22 CEREAL CHEMISTRY Gelatinizing, Pasting, and Gelling Properties of Potato and Amaranth Starch Mixtures Anil Gunaratne 1 and Harold Corke 1,2 ABSTRACT Cereal Chem. 84(1):22–29 Physicochemical properties of mixtures of native potato and native amaranth (Amaranthus cruentus), heat-moisture treated (HMT) potato and heat-moisture treated amaranth, cross-linked potato and cross-linked amaranth, native potato and heat-moisture treated amaranth, and heat- moisture treated potato, and native amaranth were tested at different ratios. Two peaks were noticed in the pasting curves when large differ- ences of swelling factor and amylose leaching existed between individual components in the mixture. It seems that amylose leaching from one starch in a mixture may affect the swelling and much of the granular break down of the other. The mixtures showed stabilities in hot pastes that were higher than the less stable components in a mixture. Some mixtures such as HMT potato and native amaranth showed very specific nonadditive pasting behavior. Mixing 10% of native amaranth to HMT potato starch caused a large reduction of peak viscosity and cold paste viscosity, resulting in a very soft gel. In the differential scanning calorimeter, each component of a mixture gelatinized independently, showing two peaks corresponding to the individual components. When transition temper- atures of both components were similar in DSC, the result was a single endotherm. Dramatic changes of pasting and subsequent gel properties resulted when thermal transition of the two components occurred in the same temperature range. Retrogradation enthalpies as measured by DSC were between the two individual components in all tested mixtures. Functional properties of starch play a key role in its diverse applications in food and nonfood industries. Native starches generally do not possess desirable functional properties for a wide range of utilization, so they are frequently modified to improve these properties. Chemical modification is widely used to attain this objective, however, with the growing market demand for natural food, there is greater necessity to search for alternatives to chemical modification. One possibility may be the use of blends of different starches, although this is not a common practice. Not much work has been done in this area despite its high potential. Obanni and BeMiller (1997) found that pasting properties of some starch blends behave similarly to cross-linked starches and the tendency to retrogradation decreased after blending. Karam et al (2005) found that blending native starches from maize, cassava, and yam improves some specific sensory properties. In a study of starch gelatinization in a rice and wheat starch blend, Liu and Lelievre (1992) found at low starch concentration (<30%) DSC thermograms are the sum of each individual components in the mixture, but nonadditive behavior was found at higher starch concentration due to the competition for water. The peak temper- ature for the gelatinization of rice starch increased because the low-temperature gelatinizing starch (wheat) can access more water. Ortega-Ojeda and Eliasson (2001) reported that at low starch concentration (20%), each individual component in the mixture independently gelatinized, whereas at higher starch concentration (50%) they did not. From the survey of literature, it seems that most studies on starch blending have been limited to the use of native starches; thus, it is worth studying the physical properties of modified and unmodified starch blends, especially using physically modified starch. The size of the starch granule in individual starch com- ponents in the mixture could also affect the properties such as starch pasting. Thus, in this study, we chose blends of native, heat- moisture treated, and cross-linked potato and amaranth starches. Amaranth is not a cereal, but its starch properties are similar to those of cereals. Its extremely small starch granules may contri- bute specific functional properties to the starch blends. MATERIALS AND METHODS Materials Potato starch and phosphoryl chloride were obtained from Sigma Chemical (St. Louis, MO). Amaranth starch was extracted from Amaranthus cruentus K 350 (Wu et al 1995). Isolation of Amaranth Starch Amaranth starch was isolated by the method of Wu et al (1995). Grain was soaked in 0.25% NaOH solution at 4°C for 24 hr then ground for 6 min in a Waring blender with 6 volumes of 0.25% NaOH. The slurry was filtered through filtering cloth using a small amount of water; the filtrate was then centrifuged at 3,000 × g for 10 min. The sediment was washed with distilled water several times, followed by centrifuging at 3,000 × g for 15 min each time. The starch cake was then dried at 35°C. Swelling Factor Swelling factor, the ratio of the volume of swollen starch gran- ules to the volume of dry starch, was determined by the method of Tester and Morrison (1990a) where starch (50 mg, db) was heated from 60 to 90°C in 5 mL of water. Amylose Leaching Distilled water (10 mL) was added to starch (20 mg, db) in a screw-cap tube. Tubes were then heated from 60 to 90°C for 30 min with occasional stirring. After cooling to ambient temperature, samples were centrifuged at 2,000 × g for 10 min. The amylose content of the supernatant (0.1 mL) was estimated as described by Chrastil (1987) and the percent of leached amylose calculated based on starch weight. Differential Scanning Calorimetry (DSC) Gelatinization parameters of individual starch and the starches and mixtures were measured using differential scanning calori- metry (DSC) (TA 2920 modulated thermal analyzer, Newcastle, DE) equipped with a thermal analysis data station. Starch (3 mg) was directly measured into an aluminum DSC pan and relevant proportions of individual starches were directly measured for the mixtures in the pan separately. Then distilled water (9 μL) was added with a microsyringe and the components were mixed for homogenization. Pans were sealed and allowed to stand for 1 hr at room temperature for even distribution of water. The scanning tem- perature and heating rates were 30–120°C and 10°C/min, respec- tively. An empty pan was used as reference for all measurements. 1 Cereal Science Laboratory, Department of Botany, University of Hong Kong, Pokfulam Road, Hong Kong. 2 Corresponding author. Phone: 00852-2857-8522. Fax: 00852-2857-8521. E-mail: hcorke@yahoo.com DOI: 10.1094 / CCHEM-84-1-0022 © 2007 AACC International, Inc.