Influence of Chemical Extraction on Rheological Behavior,Viscoelastic Properties and Functional Characteristics of Natural Heteropolysaccharide/Protein Polymer from Durio zibethinus Seed

In recent years, the demand for a natural plant-based polymer with potential functions from plant sources has increased considerably. The main objective of the current study was to study the effect of chemical extraction conditions on the rheological and functional properties of the heteropolysaccharide/protein biopolymer from durian (Durio zibethinus) seed. The efficiency of different extraction conditions was determined by assessing the extraction yield, protein content, solubility, rheological properties and viscoelastic behavior of the natural polymer from durian seed. The present study revealed that the soaking process had a more significant (p < 0.05) effect than the decolorizing process on the rheological and functional properties of the natural polymer. The considerable changes in the rheological and functional properties of the natural polymer could be due to the significant (p < 0.05) effect of the chemical extraction variables on the protein fraction present in the molecular structure of the natural polymer from durian seed. The natural polymer from durian seed had a more elastic (or gel like) behavior compared to the viscous (liquid like) behavior at low frequency. The present study revealed that the natural heteropolysaccharide/protein polymer from durian seed had a relatively low solubility ranging from 9.1% to 36.0%. This might be due to the presence of impurities, insoluble matter and large particles present in the chemical structure of the natural polymer from durian seed.     

MEMS-based optical limiter

We propose the design of an optical limiter based on a microelectromechanical systems deformable mirror. The design is based on aperturing focused light reflected out of an optically driven deformable mirror, deformed in a parabolic form. We derive an expression for the reflected light intensity, and we show that the reflected light saturates as a function of back illumination light intensity.     

Method for the direct observation and quantification of survival of bacteria attached to negatively or positively charged surfaces in an aqueous medium

The risk of groundwater contamination by microbial pathogens is linked to their survival in the subsurface. Although there is a large body of literature on the inactivation behavior of suspended (planktonic) microorganisms, little is known about the inactivation of bacteria when attached to sand grain surfaces in groundwater aquifers. The main goal of this study was to develop a fluorescence-based experimental technique for evaluating the extent of inactivation over time of bacteria adhered onto a surface in an aqueous environment. Key features of the developed technique are as follows: (i) attached cells do not need to be removed from the surface of interest for quantification, (ii) bacterial inactivation can be examined in real-time for prolonged time periods, and (iii) the system remains undisturbed (i.e., the aqueous environment is unchanged) during the assay. A negatively or positively charged substrate (i.e., bare or coated glass slide) was mounted in a parallel-plate flow cell, bacteria were allowed to attach onto the substrate, and the loss of bacterial membrane integrity and respiratory activity were investigated as a function of time by fluorescence microscopy using Live/Dead BacLight and BacLight RedoxSensor CTC (5-cyano-2,3-ditolyl tetrazolium chloride) viability assays. These two different measures of bacterial inactivation result in comparable trends in bacterial inactivation, confirming the validity of the experimental technique. The results of this work show that the developed technique is sensitive enough to distinguish between the inactivation kinetics of different representative bacteria attached to either a negatively charged (bare glass) surface or a positively charged (coated glass) surface. Hence, the technique can be used to characterize bacterial inactivation kinetics when attached to environmentally relevant surfaces over a broad range of groundwater chemistries.     

Antioxidant and angiotensin converting enzyme (ACE) inhibitory activities of cocoa (Theobroma cacao L.) autolysates

The present study investigated antioxidant and angiotensin converting enzyme (ACE) inhibitory activities of cocoa autolysates. After removal of cocoa fat, alkaloids and polyphenols, the remaining proteinous powder was autolyzed at pH 3.5 and 5.2. At similar concentrations, autolysates produced at pH 3.5 indicated the highest reducing power and ACE inhibition activity. However, those generated at pH 5.2 showed the highest antioxidant activity based on ??-carotene bleaching assay. The results displayed a dose-dependent trend. Based on amino acids composition, slight differences were detected between autolysates, and as it was found, they were rich in hydrophobic amino acids. Qualitative and quantitative tests were applied to assure that the results from the assays were not due to the polyphenols of cocoa autolysates. Based on the results no polyphenols could be detected from cocoa autolysates. It can be indicated that among other useful substances of cocoa, its peptides and amino acids could contribute to its health-promoting properties. Furthermore, these bioactive substances can be exploited into functional foods or used as a source of nutraceuticals.