Preparation of Saccharomyces boulardii powder by spray drying: thermoprotectants optimization and stability evaluation.

Saccharomyces boulardii as the probiotic yeast was widely used in the pharmaceutical, feed and food industries. The influence of skim milk, gelatin, and carbohydrates on the heat resistance of S. boulardii is explored in the article. Response surface methodology was effectively applied to optimize the thermoprotectant composition for S. boulardii during spray-drying. The accelerated test is applied to evaluate its the subsequent storage stability. The results show that the thermoprotectants composition was comprehensively optimized such as: 15.12% skim milk, 1.81% gelatin, and 9.73% trehalose. The highest viability was 17.77%, which was basically the same as the predicted value of 18.21%. The inactivation rate constant of spray-dried powder was k-18 = 1.04 × 10-5 h-1, the quantity of viable cells stored at this temperature for 1 and 10 years was 8.25 × 108 CFU/g and 1.25 × 108 CFU/g, separately. This work provides a thermoprotectants formula for the S. boulardii during the spray drying process.

A strategy for the determination of flavor substances in goat milk by liquid chromatography-high resolution mass spectrometry.

A new analytical method for untargeted screening of flavor compounds in goat milk and milk flavor using mass spectrometry was developed and validated. All compounds of low molecular weight were considered as candidate chemicals, instead of focusing only on compounds that already have a known affect on the flavor quality of goat milk. High performance liquid chromatography coupled with high resolution quadrupole orbitrap mass spectrometry based on external standard was used to analyse flavor compounds in complex samples. The untargeted screening strategy is data pre-processing, automated componentization, suspect library spectra searching and the retained analytes confirming based on the reference standard solutions. Forty-two flavor compounds were confirmed and analyzed. The established method was validated by considering the guidelines specified in Commission Decision 2002/657/EC and European SANCO/12571/2013 Guideline 2013. This validated method was successfully applied to samples detection, and some unique flavor compounds were found between goat milk and milk flavor samples, which can provide some useful references for the illicit addition of flavors and fragrances in dairy products.

Ultrasensitive colorimetric sensing strategy based on ascorbic acid triggered remarkable photoactive-nanoperoxidase for signal amplification and its application to α-glucosidase activity detection.

Recently, exploitation of nanozymes for signal amplification has aroused extensive research interesting in the fields of analytical chemistry and nanoscience. Herein, we introduced a new sensing strategy based on the ascorbic acid (AA) precisely regulated Ag3PO4 nanozyme for signal amplification. AA can reduce the partial Ag+ on the surface of Ag3PO4 nano-particles to form Ag° particles and result in the formation of Ag°/Ag3PO4 heterostructure. Due to surface plasmon resonance (SPR), the Ag° particles in heterostructure can act as the co-catalysts to enhance the electron-hole separation and the interfacial charge transfer, leading to a highly efficient oxidase mimicking activity for catalyzing the oxidation of the substrate of 3,3,5,5-tetramethylbenzidine (TMB) under visible light. Impressively, the activity enhancement of Ag3PO4 nano-peroxidase was linearly depended on the AA concentrations. Based on this feature, we employed it for multiple biological detections. For example, L-ascorbic acid-2-O-α-D-glucopyranosyl (AAG) was designed for α-glucosidase substrate, which can be hydrolyzed by α-glucosidase and lead to AA release. Further, the signal of α-glucosidase activity can be efficiently enlarged by Ag3PO4 nanozyme. Taking advantages of the powerful signal amplification by Ag3PO4 nanozymes, we developed the multiple sensing assays for monitoring AA in rat brain microdialysates, detection of α-glucosidase activity and its inhibitors (anti-diabetic drugs). The assay allowed the ultrasensitive colorimetric detection of α-glucosidase inhibitor with an ultra-low detection limit of 10 nM, and a naked-eye detection of the inhibitor concentration as low as 1 µM. The sensing strategy based on AA precisely regulated Ag3PO4 nano-peroxidase provides a promising candidate platform for highly stable and efficient cascaded signal amplification in biosensing field.

Robust hybrid enzyme nanoreactor mediated plasmonic sensing strategy for ultrasensitive screening of anti-diabetic drug.

Enzyme inhibition based drug screening strategy has been widely employed for new drug discovery. But this strategy faces some challenges in practical application especially for the trace active compound screening from natural products such as the stability of enzyme and the sensitivity of screening approach. Inspired by the above, we for the first time demonstrate the self-assembly of α-glucosidase (GAA) and glucose oxidase (GOx) into one multi-enzymes-inorganic nanoreactor with hierarchical structure (flower shape). The hybrid enzyme nanoreactor enjoys the merits including the character of assembly line, the enhanced enzymatic activity and robust stability. The flower shape of enzyme nanoreactor possessed a bigger specific surface area, facilitating the trace GAA inhibitor detection. Based on the above, we proposed an enzyme nanoreactor mediated plasmonic sensing strategy for anti-diabetic drug screening. First, maltose was chosen as the substrate for GAA and the generated glucose were immediately utilized by GOx to generate H2O2, and finally, H2O2 etched the Ag nanoprism to round nanodiscs, resulting in the blue shift of surface plasmon resonance (SPR) absorption band. With the aid of hybrid enzyme nanoreactor guided SPR, the ultrasensitive screening of GAA inhibitor (i.e. anti-diabetic drug) can be realized with the detection limit of 5nM for acarbose. The proposed approach was successfully utilized for GAA inhibitor screening from natural products. We anticipate that the proposed sensing method may provide new insights and inspirations in the enzyme inhibition based drug discovery and clinical diagnosis.