Background: Chitooligosaccharides (COS) with degrees of polymerization (DP) 6 to 8 are degraded from chitosan, which possess excellent bioactivities. However, technologies that could purify them from hydrolysis mixtures in the narrow DP range (984 to 1,306 Da) are absent. The objective of this research is to purify DP 6 to 8 COS by nanofiltration on the basis of appropriate adjustments of the feed condition. Methods: Syrup containing DP 6 to 8 COS at different concentrations (19.0 to 46.7 g/L) was prepared. A commercial membrane (QY-5-NF-1812) negatively charged was applied. Experiments were carried out in full recycle mode, so that the observed COS retentions were investigated at various transmembrane pressures (6.0 to 20.0 bar), temperatures (10°C to 50°C), and pHs (5.0 to 9.0). Then, the feasibility of separation of DP 6 to 8 COS was further studied by concentration ratio under optimum conditions. Results: The results indicate that the purification of DP 6 to 8 COS by nanofiltration NF is feasible. It was found that the permeate flux was 95.0 L/(m 2 h) at 10.0 bar, while it reached to 140.0 L/(m 2 h) at 20.0 bar, and it increased with feed temperature, but the membrane pores were also swelled by heating and led to an irreversible wastage of target oligomers. Additionally, the retention behaviors of chitooligosaccharides are significantly influenced by pH. Conclusions: Although glucosamine and dimer were permeatable at low pH, their retention ratios were remarkably varied from 0.458 to 0.864 when pH was 9.0. With the interaction of hydrogen bonds, structural curling and overlapping of chitooligosaccharides were formed. Consequently, the rejection of chitooligosaccharides at various pHs is variable. Spray-dried products were finally characterized by the matrix-assisted laser desorption/ionization time-of-flight mass spectrum. The spectrum identified the distributions of hexamer, heptamer, and octamer. Combined with high-performance liquid chromatography profiles, the purity and yield of DP 6 to 8 chitooligosaccharides were up to 82.2% and 73.9%, respectively.

Degree of polymerization (DP) 6–8 chitooligosaccharides are edible hydrolyzates from chitosan and possess excellent bioactivities, especially for a potential antitumor ingredient. The objective of this study was to develop a promising enzymatic attempt for DP 6–8 chitooligosaccharides preparation. Chitosan (2%, w/v) was dissolved in acetic acid. Sequentially, six types of nonspecific enzymes were used to compare chitosanolytic activities under the optimum conditions. Results indicated that cellulase was most capable of hydrolysis, whereas others were slightly acted. The phenomenon resulted from the glycosidic bonds that existed in the chitosan. Based on preliminary experiments, cellulase and chitosanase were combined employing to digest chitosan. The enzyme mixture promoted the hydrolysis degree and the yield of resulting chitooligosaccharides were measured through high‐performance liquid chromatography. Data showed that the highest yield of DP 6–8 chitooligosaccharides reached to 79.8% w/w by hybrid enzymes adding simultaneously at pH 5.3 and 45°C after 6 h. Practical Applications Chitooligosaccharides are widely used in the pharmaceutical, food industry and agricultural field because of its excellent and specific bioactivities, depending on the degrees of polymerization (DPs) of chitooligosaccharides. For instance, chitooligosaccharides with DP 6–8 have potential antitumor activity that could be used as ingredients for pharmaceutical drugs, health‐care food and formula products. Another very important potential application of chitooligosaccharides with DP 6–8 is as a potent plants elicitor that could be an environment‐friendly biological stress‐resistant agent to replace chemical reagents in the agricultural field. Hence, the study of preparation methods of chitooligosaccharides with DP 6–8 is important and valuable.

A heart-cutting two dimensional liquid chromatography coupled with tandem mass spectrometry method was developed for the analysis of tobacco-specific N-nitrosamines (TSNAs) at low concentration level in Virginia-type cigarette smoke. A strong cation exchange column was utilized for the first dimensional separation, which effectively removed acidic and neutral components in the smoke, followed by a reversed phase liquid chromatography coupled with tandem mass spectrometric analysis. To capture components of the TSNAs in the effluent on the trapping column, a compensating pump was applied for online dilution and pH adjustment during the period of the TSNAs fraction transferring and enrichment. Highly sensitive determination of the TSNAs in mainstream cigarette smoke was achieved by isotope deuterated internal standards under the multiple reaction monitoring mode. Compared with traditional methodologies, the method was almost no matrix interference. Limits of quantity for the TSNAs were within 0.027-0.094 ng/mL, and the results showed good reproducibility and accuracy. Finally, the new method was applied for analysis of the Kentucky reference cigarettes and the results agreed well with joint experiments of Cooperation Centre for Scientific Research Relative to Tobacco.

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Microfiltration (MF) is a promising technique widely applied in the separation of solidliquid mixtures. However, the potential application of MF was not explored much in the purification of tobacco extracts liquid. To be efficient, it necessitates having an assessment of the fouling mechanisms involved in MF processing. In this work, a thorough design of experiments was carried out to investigate various operating conditions, while specifying their effects on permeate flux were studied. Both single-stage and multistage Hermia models were used to elucidate the fouling mechanisms. The results of the single-stage Hermia model showed that cake layer formation was the dominant model, yet with fitting accuracy lower than 0.9; the type of fouling mechanism does relate to the operating conditions. Subsequently, the multistage Hermia model was used for determining the fouling mechanism during different time stages. It was found that the determinant coefficients R 2 were significantly increased and multiple fouling mechanisms could be coupled or occurred simultaneously. A ternary plot was established to visualize the contribution of each model and to bridge the relationship between the fouling mechanism and the operating conditions. Therefore, the proposed method is a valid, convenient tool when selecting optimal operating conditions with the lowest irreversible fouling. The flux recovery of fouled membranes exceeded 95% after successive cleaning with deionized water, a 1 wt% NaOH + 0.5 wt% SDS mixed solution, and a 0.5% (vol/vol) HNO 3 solution. Practical ApplicationsCeramic microfiltration membrane could separate tiny particles and macromolecules from tobacco extracts liquid (TEL) while it can keep most of active ingredients. The present study aims to have a better understanding of the complex membrane fouling mechanism in the MF processing of TEL. The fouling mechanism involved in the MF of TEL was firstly reported and a new method to bridge operating conditions and the fouling mechanism was proposed. It demonstrated that it is feasible to reduce irreversible membrane fouling by changing operating conditions during the initial stage of the MF processing. Identification of fouling mechanisms in the present study could be used to postpone fouling of the membranes by optimizing the operating parameters, and reduce irreversible membrane fouling.