【作者】 谷风林；

【导师】 张晓鸣；

【作者基本信息】 江南大学 ， 食品科学， 2010， 博士

【摘要】 美拉德(Maillard)反应是烟草特征香味形成的重要反应之一,其产物是重要的香气前体物质,反应制备的美拉德产物在烟草燃烧时产生的香气也与烟香非常协调,因此美拉德反应已成为烟草业减害增香的一项关键技术;D-柠檬烯可以抑制烟草中致癌物质的毒性,但由于易氧化和易挥发,限制了其在烟草中应用的有效性,采用美拉德产物包埋可以提高保留率,在卷烟燃吸时释放降低烟气毒害,同时美拉德产物(MRPs)可以增强烟草香气,一定程度上解决了烟草减害增香的问题。本论文制备了酪蛋白-葡萄糖美拉德产物,研究了其组成、性质和在烟草中应用的效果,主要内容如下:分析了反应参数对产物主要性质(乳化性和抗氧化性)的影响,确定了加热温度、加热时间和起始pH是主要影响因素,采用响应面法优化了制备工艺,在酪蛋白与葡萄糖质量比为0.5,底物浓度20%(w/v),起始pH12.0,102℃下油浴回流加热130分钟时,得到的产物具有较高的抗氧化性和乳化能力;HPLC和SDS-PAGE分析表明:相对分子质量的分布从几万到几百万的组分在产物中占有较高比例,中等分子量组分较少,小分子产物占有一定比例。产物主要是大分子的蛋白黑素(melanoprotein)和蛋白质与糖或糖降解产物反应生成的物质;红外光谱表明大分子的美拉德产物是蛋白质与糖降解产物交联形成的,这些交联产物含有发色团,呈现明显的棕褐色。研究了美拉德产物的溶解性、流变性质、与风味物质的相互作用和抗氧化活性,美拉德反应能够提高酪蛋白的溶解性,使酪蛋白的等电点向低pH移动,反应得到的美拉德产物是一种典型的非牛顿型流体,存在剪切变稀性质;美拉德产物与大部分风味化合物存在相互作用,加入食品能够延缓风味的释放;氨基酸分析表明美拉德反应主要发生在蛋白质游离的赖氨酸和精氨酸侧链上。反应过程中游离氨基酸和挥发性风味物质的分析结果表明在加热过程中蛋白质会部分降解成氨基酸,生成的氨基酸与糖或糖降解产物反应生成挥发性物质和其他复杂产物,蛋白质能够促进糖降解成为糖片断,片断分子参与了挥发性物质的生成,产生了酸、酮、醛和酯等物质,氨类化合物的strecker降解生成了醛和吡嗪类物质。抗氧化结果表明MRPs具有较强的还原能力、金属离子螯合能力、抑制脂质氧化能力和清除自由基能力,在低浓度时具有量效关系。在美拉德产物中分子量大于50kDa的组分是主要MRPs;超滤组分的抗氧化结果表明:分子量大于50kDa的组分具有最强的还原能力和金属离子螯合能力,小分子的产物具有最好的清除DPPH自由基的能力,而抑制脂质氧化能力是通过清除自由基和螯合金属离子的协同作用,分子量5～10kDa和30～50kDa的组分具有较强的抑制脂质氧化能力。采用凝胶过滤色谱(Sephadex G-75)分离分子量大于50kDa的组分,得到了两个在220nm、280nm和420nm都有吸收的组分,分子量较大组分具有较强还原能力和金属离子螯合能力;红外光谱(FT-IR)结合酸水解单糖测定结果显示蛋白黑素主要为发色基团(糖降解产物)与蛋白质氨基基团共价结合的产物。蛋白黑素酶解产物仍然具有还原能力和清除自由基能力,胃蛋白酶酶解物比胰蛋白酶酶解物具有较高清除DPPH能力。采用SDS-PAGE和HPLC测定了分子量分布,结果表明蛋白黑素对胰蛋白酶水解有一定抗性。RP-HPLC和UPLC-MALDI-TOF-MS显示蛋白黑素和蛋白黑素酶解产物不能较好分离,产物是一系列的物质,发色团不是单一物质,结合裂解气相色谱-质谱(Pyrolysis-GC-MS)分析,发现蛋白黑素主要是酪蛋白与糖降解产物(如吡咯、呋喃和羰基化合物等)共价结合的产物,产物中存在苯环结构,热裂解生成苯酚和吲哚等苯衍生物。采用美拉德产物为壁材对D-柠檬烯进行了微胶囊化,将微胶囊水溶液添加到烟草中能够提高D-柠檬烯的保留率,裂解试验证明燃吸时能够释放进入烟气。D-柠檬烯微胶囊化能够提高稳定性,优化的工艺条件为:芯壁比0.125,壁材浓度20%(w/v),高速分散速度和时间分别为12000rpm和2min,均质压力和次数为45MPa和3次,干燥入口和出口温度分别为185℃和80℃;得到没有明显裂缝和空洞的球形微胶囊,干燥条件下存放具有较好稳定性。酪蛋白-葡萄糖MRPs裂解产物与酪蛋白-葡萄糖混合物裂解产物相比,杂环化合物增加了,生成了分子量相对较大的挥发性产物,其中多数产物是烟草香味物质,如呋喃酮具有果香,吲哚增加了烟草的白肋烟香气,邻苯二甲酸二异丁酯具有微香,能够增加烟草香气,苯甲醛具有苦杏仁的特殊香气,增强烟草自然香气,含氮杂环化合物能够增强烟草的烤香和焦甜香。美拉德产物在裂解过程中不仅裂解产生大量碱性香气物质,如吡嗪和吡啶类物质,而且还生成了许多的醇、醛、酮、酯和酸类成分,这些成分与烟草裂解成分相近,都是烟草烟气中的关键致香成分或烟草调香常用的香料。从添加MRPs的烟草热解化学成分来看,加入美拉德产物能够降低醛类物质、增加烟草的白肋烟香气、增强烟草的烤香和焦甜香、提高烟气浓度和烟气中含氮类物质,使烟气中游离烟碱浓度提高,增加烟气劲头,烟气更加丰满和协调,添加的D-柠檬烯能够释放进入卷烟烟气中,一方面缓和了烟气的刺激性,改善了余味,增加了香气,更为重要的是可以起到减害的功效。感官评析结果证明了这一结论,在烟草膨胀梗丝中添加酪蛋白-葡萄糖MRPs,可以明显提高烟草香气,提高膨胀梗丝的使用价值。更多还原

【Abstract】 Maillard reaction is one of the most important reactions in forming the special aroma of tobacco. The Maillard reaction products (MRPs) are the important fragrant precursors and the prepared MRPs are harmonious to the odour of the cigarette when they are smoked, so Maillard reaction has been known as one critical technique to reduce the harm and enhance the aroma of the cigarettes. D-limonene can inhibit the toxicity of the substance in cigarette smoke, which can induce the cancer of the smoker, but D-limonene is easily to be oxidized and vaporized, and is confined to be used in tobacco. MRPs can enhance the aroma of the tobacco and stabilize the D-limonene when they are encapsulated and added into cigarette, and D-limonene can be released into the main stream smoke, while MRPs improve the flavor of the smoke during the combusting course of the tobacco. The problem of reducing harm and ameliorating aroma of cigarette can be settled to a certain extent.In this study, MRPs were prepared from casein-glucose, and the composition, properties and effect on tobacco were analyzed and researched. The main contens are as follows:Analyzing the effect of processing parameters on the main properties (emulsifying activity and antioxidant activity) of the MRPs, heating temperature, heating time and initial pH were regarded to be the main factors influcing the MRPs, and response surface methodology (RSM) was applied to optimize the processing parameters of casein-glucose Maillard reaction. Substrate concentration 20%, casein-glucose ratio 1:2, heating time 130min, temperature 102°C and initial pH 12.0 were optimum conditions under refluxing for the improved emulsifying ability and antioxidant activity of the MRPs. The analysis of reverse phase high-performance liquid chromatography (RP-HPLC) and sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS–PAGE) indicated that MRPs with molecular weight (MW) from ten thousand Dalton to several million Dalton were the main fraction, and the products with medium MW were the least and the fraction with low MW was medium. Casein was covalently attached to glucose and glucose degradation products (GDPs), which results in high MW MRPs (melanoproteins). Results obtained from the high MW fraction, analysed by Fourier transform infrared spectroscopy (FT-IR) indicated that the amide I, II and III bands of casein were changed by the Maillard reaction and high molecular weight conjugated proteins were generated from native casein and sugars and sugars degradation products and were casein and carbonyls cross-linking conjugates, which includes multiple chromophores and a markedly browning can be observed.Rheological properties and solubility, interaction with flavor and antioxidant activity of MRPs were analyzed, the results showed that Maillard reaction could improve the dissolution property of casein and decrease the isoelectric point of the protein to lower pH. The solution of MRPs was a typical non-Newton fluid at the protein concentration of 200g/l, and MRPs exhibited shear thinning behavior. MRPs interacted with most flavor substances and delayed the release of aroma.Amino acid percentage composition of MRPs showed that MR caused a significant loss in lysine and arginine compared to native casein. Analysis indicated that the free amino acids were generated during the partial hydrolysis of casein and took part in the formation of volatile compounds. Hydrocarbons, acids, esters, ketones and furans were the major products and were distinctly formed at the different stages of heating. Strecker aldehydes and their corresponding substituted pyrazines were also identified at low concentrations in Maillard reaction products (MRPs).The antioxidant results showed that MRPs own strong reducing power and metal chelating ability, inhibition of lipid oxidation and free radical scavenging ability, and indicated the dose-effect relationship at low concentrations. Ultrafiltration results showed that the fraction of molecular weight (MW) higher than 50kDa was major MRPs, and antioxidant results showd that the molecular weight higher than 50kDa component exhibited the strongest reducing power and metal chelating ability, but the product of small molecules possessed the best DPPH free radical scavenging ability. Inhibition of lipid oxidation is provided by synergy with scavenging free radicals and chelating metal ions. The fractions of MW 5-10kDa and 30-50kDa component possess strong inhibition of lipid oxidation.The components of molecular weight greater than 50kDa were separated by gel filtration chromatography (Sephadex G-75), and two components were got with absorbance at 220nm, 280nm and 420nm, and the higher molecular weight component had stronger reducing power and metal ion chelating ability. The analysis of infrared spectroscopy (FT-IR) combined with acid hydrolysis determining monosaccharide showed that covalent bonding between low molecular weight colourants and proteins might, therefore, be involved in melanoidin formation, i.e. upon crosslinking of the N-terminal amino acid or an e-amino function of a lysine residue with carbohydrate-derived intermediates. Melanoprotein hydrolysates still possessed reducing power and scavenging ability and peptic hydrolysates owned higher DPPH radical-scavenging activity than tryptic hydrolysates. The molecular weight distribution with SDS-PAGE and HPLC showed that the melanoprotein had a certain resistance to trypsin hydrolysis. Analysis of RP-HPLC and UPLC-MALDI-TOF-MS showed that melanoprotein and its enzymatic hydrolysis products could not be well separated, and the product is a series of components, meanwhile, chromophore is not a single material, and the results combined with pyrolysis-gas chromatography- mass spectrometry (Pyrolysis-GC-MS) analysis show that the black pigment is mainly casein and sugar degradation products (such as pyrrole, furan and carbonyl compounds, etc.) conjugated products, in which the the benzene ring structure exists, and the derivatives of phenol and benzene, indole, etc.are produced by thermal cracking.Maillard products were used as wall material to encapsulate the D-limonene, and the results show that D-limonene encapsulated with MRPs added to tobacco can improve the retention rate and release in burning smoke. On the other hand, the stability of D-limonene can be improved by microencapsulation with MRPs.The optimal wall material concentration and the core-wall ratio were 20% and 0.125, respectively. Other optimum conditions determined were mixing speed of 12,000rpm for 2 minutes, homogenizing pressure 45MPa, inlet and outlet temperature of 185°C and 80°C, respectively. Microcapsules produced by spray drying were stable and had spherical structure with about 90% of d-limonene encapsulation yield. Results showed that MRPs could be used as an encapsulant for the protection of volatile flavors.The heterocyclic compounds were more in pyrolysates of MRPs than that of casein-glucose mixture, and the pyrolysis of MRPs generated high molecular weight volatile products, the majority of these products are tobacco flavors, such as furanone with fruit, and indole increases the aroma of burley tobacco, while o-benzene dicarboxylate with sweety flavor, benzaldehyde with bitter almond special aroma, and all these products can enhance the natural aroma of tobacco, at the same time, nitrogen-containing heterocyclic compounds can improve the sweet toast flavor of tobacco. The decomposition of MRPs in the pyrolysis process not only produces a large number of basic aroma substances, such as pyrazine and pyridine-type substances, but also generates a lot of alcohol, aldehydes, ketones, esters and acids, the composition and ingredients of MRPs are similar to tobacco pyrolysates, and they are the key materials to tobacco smoke in the aroma components or tobacco spice commonly used in perfumery. From the point of chemical composition of tobacco pyrolysis a view, adding Maillard products to tobacco can reduce aldehydes and increase burley tobacco aroma, and enhance the sweet roasted flavor of tobacco, meantime, and increase the smoke concentration and components containing nitrogen, and the free nicotine concentration can be improved in smoke, increasing momentum of smoke, and the smoke is more plentiful and harmonious. D-limonene added with MRPs can be released into the cigarette smoke so that to ease the irritation and increase the aroma on one hand, more importantly, the role of harm reduction can be achieved. Sensory assessment results prove the above conclusion, and adding casein-glucose MRPs into the tobacco expansion stem can significantly improve the aroma of tobacco and increase the value of tobacco expanding stem.更多还原