Petros Taoukis

Comparative shelf life study and vitamin C loss kinetics in pasteurised and high pressure processed reconstituted orange juice

Abstract Shelf life of reconstituted orange juice after conventional thermal (80 °C, 30 s) or high hydrostatic pressure (500 MPa, 35 °C, 5 min) pasteurisation was comparatively studied. Polypropylene bottles and laminated flexible pouches were used. Ascorbic acid loss, colour, viscosity and sensory characteristics were measured during storage at 0–15 °C. Ascorbic acid degradation rates were lower for high pressurised juice, leading to an extension of its shelf life compared to conventionally pasteurised juice. Kinetic modelling established a higher temperature dependence of ascorbic acid loss for high pressurised juice as expressed by activation energy values (61.1 and 43.8 kJ/mol respectively for high pressurised and thermally treated bottled juice). Based on ascorbic acid retention, the increase of shelf life of high pressurised juice stored in bottles compared to thermally pasteurised one ranged from 11% (storage at 15 °C) to 65% (storage at 0 °C). Respective values of shelf life increase for juices in pouches were 24% and 57%. Colour was not substantially affected by type of processing. Higher viscosity values were determined for high pressurised juice, while its sensory characteristics were judged superior.

Use of time–temperature integrators and predictive modelling for shelf life control of chilled fish under dynamic storage conditions

A systematic approach for fish shelf life modelling and Time Temperature Integrator (TTI) selection in order to plan and apply an effective quality monitoring scheme for the fish chill chain was developed. The temperature behaviour of the natural microflora of the Mediterranean fish boque (Boops boops) was studied and growth of the specific spoilage bacteria Pseudomonas spp. and Shewanella putrefaciens was modelled and correlated to organoleptic shelf life. Arrhenius and square root functions were used to model temperature dependence of maximum growth rates. Bacterial growth and shelf life models were validated under dynamic storage conditions with independent variable temperature experiments. The response of several TTIs from similar storage experiments was also modelled. The reliability of the TTI monitoring was cumulatively expressed by the error in the TTI derived effective temperature (Teff) for different variable temperature distributions. Teff was directly translated to shelf life of the fish.

Application of shelf life decision system (SLDS) to marine cultured fish quality

Growth of natural microflora of marine cultured, air-packed, sea bass (Dichentrachus labrax) was studied at isothermal conditions in the 0-15 degrees C range and kinetically modelled using the four-parameter Logistic equation. Sensory shelf life was correlated to pseudomonad population and sensory acceptability was correlated to a pseudomonad level, Ns, of 10(7). The variability of their initial population was quantitatively shown and a conductance-based rapid method specific to sea bass pseudomonad enumeration was established as a practical means of N0 determination, required in shelf life predictions. Kinetic models, shelf life correlations and N0 data were incorporated into the shelf life decision system (SLDS) shown to be an effective tool for marine cultured sea bass chill chain management leading to optimization of quality of the fish at consumers end.

Development and assessment of an intelligent shelf life decision system for quality optimization of the food chill chain.

The principles of application of a Shelf Life Decision System (SLDS) for the optimization of the distribution of chilled fresh and minimally processed food products are developed. The SLDS integrates predictive kinetic models of food spoilage, data on initial quality from rapid techniques, and the capacity to continuously monitor temperature history of the food product with Time Temperature Integrators (TTIs) into an effective chill chain management tool that leads to an improved narrow distribution of quality at consumption time, effectively reducing the probability of products consumed past shelf life end. The applicability and effectiveness of the SLDS is demonstrated and evaluated based on actual food spoilage and TTI kinetics and chill chain data employing the Monte Carlo simulation method.

Application and validation of the TTI based chill chain management system SMAS (Safety Monitoring and Assurance System) on shelf life optimization of vacuum packed chilled tuna.

The objective of the study was to establish a validated kinetic model for growth of spoilage bacteria on vacuum packed tuna slices in the temperature range of 0 to 15 degrees C and to evaluate the applicability of the TTI (Time Temperature Integrators) based SMAS (Safety Monitoring and Assurance System) system to improve tuna product quality at the time of consumption in comparison to the conventional First In First Out (FIFO) approach. The overall measurements of total flora and lactic acid bacteria (LAB) on the tuna samples used in a laboratory simulated field test were in close agreement with the predictions of the developed kinetic model. The spoilage profile of the TTI bearing products, handled with SMAS, was improved. Three out of the thirty products that were handled randomly, according to the FIFO approach, were already spoiled at the time of consumption (logN(LAB)>6.5) compared to no spoiled products when handled with the SMAS approach.

Evaluation and modelling of rheological properties of high pressure treated waxy maize starch dispersions

Abstract Samples of 10% waxy maize starch dispersions were treated at pressures from 450 to 600 MPa for 0–120 min. The rheological properties of the dispersions were studied by viscosity and low deformation viscoelastic measurements. At 450 MPa, the consistency coefficient did not exceed 7 Pa s n even after a treatment time of 110 min, whereas at 550 MPa a value of 20 Pa s n was reached in about 5–10 min. G ′ measurements as a function of treatment times at different pressures gave almost identical results to viscosity measurement, except that at longer treatment times G ′ decreased, indicating that excessive pressurisation seemed to weaken the gel structure. A sigmoidal type model was found to adequately correlate the consistency coefficient values, obtained at different holding times and processing pressures, with the F value of the process, a value representing an equivalent processing time at specified reference pressure and temperature conditions, defined analogously to the traditional thermal processing terminology.

A theoretical procedure for using multiple response time-temperature integrators for the design and evaluation of thermal processes

Abstract Time-temperature integrators (TTI) offer a sound alternative to in situ and physical-mathematical methods for thermal process design and evaluation. In the present work, the use of multi-component TTI systems, in cases where a single-component TTI with a particular z value is not available, was investigated. A procedure in using double or triple response TTI systems to evaluate the impact of a thermal process on a particular target heat labile substance was proposed and evaluated, based on a large number of product time-temperature profiles. Parameters to be considered in using a multi-component TTI included the z values of the TTI, in relation to the target z value, as well as the reference temperature used for the calculations. Guidelines for proper selection of the parameters involved are given. Although, generally, triple response TTIs performed better compared with double response TTIs, the results of double response TTIs were also satisfactory, and for practical applications, the use of a double response TTI might be sufficient.

Effect of high-pressure treatment at various temperatures on indigenous proteolytic enzymes and whey protein denaturation in bovine milk

The objective of the present study was to determine the effect of high pressure (HP) processing (200, 450 and 650 MPa) at various temperatures (20, 40 and 55 degrees C) on the total plasmin plus plasminogen-derived activity (PL), plasminogen activator(s) (PA) and cathepsin D activities and on denaturation of major whey proteins in bovine milk. Data indicated that transfer of both PL and PA from the casein micelles to milk serum occurred at all pressures utilized at room temperature (20 degrees C). In addition to the transfer of PL and PA from micelles, there were reductions in activities of PL (16-18%) and PA (38-62%) for the pressures 450 and 650 MPa, at room temperature. There were synergistic negative effects between pressure and temperature on residual PL activity at 450 and 650 MPa and on residual PA activity only at 450 MPa. Cathepsin D activity in the acid whey from HP-treated milk was in general baroresistant at room temperature. The residual activity of cathepsin D decreased significantly at 650 MPa and 40 degrees C and at the pressures 450 and 650 MPa at 55 degrees C. Synergistic negative effects on the amount of native beta-lactoglobulin were observed at 450 and 650 MPa and on the amount of native alpha-lactalbumin at 650 MPa. There were significant correlations between enzymatic activities (PL, PA and cathepsin D) and the residual native beta-lactoglobulin and alpha-lactalbumin in bovine milk. In conclusion, HP significantly affected the activity of indigenous proteolytic enzymes and whey protein denaturation in bovine milk. Reduction in activity of indigenous enzymes (PL, PA and cathepsin D) and transfer of PL and PA from the casein to milk serum induced by HP is expected to have a profound effect on cheese yield, proteolysis during cheese ripening and quality of UHT milk during storage.

Kinetic study of the combined effect of high hydrostatic pressure and temperature on the activity of Lactobacillus delbrueckii ssp. bulgaricus aminopeptidases.

The effect of high hydrostatic pressure (HHP) (100 to 700 MPa) combined with temperature (20 to 40 degrees C) on the activity of 5 aminopeptidases (PepN, PepX, PepY, PepC, and PepA) of Lactobacillus delbrueckii ssp. bulgaricus ACA-DC 0105, used as starter culture for feta cheese production, was studied. Aminopeptidases PepN, PepX, and PepA were activated at pressures up to 200 MPa, at temperatures up to 40 degrees C. PepY and PepC appeared to be more sensitive to pressure and temperature treatment leading to inactivation for pressures above 100 and 200 MPa, respectively, combined with temperature above 30 degrees C. A multi-parameter equation was used for predicting the activation of PepN, PepX, and PepA aminopeptidases in the pressure and temperature domain. Overall, processing at 200 MPa and 20 degrees C may be selected as the optimum conditions for maximum activation of 4 out of 5 aminopeptidases of L. delbrueckii ssp. bulgaricus. A 20-min treatment at these conditions leads to an average 3-fold increase in activity, which could lead to better and faster maturation of white cheese.

Monitoring the effect of high pressure and transglutaminase treatment of milk on the evolution of flavour compounds during lactic acid fermentation using PTR-ToF-MS

In this study, the effects of thermal or high hydrostatic pressure (HHP) treatment of a milk base in the absence or presence of a transglutaminase (TGase) protein cross-linking step on the flavour development of yoghurt were investigated. The presence of several tentatively identified volatile flavour compounds (VOCs), both during the enzymatic treatment and the lactic acid fermentation of the milk base, were monitored using a proton transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS). The formation of the major flavour compounds (acetaldehyde, diacetyl, acetoin, and 2-butanone) followed a sigmoidal trend described by the modified Gompertz model. The HHP treatment of milk increased significantly the volatile compound formation rate whereas it did not affect the duration of the lag phase of formation, with the exception of acetaldehyde and diacetyl formation. On the contrary, the TGase cross-linking of milk did not significantly modify the formation rate of the volatile compounds but shortened the duration of the lag phase of their formation.