Infrared drying effects on the quality of eggplant slices and process optimization using response surface methodology

Evaluation of Organic Acids and Ultrasound as Pretreatment in Convective Drying Kinetics and Quality Parameters of Pumpkin

There is a growing interest in the food industry in new drying technologies that reduce the time required for dehydration, combined with low energy consumption, low environmental impact, and maintenance of the overall quality of the product. This work investigated convective drying of pumpkin with and without ultrasound-organic (citric or acetic) acid pretreatment for different durations (10, 20, and 30 min). Drying was carried out at 60 °C, and the Wang and Singh model had the best fit for the experimental data. Samples pretreated for 30 min had the shortest drying times. Water diffusivities ranged from 6.68 × 10-8 m2/s to 7.31 × 10-8 m2/s, with the pretreated samples presenting the highest values. The dried pumpkin water activity values were below 0.60. Regarding color parameters, there was a slight increase in luminosity, a slight reduction in a*, and a significant increase in b*. Drying resulted in the loss of ascorbic acid and phenolic compounds, but the samples pretreated with citric acid showed better retention. There was also a reduction in the total carotenoid content, but samples pretreated with acetic acid for 10 and 20 min showed the best retention.

Assessment of freeze, continuous, and intermittent infrared drying methods for sliced persimmon

Persimmons contribute positively to human health. Although off-season utilization typically presents a challenge due to permissions' perishable nature, it may become feasible through the implementation of appropriate drying methods. In this study, round sliced samples were dried to assess drying kinetics, modeling potential, color attributes, rehydration capacity, energy consumption (EC), cost index, and thermal properties. The fruits were subjected to distinct drying methodologies including freeze-drying, continuous infrared drying (300, 400, and 500 W), and intermittent infrared drying (PR = 1 [continuous], PR = 2 [30 s on-30 s off], and PR = 3 [20 s on-40 s off]). The duration of the drying process ranged from 40 to 390 min. It was determined that the most suitable models for depicting continuous and infrared drying kinetics of persimmon fruit were the Midilli et al. and Page models, whereas the Logarithmic model was identified as the optimal choice for characterization of freeze-drying kinetics. Assessment of EC revealed that both intermittent and continuous infrared drying methods incurred lower energy expenditure in comparison to the freeze-drying technique. Remarkably, throughout the course of the infrared drying processes, product surface temperatures varied between 106.33 and 22.65°C across different treatments. Despite its high EC, it has been found that high-quality products are produced by freeze-drying. However, infrared and intermittent infrared applications can be a low energy cost and feasible method for drying persimmon with a shorter duration. PRACTICAL APPLICATION: Persimmon is an important fruit with high nutritional value. However, as with many fresh products, they have a short shelf life. Within the scope of this research, three different drying methodologies were employed in the desiccation of persimmon specimens, and the impact of these methodologies on the overall qualitative attributes of the persimmon product was investigated. Despite its elevated energy consumption, the freeze-drying approach was found to yield high-quality products. Moreover, it was discerned that infrared drying represented a viable and expeditious alternative for drying the fruit, particularly when executed intermittently.

Effects of different drying methods on the contents of active ingredients of Saposhnikovia divaricata (Turcz.) Schischk and optimization of the drying process by response surface methodology

INTRODUCTION

Saposhnikovia divaricata (Turcz.) Schischk is one of the most widely used Chinese herbs worldwide. It has anti-inflammatory and analgesic properties and hence has a high clinical value. As the moisture level in S. divaricata is high after harvest, it requires drying.

OBJECTIVE

We aimed to find a scientific drying method and optimize the drying conditions of the best drying method of S. divaricata using response surface methodology (RSM).

METHODOLOGY

The effects of 4 different drying methods on the contents of prim-O-glucosylcimifugin, cimifugin, 5-O-methylvisamminol, and sec-O-glucosylhamaudol were determined using high-performance liquid chromatography. Chroma, the rehydration ratio, and active component content were used as indices, and slice thickness, drying temperature, and drying time were used as independent variables to optimize the drying conditions of the optimal drying method of S. divaricata using RSM combined with the Box-Behnken design.

RESULTS

The results showed that the optimal drying conditions were as follows: slice thickness, 4.00 mm; drying temperature, 60°C; and drying time, 15 h.

CONCLUSION

Under optimal drying conditions, the measured values were extremely close to the predicted values. The results of variance analysis showed that the model had a high degree of fit and the drying conditions of S. divaricata were optimized successfully.

Comparison of the dried properties of Ganoderma lucidum produced by the convective dryer and infrared dryer

Ganoderma lucidum is a promising medicine with a high amount of antioxidants and calcium. The selection of appropriate drying process methods in food science has a chief role to reach the best final characteristics. This study aimed to investigate the effects of air velocity and temperature in the convective dryer, sample distance, and infrared power in infrared dryers on the drying kinetics and quality of Ganoderma lucidum slices. In addition, Response Surface Methodology based on central composition design was used to optimize and analyze drying conditions. The ranges of temperature and air velocity were 40-60 °C and 0.5-1.5 m/s, respectively in the convective drying process while the range of distance and infrared power was 4-16 cm and 500-1500 W, respectively in the infrared drying process. It is worth mentioning that antioxidant and calcium contents were greatly enhanced during the drying procedures. Moreover, the values of the total color difference ranged between 8.21 and 19.66 for the convective dryer and 8.14 and 28.85 for the infrared dryer. A kinetic study indicated that dried samples by the infrared dryer could rapidly reach equilibrium moisture content due to exposure to IR radiation. Consequently, the results indicated that the infrared dryer has better performance than the convective dryer regarding drying time, energy consumption, and amount of calcium and antioxidant.

Infrared-assisted spouted bed drying of Chinese yam cubes: effect of constant and variable temperature drying processes on drying behavior, uniformity, and quality attributes

BACKGROUND

Infrared-assisted spouted bed drying (IRSBD) is an innovative hybrid drying technology based on infrared drying and spouted bed drying, which has the advantages of higher drying efficiency and better uniformity. Temperature is an important process parameter that affects drying characteristics and product quality. Considering the overall quality of the product, drying at a constant temperature may not be the best solution. However, there is a lack of research on dynamically varying drying schemes. In this study, the effects of constant and variable temperature drying processes on the drying characteristics, uniformity, energy consumption, and quality of Chinese yams were evaluated.

RESULTS

The shortest drying time and lowest energy consumption were obtained by IRSBD at 70 °C, followed by staged rising temperature drying (SRTD). However, SRTD achieved the best drying uniformity. The Peleg model could describe the dehydration kinetics of dried yams well (R²  > 0.99). A high drying temperature (70 °C) favored the preservation of bioactive compounds (polyphenols and flavonoids) and gave the best antioxidant activity and equilibrium rehydration ratio of dried yams but resulted in poor color. Samples dried with SRTD showed comparable good antioxidant activity and better color than those dried at 70 °C.

CONCLUSION

A reasonable variable temperature drying scheme using IRSBD is considered to be better when considering the drying performance and overall quality of the products. © 2022 Society of Chemical Industry.

Hot Air Convective Drying of Ginger Slices: Drying Behaviour, Quality Characteristics, Optimisation of Parameters, and Volatile Fingerprints Analysis

Ginger is one of the most popular spices and medical herbs with its unique pungent flavour and taste. Although there has been much research into the drying methods of ginger, the effect of drying parameters in hot air convective drying on ginger quality needs to be explored in depth. This study investigated the differences in drying behaviour and quality characteristics of ginger with the variables of temperature, thickness, and loading density. The moisture states and diffusion pattern in the different stages during the drying process were analysed using low-field NMR techniques. The results of quality evaluation showed that the temperature greatly influenced the colour and gingerol content of dried ginger, and the thickness of a ginger slice greatly influenced the rehydration rate. Optimal drying conditions were determined by considering a combination of specific energy consumptions with quality retention based on the response surface methodology: a temperature of 66.41 °C, thickness of 2 mm, and loading density of 5 kg/m2. HS-GC-IMS combined with multivariate chemometrics was used to achieve the characterisation of flavour profiles and fingerprinting of dried ginger. The principal component analysis and correlation analysis revealed that the alterations in ginger quality were intimately related to moisture diffusion during drying.

Response Surface Methodology Approach for Predicting Convective/Infrared Drying, Quality, Bioactive and Vitamin C Characteristics of Pumpkin Slices

In this research, a convective/infrared (CV/IR) dryer was used to dry pumpkin slices. For optimization of the drying conditions, the influence of three levels of independent variables including air temperature (40, 55, and 70 °C), air velocity (0.5, 1, and 1.5 m/s), and IR power (250, 500, and 750 W) were assessed by response surface method (RSM) through a face-centered central composite design. Analysis of variance (non-fitting factor and R² value) was employed to determine the desirability of the model. Response surfaces and diagrams were also utilized to show the interactive influence of the independent variables with the response variables (drying time, energy consumption, shrinkage, total color variation, rehydration ratio, total phenol, antioxidant, and vitamin C contents). According to the results, optimal drying conditions involved a temperature of 70 °C, air velocity of 0.69 m/s, and IR power of 750 W. At the mentioned conditions, response variables of drying time, energy consumption, shrinkage, color, rehydration ratio, total phenol, antioxidant, and vitamin C contents were 72.53 min, 24.52 MJ/kg, 23%, 14.74, 4.97, 617.97 mg GA/100 g dw, 81.57%, and 4.02 mg/g dw, with a confidence level of 0.948, respectively.

Optimization of a novel vacuum sublimation-rehydration thawing process

To better guarantee the quality of the thawed meat, maximize the thawing rate, and minimize the system energy consumption, the multiparameter and multi-objective coupling optimizations for the newly proposed vacuum sublimation-rehydration thawing (VSRT) process was conducted. The polynomial nonlinear regression equations of single and comprehensive objectives were established by the central composite rotatable design, and the corresponding test of fitting degree and the analysis of influencing factors order were carried out. Furthermore, the interaction effects of influencing factors were investigated through the response surface methodology and were experimentally validated to obtain the optimal process parameters. The results showed that the established regression equations were in good agreement with the experimental values. For the different objectives, there were great differences in the influence order and interaction of factors. In the sublimation and rehydration stages, there existed an optimal region in the response surface to achieve a better value for the single and comprehensive objectives. When the sublimation time was 19 min, the heating plate temperature was 26°C, the rehydration water volume was 1634 ml, the rehydration water temperature was 29°C, the thawing time was relatively short (1.00 h), and the thawing loss (1.19%), the total color difference (1.02), and the system-specific energy consumption (0.026 kW h/kg) were relatively low. The comprehensive performance of the VSRT system reached the best state. PRACTICAL APPLICATION: The purpose of this work is to make the novel vacuum sublimation-rehydration thawing method not only better guarantee the quality of thawed meat but also maximize the thawing rate and minimize the energy consumption of the system, which can provide a new idea and reference for the development of new high-efficiency thawing equipment.

Modeling and Optimization of Energy and Exergy Parameters of a Hybrid-Solar Dryer for Basil Leaf Drying Using RSM

This study deals with the optimization of energetic and exergetic parameters of a hybrid-solar dryer to dry basil leaves under determined experimental conditions at three air temperatures (40 °C, 55 °C, and 70 °C) and three bed thickness levels (2, 4, and 6 cm). The optimization of the thermodynamic parameters was performed using the response surface method (RSM) based on the central composite design (CCD) and the desirability function (DF) to maximize the drying rate, exergy efficiency, improvement potential rate and the sustainability index, and to minimize the energy utilization, energy utilization ratio and exergy loss rate. These parameters were calculated on the basis of the first and second laws of thermodynamics as the response variables. Based on the results obtained, it was determined that the optimal conditions for basil drying were at a drying air temperature of 63.8 °C and a bed thickness of 2 cm. At this point, the parameters of the drying rate, energy utilization, energy utilization ratio, exergy efficiency, exergy loss rate, improvement potential rate and sustainability index were obtained with the maximum utility function (D = 0.548) as 0.27, 0.019 (kJ/s), 0.23, 65.75%, 0.016 (kJ/s), 1.10 (kJ/s) and 0.015, respectively.

Short- and Medium-Wave Infrared Drying of Cantaloupe (Cucumis melon L.) Slices: Drying Kinetics and Process Parameter Optimization

The main objective of the present work was to study the drying kinetics and obtain the optimum process parameters of cantaloupe slices using short-and medium-wave infrared radiation (SMIR) drying technology. The effect of three independent variables of infrared radiation temperature (55–65 °C), slice thickness (5–9 mm) and radiation distance (80–160 mm) on the L value, color difference (∆E), hardness and vitamin C content were investigated by using the Response Surface Methodology (RSM). The results showed that the Page model can adequately predict the moisture content between 55 and 65 °C (R2 > 0.99). The effective moisture diffusivity (Deff) varied from 5.26 × 10−10 to 2.09 × 10−9 m2/s and the activation energy (Ea) of the SMIR drying was 31.84 kJ/mol. Infrared radiation temperature and slice thickness exerted extremely significant effects on L value and color difference (ΔE) (p < 0.01), with higher infrared radiation temperature and thin slice thickness leading to a decrease in the L value and an increase in ΔE. Hardness and vitamin C content were significantly affected by infrared radiation temperature, slice thickness and radiation distance, of which the slice thickness was the most distinct factor affecting the hardness value. Higher infrared radiation temperature and larger slice thickness and radiation distance resulted in higher vitamin C degradation. For the given constraints (maximized vitamin C content and L value, minimized ΔE and hardness value), the optimum drying parameters were infrared radiation temperature 58.2 °C, slice thickness 6 mm and radiation distance 90 mm. Under the optimum drying combination conditions, the experimental values were 65.58 (L value), 8.57 (∆E), 10.49 N (hardness) and 106.58 mg/100 g (vitamin C content), respectively. This study is beneficial to the development of the cantaloupe food processing industry and provides more insights for the application of SMIR drying technology to improve the drying rate and product quality of cantaloupe.

Effect of Pretreatments on Convective and Infrared Drying Kinetics, Energy Consumption and Quality of Terebinth

This study is focused on the influence of convective drying (50, 60, and 70 °C) and infrared (IR) power (250, 500, and 750 W) on the drying kinetics, the specific energy consumption of terebinth drying as well as quality and bioactive compounds upon various pretreatments such as ultrasound (US), blanching (BL), and microwave (MW). Compared to convective drying, IR drying decreased more the drying time and energy consumption (SEC). Application of higher IR powers and air temperatures accelerated the drying process at lower energy consumption (SEC) and higher energy efficiency and moisture diffusion. Terebinth dried by a convective dryer at 60 °C with US pretreatment showed a better color compared to other samples. It also exhibited the polyphenol and flavonoid content of 145.35 mg GAE/g d.m. and 49.24 mg QE/g d.m., respectively, with color variations of 14.25 and a rehydration rate of 3.17. The proposed pretreatment methods significantly reduced the drying time and energy consumption, and from the other side it increased energy efficiency, bioactive compounds, and quality of the dried samples (p < 0.01). Among the different pretreatments used, microwave pretreatment led to the best results in terms of the drying time and SEC, and energy efficiency. US pretreatment showed the best results in terms of preserving the bioactive compounds and the general appearance of the terebinth.

Antioxidant Activities of Eggplant (Solanum melongena) Powder with Different Drying Methods and Addition Levels to Pork Sausages

The objective of this study was to evaluate antioxidant activities of eggplant (EP) powder with different drying methods and addition levels to pork sausages to improve product quality. Antioxidant activities of EP with different drying methods, particle sizes, and solvents of extraction were determined. Freeze dried (FD) EP extracted with 100% ethanol had higher 2,2-diphenyl-1picrylhydrazyl radical-scavenging activities (DPPH-RSA) and total phenolic content (TPC) values than other drying methods. FD500 had the highest iron chelating ability (ICA) value. Oven-dried (OD) EP at 60°C had the highest reducing power. Dried EP was added to sausages of six groups: control without EP, reference added with ascorbic acid, O1 and O2 added with 0.25% and 0.5% OD EP, respectively, and F1 and F2 added with 0.25% and 0.5% FD EP, respectively. Pork sausages added with O2 had the lowest TBARS and TPC values. These values increased during storage. Purge loss (%), lightness (L*), and redness (a*) values of F2 were lower than those of other groups, whereas sausages containing F2 had the highest yellowness (b*). pH values of sausages added with EP were increased regardless of the level of EP added. Hardness values of F2 were higher. However, there were no significant differences in other textural characteristics. Sausages added with EP had higher moisture and protein contents (%), but lower fat contents (%). These results indicate that EP powder could be used to retard lipid oxidation and inhibit microbial counts during storage time.

Tailoring the Functional Potential of Red Beet Purées by Inoculation with Lactic Acid Bacteria and Drying

This study was focused on a comparative analysis of two drying methods, such as convective and infrared drying, on the red beetroot purées with lactic acid bacteria, as a strategy for tailoring the health benefits of the selected plant. For both varieties, the total betalain contents varied from 13.95 ± 0.14 mg/g dry weight in Beta vulgaris var. cylindra when compared with 11.09 ± 0.03 mg/g dry weight in Beta vulgaris var. vulgaris, whereas significant differences were found in total phenolic and flavonoid contents. Significant drying induced changes were found in selected bioactives, in terms of total betalains, flavonoids, and polyphenols, which influenced the antioxidant activities of the purées, structure, and color parameters. In general, infrared technology was more protective, leading to an increase of 20% in flavonoids content. One logarithmic decrease in cell viability was observed in all powders samples. After the in vitro digestion, the betalains decreased, in both gastric and intestinal simulated juices, with a more pronounced profile in infrared processed purées. Textural and rheological analysis of the dried purées highlighted that the infrared drying is milder compared to the conventional one, allowing us to obtain powders with enhanced functional properties, in terms of bioactives content, cell viability, color, and structural and rheological behavior.