ABSTRACT
Pectin is widely used in the food and pharmaceutical industries. However, data on sweet potato pectin extraction and structural property analyses are lacking. Here, for the high-value utilization of agricultural processing waste, sweet potato residue, a byproduct of sweet potato starch processing, was used as raw material. Ammonium oxalate, trisodium citrate, disodium hydrogen phosphate, hydrochloric acid and citric acid were used as extractants for the pectin constituents, among which ammonium oxalate had a high extraction rate of sweet potato pectin, low ash content and high molecular weight. Structural and gelation analyses were conducted on ammonium oxalate-extracted purified sweet potato pectin (AMOP). Analyses showed that AMOP is a rhamnogalacturonan-I-type pectin, with a molecular weight of 192.5 kg/mol. Chemical titration and infrared spectroscopy analysis confirmed that AMOP is a low-ester pectin, and scanning electron and atomic force microscopy demonstrated its linear molecular structure. Gelation studies have revealed that Ca2+ is the key factor for gel formation, and that sucrose significantly enhanced gel hardness. The highest AMOP gel hardness was observed at pH 4, with a Ca2+ concentration of 30 mg/g, pectin concentration of 2%, and sucrose concentration of 40%, reaching 128.87 g. These results provide a foundation for sweet potato pectin production and applications.
ABSTRACT
The phenomenon of urban heat islands has been extensively investigated in recent decades. Due to the complexity of urban systems, this phenomenon may be scale-dependent, particularly for large megaregions where a cluster of cities gather together. Despite many studies focusing on urban heat islands at scales from single-site to regional, and further to global, there are few studies addressing multi-scale effects of large urban agglomeration on thermal environment. In this study, we used the Yangtze River Delta (YRD), one of China's most important megaregions, as a pilot case to examine the spatial-temporal variations of thermal environment and its driving forces at two spatial scales in 2000, 2005 and 2010. At regional scale, the effect of the entire megaregion on thermal environment was characterized by the distribution of the highest surface temperature zone (HTZ), which was closely related to the occurrence of continuously developed land. At city scale, the effect of individual city on thermal environment was characterized by the mean land surface temperature difference (LSTD) between urban and rural areas, which showed a significant positive correlation with the economic factors. In the YRD, the secondary industry output could explain approximately 58% and 39% of the variation of the LSTD in 2000 and 2005, respectively, while in 2010 the tertiary industry output became the important factor and accounted for 36% of the variation of LSTD. Finally, cities with fast urban economic growth rate and large size of urban areas were the priority for adopting more efficient strategies to urban thermal management.