Physicochemical characterization of starches from some Nigerian and Chinese roots and tubers

Abstract

Chemical changes during germination and malting characteristics of six Nepalese finger millet varieties (GPU 0025, GE 5016, Dalle, Okhle, Kabre and Juwain) were studied. Millets were steeped in water at room temperature overnight, germinated for 48 h at 28±1°C, kilned at 50±2°C for 24 h and then, chemical characteristics of unmalted and malted millets were analyzed. Germination increased (p<0.05) total reducing sugar and glucose contents in all millet varieties. Starch, amylose and amylopectin contents in unmalted millets were between 71.32 to 79.86, 20.39 to 24.13, and 49.11 to 55.72% dry basis (db) respectively; whereas, those of malted millets were 63.74 to 67.12, 16.62 to 19.27 and 44.47 to 50.18% (db) respectively. Similarly, total phenolics (as gallic acid), total flavonoids (as rutin) and tannin (as tannic acid) contents in unmalted millets ranged from 60.9 to 229.2, 35.2 to 141.7 and 169.9 to 566.0 mg% (db) respectively; whereas, the values in malted millets were 123.1 to 247.8, 50.1 to 236.3 and 173.7 to 301.8 mg% (db) respectively. Except in GE 5016 and Juwainmillets, malting decreased (p<0.05) antioxidant activity in other varieties. Malt extract analysis revealed that all malt extracts possessed aromatic odor and showed negative starch-iodine test. Filtration rate of Juwain malt extract was slow but it was normal in other extracts. The color (EBC unit), free amino nitrogen (FAN) (mg% as glycine) and total reducing sugar (% m/v as maltose) contents in extracts were 2.77 to 5.78, 2.6 to 9.0 and 4.50 to 6.93, respectively. Glucose (%, m/v) and extract yield of malt (%, db) ranged from 1.22 to 2.51 and 80.20 to 88.83, respectively. Total soluble solids (TSS) (o Bx), pH, extract (%, m/m), FAN (mg% m/v) and total reducing sugar (% m/m as maltose) in worts derived from Dalle, Kabre and Juwain millet malts were in the range of 12.43 to 13.07, 5.44 to 5.66, 12.0 to 12.7, 19.5 to 20.3 and 7.64 to 10.45, respectively. Key words: Millet malt, amylose, polyphenols, free amino nitrogen (FAN), antioxidant activity, malt extract, wort.