Effects of Growth Temperature on Some Structural Properties of Crystalline Lamellae in Starches Extracted from Sweet Potatoes (Sunnyred and Ayamurasaki)

Abstract

Thermodynamic characteristics defining gelatinisation (modelled as ‘melting’) processes for starches extracted from two sweet potato cultivars (Ayamurasaki and Sunnyred) grown in soil at different temperatures (15, 21, 27 or 33 °C) were studied using high sensitivity differential scanning calorimetry (DSC). The gelatinisation temperatures for all starches were elevated significantly with increasing growth temperature. A linear correlation between growth temperature and gelatinisation temperature of extracted starches was found for both cultivars. The increase of gelatinisation temperatures was associated with almost constant or slightly increased enthalpy (Ayamurasaki) but with moderate elevation of crystalline lamellae thickness (Sunnyred). Elevation of gelatinisation temperatures by 8‐9 °C by DSC for starches heated in 1.5 M aqueous KCl were found in comparison with aqueous starch dispersions. The crystalline polymorphic form was confirmed as A‐type using wide angle X‐ray scattering (WAXS). The values of the thermodynamic surface parameters characterising the faces of crystalline lamellae of these starches were calculated. Two endothermic peaks were observed by DSC for starches grown at 15 °C when suspended in 1.5 M KCl solution. The first peak was ascribed to the melting of B‐type structure while the second one was attributed to the melting of A‐type structure. As a conclusion it was suggested that these starches contain C‐type polymorphic structures.

Studies on tuber starches III. Impact of annealing on the molecular structure, composition and physicochemical properties of yam (Dioscorea sp.) starches grown in Sri Lanka

“…Similar changes on annealing has also been reported for other tuber starches such as potato (Genkina et al 2004a;Hoover & Vasanthan, 1994a;Jacobs et al, 1998aJacobs et al, , 1998bJacobs et al, , 1998cTester et al, 2005), sweet potato (Genkina et al, 2004b) and cassava (Gomez et al, 2004). The increase in T o , T p , T c on annealing has been attributed to perfection of pre-existing crystallites (Hoover & Vasanthan, 1994a).…”

“…The extent of this increase although marginal was significant (P < 0.05). Marginal increases in DH on annealing has also been reported for potato (Genkina et al, 2004a;Hoover & Vasanthan, 1994a;Tester et al, 2005), sweet potato (Genkina et al, 2004b) and cassava (Gomez et al, 2004) starches. The increase in DH could be the result of crystalline perfection and/or to melting of additional crystallites that may have formed as a result of interaction between AM-AM and/or AM-AMP chains.…”

“…The increase in T o , T p , T c on annealing has been attributed to perfection of pre-existing crystallites (Hoover & Vasanthan, 1994a). Crystalline perfection on annealing has been attributed to lengthening of amylopectin double helices caused by coiling of previously uncoiled ends (Genkina et al, 2004a;Tester et al, 2005) and to improved alignment of the double helices forming the crystalline structure (Hoover & Vasanthan, 1994a). In general, the extent of increase in T o , T p and T c on annealing was nearly the same for all Dioscorea starches (Table 4).…”

“…Annealing of cereal starches has been well documented. However, among tuber starches, annealing has been studied in detail only in potato starch (Genkina et al, 2004a;Genkina, Wasserman, & Yuryev, 2004b;Hoover & Vasanthan, 1994a, 1994bJacobs, Earlingen, Rouseu, Colonna, & Delcour, 1998a;Jacobs, Eerlingen, Charwart, & Delcour, 1995;Jacobs, Eerlingen, & Delcour, 1996;Jacobs, Eerlingen, Spaepen, Grobet, & Delcour, 1998c;Jacobs et al, 1998b;Muhrbeck & Svensson, 1996;Stute, 1992;Vermeylen et al, 2006). There is also some limited information on the effect of annealing on cassava (Gomez, Mendes da Silva, Ricardo, Sasaki, & Germani, 2004) and sweet potato (Genkina et al, 2004b) starches.…”

Structure, properties, and applications of aroid starch

“…Difference in the polymorphism of Xanthosoma starches may be attributed to genetic and environmental variations or incorrect identification of the species, which should be better studied. For example, growth temperature can determine the polymorph type (A-or C-) of starch from sweetpotato roots (Genkina et al, 2003). It would also be interesting to study if starches from corms and cormels have any difference in polymorphism.…”