Food Chemistry 169 (2015) 424–429

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Influence of variety and harvest maturity on phytochemical content in corn silk Eakrin Sarepoua a, Ratchada Tangwongchai b, Bhalang Suriharn a,c, Kamol Lertrat a,c,⇑ a

Department of Plant Science and Agricultural Resources, Faculty of Agriculture, Khon Kaen University, Khon Kaen 40002, Thailand Department of Food Technology, Faculty of Technology, Khon Kaen University, Khon Kaen 40002, Thailand c Plant Breeding Research Center for Sustainable Agriculture, Faculty of Agriculture, KhonKaen University, Khon Kaen 40002, Thailand b

a r t i c l e

i n f o

Article history: Received 9 April 2014 Received in revised form 7 July 2014 Accepted 30 July 2014 Available online 17 August 2014 Keywords: Phenolic compounds Flavonoid Anthocyanin Vegetable corn Functional food

a b s t r a c t Corn silk has been used as a traditional herb in Asia. The objective of this study was to evaluate variability in phytochemicals in corn varieties at three maturity stages of corn silk. Ten vegetable corn varieties were evaluated in a completely randomized design with three replications. Data were recorded for total phenolic (TPC), total flavonoids (TFC), total anthocyanin (TAC) and antioxidant activity (AA) by DPPH free-radical-scavenging assays. Differences among corn varieties were observed for all parameters at all maturity stages, and the interactions between maturity stage and corn variety were significant. TPC and TAC were highest at the milky stage, whereas TFC and AA were highest at the silking stage. TPC, TFC and AA were highest in super sweet corn and white corn at the silking stage. PWC5 variety of purple waxy corn at the milky stage had the highest values for all parameters, and it is useful for further development of functional food products. Ó 2014 Elsevier Ltd. All rights reserved.

1. Introduction Silk of corn (Zea mays L.) has been used as a herb for traditional medicine by native Americans, Chinese and people in many parts of the world. Phytochemicals in corn silk have antioxidant properties and are beneficial for health. Therefore, it can be used as dietary fibre and as a food additive for the prevention of several diseases (Hasanudin, Hashim, & Mustafa, 2012). Corn silk is rich in polyphenol compounds with strong free radical scavenging activity, and it is a good source of natural antioxidants (Nurhanan, Rosli, & Mohsin, 2012). Corn silk contains many bioactive compounds such as proteins, vitamins, carbohydrates, calcium, potassium, magnesium and sodium salts, volatile oils and steroids, alkaloids, flavonoids and other phenolic compounds with beneficial effects on human health (Ebrahimzadeh, Pourmorad, & Hafezi, 2008). Its potential antioxidant and healthcare applications as a diuretic agent, in hyperglycemia reduction, as an antidepressant and for anti-fatigue use have been claimed in several reports. Other uses of corn silk include teas and supplements to treat urinary related problems. The potential use is very much ⇑ Corresponding author at: Department of Plant Science and Agricultural Resources, Faculty of Agriculture, Khon Kaen University, Khon Kaen 40002, Thailand. Tel.: +66 43202696. E-mail addresses: [email protected] (E. Sarepoua), [email protected] (R. Tangwongchai), [email protected] (B. Suriharn), [email protected] (K. Lertrat). http://dx.doi.org/10.1016/j.foodchem.2014.07.136 0308-8146/Ó 2014 Elsevier Ltd. All rights reserved.

related to its properties and mechanism of action of its plant’s bioactive constituents such as flavonoids and terpenoids (Hasanudin et al., 2012). Corn silk is usually considered as waste and discarded during processing of baby corn and super sweet corn products. Corn silk provides natural colour and can be used as a food additive and flavouring (Maksimovic, Malencic, & Kovacevic, 2005). For example, corn silk powder is used as a food additive to improve the nutrient content and physical characteristics of beef patties (Rosli, Nurhanan, Solihah, & Mohsin, 2011). Corn silk can be utilised commercially as an ingredient to produce a wide variety of valueadded products such corn silk tea, snacks, cosmetics and medicines. Corn is consumed at different maturity stages. It can be used as baby corn as a vegetable, immature corn, mature corn, and corn silk. At these different maturity stages there may be a difference in phytochemicals and antioxidant activity (Zˇnidarcˇicˇ, 2012). A recent study showed that the total flavonoid content of the butanol fraction of corn silk extract is in good correlation with the total phenolic content (Liu et al., 2011), and corn silk from upper parts of ears (dark brown) had higher amounts of total phenolics, total anthraquinones and total flavonoids than the lower parts of ears (Alam, 2011). Corn silk from baby corn had the highest yield and corn silk from purple waxy corn had the highest content of total phenolic, total flavonoid and total anthocyanin (Sarepoua, Tangwongchai, Suriharn, & Lertrat, 2013).

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The information on phytochemicals and antioxidant activity of corn silk at different maturity stages is still lacking. The objectives of this study were to evaluate the effects of maturity on total phenolic compounds, flavonoid and anthocyanin contents of corn and to identify corn varieties with high phytochemicals. This information will be useful in the commercial production of functional foods using corn silk and exploitation of agricultural waste to produce value-added products.

Table 1 List of 10 varieties of Thai corn used in this study. Entry No.

2. Materials and methods

Varieties

Types of corna

Silk colourb

Kernel colourc

Origin

1

PWC1

Purple waxy corn

Purple

Purple

2

PWC2

Purple

Purple

3

PWC3

Purple

Purple

4

PWC4

Purple

Purple

5

PWC5

Purple

Purple

Khon Kaen University Khon Kaen University Khon Kaen University Khon Kaen University Pacific Seeds (Thai) Ltd.

6

WWC1

Green

White

7

WWC2

Green

White

8

WWC3

Green

White

9

SSC1

Green

Yellow

10

SSC2

Green

Yellow

2.1. Plant materials and sample preparations Ten corn hybrids including five purple waxy corns, three white waxy corns and two super sweet corns were selected because of the differences in silk colours (Table 1). Silk colours and kernel colours were similar and varied from yellow-green, yellow-brown and purple. Three types of corn were classified based on harvest times at different maturity stages. Group 1 is baby corn which was harvested at the silking stage (7–10 days after anthesis) or R1. Group 2 is vegetable corn which was harvested at immature stages (18 days after anthesis) or R4, and group 3, the corn for seed production, was harvested at the physiological maturity stage (30 days after anthesis) or R6. The corn varieties were grown in a Completely Randomized Design (CRD) with three replications at the Vegetable Farm, Khon Kaen University, Khon Kaen, Thailand (18° 510 N, 98° 450 E, 200 masl) in the rainy season during May to July 2012. At anthesis, the ears were sib-pollinated to ensure good pollination of the ears, the ears were harvested at three maturity stages as described above. The samples of corn silk were washed with distilled water and oven-dried at 60 °C for 24 h until the samples reached a final moisture content of 10% (Hu, Zhang, Li, Ding, & Li, 2010). Dry samples were ground into powder using a grinder, sealed in vacuum plastic bags and stored at below 20 °C until analysis. The ground samples were analysed for bioactives and antioxidant activity in triplicates. 2.2. Extraction of phytochemicals from corn silk Corn silk samples were extracted using a modified method (Nurhanan et al., 2012). Briefly, 3 g of corn silk powder was mixed with 30 ml of 80% methanol in a flask and extracted at 70 °C in a water bath shaker (WB14/SV1422, GmbH Co. KG Memmert, Shanghai, China). After 1.5 h, the extract was filtrated through filter paper Whatman No. 1 to remove the debris. The filtrate was evaporated using a rotary flash evaporator (Eyela SB-651, Kokusan Enshinki Co., Tokyo, Japan) to remove the solvent. The residue was reconstituted with 5 ml methanol and stored at 0–4 °C until analysis. The extract was analysed on a UV–Vis spectrophotometer (10S, Thermo Scientific Genesys, Australia) to determine total phenolic content (TPC), total flavonoid content (TFC), total anthocyanin content (TAC), and antioxidant activity was analysed by DPPH free-radical-scavenging activity assay. 2.3. Determination of total phenolic content Total phenolic content was determined using the Folin–Ciocalteu colorimetric method and gallic acid was used as a standard (Liu & Yao, 2007). Folin–Ciocalteu reagent was diluted with distilled water at a ratio of 1:10. 0.5 ml of corn silk extract was mixed with 3 ml of the diluted Folin–Ciocalteu reagent and 2.5 ml of 0.2% (w/v) Na2CO3 solution. The mixture was allowed to stand for 30 min at room temperature (ca. 25 °C) and the absorbance of the resulting

a b c

White waxy corn

Super sweet corn

Khon Kaen University Khon Kaen University Khon Kaen University Pacific Seeds (Thai) Ltd. Syngenta Seeds Ltd.

Vegetable corn. Colour of silk at milky stage. Colour of kernel at milky stage.

solution was read at 750 nm using a spectrophotometer. The blank consisted of all regents and solvents except for the sample. The total phenolic content was determined using a standard calibration curve and expressed as gallic acid equivalents per dry mass of corn silk sample (lg GAE/g dried sample). 2.4. Determination of total flavonoid contents Total flavonoid content was determined using a modified colorimetric aluminium chloride method and rutin hydrate was used as a standard (Liu et al., 2011). Briefly, 0.5 ml diluted corn silk extract in 2.5 ml methanol was mixed with 3 ml of 0.01 M aluminium chloride in methanol. Then the mixture was allowed to stand for 10 min at room temperature (ca. 25 °C). The absorbance of the resulting solution was read at 400 nm using a spectrophotometer. The total flavonoid content was determined using a rutin calibration curve at concentrations from 0-0.100 mg/ml in methanol and expressed as rutin hydrate equivalents per dry mass of corn silk sample (lg RE/g dried sample). 2.5. Determination of total anthocyanin content Total anthocyanin content was determined according to the pH-differential method (Ku, Kin, & Kang, 2009). Corn silk extract from each sample was mixed with pH 1.5 buffers in 1% HCl to 6 ml in methanol extract. After extracting at room temperature (ca. 25 °C) for 20 min, absorbance was measured for each solution at 530 nm and 700 nm against blanks of pH 1.0 and 4.5 buffers. Total anthocyanin content was determined by the following equation:

Total anthocyanin ðmg=LÞ ¼ ðA  MW  1000  DFÞ=ðe  1Þ where A was adjusted absorbance calculated from (A530–A700) at buffer 1.0  (A520–A700) at buffer 4.5, 1000 was a converting factor from molar to ppm, and DF was a dilution factor. For a quantification of total anthocyanin content, external calibration was carried out for cyanidin-3-glucoside with molecular weight (MW) of 449.2, and molar absorptivity of 1% HCl in methanol (e) was 34,300. The results were expressed as microgram of cyanidin-3-glucoside equivalents per dry mass of corn silk sample (lg C3G/g dried sample).

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2.6. Antioxidant activity assay Antioxidant activity was measured using the DPPH free radical scavenging activity assay (Liu et al., 2011). Initially, 0.2 ml of corn silk extract was added to 1 ml of 0.2 mM freshly prepared DPPH methanol solution. The reaction was mixed and allowed to stand for 30 min under dark conditions. The control contained all reagents except the extract fraction was used as blank. Absorbance was read against a blank at 517 nm using a spectrophotometer. The percentage inhibition of absorbance was calculated and plotted as a function of the concentration of standard and corn silk extract to determine the ascorbic acid equivalent antioxidant concentration. The percentage of DPPH radical scavenging activity (%) of sample was calculated as follows:

DPPH radical scavenging activity ð%inhibitionÞ ¼ ð1  A sample=A controlÞ  100 where A sample is the absorbance of the extract or standard and A control is the absorbance of the control. All tests were run in duplicates and analyses of the samples were run in triplicates. 2.7. Statistical analysis Analysis of variance was performed for each parameter according to a completely randomized block design, and least significant difference (LSD) was used to compare means at p < 0.05. Data were expressed as mean ± standard deviation (SD) of three replication analysis. All analyses were done in SPSS v19 (SPSS Inc., USA).

silking stage (R1) (110.7 lg GAE/g) and physiological maturity stage (R6) (97.8 lg GAE/g), respectively (Table 6). On average across three maturity stage, PWC5 had the highest total phenolic content (189.1 lg GAE/g) followed by PWC3 (153.2 GAE/g) and PWC1 (150.8 lg GAE/g), respectively (Table 2). PWC5 was also the highest at milking stage (206.8 ± 5.5 lg GAE/g). The corn varieties with the lowest total phenolic content were WWC3 (59.6 lg GAE/g) and WWC1 (61.2 lg GAE/g) of white waxy corn. WWC1 was also the lowest at physiological maturity stage (26.5 ± 2.1 lg GAE/g). Total flavonoid contents ranging from 33.2 to 136.0 lg RE/g dried samples were observed among corn varieties across three maturity stages (Table 3). On average across corn varieties, silking stage had the highest total flavonoid content of 88.5 lg RE/g followed by milky stage (85.3 lg RE/g) and physiological maturity stage (69.1 lg RE/g) (Table 6). On average across the three maturity stages, PWC5 was the highest for total flavonoid content (119.6 lg RE/g) followed by PWC4 (111.1 lg RE/g) and PWC1 (96.1 lg RE/g), respectively, whereas WWC3, WWC2 and WWC1 had the lowest flavonoid contents (52.3, 40.1 and 41.9 lg GAE/g, respectively) (Table 3). It is clear that purple corns had the highest total flavonoid content. Super sweet corns were intermediate and white waxy corns were the lowest. PWC5 and PWC4 of purple waxy corn had the highest total flavonoid content at the milky stage (R4) (136.0 ± 2.2 and 129.2 ± 3.2 lg RE/g, respectively), whereas WWC1 and WWC2 of white waxy corn had the lowest total flavonoid content at the silking stage of 41.9 and 40.1 lg RE/g, respectively. 3.2. Total anthocyanin content

3. Results 3.1. Total phenolic content and total flavonoid content Total phenolic content ranging from 26.5 to 206.8 lg GAE/g of dry samples was observed among corn varieties evaluated across three maturity stages from silking to physiological maturity (Table 2). Based on total phenolic content, corn varieties could be roughly divided into a high or low group. The high group consisted of all varieties in purple waxy corn with total phenolic content higher than 100 lg GAE/g, and the low group comprised all corn varieties in white waxy corn and super sweet corn with total phenolic content lower than 100 lg GAE/g. Maturity stages were also different for total phenolic content. On average across the three types of corn, milky stage (R4) had the highest total phenolic content (121.3 lg GAE/g) followed by

Differences among corn varieties at three maturity stages were significant for total anthocyanin contents ranging from 0.3 to 63.4 lg C3G/g of dried samples (Table 4). On average across corn varieties, silking stage had the highest total anthocyanin content (27.9 lg C3G/g) followed by physiological maturity stage (23.8 lg C3G/g) and milking stage (4.4 lg C3G/g), respectively (Table 6). Based on total anthocyanin content, corn varieties could be clearly classified into a high and low group. The high group consisted PWC5, PWC1, PWC3, PWC2 and PWC4 in purple waxy corn with total anthocyanin contents ranging from 23.9 to 46.0 lg C3G/ g, and low group included other varieties in white waxy corn and super sweet corn (Table 4). PWC5 in purple waxy corn had the highest total anthocyanin content at milking stage (63.4 ± 1.7 lg C3G/g) and physioligical maturity stage (62.7 ± 1.7 lg C3G/g),

Table 2 Total phenolic content in silk of 10 corn varieties evaluated at different reproductive stages. Type of corn

Varieties

Total phenolic content (lg GAE/g dried sample) Silking stage (R1)

Milky stage (R4)

Maturity stage (R6)

Mean

123.8 ± 3.8 112.8 ± 2.1 127.0 ± 2.7 115.6 ± 2.2 173.4 ± 2.6

179.6 ± 3.2 169.2 ± 2.4 185.3 ± 1.9 147.7 ± 3.3 206.8 ± 5.5

149.1 ± 2.6 114.7 ± 3.1 147.4 ± 2.8 134.5 ± 2.4 187.1 ± 3.2

150.8 132.2 153.2 132.6 189.1

Purple waxy corn

PWC1 PWC2 PWC3 PWC4 PWC5

h i h i de

cd e bc f a

White waxy corn

WWC1 WWC2 WWC3

99.8 ± 1.3 j 89.6 ± 2.5 kl 85.9 ± 1.8 l

57.3 ± 2.3 q 56.8 ± 2.4 q 56.7 ± 2.1 q

26.5 ± 2.1 t 47.6 ± 1.8 r 36.1 ± 1.9 s

61.2 fg 64.7 f 59.6 g

Super sweet corn

SSC1 SSC2

85.5 ± 2.4 lm 93.4 ± 3.2 jk

75.2 ± 3.2 no 78.3 ± 3.1 mn

65.5 ± 2.0 p 69.4 ± 2.2 op

75.4 e 80.3 d

Values are mean ± standard deviation of three replicate analysis. Means with the same letter(s) in the same column are not significantly different (p < 0.05) by LSD. R1 is 7–10 days after silking, R4 is milky stage at 18 days after silking and R6 is maturity stage at 30 days after silking.

f i f g b

b c b c a

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E. Sarepoua et al. / Food Chemistry 169 (2015) 424–429 Table 3 Total flavonoid content in silk of 10 corn varieties evaluated at different reproductive stages. Type of corn

Varieties

Purple waxy corn

PWC1 PWC2 PWC3 PWC4 PWC5

White waxy corn

WWC1 WWC2 WWC3

Super sweet corn

SSC1 SSC2

Total flavonoids content (lg RE/g dried sample) Silking stage (R1)

Milky stage (R4)

Maturity stage (R6)

Mean

83.6 ± 1.9 74.1 ± 3.1 74.4 ± 2.1 99.0 ± 2.3 121.5 ± 2.4

104.6 ± 2.1 99.8 ± 3.2 94.5 ± 1.4 129.2 ± 3.2 136.0 ± 2.2

100.0 ± 1.7 61.8 ± 4.4 86.8 ± 1.0 105.3 ± 4.3 101.4 ± 1.9

96.1 78.6 85.2 111.1 119.6

k l l f c

57.6 ± 3.3 p 50.9 ± 3.2 q 87.4 ± 3.3 ij 117.6 ± 3.4 d 119.1 ± 3.2 cd

e f g b a

f o j e f

c g f b a

35.0 ± 2.3 r 35.7 ± 3.1 r 35.7 ± 3.2 r

33.2 ± 3.5 r 33.6 ± 4.1 r 33.8 ± 3.4 r

41.9 i 40.1 j 52.3 h

90.3 ± 3.1 hi 92.2 ± 3.8 gh

65.5 ± 2.4 n 69.2 ± 3.9 m

91.1 e 93.5 d

Values are mean ± standard deviation of three replicate analysis. Means with the same letter(s) in the same column are not significantly different (p < 0.05) by LSD. R1 is 7–10 days after silking, R4 is milky stage at 18 days after silking and R6 is maturity stage at 30 days after silking.

Table 4 Total anthocyanin content in silk of 10 corn varieties evaluated at different reproductive stages. Type of corn

Varieties

Total anthocyanin content (lg C3G/g dried sample) Silking stage (R1)

Milky stage (R4)

Maturity stage (R6)

Mean

5.8 ± 2.2 5.3 ± 2.4 6.0 ± 2.5 4.3 ± 2.3 11.7 ± 3.4

53.2 ± 1.5 59.9 ± 1.9 53.7 ± 1.3 39.5 ± 1.1 63.4 ± 1.7

52.2 ± 1.1 39.8 ± 1.6 48.4 ± 1.2 27.9 ± 1.5 62.7 ± 1.7

37.1 35.0 36.0 23.9 46.0

Purple waxy corn

PWC1 PWC2 PWC3 PWC4 PWC5

ij ij i jk h

cd b c f a

d f e g a

b c bc d a

White waxy corn

WWC1 WWC2 WWC3

1.7 ± 2.1 lmnop 3.1 ± 2.2 kl 1.6 ± 2.2 mnop

1.2 ± 1.2 nop 2.9 ± 1.8 klm 1.5 ± 1.4 mnop

0.5 ± 0.3 op 2.5 ± 1.3 lmn 0.3 ± 0.2 p

1.1 f 2.8 e 1.1 f

Super sweet corn

SSC1 SSC2

2.1 ± 2.3 lmn 2.3 ± 2.2 lmn

2.0 ± 1.7 lmno 1.9 ± 1.3 lmno

1.8 ± 0.4 lmnop 1.5 ± 0.3 mnop

2.0 ef 1.9 ef

Values are mean ± standard deviation of three replicate analysis. Means with the same letter(s) in the same column are not significantly different (p < 0.05) by LSD. R1 is 7–10 days after silking, R4 is milky stage at 18 days after silking and R6 is maturity stage at 30 days after silking.

whereas PWC2 and PWC1 had the highest total anthocyanin contents of 59.9 ± 1.9 and 53.2 ± 1.5 lg C3G/g, respectively, at the milky stage. 3.3. Radical DPPH scavenging activity Differences among corn varieties at three maturity stages were significant for radical DPPH scavenging activity (Table 5). The DPPH values of radical scavenging activity of corn varieties evaluated across the three maturity stages ranged from 11.0% to 86.0%. Silking stage had the highest DPPH values of 61.5% followed by milky stage (56.6%) and physiological maturity stage (43.6%), respectively (Table 6). On average across three maturity stages, purple waxy corn constituted the highest DPPH values ranging from 78.3% to 64.2%, and PWC5 and PWC3 were highest (78.3% and 71.0%, respectively) (Table 5). Super sweet corns were intermediate ranging from 61.3% to 63.7%, and white waxy corn was lowest ranging from 21.3% to 33.4%. PWC5 of purple waxy corn was highest for DPPH values at milky stage (86.0 ± 4.5%) and silking stage (78.1%), whereas WWC1 WWC3 and WWC2 of white waxy corn had the lowest DPPH values of 11.0 ± 3.3, 15.0 ± 3.3 and 19.8 ± 3.5%, respectively, at physiological maturity stage. 4. Discussion 4.1. Phytochemicals at three maturity stages Corn is usually harvested and consumed at three maturity stages such as baby corn, vegetable immature corn and mature

corn. Baby corn is harvested at the silking stage. Vegetable corns such as super sweet corn and waxy corn are harvested at the immature stage which is normally at 21 days after silking or slightly later but not at physiological maturity stage, and corn is also harvest at physiological maturity stage for seed production (Zˇnidarcic, Ban, Peršuric, Oplanic, & Koncar, 2008). At all maturity stages, ears and kernels are used for food, and silk is normally discarded as waste. However, silk can be used as a food ingredient as it is rich in photochemicals with antioxidant activity. Therefore, this study was carried out to determine total phenolic, flavonoid and anthocyanin content and antioxidant activity in the silk of purple waxy corn, white waxy corn and super sweet corn at the silking stage, immature stage and physiological maturity stage. In this study, purple waxy corn is most suitable for use as a source of phenolic compounds, flavonoids and anthocyanins as the contents of these phytochemicals were generally higher than white waxy corn and super sweet corn at all maturity stages. In the previous study, phenolic compounds (Ebrahimzadeh et al., 2008; Liu et al., 2011) and flavonoids (Ebrahimzadeh et al., 2008; Hu, Zhang, Li, Ding, & Li, 2010; Liu et al., 2011) were the major components of phytochemicals in corn silk, and the contents of these phytochemicals varied depending on extraction methods, plant tissues and the origin of the plants (Ebrahimzadeh et al., 2008). Purple waxy corn has high anthocyanin accumulation (Jian & Monica, 2010; Yang & Zhai, 2010) as there are derivatives unique among flavonoids and phenolic compounds as their structures undergo reversible transformation at different pHs in aqueous solution (Jian & Monica, 2010). Anthocyanins also accumulate in other parts of corn such as in silk, leaves and seeds (Fossen, Slimestad, & Andersen, 2001).

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Table 5 Scavenging activity in silk of 10 corn varieties evaluated at different reproductive stages. Type of corn

Varieties

Scavenging activity (%inhibition DPPH) Silking stage (R1)

Milky stage (R4)

Maturity stage (R6)

Mean

Purple waxy corn

PWC1 PWC2 PWC3 PWC4 PWC5

70.7 ± 4.1 70.3 ± 5.5 74.7 ± 4.4 57.3 ± 4.2 78.1 ± 5.3

74.7 ± 5.4 74.6 ± 6.5 77.1 ± 6.3 61.4 ± 5.3 86.0 ± 4.5

52.0 ± 5.2 47.7 ± 4.2 61.3 ± 4.3 45.9 ± 4.5 70.8 ± 4.6

65.8 64.2 71.0 54.9 78.3

White waxy corn

WWC1 WWC2 WWC3

33.2 ± 3.6 l 32.5 ± 3.1 l 61.5 ± 7.1 f

19.7 ± 3.4 n 23.6 ± 3.6 m 23.6 ± 3.9 m

11.0 ± 3.3 p 19.8 ± 3.5 n 15.0 ± 3.3 o

21.3 i 25.3 h 33.4 g

Super sweet corn

SSC1 SSC2

65.3 ± 4.2 e 71.1 ± 4.6 d

60.3 ± 5.5 f 65.2 ± 5.2 e

58.2 ± 4.6 g 54.9 ± 4.2 h

61.3 e 63.7 d

d d c g b

c c b f a

Asorbic acid (40 lg/mL)

i j f k d

c d b f a

75.5 ± 2.1 bc

Values are mean ± standard deviation of three replicate analysis. Means with the same letter(s) in the same column are not significantly different (p < 0.05) by LSD. R1 is 7–10 days after silking, R4 is milky stage at 18 days after silking and R6 is maturity stage at 30 days after silking.

Table 6 Means for total phenolic content (TPC), total flavonoids content (TFC), total anthocyanin content (TAC) and scavenging activity (SA) in silk of 10 corn varieties evaluated at different reproductive stages. Reproductive stage

TPC (lg GAE/ g dried sample)

TFC (lg RE/g dried sample)

TAC (lg C3G/ g dried sample)

SA (%inhibition DPPH)

Silking stage Milky stage Maturity stage

110.7 b 121.3 a 97.8 c

88.5 a 85.3 b 69.1 c

4.4 c 27.9 a 23.8 b

61.5 a 56.6 b 43.6 c

Means with the same letter(s) in the same column are not significantly different (p < 0.05) by LSD.

In this study, harvest of purple waxy corn at the milky stage was most suitable for higher phytochemicals. This harvest time is normal for commercial production of purple waxy corn. The best harvest time for super sweet corn that gave the highest phytochemicals was at silking stage. However, super sweet corn is also harvested commercially at milky stage which produced somewhat lower phytochemicals than at the silking stage. Harvest at physiological maturity stage is not suitable as it produced low phytochemicals for all types of corn. In previous investigations, total anthocyanin content in corn silk of purple waxy corn varieties was highest at the milky stage and maturity stage (Yang & Zhai, 2010). In general, low concentrations of anthocyanins were found in white waxy corn and super sweet corn varieties (Kasim, Sulusoglu, & Ufuk, 2011). Purple waxy corn had the highest total phenolic content, total flavonoid content and total anthocyanin content (Sarepoua et al., 2013). The results in this study supported previous reports and indicated that corn silk is suitable for use as a raw material for the production of functional food products. However, harvest at different maturity stages resulted in differences in silk quality. If phytochemicals are considered, harvest at silking stage gave the best quality of silk. Harvest at immature stage had intermediate quality, and harvest at physiological maturity stage had rather low quality. Although corn silk has been used as a traditional herb, the scientific information on the health promoting properties of corn silk has not been clearly elucidated. This study provided useful information on the differences of corn silk of different corn types harvested at different maturities for phenolic compounds, flavonoids and anthocyanins which were closely related to antioxidant activity (Ardestani & Yazdanparast, 2007). Corn silk contains phytochemicals that have health benefits, and it is useful for use as raw material for extraction of natural phytochemicals for use in food industry. The use of corn silk should reduce agricultural waste.

4.2. Antioxidant activity at three maturity stages Plants are an important source of natural antioxidants especially for phenolics, flavonoids, tannins and anthocyanidins that are safe and bioactive (Mohsen & Ammar, 2009). Natural antioxidants extracted from fruits, teas, vegetables and medicinal plants have been investigated extensively because they are effective in eliminating free radicals and less toxic than synthetic antioxidants (Zhu, Lian, Guo, Peng, & Zhou, 2011). Corn silk is an important bioactive source of natural antioxidants (Hasanudin et al., 2012), and total phenolic content in corn silk was correlated with free-radical scavenging activity (Ardestani & Yazdanparast, 2007). If DPPH radical scavenging activity is considered, corn silk with the best quality can be harvested at the silking stage, which is in accordance with the harvest time of baby corn. Therefore, silk of baby corn is the best source of antioxidant activity. Harvest at the milking stage also yielded the best quality silk especially for purple waxy corn which was the best type of corn for high DPPH radical scavenging activity. Harvest at physiological maturity stage yielded the lowest quality of corn silk. In earlier studies, DPPH radical scavenging activity was correlated with total phenolic content and total flavonoid content, and, although the relationship between DPPH radical scavenging activity and anthocyanin content was not significant, it was still high and positive (r = 0.40) (Sarepoua et al., 2013). Phenolic compounds, flavonoids and anthocyanins in corn silk can reduced DPPH radicals and provide high antioxidant activity (Nurhanan et al., 2012). Therefore, corn silk harvested at different maturity stages can be used as a raw material for production of value-added functional food products. High pigmentation generally occurs at the early maturity phase of corn silk, and it is related directly to high antioxidant activity. Different parts of corn silk also differ in antioxidant activity. The upper part of corn silk had higher pigmentation than the lower part of corn silk, and it also had a higher total antioxidant capacity (Alam, 2011). The highest antioxidant activity was found in corn silk from purple waxy corn varieties PWC5 at the milky stage and silking stage. 5. Conclusion This study evaluated total phenolic, flavonoid and anthocyanin content and antioxidant activity in corn silk of different types at different maturity stages. The questions underlying the research project were what harvest times are most suitable and which corn types and varieties are most suitable for production of corn silk

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with high concentrations of the phytochemicals and antioxidant activity. Milky stage was the best time for harvest, and corn silk that was harvest at this maturity stage had the highest total phenolic content, total flavonoid content, total anthocyanin content and antioxidant activity. Corn silk harvest at the silking stage had lower quality than corn silk harvested at the milky stage, but harvest at physiological maturity produced corn silk with the lowest quality. In general, purple waxy corn had silk with the highest total phenolic content, total flavonoid content, total anthocyanin content and antioxidant activity. Super sweet corn also provided silk of good quality although the quality was lower than that produced from purple waxy corn. However, silk of white waxy corn has the lowest quality. PWC5 of purple waxy corn was the best genotypes for silk quality especially at milking growth stage. Acknowledgements This work was supported by the Higher Education Research Promotion and National Research University Project of Thailand, Office of the Higher Education Commission, through the Food and Functional Food Research Cluster of Khon Kaen University and Plant Breeding Research Center for Sustainable Agriculture, Faculty of Agriculture, Khon Kaen University, Thailand. References Alam, E. A. (2011). Evaluation of antioxidant and antibacterial activities of Egyptian Maydis stigma (Zea mays hairs) rich in some bioactive constituents. The Journal of American Science, 7(4), 726–729. Ardestani, A., & Yazdanparast, R. (2007). Antioxidant and free radical scavenging potential of Achillea santolina extracts. Food Chemistry, 104(1), 21–29. Ebrahimzadeh, M. A., Pourmorad, F., & Hafezi, S. (2008). Antioxidant activities of Iranian corn silk. Turkish Journal of Biology, 32, 43–49. Fossen, T., Slimestad, R., & Andersen, O. M. (2001). Anthocyanins from maize Zea mais and reed canarygrass Phalaris arundinacea. Journal of Agricultural and Food Chemistry, 49, 2318–2321. Hasanudin, K., Hashim, P., & Mustafa, S. (2012). Corn silk (Stigma Maydis) in healthcare: a phytochemical and pharmacological review. Molecules, 17, 9697–9715.

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Influence of variety and harvest maturity on phytochemical content in corn silk.

Corn silk has been used as a traditional herb in Asia. The objective of this study was to evaluate variability in phytochemicals in corn varieties at ...
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