Effect of Pulsed Electric Fields on the Shelf Stability and Sensory Acceptability of Osmotically Dehydrated Spinach: A Mathematical Modeling Approach.

This study focused on the osmotic dehydration (OD) of ready-to-eat spinach leaves combined with the pulsed electric field (PEF) pre-treatment. Untreated and PEF-treated (0.6 kV/cm, 0-200 pulses) spinach leaves were osmotically dehydrated at room temperature for up to 120 min. The application of PEF (0.6 kV/20 pulses) prior to OD (60% glycerol, 25 °C, 60 min) lowered water activity (aw = 0.891) while achieving satisfactory product acceptability (total sensory hedonic scoring of 8). During the storage of the product (at 4, 8, 12, and 20 °C for up to 30 d), a significant reduction in total microbial count evolution was observed (9.7 logCFU/g for the untreated samples vs. 5.1 logCFU/g for the PEF-OD-treated samples after 13 d of storage at 4 °C). The selection of these PEF and OD treatment conditions enabled the extension of the product shelf life by up to 33 d under chilled storage. Osmotically treated spinach could find application in ready-to-eat salad products with an extended shelf life, which is currently not possible due to the high perishability of the specific plant tissue.

Shelf-Life Enhancement Applying Pulsed Electric Field and High-Pressure Treatments Prior to Osmotic Dehydration of Fresh-Cut Potatoes.

From a quality standpoint, it is desirable to preserve the characteristics of fresh-cut potatoes at their peak. However, due to the mechanical tissue damage during the cutting process, potatoes are susceptible to enzymatic browning. This study pertains to the selection of the appropriate osmotic dehydration (OD), high pressure (HP), and pulsed electric fields (PEF) processing conditions leading to effective quality retention of potato cuts. PEF (0.5 kV/cm, 200 pulses) or HP (400 MPa, 1 min) treatments prior to OD (35 °C, 120 min) were found to promote the retention of the overall quality (texture and color) of the samples. The incorporation of anti-browning agents (ascorbic acid and papain) into the osmotic solution improved the color retention, especially when combined with PEF or HP due to increased solid uptake (during OD) as indicated by DEI index (2.30, 1.93, and 2.10 for OD treated 120 min, non-pre-treated, HP pre-treated, and PEF pre-treated samples, respectively). PEF and HP combined with OD and anti-browning agent enrichment are sought to improve the quality and microbial stability of fresh-cut potatoes during refrigerator storage. Untreated fresh-cut potatoes were characterized by color degradation from the 2nd day of storage at 4 °C, and presented microbial growth (total viable counts: 6 log (CFU)/g) at day 6, whereas pre-treated potato samples retained their color and microbiologically stability after 6 days of cold storage (total viable counts, <4 log(CFU)/g).

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).

Optimization of Osmotic Dehydration of Tomatoes in Solutions of Non-Conventional Sweeteners by Response Surface Methodology and Desirability Approach.

The osmotic dehydration (OD) of tomatoes in solutions of alternative sweeteners was investigated using Response Surface Methodology (RSM), while selected desirability functions were implemented in order to define the optimum process parameters (temperature/duration of osmotic treatment, osmotic solution composition and concentration). Mass exchange, color and texture were measured during the process. Changes in color occurred rapidly at the beginning of the process, while firmness was significantly increased, indicating that OD processing led to tomato texture improvement. Color and firmness changes were adequately modeled using a polynomial model. RSM coupled with desirability functions was applied to optimize OD procedure in terms of color retention and maximum solid gain, a requirement for candied products. A maximum desirability was obtained by incorporating oligofructose into the osmotic solution, at relatively short treatment times. Results were validated and sensory analysis was conducted at the optimized conditions to assess samples' organoleptic acceptance.

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.

Evaluation and modelling of osmotic pre-treatment of peach using alternative agents in a multiple-component solution.

BACKGROUND: Peach is a perishable fruit of great importance for the Greek food export market which is prone to rapid deterioration after harvesting. Its short shelf life can be substantially prolonged by applying an appropriate osmotic dehydration (OD) pre-treatment, which is a mild, non-thermal procedure. The aim of this study was to describe mass transfer and quality retention induced by the OD process. RESULTS: Peach pieces were immersed in tertiary solutions of glycerol, erythritol, steviol glucosides and mineral salts at pre-selected OD conditions (25-45 °C for 3-240 min, wfruit /wsolution = 1:5). Water loss (WL), solid gain (SG), water activity (aw ) as well as representative quality indices (colour, texture) were measured during OD, showing that osmotically dehydrated peach presented significant aw reduction (from 0.97 to 0.88) combined with quality retention. CONCLUSION: This research showed that OD can be an effective pre-processing step in the production of intermediate moisture novel products. A second-degree polynomial model was developed describing adequately the effect of OD time and temperature and glycerol concentration on WL, SG, aw , colour and texture of osmotically dehydrated peach, and analysis of variance was applied to identify those factors that significantly affect the aforementioned parameters. It was concluded that OD using alternative osmotic agents is an efficient method with respect to product colour and texture retention, allowing for the production of novel products with extended shelf life. © 2018 Society of Chemical Industry.

Modelling dehydration of apricot in a non-conventional multi-component osmotic solution: effect on mass transfer kinetics and quality characteristics.

The quality and preservation of fresh-cut fruits can be improved by applying mild, non-thermal pre-treatments, such as osmotic dehydration (OD). The aim was to model the effect of OD on mass transfer and quality preservation. Apricot pieces were immersed in multi-component solutions comprising glycerol, erythritol, steviol glucosides and mineral salts, at various time-temperature conditions (25-45 °C for 3-240 min, wfruit/wsolution = 1/5). Water loss (WL), solid gain (SG), water activity (aw) as well as main quality indices (colour, texture) were measured during OD. OD apricot exhibited higher quality retention (acceptable level of colour change, increased firmness) suggesting that OD can be an effective pre-processing step in the production of innovative products. A second degree polynomial model was developed, describing the effect of processing conditions and glycerol concentration on WL, SG, aw, colour and texture of osmotically dehydrated apricots, and ANOVA was applied to identify the factors that significantly affect the aforementioned parameters.

Shelf-life prediction models for ready-to-eat fresh cut salads: Testing in real cold chain.

The aim of the study was to develop and test the applicability of predictive models for shelf-life estimation of ready-to-eat (RTE) fresh cut salads in realistic distribution temperature conditions in the food supply chain. A systematic kinetic study of quality loss of RTE mixed salad (lollo rosso lettuce-40%, lollo verde lettuce-45%, rocket-15%) packed under modified atmospheres (3% O2, 10% CO2, 87% N2) was conducted. Microbial population (total viable count, Pseudomonas spp., lactic acid bacteria), vitamin C, colour and texture were the measured quality parameters. Kinetic models for these indices were developed to determine the quality loss and calculate product remaining shelf-life (SLR). Storage experiments were conducted at isothermal (2.5-15°C) and non-isothermal temperature conditions (Teff=7.8°C defined as the constant temperature that results in the same quality value as the variable temperature distribution) for validation purposes. Pseudomonas dominated spoilage, followed by browning and chemical changes. The end of shelf-life correlated with a Pseudomonas spp. level of 8 log(cfu/g), and 20% loss of the initial vitamin C content. The effect of temperature on these quality parameters was expressed by the Arrhenius equation; activation energy (Ea) value was 69.1 and 122.6kJ/mol for Pseudomonas spp. growth and vitamin C loss rates, respectively. Shelf-life prediction models were also validated in real cold chain conditions (including the stages of transport to and storage at retail distribution center, transport to and display at 7 retail stores, transport to and storage in domestic refrigerators). The quality level and SLR estimated after 2-3days of domestic storage (time of consumption) ranged between 1 and 8days at 4°C and was predicted within satisfactory statistical error by the kinetic models. Teff in the cold chain ranged between 3.7 and 8.3°C. Using the validated models, SLR of RTE fresh cut salad can be estimated at any point of the cold chain if the temperature history is known. Shelf-life models of validated applicability can serve as an effective tool for shelf-life assessment and the development of new products in the fresh produce food sector.