A novel starch: Characterizations of starches separated from tea (Camellia sinensis (L.) O. Ktze) seed

BIOMAC-13021; No of Pages 7 International Journal of Biological Macromolecules 139 (2019) xxx

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A novel starch: Characterizations of starches separated from tea (Camellia sinensis (L.) O. Ktze) seed Jiajia Huang a,1, Ming'an Yuan b,1, Xiangli Kong a, Dianxing Wu a, Zhaisheng Zheng b,⁎, Xiaoli Shu a,⁎ a b

State Key Laboratory of Rice Biology and Key Laboratory of the Ministry of Agriculture for the Nuclear-Agricultural Sciences, Zhejiang University, Hangzhou, 310029, PR China Jinhua Academy of Agricultural Sciences, Jinhua 321017, Zhejiang Province, PR China

a r t i c l e

i n f o

Article history: Received 27 June 2019 Received in revised form 6 August 2019 Accepted 6 August 2019 Available online 07 August 2019 Keywords: Tea seed starch Amylopectin structure Physicochemical properties

a b s t r a c t The physicochemical, thermal and crystal properties of starches isolated from 3 different tea (Camellia sinensis (L.) O. Ktze) seeds were analyzed in this study. The shape of tea starch granules were flat spherical or oval shape, showed unimodal or bimodal distribution with average size of around 9 μm. Tea starch was typical Atype starch. Apparent amylose contents of three tea seed starches ranged from 27.06% to 33.17%. The chains having degree of polymerization (DP) 13–24 were over 50% of the total detectable chains for tea amylopectin. Peak gelatinization temperature of tea starch ranged from 65 to 77 °C and the water solubility reached up to 9.70%. The peak viscosity of tea starches were as high as 5300 cP and final viscosity ranged from 4000 to 6700 cP. The results indicated that tea seed starch had potential as gel reagents and provide some guides for comprehensive utilization of tea starch in food and non-food applications. © 2019 Elsevier B.V. All rights reserved.

1. Introduction Starch, the most abundant reserve carbohydrate in plant, contributes greatly to the textural properties of many foods and has many industrial applications as a thickener, colloidal stabilizer, gelling agent, bulking agent, water retention agent, and adhesive [1]. Its biochemical and functional characteristics as well as its variations have being investigated to better understand. While the physiochemical properties and functional characteristics that are imparted by the starches to the aqueous systems and their uniqueness in various food applications vary within the biological origin [2]. Many studies have been conducted on starch structure and functional properties of cereal crops, tuber crops, legumes and some starchy fruits, such as rice, wheat, corn, potato, pea [3], banana [4], chestnut [5], jackfruit [6] and etc. Identification of novel starch sources is required for desired functionality and unique properties [7]. Morais et al. [8] found that Solanum lycocarpum starch could be used as a sustainable non-food energy source for biofuels. While few studies on starch characteristics of non-food economic plant were found, underpinning the physiochemical properties of starch from various botanies might dig out novel starches with potential applications in food and industry. The tea plant (Camellia sinensis (L). O. Kuntze) is an evergreen bush or small tree found in tropical and sub-tropical locations around the world, gives us the widely enjoyed beverage in the world – tea. China ⁎ Corresponding authors. E-mail addresses: [email protected] (Z. Zheng), [email protected] (X. Shu). 1 Equal contribution to the work.

is the largest producer of tea in the world (2,414,802 t), produces 40% of the total tea worldwide (5,954,091 t, FAO, 2016) [9] and the annual outputs of tea (Camellia sinensis) seeds in China are more than one million tons in recent years according to the report of the Chinese Cereals and Oils Association. The seeds and fruits of tea have been used as an antitussive and expectorant in Chinese traditional medicine [10]. Additionally, the tea seed are high in oil content and have been utilized as raw materials to extract edible oils [11], which can bring greater economic benefits. A few researchers have devoted to the improvement of extraction methods and the evaluation of the nutritional value of tea oil [12]. But the residue after oil extraction has usually considered as total waste and attracted little attention. In fact, there was lots of starch left in the residue. Utility of this part of starch might realize the recycling of extraction waste, and boost the comprehensive utilization of tea seed. In this study, the structural and functional characteristics of tea seed starch isolated from three different varieties were investigated, which will help to uncover some unique characteristics of tea seed starch that could be of industrial importance. 2. Materials and methods 2.1. Chemicals Pullulanase (E-PULKP, Megazyme) and isoamylase (E-ISAMY, Megazyme) were obtained from Megazyme International Ltd., Wicklow, Ireland. Purified α-amylase from porcine pancreas (A3176, activity 15 U/mg, 1 unit will liberate 1.0 mg of maltose from starch in 3 min at pH 6.9 at 20 °C), amylose from potatoes (Fluka, 10130), amylopectin

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from maize (Fluka, 10120), amyloglucosidase from aspergillus niger (10115, activity 60.1 U/mg, 1 unit will liberate 1 μm glucose per minute at pH 4.8 and 60 °C using starch as substrate) were purchased from Sigma-Aldrich Ltd. (St. Louis, MO, USA). GOPOD kits were purchased from Ninbo Saike Biological Technology Co., Ltd. (Ningbo, China). All other chemicals were of analytical grade unless stated otherwise.

2.2. Plant materials Three tea (Camellia sinensis) cultivars grown widely in Zhejiang province, King8, Minred6 and Wun4 were provided by Jinhua Academy of Agricultural Sciences. All the accessions were planted for 5 years in Jinhua Academy of Agricultural Sciences, Zhejiang province, China. The seeds were harvested in October 2017.

2.3. Methods 2.3.1. Starch isolation Starch was isolated from the tea seed according to the method of Yang et al. [13] with minor modifications. The seeds were unshelled and the kernel was washed thoroughly with tap water and soaked in distilled water for 15 min to remove the coat. The kernel mixed with deionized water (1:4, w/v) was homogenized in a blender (Joyoung, C020E, China) at full speed for 3 min. The suspension was adjusted to pH 10 with 0.5 M NaOH. The starch slurry was incubated at 45 °C for 4 h with continuous shaking in a shaking water bath (100 strokes/ min), then filtered through a 38 μm sieve and the filter residue was washed 4 times. All filtrates were collected and centrifuged at 4000 rpm for 30 min. The supernatant was discarded and the top yellow protein layer of the sediment was scraped off carefully. The starch was washed 5 times with distilled water and dried at 40 °C, stored in a drier till analysis.

2.3.2. Moisture, protein and lipid content Moisture content was determined by using LJ16 Moisture Analyzer (Mettler-Toledo, Switzerland) according to the user manual but make sure a thin layer of starch was laid over the whole pan. The protein content was measured with the Kjeldahl method by Automatic Kieldahl analyzer (K1160, Hanon Instruments, Jinan, China) according to the User Manual. Crude lipids content was determined with the Soxhlet method standard procedures by a Soxhlet Extraction instrument (SOX406, Hanon Instruments, Jinan, China). Lipids content were determined after 3 h Soxhlet extraction of 2 g samples with 50 mL hot diethyl ether. The lipid extractions were dried at 105 °C to constant weight and expressed as percentage of dry matter (w/w, %).

2.3.3. Apparent amylose content (AAC) and resistant starch AAC was determined using the iodine reagent method [14]. The absorbance of the solution was measured at 620 nm against the blank solution using spectrophotometer (UNICAM UV300, Thermo scientific, UK). Amylose from potatoes and amylopectin from maize were used to construct AAC standard curve. Resistant starch was measured according to Shu et al. [15] with minor modifications. Briefly, 100 ± 1 mg starch were accurately weighed, placed directly into screw-cap tubes (16 × 125 mm) and boiled for 20 min with a ratio of 5:1 (water:starch), then keep at 50 °C for 10 min, samples were collected and cooled to room temperature. Then the sample was ground by a stirring rod mimicking the chewing in mouth, digested with 10 mg/mL pancreatic αamylase containing 3 U/mL amyloglucosidase for 16 h. The reaction was stopped by 50% ethanol and the residue was dissolved with 4 M KOH, then digested with 330 U amyloglucosidae at 60 °C for 1 h, the released glucose were determined with a GOPOD kit, starch content was converted from glucose with a factor of 0.9.

2.3.4. Swelling power, solubility and pasting properties Swelling power and solubility were determined according to the method of Sang and Seib [16]. Starch of 1 g was well mixed with 30 mL of distilled water, heated at 95 °C for 30 min, after cooled to room temperature, the slurry was centrifuged at 4000g for 20 min, and the weight of the swollen sediment was determined. The supernatant was dried by evaporation at 130 °C for 5 h, and the weight of the residue recorded. Swelling power was the ratio of wet sediment over its dry weight, and solubility was calculated as the ratio of dried supernatant to the initial dry weight of starch. Pasting properties of isolated tea seed starch (8.0%, w/w dry starch basis, dsb; 28 g total weight) were analyzed using a Rapid Visco Analyzer (RVA3, Newport Scientific Pty. Ltd., Warriewood, NSW, Australia) [17]. The procedure was running as following: 1 min at 30 °C, heat to 95 °C at a rate of 6.0 °C/min and hold for 5.5 min, then cool to 50 °C at the same rate and maintain at 50 °C for 5 min. The rotating speed of paddle throughout the entire analysis was 160 rpm except for a speed of 960 rpm for the first 10 s to disperse the sample. The peak viscosity (PV), tough viscosity (TV), final viscosity (FV) and paste temperature (PT) were recorded, breakdown viscosity (BV=PV-TV), setback viscosity (SV=FV-TV) were calculated. 2.3.5. Thermal properties Thermal properties of tea seed starch were determined by differential scanning calorimeter (DSC) (Q20, TA Instruments, New Castle, DE, USA) [18]. Starch (2.0 mg, dry weight basis) was weighed into an aluminum pan and 6 μL MilliQ water was added. The pan was hermetically sealed and equilibrated at room temperature for 1 h, then scanned at the heating rate of 10 °C/min from 30 to 110 °C with an empty sealed pan as a reference. The onset temperature (To), peak temperature (Tp), conclusion temperature (Tc), and ΔH were analyzed with a Universal Analysis Program, Version 4.4A. After first scanning, the scanned sample pans were placed in a refrigerator at 4 °C for 7 days. Retrogradation properties were measured by rescanning the sample pans at the rate of 10 °C/min from 25 to 110 °C. The onset (To(R)), peak (Tp(R)), conclusion (Tc(R)) temperatures, and ΔHret were determined. 2.3.6. Starch granule morphology and size analysis Starch powders were spread on silver tape and mounted on a brass disk, coated with gold powder, then observed with a HITACHI TM-1000 scanning electron microscope (SEM) (Tokyo, Japan). Granule size of starches was detected using a laser light scattering particle size analyzer (LS13320, Beckmacoulter, USA). Tea seed starch (0.25 g) was vortexed in a small glass vial with 3 mL distilled water, then sonicated for 1 h. The sample was loaded to the sample port by drops until the instrument read 45% polarization intensity differential scattering (PIDS) or 10–14% obscuration. Isopropanol was used as the suspension fluid and the sample was allowed to equilibrate with the isopropanol for 15 min before starting the analysis. 2.3.7. Starch crystallinity X-ray diffraction pattern was performed with copper Kα radiation on a Siemens D-500 X-ray diffractometer (Siemens, Madison, WI). The scanning regions of the diffraction angle 2θ were 4°–40°. Degree of crystallinity was calculated according to the method of Hayakawa et al. [19]. 2.3.8. Amylopectin fraction and amylopectin chain-length distribution determination Amylopectin fractionation was conducted as Kong et al. [20]. The chain-length distribution of the debranched sample was analyzed with the Carbo-Pac PA-100 column (250 × 4 mm, with a guard column) following a previous report using a high-performance anion-exchange

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2.3.9. Statistical analysis All tests were triplicate. The data were subjected to one-way analysis of variance (ANOVA) followed by Duncan's test using IBM SPSS version 19.0 (IBM, Chicago, USA).

Volume

chromatography (HPAEC) system (Dionex ICS-5000+, Sunnyvale, CA, USA) coupled with a BioLC gradient pump and a pulsed amperometric detector (PAD) [21].

King8 Minred6 Wun4

King8 0

10

20

30

40

50

Diameter ( m) Fig. 2. Particle size analysis of the starches separated from different tea seed.

3. Results 3.1. Structure of starch granule

Minred6

3.1.1. Starch granules morphology The starch granules of three tea seed all showed flat spherical or oval with smooth surface, some with shallow depressions in the surface. For Wun4, more small and damaged starch granules were observed and the starch granules showed liable to aggregate together (Fig. 1). Starch granules size of King8 and Minred6 showed unimodal distribution, and the diameter ranged 3.2–17.2 μm and 3.5–17.2 μm for King8 and Minred6, respectively (Fig. 2), while for Wun4, the starch granules showed bimodal distribution, with majority ranged from 2.7 to 20.9 μm. On average, Minred6 starch had the smallest granules with 9.24 μm, whereas Wun4 starch had the largest granules with 9.72 μm (Table 1). 3.1.2. Crystalline properties of tea seed starches The external chains of amylopectin interact with each other and water to form crystalline structure. The arrangement of the crystals of the granules gives rise to A-, B-, and C three-types [22]. The X-ray diffraction pattern of King8 and Minred6 showed typical A-type diffraction pattern with strong peaks at 15.2°, 17.2°, 18.1° and 23.1° (2θ) (Fig. 3). While Wun4 showed a different diffraction pattern, with a wide reflection among 22°–24° and weak diffraction peak around 15° and 18.1°. Additionally, the relative crystallinity of starches demonstrated the lowest for Wun4 (Table 1).

Wun4

3.1.3. Amylopectin branch chain-length distribution of tea seed starches Amylopectin chain-length distribution of tea seed starches were shown in Table 2. Amylopectin chain length distribution showed a peak DP (degree of polymerization) at 13 and the highest detectable DP were up to 60, 69 and 74 for King8, Minred6 and Wun4, respectively, the lowest detected DP for tea seed starch was DP 3. The average chain Table 1 Physiochemical properties of tea seed starch.⁎

Starch (%) Total lipid (%) Protein (%) Crystallinity (%) Mean diameter (μm) Swelling power (g/g) Solubility (%) Resistant Starch (%) Apparent amylose (%) Fig. 1. Scanning electron micrographs (SEM) of tea starch granules.

King8

Minred6

Wun4

91.61 ± 0.17a 0.40 ± 0.03a 0.087 ± 0.001b 19.19 ± 0.08b 9.25 ± 0.00a 40.27 ± 1.35b 8.17 ± 1.04b 1.75 ± 0.04c 27.06 ± 0.47a

91.95 ± 0.26a 0.43 ± 0.04a 0.073 ± 0.001a 18.78 ± 0.34b 9.24 ± 0.00a 36.25 ± 0.43a 9.70 ± 2.00b 1.59 ± 0.05b 30.58 ± 0.31b

92.18 ± 0.20a 0.92 ± 0.01b 0.077 ± 0.004a 9.53 ± 0.89a 9.72 ± 0.00a 40.80 ± 1.14b 2.27 ± 0.31a 1.480 ± 0.02a 33.17 ± 0.45c

⁎ The same small letters indicated there were no significant differences among the three tea (P b 0.05).

Please cite this article as: J. Huang, M. Yuan, X. Kong, et al., A novel starch: Characterizations of starches separated from tea (Camellia sinensis (L.) O. Ktze) seed..., , https://doi.org/10.1016/j.ijbiomac.2019.08.044

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Intensity

4

King8 Minred6 Wun4

4

8

12

16

20

24

28

32

2 () Fig. 3. XRD patterns of the tea starches. Data have been offset for clarify.

length was DP 19.51 for King8, DP 19.27 for Minred6 and DP 19.87 for Wun4 (Table 2). Corresponding to fractions A, B1, B2, and B3 and longer chains, the side chains of amylopectin could be classified into four fractions: fa with DP b 12, fb1 with 13 b DP b 24, fb2 with 25 b DP b 36 and fb3 with DP N 37 [23]. They three starch had similar proportion of fa (DP ≤ 12), and king8 had more chains DP 3–5. While starch from Wun4 had the highest proportion of fb3 (DP ≥ 36) chains and chains DP 8–12, whereas the fb1 (DP 13–24), fb2 (DP 25–36) chains proportion were the lowest. 3.2. Physicochemical properties of tea seed starch 3.2.1. Amylose and resistant starch The chemical components of the tea starch are presented in Table 1. The protein contents were ranged from 0.073% to 0.087%, and the total lipid contents were about 0.40%, 0.43% and 0.92% for King8, Minred6 and Wun4, respectively. Amylose content differed significantly among three Camellia sinensis cultivars. King8 starch had the lowest (27.06%) whereas Wun4 had the highest amylose content (33.17%). The amylose content observed for tea seed starches was higher than that of corn (16.9–21.3%) [24] and cassava (16.8–21.5%) [25], but similar to potato (29.7–33.3%) [26]. The resistant starch (RS) content were 1.75%, 1.59% and 1.48% for King8, Minred6 and Wun4 respectively. 3.2.2. Swell ability and solubility The swell ability and solubility of the tea seed starches in excess water also differed significantly. Swelling power of starches ranged from 36.3 g/g to 40.8 g/g, and solubility values were in the range of 2.27% to 9.70%. Wun4 had the largest swelling power and the Minred6 had the smallest, while the solubility was in verse, Minred6 had the highest and Wun4 had the lowest. 3.2.3. Gelatinization properties Thermal properties of native and retrograded starches were summarized in Table 3. King8 and Minred6 showed peak gelatinization temperature higher than 74 °C. To, Tp and Tc of Wun4 starch were 60.84 °C, 64.99 °C and 70.47 °C, respectively, which were significantly lower than that of King8 and Minred6. However, small differences (P b 0.05)

were observed for ΔHgel among three starches, which indicated the double helical structures of Wun4, King8 and Minred6 were almost the same as ΔHgel reflected the loss of double helical structure rather than crystalline order [27]. The R value of Wun4 was the lowest and that of Minred6 was the highest. While PHI was found to be the lowest for Minred6 starch (1.48) and the highest for Wun4 (3.12). The molecular interactions (hydrogen bonding between starch chains) that occur after cooling of the gelatinized starch paste are known as retrogradation [28]. To(R) of retrograded starch ranged from 46.60 to 48.22 °C, lower than that of native starches (Table 3). Compared with the native starches, retrograded tea seed starches showed lower enthalpy. ΔHret for tea seed starches ranged from 4.29 to 6.09 J/g, the lowest for Wun4 and the highest for Minred6 (Table 3). 3.2.4. Pasting properties Significant difference in the pasting properties among different tea seeds was observed (Table 4). The pasting temperature was 79.12, 78.57 and 80.73 °C for King8, Minred6 and Wun4 starches, respectively. PV of tea seed starches is about 5300 cP. SV differed significantly among three tea starches. King8 had the lowest SV (1839 cP), which indicated the less ability of retrogradation among all three tea seed starches as SV reflected the retrogradation tendency of amylose [29]. 4. Discussion 4.1. Starch granule structure The variation in size and shape of starch granules may be due to their botanical origin and the biochemistry of the chloroplast or amyloplast, as well as physiology of the plant [30], i.e. the mean granule sizes of canna, potato, mung bean, and rice starches had been reported to be 52, 48, 24, and 7 μm, respectively [31], and the starch granule size of smooth pea ranged from 14 to 37 μm [32]. The spherical or oval starch granules of tea seed starch with 2.7–20 μm were similar to the ginkgo starch granules which were smooth, no pores surface and ranged from 5 to 20 μm [33]. The tea seed starches had more regular and smaller granules when compared with potato, bean, rice [31] and kiwifruit starch granules [34]. The morphology of starch granule could be one of important factors influencing starch functionality such as digestibility in vitro, since enzyme hydrolysis took place first on the surface of starch granules. Small intact starch granules of higher crystallinity were more resistant to amylolytic degradation [35]. Though Wun4 has a large number of small starch granules (Fig. 2), Wun4 had more large-size starch granules and also more damaged starch granules (Fig. 1), which may be the partial reason for its relatively lower RS content (Table 1). Also the low relative crystallinity of Wun4 might also contribute to the lower RS content. The starch crystallinity of tea seed showed lower than other crops [3], which might because of different crops, and also the different calculation method, the crystallinity in this study was microcrystal. The lowest relative crystallinities of Wun4 (9.53%) may be due to its highest amylose content, lipids content (Table 1) and more proportions of short amylopectin chains (Table 2) among three starches, which can also be observed by its special and weaker diffraction peaks (Fig. 3). Generally, orientation of the double helices within the crystalline

Table 2 Branch chain-length distribution of tea starch amylopectins.⁎

King8 Minred6 Wun4

Peak DP

Average CL

13 13 13

19.34 19.25 19.86

fa

fb1

fb2

fb3

DP 3–5 (%)

DP 6–12 (%) (DP8–12)

DP 13–24 (%)

DP 25–36 (%)

DP ≥ 37 (%)

0.41 ± 0.01b 0.37 ± 0.01a 0.38 ± 0.01a

23.01 ± 0.46a (19.03 ± 0.11a) 22.78 ± 0.31a (19.11 ± 0.11a) 24.20 ± 0.46a (20.39 ± 0.33b)

55.14 ± 1.13b 56.05 ± 0.34b 52.84 ± 0.24a

14.67 ± 0.44b 14.18 ± 0.20b 12.48 ± 0.12a

6.76 ± 0.18a 6.61 ± 0.23a 10.12 ± 0.04b

Highest detectable DP

60 69 74

⁎ The data are averages of three replicates. The same small letters indicated there were no significant differences among the three tea (P b 0.05).

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Table 3 Thermal properties of native and retrograded tea seed starches.⁎ First scanning

King8 Minred6 Wun4

Second scanning

To (°C)

Tp (°C)

Tc (°C)

ΔHgel (J/g)

PHI

R (°C)

To(R) (°C)

Tp(R) (°C)

Tc(R) (°C)

ΔHret (J/g)

PHI

R (°C)

68.56 ± 0.97e 68.31 ± 0.61e 60.84 ± 0.10d

76.03 ± 0.77c 77.04 ± 0.89c 64.99 ± 0.04b

82.22 ± 0.92c 82.74 ± 0.80c 70.47 ± 0.27b

12.80 ± 0.62c 12.90 ± 0.73c 12.94 ± 0.43c

1.71c 1.48c 3.12d

13.66b 14.58b 9.63a

47.40 ± 0.29b 46.60 ± 0.60a 48.22 ± 0.34c

57.58 ± 0.68a 57.40 ± 0.27a 58.34 ± 0.10a

66.75 ± 0.70a 66.93 ± 0.89a 66.62 ± 0.68a

5.37 ± 0.11ab 6.09 ± 1.02b 4.29 ± 0.11a

0.53b 0.56b 0.42a

19.35c 20.33c 18.40c

⁎ The same small letters indicated there were no significant differences among the three tea (P b 0.05). To = onset temperature, Tp = peak temperature, Tc = conclusion temperature, ΔH = enthalpy of gelatinization (dwb, based on starch weight), PHI (peak height index) = ΔH / (Tp-To), R = gelatinization range (Tc-To).

domains, extent of interaction between double helices and amylopectin content, and amylopectin chain length amount of crystalline regions all influence the relative crystallinity [32]. The double helical content decreases with increasing amylose content [36]. Amylose interfered in the crystal structure, and high amylose content and higher ratio of the short-chain amylopectin will imperfect the crystalline and result in lower crystallinity [37].

4.2. Amylopectin and RS, SP and gelatinization The detectable DP of tea starch ranged from DP3-DP70, and the peak DP was 13, which is typical A-type amylopectin [38]. But tea starch had lower average CL of 19.25–19.84 than normal rice (22.7), maize (24.4), Tapioca (27.6), and etc. [38]. Aslo the sum of A and B1 chains is only about 78%, lower than previous reported for waxy rice, tapioca, kuzu (89–91%) and potato amylopectin (82%) [38]. The ratio of A- to Bchains is typically 1:1 to 2:1 on a molar basis depends on the starch source [3], while the ratio of A (DP ≤ 12) to B (DP N 12) was only 0.3:1 (Table 2). As starch morphology, cooking properties and its functional behaviors were controlled by starch molecular structure [39], this special molecular structure of tea starch might give it some special properties. The chain length profile of amylopectin has been found to be relevant to functional properties of starch [40,41]. The differences in chain length distribution among tea seed starches may contribute to their different resistant starch content. Longer chains in amylopectin were associated with resistant starch in barley [42]. In rice, chains DP 8–12 showed positive and DP N 36 showed negative correlation with RS [43]. Wun4 had relative higher proportion of DP N 36 but also more chains with DP 8–12 (Table 2), that might be part of the reason for the significantly lower RS in statistics but the absolute differences were only 0.11–0.27% (Table 1). Amylopectin molecular structure also influenced the swelling and gelatinization of starch [44]. Starch gelatinization is a combined process of the hydration of an amorphous region and subsequent melting of crystalline arrays [45]. During gelatinization, starch granule swelling with water adsorption and amylose leaching. Further heating leads to the rupture of starch granules and dissolution of molecules. The higher gelatinization temperature was an indication of more perfect crystals or a large crystal size or longer chains in the crystal [46]. The lower transition temperature of Wun4 may be due to the lower crystallinity (Table 1) and lower proportion of fb1 and fb2 (Table 2). As PHI can

reflect the uniformity in gelatinization [47], the higher PHI of Wun4 may be attributed to the coexistence of larger and smaller starch granules (Fig. 2, Table 1). Different R values can be due to the presence of crystalline regions of different strength in the granule [48]. The higher R values of Minred6 starch may suggest the presence of crystallites of varying stability within the crystalline domains of its granule. Upon cooling, the paste undergoes retrogradation, starch chains interact with each other and water to re-associate and re-order [49]. Retrograded starch is the most common starch fraction in processed foods, and starch retrogradation can positively affect the quality of some extruded products i.e. rice noodles, but usually affects the nutritional properties and shelf-life of produced food [50]. The ΔH is energy needed for melting the starch crystalline zone, the less crystalline the sample, the smaller the amount of energy needed [51]. The lower ΔHret compared to ΔHgel (Tables 3, 4) may indicate the weaker starch crystallinity of retrograded starches [52]. The difference in ΔHret among various tea seed starches indicated the differences in their tendency towards retrogradation. The existence of lipids may disturb the reordering and aggregation of amylose, thus restrain the retrogradation of amylose and prevent recrystallization with amylopectin [50]. The retrogradation of starch is responsible for RS formation, and which is confirmed by the fact that Wun4 with the lowest ΔHret (Table 4) had the lowest RS content (Table 1).

4.3. Starch structure, AAC and starch paste properties The pasting temperatures of tea starch were comparable with that of normal rice (79.9 °C) but considerably lower than that of starches from maize (82 °C) and wheat (88.6 °C) [17]. PV reflects water-binding capacity or the extent of swelling of starch granules, and often correlates with the final product quality since the swollen and collapsed starch granules affect the texture of products [53]. The tea seed starch seems to have potential as additives in the food industry, with the PV of up to 5300 cp (Table 3). Amylose and long amylopectin chains may hold the granules together through entanglement and prevent it from swelling [54], increasing amylose contents or long amylopectin chain proportions significantly increased starch pasting temperature, trough viscosity (TV) and setback viscosity (SV) [17]. The highest content of amylose and most fb3 amylopectin of Wun4 (Tables 1, 2) may be the contributors for its higher TV and SV (Table 4). FV could be an indicator for the ability of the starch to form a viscous paste [55], the FV of tea seed starches was higher than that of most studied starches with only mung

Table 4 RVA profile of tea seed starches (8.0% dsb, w/w).⁎

King8 Minred6 Wun4

PV (cP)

TV (cP)

BV (cP)

FV (cP)

SV (cP)

PT (°C)

5203 ± 59a 5404 ± 88b 5310 ± 69ab

2256 ± 32a 2402 ± 337b 3329 ± 67c

2947 ± 30b 3003 ± 63b 1981 ± 39a

4095 ± 87a 5048 ± 73b 6764 ± 25c

1839 ± 68a 2646 ± 69b 3435 ± 45c

79.12 ± 0.03a 78.57 ± 0.51a 80.73 ± 0.03b

⁎ The same small letters indicated there were no significant differences among the three tea (P b 0.05). PV, peak viscosity; TV, trough viscosity; BV, breakdown viscosity; FV, final viscosity; SV, setback viscosity; PT, pasting temperature.

Please cite this article as: J. Huang, M. Yuan, X. Kong, et al., A novel starch: Characterizations of starches separated from tea (Camellia sinensis (L.) O. Ktze) seed..., , https://doi.org/10.1016/j.ijbiomac.2019.08.044

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Please cite this article as: J. Huang, M. Yuan, X. Kong, et al., A novel starch: Characterizations of starches separated from tea (Camellia sinensis (L.) O. Ktze) seed..., , https://doi.org/10.1016/j.ijbiomac.2019.08.044