ABSTRACT
Sweet potato plants were treated with selenium (Se). Spraying Se on the sweet potato leaves was an effective Se enrichment method and proteins were extracted from the sweet potato stem. The structural characteristics of the protein were investigated. Fourier transform infrared spectroscopy (FT-IR) detected more signals from the Se-enriched sweet potato stem protein (SSP), and the number of forms of Se chemical bonds gradually increased with increasing Se content, such as the Se-O bond in high Se-enriched SSP, indicating altered secondary structures.Scanning electron microscopy-energy dispersive spectrometry (SEM-EDS) indicated more Se atoms in the Se-enriched SSPs (SSSPs). The DSC results revealed that Se enrichment enhanced the thermal stability of the samples. Moreover, selenomethionine (SeMet), selenocystine (SeCys2), and methylselenocysteine (MeSeCys) were determined to be the main Se forms in the SSSPs. Furthermore, the SSSPs showed relatively higher superoxide anion radical and DPPH radical scavenging activities than the blank, which indicates that SSSPs can be used as antioxidants. By recovering the proteins, the agricultural by-product-sweet potato stem can be further utilized, and the obtained Se-enriched proteins may contribute to human health.
ABSTRACT
Evergreen broad-leaved forest (EBF), bamboo forest (BF) and mixed conifer and broadleaved forest (MF) were selected as objects of study on Jinyun Mountain from May to October 2012. The main contents were to analyze the rainfall process and nitrogen input of atmospheric rainfall, throughfall and stemflow. The results showed that: (1) During the research period, the total precipitation was 564. 88 mm, and throughfall of EBF, BF and MF were 74.0%, 85.0% and 71.6% of rainfall, respectively, and stemflow were EBF (1.9%), BF(10.3%) and MF (1.6%), respectively. The relationship between throughfall, stemflow and atmospheric rainfall could be described by a significant linear equation (P < 0.05), and both throughfall rate and stemflow rate had an obvious logarithmic function relationship with atmospheric rainfall (P < 0.05). (2) The concentration of NO3(-) and NH4(+) of throughfall and stemflow were higher than those of atmospheric rainfall, of which the three typical forests ranked as MF > EBF > BF. The total inorganic nitrogen input of throughfall and stemflow were EBF (14.93 kg x hm(-2)), BF (15.31 kg x hm(-2)) and MF (18.93 kg x hm(-2)), respectively. (3) There was a significant linear relationship between inorganic nitrogen input and throughfall, stemflow for three typical forest stands (P < 0.05).
