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Nutritional and active ingredients of medicinal chrysanthemum flower heads affected by different drying methods
Industrial Crops & Products 104 (2017) 45–51
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Industrial Crops & Products journal homepage: www.elsevier.com/locate/indcrop
Nutritional and active ingredients of medicinal chrysanthemum flower heads affected by different drying methods ⁎
Xiao-Fei Shi, Jian-Zhou Chu , Yan-Fen Zhang, Cun-Qi Liu, Xiao-Qin Yao
MARK
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The College of Life Sciences, Hebei University, Baoding 071002, China
A R T I C L E I N F O
A B S T R A C T
Keywords: Chlorogenic acid Medicinal chrysanthemum Flavone Kill-enzyme torrefaction Microwave drying Steam kill-enzyme torrefaction
Drying treatments are considered to be the crucial step to preserve the plant’s beneficial properties in the postharvest processes. This paper mainly discussed the effects of four drying methods on quality of medicinal chrysanthemum flower heads, in order to providing the optimal drying conditions for different drying methods. The experimental design included: microwave drying, steam kill-enzyme torrefaction, kill-enzyme torrefaction and oven drying. The results showed that: (1) the contents of flavone and chlorogenic acids significantly increased with the increase of microwave power. However, microwave treatments significantly decreased amino acid content in flower heads. The optimal microwave power and microwave time were about 680–850 W and 8–13 min, respectively. In four drying methods, microwave drying was the most suitable method for keeping the higher contents of flavone, vitamin C and soluble sugar, considering efficiency and the energy consuming; (2) the contents of flavone and chlorogenic significantly increased with the increase of steam kill-enzyme time. However, the contents of amino acid, soluble sugar and vitamin C rose firstly and then decreased with the increase of steam kill-enzyme time. The optima steam kill-enzyme time was about 2–4 min; (3) the contents of flavone, chlorogenic acid and vitamin C increased firstly and then decreased with the increase of kill-enzyme time. Kill-enzyme torrefaction treatments significantly increased soluble sugar content. The optimal kill-enzyme time was about 0.5–1 min; and (4) the optimal oven temperature was about 55–65 °C, which could simultaneously gain the higher contents of active and nutritional ingredients in flowers. So, we should consider the specific conditions of each processing method when we choose the drying method.
1. Introduction Complex physiological and biochemical changes occur in harvested plant organs by the internal physiological changes and the external environment conditions, which can cause the chemical and nutritional ingredients in organs to reduce or even cause the decay of harvested plants (Cruz and Guadarrama, 2016; Lauxmann and Borsani, 2014). Drying treatments are widely used in the food industry, and considered to be the crucial step to preserve the plant’s beneficial properties in the post-harvest processes (Liu et al., 2016; Zhang et al., 2016; Yuan et al., 2015). Currently, many postharvest vegetables and fruits, such as coriander (Coriandrum sativum L.) (Sarimeseli, 2011; Divya et al., 2012), broccoli (Brassica oleracea L. var. botrytis L.) (Jin et al., 2014), cabbage (Brassica oleracea L.) (Phungamngoen et al., 2013), grapes (Vitis vinifera L.) (Kyraleou et al., 2016) and kiwifruit (Actinidia Chinensis) slices (Orikasa et al., 2014; Jafari et al., 2016) have been successfully preserved by drying treatments. From previous studies to know, most studies on drying methods
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Corresponding authors. E-mail addresses: [email protected] (J.-Z. Chu), [email protected] (X.-Q. Yao).
http://dx.doi.org/10.1016/j.indcrop.2017.04.021 Received 15 December 2016; Received in revised form 6 April 2017; Accepted 13 April 2017 0926-6690/ © 2017 Elsevier B.V. All rights reserved.
have been primarily done on fruits and vegetables. However, few works were also done on medicinal plants. Yang et al. (2007) reported that the microwave drying technology could be suitable for the concentration and dehydration of astragalus (Astragalus membranaceus) with the better preservation of astragalus active ingredients. The experiment performed by Wu (2015) indicated that freeze drying could affect physicochemical and associated functional properties in finger citron (Citrus medica L. var. sarcodactylis Swingle). In the experiment examined by An et al. (2014), different drying methods have significant influences on the quality of chinese magnoliavine fruit (Schisandrae Chinensis Fructus), and oven drying should be adopted to substitute sun drying by comprehensive analysis of the cost, content and practicality. However, previous studies have been mainly aimed at searching the suitable drying method, ignoring the systematical studies on the processing methods of medicinal plants. Medicinal chrysanthemum (Chrysanthemum morifolium Ramat) is commonly used in traditional Chinese medicine where they play a role in improving liver function, decreasing inflammation, improving eye-
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different kill-enzyme times of 0 (Z0), 0.5 (Z1), 1 (Z2), 2 (Z3), 4 (Z4) and 6 min (Z5). The samples after steam kill-enzyme torrefation were dried in thermostatic ovens at 65 °C. The final moisture contents were about 15 ± 0.73% dry basis (Jafari et al., 2016). Drying time was about 7–10 h.
sight and serving other anti-inflammatory detoxification roles (Chinese Medicine Dictionary, 2008). In recent years, the flowers of medicinal chrysanthemum act as common materials for functional and healthy tea or beverage due to their unique flavour, colour and health benefits (Yuan et al., 2015). The paper mainly explored the changing laws of active and nutritional ingredients of chrysanthemum flower heads in responses to different drying methods, and evaluated the optimal specific conditions of each processing method, in order to optimize the drying method which simultaneously preserves the higher contents of active and nutritional ingredients in flower heads.
2.2.3. Kill-enzyme torrefaction Fresh flowers samples were single-layer arranged on meshed trays, and put into thermostatic ovens to kill enzyme at 105 °C in six different kill-enzyme times of 0 (S0), 0.5 (S1), 1 (S2), 3 (S3), 5 (S4) and 7 min (S5). The samples after killing enzyme were dried in thermostatic ovens at 65 °C. The final moisture contents were about 15 ± 0.73% dry basis (Jafari et al., 2016). Drying time was 24 h.
2. Materials and methods 2.1. Equipments
2.2.4. Oven drying Fresh flowers samples were single-layer arranged on meshed trays and dried in thermostatic ovens at 55 °C (H1), 65 °C (H2) and 75 °C (H3), respectively. The final moisture contents were about 15 ± 0.73% dry basis (Jafari et al., 2016). Drying time was 24 h. After treatments, the samples were collected and ground into power and stored in airtight polythene bags until further use. Each treatment had five replicates, and all experiments were performed in duplicate.
Equipments used in this research are as the following: Microwave oven (Galanz, China), Electric blast drying oven (Teste, China), UV spectrophotometer (Unico, China), Ultrasonic cleaner (Kangjie, China), Electronic balance (Sartorius, China), and water-bath (Shengweili, China). 2.2. Plant material and experimental design
2.3. Measurement methods
Chrysanthemum seedlings obtained from Anguo Chinese herbal medicine planting base, Hebei province, China, were planted into the farmland. Fresh flowers were collected when 2/3 of the tubular flowers in the flower head were in bloom (Fig. 1). The harvested flowers were divided into four parts and treated with microwave drying, steam killenzyme torrefaction, kill-enzyme torrefaction and oven drying, respectively.
2.3.1. Malondialdehyde content Malondialdehyde (MDA) content was determined as described by Feng et al. (2009) with minor modifications. The samples (0.5 g) were homogenized in 5 mL of 20% (w/v) trichloroacetic acid (TCA), and the homogenate was centrifuged at 3500g for 20 min at room temperature. The supernatant was used to estimate MDA content. Results were expressed as μmol g−1 dried weight (DW).
2.2.1. Microwave drying Domestic microwave oven with maximum power output capacity of 850 W was used in this investigation. Fresh flowers samples were arranged as thin layer on the rotatable plate, and treated with four different power level 40%, 60%, 80% and 100% which is equivalent to 340 (W0), 510 (W1), 680 (W2) and 850 W (W3), respectively. Weight loss was recorded at regular intervals of time. Microwave drying continued till the final moisture contents were about 15 ± 0.73% dry basis (Jafari et al., 2016). Microwave time was about 22–24 min, 15–18 min, 10–13 min and 8–10 min at W0, W1, W2 and W3 treatments, respectively.
2.3.2. Phenylalanine ammonia lyase enzyme and cinnamic acid-4hydroxylase activity Phenylalanine ammonia lyase (PAL) was determined as described by Liu et al. (2016a,b) with minor modifications. PAL activity was extracted from 0.5 g fresh flower with 5 mL of borate buffer (pH 8.7) containing 5 mmol L−1 mercaptoethanol and 0.1% polyvinylpolypyrrolidone. The extracts were centrifuged at 10 000g for 15 min at 4 °C. The reaction mixture contained 0.5 mL crude enzyme, 1 mL 0.02 mol L−1 L-phenylalanine and 1 mL borate buffer (0.05 mol L−1, pH 8.7). The reaction was incubated at 30 °C for 30 min, and stopped by the addition of 1 mL HCl (2 mol L−1). The activity of PAL was estimated by measuring at 290 nm, and expressed as A h −1 g −1 DW. Cinnamic acid-4-hydroxylase (C4H) was determined according to the method described by Lamb and Rubery (1975) with minor modifications. C4H was extracted from 0.5 g fresh flower with 5 mL of 0.1 mol L−1 cold phosphate buffer (pH 7.6) containing 0.25 mol L−1 sucrose, 0.5 mmol L−1 EDTA, 2 mmol L−1 mercaptoethanol. Extracts were centrifuged at 10 000g for 15 min at 4 °C. The reaction mixture containing 0.2 mL crude enzyme, 0.2 mL 50 mmol L−1 transcinnamic acid, 0.2 mL 0.4 g L−1 NADPH and 3 mL 0.1 mol L−1 phosphate buffer (pH 7.6), was incubated at 30 °C for 30 min, and was stopped by the addition of 0.2 mL HCl (6 mol L−1). The activity of C4H was estimated by measuring at 290 nm.
2.2.2. Steam kill-enzyme torrefaction Fresh flowers samples were single-layer arranged on meshed trays, and were immediately treated with boiling steam at 100 °C in six
2.3.3. Photosynthetic pigments content Carotenoids were extracted from 0.5 g samples with 80% acetone, and calculated according to the method described by Lichtenthaler (1987). 2.3.4. Flavone and chlorogenic acid content Flavone content was determined according to the method described by He and Liu (2007) with minor modifications. Flavone was extracted from 0.5 g dried flower with 20 mL of 50% ethanol solution in
Fig. 1. The harvested flowers of medical chrysanthemum.
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3.2. The effects of drying methods on the activities of PAL and C4H in flower heads
ultrasonic bath for 30 min. The reaction mixture contained 5 mL extracted solution, 8 mL of 1.5% AlCl3 and 4 mL acetic acid-sodium acetate (pH 5.5). After 30 min, Flavone was estimated by measuring at 420 nm, and expressed as g rutin 100 g−1 DW. Chlorogenic acid content was measured according to the method described by Zhang et al. (2006a,b) with minor modification. Chlorogenic acid was extracted from 0.5 g dried flower with 20 mL of 50% methanol in ultrasonic bath for 30 min. The reaction mixture contained 5 mL extracted solution and 0.5 mL of 0.02 mol L−1 FeCl3. After 60 min, Chlorogenic acid content was estimated by measuring at 755 nm, and expressed as% DW.
PAL and C4H are the key enzymes of the phenylpropanoid pathway. PAL catalyzes the deamination of L-phenylalanine to trans-cinnamic acid, and then C4H transforms trans-cinnamic acid to p-coumaric acid (Zucker, 1969; Nadernejad et al., 2013). In the present study, the activities of PAL and C4H were not only related to drying methods, but also affected by specific drying condition for different drying methods. In four drying methods, the flower heads treated by microwave and oven temperature treatments exhibited the higher activities of PAL and C4H (Fig. 3). The activities of PAL and C4H in flower heads were significantly increased with the increase of microwave power, indicating that the higher power and the less time in microwave processing were beneficial for promoting secondary metabolism processes in harvested flower heads. In kill-enzyme torrefaction, the activities of PAL and C4H in flower heads rose firstly and dropped subsequently with the increase of the kill-enzyme time, and reached the most value at S2 (1 min) and S3 (3 min), respectively. The change of PAL and C4H activity in flower heads exhibited differently in steam kill-enzyme torrefaction and oven drying. PAL activity was significantly decreased with the increase of steam kill-enzyme time and oven temperature. However, the higher oven temperature (75 °C) significantly increased C4H activity compared with the lower oven temperature. The reason is not clear, which need to study further.
2.3.5. Free amino acid, vitamin C content and soluble sugar content Free amino acid content was measured according to the method described by Li et al. (2004) with minor modification. Amino acid was extracted from 0.5 g dried flower with 8 mL of 10% acetic acid solution in ultrasonic bath for 30 min. The reaction mixture contained 2 mL of the supernatant, 3 mL of ninhydrin and 0.1 mL of ascorbic acid, and was heated in a water bath (100 °C) for 15 min. After cooling, Amino acid content was estimated by measuring at 570 nm, and expressed as μg g−1 DW. Vitamin C (ascorbic acid) was determined according to State Standard of the People’s Republic of China (GB 12392-90) with minor modifications. Vitamin C was extracted from 0.5 g dried flower with 10 mL of 1% oxalic acid solution in ultrasonic bath for 30 min 0.5 g active carbon was added to 10 mL supernatant and filtered again. The reaction mixture contained 5 mL supernatant, 5 mL of 2% thiourea solution, 1.0 mL of 2% 2, 4-dinitrophenylhydrazine solution, and was kept in 37 ± 0.5 °C water bath for 3 h. After reaction, 5 mL of 85% sulfuric acid was gradually added to the reaction solution. Vitamin C content was estimated by measuring at 500 nm, and expressed as mg 100 g−1 DW. Soluble sugar was measured according to the method described by Machado et al. (2013). Dried flower (0.5 g) was extracted with 5 mL of distilled water in a water bath (100 °C) for 10 min. The reaction mixture contained 1 mL supernatant, 1 mL distilled water and 5 mL anthrone-H2SO4, and was heated in a water bath (100 °C) for 10 min. Soluble sugar was estimated by measuring at 625 nm, and expressed as mg g−1 DW.
3.3. The effects of drying methods on carotenoids content in flower heads Carotenoids have the function of absorbing and transmitting electron, and protect the chlorophyll, chloroplasts and cells (Tracewell et al., 2001). Microwave treatments significantly decreased carotenoids content with the increase of microwave power (Fig. 4A). Similar results were also reported in previous publication (Gao et al., 2012). The reason may be that the high microwave power could cause the absorbing of flowers to the microwave and led to rise sharply in the energy of flower, which is not conducive to the retention of carotenoids. Carotenoids content were significantly increased with the increase of oven temperatures. Long et al. (2011) reported that carotenoids in tomatoes (Lycopersicon esculentum Mill.) and carrots (Daucus carota L. var. sativa Hoffm.) could keep steady in 70 °C, but will be degradation in 100 °C. A t the same time, we also found that carotenoids content in flower heads was also related to treatment time in 100 °C or 105 °C. In the study condition, the optimal time of steam kill-enzyme (100 °C) and kill-enzyme (105 °C) was 1 min, which could better keep carotenoids steady in harvested flower heads.
2.4. Statistical analysis All data were presented as mean ± SE. The variance was analyzed by one-way ANOVA, followed by Duncan’s test for multiple comparisons. Significance was set at 0.05 levels. All analyses were executed using the Software Statistical Package for the Social Science (SPSS) version 13.0.
3.4. The effects of drying methods on flavone and chlorogenic acid content in flower heads Many studies have shown that pharmacological effects of medicinal plants were relevant with active ingredients content (Wu et al., 2012). Flavonoids and chlorogenic acid are main active ingredients in flowers of medicinal chrysanthemum. The present research indicated that flavone content in flower heads was significantly increased with the increase of the microwave power and stem kill-enzyme time (Fig. 5A), which was consistent with the changing trend of PAL and C4H activity, further indicating that the higher power and the less time in microwave processing might be beneficial for keeping secondary metabolism contents in harvested flower heads. In kill-enzyme torrefaction, flavone content first increased and then decreased with the increase of killenzyme time. The higher over temperature (75 °C) treatment significantly decreased the flavone content compared with the lower over temperature (55 and 65 °C). In the four drying methods, the flower heads treated by the higher microwave power (680 W and 850 W) exhibited the higher flavonoid content (1.43 and 1.54 mg g−1 DW), followed by kill-enzyme dried flower heads (1.52 mg g−1 DW). In
3. Results and discussion 3.1. The effects of drying methods on MDA content in flower heads MDA is usually used as an indicator in stressful physiology of plants (Yu et al., 2004). Fig. 2 indicated that MDA content in flower heads was significantly increased with the increase of microwave power and steam kill-enzyme time (except for Z3 treatment), and was the highest at W3 (850 W) and Z5 (6 min) treatments, respectively, suggested that lipid peroxidation and oxidative stress in flower heads was increased. However, MDA content in flowers decreased with the increase of killenzyme time and oven temperature, suggesting that kill-enzyme and the higher oven temperature could reduce lipid peroxidation and damage in flower heads.
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Fig. 2. The effects of four drying methods on the MDA content in medicinal chrysanthemum flower heads. Microwave drying (W0, 340 W; W1, 510 W; W2, 680 W; W3, 850 W), steam kill-enzyme torrefaction (Z0, 0 min; Z1, 0.5 min; Z2, 1 min; Z3, 2 min; Z4, 4 min; Z5, 6 min), kill-enzyme torrefaction (S0, 0 min; S1, 0.5 min; S2, 1 min; S3, 3 min; S4, 5 min; S5, 7 min) and oven drying (H1, 55 °C; H2, 65 °C; H3, 75 °C). The bars with different letters are significantly different from each other at the same drying method (P < 0.05). Values are means of five replicates ± SE.
Fig. 3. The effects of four drying methods on PAL activity (A) and C4H activity (B) in medicinal chrysanthemum flower heads. Microwave drying (W0, 340 W; W1, 510 W; W2, 680 W; W3, 850 W), Steam kill-enzyme torrefaction (Z0, 0 min; Z1, 0.5 min; Z2, 1 min; Z3, 2 min; Z4, 4 min; Z5, 6 min), Kill-enzyme torrefaction (S0, 0 min; S1, 0.5 min; S2, 1 min; S3, 3 min; S4, 5 min; S5, 7 min) and oven drying (H1, 55 °C; H2, 65 °C; H3, 75 °C). The bars with different letters are significantly different from each other at the same drying method (P < 0.05). Values are means of five replicates ± SE.
addition, the flower heads treated by 6 min steam kill-enzyme had higher flavone content (1.13 mg g−1 DW) than the oven dried flower heads. As a polyphenolic material, chlorogenic acid is thermal sensitive and oxygen sensitive and easily degraded at high temperature and atmospheric environment (Liu et al., 2015). Liu et al. (2015) studied on the changes of chlorogenic acid in Flos Lonicerae with heater’s temperature (90–130 °C). Results indicated that chlorogenic acid content climbed with the increase of heater’s temperature and reached a peak at 110 °C, then fell rapidly at higher heater’s temperature. In the present study, chlorogenic acid in chrysanthemum flower heads significantly decreased with the increase of oven temperature (55–75 °C), and rose firstly and dropped subsequently with the increase of kill-enzyme time (105 °C) (Fig. 5B). Chlorogenic acid content increased to a peak value when kill-enzyme time was 1 min, further indicated that the thermal stability of chlorogenic acid was not only affected by heater’s tempera-
ture, but also by heating duration. However, chlorogenic acid content in flower heads was significantly increased with the increase of microwave power and steam kill-enzyme time (Fig. 5B). In the four drying methods, the flower heads treated by the kill-enzyme torrefaction contained the higher chlorogenic acids content, and the chlorogenic acid reached a peak value (0.363 mg g−1 DW) when the killenzyme time was 1 min.
3.5. The effects of drying methods on the contents of free amino acid, vitamin C content and soluble sugar in flower heads Free amino acid is the precursor substance of protein synthesis. Peng et al. (2006) reported that microwave drying and oven drying (60 °C) could increase free amino acids content of flos lonicerace. Fig. 6A indicated that free amino acids content decreased with the increase of the microwave power, kill-enzyme time and oven temperature. The 48
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Fig. 4. The effects of four drying methods on carotenoids content in medicinal chrysanthemum flower heads. Microwave drying (W0, 340 W; W1, 510 W; W2, 680 W; W3, 850 W), Steam kill-enzyme torrefaction (Z0, 0 min; Z1, 0.5 min; Z2, 1 min; Z3, 2 min; Z4, 4 min; Z5, 6 min), Kill-enzyme torrefaction (S0, 0 min; S1, 0.5 min; S2, 1 min; S3, 3 min; S4, 5 min; S5, 7 min) and oven drying (H1, 55 °C; H2, 65 °C; H3, 75 °C). The bars with different letters are significantly different from each other at the same drying method (P < 0.05). Values are means of five replicates ± SE.
is involved in regulating blood pressure and preventing arteriosclerosis. Vitamin C in plant tissues can be used as substrates for the enzyme to scavenge active oxygen, protecting plant from the oxidative damage. In the experiment performed by Kumar et al. (2015), room-dried Hibiscus sabdariffa leaf powder extracts had the highest content of vitamin C than freeze-dried, infrared-dried, crossflow-dried, oven-dried, sun-dried and microwave-dried. In the present study, the vitamin C in flower heads was not only related to drying methods, but affected by specific drying conditions for the different methods (Fig. 6B). In four drying methods, the flower heads treated by the W1 (510 W) and W2 (680 W) contained the higher vitamin C content (9.32 mg g−1 DW, 8.76 mg g−1 DW). In steam kill-enzyme torrefaction and kill-enzyme torrefaction, vitamin C content in flower heads reached a peak value at Z1 (0.5 min)
reason might be that the higher microwave power, the higher oven temperature and the longer kill-enzyme time led to the degradation of amino acid. In steam kill-enzyme torrefaction, Z1 (0.5 min) and Z2 (1 min) treatments significantly increased free amino acid content in flower heads compared with the control (Z0), but the longer steam killenzyme time significantly decreased free amino acid content, speculated that the shorter steam kill-enzyme time did not cause too much damage to the flower heads, which may be the reason for the increase in free amino acids content at the shorter steam kill-enzyme time. In the four drying methods, the amino acid content in flower heads treated by microwave treatments was the lowest relative to the other drying methods. Vitamin C is very important vitamin in human body and animal that
Fig. 5. The effects of four drying methods on flavone (A) and chlorogenic acid (B) content in medicinal chrysanthemum flower heads. Microwave drying (W0, 340 W; W1, 510 W; W2, 680 W; W3, 850 W), Steam kill-enzyme torrefaction (Z0, 0 min; Z1, 0.5 min; Z2, 1 min; Z3, 2 min; Z4, 4 min; Z5, 6 min), Kill-enzyme torrefaction (S0, 0 min; S1, 0.5 min; S2, 1 min; S3, 3 min; S4, 5 min; S5, 7 min) and oven drying (H1, 55 °C; H2, 65 °C; H3, 75 °C). The bars with different letters are significantly different from each other at the same drying method (P < 0.05). Values are means of five replicates ± SE.
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Fig. 6. The effects of four drying methods on amino acid (A), vitamin C (B) and soluble sugar (C) content in medicinal chrysanthemum flower heads. Microwave drying (W0, 340 W; W1, 510 W; W2, 680 W; W3, 850 W), Steam kill-enzyme torrefaction (Z0, 0 min; Z1, 0.5 min; Z2, 1 min; Z3, 2 min; Z4, 4 min; Z5, 6 min), Kill-enzyme torrefaction (S0, 0 min; S1, 0.5 min; S2, 1 min; S3, 3 min; S4, 5 min; S5, 7 min) and oven drying (H1, 55 °C; H2, 65 °C; H3, 75 °C). The bars with different letters are significantly different from each other at the same drying method (P < 0.05). Values are means of five replicates ± SE.
methods. Soluble sugar content in flower heads rose firstly and decreased subsequently with the increase of microwave power and steam kill-enzyme time, and reached a peak value at W2 (680 W) treatment and Z3 (2 min) treatment, respectively.
and S1 (0.5 min), respectively. However, vitamin C content significantly decreased with the increase of oven temperature. These results indicated that vitamin C was easy to be decomposed at higher temperature and higher microwave power, and the longer time of steam kill-enzyme and kill-enzyme could lead to degradation of vitamin C in flower heads. Shahraki et al. (2014) also reported that the color changes and the texture of dried sesame seeds were not only related to drying temperature, but related to drying time. So, we should consider the specific conditions of each processing method when drying method was choose. Polysaccharides (carbohydrates) are utilized as a source of energy, structure-forming material, and water maintaining hydrocolloids. Drying conditions have a significant influence on technological and functional characteristics of carbohydrates (Dehnad et al., 2016). Dehnad et al. (2016) reported that the influence of drying process variable on the carbohydrate-based materials by summarizing up the published literatures. As shown in Fig. 6C, the soluble sugar content in flower heads was not only affected by drying methods, but also related to specific conditions of each processing method. In four drying methods, the flower heads treated by kill-enzyme torrefaction exhibited the lower soluble sugar content relative to the other three drying
4. Conclusions The active and nutritional ingredients content in harvested flower heads was not only related to drying methods, but also significantly influenced by the specific conditions of each processing method. Comprehensive analysis revealed that: (1) microwave drying was the most suitable method for keeping the higher contents of flavone, vitamin C and soluble sugar, considering efficiency and the energy consuming. The optimal microwave power and treatment time were about 680–850 W and about 8–13 min, respectively; (2) the optimal time of steam kill-enzyme and kill-enzyme were about 2–4 min and 0.5–1 min, respectively; and (3) the optimal oven temperature was about 55–65 °C, which could simultaneously gain the higher contents of active and nutritional ingredients in flowers. So, we should consider the specific conditions of each processing method when the drying method was selected. 50
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Acknowledgements This work has been supported by National Natural Science Foundation of China (No. 31300321), and Natural Science Foundation of Hebei Province, China (No. C2012201080). References An, K.L., Li, D.K., Zhou, D.Z., Ye, Z.L., Guo, Q.S., 2014. Influence of different drying methods on quality of Schisandrae Chinensis Fructus. China J. Chin. Meter. Med. 15, 2900–2906. Chinese Medicine Dictionary, 2008. Shanghai Science and Technology Press (in Chinese). Cruz, L.G., Guadarrama, S.V., 2016. Postharvest quality, soluble phenols, betalains content, and antioxidant activity of Stenocereus pruinosus and Stenocereus stellatus fruit. Postharvest Biol. Technol. 111, 69–76. Dehnad, D., Jafari, S.M., Afrasiabi, M., 2016. Influence of drying on functional properties of food biopolymers: from traditional to novel dehydration techniques. Trends Food Sci. Tech. 57, 116–131. Divya, P., Puthusseri, B., Neelwarne, B., 2012. Carotenoid content: its stability during drying and the antioxidant activity of commercial coriander (Coriandrum sativum L.) varieties. Food Res. Int. 45, 342–350. Feng, R.W., Wei, C.Y., Tu, S.X., Wu, F.C., Yang, L.S., 2009. Antimony accumulation and antioxidative responses in four fern plants. Plant Soil 317, 93–101. Gao, M., Liu, X.G., Chen, M.M., Xiao, S.D., Zhong, X., Liu, Z., Yao, Z.D., 2012. Effects on carotene retention in carrots by different processing. Grain Sci. Technol. Eco. 37, 53–579 (in Chinese). He, S.M., Liu, J.L., 2007. Study on the determination method of flavone content in tea. Chin. J. Anal. Chem. 35, 1365–1368 (in Chinese). Jafari, S.M., Azizi, D., Mirzaei, H., Dehnad, D., 2016. Comparing quality characteristics of oven-dried and refractance window-dried kiwifruits. J. Food Process. Pres. 40, 362–372. Jin, X., Oliviero, T., Vandersman, R.G.M., Verkerk, R., Dekker, M., van Boxtel, A.J.B., 2014. Impact of different drying trajectories on degradation of nutritional compounds in broccoli (Brassica oleracea var. italica). LWT-Food Sci. Technol. 59, 189–195. Kumar, S.S., Manoj, P., Shetty, N.P., Giridhar, P., 2015. Effect of different drying methods on chlorophyll, ascorbic acid and antioxidant compounds retention of leaves of Hibiscus sabdariffa L. J. Sci. Food Agric. 95, 1812–1820. Kyraleou, M., Koundouras, S., Kallithraka, S., Theodorou, N., Proxenia, N., Kotseridis, Y., 2016. Effect of irrigation regime on anthocyanin content and antioxidant activity of Vitis vinifera L. cv. Syrah grapes under semiarid conditions. J. Sci. Food Agric. 96, 988–996. Lamb, C.J., Rubery, P.H., 1975. A spectrophotometric assay for rans-cinnamic acid 4hydroxylase activity. Anal. Biochem. 68, 554–561. Lauxmann, M., Borsani, J., 2014. Deciphering the metabolic pathways influencing heat and cold responses during post-harvest physiology of peach fruit. Plant Cell Environ. 37, 601–616. Li, H.S., Sun, Q., Zhao, S.J., Zhang, W.H., 2004. Plant Physiological and Biochemical Principle and Experimental Technique. Higher Education Press Beijing (in Chinese). Lichtenthaler, H.K., 1987. Chlorophylls and carotenoids: pigments of photosynthetic biomembranes. Meth. Enzymol. 148, 350–382. Liu, Y.H., Miao, S.A., Wu, J.Y., Liu, J.X., Yu, H.C., Duan, X., 2015. Drying characteristics and modeling of vacuum far-infrared radiation drying of Flos Lonicerae. J. Food Proc. Preserv. 39, 338–348.
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Industrial Crops & Products journal homepage: www.elsevier.com/locate/indcrop
Nutritional and active ingredients of medicinal chrysanthemum flower heads affected by different drying methods ⁎
Xiao-Fei Shi, Jian-Zhou Chu , Yan-Fen Zhang, Cun-Qi Liu, Xiao-Qin Yao
MARK
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The College of Life Sciences, Hebei University, Baoding 071002, China
A R T I C L E I N F O
A B S T R A C T
Keywords: Chlorogenic acid Medicinal chrysanthemum Flavone Kill-enzyme torrefaction Microwave drying Steam kill-enzyme torrefaction
Drying treatments are considered to be the crucial step to preserve the plant’s beneficial properties in the postharvest processes. This paper mainly discussed the effects of four drying methods on quality of medicinal chrysanthemum flower heads, in order to providing the optimal drying conditions for different drying methods. The experimental design included: microwave drying, steam kill-enzyme torrefaction, kill-enzyme torrefaction and oven drying. The results showed that: (1) the contents of flavone and chlorogenic acids significantly increased with the increase of microwave power. However, microwave treatments significantly decreased amino acid content in flower heads. The optimal microwave power and microwave time were about 680–850 W and 8–13 min, respectively. In four drying methods, microwave drying was the most suitable method for keeping the higher contents of flavone, vitamin C and soluble sugar, considering efficiency and the energy consuming; (2) the contents of flavone and chlorogenic significantly increased with the increase of steam kill-enzyme time. However, the contents of amino acid, soluble sugar and vitamin C rose firstly and then decreased with the increase of steam kill-enzyme time. The optima steam kill-enzyme time was about 2–4 min; (3) the contents of flavone, chlorogenic acid and vitamin C increased firstly and then decreased with the increase of kill-enzyme time. Kill-enzyme torrefaction treatments significantly increased soluble sugar content. The optimal kill-enzyme time was about 0.5–1 min; and (4) the optimal oven temperature was about 55–65 °C, which could simultaneously gain the higher contents of active and nutritional ingredients in flowers. So, we should consider the specific conditions of each processing method when we choose the drying method.
1. Introduction Complex physiological and biochemical changes occur in harvested plant organs by the internal physiological changes and the external environment conditions, which can cause the chemical and nutritional ingredients in organs to reduce or even cause the decay of harvested plants (Cruz and Guadarrama, 2016; Lauxmann and Borsani, 2014). Drying treatments are widely used in the food industry, and considered to be the crucial step to preserve the plant’s beneficial properties in the post-harvest processes (Liu et al., 2016; Zhang et al., 2016; Yuan et al., 2015). Currently, many postharvest vegetables and fruits, such as coriander (Coriandrum sativum L.) (Sarimeseli, 2011; Divya et al., 2012), broccoli (Brassica oleracea L. var. botrytis L.) (Jin et al., 2014), cabbage (Brassica oleracea L.) (Phungamngoen et al., 2013), grapes (Vitis vinifera L.) (Kyraleou et al., 2016) and kiwifruit (Actinidia Chinensis) slices (Orikasa et al., 2014; Jafari et al., 2016) have been successfully preserved by drying treatments. From previous studies to know, most studies on drying methods
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Corresponding authors. E-mail addresses: [email protected] (J.-Z. Chu), [email protected] (X.-Q. Yao).
http://dx.doi.org/10.1016/j.indcrop.2017.04.021 Received 15 December 2016; Received in revised form 6 April 2017; Accepted 13 April 2017 0926-6690/ © 2017 Elsevier B.V. All rights reserved.
have been primarily done on fruits and vegetables. However, few works were also done on medicinal plants. Yang et al. (2007) reported that the microwave drying technology could be suitable for the concentration and dehydration of astragalus (Astragalus membranaceus) with the better preservation of astragalus active ingredients. The experiment performed by Wu (2015) indicated that freeze drying could affect physicochemical and associated functional properties in finger citron (Citrus medica L. var. sarcodactylis Swingle). In the experiment examined by An et al. (2014), different drying methods have significant influences on the quality of chinese magnoliavine fruit (Schisandrae Chinensis Fructus), and oven drying should be adopted to substitute sun drying by comprehensive analysis of the cost, content and practicality. However, previous studies have been mainly aimed at searching the suitable drying method, ignoring the systematical studies on the processing methods of medicinal plants. Medicinal chrysanthemum (Chrysanthemum morifolium Ramat) is commonly used in traditional Chinese medicine where they play a role in improving liver function, decreasing inflammation, improving eye-
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different kill-enzyme times of 0 (Z0), 0.5 (Z1), 1 (Z2), 2 (Z3), 4 (Z4) and 6 min (Z5). The samples after steam kill-enzyme torrefation were dried in thermostatic ovens at 65 °C. The final moisture contents were about 15 ± 0.73% dry basis (Jafari et al., 2016). Drying time was about 7–10 h.
sight and serving other anti-inflammatory detoxification roles (Chinese Medicine Dictionary, 2008). In recent years, the flowers of medicinal chrysanthemum act as common materials for functional and healthy tea or beverage due to their unique flavour, colour and health benefits (Yuan et al., 2015). The paper mainly explored the changing laws of active and nutritional ingredients of chrysanthemum flower heads in responses to different drying methods, and evaluated the optimal specific conditions of each processing method, in order to optimize the drying method which simultaneously preserves the higher contents of active and nutritional ingredients in flower heads.
2.2.3. Kill-enzyme torrefaction Fresh flowers samples were single-layer arranged on meshed trays, and put into thermostatic ovens to kill enzyme at 105 °C in six different kill-enzyme times of 0 (S0), 0.5 (S1), 1 (S2), 3 (S3), 5 (S4) and 7 min (S5). The samples after killing enzyme were dried in thermostatic ovens at 65 °C. The final moisture contents were about 15 ± 0.73% dry basis (Jafari et al., 2016). Drying time was 24 h.
2. Materials and methods 2.1. Equipments
2.2.4. Oven drying Fresh flowers samples were single-layer arranged on meshed trays and dried in thermostatic ovens at 55 °C (H1), 65 °C (H2) and 75 °C (H3), respectively. The final moisture contents were about 15 ± 0.73% dry basis (Jafari et al., 2016). Drying time was 24 h. After treatments, the samples were collected and ground into power and stored in airtight polythene bags until further use. Each treatment had five replicates, and all experiments were performed in duplicate.
Equipments used in this research are as the following: Microwave oven (Galanz, China), Electric blast drying oven (Teste, China), UV spectrophotometer (Unico, China), Ultrasonic cleaner (Kangjie, China), Electronic balance (Sartorius, China), and water-bath (Shengweili, China). 2.2. Plant material and experimental design
2.3. Measurement methods
Chrysanthemum seedlings obtained from Anguo Chinese herbal medicine planting base, Hebei province, China, were planted into the farmland. Fresh flowers were collected when 2/3 of the tubular flowers in the flower head were in bloom (Fig. 1). The harvested flowers were divided into four parts and treated with microwave drying, steam killenzyme torrefaction, kill-enzyme torrefaction and oven drying, respectively.
2.3.1. Malondialdehyde content Malondialdehyde (MDA) content was determined as described by Feng et al. (2009) with minor modifications. The samples (0.5 g) were homogenized in 5 mL of 20% (w/v) trichloroacetic acid (TCA), and the homogenate was centrifuged at 3500g for 20 min at room temperature. The supernatant was used to estimate MDA content. Results were expressed as μmol g−1 dried weight (DW).
2.2.1. Microwave drying Domestic microwave oven with maximum power output capacity of 850 W was used in this investigation. Fresh flowers samples were arranged as thin layer on the rotatable plate, and treated with four different power level 40%, 60%, 80% and 100% which is equivalent to 340 (W0), 510 (W1), 680 (W2) and 850 W (W3), respectively. Weight loss was recorded at regular intervals of time. Microwave drying continued till the final moisture contents were about 15 ± 0.73% dry basis (Jafari et al., 2016). Microwave time was about 22–24 min, 15–18 min, 10–13 min and 8–10 min at W0, W1, W2 and W3 treatments, respectively.
2.3.2. Phenylalanine ammonia lyase enzyme and cinnamic acid-4hydroxylase activity Phenylalanine ammonia lyase (PAL) was determined as described by Liu et al. (2016a,b) with minor modifications. PAL activity was extracted from 0.5 g fresh flower with 5 mL of borate buffer (pH 8.7) containing 5 mmol L−1 mercaptoethanol and 0.1% polyvinylpolypyrrolidone. The extracts were centrifuged at 10 000g for 15 min at 4 °C. The reaction mixture contained 0.5 mL crude enzyme, 1 mL 0.02 mol L−1 L-phenylalanine and 1 mL borate buffer (0.05 mol L−1, pH 8.7). The reaction was incubated at 30 °C for 30 min, and stopped by the addition of 1 mL HCl (2 mol L−1). The activity of PAL was estimated by measuring at 290 nm, and expressed as A h −1 g −1 DW. Cinnamic acid-4-hydroxylase (C4H) was determined according to the method described by Lamb and Rubery (1975) with minor modifications. C4H was extracted from 0.5 g fresh flower with 5 mL of 0.1 mol L−1 cold phosphate buffer (pH 7.6) containing 0.25 mol L−1 sucrose, 0.5 mmol L−1 EDTA, 2 mmol L−1 mercaptoethanol. Extracts were centrifuged at 10 000g for 15 min at 4 °C. The reaction mixture containing 0.2 mL crude enzyme, 0.2 mL 50 mmol L−1 transcinnamic acid, 0.2 mL 0.4 g L−1 NADPH and 3 mL 0.1 mol L−1 phosphate buffer (pH 7.6), was incubated at 30 °C for 30 min, and was stopped by the addition of 0.2 mL HCl (6 mol L−1). The activity of C4H was estimated by measuring at 290 nm.
2.2.2. Steam kill-enzyme torrefaction Fresh flowers samples were single-layer arranged on meshed trays, and were immediately treated with boiling steam at 100 °C in six
2.3.3. Photosynthetic pigments content Carotenoids were extracted from 0.5 g samples with 80% acetone, and calculated according to the method described by Lichtenthaler (1987). 2.3.4. Flavone and chlorogenic acid content Flavone content was determined according to the method described by He and Liu (2007) with minor modifications. Flavone was extracted from 0.5 g dried flower with 20 mL of 50% ethanol solution in
Fig. 1. The harvested flowers of medical chrysanthemum.
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3.2. The effects of drying methods on the activities of PAL and C4H in flower heads
ultrasonic bath for 30 min. The reaction mixture contained 5 mL extracted solution, 8 mL of 1.5% AlCl3 and 4 mL acetic acid-sodium acetate (pH 5.5). After 30 min, Flavone was estimated by measuring at 420 nm, and expressed as g rutin 100 g−1 DW. Chlorogenic acid content was measured according to the method described by Zhang et al. (2006a,b) with minor modification. Chlorogenic acid was extracted from 0.5 g dried flower with 20 mL of 50% methanol in ultrasonic bath for 30 min. The reaction mixture contained 5 mL extracted solution and 0.5 mL of 0.02 mol L−1 FeCl3. After 60 min, Chlorogenic acid content was estimated by measuring at 755 nm, and expressed as% DW.
PAL and C4H are the key enzymes of the phenylpropanoid pathway. PAL catalyzes the deamination of L-phenylalanine to trans-cinnamic acid, and then C4H transforms trans-cinnamic acid to p-coumaric acid (Zucker, 1969; Nadernejad et al., 2013). In the present study, the activities of PAL and C4H were not only related to drying methods, but also affected by specific drying condition for different drying methods. In four drying methods, the flower heads treated by microwave and oven temperature treatments exhibited the higher activities of PAL and C4H (Fig. 3). The activities of PAL and C4H in flower heads were significantly increased with the increase of microwave power, indicating that the higher power and the less time in microwave processing were beneficial for promoting secondary metabolism processes in harvested flower heads. In kill-enzyme torrefaction, the activities of PAL and C4H in flower heads rose firstly and dropped subsequently with the increase of the kill-enzyme time, and reached the most value at S2 (1 min) and S3 (3 min), respectively. The change of PAL and C4H activity in flower heads exhibited differently in steam kill-enzyme torrefaction and oven drying. PAL activity was significantly decreased with the increase of steam kill-enzyme time and oven temperature. However, the higher oven temperature (75 °C) significantly increased C4H activity compared with the lower oven temperature. The reason is not clear, which need to study further.
2.3.5. Free amino acid, vitamin C content and soluble sugar content Free amino acid content was measured according to the method described by Li et al. (2004) with minor modification. Amino acid was extracted from 0.5 g dried flower with 8 mL of 10% acetic acid solution in ultrasonic bath for 30 min. The reaction mixture contained 2 mL of the supernatant, 3 mL of ninhydrin and 0.1 mL of ascorbic acid, and was heated in a water bath (100 °C) for 15 min. After cooling, Amino acid content was estimated by measuring at 570 nm, and expressed as μg g−1 DW. Vitamin C (ascorbic acid) was determined according to State Standard of the People’s Republic of China (GB 12392-90) with minor modifications. Vitamin C was extracted from 0.5 g dried flower with 10 mL of 1% oxalic acid solution in ultrasonic bath for 30 min 0.5 g active carbon was added to 10 mL supernatant and filtered again. The reaction mixture contained 5 mL supernatant, 5 mL of 2% thiourea solution, 1.0 mL of 2% 2, 4-dinitrophenylhydrazine solution, and was kept in 37 ± 0.5 °C water bath for 3 h. After reaction, 5 mL of 85% sulfuric acid was gradually added to the reaction solution. Vitamin C content was estimated by measuring at 500 nm, and expressed as mg 100 g−1 DW. Soluble sugar was measured according to the method described by Machado et al. (2013). Dried flower (0.5 g) was extracted with 5 mL of distilled water in a water bath (100 °C) for 10 min. The reaction mixture contained 1 mL supernatant, 1 mL distilled water and 5 mL anthrone-H2SO4, and was heated in a water bath (100 °C) for 10 min. Soluble sugar was estimated by measuring at 625 nm, and expressed as mg g−1 DW.
3.3. The effects of drying methods on carotenoids content in flower heads Carotenoids have the function of absorbing and transmitting electron, and protect the chlorophyll, chloroplasts and cells (Tracewell et al., 2001). Microwave treatments significantly decreased carotenoids content with the increase of microwave power (Fig. 4A). Similar results were also reported in previous publication (Gao et al., 2012). The reason may be that the high microwave power could cause the absorbing of flowers to the microwave and led to rise sharply in the energy of flower, which is not conducive to the retention of carotenoids. Carotenoids content were significantly increased with the increase of oven temperatures. Long et al. (2011) reported that carotenoids in tomatoes (Lycopersicon esculentum Mill.) and carrots (Daucus carota L. var. sativa Hoffm.) could keep steady in 70 °C, but will be degradation in 100 °C. A t the same time, we also found that carotenoids content in flower heads was also related to treatment time in 100 °C or 105 °C. In the study condition, the optimal time of steam kill-enzyme (100 °C) and kill-enzyme (105 °C) was 1 min, which could better keep carotenoids steady in harvested flower heads.
2.4. Statistical analysis All data were presented as mean ± SE. The variance was analyzed by one-way ANOVA, followed by Duncan’s test for multiple comparisons. Significance was set at 0.05 levels. All analyses were executed using the Software Statistical Package for the Social Science (SPSS) version 13.0.
3.4. The effects of drying methods on flavone and chlorogenic acid content in flower heads Many studies have shown that pharmacological effects of medicinal plants were relevant with active ingredients content (Wu et al., 2012). Flavonoids and chlorogenic acid are main active ingredients in flowers of medicinal chrysanthemum. The present research indicated that flavone content in flower heads was significantly increased with the increase of the microwave power and stem kill-enzyme time (Fig. 5A), which was consistent with the changing trend of PAL and C4H activity, further indicating that the higher power and the less time in microwave processing might be beneficial for keeping secondary metabolism contents in harvested flower heads. In kill-enzyme torrefaction, flavone content first increased and then decreased with the increase of killenzyme time. The higher over temperature (75 °C) treatment significantly decreased the flavone content compared with the lower over temperature (55 and 65 °C). In the four drying methods, the flower heads treated by the higher microwave power (680 W and 850 W) exhibited the higher flavonoid content (1.43 and 1.54 mg g−1 DW), followed by kill-enzyme dried flower heads (1.52 mg g−1 DW). In
3. Results and discussion 3.1. The effects of drying methods on MDA content in flower heads MDA is usually used as an indicator in stressful physiology of plants (Yu et al., 2004). Fig. 2 indicated that MDA content in flower heads was significantly increased with the increase of microwave power and steam kill-enzyme time (except for Z3 treatment), and was the highest at W3 (850 W) and Z5 (6 min) treatments, respectively, suggested that lipid peroxidation and oxidative stress in flower heads was increased. However, MDA content in flowers decreased with the increase of killenzyme time and oven temperature, suggesting that kill-enzyme and the higher oven temperature could reduce lipid peroxidation and damage in flower heads.
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Fig. 2. The effects of four drying methods on the MDA content in medicinal chrysanthemum flower heads. Microwave drying (W0, 340 W; W1, 510 W; W2, 680 W; W3, 850 W), steam kill-enzyme torrefaction (Z0, 0 min; Z1, 0.5 min; Z2, 1 min; Z3, 2 min; Z4, 4 min; Z5, 6 min), kill-enzyme torrefaction (S0, 0 min; S1, 0.5 min; S2, 1 min; S3, 3 min; S4, 5 min; S5, 7 min) and oven drying (H1, 55 °C; H2, 65 °C; H3, 75 °C). The bars with different letters are significantly different from each other at the same drying method (P < 0.05). Values are means of five replicates ± SE.
Fig. 3. The effects of four drying methods on PAL activity (A) and C4H activity (B) in medicinal chrysanthemum flower heads. Microwave drying (W0, 340 W; W1, 510 W; W2, 680 W; W3, 850 W), Steam kill-enzyme torrefaction (Z0, 0 min; Z1, 0.5 min; Z2, 1 min; Z3, 2 min; Z4, 4 min; Z5, 6 min), Kill-enzyme torrefaction (S0, 0 min; S1, 0.5 min; S2, 1 min; S3, 3 min; S4, 5 min; S5, 7 min) and oven drying (H1, 55 °C; H2, 65 °C; H3, 75 °C). The bars with different letters are significantly different from each other at the same drying method (P < 0.05). Values are means of five replicates ± SE.
addition, the flower heads treated by 6 min steam kill-enzyme had higher flavone content (1.13 mg g−1 DW) than the oven dried flower heads. As a polyphenolic material, chlorogenic acid is thermal sensitive and oxygen sensitive and easily degraded at high temperature and atmospheric environment (Liu et al., 2015). Liu et al. (2015) studied on the changes of chlorogenic acid in Flos Lonicerae with heater’s temperature (90–130 °C). Results indicated that chlorogenic acid content climbed with the increase of heater’s temperature and reached a peak at 110 °C, then fell rapidly at higher heater’s temperature. In the present study, chlorogenic acid in chrysanthemum flower heads significantly decreased with the increase of oven temperature (55–75 °C), and rose firstly and dropped subsequently with the increase of kill-enzyme time (105 °C) (Fig. 5B). Chlorogenic acid content increased to a peak value when kill-enzyme time was 1 min, further indicated that the thermal stability of chlorogenic acid was not only affected by heater’s tempera-
ture, but also by heating duration. However, chlorogenic acid content in flower heads was significantly increased with the increase of microwave power and steam kill-enzyme time (Fig. 5B). In the four drying methods, the flower heads treated by the kill-enzyme torrefaction contained the higher chlorogenic acids content, and the chlorogenic acid reached a peak value (0.363 mg g−1 DW) when the killenzyme time was 1 min.
3.5. The effects of drying methods on the contents of free amino acid, vitamin C content and soluble sugar in flower heads Free amino acid is the precursor substance of protein synthesis. Peng et al. (2006) reported that microwave drying and oven drying (60 °C) could increase free amino acids content of flos lonicerace. Fig. 6A indicated that free amino acids content decreased with the increase of the microwave power, kill-enzyme time and oven temperature. The 48
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Fig. 4. The effects of four drying methods on carotenoids content in medicinal chrysanthemum flower heads. Microwave drying (W0, 340 W; W1, 510 W; W2, 680 W; W3, 850 W), Steam kill-enzyme torrefaction (Z0, 0 min; Z1, 0.5 min; Z2, 1 min; Z3, 2 min; Z4, 4 min; Z5, 6 min), Kill-enzyme torrefaction (S0, 0 min; S1, 0.5 min; S2, 1 min; S3, 3 min; S4, 5 min; S5, 7 min) and oven drying (H1, 55 °C; H2, 65 °C; H3, 75 °C). The bars with different letters are significantly different from each other at the same drying method (P < 0.05). Values are means of five replicates ± SE.
is involved in regulating blood pressure and preventing arteriosclerosis. Vitamin C in plant tissues can be used as substrates for the enzyme to scavenge active oxygen, protecting plant from the oxidative damage. In the experiment performed by Kumar et al. (2015), room-dried Hibiscus sabdariffa leaf powder extracts had the highest content of vitamin C than freeze-dried, infrared-dried, crossflow-dried, oven-dried, sun-dried and microwave-dried. In the present study, the vitamin C in flower heads was not only related to drying methods, but affected by specific drying conditions for the different methods (Fig. 6B). In four drying methods, the flower heads treated by the W1 (510 W) and W2 (680 W) contained the higher vitamin C content (9.32 mg g−1 DW, 8.76 mg g−1 DW). In steam kill-enzyme torrefaction and kill-enzyme torrefaction, vitamin C content in flower heads reached a peak value at Z1 (0.5 min)
reason might be that the higher microwave power, the higher oven temperature and the longer kill-enzyme time led to the degradation of amino acid. In steam kill-enzyme torrefaction, Z1 (0.5 min) and Z2 (1 min) treatments significantly increased free amino acid content in flower heads compared with the control (Z0), but the longer steam killenzyme time significantly decreased free amino acid content, speculated that the shorter steam kill-enzyme time did not cause too much damage to the flower heads, which may be the reason for the increase in free amino acids content at the shorter steam kill-enzyme time. In the four drying methods, the amino acid content in flower heads treated by microwave treatments was the lowest relative to the other drying methods. Vitamin C is very important vitamin in human body and animal that
Fig. 5. The effects of four drying methods on flavone (A) and chlorogenic acid (B) content in medicinal chrysanthemum flower heads. Microwave drying (W0, 340 W; W1, 510 W; W2, 680 W; W3, 850 W), Steam kill-enzyme torrefaction (Z0, 0 min; Z1, 0.5 min; Z2, 1 min; Z3, 2 min; Z4, 4 min; Z5, 6 min), Kill-enzyme torrefaction (S0, 0 min; S1, 0.5 min; S2, 1 min; S3, 3 min; S4, 5 min; S5, 7 min) and oven drying (H1, 55 °C; H2, 65 °C; H3, 75 °C). The bars with different letters are significantly different from each other at the same drying method (P < 0.05). Values are means of five replicates ± SE.
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Fig. 6. The effects of four drying methods on amino acid (A), vitamin C (B) and soluble sugar (C) content in medicinal chrysanthemum flower heads. Microwave drying (W0, 340 W; W1, 510 W; W2, 680 W; W3, 850 W), Steam kill-enzyme torrefaction (Z0, 0 min; Z1, 0.5 min; Z2, 1 min; Z3, 2 min; Z4, 4 min; Z5, 6 min), Kill-enzyme torrefaction (S0, 0 min; S1, 0.5 min; S2, 1 min; S3, 3 min; S4, 5 min; S5, 7 min) and oven drying (H1, 55 °C; H2, 65 °C; H3, 75 °C). The bars with different letters are significantly different from each other at the same drying method (P < 0.05). Values are means of five replicates ± SE.
methods. Soluble sugar content in flower heads rose firstly and decreased subsequently with the increase of microwave power and steam kill-enzyme time, and reached a peak value at W2 (680 W) treatment and Z3 (2 min) treatment, respectively.
and S1 (0.5 min), respectively. However, vitamin C content significantly decreased with the increase of oven temperature. These results indicated that vitamin C was easy to be decomposed at higher temperature and higher microwave power, and the longer time of steam kill-enzyme and kill-enzyme could lead to degradation of vitamin C in flower heads. Shahraki et al. (2014) also reported that the color changes and the texture of dried sesame seeds were not only related to drying temperature, but related to drying time. So, we should consider the specific conditions of each processing method when drying method was choose. Polysaccharides (carbohydrates) are utilized as a source of energy, structure-forming material, and water maintaining hydrocolloids. Drying conditions have a significant influence on technological and functional characteristics of carbohydrates (Dehnad et al., 2016). Dehnad et al. (2016) reported that the influence of drying process variable on the carbohydrate-based materials by summarizing up the published literatures. As shown in Fig. 6C, the soluble sugar content in flower heads was not only affected by drying methods, but also related to specific conditions of each processing method. In four drying methods, the flower heads treated by kill-enzyme torrefaction exhibited the lower soluble sugar content relative to the other three drying
4. Conclusions The active and nutritional ingredients content in harvested flower heads was not only related to drying methods, but also significantly influenced by the specific conditions of each processing method. Comprehensive analysis revealed that: (1) microwave drying was the most suitable method for keeping the higher contents of flavone, vitamin C and soluble sugar, considering efficiency and the energy consuming. The optimal microwave power and treatment time were about 680–850 W and about 8–13 min, respectively; (2) the optimal time of steam kill-enzyme and kill-enzyme were about 2–4 min and 0.5–1 min, respectively; and (3) the optimal oven temperature was about 55–65 °C, which could simultaneously gain the higher contents of active and nutritional ingredients in flowers. So, we should consider the specific conditions of each processing method when the drying method was selected. 50
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