| Nicotine as a kind of strong initial enhancer, its effect on human body changes that make smoker feel antipathy, then strengthen, last dependent on, is the key factor for smoking addiction. Besides, nicotine is the key contributor of smoke associated diseases. Since the report of “clearing the smoke” issued by the US Institute of Medicine(Io M) in 2001, the development of potential reduced exposure products(PREPs) has been encouraged to reduce the risk of tobacco use for those smokers who do not quit smoking. Various technologies have been used for the reduction of harmful substances. However, many nicotine-reduced tobacco products have not been widely used due to their significantly difference of smoking feeling compared with conventional cigarettes. For many years, solving the conflict problem of tobacco and tobacco products between “nicotine reduction” and “smoking quality” has always been a direction for tobacco researchers and enterprise.In this study, an improved gas chromatography-triple quadrupole mass spectrometry(GC-Tri Q-MS) method for the determination of organic acids in tobacco, as well as a rapid and novel method for predicting nicotine alkaloids in tobacco through electronic nose and partial least squares regression analysis have been developed. Those methods provided supports for the subsequent research. This study demonstrated the major defect of the typical low-quality tobacco(shaoyang B2F) through contrastive analysis of the typical optimal and bad unblended-tobacco. Meanwhile, this study developed some improving methods by casings added treatments(CAT) and enzymatic hydrolysis treatments(EHT). Based on those methods, present work studied the reason of nicotine reducing and quality enhancing, and found the significant compounds in tobacco leaves. Simulating cigarette combustion process, studied the pyrolysis products of tobacco leaves pyrolyzed at 300 oC, 600 oC and 900 oC, and thermodynamic properties for learning more about the smoke nicotine and various kinds of volatile components in cigarette mainstream smoke. The main contents and results are as follows:Based on GC-Tri Q-MS, optimization of the selected reaction monitoring(SRM) scan mode, including selection of the appropriate precursor-product ions and optimization of collision energy for twenty organic acids, were carried out to improve the sensitivity(recovery 80~111%) and selectivity(RSD<10%). The sample preparation was performed by derivatization-free extraction, which is rapid and convenient for the quantification of tobacco organic acids.Eight alkaloids in forty-two tobacco samples were detected by GC-Tri Q-MS in an SIM scan mode. The results showed that the total alkaloid content significantly varied in different leaf positions. Sensors’ maximum intensity(INmax) and slope(K) were significantly related to alkaloids’ level. Prediction models of alkaloids were successfully established. The calibrated(R_cal of 0.99, R2_cal of 0.98) and validated(R_val of 0.97, R2_val of 0.94) parameters for nicotine prediction model were very satisfactory. After validity checking, the established model for nicotine detection has 96% of prediction capability. Moreover, the prediction effectiveness of other alkaloids’ models(except nicotyrine) was also proved accurate. This work provided evidence that electronic nose could be used as a testing tool to rapidly and quantitatively detect the content of nicotine alkaloids in tobacco.The correlation of the chemical constituents of typical optimal and bad unblended tobacco and sensory attributes was studied through ANOVA and PLSR analysis, which results demonstrated the major defect of the typical low-quality tobacco(shaoyang B2F), incluled: a, the content of water soluble total sugar and reducing sugar was significantly lower; b, significantly high nicotine level, meanwhile the ratio of sugar and alkali was not harmonious; c, very high protein content; d, sensory evaluation of shaoyang B2 F showed higher irritating and mixed gas, smoke coordination is bad. The correlation results of tobacco constituents and sensory attributes showed: glucose, free amino acid(valine), organic acid(isobutyric acid, butyric acid, 2-methyl butyric acid, etc.) significantly contributed to sensory aroma attributes, which increased the cigarette softness and mellow, reduced sensory stimulation, and improved aftertaste(P < 0.05); however, the total amino acids, most senior fatty acid has opposite effects on the sensory. These results provided guidance for subsequent modification of low-quality tobacco(shaoyang B2F).A series of casings added and/or enzymatic hydrolysis treatments were used for modifying shaoyang B2 F tobacco, and purposely selected the optimal treatments after sensory evaluation by experts and chemical constituents analysis included the routine chemical constituents, tobacco alkaloids, etc. the results showed that “glucose+citric acid+peptide” casing added treatment(CAT), and “glucose+protease+citric acid+xylanase” enzymatic hydrolysis treatment(EHT) provided significantly nicotine reducing and quality improving effect. Besides, the effect of different treatments and heating temperature on sensory attributes, tobacco routine chemical compounds, amino acids and tobacco alkaloids was also studied, results showed that the content of total sugar, reducing sugar in tobacco leaves was significantly increased, and the content of protein, total alkaloids and tar was significantly reduced(P<0.05) after treatments. Meanwhile, the alkaloids content in tobacco leaves and mainstream smoke was also significantly reduced(P<0.05). Compared with 150 oC heating treatment, 110 oC heating treatment showed higher capacity to reduce tobacco nicotine alkaloid content.About 114 kinds of volatile components in cigarette mainstream smoke of treated tobacco samples(TBs) were indentified through GC-MS analysis and retention index. Among them, about 41 compounds were found have significantly effect on sensory attributes by PLSR analysis, and most of these 41 compounds have tobacco specific aroma. After analysis it was founds that, compared whit CAT treatments, EHT treated tobacco samples have more amount aroma compounds. Besides, 110 oC heated samples showed significantly higher aroma content than 150 oC treated samples(P<0.05). Further PLS1 analysis were performed, and results showed that among 41 compounds, about 22 compounds significantly significantly contributed to increasing sensory aroma, improving sensory comfortable, reducing irritation and off-taste(P<0.05). The 22 compounds of cigarette mainstream smoke were the contributors of improved cigarette sensory. It was found that cigarette mainstream smoke 22 compounds significantly correlated to the rate of free amino acids and hydrolyzed amino acids(R-amino acids)(P<0.05). The total sugar, reducing sugar, and some of amino acids like aspartic acid, alanine, threonine, valine, etc., significantly contributed to increasing aroma compounds in cigarette mainstream smoke(P<0.05). About 97 kinds of volatile components in treated tobacco leaf samples were indentified through GC-MS analysis and retention index, among which, 41 compounds significantly contributed to one or several kinds of the 22 compounds in cigarette mainstream smoke(P<0.05).The correlation results of cigarette mainstream smoke organic acids in TBs and sensory attributes showed that, benzoic acid and 2-furan formic acids significantly and positively corelated to sensory aroma(P<0.05); linoleic acid significantly increased cigarette sensory irritation and off-taste(P<0.05); butyric acid, octanoic acid and decanoic acid increased, and 2-furan formic acid reduced sensory impact significantly(P<0.05). The correlation between tobacco leaf acids and cigarette MS acids was investigated, its result showed that propionic acid, valeric acid, caproic acid, heptanoic acid and capric acid in cigarette smoke have significantly positive correlation with low fatty acids(C2~C10)(P<0.05); acetic acid, 2-methyl butyric acid, benzoic acid and 2-furan formic acid in cigarette smoke not only significantly correlated to the volatilization of low fatty acids, but also correlated to the degradation of senior fatty acid significantly(P<0.05).The correlation between tobacco alkaloids and sensory attributes was also been studied, its result showed that alkaloids in tobacco leaf significantly and positively related to alkaloids in cigarette mainstream smoke(P<0.05). Most of tobacco alkaloids(either existed in tobacco leaf or smoke) have significantly negative correlation with sensory aroma and comfortable, and have positive correlation with sensory irritation, off-taste and impact attribute(P<0.05).The influence of different treatments on tobacco pyrolysis products during cigarette burning was studied by Py-GC/MS. Its result showed that during cigarette burning, most volatile compounds in smoke mainly originated from cigarette combustion zone and cracking zone, but nicotine in smoke mainly originated from the evaporative zone. Tobacco CAT and EHT treatments significantly reduced the content of nicotine, hydrazine, nitrile and polycyclic aromatic hydrocarbon in pyrolysis products(P<0.05), and increased the content of ketones, esters, acids, furan, etc. At 300 oC and 600 oC pyrolysis analysis, the amount of total nicotine and pyrolysis products in 110 oC heated samples was significantly lower than that in 80 oC and 150 oC heated samples(P<0.05).The effect of different treatments on thermodynamic properties was studied and resulted that, compared with the untreated tobacco, the water in treated tobacco samples is more likely to enter cigarette smoke, which is better for cigarette sensory quality. EHT treatments limited the pyrolysis and combustion of tobacco components and reduced tobacco leaf weightless loss, meanwhile, appropriate heated treatment(110oC) was conducive to this limited effect. |
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