2016 Volume 64 Issue 7 Pages 1024-1030
We investigated the effect of steaming time on Cistanche deserticola Y. C. MA slices by analyzing levels of bioactive compounds, antioxidant activity, and weight loss compared with fresh, directly oven-dried, and blanched samples. Fresh samples had extremely low levels of phenylethanoid glycosides and antioxidant activity. Lower levels of weight loss and higher amounts of soluble sugars, polysaccharides, and dilute ethanol-soluble extracts were found when the slices were steamed rather than blanched. Slices steamed for 5 and 7 min contained significantly (p<0.05) higher amounts of acteoside, isoacteoside, and 2′-acetylacteoside than directly oven-dried samples. However, soluble sugars and dilute ethanol-soluble extracts decreased gradually throughout the steaming process. The concentration of polysaccharides fluctuated during the steaming process. The steaming time had a consistent effect on antioxidant properties evaluated by oxygen radical absorbance capacity (ORAC), 2,2-diphenyl-1-picrylhydrazyl free radical scavenging activity (DPPH) and ferric reducing antioxidant property (FRAP), showing a significant increase and reaching 108.62, 23.08, and 11.68 micromoles Trolox per mass of fresh slice (μmol TE/g FW), respectively. The present results suggest that fresh-cut C. deserticola can be subjected to approximately 5–7 min of steaming to improve phenylethanoid glycoside levels and antioxidant activity, while still preserving the amounts of soluble sugars, polysaccharides, and dilute ethanol-soluble extracts. These results would help to improve the production process for fresh-cut Chinese medicines, and increase the understanding of their associated health benefits.
Cistanche deserticola Y. C. MA (Orobanchaceae), commonly known as “Desert ginseng,” has long been used as a tonic in China and Japan. The fleshy stems are cut into slices for the treatment of various diseases including impotence, female infertility, cold sensation in the loins and knees, and geriatric constipation. In recent years, a number of studies have revealed its effectiveness in experimental models that are related to neurological disorders, especially Alzheimer’s disease and Parkinson’s disease.1) The health food market is becoming increasingly interested in this useful natural dietary supplement. Wine and tea made from the succulent stems are popular health foods that alleviate fatigue, and enhance learning and memory. C. deserticola is a rich source of phenylethanoid glycosides, polysaccharides, and soluble sugars, which mainly exhibit antioxidative,2,3) neuroprotective,4,5) hepatoprotective,6) immune-enhancing,7–9) laxative,10) and anti-aging11) effects, among which the antioxidative activity is considered to be the basis of the other pharmacological actions. Echinacoside and acteoside are representative markers for the quality control of Cistanches Herba in the Chinese Pharmacopoeia (2015 edition), owing to their predominant abundance, genus specificity, and notable bioactivities. Determination of dilute ethanol-soluble extracts is also contained in the quality control of Cistanches Herba. Cistanoside A, isoacteoside, and 2′-acetylacteoside have also been reported to be abundant in C. deserticola.12)
The increasing demand for C. deserticola has greatly stimulated its cultivation. C. deserticola belongs to a perennial parasite herb, mainly growing in arid or semi-arid areas of northwest China.13) Immediately after harvesting, these highly sugary, heavy raw stems must be dried to prevent nutrient content loss and spoilage. Fresh stems usually contain 75–85% water, and the water level should be lowered to below 10% for their preservation. In the majority of Cistanche-producing regions, whole fresh stems are placed in open fields for about 2 months for the preliminary drying process. The dried material is then transported to factories, soaked in water, cut into slices, and dried again. The delay of the slices processing may be the result of poorly-educated or ill-equipped farmers. However, the main problem is a lack of knowledge and technology to enable an efficient production process.
High-heat treatment has been widely used on vegetables and fruits, and can inhibit microbial growth and extend shelf-life.14–16) However, it can also give rise to changes in appearance and nutrient composition. Certain bioactive components,17) and pharmacological activities such as antioxidant activity,18) have been shown to increase in medicinal herbs after steaming. Thus, steaming C. deserticola may improve several health benefits. The use of steaming or blanching on fresh-cut C. deserticola has also been reported to enhance the amounts of echinacoside and acteoside.19,20) However, no detailed investigation has been carried out to compare the changes in the bioactive compounds and antioxidant activity of fresh-cut C. deserticola during the steaming process. The aim of this study was therefore to examine the effect of steaming time (1, 3, 5, 7 min) on the amount of phenylethanoid glycosides, polysaccharides, soluble sugars, dilute ethanol-soluble extracts, weight loss, and antioxidant properties in C. deserticola slices compared with three other groups (fresh, directly oven-dried, blanched).
Analytical grade chemicals: methanol, ethanol, D-glucose, sulfuric acid, potassium hydrogen phosphate, and potassium dihydrogen phosphate monohydrate were acquired from Beijing Chemical Works (Beijing, China). Formic acid and phenol were purchased from Sinopharm Chemical Reagent Co. (Shanghai, China). HPLC grade methanol was purchased from Fisher Scientific (Toronto, Canada). The deionized water was obtained using a Milli-Q system (Millipore Corp., Bedford, MA, U.S.A.). 2,2-Diphenyl-1-picrylhydrazyl (DPPH) was provided by Alfa Aesar (Ward Hill, MA, U.S.A.) and 2,2′-azobis(2-amino-propane)dihydrochloride (AAPH) by Adamas-beta (Shanghai, China). 6-Methoxy-2,5,7,8-tetramethylchromane-2-carboxylic acid (Trolox), 2,6-di-tert-butyl-p-cresol (BHT), and fluorescein (sodium salt) (FL) were obtained from TCI (Tokyo, Japan), and the total antioxidant capacity (T-AOC) assay kit from Nanjing Jiancheng Bioengineering Institute (Nanjing, China). The standards for acteoside (111530-200706) and echinacoside (111670-200503) were purchased from the National Institute for Food and Drug Control (Beijing, China). The standards for 2′-acetylacteoside, cistanoside A, and isoacteoside were presented as a gift by Dr. Zhiguo Ma. The purity of each reference compound was determined to be over 98% by normalization of the peak area detected by HPLC-diode array detector (DAD).
Material Treatment and Weight Loss DeterminationSamples were collected in spring 2014 in the Ningxia Plantation of Cistanches Herba (106.08°N, 38.24°E, 1124.2 m) in China, and identified by one of us (Prof. Jun Chen). A voucher specimen was deposited at Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences, Peking Union Medical College. About 3 kg of stems of C. deserticola were randomly collected and rinsed with clean water. The inflorescence parts were removed by a ceramic knife, then the stems were cut into 3 mm slices. Every 100 g slices was measured in weight (W0) as a replicate. Seven experimental treatments with three replicates per treatment were evaluated. For steaming, four batches of slices were put in 93°C water vapor for 1, 3, 5, or 7 min. For blanching, one treatment was put in 96°C water for 5 min. Fresh and directly oven-dried slices were the other two treatments reported in this experiment. The treated slices were weighed (W1) and dried at 60°C in the oven. The dried slices were then re-weighed (W2), ground, and pulverized (65 mesh). The sample powders were stored in vacuum bags at −20°C until the day of analysis. Weight loss was calculated as follows: weight loss after high-heat treatment (%)=[(W0−W1)/W0]×100, weight loss after oven drying (%)=[(W0−W2)/W0]×100, where W0 is the initial weight, and W1 and W2 are the weights measured after high-heat treatment and oven drying, respectively.
Phenylethanoid Glycosides and Antioxidant PropertiesSamples ExtractionA 0.5-g powdered sample was extracted with 25 mL 60% methanol-aqueous solution by KQ-250DE ultrasound (Kunshan Ultrasonic Instrument Co., Jiangsu, China) at 40 kHz, 200 W, and 40°C for 30 min. After extraction, the treated samples were centrifuged for 10 min at 4600×g (TD5; Hunan Herexi Instrument & Equipment Co., Hunan, China). The supernatant was filtered through a 0.45-µm pore size filter for subsequent analyses.
Determination of Phenylethanoid GlycosidesDetermination of echinacoside, cistanoside A, acteoside, isoacteoside, and 2′-acetylacteoside from C. deserticola samples was carried out as described by Ma et al.21) with some modifications. Analysis was performed using a 2695–2996 HPLC instrument (Waters Corp., Milford, MA, U.S.A.) with ultraviolet absorption monitored at 330 nm. The separation was carried out on a Merck Purospher® Star RP-C18 column (250 mm×4.6 mm, 5 µm) operated at 30°C. The mobile phase at a flow rate of 1 mL/min consisted of solvent A (methanol) and solvent B (0.1% aqueous formic acid, v/v). A gradient elution was operated as follows: 28% A (0–10 min), 28–38% A (10–30 min), 38% A (30–45 min), and the injection volume was 10 µL. A mixed solution containing five reference standards was prepared by dissolving the reference standards in 60% methanol to a final concentration of 0.20 mg/mL for echinacoside, 0.21 mg/mL for acteoside, 0.20 mg/mL for 2′-acetylacteoside, 0.05 mg/mL for cistanoside A, and 0.05 mg/mL for isoacteoside. The solution was then diluted to seven different concentrations to establish calibration curves. The concentration of phenylethanoid glycosides of samples was expressed in g/kg of fresh weight (FW).
Determination of Oxygen Radical Absorbance Capacity (ORAC)The ORAC assay was conducted as described by Huang et al.22) with some modifications. The synthetic antioxidant BHT was used as a positive control. In brief, 25 µL of dilute sample extracts and 160 µL FL were mixed in a 96-well microplate. The mixture was incubated at 37°C for 15 min, before the addition of 20 µL AAPH. Fluorescence was monitored using 485 nm (excitation) and 520 nm (emission) at 3-min intervals for 72 min by using Fluoroskan Ascent FL (Thermo Scientific, Waltham, MA, U.S.A.). Trolox (2.5–50.0 µmol/L) was used as a reference standard, and the results were expressed as micromoles of Trolox per mass of fresh slice, µmol TE/g FW.
Determination of 2,2-Diphenyl-1-picrylhydrazyl Free Radical Scavenging Activity (DPPH)The DPPH assay was performed as described by Goupy et al.23) with some modifications. The synthetic antioxidant BHT was used as a positive control. In brief, 1 mL of the dilute sample extract was mixed with 1 mL of 0.2 mmol/L DPPH-methanol solution. The solutions were kept in the dark at 25°C for 90 min, then the absorbance was measured at 517 nm. Trolox (4.0–119.5 µmol/L) was used as a reference standard, and the results were expressed as micromoles of Trolox per mass of fresh slice, µmol TE/g FW.
Determination of Ferric Reducing Antioxidant Property (FRAP)The FRAP assay was performed using the T-AOC assay kit in accordance with the manufacturer’s instructions.
Soluble Sugars and PolysaccharidesSample Preparation of Soluble SugarsA 0.5-g powdered sample was extracted with 25 mL of 80% ethanol-aqueous solution by KQ-250DE ultrasound at 40 kHz, 150 W, and 80°C for 30 min. The first extractive solution was filtered and transferred into a 50-mL volumetric flask. The sediments were re-extracted, and the filtrate was combined with the first extractive solution in the 50-mL volumetric flask and filled to the mark with 80% aqueous ethanol solution. Then, 1 mL of this solution was pipetted into a 10-mL glass tube to evaporate ethanol in a boiling water bath. Distilled water (5 mL) was added to dissolve the residue, then this was transferred into a 100-mL volumetric flask and filled to the mark with distilled water. Finally, 2 mL of this dilute solution was used for determination of soluble sugars.
Sample Preparation of PolysaccharidesThe sediments from extracting the soluble sugars were air dried and extracted with 25 mL of distilled water by KQ-250DE ultrasound at 40 kHz, 150 W, and 80°C for 30 min. The first extractive solution was filtered and transferred into a 50-mL volumetric flask. The sediments were re-extracted, and the filtrate was combined with the first extractive solution in the 50-mL volumetric flask and filled to the mark with distilled water. Then, a 5-mL solution of this was pipetted into a 50-mL volumetric flask and filled to the mark with distilled water. Finally, 2 mL of this dilute solution was used for determination of polysaccharides.
Determination of Soluble Sugars and PolysaccharidesThe determination of soluble sugars and polysaccharides was carried out using the phenol-sulfuric acid method, as described by Wang et al.24) One milliliter of 6% phenol solution was added into 2 mL of the sample solution and mixed well. Then, 5 mL of concentrated sulfuric acid was added rapidly and shook for 5 min. The mixture was transferred to a boiling water bath for 15 min and quickly cooled to room temperature for ultraviolet detection. The ultraviolet absorption was monitored at 490 nm in a UV2550 spectrophotometer (Shimadzu Co., Kyoto, Japan). Distilled water was utilized as a blank. The reference standard anhydrous D-glucose was accurately weighted and dissolved in distilled water to a final concentration of 0.10 mg/mL. Then 1, 2, 3, 4, 5, 6, and 7 mL of the stock solution was pipetted into seven 10-mL volumetric flasks and filled to the mark with distilled water. Then the seven different concentrations of standard solutions were used to establish calibration curves.
Dilute Ethanol-Soluble ExtractsSamples (4.0 g) were accurately weighed to determine their dilute ethanol-soluble extracts, according to the method described in the Chinese Pharmacopoeia (2015 edition).25) The powdered sample was weighed (W3) and extracted with 100 mL of 50% ethanol-aqueous solution in a 250-mL conical flask with occasional shaking for 6 h, and allowed to stand for 18 h. The extractive solution was filtered and 20 mL of the filtrate was evaporated to dryness, dried at 105°C for 3 h, and cooled in a desiccator (silica gel) for 30 min. Finally, the amount was accurately weighed (W4). The dilute ethanol-soluble extract content was expressed as g/kg FW of the sample. Dilute ethanol-soluble extracts were calculated as follows: dilute ethanol-soluble extracts (g/kg FW)=[(W4×5)/W3]×(100−W5)×10, where W3 is the initial weight, W4 is the weight measured after extraction, and W5 is the weight loss after oven drying (%).
Statistical AnalysisTo clarify any differences among treatment groups, one-way ANOVA was applied using SPSS 13.0 (SPSS Inc., Chicago, IL, U.S.A.). The differences were assessed using the Duncan test with a significance limit of 0.05. The data were expressed as the mean±standard deviation (S.D.) (n=3).
Weight of C. deserticola slices directly determines its commercial value in the medicinal herb market. As shown in Table 1, the weight loss of C. deserticola were analyzed after high-heat treatment and oven-drying. Lower levels of weight loss were found when the slices were directly oven dried rather than steamed or blanched. Blanched samples had the highest levels of weight loss. Steamed samples had higher levels of weight loss with longer steaming time. Seven minutes of steaming, the longest time for the fresh-cut slices to hold shape, showed significantly (p<0.05) higher levels of weight loss after oven-drying than 5 min of steaming. Since phenylethanoid glycosides had been detected in the hot water (data not shown), it suggested that blanching/steaming promoted more water-soluble compounds to be dissolved in the hot water. With respect to weight loss after high-heat exposure, samples steamed for 1 min exhibited extremely low weight loss. Therefore, 1 min of steaming was too short to make the Cistanche tissue brittle, so it was less able to release bioactive compounds (such as phenylethanoid glycosides) during the subsequent extraction procedure, compared with samples that had been steamed longer.
| Treatment | Weight loss after high-heat (%) | Weight loss after oven-drying (%) |
|---|---|---|
| Directly oven-dried | — | 87.42±0.20a |
| Steamed for 1 min | 3.48±0.19a | 88.41±0.46b |
| Steamed for 3 min | 14.84±0.16b | 89.26±0.66cd |
| Steamed for 5 min | 15.26±1.47b | 88.97±0.20bc |
| Steamed for 7 min | 16.52±0.54b | 89.64±0.41d |
| Blanched | 19.08±1.49c | 93.06±0.35e |
Values with different superscript letters in the same column are significant at p<0.05.
Echinacoside, cistanoside A, acteoside, isoacteoside, and 2′-acetylacteoside levels in slices of C. deserticola processed by different methods are shown in Fig. 1. Samples steamed for 7 min contained 2.16 g/kg FW of echinacoside and 0.29 g/kg FW of cistanoside A, an increase of −140 and −6 fold, respectively, compared with the fresh slices. The content of phenylethanoid glycosides rose sharply when the fresh samples were treated with high heat and drying, especially acteoside, isoacteoside, and 2′-acetylacteoside, while they were not detected in the fresh samples. One possible reason for this could be the degradation of phenylethanoid glycosides by peroxidase and β-glucosidase.26) These enzymes would be inactivated in the samples dried by high temperatures and decreased water content, leading to high levels of phenylethanoid glycosides being retained in the extracts. Moreover, phenylethanoid glycosides are phenolic compounds, which would be synthesized in fresh plants in response to the stress of high temperature and moisture loss.27)
Different letters (a–e) denote statistically significant differences between treatments (Duncan test, p<0.05, n=3).
Both steaming and blanching of fresh-cut C. deserticola were reported to enhance the content of echinacoside and acteoside.19,20) However, in the present study, blanching gave a significantly (p<0.05) lower concentration of acteoside and cistanoside A than drying directly. Regarding the total concentration of the five phenylethanoid glycosides, the blanched samples were still lower than the directly oven-dried ones (1.73, 2.35 g/kg FW, respectively). Slices steamed for 5 and 7 min contained significantly (p<0.05) higher amounts of acteoside, isoacteoside, and 2′-acetylacteoside than directly oven-dried samples. In general, the highest levels of phenylethanoid glycosides were found in the steamed samples, suggesting that the above-mentioned pharmacological activities produced by phenylethanoid glycosides in C. deserticola slices may be enhanced by steaming treatment.
Furthermore, we found that the steaming time was crucial in determining the content of phenylethanoid glycosides. Echinacoside, cistanoside A, acteoside, and isoacteoside showed a similar increasing trend during the steaming process, which increased sharply (at 1, 3 min) and reached their maximum levels at 7 min. No significant changes were observed in the four above-mentioned phenylethanoid glycosides during the steaming process from 3 to 7 min. On the contrary, 2′-acetylacteoside increased significantly (p<0.05) with processing time. It is notable that the levels of phenylethanoid glycosides in slices steamed for 1 min were significantly (p<0.05) lower than directly oven-dried slices, with the exception of isoacteoside. Therefore, 1 min steaming of 3-mm fresh-cut C. deserticola was not long enough to inactivate above-mentioned enzymes. Higher total levels of the five phenylethanoid glycosides were observed when the slices were steamed for 5 and 7 min (3.20, 3.52 g/kg FW, respectively) rather than directly oven drying. Steaming from 5 to 7 min more effectively promoted the extraction of phenylethanoid glycosides from C. deserticola, leading to a higher level of phenylethanoid glycosides in the extracts.
Antioxidant ActivityThe antioxidant properties of the slices, as assayed by ORAC, DPPH, and FRAP, are presented in Fig. 2. As expected, the ORAC values showed a wide variation among the samples, ranging from 13.34 µmol TE/g FW in fresh samples, to 108.62 µmol TE/g FW at 7 min of steaming. During the steaming process, the ORAC value increased 4-fold between 1 and 7 min steaming. Similar trends were observed in both the DPPH and FRAP assays, showing rapid increases during the steaming treatment. Although the steam-treated samples initially had lower antioxidant values (at 1 min), they showed a much better retention of antioxidant capacity during the process. In the case of blanching, no significant differences in antioxidant properties were observed compared with directly oven drying.
Different letters (a–f) denote statistically significant differences between treatments (Duncan test, p<0.05, n=3).
The ORAC antioxidant activity in either raw stems or slices of C. deserticola has not been previously reported. However, the ethanol extracts of raw stems of C. deserticola has been measured in the DPPH and FRAP assays,28) showing high antioxidant activity, slightly lower than 2(3)-t-butyl-4-hydroxyanisole (BHA) and higher than BHT. Moreover, phenylethanoid glycosides isolated from C. deserticola exhibited strong DPPH scavenging activities, slightly lower than ascorbic acid29) and higher than α-tocopherol.2) C. deserticola can be a potential source of natural antioxidants, as antioxidant properties of the isolated pure compounds from C. deserticola were higher than that of some synthetic antioxidants. As shown in Table 2, BHT exhibited significantly (p<0.05) higher antioxidant properties than C. deserticola slices steamed for 7 min. Therefore, there is still a big gap between C. deserticola slices and synthetic antioxidants of equal quality.
| Analyte | ORAC (µmol TE/g) | DPPH (µmol TE/g) | FRAP (µmol TE/g) |
|---|---|---|---|
| Slices steamed for 7 min | 1212.44±65.04a | 259.04±15.90a | 130.77±6.65a |
| BHT | 3845.12±229.66b | 3044.82±341.86b | 1251.34±92.96b |
Values with different superscript letters in the same column are significant at p<0.05. Values were expressed as micromoles of Trolox per mass of dry analyte (µmol TE/g).
The DPPH assay uses both hydrogen atom transfer (HAT) and single electron transfer (SET) mechanisms, whereas the ORAC and FRAP assays follow the principles of HAT and SET reactions, respectively.30) In the present study, the general trends of antioxidant capacity evaluated by the three assays were very similar. Thus, we confirmed that dried slices of C. deserticola (steamed, directly oven-dried, and blanched) had significantly (p<0.05) higher levels of antioxidant activity than fresh ones. Furthermore, steaming for 5 and 7 min significantly (p<0.05) enhanced levels of antioxidant activity compared with directly oven drying and blanching. Overall, our results showed that steaming of fresh-cut C. deserticola slices was effective in preserving phenylethanoid glycoside levels and antioxidant activity.
Soluble Sugars, Polysaccharides, and Dilute Ethanol-Soluble ExtractsAs shown in Fig. 3, levels of soluble sugars and polysaccharides exhibited the following descending order: fresh>directly oven-dried>steamed>blanched. Blanched slices had very low levels of soluble sugars, polysaccharides, and dilute ethanol-soluble extract, corresponding well with their high weight loss. Fresh samples had a significantly (p<0.05) higher content of soluble sugars (62.89 g/kg FW) and polysaccharides (17.36 g/kg FW) than the other samples, suggesting that heat treatment (oven drying, steaming, blanching) on fresh-cut samples would reduce the extraction of soluble sugars and polysaccharides. In fact, heat treatment inhibited the hydrolysis of phenylethanoid glycosides to release the glucose, rhamnose and so on. Moreover, heat treatment, used as abiotic stress factors on fresh slices, gave rise to the synthesis of several phenylpropanoid compounds including phenylethanoid glycosides.27) Particularly, sugars contained in the slices were dissolved in the hot water to different extent by steaming or blanching. Thus, it is not surprising to see that the content of soluble sugars decreased by 23.88% in steaming and by 60.82% in blanching, while the content of polysaccharides decreased by 41.33% in steaming and by 53.83% in blanching, compared with fresh slices. It has been reported that the steaming process can increase reducing sugars and acidic polysaccharides in Ginseng Radix et Rhizoma,18) and monosugars, including galactose and glucose, in Rehmanniae Radix.17) However, the whole dried crude drugs studied in the above-mentioned literature were quite different from the fresh-cut slices used in the present study.
Different letters (a–e) denote statistically significant differences between treatments (Duncan test, p<0.05, n=3).
Directly oven-dried slices had the highest content of dilute ethanol-soluble extracts (89.26 g/kg FW), whereas the blanched slices had the lowest (47.60 g/kg FW). Although all the processed slices of C. deserticola met the standard of the Chinese Pharmacopoeia (2015 edition) to be qualified as Cistanches Herba, the blanched slices would bring fewer health benefits than directly oven-dried samples for the severe loss of dilute ethanol-soluble extracts. Regarding the steaming process, the trend of soluble sugars was very similar to the trend observed for the dilute ethanol-soluble extracts, decreasing gradually with no significant changes seen from 3 to 7 min. The concentration of polysaccharides fluctuated with a slight increase over the whole steaming period. It is notable that 7 min of steaming showed a well preservation of polysaccharides but a great loss of soluble sugars, whereas 5 min of steaming showed inversely, compared with directly oven drying.
We have reported the effect of steaming on bioactive compounds and antioxidant activity in fresh-cut C. deserticola for the first time, and provided important information for developing effective processes for post-harvest treatment of C. deserticola stems. Fresh slices showed the worst efficiency for extracting phenylethanoid glycosides and antioxidant compounds, revealing that these substances were prone to enzymatic degradation. In contrast, steamed samples had the highest levels of phenylethanoid glycosides and antioxidant activities. Although blanching slightly enhanced the content of acteoside, isoacteoside, and 2′-acetylacteoside compared with directly oven drying, the values for weight, soluble sugars, polysaccharides, and dilute ethanol-soluble extracts all dramatically decreased. For the steaming process, the levels of phenylethanoid glycosides and polysaccharides slightly increased over time. Steaming for 5 and 7 min significantly (p<0.05) enhanced total levels of the five phenylethanoid glycosides than directly oven drying. However, the longer the steaming process, the greater the decrease in weight, soluble sugars, and dilute ethanol-soluble extracts. No significant decrease in soluble sugars was observed when slices were steamed from 1 to 5 min compared with directly oven-dried samples. The steaming time had a consistent effect on the antioxidant properties, with a significant increase evaluated by the DPPH, ORAC, and FRAP assays. It was concluded that C. deserticola slices can be successfully treated with 5 to 7 min of steaming to improve the phenylethanoid glycoside levels and antioxidant activity, while preserving the amounts of soluble sugars, polysaccharides, and dilute ethanol-soluble extracts.
This work was supported by the project of the National Natural Science Foundation of China under Grant No. U14032224 and 81102748, and was also supported by Key Technologies R & D Program of Ningxia under Grant No. YKX-12. We greatly thank Dr. Zhiguo Ma for presenting standards, and Yucheng Chang and Yuan Liu for harvesting and collecting plant materials in the Ningxia Plantation of Cistanches Herba.
The authors declare no conflict of interest.
The online version of this article contains supplementary materials.
