperoxidase (LP) system can be applied in combination with conventional preservation treatments at sub-lethal levels to inhibit pathogenic microbes. This study investigated the effect of combined heat treatments (55 °C, 60 °C and 72 °C) and milk acidification (pH 5.0) on survival of acid-adapted and non-adapted Escherichia coli O157:H7 strains UP10 and 1062 in activated LP goat milk. Heat treatment at 72 °C eliminated E. coli O157:H7. Acid-adapted strains UP10 and 1062 cells showed resistance to combined LP and heat at 60 °C in fresh milk. The inhibition of acid-adapted and non-adapted E. coli O157:H7 in milk following combined LP-activation, heat (60 °C) and milk acidification (pH 5.0) suggests that these treatments can be applied to reduce E. coli O157:H7 cells in milk when they occur at low numbers (<5 log₁₀ cfu mL^?1) but does not eliminate E. coli O157:H7 to produce a safe product.     

The increased viability of probiotic Lactobacillus salivarius NRRL B-30514 encapsulated in emulsions with multiple lipid-protein-pectin layers

Probiotics have demonstrated various health benefits but have poor stability to sustain food processing and storage conditions, as well as after ingestion. Biopolymer beads are commonly studied to encapsulate probiotic cells to improve their stability, but the millimeter-dimension of these beads may not meet the quality requirement of food products. The aim of this study was to enhance the viability of Lactobacillus salivarius NRRL B-30514 by encapsulation in emulsion droplets with multiple lipid-protein-pectin layers. Spray-dried L. salivarius was suspended in melted anhydrous milk fat that was then emulsified in a neutral aqueous phase with whey protein isolate or sodium caseinate to prepare primary solid/oil/water (S/O/W) emulsions. Subsequently, pectin was electrostatically deposited onto the droplet surface at pH 3.0 to form secondary emulsions. The encapsulation efficiency was up to 90%. After 20-day storage at 4 °C, the viable cell counts of bacteria in secondary emulsions at pH 3.0 and primary emulsions at 7.0 were 3 log higher than the respective free cell controls. After heating at 63 °C for 30 min, free L. salivarius was inactivated to be undetectable, while about 2.0 log CFU/mL was observed for primary (at pH 7.0) and secondary (at pH 3.0) emulsion treatments. Additionally, a 5 log-CFU/g-powder reduction was observed after spray drying free L. salivarius, while a 2 log CFU/g reduction was observed for emulsion treatments with capsules smaller than 20 μm. Furthermore, cross-linking the secondary emulsion with calcium enhanced the viability of L. salivarius after the simulated gastric and intestinal digestions. Therefore, the studied S/O/W emulsion systems may be used to improve the viability of probiotics during processing, storage, and gastrointestinal digestion.     

Effect of soy protein substitution for sodium caseinate on the transglutaminate-induced cold and thermal gelation of myofibrillar protein

The influence of soy protein isolate (SPI) substitution for sodium caseinate (SC) on the properties of cold-set (4 °C) and heat-induced gels of pork myofibrillar protein (MP) incubated with microbial transglutaminase (TG) was investigated. The strength of cold-set MP–SC gels (formed in 0.45 M, NaCl, 50 mM phosphate buffer, pH 6.25) increased with time of TG incubation, but those gels with more than 66% SPI substituted for SC had a >26% reduced strength (P < 0.05). Upon cooking, both incubated and non-incubated protein sols were quickly transformed into highly elastic gels, showing up to 6000 Pa in storage modulus (G′) at the final temperature (72 °C). However, no differences (P < 0.05) in G′ were observed between heated samples with SPI and SC. Myosin heavy chain, casein and soy proteins gradually disappeared with TG incubation, contributing to MP gel network formation. Both cold-set and heat-induced gels had a compact protein matrix, attributable to protein cross-linking by TG.     

Calcium-induced disaggregation of wheat germ globulin under acid and heat conditions

This work evaluated the potential of wheat germ globulin (WGG) disaggregation to improve acid and thermal stability in the presence of salts and determine the mechanism of improved solubility. Effects of CaCl₂ on disaggregation of wheat germ globulin solution (0.5%, w/w) heat-treated ranging from 55 °C to 95 °C at pH 2.0 were investigated by turbidity, solubility, H₀ (surface hydrophobicity), ζ-potential and microstructure. Maximum turbidity and minimum solubility occurred at the isoelectric point (pI 5.0) and 95 °C. The addition of Ca^2 + resulted in a steady decrease of the turbidity and increase of the solubility. Both H₀ and ζ-potential of soluble aggregates increased during disaggregation process. The results suggest that the electrostatic repulsion between the particles is sufficiently strong to overcome the attractive forces (hydrophobic interaction), leading to a degradation of large lumps and a homogeneous distribution of WGG particles. Microstructure analysis revealed that the WGG heat-treated contained rough and irregular aggregates at pH 2.0, while the CaCl₂-induced disaggregates showed a smooth and loose dispersion, suggesting a dispersive distribution of WGG and a degradation of large lumps. Separating the formation of aggregates may provide a means to manipulate the protein solution properties.     

Pressure–ohmic–thermal sterilization: A feasible approach for the inactivation of Bacillus amyloliquefaciens and Geobacillus stearothermophilus spores

The efficacy of a pressure–ohmic–thermal sterilization (POTS) for Bacillus amyloliquefaciens and Geobacillus stearothermophilus spore inactivation was investigated. Spores (2.5 × 10⁸ cfu/ml) were inoculated in 0.1% NaCl solution (pH 5.0 and 7.0), green pea puree (pH 6.1), carrot puree (pH 5.0) or tomato juice (pH 4.1). Samples were ohmically (50 V/cm) treated at 600 MPa and 105 °C for various holding times using a laboratory-scale high-pressure processor. B. amyloliquefaciens and G. stearothermophilus spores suspended in 0.1% NaCl solution (pH 7.0) were inactivated by 4.6 and 5.6 log, respectively, for a 30-min holding time. B. amyloliquefaciens and G. stearothermophilus spores in tomato juice were reduced by 3.1 and 4.8 log, respectively, for a 10-min holding time. Spore germination was highest in the G. stearothermophilus suspended in 0.1% NaCl solution (pH 7.0). POTS treatment appears to be a potent method for inactivating pressure–thermal resistant bacterial spores.Industrial RelevanceFood industry is interested in developing superior quality low-acid shelf-stable foods. This study evaluated the pressure–ohmic–thermal sterilization (POTS) for the inactivation of Bacillus amyloliquefaciens and Bacillus stearothermophilus endospores. The impact of food matrices and acidity on the spore resistance was also investigated. Knowledge gained from the study will help the food processors for understanding the importance of various POTS treatment parameters for sterilization of low-acid foods.     

Potential use of new Colombian sources of betalains. Colorimetric study of red prickly pear (Opuntia dillenii) extracts under different technological conditions

A new source of betalains to be used as natural colorant (Opuntia dillenii) has been studied. The stability of O. dillenii extracts in different pHs and temperatures over time has been scrutinized. Our attention was focused on differential tristimulus colorimetry and betalain content related to the color, not previously conducted in conjunction in that raw material. On the basis of the results, cold storage conditions (4 °C) were optimal to maintain as possible the initial red color (h_ab), lightness (L*) and betalain content of the O. dillenii extracts, regardless of pH. Highly-acidic extracts (pH 4) manifested a significantly (p < 0.05) lower colorant intensity (C*_ab) and betalain concentration (around 25% and 35%, respectively), with a clearer tendency toward yellowish tonalities (values of h_ab from 45° to 90°) over time. Furthermore, visually perceptible color changes (ΔE*_ab > 3) were induced among very acid (pH 4) and low-acidic (pH 5 and 6) extracts at each temperature.     

Effect of chemical phosphorylation on solubility of buffalo milk proteins

Buffalo milk proteins (casein, co-precipitate or whey protein concentrate) were phosphorylated with phosphorus oxychloride (POCl₃) at three different pH values (5.0, 7.0 and 9.0). The solubilities of phosphorylated milk proteins were examined over the pH range 3.0–9.0 in water and ionic (0.1 m NaCl or 10–70 mm Ca²⁺) systems. The solubilities of buffalo milk proteins decreased at pH 3.0, while there was an increase in the solubilities of casein and co-precipitate near their isoelectric points upon phosphorylation. Solubilities of these phosphorylated milk proteins were pH dependent in 0.1 m NaCl but there was a decrease in their solubilities with increase in calcium ion concentration. This alteration could be due to the shifting of isoionic points of phosphorylated buffalo milk proteins towards acidic pH.     

Kinetics of browning during accelerated storage of sweet whey powder and prediction of its shelf life

Sweet whey powder (SWP) of different pH was prepared by exposing native SWP to acetic acid vapors in a desiccator. Samples were subjected to accelerated browning at temperatures of 40, 60 and 80 °C in sealed vials and the rate of color formation was measured. Sample lightness decreased over time and the rate of decrease was faster at higher temperature and lower pH. Results were modeled using a pseudo-first-order reaction kinetic equation. The shelf life of SWP was estimated using a time–temperature plot. Increasing the temperature and decreasing the pH strongly decreased the shelf life from greater than 2 years at 53 °C for native SWP (pH∼6.3) to 5.2 days at 60 °C for intermediate acid SWP (pH∼5.0). A time–temperature–tolerance approach involving the practical storage life was used to predict the impact of temperature abuse during manufacture, transportation or storage.     

Effect of high pressure thermal processing on some essential nutrients and immunological components present in breast milk

The influence of high pressure thermal (HPT) processing (300, 600 or 900 MPa at an initial temperature of 50, 65 or 80 °C, for 1 min) on the levels of tocopherols, fatty acids, cytokines, leukocytes and immunoglobulins (IgM, IgA and IgG) was evaluated in breast milk. Breast milk treated at 65 or 80 °C at any intensity of pressure caused a significant decrease in the content of α-tocopherol compared with untreated milk. The relative proportions of some important fatty acids were affected by HPT treatment. HPT processing had a minimal effect on the levels of some cytokines, such as IL-12, IL-17 and IFN-γ. Leukocytes viable cells did not survive to any of the treatments applied. Only the treatments at 300 MPa and 50 °C maintained certain levels of Igs such as IgM (~ 75% retention), IgA (~ 48%) and IgG (~ 100%), while the rest of combinations produced important decreases of their contents.Industrial relevanceHuman milk banks use low-temperature/long-time thermal pasteurisation for the preservation of milk and to avoid risks of infections. Thermal treatment reduces nutritional and immunological properties of breast milk. The study of new methods to preserve milk quality could produce important benefits for the infants' receptor of milk. The application of high pressure processing at low temperatures has showed certain advantageous respect to the thermal treatment, however, the effect of high pressure at moderate-high temperatures have never been evaluated in breast milk.     

Mechanism of the interaction between insoluble wheat bran and polyphenols leading to increased antioxidant capacity

This study aimed to provide an in-depth investigation of the interaction between insoluble wheat bran and polyphenols. Treatment with tannic acid, but not gallic acid, increased the bound antioxidant capacity of insoluble wheat bran depending on its aqueous concentration (p < 0.05). Among the beverages tested (white and red wines, black and green tea infusions), treatment with green tea infusion caused the highest increase in the total antioxidant capacity. Temperature, time, air and pH were found to significantly affect the reaction between insoluble wheat bran and polyphenols. The bound antioxidant capacity of insoluble bran increased to above 100 mmol TE.kg^− 1 after treatment with green tea infusion at optimum conditions (50 °C, pH 9.0, no airflow). Concentration of free amino groups available in wheat bran significantly decreased (59.5%) after the treatment. The results suggested that polyphenols are oxidized to quinones under alkaline conditions further bound to free amino groups available on the surface of wheat bran.     

Gelling of microbial transglutaminase cross-linked soy protein in the presence of ribose and sucrose

Soy protein isolate (SPI) was incubated with microbial transglutaminase (MTGase) enzyme for 5 (SPI/MTG(5)) or 24 (SPI/MTG(24)) h at 40 °C and the cross-linked SPI obtained was freeze-dried, and heated with 2% (w/v) ribose (R) for 2 h at 95 °C to produce combined-treated gels. Longer incubation period resulted in more compact and less swollen SPI particle shape when reconstituted with sugar solution. Thus, this MTGase treatment affected samples in terms of flow behaviour and gelling capacity. Rheological study showed different gelling profiles with the cross-linking treatments and combined cross-linked SPI gave a higher G′ value compared to single treated samples. These are due to the formation of additional ε-(γ-glutamyl)lysine bonds and “Maillard cross-links” within the SPI protein network during the MTGase incubation and heating in the presence of ribose (i.e. reducing sugar). Network/non-network protein analysis found that network protein increased with cross-linking treatment, which also resulted in different SDS–PAGE profiles. As in non-network protein fraction, A₄ subunit was suggested to become part of the network protein as a result of combined cross-linking.     

Effect of processing parameters on the properties of transglutaminase-treated soy protein isolate films

The effects of processing parameters, including the applied amount of microbial transglutaminase (MTGase), the pH of film-forming solution, air-drying temperature, as well as the additional pre-incubation, on the properties of MTGase-treated soy protein isolate (SPI) films were investigated. The treatment with low concentration of MTGase (4–10 units per gram of SPI, U g^− 1) significantly increased the tensile strength (TS) values of SPI films, while high concentration of MTGase (over 20 U g^− 1) resulted in significant decrease in the TS values (P ≤ 0.05). The elongation at break (EB) values of corresponding films gradually decreased, and the contact angle values persistently increased with the enzyme concentration. At alkaline pH range, the TS and EB values of MTGase-treated SPI films were significantly higher than that at pH 7.0 (P ≤ 0.05). Meanwhile, the contact angle values significantly decreased with increasing pH from 7.0 to 10.0 (P ≤ 0.05). The TS, EB and contact angle values of MTGase-treated films gradually but insignificantly decreased with increasing the air-drying temperature from 18 to 50 °C (P > 0.05). The properties of MTGase-treated films were also affected by the additional pre-incubation of film-forming solutions with MTGase before casting. Furthermore, the aggregation of SPI or its components induced by MTGase has been proved to mainly account for the influence of processing parameters on the properties of SPI films (MTGase-treated). Thus, low concentration of enzyme, alkaline pH range and low air-drying temperature, at which conditions the MTGase-induced aggregation of SPI in film-forming solutions could be in some extent inhibited or delayed, might facilitate the improvement of the properties of SPI films by MTGase, especially the mechanical and surface hydrophobic properties.Industrial relevanceThe development of biodegradable protein film has attracted a lot of attention worldwide. The enzymatic cross-linking induced by transglutaminase has been confirmed to improve mechanical and surface hydrophobic properties of cast films from most of food proteins, including soy proteins. Results of this study show that, the improvement of properties of cast films of soy proteins by transglutaminase treatment is largely dependent upon many processing parameters, e.g., enzyme concentration, the pH of film-forming solution and temperature.