CHEMICAL AND PHYSICAL PROPERTIES OF CUCURBITA DIGITATA AND APODANTHERA UNDULATA STARCHES

Abstract

The xerophytic gourds, Apodanthera undulata and Cucurbita digitata, hold promise as new sources of starch for industrial and domestic use as world population increases and food demands become greater. Thus, understanding of the chemical and physical properties of the starches from these arid land plants is required. Moisture content, ash, fiber and starch content of A. undulata and C. digitata roots were comparable to Solanum tuberosum (potato) and Manihot utilissima (tapioca). High lipid content was observed in A. undulata, but C. digitata was similar to tapioca in this respect. The composition of subject starches was comparable to standard starches. The lipid content of C. digitata starch was similar to that of corn starch, but A. undulata starch exhibited a higher content. A. undulata starch showed a higher iodine binding capacity, hence a higher amylose content, than C. digitata, potato and C. foetidissima starches. The number of terminal aldehyde groups and the average granule size of subject starches were comparable to tapioca starch. Interestingly, gelatinization temperature and percent sag test values were more similar to cereal starches such as corn, than to potato or tapioca. The swelling power of both starches was intermediate between corn and tapioca, while the solubility of A. undulata was similar to corn starch. The paste viscosity of A. undulata and C. digitata, when compared to corn, potato and C. foetidissima, proved to be most similar to corn. Viscosity maxima were intermediate between corn and potato. C. digitata starch was very stable, showing little change in paste viscosity after heating for one hour at 90°C. Increases in viscosity occurred during the cooling period for A. undulata, C. digitata and corn, but negligible changes occurred in C. foetidissima and potato. Starches isolated from A. undulata, C. digitata and potato were evaluated nutritionally by an in vivo study. Increases in digestibility of autoclaved starches (85% for A. undulata, 85% for C. digitata and 91% for potato) over raw starches (40% for A. undulata, 40% for C. digitata and 24% for potato) were confirmed by statistical analysis. Feed consumption and body weight gain were higher than for the potato starch diet. Autoclaving also improved net protein ratio and protein efficiency ratio. The fine structure of the macromolecular fractions amylose and amylopectin from starches of A. undulata and C. digitata were examined. The dimethyl sulfoxide method proved to be effective for fractionation of each starch. Purity of these components was confirmed by iodine binding capacity, and they were found to be similar to standard starches. Calculated values for degree of polymerization (DP) were similar to that of potato. Study of the fine structure of these components showed beta-amylolysis limits of approximately 90% for the amyloses and above 60% for the amylopectins. These values were similar to those of potato and intermediate between tapioca and cereal starches. The average chain length of the A. undulata amylopectin was found to be 25 with an outer chain length of 18 and an inner chain length of 6. The average chain length of 18 and an inner chain length of 6. The average chain length for C. digitata amylopectin was 26 with an outer chain length of 19 and an inner chain length of 6. These relatively long exterior layers with respect to the short interior layers show the amylopectins of these starches to be asymmetric molecules comparable to potato.