The structured food systems (i.e. cellular tissues) are dissipative structures whose functionality mainly concerns their properties (physico-chemical properties, chemical and biochemical reactions), external interactions with surroundings (interactions with micro-organisms, heat and mass transport pathway) and especially, their interactions with consumers (nutritional value, quality, taste and flavour, texture, appearance: size, shape, colour). Dehydration or rehydration processes concern heat and mass transport phenomena (water, solutes) coupled with micro and macrostructure changes both producing important effects on food functionality. Control of these changes is the major concern in food product development. This control must be applied not only to the changes in physico-chemical properties but also to those related with consumers' issues. Food matrixengineering is a branch of food engineering which aims to apply the knowledge of the food matrixcomposition, structure and properties to promote and control adequate changes which can improve some sensorial and/or functional properties in the food. These changes, which are caused by some basic operations, are related to the phenomena of heat and mass transfer, vaporization-condensation, internal gas or liquid release, structure deformation-relaxation and phase transitions in matrixcomponents, and are usually coupled throughout the operation's progress. The final product may be a new product with improved composition and sensorial properties and/or more stability. All these concepts are discussed in this paper using several examples related to the application of combined food dehydration techniques.

Water affects safety, stability, quality and physical properties of food. The influence of water on physical properties of food is dependent on the state of water in food. The state, expressed as water activity, is briefly discussed in the paper. Further, the influence of water on such physical properties as rheological, thermal, mass transfer, electrical, optical and acoustic is presented in details.

[Departement_IRSTEA]Ecotechnologies [TR1_IRSTEA]SPEE | To reduce the proliferation of bacteria inside food plants, cleaning and disinfection are performed daily following production. These operations are followed by drying during which the drying rate should be as high as possible. This study shows the influence of a dehumidifier on the water mass evolution on surfaces during the drying of a food plant. The temperature, relative humidity and water mass evolution were monitored under two conditions: with and without a dehumidifier. Comparison of the results shows that the drying rate is about 1.5 times higher when a dehumidifier is used. These data were used to develop a simplified heat and mass transfer model allowing the prediction of the temperature and drying rate at different locations. The results can help the manufacturer to evaluate the benefits of a dehumidifier and consider the use of other devices to achieve better airflow distribution or greater heat supply for certain surfaces.

Heterogeneous and hygroscopic characteristics of plant-based food material make it complex in structure, and therefore water distribution in its different cellular environments is very complex. There are three different cellular environments, namely the intercellular environment, the intracellular environment, and the cell wall environment inside the food structure. According to the bonding strength, intracellular water is defined as loosely bound water, cell wall water is categorized as strongly bound water, and intercellular water is known as free water (FW). During food drying, optimization of the heat and mass transfer process is crucial for the energy efficiency of the process and the quality of the product. For optimizing heat and mass transfer during food processing, understanding these three types of waters (strongly bound, loosely bound, and free water) in plant-based food material is essential. However, there are few studies that investigate cellular level water distribution and transport. As there is no direct method for determining the cellular level water distributions, various indirect methods have been applied to investigate the cellular level water distribution, and there is, as yet, no consensus on the appropriate method for measuring cellular level water in plant-based food material. Therefore, the main aim of this paper is to present a comprehensive review on the available methods to investigate the cellular level water, the characteristics of water at different cellular levels and its transport mechanism during drying. The effect of bound water transport on quality of food product is also discussed. This review article presents a comparative study of different methods that can be applied to investigate cellular water such as nuclear magnetic resonance (NMR), bioelectric impedance analysis (BIA), differential scanning calorimetry (DSC), and dilatometry. The article closes with a discussion of current challenges to investigating cellular water.

Plant-based food materials are porous and hygroscopic in nature; therefore, it contains three water environments, namely, intercellular, intracellular water and cell wall water. The intercellular water is known as capillary water or free water which is less constrained than intracellular water, considered as loosely bound water (LBW), and cell wall water, which is recognised as strongly bound (SBW). During food processing such as drying, frying, heating and cooking, optimisation of heat and mass transfer is crucial. The existing heat and mass transfer models for food processing are developed based on the concept that all of the water inside the food material is bulk water, which can act as free water that can be easily transported. This simplistic assumption has been made due to a lack of sufficient data to enable consideration of the proportion of free and bound water in plant-based food materials. Therefore, the aim of the present study is to investigate the proportion of different types of water such as free, LBW and SBW in 11 different plant-based food materials. The water proportion was investigated using 1H NMR T2 relaxometry. The experimental results uncovers that plant-based food materials contain about 80 to 92% LBW, 6 to 16% free water and only about 1 to 6% SBW. This investigation also confirms that among the five different fruits, kiwi contains the lowest percentage of LBW while Apple contains the highest percentage of LBW. Among the vegetables, eggplant comprises the largest amount of LBW while cucumber contains least amount of SBW. An attempt was made to establish a relationship between physical properties of fruits and vegetables and the proportion of the different types of water. Interestingly, it was found that SBW strongly depends on the proportion of solid in the sample tissue whereas FW depends on the porosity of the material.Food preservation is a major concern in today's world as about one-third of the global food production is lost annually due to lack of proper processing and preservation. Food processing is very energy intensive process and it consumes about 15–20% of energy used in industrial processes. Quality of processed food is also a big concern in the industries. Therefore energy efficiency and food quality are two major concerns in the food processing industry.The current food processing techniques such as drying are unable to ensure best quality and energy efficiency as many microlevel fundamentals of hygroscopic food material are unknown. One of the major unknown is the proportions and characteristics of different types of water inside the food materials and because of this an optimised food processing cannot be designed in order to ensure high quality and energy efficiency. The existing heat and mass transfer models are based on some simplistic assumptions, for instance all of the water inside the food material is considered bulk water; which means that it acts as free water that can be transported easily. This simplistic assumption has long been used due to lack of sufficient data to enable consideration of the proportion of free and bound water. Therefore, the aim of the present study is to determine the proportion of different types of water such as free water, loosely bound water (LBW) and strongly bound water (SBW) and establish relationship between physical properties and water characteristics in hygroscopic food materials.The findings of this study will enhance the understanding of plant-based food tissue that will contribute to a better understanding of potential changes occurring during food processing and will contribute to the development of accurate heat and mass transfer models and prediction of deformation. These findings will ultimately be significant for the equipment design engineers in food processing industry.

Nylon 6 and nylon 12 food packaging materials used as sausage casings are typically exposed to fatty food on one side and boiling water on the other during the cooking process. To simulate the migration behaviour under these conditions, a special migration cell was constructed and filled with olive oil on one side of the polymer and water on the other to find out what amounts of the migrants will transfer to either side and phase at 100 °C. Results show that when a nylon 6 film is exposed to the conditions as described above, total mass transfer of the monomer—caprolactam—into the water phase occurs after 2 h at 100 °C. Nylon 12 sausage casings release similar amounts of their monomer—laurolactam—into both the aqueous and oil phase. An existing computer migration model was adapted to simulate the situation of simultaneous two-sided migration applying previously determined diffusion and partitioning coefficients. The suitability of the model was confirmed by experimental data.

Plants and algae are the main sources of natural bioactive compounds used in the food and pharmaceutical industries. It is very important to achieve an efficient and safe technique to recover bioactive compounds while maintaining their quality and properties. Subcritical water extraction is the most promising engineering approach that offers an environmentally friendly technique for extracting various compounds from plants and algae. Application of pressurized water and high temperature in subcritical phase is able to modify the dielectric constant and polarity of the solvent which then contributes to a better extraction process. The technique improves the mass transfer rate and preserves the biological potency of the extracts. This article reviews current studies on the extraction of bioactive compounds from various species of plants and algae using the subcritical water technique and discusses its effects and benefits for the food and pharmaceutical industries.

A novel method of hydrofluidisation food freezing is numerically investigated in this paper. This technique is based on freezing small food products in a liquid medium under highly turbulent flow conditions when the heat transfer coefficient is higher than 1 000 W⋅m⁻²⋅K⁻¹, which depends on the operating and flow conditions. A numerical model was developed to characterise the freezing process in terms of the heat transfer and diffusion of liquid solution components into the food product. The study investigates the freezing process of spherical samples in binary solutions of ethanol (30%) and glycerol (40%) and ternary solution of ethanol and glucose (15%/25%). The developed model was employed to determine the concentration of the liquid solution in food samples and to quantify the effect of sample size, heat transfer coefficient, solution temperature and concentration on the process. The food sample size varied from 5 to 30 mm, and the heat transfer coefficients varied from 1 000 to 4 000 W⋅ m⁻²⋅ K⁻¹. The results confirm that a freezing time of 15 min for 30 mm diameter samples or less than 1 min for 5 mm diameter samples can be achieved with the hydrofluidisation method. The solution uptake was influenced by the solution type, sample size and process parameters and varied from 8.9 to 35 g of solute per kg of product for ethanol-glucose and glycerol solutions, respectively. This paper quantifies the advantages and possible limitations of hydrofluidisation, which has not yet been entirely studied, especially in terms of the mass absorption of different solutes.

Accurate measurement of water activity (aw) is an important goal for the food industry because aw is a key parameter in microbial growth, biological reaction rates and physical properties. An experimental device was setup using air-product water balance to non-destructively estimate the time-course of mean aw at the food product surface under well-controlled airflow conditions. The device is especially suited for studying the ripening of cheeses and fermented meat products, where water fluxes exchanged between products and air are very low. The validation tests performed with aw-known model products showed that water fluxes of 10(−7) kg s−1 can be estimated with an accuracy better than 2% over very short periods of time, and that surface aw can be estimated with an absolute uncertainty of less than 0.01 aw units. A handful of cheese ripening trials illustrate the potential of the method, highlighting the effects of a low air velocity and high air RH on the water exchanges occurring at a cheese surface, thus demonstrating the strong surface sensitivity to external air conditions.

This work discusses hydrolysis of defatted grape in supercritical water (SCW) at 380 °C and 260 bar from 0.18 s to 1 s focusing attention to sugars recovery in the liquid phase of the product and detailed characterization of remaining solid phase enriched in polyaromatics (e.g. lignin, flavonoids, etc.). After the longest reaction time of 1 s, 56% of carbohydrates could be recovered in the liquid phase, as a result of carbohydrate hydrolysis. The high content of insoluble lignin in biomass (36%), acts as a mass transfer limitation and presents an important feature in the hydrolysis process, slowing down the conversion of carbohydrate fraction, as after the maximum time of 1s, 10% of carbohydrates still remained in the solid phase. Milled wood lignin, extracted from biomass and dioxane extract from the solid phase were characterized in order to understand the main structural changes during the SCW hydrolysis process. Dioxane (80%) extraction of solids produces a very complex mixture of lipophilic extractives, flavonoids and lignin with a certain amount of chemically linked carbohydrates. 2D NMR analysis of dioxane extract shows remarkably subtle changes in the amounts of main lignin moieties (β-O-4′, β-β’ (resinol) and β-5 (phenylcoumaran)). This subtle change of the main lignin structures is an important feature in the further valorisation of this sulfur-free lignin residue.