树莓汁中键合态香气物质提取方法及糖基组成的研究

本文采用Amberlite XAD-2树脂吸附洗脱分离的方法和甲醇直接提取法对树莓汁中的键合态香气物质进行了分离,对得到的键合态香气物质进行了酶水解释放,采用GC-MS分析方法对水解得到的键合态香气物质进行了分析鉴定,重点比较了这两种方法的提取效果,并对酶水解后的糖基部分进行了分析研究。结果显示,甲醇直接提取法只提取得到4种键合态香气物质,总含量为77.1μg/kg,包括2种苯系物和2种脂肪醇类物质;Amberlite XAD-2树脂吸附洗脱提取法共提取得到20种键合态香气物质,包括11种苯系物,6种醇类物质及3种萜烯类物质,总含量达3042μg/L。两种方法提取得到的键合态香气物质在种类和含量上存在很大的差异,Amberlite XAD-2树脂吸附提取法提取得到的键合态香气物质种类丰富。树莓汁中糖苷键合态香气物质的糖基部分含有甘露糖和葡萄糖两种单糖。     

RAG1 and RAG2: nuclear genes involved in the dependence/independence on mitochondrial respiratory function for growth on sugars

The analysis of five independent isolates of Kluyveromyces lactis shows that CBS 2359, CBS 683 and CBS 4574 could grow in the presence of mitochondrial inhibitors (antimycin A, oligomycin or erythromycin) and that CBS 2360 and CBS 141 were unable to grow in the presence of drugs. The resistant growth was observed only on glucose and not on other fermentable carbon sources (galactose, lactose). The phenotype 'growth on glucose in the presence of mitochondrial inhibitors' was called Rag+. This phenotype was found to be controlled by two unlinked nuclear genes: RAG1 and RAG2. Either of their recessive alleles, rag1 and rag2, led to the Rag- phenotype (i.e. the failure of growth on glucose in the presence of antimitochondrial drugs). Rag- strains represent the case in which fermentative growth becomes absolutely dependent on the functioning of the normal respiratory chain.     

香气增甜的作用机制及评价方法研究进展

食品减糖比较常见的方法是使用非营养性甜味剂,但非营养性甜味剂会带来不受欢迎的苦味或金属味及安全风险。研究表明,在某些食物中加入香气物质可以增强人体对食品的甜味感知,即利用香气增甜作用达到食品减糖效果。从气味物质种类、甜味剂浓度2个方面总结了对香气增甜作用有重要影响的因素;从正鼻途径和后鼻途径的嗅觉感受机制、脑神经及味觉感受机制、心理感受机制3个方面阐述了香气增甜的作用机制,总结了分子模拟在分析甜味剂与味觉受体结合、释放过程的应用;归纳了评价香气增甜作用大小的感官分析方法,并比较描述性感官分析法、时间强度法和感觉时间支配分析法3种感官分析方法的差异性;对香气增甜作用在食品工业中的应用现状进行了汇总;对香气增甜研究方向以及分析气味增强味觉作用机制的方法提出展望,以期为香气减糖的研究提供新思路。     

中国糖业国际贸易预警决策支持系统设计

加入WTO后,中国糖业面临着国内外市场的双重压力,大量地进口食糖使中国糖业遭受了严重打击。建立中国糖业国际贸易预警决策支持系统,有助于合理利用WTO规则保护我国糖业。作者分析了建立系统的必要性,设计了系统的整体结构、逻辑结构。     

基于正交信号校正和偏最小二乘(OSC/PLS)的苹果糖度近红外检测

采用正交信号校正法(OSC)对苹果的近红外光谱(1300nm～2100nm)进行预处理，并结合偏最小二乘法(PLS)建立了苹果光谱对糖度的预测模型。应用结果表明，经OSC法预处理后，光谱形状总体上与原始光谱没有差别，但光谱曲线变得更为光滑，排列更为整齐、紧密。这说明正交信号校正法(OSC)滤除了原始光谱中的部分噪声，但又保留了原光谱中的主要信息。苹果光谱对糖度的PLS校正模型采纳的最佳因予数会随着OSC因子的被逐个滤除而逐渐减少，甚至可减少至1(当然模型精度也有变化)。本研究中，校正模型的最佳性能产生于原始光谱被滤除10个OSC因了时，此时其采纳的最佳因了数为2，校正时的相关系数r2和标准偏差SEC分别为0．92644和0．40250，预测时的标准偏差SEP为0．50229。与OSC法处理前的PLS模型相比，其精度虽没有大幅提高，但由于采纳的因子数少，模型变得十分简洁。     

电位滴定法测定葡萄酒中还原糖含量的研究

根据直接滴定法的原理，应用电位滴定法测定了葡萄酒中的还原糖含量。结果表明，该法检测灵敏度高，方便快捷，测定结果符合葡萄酒中糖含量标准。检测结果的标准偏差为0．09，RSD为4．09％，回收率在92．8％～113.2％之间，平均回收率为102．16％。     

山楂干酒中还原性物质的分析与还原糖含量测定

用斐林试剂测定山楂酒中还原糖含量为14．2g/L，不符合干酒的还原糖要求。分析表明：半乳糖醛酸在山楂干酒中含有8．10g/L，相当于7．53g／L还原糖，多酚类物质相当于3．7g／L还原糖，是影响还原糖测定的主要还原性物质；山楂干酒中实际还原糖含量为2.97g/L,符合干酒标准。山楂干酒中的还原糖含量可以通过活性炭吸附与HPLC或活性炭与强碱性阴离子交换树脂吸附两种方法进行定量测定。     

Sugar reduction without compromising sensory perception. An impossible dream?

ABSTRACT

Sugar reduction is a major technical challenge for the food industry to address in response to public health concerns regarding the amount of added sugars in foods. This paper reviews sweet taste perception, sensory methods to evaluate sugar reduction and the merits of different techniques available to reduce sugar content. The use of sugar substitutes (non-nutritive sweeteners, sugar alcohols, and fibres) can achieve the greatest magnitude of sugar and energy reduction, however bitter side tastes and varying temporal sweet profiles are common issues. The use of multisensory integration principles (particularly aroma) can be an effective approach to reduce sugar content, however the magnitude of sugar reduction is small. Innovation in food structure (modifying the sucrose distribution, serum release and fracture mechanics) offers a new way to reduce sugar without significant changes in food composition, however may be difficult to implement in food produced on a large scale. Gradual sugar reduction presents difficulties for food companies from a sales perspective if acceptability is compromised. Ultimately, a holistic approach where food manufacturers integrate a range of these techniques is likely to provide the best progress. However, substantial reduction of sugar in processed foods without compromising sensory properties may be an impossible dream.     

甜菜含水率与还原糖含量间的相关性及对贮藏的影响

试验证明:收获期甜菜含水量与还原糖含量成正相关,含水量和还原糖含量高的甜菜不耐贮藏。生产上可以通过收获前限制灌水及施氮肥等栽培措施,降低收获前甜菜的含水量和还原糖含量。贮藏中随着时间的推移甜菜的含水量下降,而还原糖含量增加,二者成负相关,实践中采取相应减少贮藏甜菜失水的措施,使含水量下降速度缓慢,适当的大堆贮藏效果好于小堆贮藏。     

Co-consumption of sugars or ethanol and glucose in a Saccharomyces cerevisiae strain deleted in the HXK2 gene

In previous studies it was shown that deletion of the HXK2 gene in Saccharomyces cerevisiae yields a strain that hardly produces ethanol and grows almost exclusively oxidatively in the presence of abundant glucose. This paper reports on physiological studies on the hxk2 deletion strain on mixtures of glucose/sucrose, glucose/galactose, glucose/maltose and glucose/ethanol in aerobic batch cultures. The hxk2 deletion strain co-consumed galactose and sucrose, together with glucose. In addition, co-consumption of glucose and ethanol was observed during the early exponential growth phase. In S.cerevisiae, co-consumption of ethanol and glucose (in the presence of abundant glucose) has never been reported before. The specific respiration rate of the hxk2 deletion strain growing on the glucose/ethanol mixture was 900 micromol.min(-1).(g protein)(-1), which is four to five times higher than that of the hxk2 deletion strain growing oxidatively on glucose, three times higher than its parent growing on ethanol (when respiration is fully derepressed) and is almost 10 times higher than its parent growing on glucose (when respiration is repressed). This indicates that the hxk2 deletion strain has a strongly enhanced oxidative capacity when grown on a mixture of glucose and ethanol.