Pepper - chemistry, technology, and quality evaluation.
Pepper is the most important of the spices, with a long history. This article critically reviews our knowledge of the chemistry, processing, and quality evaluation of the product, with emphasis on the constituents contributing to the sensory properties of the spice for which it is valued in food. Other areas briefly summarized include its history, horticultural aspects, production and trade data, and physiological effects. Allied spices and aromatic members of the same family are also considered briefly.
Quantitative Determination of Piperine. II. Direct Determination with Phosphoric Acid
SUMMARY 
Piperine in 85% phosphoric acid forms an unstable yellow color which, when heated for 8 min at l00°C, becomes a stable bluish-green with absorption maximum at 635 mμ. This reaction was exploited for the direct determination of the piperine content of pepper samples. Pepper, ground to pass a standard U. S. 80-mesh sieve, was treated 30 min at room temperature (29 ± 1°C) with 85% phosphoric acid. The resulting yellow color was heated 8 min at l00°C, and cooled, and the absorbance was measured against a reagent blank at 635 mμ. Results were comparable to those obtained with the chromotropic acid and H2SO4–para-dimethylaminobenzaldehyde methods. Beers' law was obeyed between the levels of 0.04–0.28 PM of piperine per ml of 85% H3SPO4. The method requires only simple, readily available chemicals and equipment, and is rapid and reproducible with a standard deviation of ± 1.01% of the total amount of piperine as 100%.
Analysis of the stress wave effect during coal breakage by a high-pressure abrasive air jet
In view of the defects of borehole collapse, inhibition of gas desorption and migration of gas existing in hydraulic fracturing and other hydraulic permeability–increasing measures for soft coal seams with low-permeability technology is proposed for coal breakage by a high-pressure abrasive gas jet for relieving pressure and increasing permeability. The comparative analysis of gas jet flow field structure between convergent nozzle and Laval nozzle has been given by numerical simulation. For Laval nozzle, the expansion wave and compression wave alternate and move forward steadily in gas jet and vanish when potential core length reaches maximum. So, the Laval nozzle can form more stable flow filed structure of gas jet and avoid shock wave in gas jet. Furthermore, a high-speed camera is adopted to analyze the jet structure and verify the conclusion of numerical simulation. Based on thermodynamic theory, this article calculates and analyzes the critical local sound velocity and pressure generated from the stress wave during the process of coal breakage by the gas jet. Furthermore, experimental coal breakage by a high-pressure abrasive gas jet is carried out. The high-pressure abrasive gas jet impacts the coal body as a quasi-static load and a dynamic load and forms corrosion pits on the surface of the coal body. Penetrating cracks are formed within the coal in the pattern of the loaded stress wave which leads to coal breakage. The effects of porosity and permeability on the propagation of the stress wave in coal are analyzed by establishing the dispersion equation for the spread of the stress wave in coal. The results show that porosity has a significant effect on wave velocity and that the attenuation of the stress wave is intensified with an increase in porosity. Moreover, the stress wave attenuation is more obvious at high frequency. The effect of permeability on the wave velocity is not significant at low frequencies. In contrast, at high frequency and relatively low permeability, the wave velocity increases with the permeability, and the attenuation of the wave velocity initially increases and then decreases. When the permeability is greater than 10−11 m2, the wave velocity is not affected by the permeability. However, the stress wave is not attenuated.