Physicochemical Properties of C-Type Starch from Root Tuber of Apios Fortunei in Comparison with Maize, Potato, and Pea Starches

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Article Physicochemical Properties of C-Type Starch from Root Tuber of Apios fortunei in Comparison with Maize, Potato, and Pea Starches

Juan Wang 1,2, Ke Guo 1,2, Xiaoxu Fan 1,2, Gongneng Feng 1,2 and Cunxu Wei 1,2,* ID

1 Key Laboratory of Crop Genetics and Physiology of Jiangsu Province/Key Laboratory of Plant Functional Genomics of the Ministry of Education, Yangzhou University, Yangzhou 225009, China; [email protected] (J.W.); [email protected] (K.G.); [email protected] (X.F.); [email protected] (G.F.) 2 Co-Innovation Center for Modern Production Technology of Grain Crops of Jiangsu Province/Joint International Research Laboratory of Agriculture & Agri-Product Safety of the Ministry of Education, Yangzhou University, Yangzhou 225009, China * Correspondence: [email protected]; Tel.: +86-514-8799-7217; Fax: +86-514-8797-1747

Received: 8 August 2018; Accepted: 22 August 2018; Published: 24 August 2018

Abstract: The dry root tuber of Apios fortunei contained about 75% starch, indicating that it is an important starch resource. Starch displayed spherical, polygonal, and ellipsoidal granules with central hila. Granule sizes ranged from 3 to 30 µm with a 9.6 µm volume-weighted mean diameter. The starch had 35% apparent amylose content and exhibited CA-type crystalline structure with 25.9% relative crystallinity. The short-range ordered degree in the granule external region was approximately 0.65, and the lamellar thickness was approximately 9.6 nm. The swelling power and water solubility began to increase from 70 ◦C and reached 28.7 g/g and 10.8% at 95 ◦C. Starch had typical bimodal thermal curve in water with gelatinization temperatures from 61.8 to 83.9 ◦C. The 7% (w/w) starch-water slurry had peak, hot, breakdown, ﬁnal, and setback viscosities of 1689, 1420, 269, 2103, and 683 mPa s, respectively. Rapidly digestible starch, slowly digestible starch, and resistant starch were 6.04%, 10.96%, and 83.00% in native starch; 83.16%, 15.23%, and 1.61% in gelatinized starch; and 78.13%, 17.88%, and 3.99% in retrograded starch, respectively. The above physicochemical properties of A. fortunei starch were compared with those of maize A-type starch, potato B-type starch, and pea C-type starch. The hierarchical cluster analysis based on starch structural and functional property parameters showed that A. fortunei and pea starches had similar physicochemical properties and were more related to maize starch than potato starch.

Keywords: Apios fortunei; root tuber; C-type starch; structural properties; functional properties

1. Introduction Starch is synthesized in plastid and exists as semicrystalline granules in plants. It contains transient (also named as assimilatory) and reserve starches. The reserve starch (usually called starch) is synthesized and stored in plant storage tissues including seed, fruit, tuber, rhizome, corm, bulb, and some metamorphosis roots [1–4]. It not only provides humans and animals with nutrition and energy but is also widely utilized in food and non-food industries due to its abundant availability and low cost. Starches from different botany sources have different physicochemical properties, leading to their different applications [1–3]. Cereal endosperm, legume embryo, and some tubers are conventional starch resources and have been extensively studied and commercial used [2,5–9]. However, there is demand for new starches to be found for the development of food and non-food industries. Therefore,

Molecules 2018, 23, 2132; doi:10.3390/molecules23092132 www.mdpi.com/journal/molecules Molecules 2018, 23, 2132 2 of 15 some nonconventional starch resources have been studied in some fruit kernels [3], tubers of Arisaema species [10], and kernels of Trapa species [11,12] in recent years. Starch mainly consists of amylose and amylopectin. The amylose is a mixture of linear and poorly branched polyglucans, and the amylopectin is highly branched polyglucans. The amylopectin branch-chains form double helices, which are laterally packed to form crystalline lattice. The crystalline lattice has two crystalline structures of A- and B-type allomorphs in plants [13]. However, three types of plant starch (A-, B-, and C-type) are reported according to their X-ray diffraction (XRD) patterns. A-type starch contains only A-type allomorph, and B-type starch contains only B-type allomorph [14]. Compared with A- and B-type starches, the C-type starch is complex and contains both A- and B-type allomorphs. The different proportions of A- and B-type allomorphs further classify C-type starches into CA-(closer to A-type), CC- (typical C-type), and CB-type (closer to B-type) [15]. Recently, He and Wei [15] summarizes four distribution patterns of A- and B-type allomorphs in C-type starch. (1) A- and B-type allomorphs exist in the same granule with centric hilum and are distributed in the outer and inner regions of granule, respectively, such as pea C-type starch [16,17]. (2) A- and B-type allomorphs exist in the same granule with centric hilum but are distributed in the inner and outer regions of granule, such as C-starch from high-amylose rice TRS [18]. (3) A- and B-type allomorphs exist in the same granule with eccentric hilum and are distributed in the different regions of granules such as lotus rhizome C-type starch [19,20]. (4) A- and B-type allomorphs exist in the different granules, such as some high-amylose maize starches [21]. The different distribution patterns and proportions of A- and B-type allomorph have important effects on the physicochemical properties and applications of C-type starches [15,22], though previous studies find that A- and B-type allomorphs are distributed in the same granules of normal C-type starches [16–22]. Recently, a new C-type starch has been detected in root tuber of Apios fortunei, and its A- and B-type allomorphs are distributed in different starch granules. The B-type granules have significantly lower gelatinization temperature than A-type granules, but their morphology, size, and amylose content are similar [23]. To our knowledge, this is the first time the allomorph distribution pattern of normal C-type starch has been reported. However, its physicochemical properties have not been investigated and compared with conventional and commercial starches, which restricts its applications in the food industry. In this study, starch was isolated from root tubers of A. fortunei and its morphology, structure, and functional properties were investigated and compared with those of maize A-type starch, potato B-type starch, and pea C-type starch. Our objective was to characterize the physicochemical properties of starch from A. fortunei and provide some information for its utilization in food industry.

2. Results and Discussion

2.1. Starch and Soluble Sugar Contents in Root Tuber of A. fortunei A. fortunei had 75.1% starch and 7.6% soluble sugar in dry root tuber. Usually, plant storage tubers and roots have starch contents from 30% to 88% [5], legume seeds contain starch from 20% to 47% [9], and cereal seeds have starch contents over 65% [24]. In addition, the dry root tuber of A. americana contains 68% starch [25]. Therefore, compared with conventional and commercial starch resource of cereal, legume, tuber, and root crops, the high starch content in Apios root tuber indicated that it is an important resource of starch.

2.2. Morphology and Granule Sizes of Starch The polarized light microscope was used to observe the morphology of starch granule under normal and polarized light. This result is present in Figure1. A. fortunei starch had spherical, polygonal, and ellipsoidal shapes with central hila. Most starch granules of maize were polygonal with central hila; potato starch had small spherical granules with central hila and large ellipsoidal granules with eccentric hila; and most of pea starch granules were elliptical and had central hila. Similar morphology in Molecules 2018, 23, x FOR PEER REVIEW 3 of 15

Molecules 2018, 23, 2132 3 of 15 granules with eccentric hila; and most of pea starch granules were elliptical and had central hila. Similar morphology in A. fortunei, maize, potato, and pea starches has been reported in previous A.literature fortunei ,[1,23,26]. maize, potato, A. fortunei and pea starch starches showed has unimodal been reported size indistribution, previous literature and sizes [1 ,23ranged,26]. A. from fortunei 3 to starch30 μm. showed However, unimodal maize, size potato, distribution, and pea and starches sizes rangedhad bimodal from 3 size to 30 distribution,µm. However, and maize, the volume potato, andpercentages pea starches of small had bimodal granules size were distribution, 8.1%, 5.8%, and an thed 6.2%, volume respectively. percentages The of small sizes granules of small wereand 8.1%,large 5.8%,granules and ranged 6.2%, respectively. from 0.4 to The 3 μ sizesm and of from small 6 and to large40 μm granules in maize ranged starch, from from 0.4 0.6 to 3toµ m6 μ andm and from from 6 to 4010 µtom 100 in maize μm in starch, potato from starch, 0.6 toand 6 µ fromm and 0.6 from to 6 10μm to and 100 µfromm in 10 potato to 70 starch, μm in and pea from starch, 0.6 respectively. to 6 µm and fromA. fortunei 10 to 70 starchµm in had pea starch,the smallest respectively. granuleA. fortuneisize, andstarch potato had starch the smallest had the granule largest size, granule and potato size starchamong had four the starches largest granule(Table 1). size Similar among granule four starches sizes in (Table A. fortunei1). Similar, maize, granule potato, sizes and in peaA. starches fortunei, maize,have been potato, reported and pea [1,23,26]. starches The have morphology, been reported granule [1,23,26 size,]. The and morphology, hilum position granule of starch size, and is mainly hilum positionattributed of to starch the botany is mainly origin attributed [27]. to the botany origin [27].

FigureFigure 1.1.Morphology Morphology of starchof starch under under normal normal light microscope light microscope (NLM) and(NLM) polarized and lightpolarized microscope light (PLM)microscope and granule (PLM) and size granule distribution. size distribution. Scale bar = 20 Scaleµm. bar = 20 μm.

Table 1.1. GranuleGranule sizessizes ofof starch.starch. Starches d(0.1) (μm) d(0.5) (μm) d(0.9) (μm) D[4,3] (μm) Starches d(0.1) (µm) d(0.5) (µm) d(0.9) (µm) D[4,3] (µm) A. fortunei 5.403 ± 0.002 a 8.947 ± 0.002 a 14.760 ± 0.004 a 9.584 ± 0.002 a a a a a A. fortuneiMaize 5.403 7.519± 0.002 ± 0.031 b 8.947 13.767± 0.002 ± 0.078 b 14.760 21.305± 0.004 ± 0.173 b 9.584 13.895± 0.002 ± 0.086 b Maize 7.519 ± 0.031 b 13.767 ± 0.078 b 21.305 ± 0.173 b 13.895 ± 0.086 b Potato 16.317 ± 0.010 c 34.420 ± 0.004 d 62.406 ± 0.036 d 36.778 ± 0.006 d Potato 16.317 ± 0.010 c 34.420 ± 0.004 d 62.406 ± 0.036 d 36.778 ± 0.006 d c c c c PeaPea 16.255 16.255± 0.078 ± 0.078c 27.518 27.518± 0.169 ± 0.169c 41.917 41.917± 0.359 ± 0.359c 27.922 27.922± 0.204± 0.204c TheThe d(0.1), d(0.1), d(0.5), d(0.5), and and d(0.9) d(0.9) are the are granule the granule sizes at which sizes 10, at 50,which and 90% 10, of50, all and the granules90% of byall volume the granules are smaller, by respectively.volume are Thesmaller, D[4,3] respectively. is the volume-weighted The D[4,3] meanis the diameter. volume-weighted Data are means mean± diameter.standard deviations,Data are meansn = 3. Different± standard superscript deviations, letters n (from= 3. Differenta to d) in the superscript same column letters indicate (from significantly a to d) in difference the same at pcolumn< 0.05. indicate significantly difference at p < 0.05. 2.3. Iodine Absorption Spectrum and Apparent Amylose Content of Starch 2.3. Iodine Absorption Spectrum and Apparent Amylose Content of Starch The absorbance spectrum of starch-iodine complex is shown in Figure2, and its derived maximumThe absorbance absorption wavelengthspectrum of ( λstarch-iodinemax), iodine blue comp valuelex (BV,is shown absorbance in Figure at 680 2, nm), and and its apparent derived amylosemaximum content absorption (AAC) wavelength are presented (λmax in), iodine Table2 .blue The valueλmax (BV,can reflectabsorbance the average at 680 nm), chain and length apparent and polymerization degree of amylopectin and amylose, the BV is related to the affinity of starch and iodine,

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Molecules 2018, 23, 2132 4 of 15 amylose content (AAC) are presented in Table 2. The λmax can reflect the average chain length and polymerization degree of amylopectin and amylose, the BV is related to the affinity of starch and andiodine, the and AAC the indicates AAC indicates the absorbance the absorbance of iodine by of amylopectiniodine by amylopectin longer branch-chains longer branch-chains and amylose [and28]. A.amylose fortunei [28].and A. potato fortunei starches and potato had similar starchesλmax had, which similar was λmax signiﬁcantly, which was higher significantly than that higher of maize than starchthat of andmaize lower starch than and that lower of pea than starch. that Normally, of pea starch. AAC Normally, is an important AAC parameteris an important in determining parameter the in propertiesdetermining and the applications properties of and starch applicatio [7,21]. Thens of AAC starch in A. [7,21].fortunei Thestarch AAC was in signiﬁcantly A. fortunei higherstarch thanwas insignificantly maize starch higher and lowerthan in than maize in potatostarch andand pealower starches. than in The potato AACs and of pea maize starches. and potato The AACs starches of determinedmaize and potato by iodine starches adsorption determined method by areiodine 31% adsorption and 43%, respectively method are [ 2631%], and and were 43%, similar respectively to the present[26], and results. were similar However, to theA. present americana results.starch However, has about A. 32% americana amylose starch determined has about using 32% an amylose iodine potentiometricdetermined using autotitrator an iodine [29 potentiometric], legume starch autoti hastrator amylose [29], content legume ranging starch fromhas amylose 17% to 52%content [9], andranging tuber from starch 17% has to amylose 52% [9], content and tuber ranging starch from has 26% amylose to 45% content [8]. The ranging difference from in amylose26% to 45% content [8]. ofThe different difference starches in amylose might resultcontent from of thedifferent different starches species, might varieties, result growingfrom the environments, different species, and amylosevarieties, measuring growing environments, methods [1,9, 29and,30 am]. ylose measuring methods [1,9,29,30].

Figure 2. Spectrum of iodine absorbance of starch.

Table 2. Maximum absorption wavelength (λmax), iodine blue value (BV), apparent amylose content Table 2. Maximum absorption wavelength (λmax), iodine blue value (BV), apparent amylose content (AAC), andand relativerelative crystallinitycrystallinity (RC)(RC) ofof starch.starch.

Starches λmax (nm) BV AAC (%) RC (%) Starches λ (nm) BV AAC (%) RC (%) A. fortunei 597.3max ± 0.6 b 0.355 ± 0.007 b 35.0 ± 0.6 b 25.9 ± 0.1 c b b b c MaizeA. fortunei 597.3 594.3± ±0.6 0.6 a 0.355 0.328± ± 0.0070.003 a 35.0 30.9± ±0.6 0.3 a 25.9 20.0± 0.1 ± 0.9 b Maize 594.3 ± 0.6 a 0.328 ± 0.003 a 30.9 ± 0.3 a ± b Potato 598.3 ± 0.6 b 0.403 ± 0.008 c 41.0 ± 0.4 c 20.0 20.00.9 ± 0.6 b Potato 598.3 ± 0.6 b 0.403 ± 0.008 c 41.0 ± 0.4 c 20.0 ± 0.6 b Pea 613.3 ± 0.6 c 0.460 ± 0.006 d 47.0 ± 0.3 d 16.9 ± 0.1 a Pea 613.3 ± 0.6 c 0.460 ± 0.006 d 47.0 ± 0.3 d 16.9 ± 0.1 a Data are means ± standard deviations, n = 3. Different superscript letters (from a to d) in the same Data are means ± standard deviations, n = 3. Different superscript letters (from a to d) in the same column indicate signiﬁcantlycolumn indicate difference significantly at p < 0.05. difference at p < 0.05.

2.4. Crystalline Structure of Starch The XRD patternspatterns ofof starchesstarches areare shown shown in in Figure Figure3. 3. Maize Maize starch starch had had strong strong diffraction diffraction peaks peaks at aboutat about 15 15°◦ and and 23 23°◦ 2θ 2θand and an an unresolved unresolved doublet doublet at at 17 17°◦ and and 18 18°◦ 2 2θθ,, exhibiting exhibiting aa typicaltypical A-typeA-type XRD pattern. PotatoPotato starchstarch showed showed characteristic characteristic peaks peaks at 5.6 at◦ ,5.6°, 15◦, 15°, 17◦, 2217°,◦, and22°, 23and◦ 2 θ23°, displaying 2θ, displaying a typical a B-typetypical XRDB-type pattern. XRD pattern. Compared Compared with maize with and maize potato and starches, potato starches, pea starch pea had starch peak had at about peak 5.6at about◦ and 235.6°◦ 2θand, which 23° are2θ, thewhich characteristic are the characteristic peak of B-type peak and A-typeof B-type starch, and respectively, A-type starch, indicating respectively, that pea starchindicating contained that pea A- starch and B-type contained allomorphs A- and and B-type was allomorphs C-type starch. and The was XRD C-type pattern starch. of A. The fortunei XRD

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pattern of A. fortunei starch was similar to that of pea starch, except that the shoulder peak at 18° 2θ ◦ starchwas more was pronounced similar to that in ofA. peafortunei starch, starch, except exhibiting that the shouldera CA-type peak starch at in 18 A.2 fortuneiθ was more. Usually, pronounced normal incerealA. fortunei seeds havestarch, A-type exhibiting starch, a tuber CA-type crops starch have in B-typeA. fortunei starch,. Usually,and legume normal seeds cereal and seedssome haveplant A-typerhizomes starch, have tuber C-type crops starch have [1,2,14,15]. B-type starch, However, and legume the A-, seeds C-, and and some B-type plant starches rhizomes have have also C-type been starchreported [1,2 in,14 root,,15]. However,tuber, and the legume A-, C-, crops and B-type [5,6]. Th starchese C-type have starch also beenis detected reported in inroot root, tubers tuber, of and A. legumeamericana crops and [ 5fortunei,6]. The [23,26]. C-type starchThe environmen is detectedt, in especially root tubers growth of A. americanatemperature,and fortuneihas important[23,26]. Theeffects environment, on the crystalline especially structure growth temperature, of starch [1 has,4,30]. important In root effects tuber on of the sweet crystalline potato, structure the low of starchtemperature [1,4,30 ].forms In root B-type tuber ofcrystallinity sweet potato, and the the low high temperature temperature forms forms B-type A-type crystallinity crystallinity; and the hightherefore, temperature the proportion forms A-type of A- crystallinity; and B-type therefore,allomorphs the in proportion C-type starch of A- is and affected B-type by allomorphs growing intemperature, C-type starch resulting is affected in CA by-, C growingC-, and C temperature,B-type starch resulting[30]. The inrelative CA-, C crystallinityC-, and CB-type was the starch highest [30]. Thein A. relative fortunei crystallinity starch and the was lowest the highest in pea in starchA. fortunei (Tablestarch 2). and the lowest in pea starch (Table2).

FigureFigure 3.3. XRDXRD patternpattern ofof starch.starch.

2.5.2.5. Short-Range OrderedOrdered StructureStructure ofof StarchStarch TheThe short-rangeshort-range order ofof starchstarch reflectsreflects doubledouble helicalhelical orderorder andand cancan bebe measuredmeasured byby FourierFourier transformtransform infraredinfrared (FTIR)(FTIR) spectrometer.spectrometer. The attenuatedattenuated total reflectancereflectance (ATR)-FTIR(ATR)-FTIR spectrumspectrum isis usuallyusually usedused toto analyzeanalyze thethe short-rangeshort-range ordered structurestructure in external region of starch granule [31]. [31]. TheThe FigureFigure4 4 shows shows the the deconvoluted deconvoluted ATR-FTIR ATR-FTIR spectra spectra of of starches. starches. The The significant significant difference difference was was −1 seenseen atat bandband ofof 10221022 cmcm−1 amongamong four four starches, starches, which which is is associat associateded with with amorphous amorphous region of starch. −1 TheThe absorbanceabsorbance atat 10451045 cmcm−1 is relativerelative toto thethe ordered/crystallineordered/crystalline region ofof starch.starch. TheThe absorbanceabsorbance −1 −1 ratioratio ofof 1045/10221045/1022 cmcm−1 cancan show show the the ordered ordered degree ofof starch,starch, andand that that of of 1022/995 1022/995 cm cm−1 reflectsreflects thethe proportionproportion ofof amorphousamorphous toto orderedordered carbohydratecarbohydrate structure structure in in starch starch [ 31[31].]. The The IR IR ratios ratios of of 1045/1022 1045/1022 −1 andand 1022/9951022/995 cm cm− are1 are presented presented in in Table Table 3.3 .The The A.A. fortunei fortunei starchstarch had had significantly significantly different different ratios ratios of −1 of1045/1022 1045/1022 and and 1022/995 1022/995 cm cm from−1 from the the other other starches, starches, indicating indicating that that it it had had different short-rangeshort-range orderedordered structurestructure inin starchstarch externalexternal region.region. The ordered structure in starchstarch externalexternal regionregion hashas significantsignificant effectseffects onon swellingswelling power,power, pastingpasting viscosity, viscosity, and and hydrolysis hydrolysis of of starch starch [ 32[32].].

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Figure 4. ATR-FTIR spectrum of starch.

Table 3. Parameters of short-range ordered structurestructure and lamellar structure ofof starch.starch. Ordered Structure Parameters Lamellar Structure Parameters Starches Ordered Structure− Parameters− Lamellar Structure− Parameters Starches 1045/1022 cm 1 1022/995 cm 1 Imax (Counts) Smax (Å 1) D (nm) 1045/1022 cm−1 1022/995 cm−1 I (Counts) S (Å−1) D (nm) A. fortunei 0.648 ± 0.004 b 0.883 ± 0.018 c 215.3max ± 0.7 c 0.066max ± 0.001 b 9.60 ± 0.14 a b c c b a A.Maize fortunei 0.648 0.623± ± 0.0040.009 a 0.8370.883 ± 0.0160.018 b 217.7215.3 ± 6.50.7 c 0.0630.066 ±± 0.001 a 10.059.60 ±± 0.140.07 b Maize 0.623 ± 0.009 a 0.837 ± 0.016 b 217.7 ± 6.5 c 0.063 ± 0.001 a 10.05 ± 0.07 b Potato 0.816 ± 0.010 c 0.763 ± 0.011 a 170.1 ± 0.4 b 0.067 ± 0.001 b 9.40 ± 0.01 a Potato 0.816 ± 0.010 c 0.763 ± 0.011 a 170.1 ± 0.4 b 0.067 ± 0.001 b 9.40 ± 0.01 a a a a a b PeaPea 0.623 ± ± 0.0080.008a 0.7810.781 ± 0.0050.005 a 154.6154.6 ± 3.8 a 0.0610.061 ±± 0.001a 10.3010.30 ± 0.010.01 b Imax: lamellar peak intensity; Smax: lamellar peak position; D: lamellar thickness. Data are means ± Imax: lamellar peak intensity; Smax: lamellar peak position; D: lamellar thickness. Data are means ± standard deviations, nstandard= 2. Different deviations, superscript n letters= 2. Different (from a to csuperscript) in the same columnletters indicate(from a significantly to c) in the difference same column at p < 0.05. indicate significantly difference at p < 0.05. 2.6. Lamellar Structure of Starch 2.6. Lamellar Structure of Starch The lamellar structure of alternating amorphous and crystalline regions in starch granule can be detectedThe bylamellar small-angle structure X-ray of scatteringalternating (SAXS) amorphous instrument and crystalline [13]. The SAXS regions spectra in starch of A. granule fortunei, can maize, be potato,detected and by peasmall-angle starches areX-ray presented scattering in Figure(SAXS)5. instrument All spectra were[13]. The normalized SAXS spectra to equal of intensityA. fortunei at, highmaize, q (qpotato, = 0.2 Åand−1 )pea to accountstarches for are variations presented in in sample Figure concentration, 5. All spectra causing were normalized the spectra to to equal be at theintensity same at relative high q scale (q = and0.2 Å therefore−1) to account directly for comparablevariations in [ 33sample]. The concentration, lamellar structure causing parameters the spectra are presentedto be at the in Tablesame3 .relative The lamellar scale and peak therefore intensity directly was the highestcomparable in A. [33]. fortunei Theand lamellar maize structure starches andparameters the lowest are inpresented pea starch. in Table The peak3. The intensity lamellar reflectspeak intensity the degree was of the ordering highest inin semicrystallineA. fortunei and regionsmaize starches [34]. The and main the scattering lowest in peak pea at starch. 0.065 ÅThe−1 arisespeak fromintensity the periodicreflects arrangementthe degree of of ordering alternating in crystallinesemicrystalline and amorphousregions [34]. region The andmain corresponds scattering topeak lamellar at 0.065 repeat Å distance−1 arises [13from]. A. the fortunei periodicand potatoarrangement starches of hadalternating similar lamellarcrystalline repeat and distances,amorphous which region were and significantly corresponds larger to lamellar than those repeat of maizedistance and [13]. pea A. starches. fortunei Theand lamellar potato starches structure had of starch similar is relatedlamellar to repeat plant origindistances, but haswhich no directwere relationshipsignificantly withlarger crystalline than those type. of maize For the and starch pea starches. from the The same lamellar plant origin, structure the of amylose starch contentis related is significantlyto plant origin negatively but has correlatedno direct withrelationship peak intensity with crystalline and positively type. correlated For the starch with lamellar from the distance same ofplant SAXS origin, spectrum the amylose [34,35]. Lamellarcontent is thickness significantly and peak negatively intensity correlated have significant with peak effects intensity on swelling and power,positively thermal correlated properties, with lamellar and hydrolysis distance of of starch SAXS [32 spectrum]. [34,35]. Lamellar thickness and peak intensity have significant effects on swelling power, thermal properties, and hydrolysis of starch [32].

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FigureFigure 5.5.SAXS SAXSpattern patternof ofstarch. starch.

2.7.2.7. ThermalThermal PropertiesProperties ofof StarchStarch TheThe thermalthermal propertiesproperties ofofA. A. fortuneifortunei,, maize,maize, potato,potato, andand peapea starchesstarches areare presentedpresented inin FigureFigure6 6 andand TableTable4 .4. TheThe maize, potato, potato, and and pea pea starches starches had had single single gelatinization gelatinization peak. peak. Potato Potato starch starch had hadsignificantly signiﬁcantly lower lower gelatinization gelatinization temperature temperature and higher and higher gelatinization gelatinization enthalpy enthalpy than thanthe other the otherstarches. starches. However, However, A. fortuneiA. fortunei starchstarch had two had gelatinization two gelatinization peaks peakswith peak with temperatures peak temperatures at 68.0 atand 68.0 75.6 and °C. 75.6 The◦ C.two The peaks two resulted peaks resulted in the wide in the gelatinization wide gelatinization temperature temperature range (22.1 range °C). (22.1 Usually,◦C). Usually,A-type A-typecrystallinity crystallinity has high has highgelatinization gelatinization temperature temperature and and B-type B-type crystallinity crystallinity has has lowlow gelatinizationgelatinization temperaturetemperature [[16,30].16,30]. C-typeC-type starchstarch containscontains A-A- andand B-typeB-type crystallinitiescrystallinities andand hashas widewide gelatinizationgelatinization temperature temperature range range with with single single gelatinization gelatinization peak peak in water in water [16,30 ].[16,30]. When C-typeWhen C-type starch isstarch gelatinized is gelatinized in KCl solution, in KCl twosolution, gelatinization two gela peakstinization are detected peaks are for thedetected changes for of the gelatinization changes of temperaturesgelatinization oftemperatures A- and B-type of A- crystallinities and B-type crystallinities by KCl [16,30 by]. KCl The [16,30]. two peaks The two of C-type peaks starchof C-type in waterstarchhave in water been have reported been inreported starches in ofstarches A. americana of A. americanaand fortunei and [23fortunei,29]. For[23,29]. pea For C-type pea starch,C-type A-typestarch, crystallinityA-type crystallinity is distributed is distributed in the outer in of granule,the outer and of B-type granule, crystallinity and B-type is distributed crystallinity in the is innerdistributed of granule in the [16 inner]. However, of granuleA. fortunei [16]. However,C-type starch A. fortunei contains C-type A-type starch starch contains granules A-type and B-type starch starchgranules granules and B-type [23]. The starch different granules allomorph [23]. The distributions different allomorph in A. fortunei distributionsand pea starchesin A. fortunei might and result pea instarches different might gelatinization result in diff properties.erent gelatinization properties.

Molecules 2018, 23, 2132 8 of 15 Molecules 2018, 23, x FOR PEER REVIEW 8 of 15

FigureFigure 6. 6.DSC DSCthermogram thermogramof ofstarch. starch.

TableTable 4. 4.Thermal Thermal parameters parameters of of starch. starch. Starches To (°C) Tp1 (°C) Tp2 (°C) Tc (°C) ΔT (°C) ΔH (J/g) Starches To (◦C) Tp1 (◦C) Tp2 (◦C) Tc (◦C) ∆T(◦C) ∆H (J/g) A. fortunei 61.8 ± 0.3 b 68.0 ± 0.3 b 75.6 ± 0.1 c 83.9 ± 0.3 d 22.1 ± 0.4 d 10.2 ± 0.9 a b b c d d a A. fortuneiMaize 61.8 65.8± ±0.3 0.2 d 68.0 ND± 0.3 75.6 70.0 ±± 0.1 b 74.783.9 ±± 0.10.3 b 22.1 9.0 ±± 0.40.1 a 10.2 10.5± ±0.9 0.4 a Maize 65.8 ± 0.2 d ND 70.0 ± 0.1 b 74.7 ± 0.1 b 9.0 ± 0.1 a 10.5 ± 0.4 a Potato 61.0 ± 0.1 a 64.8 ± 0.1 a ND 70.7 ± 0.3 a 9.6 ± 0.3 b 14.9 ± 0.3 b Potato 61.0 ± 0.1 a 64.8 ± 0.1 a ND 70.7 ± 0.3 a 9.6 ± 0.3 b 14.9 ± 0.3 b c a c c a PeaPea 63.6 63.6± ±0.1 0.1c ND ND 69.3± ± 0.1 a 76.6 ±± 0.2 c 13.0 13.0± ± 0.20.2c 9.5 9.5± ±0.6 0.6a To:To: gelatinization gelatinization onset onset temperature; temperature; Tp1: peak Tp1: temperature peak temperature of the first gelatinization of the first peak;gelatinization Tp2: peak temperaturepeak; Tp2: ofpeak the secondtemperature gelatinization of the second peak; Tc: gelatinization gelatinization pe conclusionak; Tc: gelatinization temperature; ∆conclusionT: gelatinization temperature; temperature ΔT: rangegelatinization (Tc–To); ∆ H:temperature gelatinization range enthalpy; (Tc–To); ND: Δ notH: detected.gelatinization Data areenthalpy; means ±ND:standard not detected. deviations, Datan = are 3. Different superscript letters (from a to d) in the same column indicate significantly difference at p < 0.05. means ± standard deviations, n = 3. Different superscript letters (from a to d) in the same column indicate significantly difference at p < 0.05. 2.8. Swelling Power and Water Solubility of Starch 2.8. SwellingThe swelling Power power and Wa andterwater Solubility solubility of Starch of starch at different temperatures are shown in Figure7. ◦ The swellingThe swelling power power and water and water solubility solubility of potato of starch starch at increased different after temperatures 60 C, and are those shown of A. in fortunei Figure, ◦ ◦ maize,7. The andswelling pea starches power increasedand water after solubility 70 C. After of potato 80 C, starch potato increased starch had after the highest60 °C, swellingand those power, of A. maizefortunei and, maize, pea starches and pea had starches the lowest increased swelling after power, 70 °C and. After peastarch 80 °C, had potato thehighest starch waterhad the solubility. highest Theswelling swelling power, power maize and and water pea solubility starches reflect had the the lowest water-holding swelling capacity power, and dissolutionpea starch had degree the ofhighest starch water during solubility. heating, respectively.The swelling Granulepower and size, wate starchr solubility component reflect of amylosethe water-holding and amylopectin, capacity non-starchand dissolution component degree of of protein starch and during lipid, heating, and amylopectin respectively. structure Granule influence size, starch the swelling component power of andamylose water and solubility amylopectin, of starch non-starch [2,10]. The component significantly of different protein morphologies,and lipid, and granule amylopectin sizes, apparentstructure amyloseinfluence contents, the swelling and crystalline power and types water among solubilityA. fortunei of starch, maize, [2,10]. potato, The and significantly pea starches different might accountmorphologies, for their granule different sizes, swelling apparent powers amyl andose water contents, solubilities. and crystalline types among A. fortunei, maize, potato, and pea starches might account for their different swelling powers and water solubilities.

Molecules 2018, 23, 2132 9 of 15 Molecules 2018, 23, x FOR PEER REVIEW 9 of 15

FigureFigure 7. 7.Swelling Swelling power power( (AA)) andand waterwater solubilitysolubility ((BB)) ofof starch.starch.

2.9. Pasting Properties of Starch 2.9. Pasting Properties of Starch Pasting properties of starches, an important functional property determining the quality and Pasting properties of starches, an important functional property determining the quality and utilization of starch in food industry, were measured with a rapid visco analyzer (RVA). The Table 5 utilization of starch in food industry, were measured with a rapid visco analyzer (RVA). The Table5 shows the pasting property parameters. Peak viscosity indicates the bind ability of starch and water shows the pasting property parameters. Peak viscosity indicates the bind ability of starch and water by hydrogen bonds, and final viscosity reflects the stability of swelling granule. Breakdown viscosity by hydrogen bonds, and final viscosity reflects the stability of swelling granule. Breakdown viscosity is negatively relative with the pasting resistance of starch to heat, and setback viscosity shows the is negatively relative with the pasting resistance of starch to heat, and setback viscosity shows the tendency of starch paste to retrogradation. Pasting temperature can reflect the energy cost required tendency of starch paste to retrogradation. Pasting temperature can reflect the energy cost required during cooking [4,36]. The pasting properties of starches are affected by granule morphology, size, during cooking [4,36]. The pasting properties of starches are affected by granule morphology, size, amylose content, crystalline structure, and swelling power [37]. Significantly different pasting amylose content, crystalline structure, and swelling power [37]. Significantly different pasting properties properties were detected in the four starches. Potato starch had the highest peak, hot, final, and were detected in the four starches. Potato starch had the highest peak, hot, final, and breakdown breakdown viscosities and the lowest pasting time and temperature among the four starches, which viscosities and the lowest pasting time and temperature among the four starches, which might be due might be due to its large granule size (Table 1), low gelatinization temperature (Table 4), and high toswelling its large power granule (Figure size (Table 7). A.1 ),fortunei low gelatinization starch had significantly temperature higher (Table 4pasting), and highviscosities swelling and power lower (Figurepasting7). timesA. fortunei and temperaturesstarch had significantly than maize and higher pea pastingstarches, viscosities which might and be lower due pastingto its components times and of A-type starch granules and B-type starch granules.

Molecules 2018, 23, 2132 10 of 15 temperatures than maize and pea starches, which might be due to its components of A-type starch granules and B-type starch granules.

Table 5. Pasting parameters of starch.

◦ Starches PV (mPa s) HV (mPa s) BV (mPa s) FV (mPa s) SV (mPa s) PTime (min) PTemp ( C) A. fortunei 1689 ± 16 c 1420 ± 29 c 269 ± 15 b 2103 ± 37 c 683 ± 8 d 5.04 ± 0.04 b 80.80 ± 0.48 b Maize 954 ± 15 b 770 ± 9 b 184 ± 6 a 887 ± 9 b 117 ± 1 a 5.73 ± 0.01 c 91.88 ± 0.03 c Potato 7860 ± 30 d 3285 ± 32 d 4574 ± 50 c 3682 ± 18 d 396 ± 14 c 3.89 ± 0.04 a 68.67 ± 0.46 a Pea 580 ± 23 a 438 ± 21 a 141 ± 4 a 795 ± 21 a 357 ± 9 b 7.00 ± 0.01 d 94.85 ± 0.76 d PV: peak viscosity; HV: hot viscosity; BV: breakdown viscosity (PV−HV); FV: ﬁnal viscosity; SV: setback viscosity (FV−HV); PTime: peak time; PTemp: pasting temperature. Data are means ± standard deviations, n = 3. Different superscript letters (from a to d) in the same column indicate signiﬁcantly difference at p < 0.05.

2.10. Digestion Properties of Starch Native, gelatinized, and retrograded starches were digested by both porcine pancreatic α-amylase (PPA) and Aspergillus niger amyloglucosidase (AAG), and the released glucose was converted to the degraded starch. The starch fractions are classified into rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS), which are digested within 20 min, between 20 and 120 min, and after 120 min, respectively [38]. The RDS, SDS, and RS contents in native, gelatinized, and retrograded starches are presented in Table6. For native starch, A. fortunei, maize, and pea starches had similar RDS and were degraded faster than potato starch, and the RS of A. fortunei starch was significantly higher than that of maize and pea starches and lower than that of potato starch. The different digestion properties of four native starches might be affected by granule morphology and size, starch components, and crystalline structure [39]. Gelatinization destroys the granule morphology and crystalline structure through disturbing the inter- and intra-molecular hydrogen bonds of starch chains, which can cause the starch to be degraded easily. When the gelatinized starch retrogrades, the amylopectins can recrystallize to form the crystallites, and the amylose chains can associate to form the double helices structure, causing the starch to degrade more slowly than gelatinized starch [40]. A. fortunei, maize, potato, and pea had similar RDSs in their gelatinized and retrograded starches, but RS of gelatinized and retrograded starches was significantly lower in A. fortunei and pea than in maize and potato (Table6). The difference in digestion properties of gelatinized and retrograded starches among A. fortunei, maize, potato, and pea might result from the difference of apparent amylose content and amylopectin structure [28].

Table 6. Digestion properties of starch.

Starches Components A. fortunei Maize Potato Pea RDS (%) 6.04 ± 0.62 b 6.45 ± 0.03 b 2.27 ± 0.01 a 6.20 ± 0.13 b Native starch SDS (%) 10.96 ± 0.41 b 22.98 ± 0.65 d 6.33 ± 0.23 a 20.23 ± 0.29 c RS (%) 83.00 ± 0.22 c 70.56 ± 0.68 a 91.40 ± 0.24 d 73.57 ± 0.42 b RDS (%) 83.16 ± 1.33 a 81.59 ± 0.57 a 84.14 ± 0.62 a 83.66 ± 1.23 a Gelatinized starch SDS (%) 15.23 ± 0.12 d 7.97 ± 0.23 a 8.49 ± 0.14 b 14.55 ± 0.33 c RS (%) 1.61 ± 1.28 a 10.44 ± 0.44 c 7.37 ± 0.73 b 1.79 ± 1.41 a RDS (%) 78.13 ± 3.90 a 78.72 ± 0.72 a 80.15 ± 0.45 a 78.49 ± 1.26 a Retrograded starch SDS (%) 17.88 ± 2.27 b 7.99 ± 0.48 a 8.29 ± 0.21 a 17.80 ± 0.38 b RS (%) 3.99 ± 1.64 a 13.29 ± 0.26 b 11.57 ± 0.27 b 3.72 ± 0.96 a RDS: rapidly digestible starch; SDS: slowly digestible starch; RS: resistant starch. Data are means ± standard deviations, n = 3. Different superscript letters (from a to d) in the row column indicate significantly difference at p < 0.05. Molecules 2018, 23, 2132 11 of 15

2.11. Cluster Analysis of Starch In order to compare the properties of starches from A. fortunei, maize, potato, and pea, theMolecules hierarchical 2018, 23, xcluster FOR PEER analysis REVIEW was conducted based on the structural and functional property11 of 15 parameters including volume-weighted mean diameter, AAC, relative crystallinity, ordered and lamellarlamellar parameters, parameters, gelatinization gelatinization enthalpy, enthalpy, pasting pasting viscosities, viscosities, and and digestion digestion propertiesproperties (Figure(Figure8 ).8). TheThe dissimilaritydissimilarity between samples samples can can be be evaluated evaluated by by horizontal horizontal distance distance that that separates separates them. them. The Thedendrogram dendrogram consisted consisted of two of twomajor major clusters. clusters. On the On ba thesis basis of similarities of similarities and differences and differences in all inof allthe ofproperty the property parameters, parameters, potato potato starch starchwas separated was separated from the from other the three other starches three starches at a linkage at a linkagedistance distanceof 25. As of 25.for Asthe for remaining the remaining three three starches, starches, ther theree were were two two groups groups at at a a linkage distancedistance ofof approximatelyapproximately 5.0, 5.0, and and they they were were maize maize starch, starch,A. A. fortunei fortuneistarch, starch, and and pea pea starch. starch.A. A. fortunei fortuneiand and pea pea starchesstarches were were separated separated from from each each other other by approximately by approximately 1.0. These 1.0. resultsThese results indicated indicated that A. fortuneithat A. andfortunei pea starchesand pea starches showed similarshowed physicochemical similar physicochemical properties properties and were and more were related more torelated maize to starch maize thanstarch potato than starch.potato starch.

Figure 8. Dendrogram generated by hierarchical cluster analysis based on structural and functional Figure 8. Dendrogram generated by hierarchical cluster analysis based on structural and functional property parameters of starches. property parameters of starches.

3. Materials and Methods 3. Materials and Methods

3.1.3.1. Plant. Plant. MaterialsMaterials FreshFresh root root tubers tubers of ofA. A. fortunei fortuneiwere were obtained obtainedfrom fromthe thenatural natural foodfood marketmarket (Heze(Heze City,City,China). China). PotatoPotato fresh fresh tubers tubers and and pea pea mature mature seeds seeds were were obtained obtained from from the naturalthe natural food food market market (Yangzhou (Yangzhou City, China).City, China). Normal Normal maize starch maize (S4126) starch was (S4126) purchased was from purchased Sigma-Aldrich from Sigma-Aldrich (Darmstadt, Germany). (Darmstadt, Germany). 3.2. Determination of Starch and Soluble Sugar Content in Root Tuber 3.2. Determination of Starch and Soluble Sugar Content in Root Tuber The fresh root tubers of A. fortunei were washed and sliced into pieces. The samples were freeze-driedThe fresh and root ground tubers extensively of A. fortunei through were 100-mesh washed sieve and to sliced obtain into the flour.pieces. The The soluble samples sugar were in flourfreeze-dried was extracted and ground with 80% extensively (v/v) ethanol, through and 100-mesh the starch sieve in flour to obtain was hydrolyzed the flour. The into soluble soluble sugar sugar in usingflour 4.6was M extracted HClO4. The with extracted 80% (v/v and) ethanol, hydrolyzed and the soluble starch sugar in flour were was measured hydrolyzed using into anthrone-H soluble 2sugarSO4 methodusing 4.6 and M converted HClO4. toThe the contentsextracted of and soluble hydrolyzed sugar and soluble starch insugar dry rootwere tuber measured following using the methodanthrone-H of Gao2SO et4 method al. [11]. and converted to the contents of soluble sugar and starch in dry root tuber following the method of Gao et al. [11]. 3.3. Starch Isolation 3.3. Starch Isolation Starches were isolated from A. fortunei root tuber, potato tuber, and pea seeds following the methodStarches of Fan were et al. [isolated23], with from some A. modifications. fortunei root tuber, Briefly, potato the dry tuber, pea seedsand pea were seeds softened following in water the overnightmethod of at Fan 4 ◦etC, al. and [23], the withA. some fortunei modifications.root tubers andBriefly, potato the dry tubers pea wereseeds washedwere softened and chopped in water intoovernight pieces. at The 4 °C, samples and the were A. fortunei homogenized root tubers in water and potato using tubers a home were blender washed (JYL-C93T, and chopped Joyoung, into Suzhou,pieces. The Jiangsu, samples China) were and homogenized squeezed through in water 4 layers using ofa home cheesecloth. blender The (JYL-C93T, starch-slurry Joyoung, was filteredSuzhou, usingJiangsu, 100- China) and 200-meshand squeezed sieves through (Yueyang, 4 layers Taizhou, of cheesecloth. Zhejiang, The China). starch-slurry After standing was filtered about using 5 h, the100- precipitated and 200-mesh starch sieves was washed(Yueyang, 3 times Taizhou, using Zhejiang, 0.2% NaOH China). to remove After thestanding surface about protein 5 h, from the precipitated starch was washed 3 times using 0.2% NaOH to remove the surface protein from starch granules. The starch was washed 3 times with water and 2 times with anhydrous ethanol, dried at 40 °C, and ground through 100-mesh sieve.

Molecules 2018, 23, 2132 12 of 15 starch granules. The starch was washed 3 times with water and 2 times with anhydrous ethanol, dried at 40 ◦C, and ground through 100-mesh sieve.

3.4. Morphology Observation and Granule Size Analysis The 1% (w/v) starch suspension in 50% glycerol was observed and photographed under a polarized light microscope (BX53, Olympus, Tokyo, Japan) under normal and polarized light. The size distribution of starch granules was measured using a laser diffraction instrument (Mastersizer 2000, Malvern, Worcestershire, UK) following the method of Cai et al. [21].

3.5. Measurements of Iodine Absorption Spectrum and AAC The iodine absorption spectrum of starch and AAC were determined following the method of Lin et al. [28]. Brieﬂy, starch was dissolved in urea dimethyl sulphoxide solution and stained with iodine solution. The iodine absorption spectrum was scanned from 400 to 900 nm with a spectrophotometer (Ultrospec 6300 pro, Amersham Bioscience, Cambridge, UK). AAC was evaluated from absorbance at 620 nm.

3.6. Crystalline Structure Analysis Dry starch was ﬁrst wetted for 1 week in 75% humidity. The starch was scanned from 3◦ to 40◦ 2θ with a step size of 0.02◦ under an X-ray powder diffractometer (D8, Bruker, Karlsruhe, Germany). The relative crystallinity was calculated following the method of Wei et al. [18].

3.7. Short-Range Ordered Structure Analysis The starch-water slurry was analyzed using a FTIR spectrometer (7000, Varian, Santa Clara, CA, USA) with a DTGS detector equipped with an ATR cell following the method of Wei et al. [18]. Original spectrum was corrected by subtraction of the baseline in the region from 1200 to 800 cm−1 before deconvolution. For deconvolution, the assumed line shape was Lorentzian with a half-width of 19 cm−1 and a resolution enhancement factor of 1.9.

3.8. Lamellar Structure Analysis The starch-water slurry was kept in sealed cell and analyzed using a SAXS instrument (NanoStar, Bruker, Karlsruhe, Germany) equipped with Vantec 2000 detector and pin-hole collimation for point focus geometry. The test condition setting and lamellar parameter analysis were described previously by Cai et al. [19].

3.9. Measurement of Swelling Power and Water Solubility The swelling power and water solubility of starch were measured from 50 to 95 ◦C at an interval of 5 ◦C following the method of Lin et al. [7]. Brieﬂy, 2% (w/v) starch-water slurry was heated in a ThermoMixer C (Eppendorf, Hamburg, Germany) for 30 min, cooled to room temperature, and centrifuged (8000× g, 10 min). The supernatant was removed for measuring the soluble carbohydrate using anthrone-H2SO4 method to calculate the water solubility, and the precipitate was weighed to calculate the swelling power.

3.10. Measurement of Thermal Properties The ﬁve milligram of starch and 15 µL of water were mixed and sealed in an aluminium pan (Netzsch, Selb, Germany), held at 4 ◦C overnight, and equilibrated for 2 h at room temperature. The sample was heated from 25 to 130 ◦C at a rate of 10 ◦C/min using a differential scanning calorimeter (200-F3, Netzsch, Selb, Germany). Molecules 2018, 23, 2132 13 of 15

3.11. Measurement of Pasting Properties The 7% (w/w) starch-water slurry was heated and cooled using a rapid visco analyzer (3D, Newport Scientiﬁc, Warriewood, NSW, Australia). The temperature program included holding for 1 min at 50 ◦C, heating at 12 ◦C/min to 95 ◦C, holding for 2.5 min at 95 ◦C, cooling at 12 ◦C/min to 50 ◦C, and holding for 1.4 min at 50 ◦C.

3.12. Measurement of Digestion Properties The native, gelatinized, and retrograded starches were prepared and degraded by both PPA (A3176, Sigma Aldrich, St. Louis, MO, USA) and AAG (E-AMGDF, Megazyme, Bray, Ireland) following the method of Lin et al. [28]. Brieﬂy, the 10 mg of starch was incubated in 2 mL of enzyme solution (20 mM sodium phosphate buffer, pH 6.0, 6.7 mM NaCl, 0.01% NaN3, 2.5 mM CaCl2, 4 U PPA, and 4 U AAG) at 37 ◦C using a ThermoMixer C (Eppendorf, Hamburg, Germany) with shaking at 1000 rpm. The hydrolysis was terminated by adding 240 mL of 0.1 M HCl and 2 mL of 50% ethanol, and then centrifuged (4 ◦C, 8000× g, 5 min). The glucose in the supernatant was measured using a glucose assay kit (K-GLUC, Megazyme, Bray, Ireland).

3.13. Statistical Analysis The data reported in all the tables were means ± standard deviation. The one-way analysis of variance by Tukey’s test was evaluated using the SPSS 19.0 Statistical Software Program (IBM Company, Chicago, IL, USA). Differences were considered statistically signiﬁcant if p-values were less 0.05. Hierarchical cluster analysis was employed using between-groups linkage as the cluster method and Pearson correlation as the interval measure.

4. Conclusions The root tuber of A. fortunei is an important starch resource. Starch exhibited spherical, polygonal, and ellipsoidal granules with central hila and had a unimodal size distribution that ranged from 3 to 30 µm. Starch had 35% AAC and exhibited CA-type crystallinity. Starch had two gelatinization peaks in water. The swelling power of A. fortunei starch was significantly lower than that of potato starch and higher than that of maize and pea starches at 95 ◦C, but its water solubility was the lowest among the four starches. The peak, hot, breakdown, and final viscosities of A. fortunei starch were significantly lower than those of potato starch and higher than those of maize and potato starches, but its setback viscosity was the highest among the four starches. The RDS of native starches from A. fortunei, maize, and pea was similar but significantly higher than that of potato starch. The RS of gelatinized and retrograded starches from A. fortunei and pea was similar but significantly lower than that of maize and potato starches. This study could provide important information for the utilization of root tuber starch of A. fortunei.

Author Contributions: C.W. conceived the study and designed the experiments; J.W., K.G., X.F., and G.F. performed the experiments; and C.W. and J.W. wrote the manuscript. All authors discussed the contents of the manuscript and approved the submission. Funding: This study was financially supported by grants from the National Natural Science Foundation of China (31570324), the Qing Lan Project of Jiangsu Province, the Talent Project of Yangzhou University, and the Priority Academic Program Development of Jiangsu Higher Education Institutions. Conflicts of Interest: The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results. Molecules 2018, 23, 2132 14 of 15

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Sample Availability: Samples of the compounds are available from the authors.

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