This study presents an in-depth experimental analysis of thermal and airflow behaviour inside large bulk apple bins under typical cold storage conditions. Four instrumented bins were monitored at two vertical levels in a commercial cold room. Temperature sensors tracked fruit cooling in different regions of each bin, while embedded sensors were designed to measure interstitial slow air speeds. Cooling was characterised in two phases: an initial continuous cool-down followed by an intermittent cooling regime. A front bin directly exposed to cold airflow showed rapid cooling at the airflow-exposed face and noticeable temperature fluctuations reflecting ongoing convective cooling. In contrast, a bin located immediately behind the front bin cooled more slowly and experienced no temperature oscillations, indicating cooling dominated by natural convection and conduction. The bin centres cooled much more slowly, highlighting the limitation of cold air penetration. Airflow measurements confirmed that only the front regions of bins received significant forced-air infiltration (approximately 0.08 m s−1), whereas interior zones became essentially air-stagnant, with air speed nearly zero, once the fruit cooled. All bins exhibited minor vertical stratification, with top-layer fruit about 0.1 to 0.2 °C warmer than bottom-layer fruit. These findings provide direct evidence of mixed convection cooling in front bins versus purely free-convective cooling or conduction cooling in sheltered bins. The study's insights emphasise the need for improved airflow distribution in cold rooms. Practical strategies, such as improved bin design and airflow management strategies, are suggested to achieve more uniform cooling.

Postharvest cold storage plays a crucial role in maintaining the quality and extending the shelf life of fresh produce, reducing food waste, and supporting a sustainable food supply chain. However, challenges such as non-uniform cooling, energy-intensive refrigeration, and environmental concerns require continuous innovation. Improper cold storage control can lead to uneven ripening and spoilage, highlighting the need for advanced monitoring and control systems. Recent innovations, including smart monitoring systems, Internet of Things (IoT) applications, artificial intelligence (AI)-driven predictive maintenance, and digital twin technology, offer potential solutions. Integrating renewable energy sources and sustainable refrigerants can further enhance environmental sustainability. This review explores key postharvest cold storage technologies, their impact on produce quality, and strategies for improving energy efficiency and sustainability. Future research should focus on optimizing energy-efficient designs and expanding the adoption of intelligent monitoring systems to ensure both economic and environmental benefits.

The preservation of apples in cold storage relies deeply on understanding the thermal dynamics governing their environment. Within packaging, apples engage in complex thermal interactions, between themselves and the environment, affecting convective and conductive heat transfer pathways. Challenges escalate in industrial cold storage facilities, manifesting as temperature stratification and non-uniform cooling. Nonetheless, a comprehensive understanding of heat transfer dynamics is vital for optimizing cold storage equipment design and enhancing cooling system operation efficacy. Building upon previous studies validating the use of Peltier elements for detecting and quantifying heat flux in individual apples, this research extends its application to industrial cold rooms. By strategically selecting locations within the apple bin and the storage cold room and comparing changes in total heat content obtained by a conventional method and comparing with the Peltier element for its validation. Results of the convective heat transfer coefficient in an upper-layer bin were in the range of 2.7-5.9 Wm(-2) K-1 while in a bin at door level were 5.0-7.0 Wm(-2) K-1. The higher values found in the position near the door can be correlated to the faster air speed experienced between the apples in this position. By applying these values in the transient heat transfer model to predict the fruit core temperature during the cooling process, a relatable prediction was found, with apple temperature difference <0.9 degrees C between predicted by the Peltier element and experimental cooling curves. This study can aid understanding of thermal dynamics in cold storage environments, and support future development for more efficient and sustainable cold storage practices.

This study analysed condensation and mass loss in apple storage using an IoT system and predictive modelling. A condensation model, based on the mass transfer coefficient determined through the Sherwood number for the relation between convective and diffusive mass transfer, and a mass loss model incorporating transpiration and respiration, were developed to predict cumulative condensation, retention time, cumulative mass loss, and at the end, the total mass of apples in storage. The model was validated with individual and bulk apples kept under varying air temperature conditions. Data on air and surface temperature, humidity, air speed, and surface wetness were collected via sensors, processed through Raspberry Pi (embedded computer) and Kafka data streaming platform for predictions, and stored in the InfluxDB time-series database for visualisation. The realtime model predictions were effectively aligned with experimental trends. In individual apple trials, 45- and 60-minute on-off refrigeration cycles showed the predicted peak cumulative condensations of 0.05 and 0.12 g kg- 1, approximately 71 % and 77 % of experimental peaks, with mass losses of 0.27 and 0.24 g kg- 1 over 12 hours, respectively. In bulk apple trials, predicted peaks were 0.03 and 1.03 g kg- 1, around 30 % and 58 % of experimental values, with mass losses of 0.96 and 0.82 g kg- 1 over 60 hours for low and high-temperature fluctuations, respectively. Temperature fluctuations significantly influenced condensation and mass loss, with high fluctuations causing much greater cumulative condensation than low fluctuations. However, experimental peak cumulative condensation values were consistently higher than predicted ones, likely due to the accuracy of sensors, the complexity of the experimental setup, and theoretical model assumptions. Transpiration accounted for a larger portion of the total cumulative mass loss in apples compared to respiration. Additionally, longer condensation retention times resulted in reduced apple mass loss.

Refrigerated storage is crucial for maintaining the quality and safety of highly perishable and seasonal fresh fruit during the postharvest stage. Heat transfer is the primary factor that affects food decay in the storage period. However, cold storage facilities often face challenges with non-uniform airflow and temperature distribution. Therefore, this study aimed to investigate the impact of different cooling rates on heat transfer. It considered factors such as air velocity, apple surface area, initial apple temperature, air temperature, and application of a coating on apples during cold storage. Tests were conducted using a batch of apples stored in a bin as well as individually. These investigations represent the variability of conditions found within cold storage facilities. The results demonstrated that air velocity plays a significant role in the cooling kinetics of apples. Higher air velocities (>2.0 m s(-1)), at the fan outlet, were found to have a lesser pronounced influence compared to lower velocities (<1.0 m s(-1)). Heat transfer coefficients of a bin of apples ranged from 2.1 to 7.9 W m(-2) K-1, for the corresponding average air speed of 0.05 and 0.31 m s(-1) within the bin. Numerical correlations were generated for the single apple as well for the bin of apples. These findings contribute to a better understanding of how to store fresh produce effectively and suggest that adjusting the airflow in cooling facilities during different cooling phases could be guided by thermal analysis of fresh produce, potentially leading to energy-saving strategies.

This investigation explores the intricate relationship between postharvest quality losses in fruit and vegetables and the dynamic interplay of transpiration and respiration activities. It underscores the profound impact of inherent produce properties and postharvest environmental conditions on transpiration, inducing changes in both external appearance and internal quality, notably wilting. Despite their common use, produce-specific transpiration coefficients encounter limitations due to diverse assumptions in calculations. Surface conditions intricately link produce and air properties, necessitating a comprehensive understanding. Horticultural products, with high water content, undergo continuous water loss through transpiration, driven by the water potential difference between the product and ambient air. Transpiration encompasses tissue and boundary layer resistances, influenced by plant tissue properties and external factors. Fruits experiencing drought stress exhibit elevated tissue resistance, serving as a protective mechanism. Concurrently, boundary layer resistance, influenced by external parameters, significantly shapes postharvest behaviour. To address these complexities, a novel method developed allows separate analysis of produce properties, climate, and flow conditions. This innovative approach enhances the understanding of transpiration behaviour, providing a foundation for improved postharvest practices, technical configurations, and quality maintenance strategies. center dot Direct method for tissue resistance and boundary layer resistance determination for fruit and vegetables. center dot Non-destructive method to optimize postharvest by using produce as a sensor to ensure quality.

Apples are stored at temperatures close to 0 °C and high relative humidity (up to 95%) under controlled atmosphere conditions. Under these conditions, the cyclic operation of the refrigeration machine and the associated temperature fluctuations can lead to localized undershoots of the dew point on fruit surfaces. The primary question for the present study was to prove that such condensation processes can be measured under practical conditions during apple storage. Using the example of a measuring point in the upper apple layer of a large bin in the supply air area, this evidence was provided. Using two independent measuring methods, a wetness sensor attached to the apple surface and determination of climatic conditions near the fruit, the phases of condensation, namely active condensation and evaporation, were measured over three weeks as a function of the operating time of the cooling system components (refrigeration machine, fans, defrosting regime). The system for measurement and continuous data acquisition in the case of an airtight CA-storage room is presented and the influence of the operation of the cooling system components in relation to condensation phenomena was evaluated. Depending on the set point specifications for ventilation and defrost control, condensed water was present on the apple surface between 33.4% and 100% of the duration of the varying cooling/re-warming cycles.

Climate control mechanisms in the postharvest chain of fruit and vegetables are predominantly based on air temperature measurements. These, however, do not reflect the real heat exchange between the product and the environment in all situations. The direct recording of the incoming and outgoing heat flux should enable higher-quality statements to be made about the interaction between the food product and the environment since other influencing parameters are also taken into account (e.g. air velocity and radiation). Commercial heat flux sensors are readily available but expensive, and for a variety of reasons, are not suitable for use directly on horticultural products, or are suitable only to a limited extent (e.g. large products, such as melons). In this study, small and low-cost Peltier elements (PE) were primarily tested and successfully validated as an alternative for their use in measuring heat exchange. Cooling, fluctuating temperature, and re-warming tests were applied to evaluate and validate the use of PE during the heat absorption and release of individual apples. The results confirmed the reliable detection of minor heat fluxes, regardless of direction, with small temperature differences (<0.5 degree celsius) between the fruit and the air. The new heat flux measurement methodology has potential applications in agricultural technology, including optimizing packaging, and designing storage equipment.

Temperature is the most important factor affecting the quality and shelf life of fresh prduce. Varying temperature conditions are often observed during the supply chain of fresh produce. This poses a big challenge in designing modified atmosphere storage and transport containers. In this study, a system was developed to actively control CO2 and O2 concentrations inside a storage container under constant and changing temperatures. A mini air blower was used for gas exchange between the container and the external atmosphere. A thin and long tube prevented air from entering the container but facilitated air exchange when the blower was switched ON. The blower ON frequency (s h-1) was modelled as a function of storage temperature, taking into account the type and amount of fruit, blower properties, tube dimension, and the setpoint of O2 concentration. The model was then used in programming an Arduino microcontroller to control the blower in response to real-time measurement of storage temperature. The gas control system was then validated by the storage of sweet cherries. The system could control the CO2 concentration at the setpoint level (12.5%) for constant temperature of 6 degrees C and 17 degrees C and changing temperature from 17 degrees C to 9 degrees C. The blower ON frequency ranged from 32 s h-1 at 6 degrees C to 350 s h-1 at 17 degrees C. There was a good agreement between the measured and predicted values of gas concentration obtained from the simulation. The maximum RMSE value of predictions was 0.30 % at 17 degrees C storage temperature.

Edible starch-based materials have shown a positive impact on quality parameters. In this study, plums (Prunus domestica cv. Jojo) were divided into five groups: a control, two coating treatments (starch and starch-whey protein (80–20%), and two film systems (starch and starch-whey protein (80–20%). Biodegradable packaging, particularly the coating treatment, had no negative effect on color parameters. After 28 days of performed tests, firmness was boosted with starch and starch-whey protein (80–20%) films. With the coated materials, there was no significant difference compared to control group. The lowest transpiration velocity was of plums wrapped in starch films. In the case of respiration rate, no significant difference was observed between the packaging and control samples. After the conducted trials, the weight loss of untreated plums was at 10%, while 5% of weight loss was noticed for plums wrapped in starch materials, and around 6% was noticed for the other materials. Oxygen permeability was higher for S-WP films, the thickness of S and S-WP films were comparable and thickness of starch coating was around 60% higher than S-WP. Both films have an affinity to water and both show typical behavior of water vapor sensitive hydrophilic biopolymers. The starch film with the addition of 20% of proteins increased the resistance of gas exchanges, which represents one of its great benefits.

Adjusting beneficial gas concentrations in real time in response to changing storage conditions is important for fresh produce, especially throughout the supply chain when temperature abuse occurs frequently. In this study, a controlled-ventilated box for bulk transportation of fresh produce was demonstrated and tested under variable temperatures. The presented system comprised a rigid container with a miniature blower installed in the opening of its wall for facilitating the gas exchange and an additional wall opening with a metal tube protruding into the inner container’s space. The in-package atmosphere was formed by the balance between the respiratory activity of the produce and the influx of fresh air through the wall openings, regulated by switching the blower ON or OFF. The mass transfer coefficient for metal tubes of different dimensions was measured under modified atmosphere featuring 15% CO2 and 5% O2 at 10 °C. The addition of an air blower increased the mass transfer coefficient by at least 100 times. A further storage trial with cherries was successfully performed at 10 °C and 20 °C. The demonstrated trial featured some significant inputs to increase the knowledge about better storage of fresh produce throughout the supply chain and storage.

In the postharvest chain of fruit and vegetables, temperature fluctuations frequently occur in the surrounding air, which can lead to condensation of water vapour on the surface of fresh produce. Such processes can have a negative impact on the shelf life of horticultural products. Available sensors for measuring condensation phenomena, in particular on the curved surfaces of bulky fruit, are not suitable or can only be used to a very limited extent. The aim of the present study was to measure condensation on curved surfaces of bulky fruit and to evaluate the influence of the process parameters involved. Some fundamental aspects of condensation on the surface of single apples were analysed using the standard methods of condensation measurement that involve the continuous weighing of the product and measuring the dew-point undershoot. In the context of two typical postharvest scenarios, an in-house developed sensor based on the electrical resistance was tested and validated. The wetness sensor allowed reliable determination of the condensation retention time during re-warming and in both uniform and non-uniform temperature fluctuations on apple fruit. While the retention time of condensed water on the fruit surface was successfully measured, only qualitative statements can be made regarding the intensity of the condensation.

Fresh horticultural products are exposed to different environmental conditions from farm to fork. Barrier properties of packaging and physiological behaviour of produce, namely respiration and transpiration can affect headspace conditions surrounding produce and consequently remaining shelf life. Packaging material also plays a role in heat and mass transfer, such as thermal conduction and permeation of O2, CO2 and water vapour. All of these behaviours are integrated together in the form of ordinary differential equations and solved using numerical methods in MATLAB. • The simulation program is useful for designing the size and number of perforations to achieve equilibrium modified atmosphere alone or in combination with packaging material having a higher water transmission rate or active moisture absorber. • The simulation program is also useful for predicting the shelf life of fresh produce under the actual supply chain conditions. • The simulation program provides a flexible system to input predefined supply chain conditions and the properties of fresh produce and packaging material, thus, minimizing the costly and time consuming experimental procedures for selecting the optimum packaging material for fresh produce.

In order to extend the shelf life of the fruit, improve appearance, and to keep all nutrition properties of the plum from diminishing, edible coatings comprised of wheat starch and wheat starch–whey protein isolate (in ratio 80/20) were created. Stand-alone films were produced to assess properties which helped to understand the phenomena occurring on the surface level of coated plums. The properties of coatings based on starch are similar to starch coatings containing oil because the natural epicuticular wax layer of plums merges with coating materials. Adding oil doubled the contact angle value and the dispersive component of the surface tension. The workings of adhesion and cohesion, spreading coefficient, water absorption, water content, and solubility in water of the films decreased. Similar processes were observed on the fruits’ surface. In appearance, the coating process is similar to polishing the plum surface for removing crystalline wax. The color parameters of coated fruits did not significantly change. Newly formed bonds or interactions established between starch, whey proteins, water, glycerol, and oil are displayed by Fourier transform infrared (FTIR) analysis. This work revealed how the interactions between the epicuticular wax on the fruit’s surface and the hydrocolloid-based coatings affect the efficiency of the coatings.

Humidity control is one of the biggest challenges in modified atmosphere and humidity packaging (MAHP) of fresh horticultural products, especially those of high transpiration rate. Humidity absorbing trays containing active moisture absorber substance in the structure have been recently emerged as a potential solution in this area. Here packaging of strawberries using two different humidity absorbing trays of different moisture absorption capacity named T0 and T12, under fluctuating ambient conditions was simulated using an integrated mathematical modeling approach and validated experimentally. The model considered transpiration and respiration behavior of fresh produce, moisture absorption by packaging tray, gas and water vapor permeation through the perforated packaging film to predict changes in relative humidity of packaging headspace as well as moisture condensation within the package. Based on RMSE values, there was a good agreement between predicted and measured data of humidity, moisture loss, absorption and condensation inside the package. The RMSE values for prediction of the headspace humidity were 1.28, 2.38 and 4.34 and corresponding R-2 values were 0.71, 0.86 and 0.87 for control, T0 and T12 packages, respectively. Further simulations were made to design MAHP for strawberry using T12 tray and appropriate number of perforations in packaging film under different conditions of fruit mass and ambient temperature. For example, using 1 perforation of 0.8 mm diameter for 6 days storage of a 400 g strawberry package under 15 degrees C ambient temperature, resulted in desired gas composition of O-2 (7.0%) and CO2 (12.6%), while preventing humidity saturation and consequent moisture condensation by keeping in-package equilibrium humidity at 97.6% and maintaining fruit mass loss less than 0.3%.

Transpiration and respiration are physiological processes well-known as major sources of fresh produce mass loss. Besides causing impairment of external quality, it is associated with economic loss since it inevitably decreases saleable weight. To prevent postharvest mass losses, by improved modified atmosphere and humidity packaging, comprehensive knowledge on the mechanistic basis of both processes and their interactions is essential. The objective of this study was to evaluate the contribution of these processes on mass loss of packaged and unpackaged strawberries. Experiments on a single strawberry were performed at 4, 12 and 20 degrees C; and 76, 86, 96 and 100% RH. Mass loss was also investigated as a function of number of strawberries and package volume at 12 degrees C. A combined model based on Arrhenius equation and Fick's first law of diffusion for an unpackaged single strawberry and a model based on degree of filling was developed and validated with packaged strawberries. These models have potential application towards the selection of optimal moisture control strategies for strawberries. (C) 2018 IAgrE. Published by Elsevier Ltd. All rights reserved.

A method to characterising the surface water relations of coated fresh fruit has been developed. Based on a modification of the Fick's law of diffusion, application of this method allows for a quantitative assessment of the impact of produce type and of production method of coating, and environment on water losses both of the fruit body and the coating. Resistances in the water vapour pathway were analysed to determine the effects of coating on the surface water relations of plums. Experiments were conducted, evaluating the dynamic behaviour of two different starch-based coatings both at high and low potential water losses. Applying three layer-coatings, both starch and starch-whey protein coatings increased the total resistance in the water vapour pathway of individual plums by 60-75% at high transpiration potentials. Even at low transpiration potentials, an increase of 11-20% was observed. The starch coating tended to have a slightly lower effectiveness than the coating enriched with 20% whey protein.

Modified atmosphere and humidity packaging (MAHP) is used to extend shelf life and maintaining the quality of fresh fruits and vegetables by modifying desired gas concentration and relative humidity (RH) inside fresh produce package. Several factors affect the optimum design of MAHP, most of which are time and or temperature dependent. Hence, there is a vital need for a simulation tool that includes all affecting parameters and their interactive behavior on package gas composition and water vapour. In this study a comprehensive simulation program based on integrative mathematical modeling is presented. A number of validation experiments were conducted to evaluate the robustness of the simulation program under constant and varying temperature conditions during storage period and predict gas composition, humidity and moisture condensation dynamics in packaged strawberry and plum. The simulated results were satisfactory with those obtained experimentally. The validated simulation program was then used for optimization of modified humidity packaging for both plum and strawberry. The predicted equilibrium headspace humidity was 94.0 and 98.8% for strawberries and plums, respectively which was very close to measured values of 93.5 and 94.1%, respectively. Therefore, the simulation program was found to be a convenient tool to virtually test the package under a broad range of environmental conditions such as temperature and RH resembling real supply chain conditions and ensure proper selection of packaging systems for the optimum performance.

Transpiration has various adverse effects on postharvest quality and the shelf-life of fresh fruit and vegetables (FFV). If not controlled, the water released through this process results in direct mass loss and moisture condensation inside packaged FFV. Condensation represents a threat to the product quality as water may accumulate on the product surface and/or packaging system, causing defects in external appearance and promoting growth of spoilage microorganisms. Thus, moisture regulation is extremely important for extending FFV shelf-life. This review focuses on transpiration phenomenon and moisture evolution in packaged fresh horticultural produce. It provides recent information on various moisture control strategies suitable for packaging of fresh horticultural produce. It also provides an evaluation on the role and application of integrative mathematical modelling in describing water relations of FFV for packaging design, as well as, an overview of models reported in literature. (C) 2016 IAgrE. Published by Elsevier Ltd. All rights reserved.