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Sorghum proanthocyanidins - Degree of polymerisation, bioaccessibility and antioxidant properties as influenced by extrusion cooking
Thesis (PhD (Food Science))--University of Pretoria, 2018.
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2026
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| _version_ | 1867613552042311680 |
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| access_status_str | Open Access |
| author2 | Duodu, Kwaku Gyebi |
| author_browse | Duodu, Kwaku Gyebi |
| author_facet | Duodu, Kwaku Gyebi |
| collection | Thesis |
| description | Thesis (PhD (Food Science))--University of Pretoria, 2018. |
| format | Thesis |
| id | oai:repository.up.ac.za:2263/110128 |
| institution | University of Pretoria (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:37:57.427Z |
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| provenance_str_mv | Harvested via OAI-PMH from UPSpace — University of Pretoria Institutional Repository |
| publishDate | 2026 |
| publishDateRange | 2026 |
| publishDateSort | 2026 |
| record_format | dspace |
| source_str | UPSpace — University of Pretoria Institutional Repository |
| spelling | oai:repository.up.ac.za:2263/110128 Sorghum proanthocyanidins - Degree of polymerisation, bioaccessibility and antioxidant properties as influenced by extrusion cooking Duodu, Kwaku Gyebi martinsotofo@yahoo.com Adarkwah-Yiadom, Martin Extrusion cooking Radical scavenging activities Sorghum Condensed tannins Simulated In Vitro Digestion Thesis (PhD (Food Science))--University of Pretoria, 2018. Sorghum (Sorghum bicolor (L.) Moench) is an important drought-tolerant food cereal indigenous to Africa with a wide range of food uses such as porridges. It contains phenolic antioxidant compounds which are considered to confer potential health-promoting effects. Some sorghum types (type II and type III) contain condensed tannins (or proanthocyanidins). Although proanthocyanidins have well-known sensory and anti-nutritional effects, they also possess antioxidant and health-promoting properties. However, proanthocyanidins (especially high molecular weight types) are regarded as having low bioaccessibility. Modern processing technologies such as extrusion cooking, when applied to tannin sorghums for the manufacture of porridge products, could potentially depolymerise oligomeric and polymeric proanthocyanidins into more bioaccessible lower molecular weight forms. In this research, the effect of extrusion cooking of tannin sorghums to produce an instant porridge on proanthocyanidins, their bioaccessibility and antioxidant properties was studied. Porridges from type II and type III tannin sorghum were prepared by conventional cooking and extrusion cooking at different feed moisture levels (2 L/h, 3 L/h, 5 L/h and 8 L/h) (representing 16%, 19%, 23% and 30% moisture content) with a barrel temperature zone profile of 80/100/120/140/150oC and a screw speed of 300 rpm. The effect of simulated in vitro gastrointestinal (GIT) digestion on proanthocyanidins in the porridges was studied as a means of estimating their bioaccessibility. Total phenolic content (TPC) (Folin-Ciocalteu method), tannin content (TC) (vanillin-HCl method), and antioxidant properties using [(2,2-azinobis-(3- ethyl-benzothiazoline-6-sulphonic acid) (ABTS) and nitric oxide (NO) radical scavenging and oxygen radical absorbance capacity (ORAC)] of the flours, porridges and porridge digests were v determined. Normal phase liquid chromatography and liquid chromatography-mass spectrometry were used to determine proanthocyanidin types in the flours, porridges and porridge digests and their degree of polymerisation. Protective effect of the porridges and their digests against 2,2’-azobis(2-methylpropionamidine) dihydrochloride (AAPH)-induced oxidative DNA damage and cellular antioxidant protection in human carcinoma (Caco-2) cells using the dichloroflourescein diacetate (DCFH-DA) assay were determined. Extrusion cooked samples had lower total phenolic content, tannin content and radical scavenging properties than unprocessed tannin sorghum flour probably due to thermallyinduced phenolic oxidation and phenolic-biomolecule complexation which reduced tannin extractability. Extrusion cooking increased the proportion of the lower molecular weight dimeric proanthocyanidins and decreased the proportion of the higher molecular weight oligomeric proanthocyanidins. The high mechanical shear and temperature conditions during extrusion can bring about depolymerisation of condensed tannins. Lower feed moisture during extrusion cooking produced more monomeric and dimeric proanthocyanidin units compared to higher feed moisture conditions and overall, the extrudate porridges contained proanthocyanidins with degree of polymerisation up to the hexamers. Extrusion cooking had a greater ability to depolymerise higher molecular weight proanthocyanidins into lower molecular weight forms compared to conventional cooking. Proanthocyanidin units with DP 1 to 3 from the extrudate porridges of the two tannin sorghum types had higher bioaccessibility than the same proanthocyanidin units from the conventionally cooked porridges. Proanthocyanidin units with DP 4 to 6 in the type II tannin sorghum porridges mostly had percentage bioaccessibilities of zero. However, these oligomers in the type III tannin sorghum porridges had high percentage bioaccessibilities ranging from 30% to greater than 100%. These observations are a reflection of differences in extractability of proanthocyanidins in the two tannin sorghum types and may be related to the fact that proanthocyanidins are deposited differently in the testa layers of type II and type III tannin sorghums. In type II sorghum, tannins are deposited within vesicles and there could be binding between the tannins and the vesicle membranes, which may also form a protective barrier around the tannins and vi reduce their extractability. Tannins in type III sorghum are deposited freely along cell walls and are more extractable. Porridges (conventionally cooked and extrudates) from type II and type III tannin sorghums and their simulated in vitro gastrointestinal digests exhibited antioxidant properties in the form of ABTS, DPPH and NO radical scavenging as well as ORAC. This could be due to the presence of various proanthocyanidin units as well as other phenolics and non-tannin phenolic compounds with reducing properties. The antioxidant properties exhibited by the digests is an indication that when these porridges are consumed and the bioaccessible proanthocyanidin species identified in the digests were to be absorbed, they could exert antioxidant properties and protect against oxidative stress and related diseases. The porridges and their digests were able to scavenge the physiologically relevant nitric oxide radical, which is an indication of their potential anti-inflammatory properties. They also inhibited supercoiled pBR322 vector DNA from radical-induced oxidative damage (an indication of potential anti-cancer properties) and protected against oxidation in Caco-2 cells (an indication of their ability to protect against oxidative stress). In conclusion, extrusion cooking can be used to produce instant porridges from tannin sorghums with improved bioaccessibility of proanthocyanidins and health-promoting properties. The outcomes of this research can act as drivers to increase utilisation of tannin sorghums for food especially in developing countries. Food Science PhD (Food Science) 2026-05-15T17:26:23Z 2026-05-15T17:26:23Z 19/01/30 2018 Thesis http://hdl.handle.net/2263/110128 en application/pdf |
| spellingShingle | Extrusion cooking Radical scavenging activities Sorghum Condensed tannins Simulated In Vitro Digestion Sorghum proanthocyanidins - Degree of polymerisation, bioaccessibility and antioxidant properties as influenced by extrusion cooking |
| title | Sorghum proanthocyanidins - Degree of polymerisation, bioaccessibility and antioxidant properties as influenced by extrusion cooking |
| title_full | Sorghum proanthocyanidins - Degree of polymerisation, bioaccessibility and antioxidant properties as influenced by extrusion cooking |
| title_fullStr | Sorghum proanthocyanidins - Degree of polymerisation, bioaccessibility and antioxidant properties as influenced by extrusion cooking |
| title_full_unstemmed | Sorghum proanthocyanidins - Degree of polymerisation, bioaccessibility and antioxidant properties as influenced by extrusion cooking |
| title_short | Sorghum proanthocyanidins - Degree of polymerisation, bioaccessibility and antioxidant properties as influenced by extrusion cooking |
| title_sort | sorghum proanthocyanidins degree of polymerisation bioaccessibility and antioxidant properties as influenced by extrusion cooking |
| topic | Extrusion cooking Radical scavenging activities Sorghum Condensed tannins Simulated In Vitro Digestion |
| url | http://hdl.handle.net/2263/110128 |