Physicochemical, functional and structural properties of native Malawian cocoyam and sweetpotato starches
| dc.contributor.advisor | Bonnet, Susanna | |
| dc.contributor.advisor | Saka, John D. K. | |
| dc.contributor.author | Mweta, Davies Emmanuel | |
| dc.date.accessioned | 2015-11-20T09:39:53Z | |
| dc.date.available | 2015-11-20T09:39:53Z | |
| dc.date.copyright | 2009-05 | |
| dc.date.issued | 2009-05 | |
| dc.date.submitted | 2009-05 | |
| dc.description.abstract | English: Starches isolated from Malawian sweetpotato, cocoyam and cassava were comparatively studied and evaluated for physicochemical, functional and structural properties in order to unveil their characteristic properties and unravel their potential for industrial application. Further, sweetpotato and cocoyam starches were modified by physical and chemical means, and changes in their functional properties were determined. The results showed that cocoyam, sweetpotato and cassava starch exhibited properties that were unique to botanical source. The pH of the starches ranged within the 4.7 to 7.0 range required for use in low acid foods while moisture content was below the maximum limit required for prolonged storage of the starches. Ash and amylose content of the starches ranged from 0.03 to 0.28%, and 10.6 to 34.4%, respectively while protein and fat levels ranged from 0.35 to 0.84%, and 0.085 to 0.160%, respectively. All starches exhibited high levels of potassium, followed by calcium, phosphorus, magnesium and sodium. Iron, manganese and zinc were present in very low levels compared to the other elements. Cocoyam starch granules exhibited mostly round/spherical shapes similar to that of cassava starch, while sweetpotato starch granules were mostly polygonal in shape. Granule size ranged from 4.0 to 18.7 um, 4.0 to 48.0 um and 5.3 to 22.7 um for cocoyam, sweetpotato and cassava starches, respectively. Cocoyam starch had a larger fraction of smaller sized (0-10 um) granules than sweetpotato and cassava starch. Sweetpotato and cassava starches had mostly medium sized (10-25 um) granules. All starches exhibited B-type crystallinity with distinctive major diffraction peaks at 5.4-5.6° 20 angles, however relatively strong peaks at 7.6-7.8° 20 angles suggesting the presence of single helical conformations. Water absorption capacity, swelling power and solubility of all starches increased with increasing temperature. Cassava starches exhibited higher water absorption capacity, swelling power, paste clarity, resistance to retrogradation and viscosity than cocoyam and sweetpotato starches. Cocoyam starches exhibited higher gelatinization temperatures than sweetpotato and cassava starches. Cocoyam and cassava starches gave similar gelatinization enthalpies which were higher than those of sweetpotato starches. Cocoyam starches displayed higher retrogradation tendencies than sweetpotato and cassava starches. Cocoyam starches displayed higher blue values and wavelength of maximum absorption but lower reducing capacity values than sweetpotato and cassava starches. There was similarity in the packing and orientation of chains in the amorphous regions of sweetpotato and cocoyam starches as evidenced by similar values of the extent of acid hydrolysis of the starches for 12 days. Average molecular weight of amylopectin molecules of the starches studied by HPSEC ranged from 1.42 x 106 to 1.67 x 106 Da. Cocoyam starch contained amylose molecules of lower molecular weight than sweetpotato and cassava starches. Analysis of isoamylase debranched starches showed that sweetpotato starch had the largest fraction of long-chain amylopectins (47%) and the lowest fraction of short-chain amylopectins (45%), while cocoyam starch exhibited the largest fraction of short chain amylopectins (62%) and smallest proportion of large chain amylopectins (32%). Acetylation enhanced water absorption capacity, swelling power and solubility of the starches, but reduced gelatinization temperatures, gelatinization enthalpy and retrogradation tendencies of the starches. Acid hydrolysis reduced the water absorption capacity and swelling power but improved the solubility and paste clarity of starch, and increased gelatinization temperatures and enthalpy. Annealing reduced water absorption capacity, swelling power, solubility and pastes clarity but increased gelatinization temperatures and enthalpy. Due to their differences in physicochemical, functional and structural properties, starches from Malawian cocoyam, sweetpotato and cassava can play different roles in the Malawian industry. | en_ZA |
| dc.description.abstract | Afrikaans: Stysel is geïsoleer van Malawiese soetpatats, amadumbies en cassava om vergelykend met mekaar te bestudeer. Dit is geëvalueer vir fisies-chemiese, funksionele en strukturele eienskappe om hulle kenmerkende eienskappe en potensiële industriële toepassing te bepaal. Verder is soetpatat en amadumbie stysels deur fisiese en chemiese metodes gemodifiseer, en veranderings in hulle funksionele eienskappe is bepaal. Die resultate het getoon dat amadumbie, soetpatat en cassava stysel eienskappe uniek aan die botaniese bron het. Die pH van die stysel het tussen 4.7 en 7.0 gewissel, wat binne die aanvaarbare waardes vir gebruik in laesuurvoedsel val, en die voginhoud was laer as die maksimum limiet nodig vir die langtermyn storing van stysel. As en amilose inhoud van die stysels het gewissel tussen 0.03 en 0.28%, en 10.6 en 34.4%, onderskeidelik, terwyl proteïen en vetvlakke tussen 0.35 en 0.84%, en 0.085 en 0.160%, onderskeidelik gewissel het. Alle stysel het die hoogste vlak van kalium gehad, gevolg deur kalsium, fosfaat, magnesium en natrium. Yster, mangaan en sink was in baie laer konsentrasies teenwoordig as die ander elemente. Amadumbie styselgranules was meestal ‗n ronde/sferiese vorm, baie dieselfde as in cassava stysel terwyl soetpatat granules meestal ‗n poligonale vorm gehad het. Granule grootte het gewissel van 4.0 tot 18.7 um, 4.0 tot 48.0 um en 5.3 tot 22.7 um vir amadumbie, soetpatats en cassava stysel onderskeidelik. Amadumbie stysel het ‗n groter fraksie van die kleiner grootte (0-10 m) granules as in soetpatat en cassava stysel gehad. Soetpatat en cassava stysel het meestal medium grootte (10-25 m) granules gehad. Alle stysels het B-tipe kristaliniteit gehad met duidelike hoof diffraksiepieke by 5.4-5.6° 20 hoeke, maar relatiewe sterk pieke by 7.6-7.8° 20 hoeke wat die teenwoordigheid van enkel heliese konformasies voorstel. 210 Waterabsorpsiekapasiteit, swellings vermoë en oplosbaarheid van alle stysel het toegeneem met toenemende temperatuur. Cassava stysel het hoër waterabsorpsiekapasiteit, swellingsvermoë, pastahelderheid, weerstand teen retrogradering en viskositeit getoon as die stysel van amadumbie en soetpatats. Amadumbie stysel het hoër gellingstemperature as die van soetpatats en cassava getoon. Amadumbie en cassava stysel het ooreenstemmende gellingsentalpie gehad, en dit was hoër as vir soetpatat stysel. Amadumbie stysel het hoër retrograderingtendense gehad as soetpatat en cassava stysel. Amadumbie stysel het hoër ―blou‖ waardes en golflengte van maksimum absorpsie gehad, maar laer reduseringskapasiteit waardes as soetpatat en cassava stysel. Daar was ooreenkomste in die pak en oriëntasie van kettings in die amorfe areas van soetpatat en amadumbie stysel, wat gesien kon word in die ooreenstemmende waardes van die hoeveelhed suurhidrolise in stysel na 12 dae. Gemiddelde molekulêre massa van amilopektien molekules van stysel wat met HPSEC ondersoek is, het gewissel van 1.42 x 106 tot 1.66 x 106 Da. Amadumbie stysel het amilose molekules van laer molekulêre massa gehad as die van soetpatat en cassava stysel. Analise van isoamilase ontkettingde stysel het getoon dat cassava stysel die grootste fraksie lang ketting amilopektien en die laagste fraksie kort ketting amilopektien het, terwyl amadumbie stysel die grootste fraksie kort ketting amilopektien en die kleinste proporsie lang ketting amilopektien het. Asetilering het waterabsorpsiekapasiteit, swellingsvermoë en oplosbaarheid van stysel verhoog, maar het gelatineringstemperature, gelatineringsentalpie en retrogradering van stysel verlaag. Suurhidrolisering het waterabsorpsiekapasiteit en swellingsvermoë verlaag, maar het oplosbaarheid en pastahelderheid vergroot, en gelatineringstemperature en entalpie verhoog. Verbinding het die waterabsorpsiekapasiteit, swellingsvermoë, oplosbaarheid en pastahelderheid verlaag, maar gelatineringstemperatuur en entalpie verhoog. Omdat daar groot variasie is in die fisies-chemiese, funksionele en strukturele eienskappe van stysel van Malawiese amadumbie, soetpatat en cassava, kan hierdie stysels verskillende rolle speel in industrië in Malawi. | af |
| dc.description.sponsorship | Chemical Sciences (IPICS) | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/11660/1688 | |
| dc.language.iso | en | en_ZA |
| dc.publisher | University of the Free State | en_ZA |
| dc.rights.holder | University of the Free State | en_ZA |
| dc.subject | Thesis (Ph.D. (Chemistry and Plant Sciences))--University of the Free State, 2009 | en_ZA |
| dc.subject | Sweet potatoes -- Malawi | en_ZA |
| dc.subject | Starch | en_ZA |
| dc.subject | Taro -- Malawi | en_ZA |
| dc.subject | Physicochemical | en_ZA |
| dc.subject | Starch | en_ZA |
| dc.subject | Chemical composition | en_ZA |
| dc.subject | Cassava | en_ZA |
| dc.subject | Sweetpotato | en_ZA |
| dc.subject | Cocoyam | en_ZA |
| dc.title | Physicochemical, functional and structural properties of native Malawian cocoyam and sweetpotato starches | en_ZA |
| dc.type | Thesis | en_ZA |