title: Inactivation of tannins in milled sorghum grain through steeping in dilute NaOH solution.
abstract: Steeping milled sorghum in up to 0.4% NaOH was investigated as a method of tannin inactivation. NaOH steeping substantially reduced assayable total phenols and tannins in both Type III and Type II sorghums and with Type III sorghum caused a 60-80% reduction in α-amylase inhibition compared to a 20% reduction by water steeping. NaOH treatment also reduced starch liquefaction time and increased free amino nitrogen. Type II tannin sorghum did not inhibit α-amylase and consequently the NaOH treatment had no effect. HPLC and LC-MS of the tannin extracts indicated a general trend of increasing proanthocyanidin/procyanidin size with increasing NaOH concentration and steeping time, coupled with a reduction in total area of peaks resolved. These show that the NaOH treatment forms highly polymerised tannin compounds, too large to assay and to interact with the α-amylase. NaOH pre-treatment of Type III sorghums could enable their utilisation in bioethanol production.
authors.affiliation: Institute for Food, Nutrition and Well-being and Department of Food Science, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa.
authors.forename: Adeoluwa I
authors.initials: AI
authors.lastname: Adetunji
authors.affiliation: Institute for Food, Nutrition and Well-being and Department of Food Science, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa.
authors.forename: Kwaku G
authors.initials: KG
authors.lastname: Duodu
authors.affiliation: Institute for Food, Nutrition and Well-being and Department of Food Science, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa. Electronic address: John.taylor@up.ac.za.
authors.forename: John R N
authors.initials: JR
authors.lastname: Taylor
mesh_terms: D002853:Chromatography, Liquid / Q000379:methods; D002523:Edible Grain / Q000737:chemistry*; D013058:Mass Spectrometry / Q000379:methods; D012972:Sodium Hydroxide / Q000737:chemistry*; D045868:Sorghum / Q000737:chemistry*; D013634:Tannins / Q000737:chemistry*; D000516:alpha-Amylases / Q000037:antagonists & inhibitors
chemical_list: D013634:Tannins; D012972:Sodium Hydroxide; D000516:alpha-Amylases
keywords: Alpha-amylase inhibition; Bioethanol; Milled tannin sorghum; NaOH steeping; Tannin inactivation