Survival kinetics of Ephestia kuehniella eggs during 46–75 °C heat treatment

The effect of heat treatment on the survival of Ephestia kuehniella eggs was examined. Samples of 60 eggs were immersed in hot water at constant temperature in the 46–75 °C range for 5–1200 s. Following heat treatment and cooling, the eggs were stored at 24 ± 1 °C in a growth chamber for 7 days before survival evaluation. Statistical analysis of the data demonstrated that the thermal survival kinetics were best represented by a first-order reaction. The rate constant had an Arrhenius-type dependence over the 54–75 °C temperature range. Kinetic parameters were estimated by non-linear regression. The activation energy (E_a) and rate constant (k_ref) at the reference temperature (T_ref = 64.8 °C), were determined as 102.2 ± 6.2 kJ mol⁻¹ and 0.061 ± 0.003 s⁻¹, respectively, over the 54–75 °C temperature range. A 0.01% survival rate was obtained after 50 s at 75 °C. The data at temperatures below 50 °C were not in accordance with those at higher temperatures. Above this temperature, mortality was likely due to physiological disorders, as noted on a DSC thermogram.     

Comparative NMR relaxometry of gels of amylomaltase-modified starch and gelatin

With the aim of generating gelatin-like starch gel functionality, starches extracted from normal potato, high amylose potato, maize, waxy maize, wheat and pea and oxidized potato starch were modified with amylomaltase (AM) (4-α-glucanotransferase; E.C. 2.4.1.25) from Thermus thermophilus. Gel characteristics after storage for 1 and 10 days at 20 °C of 12.0% gels were assessed by monitoring proton relaxation for the resulting 51 enzyme-modified starches and two gelatins using low-field ¹H nuclear magnetic resonance (LF NMR) relaxometry. Discrete and distributed exponential analysis of the Carr–Purcell–Meiboom–Gill (CPMG) LF NMR relaxation data revealed that the pastes and gels contained one water component and that the spin–spin relaxation time constants (T₂) and distributions differed with respect to starch type and enzyme modification. Typically, AM modification resulted in starches with decreased T₂ relaxation time and a more narrow T₂ distribution indicating a more homogeneous water population. In contrast, treatment with a branching enzyme (BE) (EC 2.4.1.18) combined with AM increased T₂ relaxation time and a broadened T₂ distribution. As evaluated by the principal component analysis (PCA), long chains of amylopectin generated hard gels and decreased T₂ relaxation time at both day 1 and day 10. Especially at day 10, T₂ relaxation time could be predicted from the amylopectin chain length (CL) distribution. Reconstructed amylopectin CL distribution required to emulate gelatin LF NMR data suggest the importance of combined fractions of long (DP 60–80) and short (DP 10–25) amylopectin chains.     

Inhibitory effect of clove oil on Listeria monocytogenes in meat and cheese

The antilisteric activity of clove oil was examined in meat and cheese at both 30°C and 7°C. At concentrations of 0·5% and 1% clove oil restricted the growth of Listeria monocytogenes in the food items at both temperatures. The inhibitory activity of clove oil was more pronounced at a concentration of 1%.Listeria counts in treated samples were 1–3 log₁₀cfu g⁻¹less compared to controls at different intervals during storage. The results revealed the potential of clove oil as a natural preservative in meat and cheese.     

Sensory shelf life determination of a processed meat product ‘rullepølse’ and microbial metabolites as potential indicators

Sensory profiling was performed for a Danish lightly fermented heat-processed cold cut pork product termed ‘rullepølse’. Product samples were stored under modified atmosphere (MAP, 30% CO₂/70% N₂) for 0, 28 and 34 days and with subsequent aerobic storage for 4 days (MAP–OPEN) at temperatures of 4 °C and 8 °C. Microbial growth and metabolism was also measured with a focus on lactic acid bacteria (LAB) and their organic acid metabolites including lactic acid, acetic acid and α-ketoisocaproic acid. These acids were examined for sensory shelf life indexing potential for the ‘rullepølse’. Storage temperature exerted distinct impacts on the sensory characterised shelf life of ‘rullepølse’ stored under MAP and MAP–OPEN conditions. The MAP stored ‘rullepølse’ with subsequent 4 days storage in air (MAP–OPEN) could be stored for at least 28 days at 4 °C without a decrease in the sensory quality when opened. Whilst MAP stored ‘rullepølse’ at 8 °C with subsequent open storage (MAP–OPEN), compared to the lower temperature displayed a reduced shelf life of less than 28 days if sensory quality of the ‘rullepølse’ was to be maintained. The stage of sensory deterioration was correlated with high bacterial counts exceeding 10⁶ CFU g⁻¹. With respect to indexing ability of the examined organic acids none were found to have clear potential for prediction of the sensory deterioration.     

Combined effects of thymol, carvacrol and temperature on the quality of non conventional poultry patties

The combined effect of thymol (0–300 ppm), carvacrol (0–300 ppm), and temperature (0–18 °C) on the quality of non conventional poultry patties packaged in air and modified atmosphere (MAP: 40% CO_2; 30%O₂; 30% N₂) was investigated using a simplex centroid mixture design. The patties were monitored for microbiological (total viable count, Enterobacteriaceae, lactic acid bacteria, Pseudomonas spp.) physico-chemical (pH, colour) and sensory attributes. For the patties mixed with the antimicrobials and stored at low temperature (0–3 °C) a reduction of the cell load of about 1–1.5 log cfu/g was observed. The log reduction was lower at the end of storage time and decreased with the increase of the temperature. For the poultry patties packaged in MAP the higher log reduction for Pseudomonas spp. during all the storage time was observed. In both packaging atmospheres the combination of the essential oils and low temperature determined no modification for off-odour during the first 4 days of storage.     

Viability of multi-strain mixtures of Listeria monocytogenes, Salmonella typhimurium, or Escherichia coli O157:H7 inoculated into the batter or onto the surface of a soudjouk-style fermented semi-dry sausage

The fate of Listeria monocytogenes, Salmonella typhimurium, or Escherichia coli O157:H7 were separately monitored both in and on soudjouk. Fermentation and drying alone reduced numbers of L. monocytogenes by 0.07 and 0.74 log₁₀ CFU/g for sausages fermented to pH 5.3 and 4.8, respectively, whereas numbers of S. typhimurium and E. coli O157:H7 were reduced by 1.52 and 3.51 log₁₀ CFU/g and 0.03 and 1.11 log₁₀ CFU/g, respectively. When sausages fermented to pH 5.3 or 4.8 were stored at 4, 10, or 21 °C, numbers of L. monocytogenes, S. typhimurium, and E. coli O157:H7 decreased by an additional 0.08–1.80, 0.88–3.74, and 0.68–3.17 log₁₀ CFU/g, respectively, within 30 days. Storage for 90 days of commercially manufactured soudjouk that was sliced and then surface inoculated with L. monocytogenes, S. typhimurium, and E. coli O157:H7 generated average D-values of ca. 10.1, 7.6, and 5.9 days at 4 °C; 6.4, 4.3, and 2.9 days at 10 °C; 1.4, 0.9, and 1.6 days at 21 °C; and 0.9, 1.4, and 0.25 days at 30 °C. Overall, fermentation to pH 4.8 and storage at 21 °C was the most effective treatment for reducing numbers of L. monocytogenes (2.54 log₁₀ CFU/g reduction), S. typhimurium (5.23 log₁₀ CFU/g reduction), and E. coli O157:H7 (3.48 log₁₀ CFU/g reduction). In summary, soudjouk-style sausage does not provide a favorable environment for outgrowth/survival of these three pathogens.     

Changes in the content of biologically active polyamines during beef loin storage and cooking

Dietary polyamines putrescine (PUT), spermidine (SPD) and spermine (SPM) participate in numerous human physiological processes, including tumour growth. Reliable information on their contents in foods is thus needed. Data for processed beef are very limited. Nine experiments with beef loin (longissimus lumborum) were, therefore, carried out. Loin cuts were stored at −18 °C for 178 days or beef was stored aerobically, vacuum-packaged (VP) and packaged in a modified atmosphere (MA; 70% N₂ and 30% CO₂, v/v) at +2 °C for 9, 21 and 21 days, respectively. The effects of three usual cooking treatments were also tested. Polyamines were determined after extraction with perchloric acid as dansyl derivatives using an HPLC method. Only SPM was detected at initial levels of 23.5–27.5 mg kg⁻¹, PUT and SPD contents were below the detection limits of 1.2 and 1.7 mg kg⁻¹, respectively. SPM content increased during the initial weeks of frozen storage and then gradually decreased to about 70% of the initial values at the end of the storage period (P < 0.05). No apparent SPM decrease was observed during aerobic storage for 9 days, while in VP and MA variants the losses were about 20% of the initial values on day 21 (P < 0.05). Slightly higher mean SPM losses were observed during boiling and stewing with and without added water. The differences among the cooking treatments were not significant. However, significant differences were observed among the loins used.     

Shear-induced structuring of particulate whey protein gels

The effects of steady shear on particulate whey protein isolate (WPI) gels, at pH 5.4, have been investigated by light microscopy (LM) and dynamic oscillatory measurements. The steady shear was performed on suspensions at constant rates between 0.5 and 126/s. The gel point under static conditions (T_g) was around 78 °C and the shearing was performed during heating from 20 to 76 or to 82 °C. The gel point was postponed by the shear up to 82 °C. Steady shear up to 76 °C, at rates less than 6/s, resulted in a weaker storage modulus (G′), less frequency dependence and a higher stress at fracture compared to the unsheared gel. Steady shear up to 82 °C, at rates below 6/s, resulted in the formation of two different types of network structure. One structure was similar in appearance to the unsheared network, showing pores in the range of 50 μm. The other structure was dense, composed of smaller particles than the unsheared network and with pores in the range of 10 μm. The gels composed of two structures showed a lower G′ and stress at fracture compared to the unsheared gel. A shear rate above 24/s up to 76 °C resulted in irregular networks, which were composed of two different types of structures. One was loose and open, similar in appearance to the unsheared network structure. The other structure was dense and compact, and was present as individual aggregates. These gels also showed a weaker G′ than the unsheared gel. A shearing up to 82 °C at rates above 24/s resulted in a coarse, inhomogeneous network structure. The gels showed a weak G′, indicating aggregate break-up during the steady shear.     

Structural properties of single and mixed milk/soya protein systems

Single-component gels were prepared by cold-setting aqueous preparations of thermally processed milk and soya proteins. Small deformation mechanical measurements on soya protein samples showed a strong elastic response (G′) even at the hydration temperature (50°C). Both proteins produced an initial monotonie increase in G′ on cooling, followed by a relatively constant modulus during a subsequent time sweep at the setting temperature (5°C). Networks were fully reversible on heating; the milk protein gels melting out completely at temperatures >60°C, whereas the soya protein gels maintained significant structure even at the highest accessible temperature (95°C). The lack of thermal hysteresis or of sharp, cooperative melting was also confirmed by differential scanning calorimetry. Further investigation of the macromolecular properties of the gels, comprising G′ dependence as a function of frequency of oscillation and creep experiments, suggests that gels remain stable within the time scale of the measurements (90 min). Finally, under increasing amplitude of oscillation, networks withstood structural breakdown up to strain levels of ~70%; behaviour anticipated for biopolymer gels. Mixed gels were studied using a fixed amount of milk protein (10% w/w) with soya protein concentrations from 6 (minimum gelling requirement) to 16% w/w (solubility limit). Comparison of melting profiles (G′ vs. T) for the phase separated systems with those obtained for the individual components indicated phase-inversion from a milk protein continuous network to a soya continuous system at a soya protein concentration of ~11%. Analysis of solvent partition between the constituent phases utilized classical theory of network deswelling for polymer combinations below the phase inversion point and phase equilibria treatment for the soya continuous network with milk protein inclusions. In the case of equilibrium separation of the two components, results were expressed in terms of a single adjustable parameter, p (the ratio of solvent to polymer in one phase divided by the corresponding ratio in the other phase), indicating a soya hydrophilicity of ~1.25 times that of milk protein.     

Effect of controlled gelatinization in excess water on digestibility of waxy maize starch

An aqueous dispersion of waxy maize starch (5%, w/w) was controlled gelatinized by heating at various temperatures for 5 min. The treated samples were analysed using in vitro Englyst assay, light microscopy, differential scanning calorimetry, X-ray diffraction, and Fourier-transform infrared spectroscopy. When heated, SDS and RS levels were decreased inversely with RDS. A high SDS content (>40%) was kept prior to the visible morphological and structural changes (before 60 °C). Swelling factor began to increase slightly at 50–60 °C and continued to maximum value at 80 °C. A large decrease in ΔH, crystallinity, and ratio of 1047/1022 cm⁻¹ attributed to partially dissociation of crystalline clusters and double helices occurred at 65–80 °C. These changes showed that controlled gelatinized starch with slow digestion property occurred in the molecular rearrangement process before granule breakdown and SDS mainly consists of amorphous regions and a small portion of less perfect crystallites.     

Thermomechanical properties of biodegradable films based on blends of gelatin and poly(vinyl alcohol)

The aim of this work was to study the effect of the poly(vinyl alcohol) (PVA) concentration on the thermal and viscoelastic properties of films based on blends of gelatin and PVA using differential scanning calorimetry (DSC) and dynamic-mechanical analysis (DMA). One glass transition was observed between 43 and 49 °C on the DSC curves obtained in the first scanning of the blended films, followed by fusion of the crystalline portion between 116 and 134 °C. However, the DMA results showed that only the films with 10% PVA had a single peak in the tan δ spectrum. However, when the PVA concentration was increased the dynamic mechanical spectra showed two peaks on the tan δ curves, indicating two T_gs. Despite this phase separation behavior the Gordon and Taylor model was successfully applied to correlate T_g as a function of film composition, thus determining k=7.47. In the DMA frequency tests, the DMA spectra showed that the storage modulus values decreased with increasing temperature. The master curves for the PVA–gelatin films were obtained applying the TTS principle (T_r=100 °C). The WLF model was thus applied allowing for the determination of the constants C₁ and C₂. The values of these constants increased with increasing PVA concentrations in the blend: C₁=49–66 and C₂=463–480. These values were used to calculate the fractional free volume of the films at the T_g and the thermal expansion coefficient of the films above the T_g.     

To improve the gel properties of liquid whole egg by short-term lactic acid bacteria fermentation

Fermentation, as a simple, safe and environmentally friendly technology, is promising in the modification of proteins. In this study, the liquid whole egg (LWE) was fermented at 37 °C by Lactiplantibacillus plantarum 90 (L. plantarum 90) which the dose of inoculation was about 8 Log 10 CFU mL⁻¹. During the process, the total aerobic mesophilic count (TAM) and the number of lactic acid bacteria (LAB) of LWE increased at 3 h and then decreased, consistent with the changes in protein solubility. Besides, the T₂ relaxation time of fermented egg gels moved to low relaxation time (T₂₂ shifted from 2154.44 ms (0 h) to 1232.85 ms (9 h)), indicating that the water retention of fermented egg gels was enhanced. After fermentation, it could be seen intuitively that the porous structure of the gel surface almost disappeared, along with the improved springiness and brightness by texture and color measurement. This study suggested that moderate fermentation (L. plantarum 90, 1% v/v, 9 h) could effectively improve the gel property of LWE, and thus had a potential to expand the application of LWE in the food industry.     

Migration of α-tocopherol from an active multilayer film into whole milk powder

Antioxidant active packaging is a promising technology for whole milk powder (WMP) protection. In this study, the migration of α-tocopherol from a multilayer active packaging (made of high density polyethylene, ethylene vinyl alcohol and a layer of low density polyethylene containing the antioxidant) to WMP was studied. A model based on the Fick’s diffusion equation was used to calculate the diffusion coefficients (D) of α-tocopherol as 2.34 × 10⁻¹¹, 3.06 × 10⁻¹¹, and 3.14 × 10⁻¹¹ cm² s⁻¹ at 20, 30 and 40 °C, respectively. The D at 20 °C was different from those at 30 and 40 °C (P < 0.05); but it was similar at 30 and 40 °C. This low influence of temperature on the migration of α-tocopherol from 20 to 40 °C assures the release at real storage and commercialization conditions in regions with warm/hot climate. The antioxidant delivering system delayed the lipid oxidation of WMP and it was more effective at 30 and 40 °C since the rate of oxidative reactions was higher at these temperatures than at 20 °C.     

Storage stability of jackfruit (Artocarpus heterophyllus) powder packaged in aluminium laminated polyethylene and metallized co-extruded biaxially oriented polypropylene during storage

Total colour difference (ΔE), rates of adsorbed moisture and sensory attributes of drum-dried jackfruit powder packaged in aluminium laminated polyethylene (ALP) and metallized co-extruded biaxially oriented polypropylene (BOPP/MCPP) pouches stored at accelerated storage (38 °C, with 50%, 75% and 90% relative humidity (RH)) were determined over 12 weeks period. The changes in total colour followed zero order reaction kinetics. Packaging materials, storage temperature and RH values significantly (p < 0.05) influenced the rates of adsorbed moisture of jackfruit powder. There was a significant (p < 0.05) decrease in the intensities of the fruity odour, taste and increase in the lumpiness of the jackfruit powder stored at 38 °C with 90% RH. The shelf life of jackfruit powder stored at 38 °C and 90% RH was limited by overall acceptability and the intensity of fruity odour, taste and lumpiness at week 8 of storage. Jackfruit powder stored at 28 °C remained stable and acceptable throughout the storage period for all RH values. The powder packaged in ALP significantly (p < 0.05) reduced total colour change, rates of adsorbed moisture, lumpiness intensity of jackfruit powder and was rated higher in terms of overall acceptability over BOPP/MCPP. Results of this study suggested that ALP packaging with storage conditions of 28 °C and RH less than 75% was better suited for keeping jackfruit powder.     

Texture changes in dry-cured ham pieces by mild thermal treatments at the end of the drying process

The present study evaluated the effects of mild thermal treatments at the end of the drying process on physicochemical characteristics and instrumental and sensory texture in dry-cured ham. Experiment 1: effect of thermal treatments (4–46 °C) for 4 h and 24 h. Experiment 2: time effect (4–168 h) of thermal treatments at 30 °C and 36 °C. Both experiments were done on small dry-cured ham dices. Experiment 3: time effect (4–168 h) of thermal treatment at 30 °C on both instrumental and sensory texture of 4-cm-thick sections of dry-cured ham. The thermal treatment at 30 °C for 168 h on both dry-cured ham muscle dices (20 mm × 20 mm × 15 mm) and dry-cured ham sections (4 cm thick) decreased softness, adhesiveness and pastiness in BF muscle, without increasing hardness in SM muscle or affecting moisture, a_w and proteolysis index.     

Biochemical and thermal characterization of crude exo-polygalacturonase produced by Aspergillus sojae

Crude exo-polygalacturonase enzyme (produced by Aspergillus sojae), significant for industrial processes, was characterized with respect to its biochemical and thermal properties. The optimum pH and temperature for maximum crude exo-polygalacturonase activity were pH 5 and 55 °C, respectively. It retained 60–70% of its activity over a broad pH range and 80% of its initial activity at 65 °C for 1 h. The thermal stability study indicated an inactivation energy of E_d = 152 kJ mol⁻¹. The half lives at 75 and 85 °C were estimated as 3.6 and 1.02 h, respectively. Thermodynamic parameters, ΔH^*, ΔS^* and ΔG^*, were determined as a function of temperature. The kinetic constants K_m and V_max, using polygalacturonic acid as substrate, were determined as 0.424 g l⁻¹ and 80 μmol min⁻¹, respectively. SDS-PAGE profiling revealed three major bands with molecular weights of 36, 53 and 68 kDa. This enzyme can be considered as a potential candidate in various applications of waste treatment, in food, paper and textile industries.     

Salmon by-product storage and oil extraction

Oils extracted from wild salmon by-products are excellent sources of long chain omega-3 polyunsaturated fatty acids including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). However, quality loss is expected if time delays are encountered before oil extraction. The free fatty acid levels (FFA), fatty acid profile and total fat soluble antioxidant activity in extracted oil from aging pink salmon heads and viscera stored at two temperatures (6 and 15 °C) for four days were determined. The FFA values in raw salmon heads and viscera increased with storage time and temperature. A significant difference (p < 0.05) from the starting material was noted at day 1 at both temperatures for FFA. Fatty acid composition data indicated no changes in the levels of long-chain omega-3 fatty acids with the respective temperature. The concentration of long-chain omega-3 fatty acids EPA ranged from 9.3 to 11.3 g/100 g of crude oil and DHA ranged from 12.3 to 13.1 g/100 g of crude oil. The antioxidant activity of the pink salmon oils at day 0 was 0.89 ± 0.15 μmole Trolox equivalent/g of crude oil. Significant decreases (p < 0.05) from the starting material were noted on day 2 for 15 °C samples and day 3 for 6 °C samples. After four days of storage antioxidant levels (Trolox equivalent/g of crude oil) were approximately 25% of initial values. Oil extracted from raw salmon heads and viscera remained a good source of long chain omega-3 fatty acids even after 4 days of raw material storage at 15 °C; however, fat soluble antioxidant activity was reduced and free fatty acid levels increased with increased raw material storage temperature and time.     

Maturation effects in fish gelatin and HPMC composite gels

This study assessed the effectiveness of using hydroxylpropylmethylcellulose (HPMC) to enhance mechanical strength and thermal stability in fish skin gelatin (FG). The significant increase in absorbance (A₄₀₀) observed after HPMC had been added to FG and then matured indicated successful formation of a composite gel. Increased gel strength and storage modulus (G′) indicated the enhanced gelation ability of the matured composite gel, while increased melting temperature (T_m) and enthalpy (ΔH) indicated its improved thermal stability. Maturation-related rheological property improvements were more noticeable at 4 °C than 10 °C, but no apparent differences in T_m improvement were observed between 4 °C and 10 °C maturation. Nevertheless, the composite gel exhibited reversible cold and thermal gelation properties.     

Effect of heat and thermosonication treatments on watercress (Nasturtium officinale) vitamin C degradation kinetics

The use of ultrasound in food processing creates novel and interesting methodologies, which are often complementary to classical techniques. In this work, the effect of heat and the combined treatment heat/ultrasound (thermosonication) on the thermal degradation kinetics of vitamin C in watercress (Nasturtium officinale) was studied in the temperature range of 82.5 to 92.5 °C. First order reaction kinetics adequately described the vitamin C losses during both blanching processes.The activation energies and the reaction rates at 87.5 °C for heat (H) and thermosonication (Ts) treatments were, respectively, E_avitCH = 150.47 ± 42.81 kJ mol^− 1 and E_avitCTs = 136.20 ± 60.97 kJ mol^− 1, and k_{87.5 °CvitCH} = 0.75 ± 0.10 min^− 1 and k_{87.5 °CvitCTs} = 0.58 ± 0.11 min^− 1. No significant differences (P > 0.05) were detected between both treatments. The thermosonication treatment was found to be a better blanching process, since it inactivates watercress peroxidase at less severe blanching conditions and consequently retains vitamin C content at higher levels. The present findings will help to optimise the blanching conditions for the production of a new and healthy frozen product, watercress, with heat and a new blanching process methodology.

Industrial relevance

Thermosonication blanching can be useful since it reduces processing times, and consequently minimizes the adverse effects of heating on watercress quality. This new application will provide good material, in terms of vitamin C, for further processes, and can be an excellent alternative to the traditional heat treatment.     

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.