High Pressure Destruction Kinetics of Clostridium Sporogenes Spores in Salmon Slurry at Elevated Temperatures

Salmon slurry containing C. sporogenes spores was subjected to high pressure (HP) treatments (700–900 MPa; 80–100°C, and 0–24 min). Destruction rates (D value) and pressure/temperature sensitivity parameters (Z_P and Z_T ) were evaluated. Thermal treatment D values were an order of magnitude higher than those under HP. Higher pressures and temperatures accelerated the spore destruction rates. Z_P values were 14.5, 17.3 and 15.5°C at 700, 800 and 900 MPa respectively, while Z_T values (at constant temperature) were 440, 540, 550 MPa at 80, 90, and 100°C, respectively. The z value under thermal treatment was 8.8°C. The spores were relatively more sensitive to temperature than to pressure.     

Compression Heating and Temperature Control for High-Pressure Destruction of Bacterial Spores: An Experimental Method for Kinetics Evaluation

High-pressure (HP) processing is considered as an alternative technique for thermal sterilization of high quality foods. Adiabatic compression during pressurization allows for quick increase in temperature of food products, which is reversed when the pressure is released, thereby providing rapid heating and cooling conditions and hence short process times. However, during the pressure holding time, the product experiences a temperature drop as a result of heat loss to the vessel. The temperature variation during the process and the synergistic effect of temperature and pressure make it difficult to get the required accurate data on microbial spore destruction kinetics. In this study, a polyoxymethylene (POM)-insulated chamber was evaluated for temperature control in the test sample during pressure treatment. Temperature variations in the HP system were measured in milk test samples inside the POM insulator and pressure medium in the HP vessel under various conditions of pressures (500–900 MPa) and initial temperatures (20–80 °C). Results demonstrated that the POM chamber had good thermal-insulation characteristics under pressure and was able to maintain stable operating conditions for microbial spore destruction kinetics. Based on the measured adiabatic temperature change, the required initial temperatures for the test sample and pressure medium were generated as a quadratic function of pressure and temperature. The setup was then verified for pressure inactivation of Clostridium sporogenes (PA 3679) spores in ultra-heat-treated milk. The better temperature stability of test samples during treatment provided a means to gather accurate data on HP destruction kinetics of the microbial spores.     

Optimization and evaluation of heat-shock condition for spore enumeration being used in thermal-process verification: Differential responses of spores and vegetative cells of Clostridium sporogenes to heat shock

To evaluate a heat-shock condition for the enumeration of Clostridium sporogenes spores, a surrogate for C. botulinum spores, we examined the heat tolerance of C. sporogenes spores and vegetative cells exposed to a heat shock at 90°C. From the D values of the spores determined in the temperature range of 113–121°C, z value (±SD) and D_90°C value were estimated to be 10.16±0.90°C and 1,071.52 min, respectively, and the inactivation rates were predicted to be only approximately 2% at 90°C for up to 10 min. Meanwhile, the viable count of spores was significantly higher when activated under a heat-shock condition of 90°C for over 9 min than those activated for shorter time periods. The heat tolerance of vegetative cells was extremely low, showing a D_90°C value (±SD) of 0.21±0.01 min. Finally, 3 different heat-shock conditions were compared: 70°C for 30 min, 80°C for 20 min, and 90°C for 10 min, and the experimental comparative data showed no significant differences in viable spore counts. Consequently, these results support that the heat-shock treatment at 90°C for 10 min is suitable to activate spores and to inactivate vegetative cells of C. sporogenes.     

High-pressure destruction kinetics of Clostridium sporogenes ATCC 11437 spores in milk at elevated quasi-isothermal conditions

The high-pressure sterilization establishment requires data on isobaric and isothermal destruction kinetics of baro-resistant pathogenic and spoilage bacterial spores. In this study, Clostridium sporogenes 11437 spores (10⁷ CFU/ml) inoculated in milk were subjected to different pressure, temperature and time (P, T, t) combination treatments (700–900 MPa; 80–100 °C; 0–32 min). An insulated chamber was used to enclose the test samples during the treatment for maintaining isobaric and quasi-isothermal processing conditions. Decimal reduction times (D values) and pressure and temperature sensitivity parameters, Z_T (pressure constant) and Z_P (temperature constant) were evaluated using a 3 × 3 full factorial experimental design. HP treatments generally demonstrated a minor pressure pulse effect (PE) (no holding time) and the pressure hold time effect was well described by the first order model (R² > 0.90). Higher pressures and higher temperatures resulted in a higher destruction rate and a higher microbial count reduction. At 900 MPa, the temperature corrected D values were 9.1, 3.8, 0.73 min at 80, 90, 100 °C, respectively. The thermal treatment at 0.1 MPa resulted in D values 833, 65.8, 26.3, 6.0 min at 80, 90, 95, 100 °C respectively. By comparison, HP processing resulted in a strong enhancement of spore destruction at all temperatures. Temperature corrected Z_T values were 16.5, 16.9, 18.2 °C at 700, 800, 900 MPa, respectively, which were higher than the thermal z value 9.6 °C. Hence, the spores had lower temperature sensitivity at elevated pressures. Similarly, corrected Z_P values were 714, 588, 1250 MPa at 80, 90, 100 °C, respectively, which illustrated lower pressure sensitivity at higher temperatures. By general comparison, it was concluded that within the range operating conditions employed, the spores were relatively more sensitive to temperature than to pressure.     

Effects of high pressure treatment on physicochemical characteristics of fresh sea bass (Dicentrarchus labrax)

The effects of high pressure (HP) treatment (pressure: 220–250–330 MPA; holding time: 5 and 10 min; temperature: 3, 7, 15 and 25°C) on physicochemical characteristics (colour, thiobarbituric acid, trimethylamine nitrogen values) of fresh sea bass fillets were investigated. HP-treated sea bass fillets had higher lightness (Hunter L*) values than untreated sea bass fillets; the magnitude of changes increased with treatment pressure. HP-induced changes in colour generally imparted a cooked sample. The TBA value of HP treated sea bass samples (except 220–330 MPa, 3°C for 5 min) were found to be insignificant (P > 0.05) or significantly (P < 0.05) lower than the untreated samples. TMA-N content of HP treated at 220–250–330 MPa, 3–7–25°C for 10 min sea bass samples were found to insignificant according to the untreated samples. The results obtained from this study showed that the quality of high pressure treated sea bass is best preserved at 220 MPa, 25°C for 5 min.     

High-pressure destruction kinetics of Clostridium sporogenes spores in ground beef at elevated temperatures

High pressure (HP) is an alternative technique for thermal sterilization of foods with minimum quality loss. HP destruction kinetics of bacterial spores is essential to establishing sterilization process, but knowledge in this field is still very limited. In this study, destruction kinetics was investigated using Clostridium sporogenes PA 3679 (ATCC7955) spores in extra-lean ground beef (5 g each sealed in a sterile plastic bag). Duplicated samples were subjected to HP treatments at 700, 800 and 900 MPa in a HP system equipped with a Polyoxymethylene insulator to maintain constant temperatures at 80, 90 and 100 degrees C during pressure-holding time. The kinetic parameters of the spores (D- and Z-values) were evaluated at these pressures and temperatures. For the pressure from 700 to 900 MPa, D-values ranged from 15.8 to 7.0 and 1.5 to 0.63 min at 80 and 100 degrees C, respectively. The pressure resistance of Z(T)(P) value was 520-563 MPa at 80-100 degrees C. The temperature resistance of Z(P)(T) value was 19.1-19.7 degrees C at 700-900 MPa, much higher than that at atmospheric condition (12.4 degrees C). A regression model was generated which can be used to predict D-value or the death time of a minimum process under given pressure and temperature conditions. HP treatment with elevated temperatures can destroy bacterial spores with a shorter time or lower temperature than conventional thermal processing. This study provides useful information for the achievement of a safe HP sterilization process.     

Effect of High Hydrostatic Pressure (HHP) Treatment on Physicochemical Properties of Horse Mackerel (Trachurus trachurus)

The basic objective of this study was to determine the effect of high hydrostatic pressure (HHP; 220, 250 and 330 MPa), holding time (5 and 10 min) and temperature (7, 15 and 25 °C) on some quality parameters of horse mackerel such as colour changes, thiobarbituric acid (TBA-i) and trimethylamine nitrogen (TMA-N), free amino acid content. HHP increased L ^* values of horse mackerel. The a ^* and b ^* of treated horse mackerel did not change significantly after HHP applications. After, HHP, TBA-i and TMA values of all HHP-treated horse mackerel samples remained unchanged than those of untreated samples. The results obtained from this study showed that the quality of high pressure treated horse mackerel is best preserved at 250 MPa, 7–15 °C for 5 min, 220 MPa, 15–25 °C for 5 min, 250 MPa, 15 °C for 10 min and 330 MPa, 25 °C for 10 min.     

Effect of high hydrostatic pressure and high-pressure homogenisation on <Emphasis Type="Italic">Lactobacillus plantarum</Emphasis> inactivation kinetics and quality parameters of mandarin juice

The inactivation kinetics of Lactobacillus plantarum in a mandarin juice treated by thermal treatment (45–90 °C), high-pressure homogenisation (HPH) (30–120 MPa at 15 and 30 °C) and high-pressure processing (HPP) (150–450 MPa at 15, 30 and 45 °C) were fitted to different Weibullian equations. A synergic effect between pressure and temperature was observed in HPH and HPP treatments achieving 2.38 log cycles after 120 MPa at 30 °C for 10 s (final T of 45 °C) and 6.12 log cycles after 400 MPa at 45 °C for 1 min (final T of 60 °C), respectively. A combined treatment of 100 MPa at 15 °C for 10 s and 300 MPa at 15–30 °C for 1 min in HPH and HPP, respectively, was needed to the first logarithm microbial population decline. Weibull model accurately predicted microorganism inactivation kinetics after HPH and HPP processing when displaying single shoulder or tail in the survivor curves, whereas when a more complex trend was observed after thermal treatment, the double-Weibull equation was found more appropriate to explain such behaviour. Equivalent treatments that achieved the same degree of microbial inactivation (77 °C–10 s in thermal processing, 120 MPa–10 s at 30 °C in HPH processing and 375 MPa–1 min at 30 °C in HPP) were selected to study the effects on quality parameters. The application of dynamic pressure led to a decrease in sedimentable pulp, transmittance and juice redness, thus stabilising the opaqueness and cloudiness of mandarin juice. Pectin methyl esterase (PME) was found to be highly baroresistant to static and dynamic pressure. Carotenoid content remained unaffected by any treatment. This study shows the potential of high-pressure homogenisation as an alternative for fruit-juice pasteurisation.     

Effects of nisin and reutericyclin on resistance of endospores of Clostridium spp. to heat and high pressure

The effects of high pressure, temperature, and antimicrobial compounds on endospores of Clostridium spp. were examined. Minimal inhibitory concentrations (MIC) of nisin and reutericyclin were determined for vegetative cells and endospores of Clostridium sporogenes ATCC 7955, Clostridium beijerinckii ATCC 8260, and Clostridium difficile 3195. Endospores of C. sporogenes ATCC 7955 and C. beijerinckii ATCC 8260 were exposed to 90 °C and 90 °C/600 MPa in the presence of 16 mg L⁻¹ nisin or 6.4 mg L⁻¹ reutericyclin for 0–60 min in a 0.9% saline solution. Dipicolinic acid (DPA) release was measured using a terbium-DPA fluorescence assay, and endospore permeability was assessed using 4′,6-diamidino-2-phenylindole (DAPI) fluorescence. Vegetative cells of C. sporogenes ATCC 7955 exhibited higher sensitivity to nisin relative to endospores, with MIC values 0.23 ± 0.084 mg L⁻¹ and 1.11 ± 0.48 mg L⁻¹, respectively. Nisin increased DPA release when endospores were treated at 90 °C; however, only C. sporogenes ATCC 7955 exhibited higher inactivation, suggesting strain or species specific effects. Reutericyclin did not enhance spore inactivation or DPA release. Use of nisin in combination with high pressure, thermal treatments enhanced inactivation of endospores of Clostridium spp. and may have application in foods.     

Improvement in Texture of Pressure-Assisted Thermally Processed Carrots by Combined Pretreatment using Response Surface Methodology

The effect of pretreatment pressure (0.1 to 400 MPa), temperature (25 to 75 °C), and calcium chloride concentration (0 to 1.5%) and their complex interaction on hardness, residual pectinmethylesterase (PME) activity, and diffused calcium content of pressure-assisted thermal processed (PATP, 700 MPa, 105 °C for 15 min) carrot have been studied using response surface methodology. Predicted values of carrot hardness, calcium content, and residual PME activity were found to be in good agreement with experimental values as indicated by the high R ² values of 0.98, 0.96 and 0.96, respectively. The optimum processing conditions, namely, calcium chloride concentration 1.0%; pretreatment pressure ranging from 286 to 314 MPa; pretreatment temperature varying from 53.8 to 58.3 °C, fulfill the conditions to obtain the PATP carrot with hardness ≥145 N, calcium content ≥ 2.5 mg/g, and residual PME activity ≥ 70%. These conditions resulted in more than tenfold increase in the hardness of PATP carrot (14.08 to 145 N) as compared to PATP carrot without any pretreatment. The study demonstrated that response surface methodology can be used for modeling carrot quality parameters of PATP.     

Supercritical Carbon Dioxide Extraction of Valuable Compounds from Citrus junos Seed

Extraction of Citrus junos seed was carried out at temperatures of 40–70 °C, pressures of 20–50 MPa, and CO₂ flow rate of 3 ml/min with supercritical carbon dioxide to obtain the valuable compounds. Seed oil was also extracted by using Soxhlet extraction with hexane as the solvent during 360 min for comparison with the efficiency of supercritical carbon dioxide extraction. Gas chromatography–mass spectrometry (GC–MS) was used to analyze the components present in the seed oil and Gas chromatography-flame ionization detector (GC-FID) was used to quantify their amounts. Among the conditions studied, the highest extraction yield was obtained at higher pressure and temperature (50 MPa and 70 °C). The extraction yield was about 29.5% of the seed, which was almost comparable to that of hexane Soxhlet extraction (33.8%). The results of the GC–MS analyses showed that the seed oil extracted contained N-methylanthranyl acid methyl, fatty acids (such as palmitic, stearic, oleic, linoleic, and linolenic acid), and physiologically active substances of β-sitosterol and squalene.     

Application of electro-activated potassium acetate and potassium citrate solutions combined with moderate heat treatment on the inactivation of Clostridium sporogenes PA 3679 spores

Combined effects of moderate temperatures and the electro-activated aqueous solutions of potassium acetate and potassium citrate on the inactivation of C. sporogenes PA 3679 spores (D_121°C = 1.18 min) were studied. Four types of solutions (potassium acetate with/without KCl and potassium citrate with/without KCl) were activated at 400 mA for 60 min. The oxidation reduction potential (ORP) and pH values ranged from + 417.50 to + 1043.33 mV and 3.18 to 3.47, respectively. The combination of these solutions with a moderate heat treatment (95 °C, 105 °C, and 115 °C) for different time (5, 10, 20, and 30 min) was sufficient to reach a 100% of spore destruction (inactivation) in a medium with an initial contamination level comprised between 7.0 and 7.8 log CFU/mL. The sporicidal effect of solutions was also present even if activated solutions were applied alone against spores without being combined with heat treatment. Spore morphology was determined under transmission electron microscopy and showed that there were important damages, such as rupture of spores and release of spore components in all of the treated spores. Thus, the sporicidal effect detected was the result of inactivation mechanisms of electro-activated solutions on spores. In almost all of observed micrographs, there were coreless spores, deformed spores, or debris of spores. The current investigation can be used for achieving further studies in order to better understand the mechanisms of inactivation of C. sporogenes spores by electro-activated solutions.Industrial relevanceThis research article aims to study the combined effect of electro-activated potassium acetate and citrate solutions and moderate heat treatment on the viability of Clostridium sporogenes in model solutions as a non-pathogenic surrogate of Clostridium botulinum. The objective was to use hurdle technology to produce nutritious, minimally processed foods while ensuring food safety. Moreover, this approach allowed for a reduced level of sodium in canned foods since the solutions were sodium-free.     

Combined thermal and high pressure inactivation kinetics of tomato lipoxygenase

The combined isothermal (10–60 °C) and isobaric (0.1–650 MPa) inactivation kinetics of lipoxygenase (LOX) extracted from tomatoes and reconstituted in a tomato purée were studied. Thermal inactivation of LOX at atmospheric pressure proceeded in the temperature range of 45–65 °C. LOX inactivation did not follow first order kinetics; the data could be fitted assuming that the two isoforms of LOX with different thermostability were present. Combined thermal and high pressure inactivation occurs at pressures in the range of 100–650 MPa combined with temperatures from 10–60 °C, and followed first-order kinetics. In the high-temperature/low-pressure range, (T≥50 °C and P≤300 MPa) an antagonistic effect is observed, therefore, the Arrhenius and Eyring equation cannot be used over the entire temperature and pressure range. Small temperature dependence is found in the low-temperature/high pressure range. A third degree polynomial model was successfully applied to describe the temperature–pressure dependence of the inactivation rate constants, which can be useful to predict inactivation rate constants of tomato LOX reconstituted in tomato purée in the temperature–pressure range studied.     

Combined effects of high pressure,moderate heat and pH on the inactivation kinetics of Bacillus licheniformis spores in carrot juice

The objective of this research was to evaluate the combined effect of high pressure processing (temperature, pressure and time) and product (pH) related variables on destruction kinetics of spores of Bacillus licheniformis in carrot juice. A 3-level factorial experimental design was used with the microbial spores inoculated into carrot juice at the natural pH (6.2) and acidified pH (4.5 and 5.5), pressure (400, 500 or 600 MPa), temperature (40, 50, and 60 °C) and time (0–40 min) conditions. D values found varied from 0.6 to 14.1 min based on the temperature, pressure and pH level combinations. The corresponding temperature and pressure dependency of D values were in the range 23.3 to 31 °C and 241 to 465 MPa, respectively. The destruction pattern was also dependent on pH, with lower pH contributing to higher destruction rate. Conventional log-linear model and Weibull model were used to describe the survivor curves and for predicting processing time to achieve a 5D spore reduction. The survivor curves exhibited slightly upward concavity and therefore better described by a Weibull than the log-linear model. Treatment combinations showed significant (p ≤ 0.05) effects on D and z values of log-linear model and rate parameter (α) of Weibull model. The 5D spore count reduction times estimated using Weibull model parameters were longer than those from the log-linear model, generally demonstrating an over-treatment. Overall, the pH reduction of low acid foods showed a significant enhancement of rate of destruction of B. licheniformis spores.     

Effects of high pressure and temperature on buckwheat starch characteristics

Pressure-induced gelatinisation of buckwheat starch suspensions (25% w/w) was studied and compared to heat-induced gelatinisation. Starch suspensions were treated at increased pressure (200–600 MPa) or temperature (60–95 °C) for 10 min. The degree of gelatinisation and the temperature and pressure ranges of gelatinisation were determined using differential scanning calorimetry, changes in birefringence and pasting behaviour. Furthermore, the structural changes during gelatinisation were investigated using microscopy. The pressure-induced as well as the temperature-induced gelatinisation curves were sigmoid shaped. Gelatinisation occurred between 300 and 500 MPa or between 60 and 70 °C. Scanning electron microscopy images showed retention of the granular structure after treatment with 600 MPa. However, when heated at temperatures above 65 °C, the formation of a “sponge-like” structure was observed. Better preservation of the granular structure for pressure treatment compared to temperature treatment resulted in stronger gels for the former. Pre-treatment with pressure as well as temperature made the buckwheat starch granules more resistant to swelling and disintegration under the influence of additional heat.     

High pressure CO2 reduces the wet heat resistance of Bacillus subtilis spores by perturbing the inner membrane

Spores of wild-type Bacillus subtilis PS533 were treated by wet heat at 75 °C for 30 min, and high pressure CO₂ (HPCD) at 6.5 MPa and 30 °C or 75 °C for 30 min. The spores were analyzed for wet heat resistance (85 °C, 90 °C, 95 °C) and typical germination events including DPA release and cortex hydrolysis, inner membrane permeability, and germination triggered by nutrient (L-valine and AGFK) or non-nutrient (dodecylamine and high pressure at 150 MPa or 550 MPa) germinants. The results showed that (i) HPCD-treated spores exhibited reduced wet heat resistance compared to the untreated or wet heat-treated spores; (ii) HPCD-treated spores did not undergo typical germination events such as DPA release or cortex hydrolysis compared to normally germinated spores; (iii) HPCD-treated spores released more metal ions and exhibited decreased ability to maintain DPA, indicating that the permeability of inner membrane of HPCD-treated spores was increased; (iv) HPCD-treated spores exhibited reduced germination rate when triggered by L-valine or 150 MPa, but increased germination rate when triggered by dodecylamine or 550 MPa, suggesting that the fluidity of the inner membrane of HPCD-treated spores might be increased. These results indicated that HPCD could reduce the wet heat resistance of spores, and this resistance decrease was probably due to the modification of the inner membrane caused by HPCD.Industrial relevanceThe extremely high wet heat resistance of spores makes them a significant problem in the thermal processing of foods. Thus, it of great interest to develop a process to reduce the wet heat resistance of spores. In this work, we found that HPCD can significantly reduce the wet heat resistance of B. subtilis spores, and this was achieved by perturbing the inner membrane of spores. These results can improve our understanding of the inactivation mechanism of spores by HPCD, and also provide an alternative approach for spore inactivation in foods.     

Effect of High Hydrostatic Pressure on Physicochemical and Structural Properties of Rice Starch

Rice starch–water suspension (20%) were subjected to high hydrostatic pressure (HHP) treatment at 120, 240, 360, 480, and 600 MPa for 30 min. Polarizing light microscope, scanning electron microscopy (SEM), rapid visco analyzer (RVA), differential scanning calorimeter (DSC), and X-ray diffraction were used to investigate the physicochemical and structural changes of starch. Microscopy studies showed that the treatment of starch with HHP under 600 MPa for 30 min resulted in a complete loss of birefringence and a gel-like appearance. The treatment of starch suspension with HHP at 600 MPa resulted in a significant increase in swelling power and solubility at low temperature (50–60 °C), but opposite trends were found at high temperature (70–90 °C). The DSC analysis showed a decrease in gelatinization temperatures and gelatinization enthalpy with increase of pressure levels. RVA viscograms of starches exhibited an increase in peak, trough, and final viscosities, peak time, and pasting temperature but decrease of breakdown, setback viscosities, and pasting temperature when pressure was increased. X-ray diffraction studies showed that the HHP treatment converted rice starch that displayed the A-type X-ray patterns to the B-type-like pattern. These results showed that the treatment of rice starch in 20% starch/water suspension at a pressure of 600 MPa for 30 min led to a complete gelatinization of starch granules.     

The effect of high hydrostatic pressure on the microbiological, chemical and sensory quality of fresh gilthead sea bream (Sparus aurata)

The effect of different temperature/time/pressure high hydrostatic pressure (HHP) treatment on quality and shelf life of sea bream were studied. Different high-pressure treatments (at 3, 7, 15 and 25 °C, 5–10 min and 220, 250 and 330 MPa) were tested to establish the best processing conditions for quality of sea bream. The effect of the process on the quality of the sample was examined by colour, trimethylamine nitrogen and thiobarbituric acid number analysis. Based on the results of the parameter, the best combinations of HHP treatments were determined as 3 °C/5 min/250 MPa–15 °C/5 min/250 MPa for sea bream. The effects of this combination treatment on sensory, chemical and microbiological properties of sea bream stored at 4 °C were studied. The results obtained from this study showed that the shelf life of untreated and HHP treated stored in refrigerator, as determined by overall acceptability of sensory and microbiological data, is 15 days for untreated sea bream and 18 days for treated sea bream at 3 °C/5 min/250 MPa and at 15 °C/5 min/250 MPa treated sea bream.     

Inactivation kinetics and injury recovery of Bacillus amyloliquefaciens spores in low-acid foods during pressure-assisted thermal processing

Pressure-assisted thermal processing (PATP) inactivation kinetics of Bacillus amyloliquefaciens spores in deionized water (DIW) were evaluated for egg patty mince (EPM) and green pea puree (GPP). Recovery of PATP-injured spores during storage was determined. The number of B. amyloliquefaciens spores in DIW was reduced more than 6 log when treated at 121°C and 700 MPa, including a come-up time reduction (3.32 log MPN/g) and a pressure holding time reduction (3.55 log MPN/g). Treatments at 700 MPa in combination with 105°C for 16 min, 115°C for 5 min, or 121°C for 3 min, decreased B. amyloliquefaciens spore populations in EPM to levels undetectable using an enrichment procedure. No significant (p>0.05) recovery of PATP-injured spores was observed in EPM and GPP during storage for 8 weeks, compared with controls. These results provide useful information for enhancing microbial lethality of PATP-resistant bacterial spores in low-acid foods.     

DSC Determination of Glass Transition Temperature on Sea Bass (Dicentrarchus labrax) Muscle: Effect of High-Pressure Processing

Differential scanning calorimetric determination of glass transition temperature in the freeze-concentrated matrix ( T_\textg^\text￠ T_{\text{g}}^{\text{'}} ) of sea bass muscle was optimized. Conventional and modulated differential scanning calorimetry (DSC) techniques (using diverse cooling/heating rate and modulation parameters) and effect of an annealing step (−30, −20, or −15°C, 30min) were assayed. Transition was more evident using conventional DSC assays, cooling/heating rate: 10°C/min, annealing step at –20°C. A T_\textg^\text￠ T_{\text{g}}^{\text{'}} value of –15.2 ± 0.3°C was observed for sea bass fresh muscle. This method was chosen for T_\textg^\text￠ T_{\text{g}}^{\text{'}} determination on high-pressure (HP) treated and pressure shift freezing (PSF)—stored at –20°C—sea bass muscle. Thus, in both cases, transition at –15°C was less evident as a function of the pressure level applied, being very difficult to detect after treatment at 400 and 600MPa. It was observed that T_\textg^\text￠ T_{\text{g}}^{\text{'}} values were shifted to slightly higher temperatures (around 1°C higher) after HP treatment at 400 and 600MPa. The present work constituted a first approach to the study on the effect of HP on the glass transition of a complex food matrix, giving useful information about stability of the frozen food.