Drying Of Fruits Research Articles

Drying of Red Chili Pepper (Capsicum annuum L.): Process Kinetics, Color Changes, Carotenoid Content and Phenolic Profile.

Studies were conducted focusing on the drying of chili pepper fruits (Capsicum annuum L.), cultivar Cyklon, using convective (AD), convective-microwave (AMD), vacuum (VD), and freeze-drying (FD) methods. The influence of the drying method and temperature on the kinetics of the process and selected quality attributes of the dried product were evaluated. It was demonstrated that the Midilli model best described the drying kinetics for all methods across the entire measurement range. FD and VD produced dried products with the highest brightness and the greatest value of the a* color parameter. The lowest b* color parameter was observed for the product dried using FD at 40 °C, while the highest b* value was noted for samples dried using AMD (100 W) at 60 °C. The highest carotenoid retention was achieved with the FD method at 40 °C, while the lowest carotenoid content was found in the product obtained using the AMD method (100 W) at 60 °C. The smallest losses of capsaicinoids were observed after FD drying at 40 °C, while the largest were found for AMD (100 W) at 60 °C. The analysis of chili pepper fruit extracts revealed the quantitative composition of 12 main phenolic compounds using the UHPLC-UV method. The highest polyphenol content was obtained with FD, while the lowest total polyphenol content was recorded after AD. Regardless of temperature, the total flavonoid content was highest in extracts from FD products, and the lowest flavonoid content was found after AMD at 100 W. For all drying methods analyzed, the total flavonoid content in the pepper extracts decreased with increasing temperature.

Exploring Mathematical Modeling and CFD in Convective Drying of Fruits and Vegetables: A Review

Exploring Mathematical Modeling and CFD in Convective Drying of Fruits and Vegetables: A Review

Pulsed vacuum drying of fruits, vegetables, and herbs: Principles, applications and future trends.

Pulsed vacuum drying (PVD) is a novel vacuum drying method that has demonstrated significant potential in improving energy efficiency and product quality in the drying of foods and agricultural products. The current work provides a comprehensive analysis of the latest advancements in PVD technology, including its historical development, fundamental principles, and mechanistic aspects. The impact of periodic pulsed pressure changes between vacuum and atmospheric pressure on heat and moisture transfer, as well as structural changes in foods at micro- and macro-scales, is thoroughly discussed. The article also highlights the influential drying parameters, the integration of novel auxiliary heaters, and the applications of PVD across various fruits, vegetables, and herbs. Furthermore, the review examines the current status and needs for mathematical modeling of PVD processes, identifying key challenges, research opportunities, and future trends for industrial application. The findings suggest that PVD not only enhances drying efficiency and reduces energy consumption but also preserves the nutritional value, color, and texture of dried products better than traditional methods. Future research should focus on optimizing process parameters and integrating advanced control systems to further improve the scalability and applicability of PVD technology in the food industry.

Effect of Different Drying Techniques on the Bioactive Compounds, Antioxidant Ability, Sensory and Volatile Flavor Compounds of Mulberry.

Mulberry perishes easily due to its high water content and thin skin. It is important to extend the shelf life of mulberry by proper processing methods. In the present study, the influence of three drying techniques, including hot air drying (HAD), vacuum drying (VD), and vacuum freeze-drying (VFD) on the quality maintenance of mulberry was comprehensively evaluated. Bioactive compounds, antioxidant activity, and the sensory and volatile flavor compounds of mulberry have been researched. The results showed that VFD treatment maintained the highest anthocyanins (6.99 mg/g), total flavones (3.18 mg/g), and soluble sugars (2.94 mg/g), and exhibited the best DPPH· (81.2%) and ABTS+· (79.9%) scavenging ability. Mulberry also presented the lowest hardness and the greatest brittleness after VFD. Additionally, VFD maintained the optimal color and presented the best sensory attributes. Furthermore, 30, 20, and 32 kinds of volatile flavor compounds were detected in HAD, VD, and VFD, respectively, among which aldehydes, esters, and ketones were the most abundant compounds. This study indicated the potential application value of VFD for the drying of fruit and vegetable foodstuffs.

MULTITHMT: A MATLAB Application for Multidimensional Transient Heat and Mass Transfer Processes

Transient heat conduction and mass transfer have many applications in industry such as heating, cooling, cooking, quenching of steels, freezing, and convective drying of vegetables or fruits. A novel, interactive, and fast MATLAB application, named MULTITHMT, is improved to solve multidimensional transient heat and mass transfer problems. Exact solutions are obtained for infinite rectangular bars, short cylinders, rectangular prisms, and spherical geometries. Instantaneous temperature and moisture content at any location in the objects are obtained and temperature and moisture content at the final time are displayed in two- and three-dimensional graphics. Quenching of steel for rectangle bars and cooking of cylindrical or rectangular prism-shaped meat are represented for transient heat transfer. Cooling of spherical commercial bronze and iron is also investigated. For transient mass transfer, convective drying of rectangular prunes, bananas of short cylinders, and spherical cornelian cherries with different operational conditions is calculated. Drying of cubes with the same shape and different moisture diffusivities is investigated. MULTITHMT is the only program that uses exact solutions to calculate multidimensional heat and mass transfer problems in the available literature. It is also the only application that can calculate the target time with a given temperature or moisture content for any specific location in the studied multidimensional objects. This application can be used for educational purposes in several engineering departments and industrial applications where transient heat and mass transfer processes are needed.

Influence of Conservation Methods on the sour cherry (Cerasus vulgaris Mill.) fruits quality

Objective: Sour cherry fruits (Cerasus vulgaris Mill.) belong to the Rosaceae family and are designed as a GRAS ingredient based on the FDA data. Animal experiments and clinical practice confirm that there are many positive pharmacological effects mainly related to anthocyanins. Development of standard regulations for this kind of medicinal plant raw materials is actual to introduce sour cherry fruits into official medical practice. In our research, we investigate macroscopic and microscopic properties and determine the content of tanning substances and anthocyanins in sour cherry fruits of various kinds of conservation. Materials and methods: Modern complex of physicochemical methods was used in pharmacognostical research. Microscopic analysis was performed on a LOMO Micmed-6 microscope with 10× eyepieces, 4×, 10×, 40× and 100× objectives, photographies were taken with a Sony Xperia Z3 compact digital camera. The content of total anthocyanins in terms of cyanidin-3-О-glucoside was determined by differential UV-spectrophotometry, total tannins content – by redox titration. Results and discussion: The anomocytic stomatal complex, fruits pulp druses, anthocyanins containing in the epidermis and fruits pulp cells, and vessels are typical signs for the sour cherry fruits anatomy structure. A conservation method has not to effect on visual representation of diagnostic signs. The contents of tanning substances are little; it is from 2.73±0.08% to 4.12±0.13% in terms of tannin. Maximal anthocyanin contents (in terms of cyanidin-3-glucoside and in absolutely dried raw material) were determined in fresh-frozen sour cherry fruits (after defrosting (with juice and without kernel) is 5.40±0.15% or in terms of moisture-containing raw materials (without kernel) – 0.690±0.019%. In the defrosted fruits without juice, the content of anthocyanins is two times lower in terms of completely dried raw material (without kernel), it is 2.77±0.12% or in terms of moisture-containing raw material (without kernel), it is 0.410±0.018%. In the juice released from cherry fruits after defrosting anthocyanin content in terms of cyanidin-3-glucoside is of 0.450±0.007% (g/100ml juice), in dried sour cherry fruits (without kernel) – 4.34±0.17%, which is lower than in fresh-frozen raw materials. It can be explained by the varietal features, as well by the conservation conditions; this matter is to be further studied. Contents of tanning substances in fresh-frozen and dried sour cherry fruits when storage during 4 months is insignificantly reduced, but it is established that contents of anthocyanin in terms of cyanidin-3-glucoside reduces 1.5 times in 4 months, if the raw material is frozen, and it reduces by 10% if the raw material is dried. Conclusion: Diagnostic signs of macroscopic and microscopic structures, contents of tanning substances and anthocyanins in terms of cyanidin 3-glycoside in sour cherry fruits were studied. The content of the main groups of biologically active substances decreases equally during storage of dried and frozen cherry fruits. When defrosting, it is necessary to carefully collect the juice, as it contains the bulk of the anthocyanins. It is promising to study various options for freezing and drying of cherry fruits with kernels in order to reduce the loss of fruits juice to a minimum. In this case, it is important to ensure that the kernels are whole (not destroyed), in order to avoid the ingress of cyanogenic glycosides into the medicinal plant material. The results will be used to develop normative documentation for sour cherry fruits.

Effects of Freeze-Thaw Pretreatment Combined with Hot Air on Snake Gourd (Trichosanthes anguina L.).

Snake gourd is a seasonal vegetable with a high water content and medicinal value, but the short harvest period limits the large-scale application of snake gourd. Therefore, the effects of freeze-thaw pretreatment (FT) combined with hot air (HD) on the drying characteristics, active ingredients and bioactivities of snake gourd were investigated. The results showed that FT pretreatment reduced browning and shortened the drying time by 44%; the Page model was the best fit for describing the drying process. The polysaccharide contents (21.70% in alcoholic extract (TG1) and 44.34% in water extract (TG2)) and total phenol contents (1.81% in TG1 and 0.88% in TG2) of snake gourd pretreated by FT-HD were higher than those of snake gourd pretreated by the corresponding HD treatment. The FT pretreatment decreased the molecular weight of snake gourd polysaccharides and increased the molar ratio of glucose. The extracts pretreated by FT-HD showed greater chemical, cellular antioxidant capacity and α-amylase and α-glucosidase inhibition than those pretreated by HD. FT-HD can be recommended for achieving a short drying time and high quality of snake gourd and can be used for the drying of other fruits and vegetables.

Analysis of the influence of heating temperature on the convective drying process

The study examines the influence of heating temperature during the convective drying of fruits on the mass fraction of moisture in the finished product. Convective drying is a promising method for preserving products, allowing the production of dried fruits that can provide essential nutrients year-round. The experiments detailed in this article aim to establish optimal fruit drying modes. Standard methods were used to analyze the experiments according to regulatory documents in force in Kazakhstan. The authors proposed diagrams of convective drying of the fruits in the south of Kazakhstan. According to the constructed schemes, it can be seen that the heating temperature during the drying process affects the final product. According to the analysis, an increase in heating temperature results in a decreased drying time. At the specified time, the highest conversion rate of the relative mass of the dried product is detected. Additionally, it was obtained that the temperature, size, and structure of fresh raw materials affect the period of maximum moisture volatilization rate. The authors carried out a sensory evaluation of the main quality indicators: taste, color, odor and consistency. The optimal characteristics of the indicators were determined. They were extracted at a heating temperature of 50 ....65 °C. Numerous experiments have shown that it is necessary to offer such convective drying parameters. Convective drying temperature for apples is 50-55 °C, for apricots - 55-65 °C, for prune plums - 60-65 °C. Such results will be useful in the technology of fruit and vegetable processing.

Enhancing infrared drying of red dragon fruit by novel and innovative thermoultrasound and microwave-mediated freeze-thaw pretreatments

This study investigated the effectiveness of novel and innovative pretreatments (NIP) using thermoultrasound and microwave-mediated freeze-thaw (TSFT, MWFT) for improving the mid-infrared drying of dragon fruit, as compared with recent pretreatment methods using cold plasma (CP), ultrasound (US), edible coating (EC), microwave and infrared blanching (MWB, IRB). Except for EC, all selected pretreatment methods induced ultrastructural changes, resulting in accelerated moisture removal and reduced drying time. In addition, all the pretreatments also induced modifications in colour, structure, and texture, with NIP demonstrating superior outcomes for colour, rehydration, shrinkage, and hardness properties. Blanching pretreatments (MWB and IRB) improved phytochemical and antioxidant properties, including total phenolics, betacyanin, betaxanthin, CUPRAC, hydroxyl radical scavenging, and ABTS, except for ascorbic acid, which was better preserved by TSFT. The study underscores the time-saving and quality enhancement advantage of NIP, over other recent methods for improving mid-infrared drying.

Investigation of the influence of pre-treatment with ultrasound + ethanol on the drying of mature fruits of Schinus terebinthifolius Raddi

The aim of this study was to evaluate the influence of pretreatment (ultrasound + etanol), associated with different drying air temperatures, on the yield and quality of the essential oil of ripe fruits of Schinus terebinthifolius Raddi and to adjust previously described mathematical models in the specialized literature in order to obtain graphical representation of the drying kinetics. The experiments were conducted according to a Central Composite Design considering two factors with the following ranges: pre-treatment duration (ultrasound+ethanol) from 0 to 12 minutes and drying air temperature from 40 to 80 ºC. Four mathematical models, namely: Lewis, Page, Midilli, and Henderson & Pabis, were fitted to the experimental data. The essential oil was extracted by hydrodistillation and its constituents were identified by gas chromatography coupled with mass spectrometry (GC–MS). The Midilli model best represented the drying kinetics of ripe fruits of S. terebinthifolius pretreated with ultrasound + ethanol. The drying time of S. terebinthifolius fruits was influenced both by the pretreatment duration (with linear effect) and by the drying air temperature (linear and quadratic effects). None of the evaluated factors showed significance on the essential oil yield. It was not possible to adjust a model that simultaneously optimized the drying time and the yield of the essential oil of ripe and dried fruits of S. terebinthifolius, previously treated with ultrasound + ethanol.

Biological and ecological characteristics of representatives of the genus Rosa L. (introduction, fruit characteristics, use)

In the steppe region an increase in the level of environmental pollution inevitably leads to a deterioration in the ecological condition of all components of ecosystems and leads to growth in the incidence of diseases among the population of the territory. It is possible to strengthen the natural immunity of the human body due to the introduction into the diet of products that contain biologically active compounds obtained from fruits, leaves, roots, etc. of representatives of the flora. Such plants include, first of all, representatives of the genus Rosa L. The high prophylactic and therapeutic effect of rose hips is confirmed by modern research by scientists. Among the vitamins that are part of the fruit, the highest content of vitamin C (ascorbic acid). Physiological and ecological studies of plants of the genus Rosa, in particular, indicators of success of introduction and vitamin C content, were carried out on the territory of the Botanical Garden of Oles Honchar Dnipro National University (DNU). It was found that due to their decorative properties and high-vitamin fruits, these plants are indispensable in the conditions of the steppe Dnieper region. Representatives of the genus Rosa are characterized by a variety of life forms and the specifics of the architectonics of the crown, the shape and color of the leaves and abundant flowering. It is shown that the climatic conditions of the new place of growth directly affect the growth and formation of shoots, and the annual cycle of plant development has its own characteristics, which are manifested during the growth of shoots, differentiation, the phase of physiological rest or forced dormancy depending on the geographical origin of species. Rose hips also differ in the size of fruits and seeds. Large fruit sizes and a significant number of seeds were observed both in the local species R. canina and in some introduced species of R. micrantha, R. iberica, R. hugoni. In the species R. multiflora and R. borboniana, small fruits and a small number of seeds were found. In this group of plants significant interest is associated with the high content of vitamin C in their fruits, which should not be destroyed during storage. As a result of our many years of research, it has been found that during fruit drying, there is a certain loss of ascorbic acid depending on the species characteristics of plants. The vitamin is best preserved in the fruits of R. rugosa (up to 58%) and R. hugonis (up to 55%). Other types are recommended to be used fresh. In addition, rose hips are highly decorative plants with long flowering and brightly colored fruits, which allows you to use this group of plants when creating compositions in modern landscape design.

Optimization of production of blanched apple chips using sublimation drying

AbstractThe aim of the research is to investigate the efficiency of producing blanched apple chips utilizing an innovative technology, namely sublimation drying. Apples of the “Aport Almaty” variety were stored at a temperature of 4°C prior to processing. They were peeled, seeded, sliced into segments of specific thickness, and subjected to drying in a drying chamber at temperatures of 45, 50, and 60°C. Following drying, the samples were analyzed for antioxidant content, phenolics, minerals, and vitamins. For comparative analysis, methods such as sublimation drying, conventional drying, and low‐temperature drying were also employed. Atomic absorption spectroscopy and high‐performance liquid chromatography methods are employed for the analysis of the mineral and vitamin composition. Each group consists of 30 samples. Analysis of variance revealed statistically significant differences in antioxidants (F(3, 116) = 12.48, p < .001), water activity (F(3, 116) = 7.22, p < .01), and phenols (F(3, 116) = 9.85, p < .001) among the drying methods. Sublimation drying demonstrated higher levels of antioxidants and phenols (p < .05). At 45°C, sublimation drying resulted in higher levels of antioxidants (p < .05) and vitamin C, as well as low water activity (p < .05). Dry mass significantly correlated with storage stability (r = −0.75, p < .05). Sublimation drying exhibited superiority in moisture loss (F > 24.17, p < .001). The correlation coefficient between dry mass and moisture content was −0.82 (p < .01). Blanching improved antioxidant activity (75% vs. 65%) and color preservation.Practical applicationsOur study deepened the understanding of sublimation drying processes in apple chip production by determining optimal conditions for achieving high product quality. The obtained results provide valuable recommendations for practical application in the food industry, including optimal temperature regimes and the use of blanching to enhance chip quality. The universality of our study results supports their applicability in various sectors of the food industry that involve the drying of fruits and vegetables. Sublimation drying with blanching demonstrated high effectiveness in preserving the biochemical characteristics of the product, extending shelf life, and enhancing organoleptic properties.

The Mathematical Modeling, Diffusivity, Energy, and Enviro-Economic Analysis (MD3E) of an Automatic Solar Dryer for Drying Date Fruits

Date fruit drying is a process that consumes a significant amount of energy due to the long duration required for drying. To better understand how moisture flows through the fruit during drying and to speed up this process, drying studies must be conducted in conjunction with mathematical modeling, energy analysis, and environmental economic analysis. In this study, twelve thin-layer mathematical models were designed utilizing experimental data for three different date fruit varieties (Sakkoti, Malkabii, and Gondaila) and two solar drying systems (automated solar dryer and open-air dryer). These models were then validated using statistical analysis. The drying period for the date fruit varieties varied between 9 and 10 days for the automated solar dryer and 14 to 15 days for open-air drying. The moisture diffusivity coefficient values, determined using Fick’s second law of diffusion model, ranged from 7.14 × 10−12 m2/s to 2.17 × 10−11 m2/s. Among the twelve thin-layer mathematical models, we chose the best thin drying model based on a higher R2 and lower χ2 and RMSE. The Two-term and Modified Page III models delivered the best moisture ratio projections for date fruit dried in an open-air dryer. For date fruit dried in an automated solar dryer, the Two-term Exponential, Newton (Lewis), Approximation diffusion or Diffusion Method, and Two-term Exponential modeling provided the best moisture ratio projections. The energy and environmental study found that the particular amount of energy used varied from 17.936 to 22.746 kWh/kg, the energy payback time was 7.54 to 7.71 years, and the net CO2 mitigation throughout the lifespan ranged from 8.55 to 8.80 tons. Furthermore, economic research showed that the automated solar dryer’s payback period would be 2.476 years.

Microwave-vacuum drying: Modeling validation of drying and rehydration kinetics, moisture diffusivity and physicochemical properties of dried dragon fruit slices

This study investigated the drying of dragon fruit slices with varying samples (0.5 cm, 1 cm, and 1.5 cm) using a microwave-vacuum dryer at power levels of 400 W, 600 W, and 800 W, under a vacuum pressure of 600 mm Hg. The comprehensive assessment included drying kinetics, effective moisture diffusivity (Deff), rehydration behavior, color changes, and ascorbic acid content. Results indicated a substantial moisture content reduction from an initial 614.28% to an average of 7.14% (dry basis) post-microwave vacuum drying. The Wang and Singh model proved most suitable, exhibiting high R2 values and low RMSE values, providing accurate insights into the drying process. Dragon fruit samples showed Deff values from 4.381 × 10−3 to 4.084 × 10−2 cm2/min, increasing with microwave power level. Rehydration, modeled by the Peleg model, revealed that the highest power level had the highest R2 and lowest RMSE values. Notably, 1.5 cm slices at 400 W exhibited minimal color change (18.32) and retained the most ascorbic acid (6.94 mg/100 g). This study offers valuable insights into dragon fruit drying, highlighting its impact on moisture content, modeling, and product quality.

Experimental investigation, performance analysis, and optimization of hot air convective drying of date fruits via response surface methodology

A laboratory-scale hot air convective dryer (HACD) was used to dry date fruits surplus at 0.5 ± 0.02 kg kg−1 to a safe moisture level of 0.35 kg kg−1 under drying temperatures (T) of 50–70 °C with airflow rates (Q) of 0.18 and 0.28 m3 h−1. Kinetics, modeling, energy, economic feasibility, and color difference of the date fruits were analyzed and then optimized using response surface methodology (RSM) with two drying factors and eight responses. The drying time to reach the desired moisture level ranged from 9 to 28 h under different drying conditions. The proposed mathematical model expressed the moisture behavior over drying time with the highest R2 = 0.9998 and 0.9999, respectively, for 0.18 and 0.28 m3 h−1. Effective moisture diffusivity (Deff) was calculated using the starting accessibility parameter and varied between 9.9 × 10−8 and 3.3 × 10−7 m2 s−1. The energy analysis revealed that the specific energy consumption (SEC) varies between 22.04 and 43.05 kWh.kg−1 and the drying efficiency (η) are 16.91, 16.14, and 25.38% for 50, 60, and 70 °C, respectively. The RSM optimization using a multi-level design with two centurium points denoted the optimum responses for the highest drying temperature. The lowest payback period (Pb) of the drying system was estimated to be 0.45 years for T = 70 °C and Q = 0.28 m3 h−1. The optimum drying time, Deff, total energy consumption (Et), SEC, η, and total color change (ΔE) were estimated to be 9 h, 3.3 × 10−7 m2 s−1, 33.91 kWh, 22.04 kWh.kg−1, 27.69%, and 1.69, respectively.

Developing a spouted bed for combined radio frequency-hot air treatments to improve the heating uniformity in high-moisture carrot cubes

Uneven and thermal runaway heating is the biggest obstacle to industrial applications of radio frequency (RF) technology, while the existing research mainly focuses on the RF heating uniformity of low-moisture foods with fewer reports about the useful solutions to avoid heterogeneous heating of high-moisture foods. Thus, the combined RF-hot air treatment in a newly designed spouted bed (RFHASB) was developed in this study to improve the RF heating uniformity of fresh carrot cubes selected as the high-moisture model sample. This RFHASB was used to evaluate effects of four processing parameters (cone angle, nozzle diameter, inlet air speed and electrode gap) on the RF heating rate and uniformity of carrot cubes with comparison of those between the RFHASB and the hot air treatment alone in the spouted bed (HASB). The results showed that the RFHASB effectively alleviated the non-uniform heating in the treated high-moisture carrot cubes through mixing and stirring particles. Both heating rate and uniformity index in RFHASB increased with decreasing cone angles and electrode gaps but decreased when nozzle diameters and inlet air speeds were reduced. The RFHASB had better heating performances than the HASB. These findings may provide the theoretical basis for the effective drying of high-moisture fresh fruits and vegetables in RFHASB.

Microwave drying vs hot-steam-air drying of seedless noni fruit: drying performance and post-drying quality

Noni fruit contains several beneficial compounds for health, including scopoletin as its active component. The fruits contain a high moisture content, generally above 80%, rendering them to rot quickly. The drying process can potentially increase the fruit’s shelf life as it reduces the moisture content, stop the enzymatic reactions/microorganism activities and inhibit the quality degradation. This study compared the drying performance and post-process quality of noni fruit slices from the microwave and hot-steam-air drying at 50°C and 60°C. The drying performance parameters were time and rate. Several post-drying quality parameters stipulated in Indonesia pharmacopoea standard, such as scopoletin, total ash, and insoluble-acid ash contents, were observed. The results show the drying rate of noni fruit ranged from -3.51 x 10−3 % min−1 (for microwave-drying) to -2.45 x 10-5 % min−1 (for hot-steam-air drying at 50°C). Noni fruits from hot-steam-air drying at 60°C had the highest scopoletin content (22.47 mg kg−1) and the lowest total ash content (4.78%). Microwave-dried noni fruit had the lowest insoluble-acid ash content (0.02%). Drying methods significantly affected the drying rate, total ash content, and insoluble-acid ash content of noni fruit. Treatment scoring shows microwave- and hot-steam-air drying at 60°C are potential options for drying noni fruit.

Biochemical Profile and Antioxidant Activity of Dried Fruit Produced from Apricot Cultivars Grown in Latvia

The present study focused on evaluating the biochemical profiles of four apricot cultivars (cv.) (Prunus armeniaca L.) grown in Latvia and demonstrating their processing to obtain the food product, dried candied fruit (DCF). The fingerprinting of apricot fruit approached by LC-MS and ultraviolet–visible spectroscopy revealed the abundance of bioactives responsible for the antioxidant activity. The outstanding composition of group compounds, i.e., phenolics, flavonoids, and vitamin C, was observed in the cv. ‘Dimaija’, followed by cv. ‘Gundega’ and cv. ‘Velta’. The lowest values were found in the cv. ‘Boriss’ and fruit from a market of Greek origin. However, the latter two contained the highest carotenoid levels due to a more pronounced maturity. Amongst the 13 individual phenolics detected, rutin, chlorogenic and neochlorogenic acids, catechin, and epicatechin prevailed. The concentrations observed were the highest in cv. ‘Dimaija’, followed by cv. ‘Velta’ and cv. ‘Gundega’. Osmotic dehydration and convective drying of apricot fruit variedly influenced the content of bioactives in DCF products. The most substantial decrease due to thermal lability was observed in the vitamin C content in DCF, accounting for a 95.3% loss for all cultivars. The content of total phenolics, flavonoids, and carotenoids in DCF, on average, was 62.7%, 49.6%, and 87.6% lower than that observed in the raw fruit, respectively. On average, the content of individual phenolics in DCF, such as rutin and chlorogenic acid, decreased by 63.8% and 20.8%, respectively. The decline in the content of bioactives was conditioned by the physical migration of the cell components to the hypertonic solution. However, the increase in the content of cell wall-bound phytochemicals, such as catechin and epicatechin, after osmotic dehydration and convective drying, was observed in DCF, corresponding to a 59.5% and 255.64% increase compared with the raw fruit, respectively. Panelists generally responded positively to the developed DCF; however, greater preference was given to products with a lower phenolic content, such as cv. ‘Boriss’ and those produced from the market fruit. It is believed that the high flavan-3-ols content, along with chlorogenic acid, contributed to the bitter taste of DCF. Overall, apricot fruits represent the abundance of bioactives retained in DCF after osmotic dehydration and convective drying. The findings observed in the current study allow to consider DCF as a functional food; however, given the high sugar content, their consumption should be in moderation.

PEF pre-treatment and ultrasound-assisted drying at different temperatures as a stabilizing method for the up-cycling of kiwifruit: Effect on drying kinetics and final quality

The drying of food by-products, such as kiwifruit discards and surpluses, constitutes an interesting option as a means of stabilizing them for later use. This study assesses the combined influence of the drying temperature (40–70 °C), pulsed electric field (PEF) pretreatment (0–5000 V) and ultrasound (US; 0–50 W) application during the drying of kiwifruit. The increase in temperature, the use of PEF pretreatment or the US application during drying accelerated the process, but it was the combination of the three which led to the highest values of the effective diffusivity and the mass transfer coefficient. Over the range of different conditions studied, the functional and antioxidant properties of dried kiwifruit were not significantly affected, while the color presented some differences, mainly related to the L* and a* coordinates. Therefore, the combination of temperature, PEF and US allowed the processing time to be shortened without significantly affecting the final quality of kiwifruit. Industrial relevance textKiwifruit is one of the most globally popular fruits. Its high moisture content makes its by-products susceptible to chemical and microbiological degradation, so a drying step is needed to prolong its shelf-life and make up-cycling possible. To this end, hot air drying is one of the most widely-used techniques in the food industry, whose main drawback is a large amount of energy consumed. Therefore, there is a need to look for alternatives to reduce its economic and environmental impact and achieve a quality dried product. This study points out the combination of drying temperature, PEF pretreatments and ultrasound-assisted drying for the purposes of shortening the drying process while preserving the quality of the final product. These results, therefore, underline the promising nature of these techniques not only as regards their application in kiwifruit drying but also in the drying of other fruits and vegetables.

A Review of Hybrid and Green House Type Solar Dryers

Solar drying is a renewable, efficient, cheap, and sustainable method of preserving agricultural produce. Recent trends in hybrid and greenhouse–type solar dryers were studied. The study revealed that hybrid and greenhouse–type dryers are robust and efficient because they are mostly embedded with heat generating and circulation systems. They are designed to accommodate large-scale drying of fruits and vegetables with higher rates of drying, reduced drying time and some other specific advantages. Findings also revealed that hybrid and greenhouse type solar dryers are mostly designed for optimum retention of heat to compensate for periods with low illumination. The study also gave insight into design challenges peculiar to these types of dryers, and further revealed that most of the fabrications were based on assumptions, with limited data as references. This review also highlights the cost of procurement, uniformity of airflow, sizing of blower and material selection as some of the factors limiting the utilization of hybrid and greenhouse type solar dryers for drying of fruits, vegetables, and other staple crops.