Chapter 食品的气味化学 46.pptVIP

Chapter 10 食品的气味化学 Odor chemistry of food An odor or odour is the object of perception of the sense of olfaction. Odors are also called smells. The term stench恶臭, or pong 难闻的气味is used to describe an unpleasant odor. The term fragrance or aroma is used primarily by the food and cosmetic industry to describe a pleasant odor, and is sometimes used to refer to perfumes. ODORS There are thousands of odors, and the sensitivity of the smell organ is about 10000 times greater than that of the taste organ. The outstanding feature of olfaction 嗅觉 of chemical substances as compared to taste is its extreme sensitivity to low concentrations of chemical substances and its ability to differentiate among them Theory of olfactionhow olfaction work? As discovered by [Linda B. Buck] and [Richard Axel](who were awarded the [Nobel Prize] in 2004), mammals generally have about 1000 genes for odor receptors. Each olfactory receptor neuron in the nose expresses only one functional odor receptor. The axons from all the thousands of cells expressing the same odor receptor converge in the olfactory bulb. Mitral cells 僧帽细胞in the olfactory bulb send the information about the individual features to other parts of the olfactory system in the brain, which puts together the features into a representation of the odor. Since most odor molecules have many individual features, the combination of features gives the olfactory system a broad range of odors that it can detect. DESCRIPTION OF ODORS: ???Odors can be described by the combination of the threshold value and odor quality. Threshold value relates to the lowest concentration that gives an odor impression and this is called the intensity factor 香气阈值是指香气物质与空白实验作比较时，能用嗅觉辨别出该物质存在的最低浓度。 判断一种呈香物质在食品香气中的作用的数值称为香气值，香气值=呈香物质的浓度/阈值 Tricyclic 三环的compounds, macrocyclic大环化合物 ketones and lactones内酯, steroids固醇, nitrocyclhexanes环已烷, indanes六氯化苯 , tetrahydronaphthalenes and acetophenoses are all examples of different structures that