Combined effect of pulsed electric field and osmotic dehydration pretreatments on mass transfer and quality of air-dried pumpkin.

Pulsed electric field (PEF) and osmotic dehydration (OD) pretreatment can accelerate the time-consuming drying process and minimize its high energy demands. The effect of PEF and OD pre-processing conditions and osmotic solution composition on mass transfer kinetics (water loss, solid gain, water activity) and quality properties (color, texture, total sensory quality) during OD and subsequent air-drying (AD) of pumpkin was studied. Application of PEF (2.0 kV/cm-1500 pulses) significantly enhanced mass transfer during subsequent air-drying (increased effective diffusivity coefficient Des and drying rate kdrying , respectively). PEF and OD treatments led to a significant reduction of the processing time by 12 and 10%, respectively (p < 0.05). The maximum reduction of processing time by 27% (p < 0.05) (compared to untreated sample) resulted in combined use of PEF and OD as pretreatments prior to AD. When PEF pretreatment was combined with OD prior to AD, the corresponding energy was by 50% less than the respective energy required for nonprocessed samples. PRACTICAL APPLICATION: Pulsed electric fields (PEF) and osmotic dehydration (OD) can be applied for the production of air-dried pumpkin cuts of superior quality (in terms of quality and sensory characteristics) and reduced energy requirements (as a result of total processing time decrease).

Effect of Alternative Preservation Steps and Storage on Vitamin C Stability in Fruit and Vegetable Products: Critical Review and Kinetic Modelling Approaches.

Vitamin C, a water-soluble compound, is a natural antioxidant in many plant-based products, possessing important nutritional benefits for human health. During fruit and vegetable processing, this bioactive compound is prone to various modes of degradation, with temperature and oxygen being recognised as the main factors responsible for this nutritional loss. Consequently, Vitamin C is frequently used as an index of the overall quality deterioration of such products during processing and post-processing storage and handling. Traditional preservation methods, such as thermal processing, drying and freezing, are often linked to a substantial Vitamin C loss. As an alternative, novel techniques or a combination of various preservation steps ("hurdles") have been extensively investigated in the recent literature aiming at maximising Vitamin C retention throughout the whole product lifecycle, from farm to fork. In such an integrated approach, it is important to separately study the effect of each preservation step and mathematically describe the impact of the prevailing factors on Vitamin C stability, so as to be able to optimise the processing/storage phase. In this context, alternative mathematical approaches have been applied, including more sophisticated ones that incorporate parameter uncertainties, with the ultimate goal of providing more realistic predictions.

Structure conformational and rheological characterisation of alfalfa seed (Medicago sativa L.) galactomannan.

In the present work a galactomannan extract of low protein residue (< 1.3 % wt dry basis) was isolated from alfalfa (Medicago sativa L.) seed endosperm meal. The alfalfa gum (AAG) comprised primarily mannose and galactose at a ratio of 1.18:1, had a molecular weight of 2 × 106 Da and a radius of gyration of 48.7 nm. The average intrinsic viscosity of the dilute AAG dispersions calculated using the modified Mark-Houwink, Huggins and Kraemer equations was 9.33 dLg-1 at 25 °C. The critical overlap concentration was estimated at 0.306 % whereas the concentration dependence of specific viscosity for the dilute and semi-dilute regimes was ∝ C2.3 and C4.2, respectively. The compliance to the Cox-Merz rule was satisfied at 1% of AAG, whereas a departure from superimposition was observed at higher concentrations. Viscoelasticity measurements demonstrated that AAG dispersions exhibit a predominant viscous character at 1 % wt, whereas a weak gel-like behaviour was reached at AAG concentrations ≥3 %.

Quality and Shelf-Life Modeling of Frozen Fish at Constant and Variable Temperature Conditions.

The objective of this study was the investigation of the effect of variable conditions on quality parameters and the shelf life of fish during frozen storage. Three different fish products were tested, i.e., gilthead sea bream (Sparus aurata) fillets, sea bass (Dicentrarchus labrax) fillets, and yellowfin tuna (Thunnus albacares) slices stored in the range of -5 to -15 °C. The kinetic modeling of different shelf-life indices was conducted. Sensory scoring of frozen fish showed high correlation with color (L-value) and total volatile basic nitrogen (TVBN). The temperature dependence of the rates of quality degradation was expressed via the activation energy values, calculated via the Arrhenius equation, and ranged, for the tested quality indices, between 49 and 84 kJ/mol. The estimated kinetic parameters were validated at dynamic conditions and their applicability in real conditions was established, allowing for their practical application as tools for cold chain management.

Osmodehydrofreezing: An Integrated Process for Food Preservation during Frozen Storage.

Osmodehydrofreezing (ODF), a combined preservation process where osmotic dehydration is applied prior to freezing, achieves several advantages, especially in plant tissues, sensitive to freezing. OD pre-treatment can lead to the selective impregnation of solutes with special characteristics that reduce the freezing time and improve the quality and stability of frozen foods. ODF research has extensively focused on the effect of the osmotic process conditions (e.g., temperature, duration/composition/concentration of the hypertonic solution) on the properties of the osmodehydrofrozen tissue. A number of complimentary treatments (e.g., vacuum/pulsed vacuum, pulsed electric fields, high pressure, ultrasound) that accelerate mass transfer phenomena have been also investigated. Less research has been reported with regards the benefits of ODF during the subsequent storage of products, in comparison with their conventionally frozen counterparts. It is important to critically review, via a holistic approach, all parameters involved during the first (osmotic dehydration), second (freezing process), and third stage (storage at subfreezing temperatures) when assessing the advantages of the ODF integrated process. Mathematical modeling of the improved food quality and stability of ODF products during storage in the cold chain, as a function of the main process variables, is presented as a quantitative tool for optimal ODF process design.

Greek Coffee Quality Loss During Home Storage: Modeling the Effect of Temperature and Water Activity.

The aim of this study was to monitor and characterize Greek coffee staling during home storage (secondary shelf life, SSL) using sensory evaluation techniques. Storage temperature (T) and product water activity (aw ) are considered as the major factors affecting SSL. Water sorption isotherms fitted to Guggenheim Anderson-de Boer model were used to predict product stability; coffee samples were stable at aw < 0.52. Coffee samples equilibrated at aw = 0.15 (the fresh sample), 0.22, 0.33, and 0.52 were stored at T = 25 °C, 35 °C, and 45 °C under simulated home storage conditions. Samples were obtained at appropriate times for each T and aw condition and sensorially evaluated. Greek coffee brews were prepared and freshly served during sensory evaluation. The use of Weibull hazard analysis provided an effective approach to SSL determination as a function of T and aw . SSL values ranged from 20 (Τ = 45 °C, aw = 0.52) to 104 days (Τ = 25 °C, aw = 0.15). Quality loss based on coffee aroma changes (aroma quality, aroma intensity, aftertaste, off-flavor) was also studied (Si , sensory scoring using 9-point magnitude scale) and kinetically modeled. Quality loss rates (ki ) were calculated and used to predict SSL values. Based on the results of both Weibull hazard analysis and sensory scoring of individual aroma characteristics, it was concluded that the lowest SSL was calculated for aw = 0.52 at T = 35 °C to 45 °C. The temperature dependence of aftertaste, aroma quality loss, and off-flavor production was not statistically significant for 0.15 < aw < 0.33 (P > 0.05); the aroma intensity was the most sensitive parameter. PRACTICAL APPLICATIONS: Secondary shelf life (SSL) represents the time after pack opening during which a food maintains an acceptable quality level. During home/catering usage, coffee is not consumed immediately after pack opening. During consumption, quality degradation reactions proceed with higher rates due to variable storage conditions mainly related to atmosphere changes in the pack, leading to the entrance of oxygen/moisture and temperature. Therefore, SSL is important, and can be used as a tool for product management during consumption reducing food waste. There is a lack of studies dealing with SSL prediction of coffee, while no studies have been carried out on Greek coffee.

Does kappa-carrageenan thermoreversible gelation affect ß-carotene oxidative degradation and bioaccessibility in o/w emulsions?

In the present work oil-in-gel (o/g) emulsions comprising 0.4-1% w/w κ-carrageenan in the absence and presence of Ca2+ (20mM) were investigated for their ability to hamper the oxidative degradation under isothermal (5, 20 and 37°C) ambient air storage conditions and promote the in vitro bioaccessibility of ß-carotene. The mechanical and structure conformational aspects of the o/g emulsions throughout in vitro digestion were measured by means of oscillatory rheology and optical microscopy. Although the addition of κ-carrageenan reduced by more than 50% (from 0.85 to 0.40day-1) the ß-carotene oxidative degradation rates, only minor differences were detected in terms of gelation method (ca. 0.42 and 0.39day-1 for ionotropic and coldset systems) and biopolymer concentration (0.38-0.42day-1). The bioaccessibility of ß-carotene was significantly higher in coldset o/g emulsions (ca. 43%) compared to the ionically mediated ones (ca. 36%). With the exception of 0.4% κ-carrageenan containing o/g emulsions (55.4 and 49.7% for control and 0.4% κ-carrageenan respectively), the ß-carotene bioaccessibility was significantly reduced with the increase in κ-carrageenan concentration (ranging from 34 to 38.9%).

Modulation of chemical stability and in vitro bioaccessibility of beta-carotene loaded in kappa-carrageenan oil-in-gel emulsions.

In the present paper, ionotropically structured κ-carrageenan based oil-in-gel (o/g) emulsions were tested as potential carrier systems for the delivery of ß-carotene. In situ ionic gelation was induced by Na+, K+ or Ca2+ added at the level of 0.2-0.6% (w/w). All o/g emulsions exerted a true gel like behaviour with storage modulus (G') being reduced according to the order: K+>Ca2+>Na+. Ionic gelation induced a moderate increase in the microscopically assessed lipid droplets radii. O/g emulsions containing monovalent ions exerted the highest ß-carotene retention throughout isothermal storage particularly at high (37 and 55°C) temperatures. Notwithstanding, increasing ionic strength resulted in acceleration of ß-carotene degradation rates for all cation species. ß-Carotene bioaccessibility was significantly lower in Ca2+o/g emulsions due to the formation of complexes between the biopolymer matrix containing ß-carotene and bile salts. A good correlation between ß-carotene bioaccessibility, physical and colloidal aspects of the micellar digesta fractions was observed.

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.

High pressure inactivation kinetics of a Thermomyces lanuginosus xylanase evaluated as a process indicator.

The potential use of Thermomyces lanuginosus xylanase to develop a pressure-temperature-time integrator (PTTI) for high pressure processing was investigated. The combined effect of pressure and temperature on the inactivation of xylanase was studied in the pressure range of 100 to 600 MPa and temperature range of 50 to 70 degrees C. A synergistic effect of pressure and temperature was observed. Xylanase inactivation at the studied processing conditions followed first-order kinetics and was found to be very sensitive to changes in pressure and temperature. The values of activation energy and activation volume were estimated as 92.8 kJ/mol and -23.3 mL/mol at a reference pressure of 450 MPa and a reference temperature of 60 degrees C, respectively. A mathematical model of xylanase inactivation, having as variables time, pressure, and temperature allows the calculation of remaining enzyme activity at any combination of processing conditions within the studied domain. Practical Application: To ensure the optimization and control of high pressure processing, evaluation of the process impact on both safety and quality attributes of foods is essential. Enzymes can serve as effective tools in evaluating the impact of high pressure processes of foods.

Modeling microbial spoilage and quality of gilthead seabream fillets: combined effect of osmotic pretreatment, modified atmosphere packaging, and nisin on shelf life.

The objective of the study was the kinetic modeling of the effect of storage temperature on the quality and shelf life of chilled fish, modified atmosphere-packed (MAP), and osmotically pretreated with the addition of nisin as antimicrobial agent. Fresh gilthead seabream (Sparus aurata) fillets were osmotically treated with 50% high dextrose equivalent maltodextrin (DE 47) plus 5% NaCl. Water loss, solid gain, salt content, and water activity were monitored throughout treatment and treatment conditions were selected for the shelf life study. Untreated and osmotically pretreated slices with and without nisin (2 x 10(4) IU/100 g osmotic solution), packed in air or modified atmosphere (50% CO(2)-50% air), and stored at controlled isothermal conditions (0, 5, 10, and 15 degrees C) were studied. Quality assessment and modeling were based on growth of several microbial indices, total volatile nitrogen, trimethylamine nitrogen, lipid oxidation (TBARS), and sensory scoring. Temperature dependence of quality loss rates was modeled by the Arrhenius equation, validated under dynamic conditions. Pretreated samples showed improved quality stability during subsequent refrigerated storage, in terms of microbial growth, chemical changes, and organoleptic degradation. Osmotic pretreatment with the addition of nisin in combination with MAP was the most effective treatment resulting in significant shelf life extension of gilthead seabream fillets (48 days compared to 10 days for the control at 0 degrees C).

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.

Prediction for Shelf Life and Safety of Minimally Processed CAP/MAP Chilled Foods: A Review.

The reliance of minimally processed chilled foods on low temperature for distribution with optimized controlled/modified atmospheric packaging to maintain safety and quality poses new challenges to food microbiologists. Effects of controlled/modified atmospheric packaging conditions on microbial growth are briefly discussed. Microbial growth models are systematically examined with emphasis on the temperature dependence models-the Arrhenius model and the square root model. Their applicability for making predictions of both shelf life and safety under nonisothermal conditions is assessed. The use of time-temperature integrators for shelf-life prediction and safety assurance is also addressed.

A Systematic Evaluation of Time-Temperature Indicators for Use as Consumer Tags.

The applicability of single end point, consumer readable Time-Temperature Indicators (TTIs) as monitors of the end of shelf life of refrigerated food products was examined. Two types of consumer TTIs, an enzymatic and a polymer based, were tested under isothermal and nonisothermal conditions. Their temperature dependence followed the Arrhenius equation (activation energy 11 to 24 kcal/mol), and except for one tag model, the response obtained under variable temperature conditions agreed well with that predicted from the Arrhenius equation. Evaluation showed satisfactory visual recognition of the end point as compared to an instrumental measurement. Consumer TTIs can be reliably used as end of shelf-life indicators for foods with a similar activation energy for deterioration.