Starch/Staărke 2012, 00, 18 DOI 10.1002/star.201200039 RESEARCH ARTICLE Effect of debranching and storage condition on crystallinity and functional properties of cassava and potato starches Pham Van Hung1, Nguyen Thi Lan Phi2 and Tran Thi Vy Vy1 School of Biotechnology, International University, Vietnam National University in HoChiMinh City, Thu Duc District, HoChiMinh City, Vietnam Faculty of Chemical Engineering, HoChiMinh City University of Technology, HoChiMinh City, Vietnam Debranching starch by pullulanase is considered to improve the RS content of starch which is widely used to produce the starch-based foods with high-health benefit impacts In this study, the cassava and potato starches were debranched by pullulanase, followed by an autoclave treatment and storage at À188C, 48C, or 258C to investigate their crystallinity and functional properties After debranching, the potato starch contained significantly higher CL (35.4 glucose units) than did the cassava starch (32.4 glucose units) The debranched cassava and potato starches after retrogradation at the storage temperatures had a typical B-type crystalline structure although the native cassava and potato starches exhibited the different crystalline forms (A- and B-type, respectively) The RS contents of the debranched cassava and potato starches significantly improved with higher RS content of the debranched potato starch than that of the debranched cassava starch at the same storage condition The storage temperature significantly affected the RS formation of the debranched starches with the highest RS content at storage temperature of À188C (35 and 48% for the debranched cassava and potato starches, respectively) The debranched starches had significantly lower viscosities and paste clarities but higher solubilities than did the native starches As a result, the debranched cassava and potato starches can be considered for use not only in functional foods with enhanced health benefits but also in pharmaceutical and cosmetic industries Received: February 29, 2012 Revised: May 15, 2012 Accepted: May 31, 2012 Keywords: Cassava starch / Crystallinity / Debranched starch / Functional properties / Potato starch Introduction AM and AP play an important role in starch characteristics and are considered to have great impact on the formation of texture and quality of starch-based food products [1] AM has been known as an essentially linear molecule joined by a-(1,4)-linked D-glucopyranosyl bonds It is now well rec- Correspondence: Dr Pham Van Hung, School of Biotechnology, International University, Vietnam National University in HoChiMinh City, Quarter 6, Linh Trung Ward, Thu Duc District, HoChiMinh City, Vietnam E-mail: pvhung@hcmiu.edu.vn Fax: ỵ84-837-244-271 ß 2012 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim ognized that a fraction of the AM molecules is slightly branched by a-(1,6)-linkages [2, 3] AM has a MW of approximately  105 to  106 [4–6] with average degree of polymerization (DPn) of 324–4920 [7–11] In contrast, AP is a very large, highly branched chain molecule with a MW ranging from  107 to 5.7  109 and consists of a-(1,6)-linked D-glucopyranosyl units attached to a-(1,4)-bonds [4–6, 12], in which the MW of A-type APs varied to a larger range (7.0  107 to 5.7  109) than did that of B-type AP (1.7–3.4  108) [12] These chains can be classified as either the unbranched outermost chains (A) or the branched inner Colour online: See the article online to view Figs 2–4 in colour www.starch-journal.com Starch/Staărke 2012, 00, 18 P V Hung et al chains (B) In addition, there is a single chain (C) per molecule which contains a sole reducing residue [13] The B chains can be further divided in B1, B2, B3, and B4 chains [8] Branch points occur at approximately every 20–25 glucopyranose residues The DPn of AP molecules is typically within the range 1278–15 900 in which high-AM starch showed lower DPn than the normal starch AP unit chains are relatively short compared to AM molecules with typically ranging in 17–35 units long on average The AP molecules are debranched by debranching enzymes such as isoamylase or pullulanase which cleaves a-(1,6)-linked D-glucopyranosyl points to form linear chains [14, 15] Shi et al [16] reported that debranching of normal starches releases a mixture of short and long linear chains because both AM and AP in starch granules were debranched, whereas debranching of wx starch releases short linear side chains from AP During retrogradation, AM or the linear chains formed from debranched AP can form double helices by hydrogen bonds between molecules resulting in rigid gels called crystallinity In nature, native starch granules exhibited three main types of crystallinity, the A-, B-, and C-type crystals, which can be monitored by XRD analysis [17] After debranching and crystallization, the short-chain AM from debranched wx maize starch formed a typical A-type crystalline structure when debranched at high concentration (25% solids) [18], whereas a dilute starting concentration (5% solids) led to the formation of B-type crystalline structure [19] The debranching combined with physical treatment such as ANN or heating and cooling cycles have been applied to produce re-crystallized AM products, which had various degrees of crystallinity and differing functional properties The debranched and recrystallined starch products were reported to have high amounts of slowly digestible starch (SDS) [20, 21] or RSs [22–24] The solubility and waterbinding values of autoclaved and debranched samples of the high-AM corn starches were higher than those of their respective native starches, whereas autoclaving–storing cycles after debranching caused decreases in peak, breakdown, and final viscosity values [23] Debranching caused decreases in DSC peak temperature (Tp) and increases in enthalpy of the high-AM corn starches [23] However, Cai and Shi [19] reported that all three crystalline short chain AMs (CSCA) from wx wheat, wx maize, and wx potato starches had larger melting temperature range (80– 1408C) as compared to did the native starches (59–958C), in which the CSCA from debranched wx potato starch displayed a higher peak melting temperature (116.28C) than those from debranched wx wheat (99.78C) and wx maize (99.98C) starches Although the relationship between debranching and heat treatments and the formation of RSs and their functional properties from highAM starches [23], banana starch [24], or wx starches ß 2012 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim [18, 19] have been recently reported, the relationship between the debranching and autoclave treatment with different storage conditions and recrystallinity of debranched starches as well as their functional properties of cassava and potato starches has not been examined Therefore, the objective of this study is to investigate crystallinity forms, functional properties, and RS contents of debranched and recrystallined starches by debranching cassava and potato starches using pullulanase, autoclave treatment, and storage at different temperatures Materials and methods 2.1 Materials Cassava (Manihot esculenta) and potato (Solanum tuberosum) grown in the southern part of Vietnam were used in this study Cassava and potato starches were isolated from raw cassava roots and potato tubes at the Laboratory of Applied Chemistry, International University, Vietnam The raw cassava roots and potato tubes were ground using an engine-driven drum grater Then the slurry was kept in a solution of 4.5% NaHSO3 and passed through the sieves (0.232 and 0.105 mm in aperture size) Resultant starches were washed thoroughly in clean water to remove the contaminant substances Finally, the starch sediment was recovered by centrifugation and dried in an oven at 408C to 10–11% moisture The isolated starches were deffated by hexane in a sohxlet system for h before using for debranching Pullulanase from Bacillus acidopullulyticus (!400 U/mL), a-amylase from Aspergillus oryzae ($30 U/mg), and amyloglucosidase from Aspergillus niger (!300 U/mL) used in this study were purchased from Sigma–Aldrich Co (St Louis, MO, USA) Other chemicals were purchased from Merck Co (Darmstadt, Germany) 2.2 Debranching and storage of starches Cassava and potato starches were debranched by pullulanase according to the method of Gonzalez-Soto et al [23] with slight modification as follows The deffated starch (10 g, db) was well mixed with 100 mL of acetate buffer 0.1 M (pH 5.2) and cooked in a boiling water bath (with stirring) for 10 with continuously stirring The hot paste was then autoclaved at 1218C for 30 using an autoclave (model HV-85, Hirayama Manufacturer Corp., Japan) After autoclaving, the paste was cooled to 508C and mixed with pullulanase (20 U/g starch) The mixture was incubated with constant stirring for 24 h at 508C After 24 h, the debranched starch gel was autoclaved at 1218C for 30 min, cooled down and stored at 25, 4, or À188C for another 24 h The debranched starches were then dried at www.starch-journal.com Starch/Staărke 2012, 00, 1–8 508C in an oven overnight and stored in closed glass containers until further use 2.3 Scanning electron microscopy (SEM) of starches Appearances of the native starch granules and crystals of the debranched starches were observed by a SEM (JEOL-JSM-6480LV, Tokyo, Japan) The preparation and operation procedures were carried out as previously described [25] The samples were coated with Pt/Pd and photographed at an accelerating potential of 10 kV 2.4 Measurements of iodine absorption of starches Blue value of the native and debranched cassava and potato starches were measured as previously described [25] Each starch was suspended in M aqueous NaOH, followed by heating in a boiling water bath with shaking An aliquot of the solution was mixed with iodine solution (0.2% I2 and 2.01% KI) and then blue value of the iodine– starch complex was measured at 680 nm AM content of the starches was calculated based on a calibration curve of a mixture of AM and AP according to the equation: AM%ị ẳ 110:786BV 24:481; R ¼ 0:995 (1) in which BV is the blue value of starches measured at 620 nm 2.5 Determination of degree of polymerization of debranched starches The number–average degrees of polymerization ðDPn Þ and the CL ðCLÞ after debranching were determined as previously described by Hung and Morita [26] DPn was calculated as the difference between reducing residues and total glucose concentration of the native starches, whereas CL was calculated as the difference between reducing residues and total glucose concentration of the debranched starches The average number of chains per molecule was calculated as follows: NC ẳ ẵDPn =CLị À 1Š 2.6 X-ray diffraction pattern of starches The crystalline structure of the native and debranched cassava and potato starches was observed using an X-ray diffractometer (Rigaku Co., Ltd., Rint-2000 type, Tokyo, Japan) according to the operation described by Hung and Morita [25] The XRD system was operated at 40 kV and 80 mA and diffractograms of the starches were recorded from 28 2u to 358 2u with a scanning speed of 88/min and scanning step of 0.028 ß 2012 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim 2.7 Resistant starch determination Resistant starch contents (%RS) of the native and debranched cassava and potato starches were measured based on the method of Englyst et al [27] with moderate modification as follows Starch (1 g, db) was mixed with 25 mL of acetate buffer (pH 6.0) and then boiled for 30 in a water bath After cooling to 378C, amylase solution (7000 U/g starch) was added and the slurry was incubated at 378C for h The suspension was then cooled to 258C and adjusted to pH 4.5 before adding amyloglucosidase (50 U/g starch) The mixture was then incubated at 608C for 30 and then centrifuged (1500  g, 15 min) to obtain the sediment The sediment was washed with distilled water for three times and then dried at 508C for 48 h The %RS3 was calculated as weight of remained residue (db) compared to that of the initial sample A blank with no starch was used to minus the contamination of the enzymes 2.8 Determination of pasting properties of starches Viscosity of the debranched starches was measured using a Brookfield Viscometer LVDV-E according to the official method described by the International Starch Institute (ISI17, Science Park Aarhus, Denmark) with slight modification [28] A starch slurry (2% starch) was cooked in a boiling water bath for 15 with continuously stirring and additional 15 without stirring The paste was cooled down to 508C and measured the viscosity in centipoises (cP) at 508C at 50 rpm with spindle SC4-18 Paste clarity of starches was determined according to the method of Craig et al [29] Starch (0.05 g, db) was suspended in mL of distilled water in a glass-stoppered tube Then the slurry was heated at 958C for 30 with shaking every and cooled The clarity of paste was measured for transmittance (%T) using a spectrophotometer (UVD-2960, Labomed, USA) at 650 nm against a water blank Solubility of starch (%) was determined as the method previously described by Singh and Singh with slight modification [30] The starch (0.5 g, db) was suspended in 50 mL of distilled water and shaked thoroughly for 30 on a rotary shaker The starch suspension was centrifuged at 1200  g for 10 A 25 mL aliquot of the supernatant was taken in a preweighed beaker and dried in an air oven at 1108C for h The cold water solubility was calculated as degree of solubility (%) ¼ grams of solid in supernatant  2/grams of samples  100 2.9 Statistical analysis Data were expressed as the mean values Æ SE of the three separate determinations Comparison of means www.starch-journal.com P V Hung et al was performed by one-way analysis of variance (ANOVA) followed by Duncan’s multiple comparison tests ( p2%) according to the method described above At 2% of starch concentration, the viscosities of native cassava and potato starches were 45.7 and 45.9 cP, respectively After debranching, the viscosities of pastes from the cooked debranched cassava and potato starches significantly reduced because of low-MWs of the linear chains presented in those starches The viscosities of the debranched starches at different storage condition Table Viscosities (cP) of native and debranched cassava and potato starches at different storage conditionsa),b) 50 RS content (%,db) the starches having the A-type crystallinity [18, 25] The result in this study also shows that the native potato starch after cooking still contained higher RS content than did the cassava starch Moreover, the RS3 content of the debranched potato starch was significantly higher than that of the debranched cassava starch at the same storage condition The differences might be due to the chain length distribution and degree of crystalline structure of the short chain AMs obtained by debranching of starches The debranched potato starch with significantly higher CL (35.4 glucose units) formed double helices with more dense crystalline structure resulting in more resistance to enzyme digestion as compared to the debranched cassava starch having the CL about 32.4 glucose units This result is consistent with other studies on wx starches [19] The highest RS3 contents obtained in this study were 35 and 48% for the debranched cassava and potato starches stored at À188C, respectively, suggesting that the debranching and autoclaving process followed by storage at À188C is preferred to prepare products with high-RS content 40 Cassava Potato 30 20 10 NS DS+25 DS+4 Sample Cassava NS DSỵ25 DSỵ4 DS-18 45.7 0.6 0.7 0.6 Ỉ Ỉ Ỉ Ỉ 0.2b 0.1a 0.1a 0.1a Potato 45.9 1.8 1.7 1.6 Ỉ Ỉ Ỉ Æ 0.2b 0.1a 0.2a 0.1a DS-18 o Storage temperature ( C) Figure RS content (%, db) of native and debranched cassava and potato starches at different storage conditions NS, native starch; DS ỵ 25, DS ỵ 4, and DS 18, debranched starches stored at ỵ258C, ỵ48C, and 188C ß 2012 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim a) Values with the same letter in the same column are not significantly different b) NS, native starch; DS ỵ 25, DS ỵ and DS 18, debranched starches stored at ỵ258C, ỵ48C, and 188C www.starch-journal.com Starch/Staărke 2012, 00, 18 were not significantly different However, the viscosities of the debranched cassava starches were significantly lower than those of the debranched potato starches at the same storage conditions This result might be due to the lower CL of the debranched cassava starch which reduced the viscosity as compared to that of the debranched potato starch 3.6 Paste clarity of native and debranched starches Figure shows the results of paste clarity (%T) of native and debranched cassava and potato starches at different storage conditions Transparences of the pastes from the debranched starches were significantly lower than those of the native starches The remarkable changes from the starch polymer solution at the beginning of debranching to the cloudy slurry after 24 h of crystallization at 508C were also observed by Cai et al [18] These results are due to the small and fine crystallites formed by the double helices of the short chain length of AMs of the debranched starches as compared to the high molecules of AM and AP of the native starches In this study, the lowest transparences of the pastes of the debranched starches stored at 48C were observed among the tested samples because the smallest and finest crystallites were formed at this temperature [29] 3.7 Solubility (%) of native and debranched starches Solubility of native and debranched cassava and potato starches were determined by stirring the starches in excess water at ambient temperature and the results Table Solubility (%) of native and debranched cassava and potato starches at different storage conditionsa),b) Sample Cassava NS DSỵ25 DSỵ4 DS-18 0.5 12.1 12.6 12.2 Ỉ Ỉ Ỉ Ỉ 0.0a 0.5b 0.5b 0.6b Potato 0.5 9.8 10.2 9.9 Ỉ Ỉ Æ Æ 0.0a 0.3b 0.3b 0.4b a) The same letter in the same column is not significantly different b) NS, native starch; DS ỵ 25, DS ỵ and DS 18, debranched starches stored at ỵ258C, ỵ48C, and 188C are shown in Table The native starch hardly dissolved in the water, whereas the debranched starches containing the short-chain molecules had higher solubilities The solubilities of the debranched cassava starch (12.1–12.6%) were significantly higher than those of the debranched potato starch (9.8–10.2%) because the debranched cassava starch had lower short-chain molecules as compared to the debranched potato starch The solubilities of the debranched starches stored at different temperatures were not significantly different indicating that the solubilities of the debranched starches were dependant on the chain length distribution rather than the form of crystallites As a result, the debranched starches with high-RS contents and low viscosities and solubilities are considered to be not only used in functional foods with enhanced health benefits but also used in pharmaceutical and cosmetic industries Conclusions 80 Transmittance (%) 70 60 50 40 30 20 10 Potato NS DS+25 Cassava DS+4 DS-18 o Storage temperature ( C) Figure Paste clarity (%T) of native and debranched cassava and potato starches at different storage conditions NS, native starch; DS ỵ 25, DS ỵ 4, and DS 18, debranched starches stored at ỵ258C, ỵ48C, and À188C ß 2012 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim The crystallinity and functional properties of cassava and potato starches after debranching by pullulanase and autoclave treatment with different storage temperatures are successfully investigated in this study The debranched potato starch had higher CL and RS content than did the debranched cassava starch Both debranched cassava and potato starches exhibited the typical B-type structure with reduced viscosity and paste clarity and increased solubility as compared to the native starches The storage temperature did not affect the crystallinity and functional properties of the debranched starches but significantly influenced in RS formation The RS contents of both cassava and potato debranched starches were the highest at storage temperature of À188C As a result, the potato starch is considered to be a good starting material to produce high amount of RS by debranching and autowww.starch-journal.com P V Hung et al clave treatment However, both debranched cassava and potato starches can be used for functional food processing and pharmaceutical and cosmetic industries The authors thank the National Foundation for Science and Technology Development, Vietnam (NAFOSTED), research grant no 106.99-2010.66 for the financial support The authors have declared no conflict of interest References [1] Hung, P V., in: Papadopoulos, K N (Ed.), Food Chemistry Research Developments, Nova Science Publishers, Inc., New York 2008, pp 141–166 [2] Hizukuri, S., Takeda, Y., Yasuda, M., Multi-branched nature of amylose and the action of 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between the debranching and autoclave treatment with different storage conditions and recrystallinity of debranched starches as well as their functional properties of cassava and potato starches. .. degree of polymerization were 1400 and 1520 glucose units for native cassava and potato starches, respectively Figure SEM of native and debranched cassava and potato starches NCS, native cassava. .. study Cassava and potato starches were isolated from raw cassava roots and potato tubes at the Laboratory of Applied Chemistry, International University, Vietnam The raw cassava roots and potato