Development of fractional viscoelastic model for characterizing viscoelastic properties of food material during drying

Pore development in viscoelastic foods during drying

In this paper, we present a numerical model that can describe the pore formation/cavitation in viscoelastic food materials during drying. The food material has been idealized as a spherical object, with a core/shell structure and a central gas-filled cavity. The shell represents a skin as present in fruits/vegetables, having a higher elastic modulus than the tissue, which we approximate as a hydrogel. The gas-filled pore is in equilibrium with the core hydrogel material, and it represents pores in food tissues as present in intercellular junctions. The presence of a rigid skin is a known prerequisite for cavitation (inflation of the pore) during drying. For modeling, we follow the framework of Suo and coworkers, describing the inhomogeneous large deformation of soft materials like hydrogels - where stresses couple back to moisture transport. In this paper, we have extended such models with energy transport and viscoelasticity, as foods are viscoelastic materials, which are commonly heated during their drying. To approach the realistic properties of food materials we have made viscoelastic relaxation times a function of Tg/T, the ratio of (moisture dependent) glass transition temperature and actual product temperature. We clearly show that pore inflation only occurs if the skin gets into a glassy state, as has been observed during the (spray) drying of droplets of soft materials like foods.

Bread staling prediction with a multiobjective particle swarm optimization-based bread constitutive modeling method

Aiming at the complex and cumbersome problems of current bread staling detection technology, a food constitutive modeling method based on the multiobjective particle swarm optimization (MOPSO) was proposed, which can quickly and efficiently identify the creep test parameters for bread, and predict the viscoelastic parameters of bread staling using the analyzed viscoelastic parameters, resulting in convenient and efficient detection of bread staling. Firstly, airflow-laser detection technology was used to carry out rapid, efficient, and non-destructive bread rheological tests to obtain bread creep test data. The MOPSO based on the Pareto set was then used to identify the generalized Kelvin model, and the discrimination accuracy was evaluated by using the inversion results established by the viscoelastic parameters, which resulted in efficient discrimination of creep test data of starch-based products represented by bread. Finally, using extreme learning machine regression (ELM), a prediction model between the analysis results and the moisture content of bread staling was established, and the prediction effect of the analysis results on bread staling was verified. The experimental results show that, when compared to finite element analysis (FEA) and non-linear regression (NLR) to identify creep parameters, the MOPSO overcomes the shortcomings of easy falling into the local optimal solution, is easy to implement, has strong global search ability, and is suitable for the analysis of high-dimensional viscoelastic models of complex foods. The correlation coefficient (R) of the prediction set established by the 12-membered viscoelastic parameters in the prediction model established by multi-element viscoelastic parameters and bread moisture content was 0.847, and the root mean square error (RMSE) was 0.021. This demonstrated that, when combined with MOPSO, airflow-laser detection technology could effectively identify the viscoelastic parameters of bread and establish a method suitable for monitoring bread staling in industrial production. The results of this study provide a reference for the identification of viscoelastic parameters of complex foods and to detect bread staling quickly and efficiently.

Mixed pretreatment based on pectinase and cellulase accelerates the oil droplet coalescence and oil yield from olive paste

Commercial enzymatic pretreatment is being classically used for enhancing the oil extraction yield in the olive oil industry in China. Nevertheless, the mechanism is not yet clearly defined. The aim was to study the action of pectinase and cellulase for improving the oil yield from the aspects of oil droplets coalescence and rheological properties changes of olive paste during malaxation process. From confocal laser scanning microscopy imaging, the bound oil droplets were released and gradually coalesced into larger droplets, eventually formed a continuous oil phase with enzymatic pretreatment. Furthermore, the mixed enzymatic pretreatment effectively decreased viscosity of the olive pastes and promoted the depolymerization and solubilization of pectic polymers involved in the cell-cell adhesion, thus further enhanced the oil extraction yield from 7.15 % to 11.68 % (w/w). Finally, the mixed enzymatic pretreatment improved the droplet release and coalescence, reduced the viscosity of olive paste, and increased the oil yield.

Instrumentation and methods for rapid estimation of selected viscoelastic parameters in foods

A new method to estimate the selected viscoelastic parameters of foods using damped vibration analysis is presented for the evaluation of fruits and baked products. A flat disk is attached to the flat sample surface using a laser rangefinder that measures the sample thickness in advance, and it is locked by a trigger. Next, the trigger is released to allow the probe to press the sample through the force of gravity. The damped vibration of the probe caused by the deformation of the food is measured by monitoring the displacement of the probe via a linear encoder. The bulk modulus and viscosity are estimated using the fractional Zener model and mass. Young's modulus (E) is estimated independently by determining the maximum velocity of the probe using Hooke's law. Poisson's ratio (ν), and the shear modulus and viscosity are calculated by employing the estimated E and bulk modulus. The bulk modulus, bulk viscosity, shear modulus, shear viscosity, and E of apples were found to be higher than those of bananas. The bulk modulus, bulk viscosity, E, and shear modulus for white bread were lower than those for pound cake, but the ν values were higher, whereas those of sponge cake were intermediate. After drying the baked products for 1 day, most of the parameters of the samples increased, but the value of ν for white bread decreased. The proposed free-falling device estimated the four viscoelastic coefficients, Poisson's ratio, and Young's modulus of the food sample in less than 1 s.

Sustainable food drying technologies based on renewable energy sources

Waste in the food supply chain is estimated to be about 30-40% of the total food production, which aggravates the world hunger and increases waste management burden and environmental impact. Despite the dire food scarcity, majority of this food waste takes place in developing countries because of the lack of appropriate and affordable preservation techniques. Traditional open sun drying is the most popular food-reservation technique to the local farmers due to near-zero capital cost and cheap labor cost. However, this method is highly energy intensive, unhygienic, and time demanding. The high energy consumption resulting from uncontrolled simultaneous heat, mass, and momentum transfer processes in traditional drying systems highlights the necessity of pursuing sustainability in drying process targeting reduced energy consumption, environmental and social impacts. This paper presents a comprehensive review on the sustainable food drying technologies based on renewable energy sources, with emphasis on the developing countries. It was observed that the integration of thermal energy storage with heat pump makes the integrated drying system more efficient, and dries food with better quality. Likewise, advanced integrated drying systems, such as, solar with microwave, and heat pump with microwave make the drying process more cost and quality competent. Finally, impact of resource distribution and governmental incentives for renewable energy use in sustainable drying is discussed.

Effect of drying methods and storage with agro-ecological conditions on phytochemicals and antioxidant activity of fruits: a review

Choice of drying methods significantly impacts the nutritive and non-nutritive compounds in fruits and vegetables. Phytochemicals such as total phenolics and total flavonoids are non-nutritive bioactive compounds and are found in plants which are of important value due to their antioxidant properties in minimizing the oxidation reaction. However, drying and storage conditions and duration significantly affect these important quality attributes. There is currently no review article on the impact of the drying and storage conditions on these quality attributes. Therefore, the aim of this review paper is to investigate the impact of drying methods on these important phytochemicals and their antioxidant activity on dried products during the storage period. Different drying methods cause desirable and undesirable changes to dried products both physically and chemically. It is found that during the drying process at various temperature ranges from 40 to 80 °C, chemical changes occurs which affects the phenolic and the flavonoid content of dried products to increase or decrease. The increase in antioxidant activity after drying is also due to oxidized polyphenols and Maillard reaction products. This results to changes in the antioxidant potential of the dried food product and its impact on the shelf life.

Fractional order calculus approach for drying modeling of eggplants

In order to determine the drying modeling of eggplants, fractional order calculus modeling was applied and compared to regression analysis in this study. The fractional order calculus based on the Caputo derivative approach was considered and applied for modeling of eggplant drying. The drying experiments were performed on three levels of drying air temperatures (60, 70, and 80 ℃), with two different air flow velocity levels (0.5 and 1 m/s), and three levels of thickness (3.5, 6.5, and 9.5 mm) to measure the effects of different drying conditions for eggplants in a convective dryer. Four different commonly used mathematical models from the literature were fitted to the experimental data with regression analysis. Based on obtained results, the coefficient of determination (R²) was found as 0.9956 for the values of 80 ℃, 0.5 m/s, and 3.5 mm, while sum squared error was 0.0061 and root mean square error was 0.0235 for the Page model. However, better and more accurate results were obtained using fractional order modeling with the values of R² found as 0.9981, sum squared error as 0.0012, and root mean square error as 0.0099 for the considered case.

Physical and viscoelastic properties of carrots during drying

It is essential to understand the physical and mechanical properties of a product since these properties affect the structure, texture, and ultimately consumer acceptance. The effect of drying conditions on dynamic viscoelastic properties, stress relaxation function and creep compliance, and physical properties, such as moisture distribution, color parameters, and shrinkage, was studied. An increase in drying temperature and duration resulted in a decrease in moisture content and volume, which were highly correlated (R = .988). Water evaporation followed the falling rate period, demonstrating that the water transport was limited by internal resistances. The decomposition of carotenoids led to a decrease in magnitude of color parameters (L, a, and b), between 30.1% and 51.6% with 4 hr drying. It was observed that the material shrinkage and moisture content highly affected the mechanical properties; increased stress relaxation modulus and decreased creep compliance values of the sample. The creep behavior, expressed with Burger's model (R²  ≥ .986), was highly dependent on moisture content. The linear viscoelastic region of carrots was found to be at strains lower than 3%. The three-element Maxwell model well fitted to describe the viscoelastic behavior of carrots (R²  ≥ .999, RMSE ≤ 2.08 × 10^-4 ). The storage moduli (G') were higher than loss moduli (G″), indicating that samples presented solid-like behavior. The findings can be used to improve the textural attributes of carrots and carrot-based products.

Fundamental Understanding of Cellular Water Transport Process in Bio-Food Material during Drying

Bio-food materials are heterogeneous in structure with cellular diversity, where the majority of the water is located in the intracellular spaces. Understanding of the nature of the microscopic behaviour of water transport is crucial to enhance the energy efficiency in food processing and obtain the better quality of processed food. In this research, apoplastic and symplastic transport of cellular water in the bio-food material during drying was investigated using 1H-NMR-T2 relaxometry. We found that intracellular water (ICW) migrates from intracellular spaces to the intercellular spaces by progressive rupturing the cell membranes while drying at a higher temperatures (60 °C-70 °C). In this case, apoplastic process dominates the transport process. However, at lower temperature (45 °C), cell membranes do not rupture and therefore ICW migrates from cell to the neighbouring cell through micro-capillaries, where the symplastic process dominates the mass transfer at different stages of drying.