chapter6食品化学.ppt

Chapter 6 Vitamin and Minerals 6.1 概述 Introduction 辅酶或辅酶前体:如烟酸,叶酸等 维生素的功能 抗氧化剂:VE,VC 遗传调节因子:VA,VD 某些特殊功能: VA-视觉功能 VC-血管脆性 VB1,VB2,VPP B族 VB5,VB6,VH water-soluble Vit VB11,VB12 Vit VC VA fat-souble Vit VD VE VK 6.2 水溶性维生素The Water-soluble vitamin Overview of Water-Soluble Vitamins Dissolve in water Generally readily excreted Subject to cooking losses Function as a coenzyme Participate in energy metabolism 50-90% of B vitamins are absorbed Marginal deficiency more common 1.维生素VB1 thiamin ① 具有酸-碱性质 ② 对热非常敏感,在碱性介质中加热易分解. ③ 能被VB1酶降解,同时,血红蛋白和肌红蛋白可作为降解的非酶催化剂. ④ 对光不敏感,在酸性条件下稳定,在碱性及中型 介质中不稳定. ⑤ 其降解受AW影响极大,一般在AW为0.5-0.65范围降解最快. 两环间亚甲基易与强亲核试剂反应。 与亚硝酸盐反应,使VB1失活. 在碱性条件下易降解,其降解机制为: Coenzyme: Thiamin Pyrophosphate (TPP) Synthesis of neurotransmitter Hexose monophosphate shunt Removes CO2 from some amino acids Convert pyruvate to acetyl-CoA CoA NAD+ NADH + H+ Glucose Pyruvate Acetyl-CoA Citric CO2 Acid Cycle （4）VB1缺乏症Deficiency of Thiamin Occurs where polished rice is the only staple Dry beriberi Weakness, nerve degeneration, irritability, poor arm/leg coordination, loss of nerve transmission Wet beriberi Edema, enlarge heart, heart failure （5）食物来源Food Sources of Thiamin Wide variety of food White bread, pork, hot dogs, luncheon meat, cold cereal Enriched grains/ whole grains Thiaminase found in raw fish （6）易缺人群Who is at Risk For Deficiency? Poor Alcoholics Elderly Diet consisting of highly processed foods ① 对热稳定，对酸和中性pH也稳定,在120 ℃加热