No abstract

One of the factors that inhibits the development of the Chinese wine industry is that the sugar content of the grape feedstock is insufficient. In order to produce wine with better qualities using these materials, concentrating the grape juice could be a good alternative to adding sugars. In this study, suspension freezeconcentration technology was applied to concentrating grape juice with a low sugar content. The freezeconcentrated grape juice was made into red and white wines separately. In the control group, red and white wines were made from chaptalized (sugar-enriched) grape juice. The physical and chemical indexes, sensory evaluation results and polyphenolic content of the wine were analysed to evaluate the practicality of applying the freeze-concentration technology in the wine industry. The results show that, after removing ice every 30 min for approximately 14 h with a -18°C coolant, grape juice with an initial sugar content of 14°Brix reached 23°Brix. Both the red wines and white wines made from freeze-concentrated grape juice were of a higher quality than the wines made from chaptalised grape juice. Moreover, the phenolic content was concentrated, which may provide health benefits. Thus, suspension freeze-concentration technology is a promising alternative to traditional chaptalisation technology.

This work presents a high-precision fiber optic pressure sensor based on frequency-modulated continuous-wave (FMCW) laser interference. The pressure sensor is primarily composed of a diaphragm-type Fabry–Pérot (F–P) cavity, with the diaphragm fabricated using high-elasticity SUS631 stainless steel. The external air pressure causes the center of the elastic diaphragm to deform, and this deformation results in a change in the F–P cavity length. The FMCW laser-interference method was used to demodulate the change in the length of the cavity and realize high-precision pressure measurements. The experimental results showed that when the pressure measurement is in the range of 0 kPa–600 kPa, an accuracy of 3.8 Pa can be obtained. In addition, the sensor had very good linearity with pressure change (R2 = 0.999 94), repeatability, and stability.

Determination of the biogenic amines in Pu'er tea is very important for its production and quality control. An analytical method for the quantification of biogenic amines in Pu'er tea using high performance liquid chromatography (HPLC) has been developed. Eight biogenic amines (Methylamine, Ethylamine, Cadaverine, Putrescine, Tryptamine, Histamine, Tyramine, Spermidine) in 106 Pu'er ripe tea, 60 raw tea and 41 sun dried green tea and their corresponding boiled tea liquor were analyzed by this method. The tea sample solutions were pretreated with homogenization, liquid-liquid extraction and centrifugal ultrafiltration. Dansyl chloride (DnsIC) was employed as the pre-column derivatization reagent, and subsequent separation of eight biogenic amines was conducted on a Waters-Atlantisd C18 (PR-18e ID 5 μm) column with a mixture of acetonitrile and water (65:35, V/V) as the mobile phase. The analytes were monitored using a fluorescence detector with absorbance detection between 230 nm and 280 nm. The method was consistent (RSD<2.6%) and linear(R>0.99). The recoveries from all kinds of Pu'er tea satisfactorily ranged from 94% to 102% and the lowest quantification limit was estimated to be 0.55-1.03μg /L. Our results showed that among 207 kinds of tea tested, Pu'er ripe tea contains the most kinds of and the highest content of the biogenic amines, followed by Pu'er sun dried tea, and Pu'er raw tea contains the least. The method should be helpful for the quantification of biogenic amines in the tea product and the tea quality control.