DOI: 10.57760/sciencedb.32810
title: Dataset on the Drying Characteristics of Folium Isatidis
title: 大青叶干燥特性数据集

description: Abstract: To achieve high-quality drying of the medicinal plant Folium Isatidis, which has a traditional consumption habit, this study used folk-edible Isatis indigotica leaves from the Wenzhou region of Zhejiang Province as raw material. It compared the effects of hot air drying (HAD), radio frequency drying (RFD), and vacuum freeze drying (VFD) on their processing quality. The results showed that: The color of VFD-treated samples was closest to that of fresh leaves (L* value of 75.69), and it best preserved the contents of total chlorophyll (3.31 mg/g), flavonoids (41.67 mg/g), and total phenols (38.08 mg/g), exhibiting optimal antioxidant activity. RFD-treated samples demonstrated the best wettability and solubility, making them more suitable for dissolution and preparation by stirring, with a drying time of only 1.89 h, which was 92% shorter than that of VFD. Their antioxidant capacity showed no significant difference from VFD. In contrast, HAD treatment led to significant quality deterioration due to thermal damage. Microstructural analysis revealed that VFD samples presented a loose, porous, sponge-like structure without significant cellular disruption, which better preserved quality. Meanwhile, HAD samples showed particle aggregation and adhesion with damaged structure, leading to easier loss of nutritional components.1 Materials and Methods1.1 Materials and InstrumentsMaterials: Fresh Folium Isatidis were purchased from a farmers' market in Wencheng County, Wenzhou City, Zhejiang Province. Rutin (≥95%) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Folin-Ciocalteu Reagent and Gallic Acid (99%) were purchased from Shanghai Macklin Biochemical Technology Co., Ltd. All other reagents were of analytical grade and purchased from Sinopharm Chemical Reagent Co., Ltd. 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assay kits were purchased from Grace Biotechnology Co., Ltd.Instruments:YP30002 Electronic Balance (Shanghai Youke Instrument Co., Ltd.); Moisture Analyzer (Shanghai Sunny Hengping Scientific Instrument Co., Ltd.); Electric Thermostatic Water Bath (Shanghai Jinghong Laboratory Equipment Co., Ltd.); DHG-9240A Electric Thermostatic Drying Oven (Shanghai Yiheng Scientific Instrument Co., Ltd.); SCIENTZ-30N Vacuum Freeze Dryer (Ningbo Scientz Biotechnology Co., Ltd.); HGJL-5RFS Food Radio Frequency Processing Equipment (Hefei Hit Golden Wave Equipment Technology Co., Ltd.); CR-10 Colorimeter (Konica Minolta, Japan); Verios G4 UC Thermal Field Emission Scanning Electron Microscope (Thermo Scientific, USA); Readmax 1900 Microplate Reader (Shanghai Shanpu Biotechnology Co., Ltd.）1.2 Experimental Methods1.2.1 Preparation of Folium Isatidis PowderThe Folium Isatidis were washed and subjected to blanching for 5 seconds in boiling water for enzyme inactivation, followed by rapid draining. Three drying methods were applied to the blanched samples:Hot Air Drying (HAD): The samples were spread evenly in an electric thermostatic drying oven and dried at 50 °C.Radio Frequency Drying (RFD): The samples were placed in the radio frequency drying equipment with parameters set to a temperature of 50°C, electrode gap of 110 mm, and air velocity of 0.50 m/s for drying.Vacuum Freeze Drying (VFD): The samples were pre-frozen at -80°C in a freezer for 12 hours, then thinly spread and dried in the vacuum freeze dryer at -45°C.Drying was terminated when the sample moisture content fell below 6%, and the drying time was recorded. The dried leaves were then ground into powder, sieved through a 60-mesh sieve, stored in a desiccator, and reserved for subsequent index determinations.1.2.2 Determination of Physicochemical Indices1.2.2.1 Determination of Moisture ContentMoisture content was determined using a moisture analyzer. A 3.00 g sample of Folium Isatidis powder was weighed and evenly spread on the sample pan with a thickness ≤ 2 mm. The instrument temperature was set to 105 °C, and drying continued until the mass change within 30 s was ≤ 1 mg, indicating constant weight. The moisture content (%) was read immediately.1.2.2.2 Color MeasurementA handheld colorimeter was used to measure the L, a*, and b* values of the samples.1.2.2.3 Wettability MeasurementReferring to the method of Li et al(2021)[1]. with slight modifications, 0.50 g of sample powder was weighed and evenly sprinkled onto the surface of 100 mL of deionized water. The time (s) required for the entire sample to be completely wetted by water was measured.1.2.2.4 Water-Holding Capacity MeasurementThe water-holding capacity (WHC) was determined with slight modifications according to the method described by Zheng et al(2006)[2]. Precisely 1.00 g of powder was weighed into a centrifuge tube. Then, 25 mL of deionized water was added. The mixture was magnetically stirred at room temperature for 30 minutes, followed by centrifugation at 3000 r/min for 20 minutes. After centrifugation, the supernatant was discarded. The residual water on the inner wall of the centrifuge tube was removed using filter paper, and the tube containing the sediment was weighed. The water-holding rate (%) was calculated using the following formula:WHC（%）=(M1-M0)×100/M0Where:M1is the mass (g) of the centrifuge tube with the sediment after water removal.M0 is the initial mass (g) of the centrifuge tube with the dry Folium Isatidis powder.1.2.2.5 Determination of SolubilityThe solubility was measured following the method reported by GONG et al(2007)[3] with minor modifications. Briefly, 0.50 g of Folium Isatidis powder was weighed into a centrifuge tube, mixed with 25 mL of deionized water, and vortexed for 5 minutes. The mixture was then centrifuged at 5000 r/min for 30 minutes. The supernatant was collected and diluted to a final volume of 50 mL. An aliquot of the supernatant was transferred into a pre-weighed aluminum dish, dried at 105°C for 7 h, and then weighed to obtain the mass m. Solubility was calculated according to the following formula:Solubility(%)=（M1/M0）×100Where:M1 is the mass (g) of the solid matter in the supernatant.M0 is the initial mass (g) of the Folium Isatidis powder.1.2.2.6 Determination of Chlorophyll ContentThe chlorophyll content was determined following the method reported by Yan et al(2018)[4]. with minor modifications. Briefly, a homogenate was prepared by mixing the powdered sample with deionized water at a 1:1 ratio (w/v). Exactly 0.50 g of the homogenate was weighed, and 10 mL of an extraction solvent (acetone:ethanol = 1:1, v/v) was added. The mixture was then extracted at room temperature in the dark for 5 hours. After extraction, the mixture was filtered. The absorbance of the filtrate was measured at 663 nm and 645 nm. The chlorophyll content was calculated according to the following formula:Chlorophyll a content（mg/g）=(12.72×A663-2.59×A645）×（V/(1000×M））Chlorophyll b content（mg/g）=(22.88×A645-4.67×A663）×（V/(1000×M））Total chlorophyll content（mg/g）=(8.05×A663-20.29×A645）×（V/(1000×M)）Where:A663 is the absorbance of the solution at 663 nm.A645 is the absorbance of the solution at 645 nm.V is the volume of the extraction solvent (mL).M is the mass of the sample (g).1.2.3 Determination of Bioactive Compounds1.2.3.1 Extraction of Bioactive CompoundsBioactive compounds were extracted with slight modifications according to the method described by Zhao et al(2021)[5]. Briefly, 1.00 g of Folium Isatidis powder was mixed with 30 mL of 70% methanol solution. The mixture was subjected to ultrasonic-assisted extraction in a 65 °C water bath for 30 min, followed by centrifugation at 8000 r/min for 10 minutes. The supernatant was collected and diluted to a final volume of 50 mL with 70% methanol for subsequent analysis.1.2.3.2 Determination of Flavonoid ContentThe flavonoid concentration in the extract was determined using the sodium nitrite-aluminum nitrate colorimetric method[6]. The flavonoid content was then calculated according to the following formula:flavonoid concent（mg/g）=(C×N×V)×100/M0Where:C is the flavonoid concentration of the Folium Isatidis powder extract (mg/mL);N is the dilution factor;V is the volume of the reaction system (mL);M0 is the mass of the Folium Isatidis powder sample (g).1.2.3.3 Determination of Total Phenolic ContentThe total phenolic content was determined using the Folin-Ciocalteu method [7]. Precisely 100 µL of the extract was transferred into a test tube. Then, 0.5 mL of 0.20 mol/L Folin-Ciocalteu reagent was added, mixed, and allowed to stand for 3 minutes. Subsequently, 1.5 mL of a 5% (w/v) sodium carbonate (Na₂CO₃) solution was added. The mixture was diluted to a final volume of 10 mL with distilled water. The resulting mixture was heated in a water bath at 50 °C for 15 minutes, then cooled to room temperature. The absorbance was measured at 765 nm. The total phenolic content was calculated according to the following formula:total phenolic concent（mg/g）=(C×N×V)×100/M0Where:C is the total phenolic concentration of the Folium Isatidis powder extract (mg/mL);;N is the dilution factor;V is the final volume of the reaction system (mL);M0 s the mass of the total phenolic powder sample (g);1.2.4 Determination of Antioxidant ActivityThe DPPH and ABTS radical scavenging capacities were both determined according to the instructions provided in the assay kits from Grace Biotechnology Co., Ltd.1.2.5 Microstructural ObservationThe morphology of the Isatis indigotica leaf powder was observed using scanning electron microscopy (SEM). A small amount of the sample was evenly adhered onto a conductive adhesive stub and sputter-coated with platinum. The microstructure of the powder was then observed under an accelerating voltage of 2.0 kV.1.2.6 Data Statistics and AnalysisAll experiments were performed in triplicate. The results are expressed as mean ± standard deviation.
description: Abstract: To achieve high-quality drying of the medicinal plant Folium Isatidis, which has a traditional consumption habit, this study used folk-edible Isatis indigotica leaves from the Wenzhou region of Zhejiang Province as raw material. It compared the effects of hot air drying (HAD), radio frequency drying (RFD), and vacuum freeze drying (VFD) on their processing quality. The results showed that: The color of VFD-treated samples was closest to that of fresh leaves (L* value of 75.69), and it best preserved the contents of total chlorophyll (3.31 mg/g), flavonoids (41.67 mg/g), and total phenols (38.08 mg/g), exhibiting optimal antioxidant activity. RFD-treated samples demonstrated the best wettability and solubility, making them more suitable for dissolution and preparation by stirring, with a drying time of only 1.89 h, which was 92% shorter than that of VFD. Their antioxidant capacity showed no significant difference from VFD. In contrast, HAD treatment led to significant quality deterioration due to thermal damage. Microstructural analysis revealed that VFD samples presented a loose, porous, sponge-like structure without significant cellular disruption, which better preserved quality. Meanwhile, HAD samples showed particle aggregation and adhesion with damaged structure, leading to easier loss of nutritional components.1 Materials and Methods1.1 Materials and InstrumentsMaterials: Fresh Folium Isatidis were purchased from a farmers' market in Wencheng County, Wenzhou City, Zhejiang Province. Rutin (≥95%) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Folin-Ciocalteu Reagent and Gallic Acid (99%) were purchased from Shanghai Macklin Biochemical Technology Co., Ltd. All other reagents were of analytical grade and purchased from Sinopharm Chemical Reagent Co., Ltd. 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assay kits were purchased from Grace Biotechnology Co., Ltd.Instruments:YP30002 Electronic Balance (Shanghai Youke Instrument Co., Ltd.); Moisture Analyzer (Shanghai Sunny Hengping Scientific Instrument Co., Ltd.); Electric Thermostatic Water Bath (Shanghai Jinghong Laboratory Equipment Co., Ltd.); DHG-9240A Electric Thermostatic Drying Oven (Shanghai Yiheng Scientific Instrument Co., Ltd.); SCIENTZ-30N Vacuum Freeze Dryer (Ningbo Scientz Biotechnology Co., Ltd.); HGJL-5RFS Food Radio Frequency Processing Equipment (Hefei Hit Golden Wave Equipment Technology Co., Ltd.); CR-10 Colorimeter (Konica Minolta, Japan); Verios G4 UC Thermal Field Emission Scanning Electron Microscope (Thermo Scientific, USA); Readmax 1900 Microplate Reader (Shanghai Shanpu Biotechnology Co., Ltd.）1.2 Experimental Methods1.2.1 Preparation of Folium Isatidis PowderThe Folium Isatidis were washed and subjected to blanching for 5 seconds in boiling water for enzyme inactivation, followed by rapid draining. Three drying methods were applied to the blanched samples:Hot Air Drying (HAD): The samples were spread evenly in an electric thermostatic drying oven and dried at 50 °C.Radio Frequency Drying (RFD): The samples were placed in the radio frequency drying equipment with parameters set to a temperature of 50°C, electrode gap of 110 mm, and air velocity of 0.50 m/s for drying.Vacuum Freeze Drying (VFD): The samples were pre-frozen at -80°C in a freezer for 12 hours, then thinly spread and dried in the vacuum freeze dryer at -45°C.Drying was terminated when the sample moisture content fell below 6%, and the drying time was recorded. The dried leaves were then ground into powder, sieved through a 60-mesh sieve, stored in a desiccator, and reserved for subsequent index determinations.1.2.2 Determination of Physicochemical Indices1.2.2.1 Determination of Moisture ContentMoisture content was determined using a moisture analyzer. A 3.00 g sample of Folium Isatidis powder was weighed and evenly spread on the sample pan with a thickness ≤ 2 mm. The instrument temperature was set to 105 °C, and drying continued until the mass change within 30 s was ≤ 1 mg, indicating constant weight. The moisture content (%) was read immediately.1.2.2.2 Color MeasurementA handheld colorimeter was used to measure the L, a*, and b* values of the samples.1.2.2.3 Wettability MeasurementReferring to the method of Li et al(2021)[1]. with slight modifications, 0.50 g of sample powder was weighed and evenly sprinkled onto the surface of 100 mL of deionized water. The time (s) required for the entire sample to be completely wetted by water was measured.1.2.2.4 Water-Holding Capacity MeasurementThe water-holding capacity (WHC) was determined with slight modifications according to the method described by Zheng et al(2006)[2]. Precisely 1.00 g of powder was weighed into a centrifuge tube. Then, 25 mL of deionized water was added. The mixture was magnetically stirred at room temperature for 30 minutes, followed by centrifugation at 3000 r/min for 20 minutes. After centrifugation, the supernatant was discarded. The residual water on the inner wall of the centrifuge tube was removed using filter paper, and the tube containing the sediment was weighed. The water-holding rate (%) was calculated using the following formula:WHC（%）=(M1-M0)×100/M0Where:M1is the mass (g) of the centrifuge tube with the sediment after water removal.M0 is the initial mass (g) of the centrifuge tube with the dry Folium Isatidis powder.1.2.2.5 Determination of SolubilityThe solubility was measured following the method reported by GONG et al(2007)[3] with minor modifications. Briefly, 0.50 g of Folium Isatidis powder was weighed into a centrifuge tube, mixed with 25 mL of deionized water, and vortexed for 5 minutes. The mixture was then centrifuged at 5000 r/min for 30 minutes. The supernatant was collected and diluted to a final volume of 50 mL. An aliquot of the supernatant was transferred into a pre-weighed aluminum dish, dried at 105°C for 7 h, and then weighed to obtain the mass m. Solubility was calculated according to the following formula:Solubility(%)=（M1/M0）×100Where:M1 is the mass (g) of the solid matter in the supernatant.M0 is the initial mass (g) of the Folium Isatidis powder.1.2.2.6 Determination of Chlorophyll ContentThe chlorophyll content was determined following the method reported by Yan et al(2018)[4]. with minor modifications. Briefly, a homogenate was prepared by mixing the powdered sample with deionized water at a 1:1 ratio (w/v). Exactly 0.50 g of the homogenate was weighed, and 10 mL of an extraction solvent (acetone:ethanol = 1:1, v/v) was added. The mixture was then extracted at room temperature in the dark for 5 hours. After extraction, the mixture was filtered. The absorbance of the filtrate was measured at 663 nm and 645 nm. The chlorophyll content was calculated according to the following formula:Chlorophyll a content（mg/g）=(12.72×A663-2.59×A645）×（V/(1000×M））Chlorophyll b content（mg/g）=(22.88×A645-4.67×A663）×（V/(1000×M））Total chlorophyll content（mg/g）=(8.05×A663-20.29×A645）×（V/(1000×M)）Where:A663 is the absorbance of the solution at 663 nm.A645 is the absorbance of the solution at 645 nm.V is the volume of the extraction solvent (mL).M is the mass of the sample (g).1.2.3 Determination of Bioactive Compounds1.2.3.1 Extraction of Bioactive CompoundsBioactive compounds were extracted with slight modifications according to the method described by Zhao et al(2021)[5]. Briefly, 1.00 g of Folium Isatidis powder was mixed with 30 mL of 70% methanol solution. The mixture was subjected to ultrasonic-assisted extraction in a 65 °C water bath for 30 min, followed by centrifugation at 8000 r/min for 10 minutes. The supernatant was collected and diluted to a final volume of 50 mL with 70% methanol for subsequent analysis.1.2.3.2 Determination of Flavonoid ContentThe flavonoid concentration in the extract was determined using the sodium nitrite-aluminum nitrate colorimetric method[6]. The flavonoid content was then calculated according to the following formula:flavonoid concent（mg/g）=(C×N×V)×100/M0Where:C is the flavonoid concentration of the Folium Isatidis powder extract (mg/mL);N is the dilution factor;V is the volume of the reaction system (mL);M0 is the mass of the Folium Isatidis powder sample (g).1.2.3.3 Determination of Total Phenolic ContentThe total phenolic content was determined using the Folin-Ciocalteu method [7]. Precisely 100 µL of the extract was transferred into a test tube. Then, 0.5 mL of 0.20 mol/L Folin-Ciocalteu reagent was added, mixed, and allowed to stand for 3 minutes. Subsequently, 1.5 mL of a 5% (w/v) sodium carbonate (Na₂CO₃) solution was added. The mixture was diluted to a final volume of 10 mL with distilled water. The resulting mixture was heated in a water bath at 50 °C for 15 minutes, then cooled to room temperature. The absorbance was measured at 765 nm. The total phenolic content was calculated according to the following formula:total phenolic concent（mg/g）=(C×N×V)×100/M0Where:C is the total phenolic concentration of the Folium Isatidis powder extract (mg/mL);;N is the dilution factor;V is the final volume of the reaction system (mL);M0 s the mass of the total phenolic powder sample (g);1.2.4 Determination of Antioxidant ActivityThe DPPH and ABTS radical scavenging capacities were both determined according to the instructions provided in the assay kits from Grace Biotechnology Co., Ltd.1.2.5 Microstructural ObservationThe morphology of the Isatis indigotica leaf powder was observed using scanning electron microscopy (SEM). A small amount of the sample was evenly adhered onto a conductive adhesive stub and sputter-coated with platinum. The microstructure of the powder was then observed under an accelerating voltage of 2.0 kV.1.2.6 Data Statistics and AnalysisAll experiments were performed in triplicate. The results are expressed as mean ± standard deviation.