| Roots and tuberous crops are important food crops providing the major caloric intake in a variety of diets of people worldwide as a result of their richness in starch. Growing interest in new starch products has lead to studies being carried out on the properties and modification of roots and tuber starches. Thus, this study characterized the physicochemical properties of starches isolated from starches of11sweet potato cultivars (Mi xuan no.1(CSP), Chuan shu217, Chuan shu34, Shangshu19, Luoshu10, Shi5, Xichengshu007, Xushu18, Xushu22, Xushu27&Xushu28) popularly used in the Chinese starch industry. Starches from2Nigerian sweet potato cultivars (NSP1&2), Chinese potato (CP) and Chinese cassava (CC) were also considered for comparative purposes. The mineral content (K, Mg, Mn, P, Ca, Cu, Fe, Zn, As, Cd, Cr&Pb) and the proximate composition of the roots of CC, CSP, CP, NSP1&2were carried out before investigating their starches. The effect of varying degree of heat treatment (45and60℃for30min) on the hydrolysis of sweet potato and cassava starches were investigated. Also the effect of varying degrees of high hydrostatic pressure treatments (200,400&600MPa) on the particle size, structural thermal and retrogradation properties of sweet potato starch was evaluated. The results of the mineral composition of CC, CSP, CP, NSP1&2indicated that the crops were high in K with values in the range of7164-13087μg/g but low in Cu having values also in the range of2.52-5.82μg/g. In comparison with the sweet potato roots, higher protein, ash and moisture content was observed in the Chinese potato tuber. Moisture, protein, ash, lipid and phosphorus contents of the starches varied from3.86-9.48%,0.05-0.75%,0.10-0.47%,0.14-0.26%and0.02-1.00%respectively. Amylose content of the starches varied between13.33and26.83%. The starches differed in their mean granule sizes, particle size distribution, swelling power, solubility and susceptibility to pancreatin hydrolysis. Higher retrogradation tendency was observed in pastes of starches having high amylose content. Thermal and pasting properties varied among the starch samples. In comparing the sweet potato, cassava and potato starches, Sweet potato and cassava showed some similarities while both differed significantly from the potato starch. Pearson’s correlation analysis showed that amylose, mean granule size and phosphorus had substantial effect on their physicochemical properties. Swelling power and solubility siginificantly correlated with each other. Significant correlations were also observed in their thermal and pasting parameters. Heat treatment prior to hydrolysis significantly altered the physicochemical properties of the starches. Swelling power and the retrogradation properties of the starches were obviously altered after hydrolysis. FTIR studies showed loss of ordered structure in hydrolysed heat treated starches. X-ray diffraction analysis showed no changes in the diffraction pattern of starches but sharper peaks were observed in the hydrolysed heat treated starches. This suggested that hydrolysis occurred in the amorphous domains. Starches treated at60℃showed higher degree of hydrolysis compared to those treated at45℃with both exhibiting modified physicochemical characteristics as compared to their native counterparts. HHP treated starches at200,400&600MPa exhibited altered structural, gelatinization and retrogradation properties. No significant difference was observed in the mean granule sizes of the native and HHP treated starches but the percentage of larger starch granule significantly increased with increasing pressure treatment. DSC analysis mostly showed a slight decrease in gelatinization temperatures (To and Tp) and gelatinization enthalpy (ΔHgel) with increasing pressure treatment. In comparison to the native starch, HHP treated starches showed higher syneresis with that treated at400MPa having the highest value. |
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