Abstract Burley tobacco-leaf protein extracted by alkali and precipitated by acid was hydrolyzed enzymatically, and optimum protease and hydrolysis parameters were determined. Pepsin was best and gave the highest hydrolysis rate (15.55%). As per results of the single-factor test, optimum hydrolysis conditions were: temperature 37 °C, pH 2, and an [E]/[S] ratio of 5%. These hydrolysis conditions were optimized by an orthogonal experiment that rendered the same results as the single factor experiment. The ratio of essential to total amino acids and that of essential to non-essential amino acids contained in the burley tobacco-leaf protease hydrolysate were higher than the FAO/WHO standard values of 0.4 and 0.6, among which hydrophobic amino acid content was the highest, followed by negatively and positively charged amino acid contents. In vitro antioxidant experiments showed that the scavenging rates of DPPH, superoxide anion, and hydroxyl radicals of tobacco-leaf protein hydrolysates were higher than those before hydrolysis. Further, the hydroxyl radical-scavenging rate was the most significant, and total antioxidant capacity was improved. The nutritive value of the burley tobacco-leaf protein hydrolysate improved upon pepsin-mediated hydrolysis, and the antioxidant activity was better. These results provide a theoretical basis for further development and utilization of tobacco protein resources.

An astigmatic detection system (ADS) based on a compact disk/digital-versatile-disk (CD/DVD) astigmatic optical pickup unit (OPU) is presented. It can achieve a resolution better than 0.3 nm in detection of the vertical displacement and is able to detect the two-dimensional angular tilt of the object surface. Furthermore, a novel scanner design actuated by piezoelectric disk buzzers is presented. The scanner is composed of a quad-rod actuation structure and several piezoelectric disks. It can be driven directly with low-voltage and low-current sources, such as analogue outputs of a data acquisition (DAQ) card and enables a sufficient scanning range of up to 15 μm. In addition, an economic, high-performance streamlined atomic force microscope (AFM) was constructed, using the buzzer-scanner to move the sample relative to the probe, and using a CD/DVD OPU to detect the mechanical resonance of a microfabricated cantilever. The performance of the AFM is evaluated. The high sensitivity and high bandwidth of the detection system makes the equipment suitable for characterizing nanoscale elements. An AFM using our detection system for detecting the deflection of microfabricated cantilevers can resolve individual atomic steps on graphite surfaces.

En este artículo se presenta un sistema de detección astigmático (ADS), basada en una unidad de lectura (óptica digital (OPU) del disco compacto (CD/DVD). Este sistema de detección astigmático puede alcanzar una resolución mejor que 0.3 nm en la detección del desplazamiento vertical y se puede detectar la inclinación angular de dos dimensiones de la superficie del objeto. También, se ha presentado un novedoso diseño para un escáner-zumbador. El escáner se compone de una estructura de accionamiento de cuatro-barras y varios zumbadores piezoeléctricos de disco. El escáner-zumbador se puede accionar con voltajes bajos como los de las tarjetas de adquisición de datos (DAQ) y permite un alcance de barrido suficiente de hasta 15 μm. Por lo tanto, el costo de construir un AFM puede reducirse significativamente juntando las dos técnicas. A partir de las dos técnicas anteriores, se construyó un AFM económico de alto rendimiento, utilizando el escáner-zumbador para mover la muestra y un OPU para detectar la resonancia mecánica de un cantiléver microfabricado. Evaluamos el desempeño del AFM. La alta sensibilidad y gran ancho de banda del sistema de detección hace que el equipo sea apropiado para la caracterización de elementos a escala nanométrica. Un AFM usando nuestro sistema de detección para detectar la deflexión del cantilever microfabricado, puede resolver pasos atómicos individuales en superficies de grafito.