Food Chemistry 155 (2014) 38–44

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Food Chemistry

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Preparation and characterization of resistant starch III from elephantfoot yam (Amorphophallus paeonifolius) starch

0308-8146/$ - see front matter � 2014 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.foodchem.2014.01.023

Abbreviations: DHgel, enthalpy of gelatinization; DSC, differential scanningcalorimetry; PHI, peak height index ; R, gelatinization range; RC, relative crystal-linity; RS, resistant starch; SEM, scanning electron microscopy; SP, swelling power;T0, onset temperature; TC, conclusion temperature; TP, peak temperature; TPA,texture profile analyzer; WAC, water absorption capacity; WSI, water solubilityindex; XRD, X-ray diffractometer.⇑ Corresponding author. Tel.: +91 9443701906; fax: +91 413 2654621.

E-mail address: shprieya@gmail.com (S. Haripriya).

Chagam Koteswara Reddy, Sundaramoorthy Haripriya ⇑, A. Noor Mohamed, M. SuriyaDepartment of Food Science and Technology, Pondicherry Central University, Puducherry 605 014, India

a r t i c l e i n f o

Article history:Received 1 July 2013Received in revised form 26 November 2013Accepted 11 January 2014Available online 23 January 2014

Keywords:Elephant foot yam starchEnzymatic hydrolysisPhysico-chemical propertiesPullulanaseResistant starch

a b s t r a c t

The purpose of this study was to assess the properties of resistant starch (RS) III prepared from elephantfoot yam starch using pullulanase enzyme. Native and gelatinized starches were subjected to enzymatichydrolysis (pullulanase, 40 U/g per 10 h), autoclaved (121 �C/30 min), stored under refrigeration(4 �C/24 h) and then lyophilized. After preparation of resistant starch III, the morphological, physical,chemical and functional properties were assessed. The enzymatic and retrogradation process increasedthe yield of resistant starch III from starch with a concomitant increase increase in its water absorptioncapacity and water solubility index. A decrease in swelling power was observed due to the hydrolysis andthermal process. Te reduced pasting properties and hardness of resistant starch III were associated withthe disintegration of starch granules due to the thermal process. The viscosity was found to be inverselyproportional to the RS content in the sample. The thermal properties of RS increased due to retrograda-tion and recrystallization (P < 0.05).

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

In the food processing industries, starch contributes to impor-tant characteristics including thickening, gelling, consistency andshelf stability in a diverse range of diverse applications. Potato, riceand wheat starch have been exclusively employed for this purposein transforming the microstructure and functionality of products inthe food industries (Wheatley, Liping, & Bofu, 1996). Though starchcontributes significantly to the quality and consistency of commer-cial products, it has a high glycemic index which often makes itunfavourable in terms of its effects to the consumer.

In order to meet the growing demands of the consumers forfunctional foods, carbohydrates which can act as functional ingre-dients and have a beneficial effect to human health are favouredover carbohydrates with a high glycemic index. Resistant starch(RS) is one of the naturally occurring carbohydrate which is definedas the sum of starch and starch degradation products which cannotbe digested in the small intestine of humans and when reached inthe large intestine, it undergoes fermentation by the commencal

intestinal microorganisms production, resulting in the productionof short chain fatty acids (Annison & Topping, 1994). These shortchain fatty acids can be partially absorbed in the small intestineand be a source of energy to the mucosal cells or can support thegrowth and metabolism of the colonic microbiota, with the undi-gested mass being excreted in the stool (Xue, Newman, & Newman,1996). Besides its vital physiological role as a functional ingredientin lowering the risk of diet-related diseases, RS when comparedwith traditional insoluble fibres also has many favourable featuresfor thea food industry. More specifically, RS is a natural white col-our powder with bland taste and has acceptable appearance andtexture (Sajilata, Singhal, & Kulkarni, 2006).

RS is classified on the basis of its botanical source and process-ing methods (Englyst, Kingman, & Cummings 1992). RS can be clas-sified in four types including RS1, physically inaccessible starch;RS2, native starch granules; RS3, retrograded starch and RS4,chemically modified starch (Sajilata et al., 2006). Sources of cerealgrains, roots, tubers and legumes produce resistant starch throughthe process of cyclic heating, autoclaving and extrusion methods.Gelatinization and cooling processes which are generally referredto as annealing procedures, are the common methods used toenhance the formation of RS3 (retrograded starch) (Thompson,2000). Ample studies are available on the RS of the cereals, pulses,and tubers, especially cassava and potato starch. One such starchsource which is not explored commercially is Amorphophalluspaeonifolius, which is also known as elephant foot yam, an herba-ceous, perennial C3 crop. It is a tropical tuber which has originated

C.K. Reddy et al. / Food Chemistry 155 (2014) 38–44 39

from the south eastern Asian region and is extensively used inIndian cuisines (Ravi, Ravichandran, & Suja, 2009).

Though several researchers have studied the flour and starchobtained from yam tubers in order to find new food applications(Okaka, Okorie, & Ozo, 1991) a limited number of studies on starchand resistant starch fr A. paeonifolius are available. Taking intoaccount the need for RS3, as this would constitute a functional foodingredient, the study was designed to elucidate the preparation ofstarch and resistant starch (RS3) from elephant foot yam. Theobjectives of the study were to prepare RS3 retrograded starchfrom isolated starch of elephant foot yam (A. paeonifolius) andcharacterise its physico-chemical and functional properties.

2. Materials and methods

2.1. Materials

The tuber of elephant foot yam (A. paeonifolius) was purchasedfrom a local market. The resistant starch assay kit was purchasedfrom Megazyme International (Ireland), whereas the enzymes usedin the study included pullulanase from Bacillus acidopullulyticus(Promozyme 400L) and heat stable a-amylase from Bacilluslicheniformis (Termamyl 120L), obtained from Sigma (USA).

2.2. Isolation of starch

The starch was isolated from elephant foot yam (A. paeonifolius)according to the method of Amani, Buleon, Kamenan, and Colonna(2004). The tuber was peeled, cut into small pieces and immedi-ately suspended in 0.1% (w/v) sodium metabisulphite solution.Then, the sample was homogenised with warring blender and sus-pended in a large amount of 4% NaCl. The slurry was filteredthrough a 100 lm sieve and the filtrate was centrifuged at 2660gfor 15 min. This procedure was repeated for four times and therecovered white coloured starch was then oven dried at 48 h at45 �C.

2.3. Preparation of resistant starch

2.3.1. Enzymatic hydrolysis of elephant foot yam starchEnzymatic hydrolysis of elephant foot yam starch was per-

formed by using the procedure used by Polesi and Sarmento(2011) with a slight modification. The elephant foot yam starch(10% w/w db) was suspended in sodium acetate buffer (0.1 Mand pH 5.3) and mixed with pullulanase enzyme (40 U/g drystarch), and the mixture incubated in a shaking water bath at60 �C for 10 h. The sample was heated in a boiling water bath for10 min to inactivate the enzyme. Starch gelatinization, prior toadding the enzyme, was performed by boiling the sample in awater bath for 10 min.

2.3.2. Preparation of resistant starchStarch samples, namely elephant foot yam starch (S1), native

hydrolyzed by enzyme (S2) and gelatinized hydrolyzed by enzyme(S3) in suspensions (10% w/w db) were autoclaved at 121 �C for30 min, cooled and kept at 4 �C for 24 h. The samples (S1, S2 andS3) were then lyophilized.

2.3.3. Determination of resistant starch contentThe amount of RS in the samples was analysed by using a Mega-

zyme resistant starch assay kit, which is based on the Associationof Official Analytical Chemists (AOAC) methods (2002.02).

2.4. Scanning electron microscopy (SEM)

The morphological characteristics of S1, S2 and S3 wereevaluated using scanning electron microscope (HITACHI ModelS-3000H) with a magnification 500� to 1500�. The powderedsamples were sprinkled on double-sided stick tape placed onaluminium stubs and were covered with a gold–palladium layer.

2.5. Physicochemical characteristics

2.5.1. Chemical compositionThe moisture content of S1 was recorded in terms of weight loss

after heating at 130 ± 2 �C for 2 h using 2 g of sample. The amountof ash, protein, and fat were analysed according to AACC methods08–01, 46–13 and 30–25, respectively. The amount of starch wasanalysed using the AOAC method 8.020.

2.5.2. Amylose contentThe total amylose content of the starch samples (S1, S2and S3)

was analsyed according to the method described by Williams,Kuzina, and Hlynka (1970). Starch samples (20 mg) were addedto 10 mL of 0.5 N KOH and the resultant suspension wasthoroughly mixed. Subsequently, the dispersed sample wastransferred into a 100 mL volumetric flask and diluted to the markwith distilled water. An aliquot (10 mL) was pipetted into a 50 mLvolumetric flask and 5 mL of 0.1 N HCl were added followed by0.5 mL of iodine reagent, and the solution made up to 50 mL withwater; the absorbance was then measured at 625 nm. Themeasurement of amylose was determined from a standard curvedeveloped using amylose as the standard.

2.5.3. Water absorption capacity (WAC) and water solubility index(WSI)

The WAC and WSI of the samples (S1, S2 and S3) were analysedaccording to the procedure described by Anderson, Conway,Pfeifer, and Griffin (1969). Briefly, a sample of 0.5 g was mixed with6 mL of distilled water, and centrifuged. The supernatant washeated at 30 �C with continuously stirring for 30 min in a waterbath. The suspension was placed in a petridish and dried at105 �C for 4 h to obtain the dry solids weight, and the wetsediment was weighed. The WSI and WAC were determined as:WSI = (weight of dry solids in supernatant/weight of dry sample) �100; WAC = weight of wet sediment/(weight of the dry sample-weightof the dry solids).

2.5.4. Swelling power (SP)The swelling power of the samples (S1, S2and S3) was anasyed

using the method described by Nattapulwat, Purkkao, andSuwithayapan (2009). A sample (0.2 g) was dispersed in water(20 mL) to form a suspension. The suspension was heated to85 �C in a water bath for 30 min with vigorous shaking every5 min. The starch gel was then centrifuged at 2200 rpm for15 min. The weight of the sediment was used to calculate theswelling power. The supernatant was dried and weighed tomeasure the amount of dissolved starch in the supernatant. Theswelling power was determined as: swelling power = weight ofsediment/(weight of dry starch �weight of dissolved starch).

2.5.5. Pasting propertiesThe viscoamylographic property of the samples (S1, S2 and S3)

were performed with a Rapid Visco Analyser (RVA starch master 2,Newport Scientific, Warriewood, NSW, Australia) using 2 g of sam-ple in 25 mL of water. The following parameters: paste tempera-ture, peak viscosity, breakdown viscosity, final viscosity andsetback viscosity were measured from the viscoamylographs.

40 C.K. Reddy et al. / Food Chemistry 155 (2014) 38–44

2.5.6. Textural characteristicsThe textural properties of RVA gels were studied using the

method Kaur, Singh, McCarthy, and Singh (2007) using a textureprofile analyzer (HDP/BS blade of texture analyzer (TA) TA–HDplus, Stable Micro Systems, Surrey). After 24 h incubation at 4 �Cthe gels formed from the RVA analysis were examined by the tex-ture analyzer using probe No. 5. From the texture profile curve,hardness, cohesiveness, gumminess, adhesiveness, springiness,chewiness and stringiness were calculated.

2.5.7. XRD and relative crystallinity (RC)The X-ray patterns of the samples (S1, S2 and S3) were studied

with a X-ray diffractometer (Shimadzu XRD 7000) according to theprocedure described by Zobel (1964). The RC of the starches wasquantitatively estimated following the method of Nara and Komiya(1983) using a software (Origin version 8, Microcal Inc., Northamp-ton, MA, USA). The graphs were plotted between 2h of 4� to 30� andsmoothed with the ‘‘Adjacent Averaging’’ tool.

2.5.8. Thermal propertiesThe thermal properties of the samples (S1, S2 and S3) were

examined using the method described by Gao, Li, Jian, and Liang(2011) based on differential scanning colorimetry (TA-Q20 DSC).The DSC curve which showed the onset (T0), peak (Tp), final (Tf),gelatinization temperatures and enthalpy (DH) were analysedusing Universal Analysis 2000 3.9A software.

2.6. Statistical analysis

The experiments were conducted in triplicate. The obtaineddata were submitted to one way ANOVA and Duncan’s MultipleRange Test (DMRT) (P 6 0.05) to analyse the significance of differ-ence between the mean values of the samples using SPSS 18 soft-ware (SPSS Institute Inc., Cary, NC, USA).

3. Results and discussion

3.1. Morphological characteristics

The SEM micrographs (Fig. 1) of S1 when compared to S2 and S3differed significantly. SEM studies revealed that the elephant footyam starch (S1) granules are round, elliptical and polygonal inshape with smooth surfaces, with no obvious effects or signs ofdamage on the surface. However, the granular structure of sampleswas destroyed after being cooked, debranched and dried. S2 and S3showed a cohesive structure, leading to the loss of granularappearance and to a irregular shape, which is the consequence ofgelatinization temperature where the coupled starch granulesforms sponge like structure within the inner region of the retro-graded starch (Ratnayake & Jackson, 2007).

3.2. Chemical composition

The proximate composition in terms of moisture, ash, proteinand fat in the isolated elephant foot yam starch (S1) was 8.5%,2.3%, 0.9% and 0.2% respectively. The moisture content of S1(8.5%) was comparatively lower when compared with cassavastarch (10.2%) and arrow root starch (9.82%). Moisture contentplays a significant role for flow and other mechanical properties(Raja & Sindhu, 2000). The moisture content of a starch powderis dependent upon the extraction procedure and drying processalong with surrounding atmosphere humidity. The starch andamylose content in the extracted starch were 87.7% and 24.2%,respectively, on a dry weight basis. These parameters were compa-

rable with the proximate composition, and the starch and amylosecontent of other yam varieties (Wang, Yu, Liu, & Chen, 2008).

3.3. Physicochemical properties

The amylose, RS content, SP, WAC and WSI of S1, S2 and S3 areshown in Table 1. The amylose content of S1 (24.21%) was found tobe significantly lower than S2 (46.78%) and S3 (50.18%). Further-more, S3 (50.18%) was found to be significantly greater than S2(46.78%). The RS content of S3 (36.27%) was significantly higherwhen compared with S2 (30.67%) and S1 (17.98%) owing to the in-creased amylose content in samples S2 and S3 which are the resul-tant retrograded starch of elephant foot yam starch upon thetreatment with pullulanase enzyme before and after gelatinization,respectively. The considerable increase of RS content in S3 fol-lowed by S2 would be attributed to the effect of pullulanase en-zyme on debranching the a-(1–6) linkage of amylopectin (Leong,Karim, & Norziah, 2007); the latter is converted into small chainlinear polysaccharides like amylose molecules, which form stronggel network through retrogradation (Polesi and Sarmento, 2011).The RS formed in S2 and S3 were subjected to retrogradation whichensures the conversion of RS2–RS3.

The swelling power measures the tenacity of the bonds in thecrystalline portion of the starch granule, showing the ease withwhich the starch will cook. Granules with greater crystalline areasalong with stronger bonds in the crystalline regions swell less incold water as well as when heated. The gels formed from thesecrystalline regions are weak and have greater tendency towardsretrogradation because of the bonds. The swelling power of ele-phant foot yam starch at 85 �C (8.14%) was significantly differedfrom the swelling power of S2 at 85 �C (5.6%) and that of S3 at85 �C (5.4%). The swelling power ascertains the magnitude of inter-action among the starch chain within the regions of crystalline andamorphous nature. The distribution of molecular weight, degree ofdebranching, length of branches and the conformation of the mol-ecules along with the ratio of amylose and amylopectin places avery important influence on the extent of water and starch interac-tion (Hoover, 2001). The observation of the decreased SP in S2 andS3, irrespective to the increase in temperature, could be attributedto the effect of gelatinization and the autoclaving process, whichwould have occurred during the preparation of S2 and S3.

The properties of WAC and WSI of all starch samples weregreatly dependent on the source, content of amylose/amylopectin,extraction procedure and thermal stability. WAC is a phenomenonlinked to the wet heat treatment of starch samples. In this study,the gelatinization induced by heating and autoclaving significantlyincreased the WAC in S3 (6.04%) when compared to S1 (3.59%) andS2 (5.46%). The WAC of all the starch samples was comparable withother studies of RS from chick pea starch (Polesi and Sarmento,2011). An increased water activity in retrograded starch was notedwhich is the result of a change in molecular structure or any othermechanisms leading to an easier mobility of the starch compo-nents, where leaching of starch was also noticed (Govindasamy,Campanella, & Oates, 1996). The parameter WSI is used as an indi-cator of the destruction of starch components. The WSI of S3(13.89%) and S2 (12.06%) was significantly different from S1(2.57%). The S2 and S3 have undergone an hydrolytic process whencompared to S1. The enzymatic hydrolysis contributed to theincreased water solubility in S2 and S3.

3.4. Pasting properties

The pasting properties of all samples were determined using arapid visco analyzer. The pasting property plays a vital role inthe application of starch and resistant starch in food industriesand these parameters are depended on the source, amount of

Fig. 1. Scanning electron micrographs (SEM) of S1 (elephant foot yam starch), S2 (retrograded enzyme hydrolyzed native starch) and S3 (retrograded enzyme hydrolyzedgelatinized starch).

Table 1Amylose, resistant starch, swelling power, water absorption capacity, water solubilityindex and relative crystallinity of S1, S2 and S3.#

Parameter Type

S1 S2 S3

Amylose (%) 24.21 ± 0.983c 46.78 ± 1.454b 50.18 ± 1.171a

RS (%) 17.98 ± 0.382c 30.67 ± 1.632b 36.27 ± 1.167a

SP (%) 8.14 ± 0.201a 5.67 ± 0.108b 5.48 ± 0.168b

WAC (%) 3.59 ± 0.176c 5.46 ± 0.415a 6.04 ± 0.185a

WSI (%) 2.57 ± 0.110b 12.06 ± 1.010a 13.89 ± 1.249a

RC (%) 19.37 ± 0.633c 25.12 ± 0.949b 27.84 ± 1.201a

RS, resistant starch; SP, swelling power; WAC, water absorption capacity; WSI,water solubility index; RC, relative crystallinity; S1, elephant foot yam starch; S2,retrograded enzyme hydrolyzed native starch; S3, retrograded enzyme hydrolyzedgelatinized starch.

# All data were means of triplicates. Values with the same superscripts in a rowdid not differ significantly (P < 0.05) by DMRT.

Fig. 2. Typical RVA starch pasting curves for of S1 (elephant foot yam starch), S2(retrograded enzyme hydrolyzed native starch) and S3 (retrograded enzymehydrolyzed gelatinized starch).

C.K. Reddy et al. / Food Chemistry 155 (2014) 38–44 41

starch, and the interaction between molecules and testing condi-tions (Liu, Donner, Yin, Huang, & Fan, 2006). In the presence ofwater, the starch suspension was subjected to a thermal process,where the starch granules swell and thus the viscosity increasesprogressively. The viscoamylographs of S1, S2 and S3 are shownin Fig. 2 and Table 2. The pasting properties of S1 showed a signif-icant difference with S2 and S3 (P < 0.05) which represents the typ-ical pasting behaviour of native starch (Miao, Jiang, & Zhang, 2009).The pasting temperature was not detectable for S3 and the lowpasting temperature for S2 (61.2 �C) could be due to the destruc-tion of starch granules when subjected to autoclave at 121 �C dur-ing RS preparation which is also comparable with other studies likethe RS from chickpea and red kidney bean starch (Polesi and Sar-mento, 2011; Reddy, Suriya, & Haripriya, 2013). S2 and S3 showa lower amylographic pattern for parameters including peak vis-cosity, hold viscosity, final viscosity, break down and set backwhen compared with S1. This attribute could be a result of the

enzymatic hydrolysis process which improves the levels of shortlinear chain molecules and RS. The formation of starch gelability was reduced in S2 and S3 when compared with S1 due toithets autoclave process (Polesi and Sarmento, 2011; Gelensceret al., 2008).

3.5. Textural properties

After 24 h incubation at 4 �C, the retrograded starch pastes (RVAgels) of S1, S2 and S3 were examined with a texture profile ana-lyzer and the obtained data are shown in Table 3. Higher peak vis-cosity and hardness was observed in S1 when compared with S2and S3 (P < 0.05), which may be due to the presence of larger sizestarch granules and lower levels of amylose. The reduced hardness

Table 2Pasting properties of S1, S2 and S3: pasting temperature (�C), peak time (min), peakviscosity (cP), hold viscosity (cP), final viscosity (cP), break down (cP) and set back(cP).#

Parameter Type

S1 S2 S3

Pasting temp (�C) 89 ± 0.7a 61.2 ± 0.5b ndPeak time (min) 4.42 ± 0.5c 7.10 ± 0.33a 5.30 ± 0.61b

Peak viscosity (cP) 1320.0 ± 31.320a 435.0 ± 55.865b 238.0 ± 16.370c

Hold viscosity (cP) 1248.33 ± 56.888a 418.66 ± 29.022b 228.0 ± 11.532c

Final viscosity (cP) 1819.33 ± 30.171a 598.33 ± 60.351b 275.0 ± 13.258c

Breakdown (cP) 122.33 ± 4.725a 16.33 ± 1.527b 13.33 ± 1.527c

Setback (cP) 626.0 ± 7.151a 131.66 ± 3.511b 42.0 ± 3.0c

S1, elephant foot yam starch; S2, retrograded enzyme hydrolyzed native starch; S3,retrograded enzyme hydrolyzed gelatinized starch; nd, not detected.

# All data were means of triplicates. Values with the same superscripts in a rowdid not differ significantly (P < 0.05) by DMRT.

Table 3Textural properties of S1, S2 and S3: hardness, cohesiveness, adhesiveness, gummi-ness, springiness, chewiness and stringiness.#

Parameter Type

S1 S2 S3

Hardness (N) 0.506 ± 0.051a 0.113 ± 0.005b 0.093 ± 0.005b

Cohesiveness 0.323 ± 0.041b 0.523 ± 0.035a 0.536 ± 0.025a

Adhesiveness (Ns) �13.04 ± 0.632b �3.963 ± 0.241a �4.04 ± 0.07a

Gumminess (N) 0.17 ± 0.01a 0.046 ± 0.011b 0.046 ± 0.005b

Springiness (s) 1.14 ± 0.026a 0.876 ± 0.096b 0.903 ± 0.06b

Chewiness (Ns) 0.127 ± 0.092a 0.04 ± 0.01a 0.0366 ± 0.005a

Stringiness 5.973 ± 0.935a 6.17 ± 0.238a 5.476 ± 0.434a

S1, elephant foot yam starch; S2, retrograded enzyme hydrolyzed native starch; S3,retrograded enzyme hydrolyzed gelatinized starch; nd, not detected.

# All data were means of triplicates. Values with the same superscripts in a rowdid not differ significantly (P < 0.05) by DMRT.

42 C.K. Reddy et al. / Food Chemistry 155 (2014) 38–44

and the formation of gel ability of S2 and S3 is due to the partialhydrolysis of starch granules and also the destruction of granulesby enzymatic hydrolysis and the autoclave process. The resultselicited significant difference between all samples (S1, S2 and S3)with respect to the texture parameters including hardness, cohe-siveness, adhesiveness, gumminess, springiness, chewiness andstringiness. The difference in the textural properties of all samplegels were influenced by rigidity in gelatinized starch, amylose con-tent as well as interaction between the dispensed and continuousphase of the gel, which in turn is dependent on the amylose andamylopectin structure (Yamin, Lee, Pollak, & White, 1999).

3.6. X-ray diffraction

The X-ray diffraction patterns of samples (S1, S2 and S3) areshown in Fig. 3. S1 gave an intermediate intensity peak at diffrac-tion angles of 2h = 17.92� and a strong peak at 2h = 23.05�, with aweak peak at 14.7� showing an intermediate diffraction patternA- and B-type (C-type). The S2 and S3 exhibited peaks at 16.85�and 16.95�, respectively, indicating a B-type crystallinity due tothe retrogradation at low temperature. Similar crystalline patternswere also observed in wheat, corn and sago starch (Leong et al.,2007) when treated with pullulanase, and were autoclaved and

Fig. 3. X-ray diffraction pattern (XRD) of S1 (elephant foot yam starch), S2 (retrogragelatinized starch).

retrograded. The type of crystallinity of samples is influenced bythe chain length of amylopectin, growth temperature and fattyacids content (Gunaratne & Hoover, 2002). S3 gave a single broadpeak when compared with S2 due to the recrystallization with ret-rogradation. The relative crystallinity of S1 (19.37%) and S2(25.12%) were lower when compared with that of S3 (27.84%).The highest crystallinity of S3 could be due to the increased RS con-tent, which could have been enhanced by gelatinization, enzymatictreatment and retrogradation (Table 1).

3.7. Thermal properties

Generally, the endothermic transition of all types of starch sam-ples are influenced by the interactions between amylose–amylose,amylose–amylopectin and the amylose–lipid contents (Shin, Byun,Park, & Moon, 2004). However in S1 there were no considerablelevels of lipid present. The thermal properties of S1, S2 and S3 wereinfluenced by the granule shape, amylopectin chain length andcrystalline regions (Singh & Kaur, 2004). Thermal analyses of S1,S2 and S3 were performed by DSC and the data are shown inTable 4 and Fig. 4. The DSC profiles of the samples showed a lowpeak temperature for S1 and S2 when compared with S3, whichis attributed to the gelatinization and retrogradation process. The

ded enzyme hydrolyzed native starch) and S3 (retrograded enzyme hydrolyzed

Table 4Thermal properties of S1, S2 and S3: transition temperatures (T0; TP; TC), enthalpy ofgelatinization (DHgel), peak height index (PHI) and gelatinization range (R).#

Parameter Type

S1 S2 S3

T0 (�C) 53.073 ± 1.471b 54.993 ± 0.655b 58.233 ± 0.773a

TP (�C) 93.66 ± 2.094c 98.25 ± 0.84b 103.21 ± 0.773a

TC (�C) 149.603 ± 1.316a 150.443 ± 2.157a 152.103 ± 3.282a

DHgel (J/g) 284.14 ± 5.65c 316.37 ± 3.815b 329.143 ± 3.3a

PHI (J/g C) 6.51 ± 0.17b 7.123 ± 0.07a 7.027 ± 0.047a

R (�C) 96.606 ± 1.272a 97.703 ± 0.401a 98.106 ± 0.15a

T0, onset temperature; TP, peak temperature; TC, conclusion temperature; DHgel,enthalpy of gelatinization; PHI, peak height index ((Dgel/(TP�T0)); R, gelatinizationrange (TC�T0); S1, elephant foot yam starch; S2, retrograded enzyme hydrolyzednative starch; S3, retrograded enzyme hydrolyzed gelatinized starch.

# All data were means of triplicates. Values with the same superscripts in a rowdid not differ significantly (P < 0.05) by DMRT.

Fig. 4. Differential scanning calorimetry (DSC) thermograms of S1 (elephant footyam starch), S2 (retrograded enzyme hydrolyzed native starch) and S3 (retrogradedenzyme hydrolyzed gelatinized starch).

C.K. Reddy et al. / Food Chemistry 155 (2014) 38–44 43

endothermic enthalpy of S3 (329.1 J/g) was higher, and directlyproportional to the amount of RS, the interaction between amy-lose–amylose molecules and the content of crystallinity. The en-thalpy of S3 was significantly different from S2 (316.3 J/g) and S1(284.1 J/g). The complete crystallinity of the samples depends onthe enthalpy of gelatinization and is an indicator of the loss ofmolecular order within the granule that occurs on gelatinization(Tester & Morrison, 1990). The difference in R values betweenthe samples suggests a transformation in the crystalline regionsof the starch granules.

4. Conclusion

Results revealed that the enzymatic hydrolysis of elephant footyam starch by pullulanase followed by thermal and retrogradationprocess increases the contents of amylose and the formation ofresistant starch with enhanced water solubility, absorption capac-ity and swelling power properties. The resistant starch III of ele-phant foot yam when compared with the native starch proved tohave a better thermal stability with high crystallinity along withthe potential to reduce the viscosity, gel forming ability and hard-ness of the gel. Reduced viscosity and hardness of the gel is inver-sely proportional to the amount of resistant starch. The inclusion ofmany tuber and root starches in food applications is very low dueto its poor functional properties. This study has shown that

resistant starch III of elephant foot yam has improved functionalproperties resulting from the enzymatic hydrolysis, thermal andretrogradation processes, and can potentially used as a substituteof native starches used currently in the food industry.

Acknowledgement

This project is financially supported by the Department of FoodScience and Technology, Pondicherry Central University, Pudu-cherry, India.

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