E: Food Engineering & Physical Properties Thermal and Rheological Properties of Breadfruit Starch Xueyu Wang, Ling Chen, Xiaoxi Li, Fengwei Xie, Hongshen Liu, and Long Yu Abstract: The thermal and rheological properties of breadfruit starch were studied using DSC and 2 different rheometers. It was found that the gelatinization temperature of starch with excess moisture content (>70%) was at approximately 75 ◦ C. A new endotherm was detected at about 173 ◦ C when the moisture content was lower than required for full gelatinization of the starch. A detailed examination revealed that this endotherm represented the melting of amylose–lipid complexes. Breadfruit starch paste exhibited shear-thinning fluid characteristics, and good thermal and pH stability. The setback viscosity of the breadfruit starch was lower than that of potato and corn starches. The rheological properties of the breadfruit starch paste was well described by the Herschel–Bulkley model at a shear rate of 0 to 100 s −1 , where R 2 is greater than 0.95, and it behaved like a yield-pseudoplastic fluid. Both the storage modulus and loss modulus of the paste initially increased sharply, then dropped after reaching the gelatinization peak. Breadfruit starch gel showed both flexibility and viscosity. Suspension with 6% starch content exhibited very weak gel rigidity; however, this increased significantly at starch contents above 20%. Keywords: breadfruit starch, DSC, dynamic rheology, rheology Introduction There is a growing tendency towards finding alternative sources of starch from novel and underutilized starch varieties rather than relying on known starch cultivars (Adebowale and others 2005). Breadfruit is the large, round fruit yielded by the tropical fruit tree Artocarpus artilis, which belongs to the Moraceae family. The tree is native to Malaysia, the South Pacific, and the Caribbean (Loos and others 1981), but it is now widely grown in tropical regions around the world, such as Africa, Brazil, and southeast Asia (Rincon and Padilla 2004). Every 100 g of breadfruit contains about 1.34 g protein, 0.31 g fat, 27.82 g carbohydrate, 1.5 g fiber, 1.23 g ash, and other nutrients such as calcium, phosphorus, iron, potassium, carotene, and vitamin B. Breadfruit powder has a high carbohydrate content (76.7%) and it is a valuable source of starch (Morton 1987). Breadfruit starch has been used as a raw material since ancient times, to not only simply bake for eating, but also to make biscuits, jams, and wines. It has good thickening and gelling properties, and it is a good texture stabilizer and regulator in food systems (Adebowale and others 2005). In addition, Adebayo and others (2008) showed that breadfruit starch powder is a suitable substitute for corn starch as an exo-disintegrant in paracetamol tablet formulations. By scanning electron microscopy (SEM), Rincon and Padilla (2004) showed that breadfruit starch granules have an irregular, rounded shape. The swelling power, water absorption, and solu- bility of breadfruit starch were found to be higher than that of MS 20100552 Submitted 5/20/2010, Accepted 8/18/2010. Authors Wang, Chen, Li, Liu, and Yu are with ERCSPP, College of Light Industry and Food, South China Univ. of Technology, Guangzhou 510640, China. Author Xie is with Australian Inst. for Bioengineering and Nanotechnology, The Univ. of Queensland, Brisbane, Queensland 4072, Australia. Author Yu is also with Commonwealth Scientific and Industrial Research Org. (CSIRO), CMSE, Melbourne, Victoria 3169, Australia. Direct inquiries to author Chen (E-mail: felchen@scut.edu.cn). corn and amaranth starches, and an amylographic study revealed a gelatinization temperature of approximately 73.3 ◦ C. Various chemical modifications to breadfruit starch, such as acetylation, oxidation, and heat-moisture treatment, have also been studied (Adebowale and others 2005). Due to recent developments in extrusion cooking of foods and thermal processing of starch under shear stress, the phase tran- sitions of starch with limited moisture content (MC) and un- der shear stress have both scientific and commercial importance. This study focused on the thermal and rheological properties of breadfruit starch, in particular gelatinization with limited moisture content (<70%), and viscosities under static and dynamic shear stress. Differential scanning calorimetry (DSC) incorporating a high-pressure pan was used to investigate the phase transitions of breadfruit starch up to 200 ◦ C, and 2 different rotational rheome- ters were used to systematically study the effects of concentration, temperature, and pH value on the rheological properties of bread- fruit starch suspensions and pastes. Descriptive and predicative models of the rheological behavior of the breadfruit starch have been evaluated. Materials and Methods Materials and sample preparation The breadfruit starch used in this study was isolated from com- mercially available unripened, peeled and dried breadfruit sheets obtained from Madagascar. The sheets were washed with water before milling to a slurry, which was dispersed in distilled wa- ter before sieving. Further impurities were removed by stirring distilled water into the slurry, allowing for sedimentation, and then decanting off supernatants, according to the method de- scribed by Adebowale and others (2005). After drying at room temperature, the resultant powder was defatted using petroleum ether (starch/petroleum ether ratio 1 : 2.5) at 84 ◦ C for 5 h in a water/oil bath using a Soxhlet extractor. The defatted samples were washed with 85% ethanol to remove soluble sugars, and the C  2010 Institute of Food Technologists R  doi: 10.1111/j.1750-3841.2010.01888.x Vol. 76, Nr. 1, 2011  Journal of Food Science E55 Further reproduction without permission is prohibited