茶多酚和咖啡碱对茶乳酪形成的影响

采用茶多酚和咖啡碱模拟构建茶乳酪成因体系,通过分析溶液的透光率、粒径、沉淀量、咖啡碱和儿茶素含量的变化,综合评价茶多酚和咖啡碱对茶乳酪形成的影响。结果表明：随茶多酚和咖啡碱质量浓度的增加,其聚合后溶液的透光率从95.5%降为24.7%;粒径从198 nm增加到475 nm;沉淀量由8 mg/L增加到244 mg/L;当固定咖啡碱或茶多酚中任一物质的质量浓度,随另一物质质量浓度的增加,上述变化趋势增强。通过分析检测咖啡碱和儿茶素各单体在模拟反应体系中的变化,表明咖啡碱和表没食子儿茶素没食子酸酯（epigallocatechin-3-gallate,EGCG）是模拟体系中茶乳酪形成的关键组分。因此,尽量选用咖啡碱含量低于200 mg/L、茶多酚含量低于1 200 mg/L的绿茶原料,可避免茶乳酪的大量生成,增强绿茶饮料透亮的感官效果。     

柑橘皮渣液态发酵制取曲酸工艺优化

以柑橘皮渣为原料,接种米曲霉,以液态摇瓶发酵的形式进行曲酸生产的研究。采用Box-Behnken中心组合设计,通过响应面法优化柑橘皮渣发酵的最佳工艺。结果表明,最佳发酵参数为米曲霉接种量4%、柑橘皮渣添加量13 g/100 mL、酵母膏添加量1.5 g/100 mL、MgSO4·7H2O添加量0.05 g/100 mL,在此条件下发酵制得的曲酸质量浓度最高,为（11.84±1.44） mg/mL。     

茶叶中没食子酸含量测定的离子化萃取分离分光光度法研究

通过离子化萃取分离的手段将没食子酸与儿茶素进行分离,并采用可见分光光度法对茶叶中没食子酸的含量进行准确测定。此外,还通过模拟实验确定离子化试剂的最佳用量以及溶媒体系的pH 值,验证离子化萃取分离的可靠性。与其他用于没食子酸含量测定的方法相比,该方法具有操作简单、成本低、仪器要求不高等优点。将该方法用于检测茶样中没食子酸含量为(1.326 ± 0.018)%,RSD 为1.36%,测定值与已见报道相符。     

基于电子鼻和ATD-GC-MS技术分析茉莉花茶香气成分的产地差异

为探究茉莉花茶香气成分的产地差异,采用电子鼻和自动热脱附-气相色谱-质谱联用仪（automatic thermal desorption-gas chromatography-mass spectrometry, ATD-GC-MS）对福州和横县两地的茉莉花茶进行测定。结果表明,电子鼻传感器对横县茉莉花茶的响应值总和明显大于福州茉莉花茶;将电子鼻数据结果进行多元统计分析可以实现茉莉花茶样品的产地区分。ATD-GC-MS数据结果表明,福州和横县茉莉花茶香气指数（Jasmine tea flavor index,JTF index）分别为7.57和2.89,两者差异显著（P<0.05）;两地茉莉花茶的29种香气组分含量差异达到显著水平（P<0.05）,其中包括影响茉莉花茶香气鲜灵度的顺-3-己烯醇苯甲酸酯、α-法呢烯和吲哚。福州茉莉花茶和横县茉莉花茶的香气成分在种类上相似,而香气成分含量差异显著。电子鼻结合ATD-GC-MS技术可作为茉莉花茶香气成分产地差异分析的有效方法。     

响应面法优化桑葚酵素食用凝胶的制备工艺

以海藻酸钠、壳聚糖、桑葚酵素为原料,氯化钙为离子交联剂,制备酵素食用凝胶。通过单因素实验和Box-Behnken响应面法,研究海藻酸钠与壳聚糖质量比、交联时间、氯化钙浓度对酵素凝胶硬度、胶着性、咀嚼性等质构指标的影响。结果表明,酵素凝胶最佳的制备工艺为:海藻酸钠与壳聚糖质量比5:2.82、交联时间131 min、氯化钙浓度17.9 mg/mL。在此优化工艺条件下,测得酵素凝胶硬度为7.19 N、胶着性为6.60 N、咀嚼性为0.70 kgf。优化所得结果准确可靠,可为酵素功能性食品的进一步开发与利用提供理论依据和技术参考。     

Zn~(2+)沉淀法提取茶多酚工艺研究

对Zn2+沉淀法提取茶多酚的工艺条件进行了研究。结果表明,影响Zn2+沉淀茶多酚的因素主要依次为,pH值、ZnSO4用量、沉淀时间;影响茶多酚Zn2+络合物转溶效果的因素依次为,转溶时间、料酸比、HCl浓度。茶多酚沉淀的最佳工艺条件为:溶液pH值7.0,按m(茶多酚)∶m(ZnSO4)=1∶3的比例加入ZnSO4,沉淀20min;茶多酚Zn2+络合物最佳转溶条件为:按1g∶4mL料酸比加入4mol/LHCl,转溶15min,在此工艺条件下,茶多酚得率为23.04%,纯度达90%。     

Use of tobacco seed oil methyl ester in a turbocharged indirect injection diesel engine

Vegetable oils and their methyl/ethyl esters are alternative renewable fuels for compression ignition engines. Different kinds of vegetable oils and their methyl/ethyl esters have been tested in diesel engines. However, tobacco seed oil and tobacco seed oil methyl ester have not been tested in diesel engines, yet. Tobacco seed oil is a non-edible vegetable oil and a by-product of tobacco leaves production. To the author's best knowledge, this is the first study on tobacco seed oil methyl ester as a fuel in diesel engines.In this study, potential tobacco seed production throughout the world, the oil extraction process from tobacco seed and the transesterification process for biodiesel production were examined. The produced tobacco seed oil methyl ester was characterized by exposing its major properties. The effects of tobacco seed oil methyl ester addition to diesel No. 2 on the performance and emissions of a four cycle, four cylinder turbocharged indirect injection (IDI) diesel engine were examined at both full and partial loads. Experimental results showed that tobacco seed oil methyl ester can be partially substituted for the diesel fuel at most operating conditions in terms of performance parameters and emissions without any engine modification and preheating of the blends.     

Determination of apparent amylose content,pasting properties and gel texture of rice starch by near‐infrared spectroscopy

For breeding rice with improved quality, apparent amylose content (AAC), rapid visco analyser (RVA) pasting viscosities and gel texture properties may be routinely measured. As a direct measurement is time‐consuming and expensive, rapid predictive method based on near‐infrared spectroscopy (NIRS) is useful for measurement of these quality parameters. In this study, calibration models were developed using modified partial least‐squares regression with different mathematical treatments based on the grain and flour spectra of non‐waxy rice alone or in combination with waxy rice. The results showed that calibration models built with flour spectra are more robust than those with grain spectra, and with total rice including waxy rice are superior to those with only non‐waxy rice. Some starch quality parameters, such as AAC, setback viscosity (SB), pasting temperature (PT), hardness (HD) and cohesiveness (COH) could be predicted with sufficient accuracy by NIRS based on flour spectra, whereas only AAC and PT could be predicted with sufficient accuracy based on grain spectra. All the models reported here are usable for rough sample screening (cold paste viscosity and breakdown viscosity), sample screening (SB, PT and COH) and for most applications (AAC and HD) for routine screening of a large number of samples in the early generation selection in breeding programs. However, for accurate assay of the pasting viscosity and gel textural parameters, direct instrumental measurement should be employed in later generations. Copyright © 2007 Society of Chemical Industry