紫胶热稳定性改性的研究进展

紫胶是一种在医药、食品、国防和日用化工中有着重要应用的天然树脂,但软化点低、受热易聚合等缺点又限制了其在这些领域的进一步应用。文章综述了紫胶热稳定改性的最新研究进展,重点介绍了基于紫胶中羧基、羟基、醛基、双键等活泼性基团的如酯化、聚合、氢化等反应对改进紫胶热性能的影响,并总结了目前紫胶改性的研究对热稳定性改性的启示及未来可能的发展方向。     

Investigation of various shellac grades: additional analysis for identity

Background: A number of different grades of shellac are commercially available and most of them are known only as generic shellac and are not further differentiated. The investigated grades of shellac in this study are based on different insect strains, host trees, refining methods, and products from different suppliers. Method: The Gardner/Iodine color values of alcoholic and aqueous solutions of the various shellac grades were measured. Glass transition temperatures and pK_a-values were determined. To assess chemical differences in the tested shellac grades, MALDI-TOF analysis was performed. Results: Differences were found in color, T_G, and pK_a-values and in the mass spectra by MALDI-TOF analysis. Conclusions: The results indicate that these methods can facilitate the determination of identity and are quality control parameters for shellac.     

响应曲面法漂白紫胶微波-真空干燥工艺研究

为提高漂白紫胶产品质量及生产效率,采用微波-真空干燥漂白紫胶研究了不同压强、微波功率和干燥时间对漂白紫胶产品颜色指数和含水率的影响,用响应曲面法（RSM）设计试验并建立了该工艺条件的拟合方程。结果表明,拟合方程的拟合度较高,所建立的数学模型可以用于描述漂白紫胶的微波-真空干燥。漂白紫胶微波-真空干燥的最优条件：干燥压强为3.0 kPa,微波功率为795 W,干燥时间为30 min。在优化条件下进行了验证实验,得到了颜色指数为0.9、含水率为0.028 9kg水/kg干料的产品。     

Effect of Hydroxypropyl Methylcellulose-Lipid Edible Composite Coatings on Plum (cv. Autumn giant) Quality During Storage

ABSTRACT 'Autumn Giant' plums were coated with edible hydroxypropyl methylcellulose-lipid composite coatings. The coatings consisted of beeswax or shellac, at 2 lipid content levels (20% and 60% dry basis). Weight loss of coated plums decreased as lipid content increased. No differences on weight loss were observed between uncoated and 20% lipid-coated plums, indicating that the natural waxes of plums are as effective as coatings having 20% lipid. Water-dipped plums experienced the highest weight loss. Fruit texture was not affected by coating after short-term storage at 20 °C. However, for prolonged storage at 20 °C, the coatings significantly reduced texture loss and internal breakdown compared to uncoated and water-dipped plums.     

乳糖酸复合保鲜剂对冷鲜肉品质的影响

为了制备出一款机械性能和保鲜性能良好的复合薄膜,以1.5%的海藻酸钠为基础膜液,添加不同浓度的漂白紫胶微粒乳液,负载抗氧化剂生育酚,制成不同的漂白紫胶/海藻酸钠复合膜。比较其机械性能和透过性能,通过红外光谱分析和电镜表征其结构,并比较其对冷鲜肉保鲜效果的差异。结果表明,漂白紫胶含量5%的复合膜机械性能较好,相比PE膜透光率降低了37.37%,紫外阻隔率提高了43.00%,具有较好的CO₂/O₂选择性,并且复合膜微观结构表征结果与其性能相互印证。用该膜对冷鲜猪肉进行覆膜保鲜,可有效降低贮藏期间肉的TVB-N含量、汁液流失率、pH和高铁肌红高蛋白含量,货架期提升至9 d。本研究对复合保鲜膜的研制和减缓冷鲜猪肉在贮藏过程中的腐败变质,保护猪肉色泽、口感及提升其营养价值具有一定的参考意义。     

紫胶脱蜡及精制紫胶蜡制备

介绍了用离心沉降对紫胶脱蜡和四氯化碳萃取精制紫胶蜡的研究过程和结果．在大量试验的基础上，证明经过脱蜡后的紫胶含蜡低，符合GB8139—8147—1987标准，其耐热性和附着力增强，耐腐蚀性提高，颜色得到改善，另外，用四氯化碳回收紫胶蜡。因此，找到了一条经济而又快捷的方法来对紫胶脱蜡和精制紫胶蜡。     

Cohesive-energy density of shellac

The solubility parameter ($\text{δ}$) of shellac has been ascertained by the methods of solubility, structural contributions and intrinsic viscosity [η]. From the solubility method, respective δ ranges for shellac have revealed that shellac is not soluble in poorly H-bonded solvents but dissolves in moderately and strongly H-bonded solvents. The δ value of shellac estimated by the structural contribution technique has been found to be slightly lower. The δ values of shellac computed from [η]_max and related extrapolation are in close agreement with each other and with average value ascertained from the solubility spectra method. The molar volume of shellac from contribution technique has also been estimated. Shellac has been classified as a class III type of material for encapsulation having excessive polar groups.     

Preparation of environmental friendly coatings based on natural shellac modified by diamine and its applications for copper protection

An environmental friendly coating based on natural product—shellac was prepared by using aliphatic diamine as a crosslinking agent and ethanol as a solvent. The amide group appeared in FTIR spectra in the modified shellac structure suggested the 1,3-propanediamine could successfully react with the acid groups in shellac. The enhancement in anticorrosive performance of the modified shellac could be observed directly from the color changes of the surface images of copper, copper coated with shellac and modified shellac after 60 h salt spray test. The EIS results indicated that after 24 h immersion in 0.5 M NaCl solution, the ionic Cl⁻ and water had reached the copper electrode and the shellac lost its protection to copper. However, the corrosive behavior of the copper electrode coated with modified shellac immersed in 0.5 M NaCl solution for 24 h still showed a characteristic of middle period of immersion and the coating layer hindered the ionic and water penetrating onto the surface of the copper; while after 72 h immersion, the modified shellac began to lose its protection to copper. The improvement in anticorrosive performance of modified shellac was attributed to the formation of network structure and the introduction of hydrophobic aliphatic group in shellac structure, which slowed down the speed of the ionic and water moving onto the copper surface.     

响应面试验优化紫胶全无氯漂白工艺及其产物性能

为避免传统含氯漂白紫胶的潜在风险,提高漂白紫胶在食品、医药等领域的使用安全性,本研究开发了紫胶的全无氯漂白工艺,采用响应面法研究了紫胶漂液质量浓度、H2O2用量、漂白温度、漂白时间、稳定剂用量等因素对漂白效果的影响,得出了紫胶全无氯漂白的最佳工艺条件：漂液中紫胶质量浓度0.08 g/mL、H2O2用量2.09 mL/g（以紫胶质量计）、漂白温度80 ℃、漂白时间7 h、稳定剂用量3.125%（以紫胶质量计）。在此基础上,通过傅里叶红外光谱、差示扫描量热、质量指标测定等方法对所得H2O2漂白胶进行了表征分析,结果发现：与次氯酸钠漂白胶和碱提紫胶相比,H2O2漂白胶分子整体结构基本一致,H2O2漂白胶热寿命、冷乙醇可溶物、酸值等指标明显提高,热乙醇不溶物、软化点等指标明显下降,颜色指数可达0.979（＜1.0）,漂白胶得率为82.03%。所得无氯漂白紫胶可作为优良的食品添加剂和加工原材料。