Hot Air Drying Research Articles

Preserving potato perfection: Optimizing innovative drying techniques for maintaining physicochemical attributes and starch structure

To address the limitations of conventional hot air drying (HAD) for potato dehydration, pulsed vacuum drying (PVD) and humidity-controlled HAD (HC-HAD) were proposed as innovative techniques. In PVD, varying vacuum pulse durations (6, 8, 10, 12, and 14 min) and atmospheric pulse durations (2, 3, 4, and 5 min) were investigated. Under HC-HAD, different humidity control scenarios (40,30+30,90+CF, 50,30+30,90+CF, 40,30+CF, and 50,30+CF) were examined. The study revealed that a 14:2 duration pulsing in PVD retained the color and achieved the highest total phenol content (TPC) and antioxidation activity (conserving 97.50 % and 84.67 % of their fresh values, respectively) but had the longest drying time (260.00 min) compared to HC-HAD and HAD (139.45 min). The 50,30+CF strategy of HC-HAD exhibited the quickest drying time (116.79 min), maintained the color, TPC (87.97 % of the fresh value), and antioxidation activity (71.40 % of the fresh value), and achieved the best potato microstructure and starch structure. Furthermore, Artificial Neural Network simulations for HC-HAD conditions demonstrated significant reliability. These findings provide valuable insights for potato researchers and producers seeking to enhance preservation techniques and prolong the shelf life of potatoes as a staple crop.

A Comparison Analysis of Quality and Metabolic Compounds in Lilies with Different Drying Treatments.

The present study aimed to investigate the variations in the nutritional composition, antioxidant capacity, and metabolite profile of lilies subjected to different drying treatments, including vacuum freeze drying (VFD), hot air drying (HAD), vacuum drying (VD), and infrared drying (ID). The results show that VFD provided better preservation of the original coloration and displayed the highest levels of total amino acid content, total phenolic content, total flavonoid content, and polysaccharide and alkaloid content. Our results reveal that VFD treatment can be employed to obtain high-quality lilies with desirable appearance characteristics and nutrient compositions. Metabolomics analysis identified a total of 464 metabolites from various dried lilies. Differential metabolite screening found 150 differential metabolites across all pairwise comparisons. Hierarchical clustering analysis (HCA) indicated that lilies subjected to VFD treatment exhibited a higher abundance of steroids, saponin, flavonoids, and phenolic glycoside, whereas those subjected to HAD, VD, or ID treatments showed relatively elevated levels of specific amino acids or derivatives. This study elucidates the significant impact of various drying treatments on the quality and metabolic profile of lilies, thereby providing valuable insights for enhancing the nutritional quality of processed lilies.

Study on the Drying Characteristics and Physicochemical Properties of Alfalfa under High-Voltage Discharge Plasma

High-voltage discharge plasma drying (HVDPD) is a non-thermal and efficient drying technique. In this study, we compared the drying characteristics and physicochemical properties of alfalfa dried via HVDPD, hot-air drying (HAD), and natural air-drying (AD) and analyzed the experimental results using infrared spectroscopy, scanning electron microscopy, colorimetry, and other detection techniques. The results showed that HVDPD had a higher drying rate than AD and saved more energy than HAD. Alfalfa dried via HVDPD had the most intact internal structure, the highest rehydration ratio (RR), the best color quality, and the best nutrient retention, resulting in the highest relative quality and feeding value. Therefore, HVDPD is an excellent drying technique for alfalfa, providing a new and effective way to improve the storage, transportation, and drying quality of alfalfa.

Extraction Optimization of Phenolic Compounds from Triadica sebifera Leaves: Identification, Characterization and Antioxidant Activity.

Triadica sebifera (T. sebifera) has attracted much attention because of the high oil content in its seeds, but there are few systematic studies on the phenolic compounds of T. sebifera leaves (TSP). In this study, the extraction process of TSP was optimized by response surface methodology. The phenolic components of these extracts were analyzed by high-performance liquid chromatography (HPLC). Moreover, the effects of hot air drying (HD), vacuum drying (VD) and freeze drying (FD) on the antioxidant activity and characterization of T. sebifera leaf extract (TSLE) were evaluated. Under the conditions of ethanol concentration 39.8%, liquid-solid ratio (LSR) 52.1, extraction time 20.2 min and extraction temperature 50.6 °C, the maximum TSP yield was 111.46 mg GAE/g dw. The quantitative analysis and correlation analysis of eight compounds in TSP showed that the type and content of phenolic compounds had significant correlations with antioxidant activity, indicating that tannic acid, isoquercitrin and ellagic acid were the main components of antioxidant activities. In addition, through DPPH and ABTS determination, VD-TSLE and FD-TSLE showed strong scavenging ability, with IC50 values of 138.2 μg/mL and 135.5 μg/mL and 73.5 μg/mL and 74.3 μg/mL, respectively. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) infrared spectroscopy revealed small differences in the extracts of the three drying methods. This study lays a foundation for the effective extraction process and drying methods of phenolic antioxidants from T. sebifera leaves, and is of great significance for the utilization of T. sebifera leaves.

Effects of different cocoon-stifling methods on the reeling and quality characteristics of raw silk

In this study, we evaluated the effects of five stifling methods on the reeling parameters and raw silk characteristics of double hybrid cocoons. The methods were open sun drying, sun drying under a black cloth, drying in the SKUAST-K-fabricated solar cocoon dryer, multifuel hot air drying, and hot air drying. Our findings showed that hot air drying produced the best results in terms of reeling parameters, i.e. average filament length (805.750 m), average non-breakable filament length (800.750 m), average denier (2.777), renditta (2.805), silk waste percentage (15.17), raw silk percentage (30.382), reelability percentage (80.982), and degumming loss percentage (16.285). The method also yielded superior results for raw silk characteristics, such as winding (0.000 breaks), evenness first (1.000 count), evenness second (0.000 count), neatness percentage (95.000), cleanness percentage (96.500), tenacity (4.032 g/denier), elongation percentage (23.000), and cohesion (68.250 strokes). The SKUAST-K-fabricated solar cocoon dryer produced the second-best results.

Segmented variable-frequency ultrasound synergistic hot-air drying of Rhubarb: Effect on drying characteristics and quality and thermal analysis

This study employed segmented variable-frequency ultrasound synergistic hot-air drying (SVFU-HAD) for Rhubarb slices, selected two sets of time nodes for frequency conversion (60 min, 120 min, and 90 min, 150 min), and two sequences of frequency conversion (high-frequency to low-frequency, and low-frequency to high-frequency). It aimed to investigate the effects of SVFU-HAD on the drying characteristics, quality, and heat transfer of Rhubarb slices. The findings indicated that segmented variable-frequency ultrasound has advantages in increasing drying rate and improving uniformity of cavitation effects compared to constant-frequency ultrasound. Analysis of physical properties revealed that the rehydration performance of dried products subjected to ultrasonic variable-frequency treatment (90 min, 150 min) according to the drying rate was better (RR > 3.3). The transition mode from high-frequency to low-frequency in variable-frequency ultrasonic treatment contributes to maintaining the overall color of Rhubarb. Analysis of chemical properties unveiled that Rhubarb treated with 40 kHz (0 min)–28 kHz (60 min)–25 kHz (120 min) segmented variable-frequency ultrasound contained overall higher levels of tannins, dianthrones and free anthraquinones content, which exceeded the average values by 3.24%, 26.65%, and 14.42%, respectively. In addition, thermal analysis results based on ANSYS Workbench software demonstrated that the drying uniformity of SVFU-HAD is superior to that of hot-air drying and constant-frequency ultrasound synergistic hot-air drying (CFU-HAD). Overall, the SVFU-HAD method employed in this study presents an innovative approach to ultrasound synergistic hot-air drying research with promising potential for enhancing the efficiency and quality characteristics of Rhubarb slices.

Radio frequency drying on functional diversity of tiger nut flour: Effects on physicochemical, structural, and rheological properties

Tiger nut (TN) is a valuable nutrient and gluten-free tuber. To achieve high-quality TN flour as functional ingredients in food, it is essential to develop effective drying technologies for TN. Five drying methods including natural drying (Control), hot-air drying (HD), radio frequency single drying (RFSD), RF assisted hot-air drying (RFHD), and RF- vacuum drying (RFVD) were selected and compared to determine their effects on physiochemical, structural, and rheological properties of TN flour. Results showed that RF drying (RFD) significantly improved the hydration, oil-absorbing, and antioxidant activity capacity, especially for RFVD. RFHD exhibited greater color (BI = 13.80 ± 0.05 and C = 10.26 ± 0.05) and reducing sugar content (253.50 ± 2.27 mg d.b.) than RFSD and RFVD. The gelatinization temperature, enthalpy value, and particle size (57.30–269.33 μm) of TN flour were reduced. The structural property results indicated that RFD reduced the relative crystallinity and short-range ordering of the flour, altered protein secondary structure, and caused the damaged microstructure in comparison with Control and HD groups. All sample gels exhibited a weak strain overshoot behavior (type III) under large amplitude oscillations, and RFD resulted in a reduced viscoelastic behavior. RFD could be an effective method to produce functional TN flour.

Flavor Variations in Precious Tricholoma matsutake under Different Drying Processes as Detected with HS-SPME-GC-MS.

By employing headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS), this study displayed the compositional changes in volatile organic compounds (VOCs) in Tricholoma matsutake samples subjected to hot-air drying (HAD) and vacuum freeze-drying (VFD) processes from their fresh samples. A total of 99 VOCs were detected, including 2 acids, 10 aldehydes, 10 alcohols, 13 esters, 12 ketones, 24 alkanes, 14 olefins, 7 aromatic hydrocarbons, and 7 heterocyclic compounds. Notably, the drying process led to a decrease in most alcohols and aldehydes, but an increase in esters, ketones, acids, alkanes, olefins, aromatic, and heterocyclic compounds. Venn diagram (Venn), principal component analysis (PCA), and partial least squares-discriminant analysis (PLS-DA) analyses enabled an easy and rapid distinction between the VOC profiles of T. matsutake subjected to different drying methods. Among the identified VOCs, 30 were designated as marker VOCs indicative of the employed drying process. And the VFD method was more capable of preserving the VOCs of fresh T. matsutake samples than the HAD method. Benzaldehyde, 1-Octen-3-ol, 3-Octanol, and (E)-2-Octen-1-ol were identified as markers for FRESH T. matsutake. Conversely, (E)-3-Hexene, lavender lactone, and α-Pinene were associated with VFD T. matsutake. For HAD T. matsutake, olefins, pyrazine, and esters, particularly ocimene, 2,5-Dimethyl-pyrazine, and methyl cinnamate, significantly contributed to its particularities. The results from this present study can provide a practical guidance for the quality and flavor control of volatile organic compounds in preciously fungal fruiting bodies by using drying processes.

Effects of contact ultrasound coupled with infrared radiation on drying kinetics, water migration and physical properties of beef during hot air drying

Drying, as a critical step in the production of air-dried beef, has a direct impact on the quality of the final product. Innovatively, a composite system incorporating contact ultrasound (CU) and infrared radiation (IR) as auxiliary measures within a hot air drying (HAD) framework was built in this research, and the effects of these techniques on the drying kinetics, protein denaturation, and moisture transformation of air-dried beef were investigated. In comparison to HAD treatment, the integrated CU and IR (CU-IRD) system displayed marked enhancements in heat and moisture transport efficiency, thereby saving 36.84% of time expenditure and contributing favorably to the improved moisture distribution of the end-product. This was mainly ascribed to the denaturation of myosin induced by IR thermal effect and the micro-channel produced by CU sponge effect, thus increasing T2 relaxation time and the proportion of free water. In conclusion, the composite system solved the problem of surface hardening and reduces hardness and chewiness of air-dried beef by 40.42% and 45.25% respectively, but inevitably increased the energy burden by 41.60%.

INCREASING THE STABILITY OF POLYPHENOLS AND BETACYANINS IN BEETROOT CHIPS BY TREATMENT BEFORE DRYING

An innovative trend in the production of snack products is the use of selected vegetables for the production of dried vegetable chips. Beetroot is a suitable vegetable for this type of product, as it is characterised by its high biological potential and its content of a wide range of phytonutrients with beneficial effects on human health. The aim of this work was to compare five varieties of beetroot in terms of the content of total polyphenols and betacyanins, to assess the effect of hot-air drying on these important components and to determine the appropriate method of treatment of beetroot slices before drying in terms of improving the stability of polyphenols and betacyanins during drying. In this work, 5 beetroot varieties (Betina, Renova, Cervena kulata, Pablo F1, Karkulka) were evaluated. The beetroot chips were dried at 70°C until a residual moisture content of 15±1% was reached. To treat the slices before drying a 0.1% solution of ascorbic acid, 0.01% solution of CaCl2, 0.01% solution of K2S2O5, 1% solution of NaCl was used followed by blanching in a water bath at 96°C for 2 minutes. The highest content of total polyphenols and beta-cyanins was statistically significant (p<0.05) in the variety Pablo F1. During hot air drying, both polyphenols and betacyanins decreased significantly. The average decrease in betacyanins and total polyphenols was 50.97% and 48.70% respectively. To mitigate these changes, treatment with 0.1% solution of ascorbic acid and blanching appeared to be the most effective of the treatments tested. After treatment with ascorbic acid solution, the dried products retained on average 27.6% more betacyanins and 32.67% more total polyphenols than the control sample.

Effects of different pretreatment on the drying characteristics and pectin properties of jujube by microwave coupled with pulsed vacuum drying

AbstractThe effects of ultrasound (US), ultrahigh pressure (UP), cold plasma (CP), and high pressure and pulsed electric fields (PEF) pretreatments were evaluated for drying characteristics, bioactive components, and pectin properties of jujube slices during microwave coupled with pulsed vacuum drying (MPVD). US, CP, and PEF reduced drying time by 18.75%, while UP reduced it by 6.25%. Samples treated with US and PEF showed improved color and rehydration (345.11%, 319.24%), with SEM revealing larger pores post‐pretreatment. PEF‐treated jujube had highest phenol (16.95 mg GAE/g DW) and water‐soluble pectin(WSP) (43.71 mg/g AIR), correlating positively with rehydration (r = 0.67). CP had highest flavonoid content (17.01 mg RE/g DW) and US showed highest antioxidant activity (DPPH 80.57%, ABTS 89.65%). Chelate‐soluble pectin (CSP) Sodium carbonate‐soluble pectin (NSP) was positively correlated with hardness (r = 0.71, 0.69). These findings suggest pretreatments improve drying efficiency, nutrient retention, and pectin functionality in jujube products. Practical ApplicationsDrying for jujube (Ziziphus jujuba Mill.) is the most common method of processing and ensure the sale. Three kinds of non‐thermal processing pretreatment method (ultrasound, ultrahigh pressure, and cold plasma) combined with novel drying method, microwave coupled pulsed vacuum drying (MPVD) was studied in the application on the dehydration of jujube slice in this paper. The drying characteristics and pectin properties of winter jujube were analyzed and treated by MPVD compared with freeze drying and hot air drying, for both technological research and processing practice. The drying kinetics, bioactive compounds, antioxidant capacity, sensory attributes, and pectin properties were also used as descriptors in order to promising dehydration method for obtaining high value‐added jujube products. Moreover, the relationship between the cell wall pectin and the phenols, hardness and crispness were analyzed, which give a new insight to study the changing scheme in the nutrients and the texture during the dehydration for fruits and vegetables.

Development of radio frequency drying protocols for preserving the color and fragrance of lotus bee pollen

This investigation delves into radio frequency (RF) drying as a novel approach for preserving the inherent quality and extending shelf life of lotus bee pollen, a primary agricultural product enriched with essential nutrients and bioactive compounds. Through a comparative analysis with conventional hot air (HA) drying conducted at 50 °C, 55 °C, and 60 °C, this study evaluated the impact of both drying techniques on critical quality parameters of bee pollen. These parameters included moisture content, fatty acid profile, color, aroma characteristics, pigment concentrations, and malondialdehyde levels. Findings revealed that RF drying significantly reduced drying time while maintaining superior quality attributes of bee pollen, such as enhanced color retention (ΔE < 5) and diminished lipid oxidation, in comparison to HA drying. Notably, RF drying at 55 °C for 130 min emerged as the optimum condition for preserving the sensory and nutritional qualities of lotus bee pollen. The study underscores the potential of RF drying as an efficient and quality-preserving method that could be advantageous for commercial applications in food industry, aiming at enhancing shelf life and safety of bee pollen.

Comprehensive comparison of cellulose nanocrystal (CNC) drying using multi-frequency ultrasonic technology with selected conventional drying technologies

Cellulose nanocrystals (CNCs) have garnered increased attention due to their renewable nature, abundant feedstock availbility, and good mechanical properties. However, one of the bottlenecks for its commercial production is the drying process. Because of the low CNC concentrations in suspension after isolation, CNC drying requires the removal of a large amount of water to obtain dry products for the following utilization and saving shipping costs. A novel multi-frequency, multimode, modulated ultrasonic drying technology was developed for CNC drying to improve product quality, reduce energy consumption, and increase production rate. CNCs dried with different drying technologies were characterized by Fourier transform infrared (FT-IR) spectra analysis, X-ray diffraction (XRD) analysis, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and redispersibility to measure the quality and property changes. Under the same temperature and airflow rate, ultrasonic drying enhanced drying rates, resulting in at least a 50% reduction in drying time compared to hot air drying. The mean particle sizes of CNC from ultrasonic drying changed little with settling time, indicating good redispersibility. In addition, ultrasonic dried CNCs exhibited good stability in aqueous solutions, with the zeta potentials ranging from –35 to –65 mV. Specific energy consumption and CO2 emissions of various CNC drying technologies were evaluated. Energy consumption of ultrasonic drying is significantly reduced compared to other drying technologies. Moreover, the potential CO2 emissions of the fully electrified ultrasonic drying could be net zero if renewable electricity is used.

Effect of Blanching Temperature and Convective Hot Air-drying Temperature of Orange Peel Slices on Its Quality Evaluation

Drying characteristics of orange peel was investigated by blanching and convective hot air drying of orange peel slices (of 3mm thickness) at the temperature 40ºC, 50ºC and 60ºC. Drying models i.e. Lewis, Henderson and Pabis and Page were fitted to the experimental data on moisture ratio with respect to time. The page model fitted well r^2≥0.976 and MSE≤0.0012 among all the models tested for the experimental data. Effective diffusivity (Deff) at time (t) for orange peel were 0.086×10-8m2/s, 1.834×10-8m2/s and 2.017×10-8m2/s which was blanched at 72ºC:10 min, 82ºC:8min and 92ºC:5 min and dried at 40ºC; 0.0903688×10-8m2/s, 1.077×10-8m2/s and 1.898×10-8m2/s which was blanched at 72ºC:10 min, 82ºC:8min and 92ºC:5 min and dried at 50ºC; 1.168×10-8m2/s, 1.422×10-8m2/s and 1.579×10-8m2/s which was blanched at 72ºC:10 min, 82ºC:8min and 92ºC:5 min and dried at 60ºC. The activation energy (Ea) for moisture diffusion was found to be 2.244×104 kJ/mole, 2.523×104 kJ/mole and 1.262×104 kJ/mole. The quality parameter i.e. T.S.S was in 20 to 60(°B), acidity was in the range of 0.32 to 18.09 %, reducing sugar was in the range of 19.05 to 6.21 % non-reducing sugar was in the range of 2.56 to 10.13%, total sugar was in the range of 9.08 to 25.8%, pH was in the range of 5.4 to 3.6%, ascorbic acid was in the range of 18.2 to 34.76%, yellowness index was in the range of 77.76 to 154.40 and protein was in the range of 8.60 to 11.24% on orange peel powder prepared from blanching at 72ºC: 10 min, 82ºC: 8min and 92ºC: 5 min dried at 40⁰C, 50⁰C and 60⁰C respectively were determined and discussed.

Comparison of non-volatile compounds of Penaeus vannemei with different drying treatments via multidimensional infrared spectroscopy

To analyze the effect of various drying treatments (microwave drying (MD), hot air drying (HAD), vacuum drying (VD), and vacuum freeze drying (VFD)) on taste compounds in Penaeus vannamei, relevant indicators such as free amino acids, 5′-nucleotides, and organic acids were performed. Multidimensional infrared spectroscopy (MM-IR) results found that there were notable variations in taste properties of P. vannamei. There were 18 autocorrelation peaks in 3400–900 cm−1 were screened using second-derivative infrared spectroscopy (SD-IR) and two-dimensional correlation infrared spectroscopy (2DCOS-IR). Variations in functional groups were the major contributors to taste profiles. The TAV of glutamic acid (Glu), guanine (GMP), and inosinemonphosphate (IMP) were greater than one and had notable impacts on taste profiles. VD had the highest equivalent umami value, followed by VFD, HAD, and MD. This study may provide a theoretical guide for the production of dried P. vannamei products on an industrial scale.

Multi-objective Investigation and Optimization of Paddy Processing in a Hot Air Dryer

Multi-objective Investigation and Optimization of Paddy Processing in a Hot Air Dryer

Convective Hot Air Drying of Aloe vera Slices and its Quality Evaluation

Convective Hot Air Drying of Aloe vera Slices and its Quality Evaluation

Development of Powder from Amaranthus by Convective Hot Air Drying at Varied Temperatures and its Quality Evaluation

Development of Powder from Amaranthus by Convective Hot Air Drying at Varied Temperatures and its Quality Evaluation

Effects of Drying Temperatures and Drying Methods on Physicochemical and Antioxidant Properties of Celery Powder

ABSTRACT The Celery (Apium graveolens Linn.) were hot air dried at 60, 70, and 80°C. Drying temperatures had no significant impact on the bulk density, water holding capacity, or swelling capacity of celery powder. High drying temperatures (80°C) generated a significant color shift, whereas antioxidants were decreased at a low temperature (60°C). Thus, the temperature of 70°C was recommended because the powder had satisfying green color, high phenolic content (597.35 mg GAE/100 g), and DPPH inhibition (39.37%). Subsequently, celery samples were dried using hot air drying (at 70°C) and freeze-drying and the juice was foam mat dried. The foam mat dried powder had less water holding capacity, whereas the hot air and freeze-dried powders had similar characteristics. But the freeze-dried powder had a pleasant green color, low bulk density, high swelling and water holding capacity, and remarkably high phenolic content (718.00 mg GAE/100 g) and DPPH inhibition (64.14%).

Effects of cold plasma pretreatment before different drying process on the structural and functional properties of starch in Chinese yam

This article compared the effects of hot air drying (HAD), infrared drying (IRD), and cold plasma (CP) as a pretreatment on the structure, quality, and digestive characteristics of starch extracted from yam. As the most commonly used drying method, HAD was used as a control. SEM and CLSM images showed that all treatments preserve the integrity of the yam starch. CP caused some cracks and breaks in the starch granules. IRD did not destroy the crystal structure of starch molecules, but made the spiral structure tighter and increased short-range orderliness. However, CP led to the depolymerization and dispersion of starch molecular chains, resulting in a decrease in average molecular weight and relative crystallinity. These molecular conformation changes caused by different processes led to differences in solubility, swelling power, pasting parameters, digestion characteristics, and functional characteristics. This study provided an important basis for the reasonable drying preparation and utilization of yam starch.