Kinetics of conductive hydro-drying of pumpkin (Cucurbita moschata) pulp

Pumpkin (Cucurbita moschata) samples were dehydrated by conductive hydro-drying (CHD) (1 atm, 80 °C), sliced and purées, both structures with thicknesses of 1.5, 3 and 6 mm. Drying kinetics were analyzed and the effective diffusivity (D ef) was determined in both structures at the three thicknesses. Drying curves were fitted to ten kinetic models: Lewis, Henderson & Pabis, Logarithmic, Page, Wang & Singh, Page Modified, Midilli, Diffusion Approximation, Two-term Exponential and Verma. D ef was determined by analytical solution of Fick's Second Law in rectangular coordinates by Crank's method. In general, the semi-empirical model that best fit showed was Midilli's model. However, the importance of phenomenological models such as the analytical solution of Fick's second law for process scaling and equipment design should be considered. These modeling results aid in predicting performance and fine-tuning hydrodrying processes for sustainable, high-quality food. Future applications may involve integrating these models into industrial-scale hydrodryers, reducing energy consumption and environmental impact.

Current trends in cacti drying processes and their effects on cellulose and mucilage from two Colombian cactus species

The effect of temperature and drying technologies on mucilage and cellulose (obtained by the microwave-assisted extraction technique, MAE) from Opuntia ficus-indica (OFI) and Austrocylindropuntia cylindrica (CC) was determined using a conventional oven (CO) and Refractive Window (RW). Mathematical modeling was performed from drying kinetics data using the Lewis, Henderson-Pabis, Page, and Logarithmic models. Activation Energy (Ea) and Diffusivity (D) were also determined. The model with the best fit was the logarithmic one, with a correlation coefficient (R²) greater than 0.99. The obtained activation energies were 22.81 kJ mol^-1 for Refractance window (RW) and 31.44 kJ mol^-1 using conventional hot air drying (CO) while a diffusivity of 2.9 ∗10^-8 m² s^-1 for RW and 1.3∗10^-8 m² s^-1 for CO were found as well. According to our results, a greater drying efficiency and a less chemical deterioration of the plant sample are obtained by drying with Refractance window.

Factors Affecting the Time and Process of CMC Drying Using Refractance Window or Conductive Hydro-Drying

Intensive research on biodegradable films based on natural raw materials such as carboxymethyl cellulose (CMC) has been performed because it enables the production of transparent films with suitable barrier properties against oxygen and fats. Considering the importance of the production of this type of film at the industrial level, a scalable and continuous drying method is required. Refractance window-conductive hydro drying (RW-CHD) is a sustainable and energy-efficient method with high potential in drying this kind of compound. The objective of this study was to evaluate the factors (CMC thickness, heating water temperature, and film type) and radiation penetration depth that affect drying time and energy consumption. It was found that drying time decreased with increasing temperature and decreasing thickness. Similarly, energy consumption decreased with decreasing temperature and thickness. However, the drying time and energy consumed per unit weight of product obtained were equivalent when drying at any of the thicknesses evaluated. Film type had little effect on time and energy consumption compared to the effects of temperature and CMC thickness. The radiation penetration depth into the CMC was determined to be 1.20 ± 0.19 mm. When the thickness was close to this value, the radiation energy was better utilized, which was reflected in a higher heating rate at the beginning of drying.

Aloe vera Gel Drying by Refractance Window®: Drying Kinetics and High-Quality Retention

In most cases, conventional drying produces inferior quality products and requires higher drying times. A continuous pilot Refractance Window^® equipment was used to dry Aloe vera gel slabs of 5 and 10 mm thick at 60, 70, 80, and 90 °C, seeking a dry product with high-quality retention. Based on five empirical models, drying kinetics, diffusion coefficient, and activation energy were analyzed. Midilli–Kuck was the best predicting model. Short drying times (55–270 min) were needed to reach 0.10 g water/g solid. In addition, the technique yielded samples with high rehydration capacity (24–29 g water/g solid); high retention of color (∆E, 3.74–4.39); relatively low losses of vitamin C (37–59%) and vitamin E (28–37%). Regardless of the condition of temperature and sample thickness, a high-quality dried Aloe vera gel could be obtained. Compared with other methods, Refractance Window^® drying of Aloe vera achieved shorter drying times with higher quality retention in terms of color, vitamins C and E, and rehydration. Finally, the dried Aloe vera gel could be reconstituted to a gel close to its fresh state by rehydration.

Process and product characteristics of refractance window dried Curcuma longa

This work addresses the optimality of hot water bath based refractance window drying (RWD) characteristics of 1 mm Curcuma longa (turmeric) slices. Mylar film thickness (125 to 350 µm) and water bath temperature (65 to 95 °C) have been considered as independent variables to evaluate drying kinetics and nutritional characteristics of the process product combination. Equilibrium drying time, moisture diffusivity, fitness of thin layer models, moisture content, total phenolic content, total flavonoids content, curcumin content, and antioxidant activity have been considered to evaluate the optimality of the RWD process parameters. It has been analyzed that while both parameters critically influence equilibrium drying time, only temperature had profound influence on nutritional characteristics. PRACTICAL APPLICATION: There is a need for a fast-drying method without significant loss in bioactive compounds. Refractance window drying (RWD) method is such a process. The study of RWD of turmeric slices will help in understanding the relations between different drying temperatures and mylar film thickness and its relation to nutritional characteristics of the product.

Effects of Infrared-Assisted Refractance Window™ Drying on the Drying Kinetics, Microstructure, and Color of Physalis Fruit Purée

The objective of this work was to study the influence of the drying temperature, infrared (IR) radiation assistance, and the Mylar™ film thickness during Physalis fruit purée drying by the Refractance Window™ (RW™) method. For this, a RW™ dryer layout with a regulated bath at working temperatures of 60, 75, and 90 °C, Mylar™ thicknesses of 0.19, 0.25, 0.30 mm and IR radiation of 250 W for assisting RW™ drying process was used. Experimental curves data were expressed in moisture ratio (MR) in order to obtain moisture effective diffusivities (non-assisted RW™: D_eff = 2.7-10.1 × 10^-10 m²/s and IR-assisted RW™: D_eff = 4.2-13.4 × 10^-10 m²/s) and further drying curves modeling (Page, Henderson-Pabis, Modified Henderson-Pabis, Two-Term, and Midilli-Kucuk models). The Midilli-Kucuk model obtained the best-fit quality on experimental curves regarding statistical tests applied (Coefficient of Determination (R²), Chi-Square (χ²) and Root Mean Square Error (RMSE). Microscopical observations were carried out to study the RW™ drying conditions effect on microstructural changes of Physalis fruit purée. The main findings of this work indicated that the use of IR-assisted RW™ drying effectively accelerates the drying process, which achieved a decrease drying time around 60%. Thus, this combined RW™ process is strongly influenced by the working temperature and IR-power applied, and slightly by Mylar™ thickness.

Refractance window drying of fruits and vegetables: a review

Fruit and vegetable drying to make leather, pestil or powder products is a challenging task. Traditional drying adversely affects the taste, colour, nutritional qualities and preservation of bioactive compounds due to high-temperature exposure of the product. The substitute for traditional drying processes is consequently necessary to impart superior quality and preserve greater nutritional value in processed foods. Refractance window (RW) drying is a thin film drying system having high heat and mass transfer rates that speeds up the rate of drying. Polyester (Mylar), an infrared transparent plastic sheet transmits radiative heat to food during the RW drying process with higher drying rate, more retention of nutrients and low aroma and flavour loss. RW drying is reported to be affected by the thickness of puree or slices and temperature of drying, as thick samples need longer drying time, generate higher water activity, bring changes in colour parameters, experience higher effective diffusion coefficient (D_eff ) and result in lower solubility of powder. RW drying was compared with different drying processes and was observed to have more retention of nutrients and be more economical. RW dried samples were better in terms of colour and textural quality when compared with other traditional drying methods. © 2018 Society of Chemical Industry.

Arrhenius equation modeling for the shelf life prediction of tomato paste containing a natural preservative

BACKGROUND

The shelf life of tomato paste with microencapsulated olive leaf extract was compared with that of samples containing a commercial preservative by accelerated shelf life testing. Based on previous studies showing that olive leaf extract as a rich source of phenolic compounds can have antimicrobial properties, application of its encapsulated form to improve the storage stability of tomato paste is proposed here.

RESULTS

Regarding total soluble solids, the control and the sample containing 1000 µg g^-1 sodium benzoate had the lowest (Q₁₀  = 1.63) and highest (Q₁₀  = 1.88) sensitivity to temperature changes respectively; also, the microencapsulated sample containing 1000 µg g^-1 encapsulated olive leaf extract (Q₁₀  = 1.83) followed the sample containing 1000 µg g^-1 sodium benzoate in terms of the highest kinetic rates. In the case of consistency, the lowest and highest activation energies (E_a ) corresponded to samples containing 1000 µg g^-1 non-encapsulated olive leaf extract and 1000 µg g^-1 microencapsulated olive leaf extract respectively.

CONCLUSION

Interestingly, samples containing microencapsulated olive leaf extract could maintain the original quality of the tomato paste very well, while those with non-encapsulated olive leaf extract rated the worst performance (among all specimens) in terms of maintaining their quality indices for a long time period. Overall, the shelf life equation was able to predict the consistency index of all tomato paste samples during long-time storage with high precision. © 2017 Society of Chemical Industry.