A predictive model for astringency based on in vitro interactions between salivary proteins and (-)-Epigallocatechin gallate.

Astringency is an important quality attribute of green tea infusion, and (-)-Epigallocatechin gallate (EGCG) is the main contributor to astringency. Turbidity was used to predict the intensity of astringency for EGCG. The interactions between the selected proteins and EGCG, and the impacts of temperature, pH, protein structure, and EGCG concentration were studied. Mucin was selected as the protein in study for the prediction of EGCG astringency intensity. A predictive model (R2 = 0.994) was developed based on the relationship between the astringency of EGCG and the turbidity of EGCG/mucin mixtures at pH 5.0 and 37 °C. The fluorescence quenching analyses showed the interactions between EGCG and the selected proteins, which induced the reversible protein molecule conformational changes. The interactions were considered as the main reason that causes the astringency of tea infusions. The results provided a biochemical approach to explore the sensory qualities of green tea.

[Phosphorus pollution of the sediment from Hangzhou urban river and hydraulic simulation of phosphorus release].

The phosphorus pollution of the sediment from Dongxin River, an urban river in Hangzhou, was surveyed. Phosphorus release under various flow velocity (0.002-0.02 m x s(-1)), quality of overlying water (the total phosphorus concentration: 0.18, 0.072 and 0.007 mg x L(-1)), depth of overlying water (5, 10 cm) were carefully studied in a hydraulic simulation setup. The results indicate that phosphorus was feasible to release from the sediment with high ratio of water content (40.09%-68.57%) under alkali condition (pH 7.2-8.3). The phosphorus release was also influenced by high content of phosphorus (1.04-2.51 g x kg(-1)) in the sediment. Phosphorus release was mainly in the form of suspended solid under dynamic hydraulic condition, and depended definitely on flow velocity. The release rate reached 147.36 g x (m2 x h)(-1), which approached the maximum value, at flow velocity 0.008 m x s(-1) (i.e. 0.05 m x s(-1) in archetype). Phosphorus release, especially the initial release rate, was obviously affected by the quality of overlying water. Phosphorus tended to release under river water than tap water. However, the depth of overlying water had little influence on phosphorus release in shallow water. Therefore, it is possible to restrain or enhance phosphorus release by adjusting the hydraulic conditions and the quality of overlying water.