Starches obtained from different cultivars of sweet potatoes commonly consumed in Sri Lanka, were chemically modified with hydroxypropyl substitution, to analyze the changes in the physicochemical properties. Significant changes ( ) in the crude digestibility level, thermal properties, and the water separation (syneresis) of starch gels (7.0%？db) during cold and frozen storage were observed due to the modification. Hydroxypropylation increased the gel stability, water solubility, digestibility, and storage stability of the native starches in the cold storage to a significant level. Lowered gelatinization and retrogradation enthalpies as well as gelatinization temperature were observed for derivatized starches compared to the native starch. Low levels of pasting stability with increased levels of breakdown and reduced cold paste viscosity were observed in the hydroxypropylated starch samples except for the Malaysian cultivar (S5). Chemically modified starch gels stored under cold storage did not show a syneresis for two weeks in the cycle and the frozen storage showed much improved stability in the starch gels within the four-week cycle. Chemical modification of sweet potato starch with hydroxyl propyl substitution can enhance the functional characteristics of the native starch which will improve its potential application in the food industry. 1. Introduction Starches have a wide spectrum of applications both in food and other industries such as textile and cosmetics. Native starches have restricted usage in food processing operations, distribution, and storage conditions due to the unfavourable characteristics prevailing. Native starches which have been modified either by physical or chemical treatments show much improved functional attributes that will have a broader area of usage in food processing operations [1]. Chemically modified food grade starches show increased levels of starch paste consistency, smoothness, paste clarity, and cold storage and freeze-thaw stability [2–4]. Rheological, morphological, and physicochemical characteristics can be improved through the chemical modification of the native starch by cross-linking, substitution, or reacting with acids or alkali. The amount of the chemical reagent required to achieve the functional properties needed in the starch may vary depending on the starch source, reagent type required for the substitution, the degree of substitution of the chemical reagent on the starch source, and the required range of properties in the final modified starch product [5, 6]. The changes occur in the starch
References
[1]
N. S. Sodhi and N. Singh, “Characteristics of acetylated starches prepared using starches separated from different rice cultivars,” Journal of Food Engineering, vol. 70, no. 1, pp. 117–127, 2005.
[2]
J. Singh, L. Kaur, and O. J. McCarthy, “Factors influencing the physico-chemical, morphological, thermal and rheological properties of some chemically modified starches for food applications—a review,” Food Hydrocolloids, vol. 21, no. 1, pp. 1–22, 2007.
[3]
C. S. Raina, S. Singh, A. S. Bawa, and D. C. Saxena, “Some characteristics of acetylated, cross—linked and dual modified Indian rice starches,” European Food Research and Technology, vol. 223, no. 4, pp. 561–570, 2006.
[4]
S. Singh, C. S. Raina, A. S. Bawa, and D. C. Saxena, “Effect of heat-moisture treatment and acid modification on rheological, textural, and differential scanning calorimetry characteristics of sweetpotato starch,” Journal of Food Science, vol. 70, no. 6, pp. E374–E378, 2005.
[5]
S. Wattanachant, K. Muhammad, D. Hashim, and R. A. Rahman, “Effect of cross—linking reagents and hydroxypropylation levels on dual-modified sago starch properties,” Food Chemistry, vol. 80, no. 4, pp. 463–471, 2003.
[6]
P. V. Hung and N. Morita, “Effects of granule sizes on physicochemical properties of cross-linked and acetylated wheat starches,” Starch/Staerke, vol. 57, no. 9, pp. 413–420, 2005.
[7]
L. Kaur, N. Singh, and J. Singh, “Factors influencing the properties of hydroxypropylated potato starches,” Carbohydrate Polymers, vol. 55, no. 2, pp. 211–223, 2004.
[8]
FAC, “Food additives and contaminants committee report on modified starches,” Report 31, Ministry of Agriculture, Fisheries and Food, London, UK, 1980.
[9]
B.-Y. Kim and B. Yoo, “Effects of cross-linking on the rheological and thermal properties of sweet potato starch,” Starch/Staerke, vol. 62, no. 11, pp. 577–583, 2010.
[10]
C. G. Biliaderis, “Physical characteristics, enzymatic digestibility, and structure of chemically modified smooth pea and waxy maize starches,” Journal of Agricultural and Food Chemistry, vol. 30, no. 5, pp. 925–930, 1982.
[11]
J. A. Gray and J. N. BeMiller, “Influence of reaction conditions on the location of reactions in waxy maize starch granules reacted with a propylene oxide analog at low substitution levels,” Carbohydrate Polymers, vol. 60, no. 2, pp. 147–162, 2005.
[12]
R. Hoover, D. Hannouz, and F. W. Sosulski, “Effect of hydroxypropylation on thermal properties, starch digestibility and freeze—thaw stability of field pea (Pisum sativum cv Trapper) starch,” Starch/Starke, vol. 40, pp. 383–387, 1988.
[13]
K. C. Huber and J. N. BeMiller, “Visualization of channels and cavities of corn and sorghum starch granules,” Cereal Chemistry, vol. 74, no. 5, pp. 537–541, 1997.
[14]
S. Senanayake, A. Gunaratne, K. K. D. S. Ranaweera, and A. Bamunuarachchi, “Comparative analysis of nutritional quality of five different cultivars of sweet potatoes (Ipomea batatas (L) Lam) in Sri Lanka,” Food Science & Nutrition, vol. 4, pp. 284–291, 2013.
[15]
A. Gunaratne and H. Corke, “Effect of hydroxypropylation and alkaline treatment in hydroxypropylation on some structural and physicochemical properties of heat-moisture treated wheat, potato and waxy maize starches,” Carbohydrate Polymers, vol. 68, no. 2, pp. 305–313, 2007.
[16]
A. Gunaratne and R. Hoover, “Effect of heat–moisture treatment on the structure and physicochemical properties of tuber and root starches,” Carbohydrate Polymers, vol. 49, no. 4, pp. 425–437, 2002.
[17]
Z. Zhang, C. C. Wheatley, and H. Corke, “Biochemical changes during storage of sweet potato roots differing in dry matter content,” Postharvest Biology and Technology, vol. 24, no. 3, pp. 317–325, 2002.
[18]
G. H. Zheng and F. W. Sosulski, “Determination of water separation from cooked starch and flour pastes after refrigeration and freeze–thaw,” Journal of Food Science, vol. 63, pp. 134–139, 1998.
[19]
J. Zhao, H. A. Schols, Z. Chen, Z. Jin, P. Buwalda, and H. Gruppen, “Substituent distribution within cross-linked and hydroxypropylated sweet potato starch and potato starch,” Food Chemistry, vol. 133, no. 4, pp. 1333–1340, 2012.
[20]
H. L. Lee and B. Yoo, “Effect of hydroxypropylation on physical and rheological properties of sweet potato starch,” Food Science and Technology, vol. 44, no. 3, pp. 765–770, 2011.
[21]
V. Rasper, “Investigation on starches from major starch crops grown in Ghana: I. Hot paste viscosity and gel forming power,” Journal of the Science of Food and Agriculture, vol. 20, p. 165, 1969.
[22]
J. A. Woolfe, Sweet Potato: An Untapped Food Resource, Cambridge University Press, Cambridge, UK, 1992.
[23]
C. G. Oates, “Towards an understanding of starch granule structure and hydrolysis,” Trends in Food Science and Technology, vol. 8, no. 11, pp. 375–382, 1997.
[24]
H.-L. Lee and B. Yoo, “Dynamic rheological and thermal properties of acetylated sweet potato starch,” Starch/St？rke, vol. 61, no. 7, pp. 407–413, 2009.
[25]
L. Mirmoghtadaie, M. Kadivar, and M. Shahedi, “Effects of cross-linking and acetylation on oat starch properties,” Food Chemistry, vol. 116, no. 3, pp. 709–713, 2009.
