High hydrostatic pressure protection of a pectinase cocktail against thermal inactivation

Pectinase cocktails, containing pectinases, hemicellulases, and cellulases are used in the production of commercial apple juice to reduce juice viscosity, increase yield, and to clarify the final product. The kinetics of inactivation of a commercial pectinase formulation was studied at 0.1–400 MPa and 55.0–85.0 °C. High hydrostatic pressure slowed the rate of inactivation of the pectinase cocktail treated at inactivating temperature conditions by up to 19-fold at 77.0 °C, 350 MPa compared to inactivation at atmospheric pressure at the same temperature. Apparent activation energies of enzyme inactivation at 200–400 MPa were lower (107.3–154.4 kJ mol⁻¹) than at 0.1 MPa (195.6 kJ mol⁻¹).     

Kinetics of formation of acrylamide and Schiff base intermediates from asparagine and glucose

From the concentration of glucose and asparagine as reactants and of acrylamide as product each determined by LC–MS during reaction in an acetonitrile/water (68:32) model system at pH 7.6 (0.04 M phosphate buffer) and from the relative concentration of the Schiff base intermediate, the decarboxylated Schiff base intermediate, the Amadori product and aminopropionamide determined in the same reaction mixtures at 120 °C, 140 °C, 160 °C and 180 °C for up to 16 min, the energy of activation for formation of the Schiff base intermediate was found to have the value 50 ± 2 kJ mol⁻¹, while the apparent activation energy for formation of acrylamide was 64.4 ± 0.6 kJ mol⁻¹, for formation of the decarboxylated Schiff base intermediate 92 ± 2 kJ mol⁻¹, and for formation of the Amadori compound 59 ± 4 kJ mol⁻¹, respectively. At high temperature conditions, formation of the Schiff base is accordingly rate determining, while at lower temperatures, decarboxylation becomes rate determining. Aminopropionamide was only detected at reaction times at which acrylamide formation already is significant in favor of, a reaction path including direct formation of acrylamide from the decarboxylated Schiff base, rather than including dissociation of ammonia from aminopropionamide.     

Effects of temperature,solid content and pH on the stability of black carrot anthocyanins

Anthocyanin stability of black carrots was studied at various solid contents (11, 30, 45 and 64° Brix) and pHs (4.3 and 6.0) during both heating, at 70–90 °C, and storage at 4–37 °C. Monomeric anthocyanin degradation fitted a first-order reaction model. Degradation of monomeric anthocyanins increased with increasing solid content during heating, while it decreased during storage. For example, at pH 4.3, half-life periods for anthocyanins at 30, 45 and 64° Brix were, respectively, 8.4, 6.9 and 5.2 h during heating at 80 °C and 18.7, 30.8 and 35.9 weeks during storage at 20 °C. At 30–64° Brix, increasing pH from 4.3 to 6.0 enhanced the degradation of anthocyanins during heating. The effect of pH on thermal stability of anthocyanins was also studied at six different pHs (2.5–7.0) in citrate-phosphate buffer solutions and significant decrease in anthocyanin stability was observed at pHs above 5.0. Higher activation energies (E_a) were obtained during heating than during storage with increasing solid contents. At 30–64° Brix, E_a values ranged from 68.8 to 95.1 kJ mol⁻¹ during heating and from 62.1 to 86.2 kJ mol⁻¹ during storage. Q₁₀ values at 20–37 °C were as high as 3.1 at 45° Brix and 3.6 at 64° Brix.     

Thermal inactivation of lactoperoxidase in goat,sheep and bovine milk – A comparative kinetic and thermodynamic study

Using isothermal heating, inactivation of lactoperoxidase (LPO) in goat, sheep and cow milk was studied in the temperature range of 70–77 °C. Kinetic and thermodynamics studies were carried out at different time–temperature combination in order to evaluate the suitability of LPO as marker for the heat-treatment of milk and dairy products from different species. The thermal inactivation of LPO followed the first-order kinetics. D- and k-values decreased and increased, respectively with increasing temperature, indicating a more rapid LPO inactivation at higher temperatures. The influence of temperature on the inactivation rate constant was quantified using the Arrhenius and thermal death time models. The corresponding z-values were 3.38 ± 0.013, 4.11 ± 0.24 and 3.58 ± 0.004 °C in goat, sheep and cow milk, respectively. Activation energy values varied between milk species with 678.96 ± 21.43 kJ mol⁻¹ in goat milk, 560.87 ± 28.18 kJ mol⁻¹ in sheep milk and 641.56 ± 13.12 kJ mol⁻¹ in cow milk, respectively.     

Degradation kinetics of anthocyanins in acerola pulp: Comparison between ohmic and conventional heat treatment

Degradation kinetics of monomeric anthocyanins in acerola pulp during thermal treatment by ohmic and conventional heating was evaluated at different temperatures (75–90 °C). Anthocyanin degradation fitted a first-order reaction model and the rate constants ranged from 5.9 to 19.7 × 10⁻³ min⁻¹. There were no significant differences between the rate constants of the ohmic and the conventional heating processes at all evaluated temperatures. D-Values ranged from 116.7 to 374.5 for ohmic heating and from 134.9 to 390.4 for conventional heating. Values of the free energy of inactivation were within the range of 100.19 and 101.35 kJ mol⁻¹. The enthalpy of activation presented values between 71.79 and 71.94 kJ mol⁻¹ and the entropy of activation ranged from −80.15 to −82.63 J mol⁻¹ K⁻¹. Both heating technologies showed activation energy of 74.8 kJ mol⁻¹ and close values for all thermodynamic parameters, indicating similar mechanisms of degradation.     

Effects of light,temperature and water activity on the kinetics of lipoxidation in almond-based products

Lipoxidation in almond-derived products was investigated using the chemiluminescence (CL) and thiobarbituric acid-reactive substances (TBARS) methods to detect the first and later reaction products, respectively. The effects of light during storage at 5 °C, 22 °C and 40 °C were studied, as well as the effects of combined heat/water activity treatments in the 60–120 °C and 0.38–0.72 range. During storage, light was found to enhance the CL and TBARS values, and specific responses were observed in almond paste and the final Calisson product. During the heating of almond paste, as the initial water activity (a_w) increased, the CL rate constants increased during heating to 60 °C and 80 °C, but interestingly, these values decreased during further heating to 120 °C, whereas the maximum TBARS rate constants occurred at a_w 0.57 at all the heating temperatures tested. The activation energies, based on the CL and TBARS values, decreased specifically when the a_w increased from 0.38 to 0.72, giving overall values ranging from110 kJ mol⁻¹ to 60 kJ mol⁻¹. Likewise, in the same water activity range, the temperature-dependent rate constant enhancing factor (Q₁₀) decreased from 3.3 to 1.6.     

Stability of black carrot anthocyanins in various fruit juices and nectars

Fruit juices (apple, grape, orange, grapefruit, tangerine and lemon) and nectars (apricot, peach and pineapple) were coloured with black carrot juice concentrate and stability of black carrot anthocyanins in these matrices was studied during heating at 70–90 °C and storage at 4–37 °C. Anthocyanin degradation, in all coloured juices and nectars, followed first-order reaction kinetics. During heating, black carrot anthocyanins in apple and grape juices showed higher stability than those in citrus juices at 70 and 80 °C. High stability was also obtained for the anthocyanins in peach and apricot nectars at these temperatures. Black carrot anthocyanins were the least stable in orange juice during both heating and storage. During storage, degradation of anthocyanins was very fast at 37 °C, especially in pineapple nectar. Refrigerated storage (4 °C) markedly increased the stability in all samples. Activation energies for the degradation of black carrot anthocyanins in coloured juices and nectars ranged from 42.1 to 75.8 kJ mol⁻¹ at 70–90 °C and 65.9–94.7 kJ mol⁻¹ at 4–37 °C.     

Immobilization of naringinase from Aspergillus niger CECT 2088 in poly(vinyl alcohol) cryogels for the debittering of juices

Naringinase, induced from Aspergillus niger CECT 2088 cultures, was immobilized into a polymeric matrix consisting of poly(vinyl alcohol) (PVA) hydrogel, cryostructured in liquid nitrogen, to obtain biocatalytically active beads. The effects of matrix concentration, enzyme load and pH on immobilization efficiency were studied. Between 95% and 108% of the added naringinase was actively entrapped in PVA cryogel, depending on the conditions of immobilization used. The optimal conditions were: 8% (w/v) PVA at pH 7 and 1.6–3.7 U ml⁻¹ of enzyme load. The pH/activity profiles revealed no change in terms of shape or optimum pH (4.5) upon immobilization of naringinase. However, the optimum temperature was shifted from 60 °C to 70 °C and the activation energy of reaction, E_a, was decreased from 8.09 kJ mol⁻¹ to 6.36 kJ mol⁻¹ by immobilization. The entrapped naringinase could be reused through six cycles (runs of 24 h at 20 °C), retaining 36% efficacy for the hydrolysis of naringin in simulated juice.     

Kinetic and thermodynamic study of thermal inactivation of the antimicrobial peptide P34 in milk

The knowledge on thermal inactivation of biopreservatives in a food matrix is essential to allow their proper utilisation in food industry, enabling the reduction of heating times and optimisation of heating temperatures. In this work, thermal inactivation of the antimicrobial peptide P34 in skimmed and fat milk was kinetically investigated within the temperature range of 90–120 °C. The inactivation kinetic follows a first-order reaction with k-values between 0.071 and 0.007 min⁻¹ in skimmed milk, and 0.1346 and 0.0119 min⁻¹ in fat milk. At high temperatures, peptide P34 was less resistant in fat milk, with a significant decrease in residual activity as compared with skimmed milk. At temperatures below 110 °C, the fat globules seem to have protective effect to the peptide P34. Results suggest that peptide P34 is heat stable in milk with activation energy of 90 kJ mol⁻¹ in skimmed milk and 136 kJ mol⁻¹ in fat milk.     

Release kinetics of nisin from biodegradable poly(butylene adipate-co-terephthalate) films into water

The release kinetics of nisin from poly(butylene adipate-co-terephthalate) (PBAT) to distilled water was studied at of 5.6, 22 and 40 °C. The release kinetics of nisin from PBAT film was described using Fick’s second law of diffusion, partition coefficient, and Weibull model. The diffusion coefficients (D) determined were 0.93, 2.29, and 5.78 × 10⁻¹⁰ cm²/s at 5.6, 22, and 40 °C, respectively. The partition coefficients (K) calculated were 0.84, 3.89, and 5.2 × 10³ at 5.6, 22, and 40 °C, respectively. The nisin release data at selected temperatures were fitted with the Weibull model (R² > 0.97) with b and n values ranging from 0.02 to 0.98 and from 0.28 to 0.45, respectively. The temperature dependence of D, K, and Weibull model parameter b was modeled using the Arrhenius equation giving values of activation energy (E_a) of 38.3 kJ mol⁻¹ (for D), 38.5 kJ mol⁻¹ (for K), and 79.5 kJ mol⁻¹ (for b).     

Neriifolin S, a dimeric serine protease from Euphorbia neriifolia Linn.: Purification and biochemical characterisation

A dimeric serine protease Neriifolin S of molecular mass 94 kDa with milk clotting activity has been purified from the latex of Euphorbia neriifolia by anion exchange and size-exclusion chromatography. It hydrolyses peptidyl substrates l-Ala-pNA with highest affinity (K_m of 0.195 mM) and physiological efficiency (K_cat/K_m of 144.5 mM s). Enzyme belongs to the class of neutral proteases with pI value of 6.8, optimal proteolytic activity displayed at pH 9.5 and temperature 45 °C. Its proteolytic activity is strongly stimulated in the presence of Ca⁺² ions and exclusively inhibited by serine protease inhibitors. Enzyme is fairly stable toward chemical denaturants, pH and temperature. The apparent T_m, was found to be 65 °C. Thermal inactivation follow first order kinetics with activation energy (Ea), activation enthalpy (ΔH∗), free energy change (ΔG∗) and entropy (ΔS∗) of 27.54 kJ mol⁻¹, 24.89 kJ mol⁻¹, −82.34 kJ mol⁻¹ and 337.20 J mol⁻¹ K⁻¹.     

High pressure induced changes on sarcoplasmic protein fraction and quality indicators

The combined effect of pressure and mild temperature treatments on bovine sarcoplasmic proteins and quality parameters was assessed. M. longissimus dorsi samples were pressurised in a range of 200–600 MPa and 10–30 °C. High Pressure Processing (HPP) induced a reduction of protein solubility (p < 0.001) compared to non-treated controls (NT), more pronounced above 200 MPa. HPP at pressures higher than 200 MPa induced a strong modification (p < 0.001) of meat colour and a reduction of water holding capacity (WHC). SDS–PAGE analysis demonstrated that HPP significantly modified the composition of the sarcoplasmic protein fraction. The pressurisation temperature mainly affected protein solubility and colour; a smaller effect was observed on protein profiles. Significant correlations (p < 0.001) between sarcoplasmic protein solubility and both expressible moisture (r = −0.78) and colour parameters (r = −0.81 to −0.91) suggest that pressure induced denaturation of sarcoplasmic proteins could influence to some extent WHC and colour modifications of beef. Changes in protein band intensities were also significantly correlated with protein solubility, meat lightness and expressible moisture. These results describe the changes induced by HPP on sarcoplasmic proteins and confirm a relationship between modification of the sarcoplasmic protein fraction and alteration of meat quality characteristics.     

An activated-state model for the prediction of solid-phase crystallization growth kinetics in dried lactose particles

Molecular-level understanding of solid-phase crystallization growth kinetics has the potential to improve the fundamental basis for understanding this process. This understanding has been developed here as part of an activated-state model, which accounts for the effects of the moisture content and the temperature on the crystallization rate. Water-induced crystallization (WIC) at different temperatures (15 °C, 25 °C, 40 °C) and a constant relative humidity (75%) environment has been used to analyze the changes in enthalpy, entropy and Gibbs free energy of activation for the solid-phase crystallization of lactose. WIC showed that, at higher temperatures, crystallization commences at lower moisture contents. The enthalpy and Gibbs free energy of activation increased during the crystallization process, which suggested that the binding energy needed for the formation of an activated complex increased as the moisture content decreased, making the formation of the activated complex more difficult. The entropy of activation, on the other hand, decreased with the decrease in the moisture content. From the activated rate equation, the energy of activation has been estimated to be 39 ± 2 kJ mol⁻¹, which is similar to the literature value (40 kJ mol⁻¹) for the solid-phase crystallization of lactose. The reaction rate constant at 25 °C is 1.4 × 10⁻⁴ s⁻¹, which is similar to the literature value of 1.3 × 10⁻⁴ s⁻¹. The WLF equation is inconsistent and hence unreliable in predicting the rates of crystallization at the glass-transition temperature from the analysis of experimental data at different temperatures.     

Parallel enzymatic and non-enzymatic formation of zinc protoporphyrin IX in pork

Zinc protoporphyrin is formed in pork homogenates in both enzymatic and non-enzymatic reactions. Ferrochelatase is active in formation of the highly fluorescent pigment known from Parma ham as demonstrated by inhibition with N-methylmesoporphyrin and by thermal inactivation. A non-enzymatic transmetallisation reaction, exchange of iron in myoglobin by zinc(II), is demonstrated by Pb(II) inhibition of zinc protoporphyrin formation at low Pb(II) concentrations, but promoted at higher Pb(II) concentrations. The non-enzymatic reaction is characterised as a slow bimolecular reaction between protoporphyrin IX and zinc(II) with a second-order rate constant of 0.63 l mol⁻¹ s⁻¹ at 35 °C and a high energy of activation of 98 kJ mol⁻¹ for acetone:water (3:1, v/v) as solvent. Zinc protoporphyrin formation is concluded to be thermodynamically controlled with a formation constant of 4 × 10⁵ M (35 °C, acetone:water (3:1)). An efficient inhibition of formation of zinc protoporphyrin by nitrite is related to myoglobin as substrate and involves both enzymatic and non-enzymatic reactions.     

Thermal inactivation kinetics of Rabdosia serra (Maxim.) Hara leaf peroxidase and polyphenol oxidase and comparative evaluation of drying methods on leaf phenolic profile and bioactivities

Inactivation kinetics of peroxidase and polyphenol oxidase in fresh Rabdosia serra leaf were determined by hot water and steam blanching. Activation energy (52.30 kJ mol⁻¹) of polyphenol oxidase inactivation was higher than that (20.15 kJ mol⁻¹) of peroxidase. Water blanching at 90 °C or steam blanching at 100 °C for 90 s was recommended as the preliminary treatment for the retention of phenolics. Moreover, comparative evaluation of drying methods on the phenolics profiles and bioactivities of R. serra leaf were conducted. The results indicated that only intact leaf after freeze drying retained the initial quality. The sun- and air-dried leaves possessed identical phenolic profiles. The homogenised leaf (after freeze-drying) possessed a lower level of phenolics due to enzymatic degradation. Good antioxidant activities were detected for the sun- and air-dried leaves. There was insignificant difference in anti-tyrosinase and anti-α-glucosidase activities among sun-, air-, and freeze-dried leaves.     

Properties of polyphenol oxidase from Anamur banana (Musa cavendishii)

Polyphenol oxidase (PPO) was extracted from Anamur banana, grown in Turkey, and its characteristics were studied. The optimum temperature for banana PPO activity was found to be 30 °C. The pH-activity optimum was 7.0. From the thermal inactivation studies, in the range 60–75 °C, the half-life values of the enzyme ranged from 7.3 to 85.6 min. The activation energy (E_a) and Z values were calculated to be 155 kJ mol⁻¹ and 14.2 °C, respectively. K_m and V_max values were 8.5 mM and 0.754 OD₄₁₀ min⁻¹, respectively. Of the inhibitors tested, ascorbic acid and sodium metabisulphite were the most effective.     

Water absorption and starch gelatinization in whole rice grain during soaking

Hydration of rough rice grain in hot water as a function of time was studied at temperature range 25-90 °C. A simple model which considers simultaneous unsteady-state water diffusion and first-order irreversible water-starch reaction phenomenon, was used to evaluate the kinetics parameters from experimental curves. The values of the diffusion coefficients and reaction rate constants were between 1.40×10⁻¹¹ and 9.36×10⁻¹¹ m² s⁻¹ and 2.29×10⁻¹⁰ and 3.72×10⁻⁵ s⁻¹, respectively. Both parameters followed a Arrhenius-type equation with distinct activation energies below and above a break temperature of 60 °C. It was 25.4 and 289.3 kJ mol⁻¹ for the activation energies of diffusion and reaction, respectively, below 60 °C. Above this temperature the respective values of the activation energies of diffusion and reaction were 30.0 and 16.6 kJ mol⁻¹. This break temperature was in agreement with the gelatinization temperature determined experimentally.     

Purification and characterization of olive (Olea europaea L.) peroxidase – Evidence for the occurrence of a pectin binding peroxidase

Peroxidase from olive fruit (Olea europaea L., cv Douro) in a black ripening stage was purified to electrophoretic homogeneity, resulting in four cationic and four anionic fractions. The anionic fractions accounted for 92% of recovered activity and showed molecular masses of 18–20 kDa. The anionic fraction PODa4, the predominant fraction that comprised about 70% of total recovered activity, showed an isoelectric point of 4.4 and optimum pH and temperature of, respectively, 7.0 and 34.7 °C, and apparent K_m values of 41.0 and 0.53 mM, for phenol and H₂O₂, respectively. From the activity-temperature profile, the denaturation temperature and the changes in enthalpy and heat capacity for unfolding of PODa4 were estimated as being, respectively, 36.5 °C, 411.2 and −13.6 kJ mol⁻¹ K⁻¹. The activation energy for phenol oxidation by PODa4 was 99.1 kJ mol⁻¹, corresponding to a calculated temperature coefficient (Q₁₀) of 4. The arabinose (39 mol%) and galacturonic acid (38 mol%) content of the carbohydrate moiety indicated the existence of pectic material in the purified PODa4 fraction. Co-migration of the carbohydrate with the protein band in the isoelectric focusing electrophoresis, points to PODa4 fraction as being a pectin type binding peroxidase.     

Combined pH and high hydrostatic pressure effects on Lactococcus starter cultures and Candida spoilage yeasts in a fermented milk test system during cold storage

The combined effects of high pressure processing (HPP) and pH on the glycolytic and proteolytic activities of Lactococcus lactis subsp. lactis, a commonly used cheese starter culture and the outgrowth of spoilage yeasts of Candida species were investigated in a fermented milk test system. To prepare the test system, L. lactis subsp. lactis C10 was grown in UHT skim milk to a final pH of 4.30 and then additional samples for treatment were prepared by dilution of fermented milk with UHT skim milk to pH levels of 5.20 and 6.50. These milk samples (pH 4.30, 5.20 and 6.50) with or without an added mixture of two yeast cultures, Candida zeylanoides and Candida lipolytica (10⁵ CFU mL⁻¹ of each species), were treated at 300 and 600 MPa (≤20 °C, 5 min) and stored at 4 °C for up to 8 weeks. Continuing acidification by starter cultures, as monitored during storage, was substantially reduced in the milk pressurised at pH 5.20 where the initial titratable acidity (TA) of 0.40% increased by only 0.05% (600 MPa) and 0.10% (300 MPa) at week 8, compared to an increase of 0.30% in untreated controls. No substantial differences were observed in pH or TA between pressure-treated and untreated milk samples at pH 4.30 or 6.50. The rate of proteolysis in milk samples at pH values of 5.20 and 6.50 during storage was significantly reduced by treatment at 600 MPa. Treatment at 600 MPa also reduced the viable counts of both Candida yeast species to below the detection limit (1 CFU mL⁻¹) at all pH levels for the entire storage period. However, samples treated at 300 MPa showed recovery of C. lipolytica from week 3 onwards, reaching 10⁶–10⁷ CFU mL⁻¹ by week 8. In contrast, C. zeylanoides did not show any recovery in any of the pressure-treated samples during storage.     

Microbial inactivation by pressure-shift freezing: effects on smoked salmon mince inoculated with Pseudomonas fluorescens, Micrococcus luteus and Listeria innocua

Smoked salmon mince inoculated simultaneously with Listeria innocua, Micrococcus luteus and Pseudomonas fluorescens was subjected to different pressure-temperature conditions. Control freeze-thaw at 0.1 MPa with storage at −15°C or −40°C for 0-5 days did not induce microbial inactivation. Control pressurisation at 207 MPa for 23 min at 20°C (initial sample temperature) with fast (3 s) pressure release had no significant effect on Gram+bacteria while P. fluorescens underwent a 2.8 log cycle reduction. Pressurisation at 207 MPa for 23 min at −3°C (without ice crystal formation) enhanced microbial reduction to 3.8 log cycles for P. fluorescens and to about 0.5 log cycle for Gram+bacteria. “Pressure-shift nucleation” (PSN) from 207 MPa and −21°C (i.e. cooling at 207 MPa for 23 min followed by pressure release in 3 s) caused 1.2, 1.4 and 4.3 log cycle reductions of L. innocua, M. luteus and P. fluorescens, respectively. A reduction of 1.7 log cycle was observed for L. innocua and M. luteus (4.6 log cycle for P. fluorescens) when salmon mince was subjected to pressure-shift freezing (PSF) (i.e. PSN from 207 MPa and −21°C as above followed by further freezing to −25°C at 0.1 MPa). PSF with pressure release in 18 min enhanced reduction to 2 and 2.5 log cycles for L. innocua and M. luteus, respectively.