Drying kinetics of blueberry pulp and mass transfer parameters: Effect of hot air and refractance window drying at different temperatures

Performance Evaluation of a Solar-Assisted Multistage Heat Pump Drying System Based on the Optimal Drying Conditions for Solanum lycopersicum L

This study aims to evaluate the drying performance of a multi-stage solar-assisted heat pump drying system for tomatoes. The method involves theoretical calculations based on the optimal drying process and experimental investigations to assess the impact of different drying temperatures and relative humidity on drying characteristics. The results from the theoretical calculations reveal that the multi-stage solar-assisted heat pump drying system outperforms a single-stage system, particularly under lower ambient temperatures or higher fresh air volumes. In spring/autumn, with 25% fresh air, solar energy accounts for 85.12% of the total energy consumption, achieving a performance coefficient of 39.16, a moisture extraction rate of 40.7 kg/kWh, and energy consumption of 0.02 kWh/kg. Carbon dioxide emissions amount to 10.45 kg/year, with a net reduction of 7.88 kg/year. The experimental results indicate that higher relative humidity increases drying time and reduces the diffusion coefficient, which results in higher material temperatures and greater nutrient loss. The optimal drying process is achieved at 70 °C and 20% relative humidity. In conclusion, the multi-stage solar-assisted heat pump drying system demonstrates superior performance in energy efficiency and sustainability compared to single-stage systems. The optimal drying conditions for tomatoes are identified, and the findings contribute to improving drying processes in food preservation while minimizing environmental impact.

Thermoanalytical study of protein state during rehydration and rehydration kinetics in osmotically dehydrated pork meat (Longissimus dorsi): Insights from Peleg and Weibull models

Osmotically dehydrated pork meat (Longissimus dorsi), in the molasses, was used in the aim to study the protein state during rehydration. Protein state and rehydration kinetics are crucial for obtaining the desired meat product quality. The thermoanalytical techniques were employed to follow protein state and kinetics of rehydration. Obtained kinetic parameters were Peleg's rate constant (k1), 34.43, 6.23, and 10.15 (min (kg d.m.)(kg water)-1) and Peleg's capacity constant (k2), 0.726, 1.243, and 0.860 at 20, 30, and 40 °C, respectively. Parameters of Weibull's model, α, β (min), at 20 °C were 34.4; 0.86, at 30 °C were 6.24; 1.24, at 40 °C were 10.15; 0.86. From obtained enthalpies (ΔHd) and temperatures (Td) of meat proteins denaturation, it was found that proteins were partly denatured and gradually lost their structure and thermal stability during rehydration. Rehydration kinetic parameters indicated that most efficient rehydration was found to be at the 40 °C.

Drying: A Practical Technology for Blueberries (Vaccinium corymbosum L.)-Processes and their Effects on Selected Health-Promoting Properties

The global dried blueberry market is steadily growing, driven by the creation of innovative blueberry-based products. This trend presents an opportunity to explore a previously untapped segment of the blueberry market in Chile. In this study, a comprehensive assessment of four drying techniques (hot-air drying [HAD], vacuum drying [VD], infrared drying [IRD], and freeze-drying [FD]) was conducted to determine best operating conditions and preserve the health-promoting properties of blueberries. Drying kinetics, proximate composition, color, anthocyanin content, individual phenols, and antioxidant, antiproliferative, and antidiabetic potential of blueberries were evaluated. VD showed the highest drying rates, reaching equilibrium moisture more rapidly (Deff value of 3.44 × 10-10 m2/s). Drying caused an increase in lipid content but a decrease in protein content. The color parameter L* increased in all dried samples, and C* reflected color intensification. FD best retained anthocyanin content, which decreased significantly in the other drying processes. Chlorogenic acid and rutin predominated in HAD, IRD, and FD samples. The antioxidant potential in ORAC assays increased for all drying methods but decreased in DPPH assays. Blueberry extracts from FD and HAD exhibited the greatest antiproliferative effect against A549 and H1299 cell lines, respectively. HAD showed the best inhibitory effect on α-glucosidase, with an IC50 value of 0.276 mg/mL, similar to acarbose (IC50 = 0.253 mg/mL). Given the significant retention of health-promoting properties and bioactive compounds in HAD-dried samples, this method is advisable as a sustainable option for drying blueberries in Chile.

Unlocking the potential of pequi (Caryocar brasiliense Camb.): Stability of phenolic compounds, carotenoid profile and vitamin A after drying

Among the fruit species of the Brazilian cerrado is pequi (Caryocar brasiliense Camb.), recognized for its nutritional properties and profile of bioactive compounds. However, it is necessary to evaluate techniques that promote its stability, reducing the moisture content without degrading the content of natural antioxidants. Therefore, this study aimed to evaluate the drying of pequi pulp in an oven at different temperatures (40 °C and 55 °C), as well as determine its kinetics and influence on the content of bioactive compounds and antioxidant capacity. The increase in temperature showed a reduction (∼50 %) of the drying time, from 720 min (40 °C) to 360 min (55 °C), with a final moisture content of approximately 39 %, which is the optimized condition of the process. (360 min - 55 °C). Drying at 55 °C showed better retention of carotenoids (β-carotene, α-carotene, and β-cryptoxanthin), especially β-carotene, an important precursor of vitamin A, with retention of approximately 57 %. The results for antioxidant capacity (ABTS and DPPH), total phenolic compounds, total phenolic acids and total flavonoids confirmed that a longer drying time resulted in greater degradation of bioactive compounds, even at lower temperatures. The profile of phenolic compounds of the sample subjected to drying under optimized conditions was identified by HPLC-DAD-ESI-MSn, which showed the presence of six phenolic acids, one isoprenoid plant hormone, nine flavonols, and one flavonoid. Optimizing pequi pulp drying in ovens, and controlling time and temperature, can significantly reduce energy expenditure. This practice not only meets the demands of the food industry but also increases the use of fruits from the cerrado, promoting the diversification and valorization of these products.

Chitosan-Based Oleogels: Emulsion Drying Kinetics and Physical, Rheological, and Textural Characteristics of Olive Oil Oleogels

Oleogels are of high interest as promising substitutes for trans fats in foods. An emulsion-templated method was used to trap olive oil in the chitosan crosslinked with vanillin matrix. Oil in water emulsions (50:50 w/w) with different chitosan content (0.7 and 0.8% w/w) with a constant vanillin/chitosan ratio (1.3) were air-dried at different temperatures (50, 60, 70, and 80 °C) and freeze-dried (-26 °C and 0.1 mbar) to produce oleogels. Only falling rate periods were determined during air-drying kinetics and were successfully modeled with empirical and diffusional models. At a drying temperature of 70 °C, the drying kinetics were the fastest. The viscoelasticity of oleogels showed that the elastic modulus significantly increased after drying at 60 and 70 °C, and those dried at 50 °C and freeze-dried were weaker. All oleogels showed high oil binding capacity (>91%), but the highest values (>97%) were obtained in oleogels with a threshold elastic modulus (50,000 Pa). The oleogels' color depended on the drying temperature and chitosan content (independent of the drying method). Significant differences were observed between air-dried and freeze-dried oleogels with respect to oxidative stability. Oxidation increased with the air-drying time regardless of chitosan content. The found results indicated that drying conditions must be carefully selected to produce oleogels with specific features.

Review of osmotic dehydration: Promising technologies for enhancing products' attributes, opportunities, and challenges for the food industries

Osmotic dehydration (OD) is an efficient preservation technology in that water is removed by immersing the food in a solution with a higher concentration of solutes. The application of OD in food processing offers more benefits than conventional drying technologies. Notably, OD can effectively remove a significant amount of water without a phase change, which reduces the energy demand associated with latent heat and high temperatures. A specific feature of OD is its ability to introduce solutes from the hypertonic solution into the food matrix, thereby influencing the attributes of the final product. This review comprehensively discusses the fundamental principles governing OD, emphasizing the role of chemical potential differences as the driving force behind the molecular diffusion occurring between the food and the osmotic solution. The kinetics of OD are described using mathematical models and the Biot number. The critical factors essential for optimizing OD efficiency are discussed, including product characteristics, osmotic solution properties, and process conditions. In addition, several promising technologies are introduced to enhance OD performance, such as coating, skin treatments, freeze-thawing, ultrasound, high hydrostatic pressure, centrifugation, and pulsed electric field. Reusing osmotic solutions to produce innovative products offers an opportunity to reduce food wastes. This review explores the prospects of valorizing food wastes from various food industries when formulating osmotic solutions for enhancing the quality and nutritional value of osmotically dehydrated foods while mitigating environmental impacts.

Integrated drying model of lychee as a function of temperature and relative humidity

Drying is a universal method applied for food preservation. To date, several models have been developed to evaluate drying kinetics. In this study, lychee was dried employing a hot air dryer, and the drying kinetics was evaluated by comparing the Newtonian model, Henderson and Pabis model, Page model, and Logarithmic model. However, temperature and relative humidity, the key driving forces for drying kinetics, are not considered by these models. Thus, an integrated drying model, as a function of temperature and relative humidity, was developed to predict the hot air-drying kinetics and mass transfer phenomena of lychee followed by the calibration and validation of the model with independent experimental datasets. The model validation consisted of Nash- Sutcliffe model coefficient (E ), coefficient of determination ( R 2 ) and index of agreement ( d ) and all of them were found close to 1 indicating perfect model fit. Besides, the developed model was applied for process optimization and scenario analysis. The drying rate constant was found as a function of temperature and relative humidity that was high at high temperature and low relative humidity. Interestingly, temperature showed a higher effect on the drying rate constant compared to relative humidity. Overall, the present study will open a new window to developing further drying model of lychee to optimize quality its quality parameters.

Drying strategies of spent coffee grounds using refractance window method

The objective of this study was to evaluate, during the drying of spent coffee grounds, the application of pretreatments with ethanol and the application of ultrasound assisting the refractive window (RW) drying, and to compare with convective drying by hot air (AC). The effect on the kinetics parameters of the Fick and Page models were evaluated, as well as on the content of total phenolics and antioxidant capacity. For AC drying, samples of spent ground coffee were prepared in the form of fixed rectangular beds 0.7 cm high, which were placed on polyester sheets and pretreated up to 10 times sprayed with ethanol, then dried by AC at 80 °C and 0.8 m/s. For RW drying, the samples prepared in the same way as for AC were used. For this case, the application of ethanol as pretreatment and the use of ultrasound during process were tested. As results, regardless of the conditions applied, drying by RW was up to 50 % faster, evidenced in the highest values of effective diffusivity (from the Fick model) and the kinetic parameter (from the Page model). Regarding the treatments applied and their effect on the drying kinetics, any treatment had a significant effect on AC drying. On the contrary, the strategies applied in RW drying had significant effects, both the application of pretreatment with ethanol as well as the application of ultrasound assisting the process accelerated the drying kinetics. However, the treatment with ethanol and RW drying was the one that best preserved the phenolic compounds and the antioxidant capacity in the samples. Therefore, these strategies could be a good option to improve RW drying by accelerating the process and preserving the bioactive compounds in the spent coffee grounds for subsequent utilization.

Effect of wall material on lipophilic functional compounds of high oleic palm oil emulsions encapsulated by Refractance Window drying

High-oleic palm oil is a food-grade oil with desirable properties, as it is characterised by having an oleic acid concentration above 50 % and a high vitamin E and provitamin A content. This study investigated the effect of different combinations of two wall materials (whey protein (WP) and Capsul®, a commercial octenyl succinic anhydride modified starch (OSA-MS)) on the concentration of provitamin A, vitamin E and oleic acid, and the physical properties of high oleic palm oil emulsions encapsulated by Refractance Window drying technology. Wall material composition significantly affected (p < 0.05) all response variables, and R2 values were above 0.75 for all responses. Phytonutrient preservation showed its highest at an OSA-MS: WP concentration ratio of 1: 3. Optimal results were achieved (minimum moisture content, water activity and hygroscopicity, and maximum encapsulation efficiency and phytonutrient preservation) at an OSA-MS concentration of 8.13 % and WP concentration of 91.87 %. Flakes were obtained as a solid structure that protects oil's phytonutrients with 94 %, 75 % and 87 % of preservation of oleic acid, vitamin E and carotenoids, respectively. It shows that the wall material combination and encapsulation technique are suitable for obtaining lipophilic functional compounds.

Drying of Chinese medicine residues (CMR) by hot air for potential utilization as renewable fuels: drying behaviors, effective moisture diffusivity, and pollutant emissions

High moisture in Chinese medicine residues (CMR) can decrease the energy efficiency of thermochemical conversion, which necessitates the pre-drying. Owing to the complex constituents and decoction, CMR may possess distinct drying characteristics. It is necessary to understand its drying behaviors, effective moisture diffusivity, and pollutant emissions for future design and optimization of an industrial-level dryer. In this study, the drying of four types of typical CMR in hot nitrogen was performed. Their condensate and exhaust gas were collected and characterized. The results indicated that their drying process was dominated by internal moisture transport mechanism with a long falling rate stage. Drying temperature influenced their drying process more greatly than N2 velocity did. Residual sum of squares, root mean square error, and coefficient of determination indicated that Weibull model demonstrated their drying process best. Their effective moisture diffusivity was in the range of 1.224 × 10-8 to 4.868 × 10-8 m2/s, while their drying activation energy ranged from 16.93 to 30.39 kJ/mol. The acidic condensate had high chemical oxygen demand and total nitrogen concentration and yet low total phosphorus concentration. The concentration of total volatile organic compounds, non-methane hydrocarbons, H2S, and NH3 in the exhaust gas met the national emission limitation, while the deodorization of exhaust gas was required to remove odor smell.

Supplementary information

The online version contains supplementary material available at 10.1007/s13399-022-03722-4.