Influence of pH on property and lipolysis behavior of cinnamaldehyde conjugated chitosan-stabilized emulsions.

In the present study, we prepared cinnamaldehyde (CA) conjugated chitosan-stabilized emulsions (CSCAEs), and the influence of pH on their properties and lipolysis behavior was investigated. Compared to the emulsions stabilized by chitosan itself (CSEs), CSCAEs had better stability against pH during storage. As pH increased from 2.5 to 6.25, the viscosity and modulus of CSCAEs increased. However, when pH shifted from 6.25 to 6.5, emulsion showed lower viscosity and modulus. Confocal laser scanning microscopy results demonstrated that oil droplets still kept intact and individually distributed, and chitosan homogenously covered on the oil droplets at low pH conditions (pH 2.5, 4.0). At higher pH conditions (pH 5.0, 5.5), a few chitosan aggregates on the oil droplets were observed. At pH 6.0 and 6.25, the compact gel network structure was formed. At pH 6.5, some void was found among the chitosan gel network. In vitro simulated digestion experiments presented that pH had no significant effect on the lipolysis process of emulsions. When the oil content varied from 10% to 50%, emulsions still kept good stability against pHs, but the lipolysis extent after digestion decreased. This knowledge provides a strategy for improving stability of chitosan-stabilized emulsion against harsh pH conditions.

[Determination of neutral chemical constituents in flue-cured tobacco by comprehensive two-dimensional gas chromatography and time-of-flight mass spectrometry].

A method was established to analyze neutral chemical constituents in tobacco accurately by comprehensive two-dimensional gas chromatography and time-of-flight mass spectrometry (GC x GC-TOFMS). A DB-Petro column (50 m x 200 microm x 0.5 microm) was chosen as the column for the first dimension, and a DB-1701 column (2.3 m x 100 microm x 0.1 microm) was chosen as the column for the second dimension. The modulation period was set at 8 s, and the column pressure was 550 kPa. The initial temperatures of the two columns were set at 80 degrees C and 85 degrees C respectively and then increased with temperature programming. The contents of the neutral chemical constituents in different positions of tobacco leaves, product regions and varieties of tobacco were compared. The results showed that the total contents of the 24 neutral fractions in the middle leaves was the most, then in the upper leaves and the least in the lower leaves. These contents in the flue-cured tobacco produced by Brazil was the highest, followed by Zimbabwe, Yunyan85, Zhongyan101, NC89 and K326. In four kinds of tobacco, the total contents of the 24 neutral fractions in Oriental tobacco was the highest, followed by Burly tobacco, Flue-cured tobacco and Maryland tobacco.