Study the effect of sun, oven and microwave drying on quality of onion slices

Effects of thermal processing on natural antioxidants in fruits and vegetables

Research on the content of polyphenolic compounds in fruits and vegetables, the extraction of bioactive compounds, and the study of their impact on the human body has received growing attention in recent years. This is due to the great interest in bioactive compounds and their health benefits, resulting in increased market demand for natural foods. Bioactive compounds from plants are generally categorized as natural antioxidants with health benefits such as anti-inflammatory, antioxidant, anti-diabetic, anti-carcinogenic, etc. Thermal processing has been used in the food sector for a long history. Implementing different thermal processing methods could be essential in retaining the quality of the natural antioxidant compounds in plant-based foods. A comprehensive review is presented on the effects of thermal blanching (i.e., hot water, steam, superheated steam impingement, ohmic and microwave blanching), pasteurization, and sterilization and drying technologies on natural antioxidants in fruits and vegetables.

Effect of microwave heating on the phenolic and carotenoid composition and antioxidant properties of Momordica charantia

Momordica charantia L. (MC) is a widely consumed vegetable known for its nutritional benefits, as it is a rich source of carotenoids and phenolic compounds. Various cooking methods are use in domestic settings, including microwave cooking. Therefore, it is crucial to investigate the impact of microwave cooking on the bioactive composition of MC. MC fruits were subjected to microwave heat for 5-, 10-, and 15-min. High performance liquid chromatography was used to identify of carotenoids and phenolic compounds, and total bioactive composition and antioxidant assays were conducted using spectroscopic techniques. There were 17 carotenoids and chlorophylls identified in MC fruit, including lutein, violaxanthin, antheraxanthin, pheophytin a, and all-E-β-carotene. The levels of these compounds significantly increased upon exposure to microwave heating. Similarly, 16 phenolic compounds were identified, and their amounts increased during the treatments, except for 3-hydroxyphloretin-6'-hexoside, quercetin-3-(6″-acetyl)-glucoside, petunidin-3-(6″-acetyl)-glucoside and petunidin-3-(6″-acetyl)-glucoside. The sample subjected to microwave treatment for 15 min exhibited the highest concentration of total phenolic compounds (TPC) at 754.5 mg/100g. The total flavonoid content (TFC) reached 94.6 mg/100g after 10 min of treatment. Additionally, the maximum total anthocyanin content, reported as 54.8 mg/L, was observed in the sample exposed to microwave heating for 15 min.

Nutrient and Bioactive Fraction Content of Olea europaea L. Leaves: Assessing the Impact of Drying Methods in a Comprehensive Study of Prominent Cultivars in Morocco

This study explores the potential of olive leaves, long integral to Mediterranean traditional medicine, as a rich source of valuable compounds. The challenge lies in their considerable water content, hindering these compounds' full valorization. Four drying methods (air-drying, oven-drying, freeze-drying and solar-drying) were investigated for their impact on nutrient and bioactive compound content in the leaves of four olive varieties ("Arbequina", "Koroneiki", "Menara" and "Picholine Marocaine") cultivated in Morocco. In their fresh state, "Picholine Marocaine" exhibited the highest protein levels (6.11%), "Arbequina" had the highest phenolic content (20.18 mg gallic acid equivalents/g fresh weight (FW)), and "Koroneiki" and "Menara" were highest in flavonoids (3.28 mg quercetin equivalents/g FW). Specific drying methods proved optimal for different varieties. Oven-drying at 60 °C and 70 °C effectively preserved protein, while phenolic content varied with drying conditions. Air-drying and freeze-drying demonstrated effectiveness for flavonoids. In addition, an analytical approach using high-performance liquid chromatography and diode array detection (HPLC-DAD) was applied to investigate the effects of the different drying methods on the bioactive fraction of the analyzed samples. The results showed qualitative and quantitative differences depending on both the variety and the drying method used. A total of 11 phenolic compounds were tentatively identified, with oleuropein being the most abundant in all the samples analyzed. The freeze-dried samples showed the highest content of oleuropein in the varieties "Arbequina" and "Picholine Marocaine" compared to the other methods analyzed. In contrast, "Koroneiki" and "Menara" had higher oleuropein content when air dried. Overall, the obtained results highlight the importance of tailored drying techniques for the preservation of nutrients and bioactive compounds in olive leaves.

Quantification of quercetin from red onion (Allium cepa L.) powder via high-performance liquid chromatography-ultraviolet (HPLC-UV) and its effect on hyperuricemia in male healthy Wistar albino rats

Onions (Allium cepa L.) contain various flavonols, including quercetin, kaempferol, anthocyanin, luteolin, and myricetin. Quercetin in onions is considered the primary bioactive component. To assess the impact of quercetin on hyperuricemia in healthy Wistar albino rats, this study used high-performance liquid chromatography with ultraviolet (HPLC-UV) to identify and measure quercetin in onion powder. Twenty-four 160 ± 10 g, six wistar albino male rats in each group were kept: NC (control sample, no onion powder), OT1, OT2, and OT3, which contained 11.13, 14.84, and 18.61 g/100 g onion powder, respectively. The treatment lasted 28 days, during which the last 7 days were for urine, feces, and blood collection. The results showed a trend of decreasing levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase, total bilirubin, total cholesterol, and low-density lipoprotein in rats fed OT1, OT2, and OT3 diets. Improvements were observed in feed, water, and nutrient intake, feed conversion ratio, feed efficiency ratio, nutrient digestibility, nitrogen balance, body weight, blood urea nitrogen, creatinine, and uric acid levels (p ≤ .05). In contrast, high-density lipoprotein, triglycerides, serum total protein, neutrophils, and lymphocytes did not change (p ≥ .05). White blood cells, red blood cell count, platelet count, hemoglobin, and monocytes showed an upward trend. Based on our calculations, we determined the optimal human dosage from the most effective amount of onion powder. By taking into account the ratio of human-to-rat surface area, we estimate that the equivalent human dose of onion is 181.04 grams with 204 mg of quercetin. Additionally, when factoring in the dry matter content, the recommended dose of onion is 29.19 grams with 220 mg of quercetin.

Effects of different levels of dried onion powder on nutrient digestibility, biochemical parameters, and nitrogen balance in Wistar albino rats with induced hyperuricemia

Introduction: Onions (Allium cepa L.) are excellent sources of bioactive compounds and phytochemicals such as allicin, quercetin, fisetin, and other sulfurous compounds. Therefore, our study aimed to investigate the effects of dried onion powder on growth performance, nitrogen balance, and biochemical parameters in Wistar albino rats with induced hyperuricemia. Methods: A total of 24 rats were randomly divided into four groups, with six in each group: HU (positive control) and HOT1, HOT2, and HOT3 groups, which received a diet containing onion powder at concentrations of 11.13, 14.84, and 18.61 g/100 g, respectively. Hyperuricemia was induced in rats by administering a new formulation intraperitoneally (250 mg/kg potassium oxonate) and orally (40 mg/kg potassium bromate) daily for 14 days. After confirmation of hyperuricemia induction, rats were fed with onion-treated diets with various concentrations of quercetin for 21 days. Results: Significant decreases (p ≤ 0.05) in serum uric acid, alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, total bilirubin, total cholesterol, and low-density lipoprotein were observed. An increasing trend (p ≤ 0.05) in the levels of hemoglobin (Hb), white blood cell (WBC), red blood cell (RBC), and platelet count was observed. An improvement in the levels of serum high-density lipoprotein, triglycerides, blood urea nitrogen, serum creatinine, serum total protein and neutrophils, lymphocytes, and monocytes was observed. A positive progress (p ≤ 0.05) was observed in growth performance and nutrient digestibility. Conclusion: In conclusion, a significantly lower uric acid level was observed in rats fed with HOT2 diet. Based on the ratio of the surface area (human/rat), the best recommended dose of onion for the incidence and prevention of hyperuricemia is 189.95 g, corresponding to the dose of 204 mg/day of quercetin in humans.

Effects of gradually increasing drying temperatures on energy aspects, fatty acids, chemical composition, and in vitro ruminal fermentation of acorn

Acorns are commonly used to meet energy, protein, and mineral needs of livestock in various parts of the world. However, since acorns have quite a high moisture content at harvest, they should be stored as dried to prevent loss of nutrients and spoilage throughout storage periods. The aim of this study is to determine the drying kinetics, color, energy aspects, crude protein, crude ash, crude oil, fatty acid composition, ADF, NDF, condensed tannin, and mineral composition properties of acorns dried at gradually increasing drying temperatures. Drying processes were carried out in an air-convective dryer at temperatures of 40, 60, 80, 100, and 120 °C. The Logistic model was identified as the best model for describing current drying conditions. Increasing drying temperatures reduced L* (lightness) values and increased thermal efficiency and effective moisture diffusion values. In terms of energy efficiency, the best outcomes were achieved at 80 °C and 120 °C drying temperatures. Drying temperatures had highly significant effects on nutritional traits of acorn samples. Increasing drying temperatures increased fiber content, gas-methane production, and energy values and reduced crude protein and oil contents. Some minerals decreased and some others increased with increasing drying temperatures. Increasing drying temperatures caused slight changes in fatty acid compositions. In terms of animal drying and feeding characteristics, it was determined that a drying temperature of 80 °C was ideal for acorn drying.

Stability of polyphenols in food processing

In recent years, polyphenols have attracted considerable attention due to their diverse potential health-beneficial effects on humans. Polyphenols are widely distributed in natural plants, and therefore play an important role in human food. Thermal processing, irradiation, fermentation, high pressure, microwave, and drying are several popular food processing methods. However, polyphenols are instable in food processing, which easily degrade and react with other components because of their polyhydroxy characteristic. Traditional and advanced technologies have been used to characterize the stability of polyphenols. The main influence factors of stability of polyphenols such as pH, temperature, light, oxygen, enzymes, metal ions, as well as macromolecules, are summarized. Besides, thermal processing greatly promoted the degradation of polyphenols. Thermal degradation mechanisms and products of some polyphenols, such as quercetin and rutin, have been intensively demonstrated. Nevertheless, the structural changes of polyphenols caused by food processing, may lead to different bioactivities from the obtained results based on unprocessed polyphenols. Therefore, to maximize the beneficial effects of polyphenols ingested by human from processed food, the stability of polyphenols in food processing must be thoroughly investigated to assess their real bioactivities. In addition, some available technologies for improving the stability of polyphenols in food processing have been proposed.

Review on solar dryers for drying fish, fruits, and vegetables

India is one of the highly developing countries in the world and it has the second-largest agricultural source of income, which covers 61% of the entire income of the country. The most valuable income group, by giving the appropriate training in this technology, will make their entire country to become one of the most highly developing counties in the world. In recent years, many developing, developed, and underdeveloped countries face shortages of fish, fruits, and vegetables due to natural disasters like earthquakes, tsunami, and any other unexpected events. Now the main issue of this paper is to preserve the food products from post-harvest to consumer-level, which cover 60% of losses due to the unavailability of preservative methods. This paper mainly focused on the conventional methods to advanced solar drying technologies for perseverating fish, fruits, and vegetables and also it discusses the technology used for drying the yield range of fish like Atheriniformes, Catfish, Chilwa, etc. Fruits like banana, mango, and papaya, and vegetables like bitter gourd, cabbage, and cocoa beans have been reviewed and also discussed some problems along with their solutions in concern with food products drying, thereby the selection of dryer for drying products will be made easy by this review article. On the whole, this investigation would help researchers in fish drying to choose the better drying methods for acquiring better results for particular fish, fruits, and vegetables that enable any entrepreneur to select the appropriate method reducing the cost and time.

Anti-migraine activity of freeze-dried latex obtained from Calotropis gigantea Linn

Migraine which is characterized by a pulsating headache affected an estimated population of 12% worldwide. Herbal products like latex derived from Calotropis gigantea R. Br. (Asclepiadaceae) are a representative intervention to treat migraine traditionally. However, post-harvesting stability issues of latex affect its biological potential. Freeze-drying has been successfully employed for the encapsulation of herbal bioactive compounds resulting in stable dried preparations. Latex derived from Calotropis gigantea (C. gigantea) was microencapsulated using chitosan by freeze-drying (FDCG) method and compared with sun ray-dried latex (ADCG). Current investigation was aimed to improve the shelf life of latex by freeze-drying microencapsulation technique and evaluation of its anti-migraine potential. Dried latex powders (ADCG and FDCG) were evaluated in terms of phenolic content, coloring strength, first-order kinetic, color parameters (L*, a*, b*, C*, and E*), moisture, water activity, solubility, and hygroscopicity. Additionally, apomorphine-induced climbing behavior, L-5-HTP-induced syndrome, and MK-801-induced hyperactivity were used to evaluate the anti-migraine potential of powdered latex. FDCG showed good physicochemical properties due to its higher concentration of phenolic and flavonoid contents. Moreover, FDCG significantly reduced the apomorphine-induced climbing behavior, L-5-HTP-induced syndrome, and MK-801-induced hyperactivity in a dose-dependent manner through an interaction of dopaminergic and serotonergic receptors. In conclusion, the method developed for shelf life improvement of latex offered maximum protection over a period of 10 weeks with retaining its natural biological potential; thus, it can be effectively utilized in the treatment or management of migraine. Anti-migraine effect of Calotropis gigantea freeze-dried latex by inhibition of dopamine and serotonin receptors (D1 and D2: dopamine receptors; 5-HT: serotonin receptors); yellow color represents serotonergic, and blue color indicates dopaminergic neurons.

Investigation of the anti-hyperglycemic and antioxidant effects of wheat bread supplemented with onion peel extract and onion powder in diabetic rats

AIM

Onion is one of the commonly cultivated and consumed vegetables rich in nutrients and phytochemicals. Various nutraceuticals are found in the outer fleshy layers and dry peel of onion which usually is treated as a common biowaste. Diabetes mellitus is a leading non communicable disease causing hyperglycemia and increased production of free radicals that potentially disrupts antioxidant enzymatic activity. Considering global consumption of wheat, the present study was designed to evaluate the anti-hyperglycemic and antioxidant effects of wheat bread supplemented with onion peel extract (OPE) or onion powder (OP) on diabetic rats.

METHODS

In this study, ethanolic extract of onion peel and onion bulb were prepared separately. Male Sprague Dawley rats were divided into 6 groups (n = 7). Different regimens of supplemented wheat bread (OPE (1% and 3%) and OP (5% and 7%)) were given to diabetic rats for eight weeks, plain bread was used as the control. Blood glucose level, body weight and activities of SOD, CAT, GPx, GR, GSH and MDA in the liver and kidney tissues were evaluated. Statistical analysis was performed using SPSS Version (25) and Dunnett's multiple comparison test.

RESULTS

Bread supplemented with 1% and 3% onion peel extract and 7% onion powder significantly reduced blood glucose levels and MDA in the treated rats compared with the control group diabetic rats. Body weight of diabetic rats was reduced for control group, while onion supplemented diet improved the body weight of treated rats. Onion supplementation also brought significant improvement in antioxidant enzyme activities among the treated diabetic rats.

CONCLUSION

These findings suggested that onion supplementation is effective in lowering blood glucose and could potentially aid in protecting organs from oxidative stress.

Modeling and simulation of heat and mass transfer in an Ethiopian fresh injera drying process

In this paper, we developed a mathematical model to simulate the heat and mass transfer during the convective drying of injera. The coupled set of heat and moisture partial differential equations (PDEs) were numerically solved by the finite element method (FEM) using COMSOL Multi-physics, 5.5. To validate the simulated results, drying experiments were performed using a tunnel dryer at two air temperatures (313.15 and 333.15 K) and velocities (0.25 and 0.5 ms⁻¹). The predicted versus the experimental results showed a very good agreement with a coefficient of determination, R2>0.95 for both temperature and moisture ratio and a Root Mean Square Error, RMSE < 0.05 for moisture ratio and <3.5 K for temperature. The predicted temperature and moisture ratio distributions of the injera at different times and positions (thickness and diameter) clearly showed the uniformity of drying. The time required to reduce the moisture ratio of injera from 1 (-) to 0.03 (-) at a temperature of 333.15 K, relative humidity of 11% and air velocity of 0.5 ms⁻¹ was 125 min. Both temperature and velocity have a significant effect on moisture reduction when drying was conducted (p < 0.05). The interaction effect between them also indicates a significant difference (p < 0.05) in the moisture removal rate of injera.

Quality attributes of convective hot air dried spine gourd (Momordica dioica Roxb. Ex Willd) slices

In the present study, spine gourd slices were dried in a convective dryer at 40, 50, 60 and 70 °C temperature. The change in quality of spine guard was determined by analyzing the change in proximate, minerals, functional group, chlorophyll, ascorbic acid, and antioxidant characteristics. Increase in drying temperature changed the protein (4.62-12.88 g/100 g), fiber (3.14-3.53 g/100 g), total phenolic (14.85-14.99 mg gallic acid equivalent/g) and total flavonoid (30.1-64.8 mg quercetin equivalent/100 g) content while reduction occurred in fat (4.02-3.07 g/100 g), carbohydrate (76.13-55.22 g/100 g), chlorophyll (0.34-0.100 mg/g), ascorbic acid (29.94-4.50 mg/100 g) and antioxidant activity (96.58-85.06%). Mineral content of fresh SG differed significantly with dried samples (p < 0.05), while variable effects were associated with the change in drying temperatures. Changes in functional groups were analyzed by Fourier transform infrared spectrophotometer. The observed parameters were optimized using principal component analysis. The sample dried at 40 °C was superior in quality whereas higher protein and antioxidants were found at 70 °C.

Effects of Various Drying Methods on Selected Physical and Antioxidant Properties of Extracts from Moringa oliefera Leaf Waste

This study aims to evaluate the effects of different drying methods on the physical properties, total phenolic content, total flavonoid content, and antioxidant activity of extracts from Moringa oliefera L. (MO) leaf waste. The effects of two drying techniques, namely, sun drying (A1) and tray drying (A2), on the physical and antioxidant properties of the extracts obtained using three extracting solvents, i.e., water (b1), ethanol (b2), and ethyl acetate (b3), were investigated. These extracts were analyzed for their physicochemical and antioxidant properties. The antioxidant properties were determined with the Folin Ciocalteau, aluminum chloride, and 1,1-diphenyl-2-picrylhydrazyl (DPPH) assays. Fourier transform infrared spectrophotometry (FTIR) was used to identify functional groups in the active compounds. It was found that the physical properties of the MO extract, including yield, pH, total solids, and color, showed significant differences for the two drying methods (p < 0.05). The b3 extract had the highest value for total phenolic contents, total flavonoid contents, and antioxidant activities, followed by b2 and b1, respectively, for both the sun drying and tray drying methods. There was a significant correlation between the total phenolic and flavonoid contents and antioxidant activity (IC50). This study reveals that waste material from MO leaves could be utilized as an antioxidant agent, which is expected to reduce environmental pollution from the MO processing industry.

Minimization of the adverse environmental effects of discarded onions by avoiding disposal through dehydration and food-use

Onion is a commonly used vegetable in the Cuyo Region, Argentina, and important in the world global vegetable production ranking. Production levels often exceed immediate markets of fresh sale, and excesses, although still edible, are currently discarded (mostly incinerated and disposed in landfill, creating numerous environmental hazards). To minimize these adverse environmental problems, this research investigates upgrading the discarded products by dehydration, hence guaranteeing their ultimate food-use. The dehydration process of discarded onion cv. Crioula Roxa was hence studied at 60 and 70 °C, temperatures selected to maintain the main physicochemical characteristics of the onions, while also creating optimum heat and mass transfer coefficients while significantly reducing the energy consumption and CO₂ emissions. When using an electrically-heated convective dryer, the Specific Energy Consumption (SEC) values and the CO₂ emissions during dehydration at 70 °C are 738.89 kWh.kg^-1 and 264.74 kg of CO₂ kg^-1, respectively. These values are only 41.61 kWh.kg^-1 and 2-4 kg of CO₂ kg^-1 if a solar dryer is applied. The thermal diffusivities were 1.86✕10^-10 m² s^-1 (dehydration) and 1.08✕10^-10 m² s^-1 (rehydration), showing a weak effect of the dehydration process on the solid structure and properties.

Effects of onion bulb processing conditions on drying characteristics, physicochemical and functional properties profile of onion (Allium cepa L.) powder

Onion (Allium cepa L.) is one of the most perishable consuming vegetable in the world as an aromatic seasoning and for its health promoting bioactive compounds. However, drying and blanching are two essential thermal treatments in vegetables processing which lead to considerable changes in their properties. This study investigated the effects of temperature (70, 80, and 90 °C), time (2, 4, 6, and 8 hr), and blanching (100 °C for 5 min) followed by drying at 70 °C for 8 hr on the drying kinetics, physicochemical (Ash and total polyphenol content, pH, and titratable acidity), and functional (water solubility index and particle size) properties of onion powder, as well as compared to local market powders. The variety violet of Galmi was used. The results revealed that the moisture content of non-blanching powder was below 13 ± 0.76 g/100 g with pH under 4. In addition, total polyphenol contents were higher than 512 ± 15.06 mg GAE/100 g DM. These powder showed a small particle size (under 400 µm) and high solubility (≤81.36 ± 2.3 g/100 g DM). Blanching did not affect the powders quality. Local market powders showed a lowest total polyphenol content (386.60 ± 10.02 mg GAE/100 g DM) with large particles (≤800 µm) and a lowest solubility (65.33 ± 1.62 g/100 g DM). Drying at 80 °C for 8 hr without blanching emerge as the best compromise drying conditions resulting in optimal physico-chemical and functional properties (10.8 ± 0.8 g/100 g, 846.6 ±15.09 mg GAE/100 g DM and 88.12 ± 2.31 g/100 g DM of moisture content, total polyphenol content, and water solubility index, respectively. These findings can contribute to reduce postharvest losses in onion and to stimulate the industrialization of onion enriched-powder production in Africa. PRACTICAL APPLICATION: This study provides critical information on onion properties profile during its transformation, on which processor might build on its decision to make an appropriate choice of processing parameters and tools for producing health promoting onion powder meeting modern consumer requirements. In this study, oven-drying at 80 °C for 8 hr without blanching might be the suitable condition to deliver innovative onion powder tailored specifically to functional ingredients of many food formulations.

Effects of Hot Air and Microwave Drying on the Phenolic Components and Physicochemical Properties of Unripe Grapes (Qoura)

Background::

Unripe grape (Qoura) in the forms of either intact or juice can be used as a flavoring agent in several foods of Iranian cuisines such as soup and salad due to its sour taste.

Methods::

In the current study, the effects of microwave (270, 540, and 720 W) and hot air drying (40, 50 and 60°C) on the polyphenol components content and chemical properties (including chroma, hue angle, L* value, total color difference, soluble sugars, acidity, total phenols and phenolic components including rutin, gallic acid, hydroxybenzoic acid, syringic acid, p-coumaric acid, and resveratrol) of Qoura obtained from unripe white seedless grape were investigated.

Results::

The obtained results showed that in both methods, by increasing the oven temperature and microwave power, the L value (The L* value was used to express the whiteness and darkness) was decreased. There was a notable reduction in the initial phenolic content of the sample (381.671 mg gallic acid/ 100 g) as a result of both of the used techniques. The initial content of resveratrol was decreased from 30.27 mg/100 g; to 23.07, 16.64, 10.73 mg/100 g sample in the samples treated with the air-drying method at 40, 50, 60°C, respectively. Also, by using the microwave in 270, 540, 720 W, it decreased to 5.77, 5.38. 5.26 mg/100 g sample at 270, 540, 720 Watt, respectively.

Conclusion::

The results of the present study revealed that the drying method affects the amount of polyphenolic compounds and physicochemical properties.

Characterization of dried horseradish leaves pomace: phenolic compounds profile and antioxidant capacity, content of organic acids, pigments and volatile compounds

Horseradish (Armoracia rusticana) leaves pomace, which contains high-value bioactive compounds, is the product resulting from pressing horseradish leaves for juice production. The aim of the current research was to investigate the effect of convective, microwave-vacuum and freeze-drying on the content of bioactive compounds in horseradish leaves pomace. Convective hot air-drying was performed at 40, 60 and 80 °C. The total phenolic content (TPC), total flavonoid content (TFC), total flavan-3-ol content, total phenolic acid content, total flavonol content, chlorophylls and total carotenoids, and antioxidant activity were determined by spectrophotometric methods. Individual profiles of phenols and organic acids are estimated by high-performance liquid chromatography (HPLC), but volatile compounds are estimated by gas chromatography (GC). Totally, 14 individual phenolic compounds, 8 organic acids, and 49 volatile compounds were analysed in the studied samples. The main phenolic compound identified in horseradish leaves pomace was rutin (3231 mg/100 g DW), among organic acids—quinic and malic acids, and volatile compounds—allyl isothiocyanate, 3-butenenitrile and benzyl alcohol. In the drying process, the content of some (total flavan-3-ols, total carotenoids content) compounds increased, but others (TPC, total organic acids content) decreased, and it was drying method-dependent. Freeze-drying caused the reduction of TPC by 29%, whereas convective drying by 53–59%. Fresh pomace contains such isothiocyanates as allyl isothiocyanate and butyl isothiocyanate, which were completely lost in the drying process. Freeze-drying allowed the best retention of various phenolic and volatile compounds in horseradish leaves pomace.

Modelling and kinetic study of microwave assisted drying of ginger and onion with simultaneous extraction of bioactive compounds

Onion and ginger are rich sources of bioactive compounds which are lost during conventional drying process. The present study was designed to optimize the novel Microwave Assisted Drying and Extraction technique (MADE) for simultaneous drying and extraction/recovery of bioactive compounds from model food products. The time required for drying of samples was 11 (onion) and 16 (ginger) minutes with recovery yield of 87% (onion) and 85% (ginger). The drying time was reduced to 100 times compared to hot air drying and moisture ratio of dried samples was best described by Midilli model. The diffusivities of onion and ginger slices were 1.27 e^-11 and 1.43 e^-11 m²/s, respectively. Moreover, microwave-based extraction was compared with conventional one. The results of antioxidant activity and total phenolic contents of condensates obtained through MADE were higher compared to conventional method. In short, MADE exhibited better yield of extraction and drying properties compared to conventional methods.

Utilisation of the REA-method to a Convective Drying of Apple Rings at Ambient Temperature

This study focuses on the convective drying of apple rings by air at ambient temperature. The lumped reaction engineering approach (REA) model has been employed to determine the rate of drying for apple rings under forced convection considered as a normal processing regime. The algorithm implies origination of the activation energy curve from accurate ‘reference’ measurements of the drying rate under natural convection conditions. Mass transfer coefficients for the apple ring samples required for the model implementation were obtained in a series of experiments under natural and forced conditions. These were compared to the values of mass transfer coefficients obtained from numerical simulation using COMSOL Multiphysics® software. The study extends the application of REA for the limiting simplest case of convective drying of thick samples under ambient temperature conditions.

Characterization of Volatile and Flavonoid Composition of Different Cuts of Dried Onion (Allium cepa L.) by HS-SPME-GC-MS, HS-SPME-GC×GC-TOF and HPLC-DAD

Onion is widely used worldwide in various forms for both food and medicinal applications, thanks to its high content of phytonutrients, such as flavonoids and volatile sulfur compounds. Fresh onion is very perishable and drying is widely applied for extending shelf-life, thus obtaining a very easy-to-use functional food ingredient. The flavonoid and volatile fractions of different onion cuts (flakes, rings) prepared through different drying cycles in a static oven, were characterized by high-performance liquid chromatography with a diode-array detector HPLC-DAD, Head Space-Solid Phase Micro Extraction followed by Gas Chromatography coupled with Mass Spectrometry (HS-SPME-GC-MS) and Head-Space Solid Phase Micro Extraction followed by comprehensive two-dimensional Gas-Chromatography (HS-SPME-GC×GC-TOF). Onion flakes showed a significantly higher flavonoid content (3.56 mg g⁻¹) than onion rings (2.04 mg g⁻¹). Onion flakes showed greater amount of volatile organic compounds (VOCs) (127.26 mg g⁻¹) than onion rings (42.79 mg g⁻¹), with different relative amounts of di- and trisulfides—disulfides largely predominate the volatile fraction (amounts over 60% on the total volatile content), followed by trisulfides and dipropyl disulfide and dipropyl trisulfide were the most abundant VOCs. HS-SPME-GC×GC-TOF allowed for the detection of the presence of allylthiol, diethanol sulfide, 4,6-diethyl1,2,3,5-tetrathiolane, not detected by HS-SPME-GC-MS, and provided a fast and direct visualization and comparison of different samples. These results highlight different nutraceutical properties of dried onion samples processed otherwise, only differing in shape and size, thus pointing out potentially different uses as functional ingredients.

Effect of storage, food processing and novel extraction technologies on onions flavonoid content: A review

Onions play an important part in the daily diet for most populations around the world owing to their nutritional composition and their unique capacity to naturally flavor dishes. Onions contain quercetin and its derivatives - the predominant flavonoid in onions that exert a great contribution to the effective bioactive properties of onion, including its derived products. The present paper comprehensively reviewed flavonoids (with a specific focus on quercetin in onions): their chemical composition, distribution, bioactivities in onion, and impacting factors with a focus on how they can be affected by various post-harvest conditions (storage and food processing). In addition, research on the extraction of flavonoid compounds from onions using a number of novel technologies was also reviewed.

Kinetic Studies and Moisture Diffusivity During Cocoa Bean Roasting

Cocoa bean roasting allows for reactions to occur between the characteristic aroma and taste precursors that are involved in the sensory perception of chocolate and cocoa by-products. This work evaluates the moisture kinetics of cocoa beans during the roasting process by applying empirical and semi-empirical exponential models. Four roasting temperatures (100, 140, 180, and 220 °C) were used in a cylindrically designed toaster. Three reaction kinetics were tested (pseudo zero order, pseudo first order, and second order), along with 10 exponential models (Newton, Page, Henderson and Pabis, Logarithmic, Two-Term, Midilli, Verma, Diffusion Approximation, Silva, and Peleg). The Fick equation was applied to estimate the diffusion coefficients. The dependence on the activation energy for the moisture diffusion process was described by the Arrhenius equation. The kinetic parameters and exponential models were estimated by non-linear regression. The models with better reproducibility were the pseudo first order, the Page, and the Verma models (R2 ≥ 0.98). The diffusion coefficients that were calculated were in the order of 1.26 to 5.70 × 109 m s−2 and the energy activation for moisture diffusion obtained was 19.52 kJ mol−1.

Effects of hot air, microwave and vacuum drying on drying characteristics and in vitro bioaccessibility of medlar fruit leather (pestil)

The effects of microwave (90 W and 180 W), hot air (60 and 70 °C) and vacuum (60 and 70 °C with 200 and 300 mbar) drying methods on drying characteristics, total phenolic content, antioxidant capacity, color and in vitro gastrointestinal digestion of medlar pestil were investigated. Medlar showed a good potential for pestil production while being the most applicable in microwave treatments. For drying kinetics, five thin-layer drying models were applied and the Page and Modified Page were the best fitted models. L*, b*, chroma and hue angle decreased while a* generally increased in dried pestils. Dried samples showed a general decrement in phenolics and antioxidant capacity. According to in vitro gastrointestinal digestion, intestinal phase of all the samples resulted with an increment in phenolics, FRAP and DPPH compared to undigested extracts. In conclusion, different drying methods may affect the release of phenolics and antioxidant capacity, while leading to increased bioaccessibility during intestinal digestion.

Experimental Verification of Yam (Dioscorea rotundata) Drying with Solar Adsorption Drying

This work evaluates the yam (Dioscorea rotundata) drying performance of solar adsorption drying (SAD) compared to solar drying (SD) and open sun drying (OSD). The evaluation concerns the drying cycle for batches of yam, the effect on vitamin C, color and composition. As SAD can be applied during the night, by using air dehumidified by passing through a bed of silica gel, the cycle time for drying batches of yam can be reduced over 20–25% compared to SD and halved compared to OSD. SAD is thereby most effective during the first nights of drying when the driving force is the highest. Composition was not affected by drying methods but did affect vitamin C content. Vitamin C retention is not significant different for SD and SAD, but with a slight preference for SD. For three yam cultivars (‘Pona’, ‘Lilii’ and ‘Dente’), ‘Lilii’ dried fastest and ‘Dente’ drying slowest. SAD maintained 16 the whitish color of yam better than the other drying methods.

Effect of microwave and oven drying processes on antioxidant activity, total phenol and phenolic compounds of kiwi and pepino fruits

Kiwi and pepino fruits are most valuable fruits as they contains substantial amounts of nutrients and bioactive compounds. These fruits exhibited several health potentials such as antioxidant, antiinflammatory, antiobesity, antihyperlipidemia, and anticancer properties. However, studies on the effect of microwave and conventional drying methods on the antioxidant activity and bioactive compounds of kiwi and pepino fruits are limited. Therefore, this study was conducted to assess the effect of microwave and oven drying methods on antioxidant activity, total phenolic, and phenolic compounds of kiwi and pepino fruits. Drying of the fruit samples was carried out using conventional (70 °C for 20 h) and microwave (720 W for 3 min) ovens. 1,1-diphenyl-2-picrylhydrazyl scavenging and colorimetric Folin-Ciocalteu assays were used to assess the antioxidant activity and total phenolic contents, respectively, of fresh and dried fruits. Both drying methods significantly (p < 0.05) decreased the moisture contents of both fruits compared to untreated controls. Concomitantly, drying methods also enhanced (p < 0.05) antioxidant activity and total phenolic content of both fruits with the highest improvement being observed for microwave-dried fruits compared to untreated controls. In addition, a significant increase was observed in catechin and 1,2-dihydroxybenzene content of kiwi and pepino after drying process. However, microwave drying method reduced the amount of 3,4-dihydroxybenzoic acid in kiwi (ranging from 34.120 to 9.350 mg/100 g) and pepino (varied from 33.414 to 15.445 mg/100 g). Generally, the highest antioxidant activity and phenolic contents were reported in microwave oven dried samples, followed by samples dried in oven and fresh fruits. The results revealed that microwave drying could be more useful in fruit drying than conventional drying. In addition, dried kiwi and pepino fruits contains substantial quantities of phenolic compounds with high antioxidant activity compared to fresh fruits, and thus they are considered as healthy food.

Convective drying of onion: modeling of drying kinetics parameters

Drying is a simultaneous heat and mass transfer processes. Drying kinetics is determined by both internal properties and external drying conditions. In this study, two important drying kinetics parameters of onions i.e. effective water diffusivity and relative activation energy of reaction engineering approach (REA) are determined. The generated parameters are used to model thin layer drying of onion at different temperatures (40, 50, 60, and 70 °C) and relative humidity of 20%. The effective water diffusivity is in the range of 2.8 × 10^-10 m² s^-1 and 8.1 × 10^-10 m² s^-1. Unlike the diffusivity, the relative activation energy of the REA is independent on drying conditions and thus the latter approach requires less effort in generating the transport properties. The transport parameters can be applied for assisting in designing dryer units and evaluating the performance of existing dryer units.

Effect of Microwave Drying on the Drying Characteristics, Color, Microstructure, and Thermal Properties of Trabzon Persimmon

In this study, changes in the drying kinetics, color change, and the energy consumption for microwave energy were investigated for Trabzon persimmon. In addition to that, the microstructure of the persimmon was also investigated by considering its thermal changes. It is important to be aware of the purpose of the drying process for determining the drying system. Results of this research showed that 460 W for 7 mm slice thickness depending on energy consumption, 600 W for 5 mm slice thickness depending on drying time, and 600 W depending on color changes were found as suitable drying processes depending on drying conditions. The effective diffusion values varied between 2.97 × 10⁻⁸ m² s⁻¹ and 4.63 × 10⁻⁶ m² s⁻¹. The activation energy values for 5 mm, 7 mm and 9 mm slice thickness were estimated as 32.82, 18.64, and 12.80 W g⁻¹, respectively. The drying time and energy consumption decreased, whereas drying rate increased with an increase in the microwave energy. The number of pores increased compared to structure of fresh sample, and the pores got to be larger for 5 mm slice thickness as the power level increased. Results showed that the applied microwave energy had an important effect on the heating of the material and the change in the microstructure.