脂类理化性质.ppt

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1、LIPID PHYSICAL AND CHEMICAL CHARACTERISTIC,Zhang Dequan,物理性质,气味和色泽 芝麻油香气：乙酰吡嗪 椰子油香气：壬基甲酮 菜子油气味：黑芥子苷分解 熔点和沸点 油脂熔点最高40-55 熔点温度低于37，消化率达到96% 熔点高于37，不容易消化,烟点、闪点和着火点 smoking point：发烟的温度 flash point：被点燃但不能燃烧的温度 fire point：持续燃烧5s以上的温度 精练油脂烟点在240左右 折射率 分子量大分子量小的饱和脂肪酸 饱和脂肪酸不饱和脂肪酸 油脂鉴别,结晶特性 Polymorphism 转变 -2

2、排列(DCL) -3排列(TCL) 简单甘油酯容易形成稳定的结晶,DCL排列 混合甘油酯容易形成结晶,TCL排列,结晶：大豆油、玉米油、花生油、椰子油、橄榄油、可可脂油、猪油 结晶：棉子油、棕榈油、菜子油、乳脂、牛脂、改性猪油 “调温”获得某种结晶产品 可可脂生产 Sn-StOSt、Sn-POSt,熔融特性 融化 SFI（Solid Fat Index） SFI测定方法： 差示扫描量热仪（DSC） NMR 脉冲NMR为AOCS的官方方法,油脂塑性 塑性是指在一定的外力下，表观固体脂肪具有的抗变形的能力，油脂塑性取决于： SFI、脂肪晶型、熔化温度范围 Shortening oil 油脂的液晶态

3、（介晶相） 层状： 六方 立方,乳化与乳化剂 分散相（01-50微米的小滴）分散在连续相中 乳浊液的制备：油脂、水、乳化剂、能量 乳浊液不稳定的因素：分层、絮凝、聚结 乳化剂选择方法：HLB值,一些常见乳化剂的HLB值,化学性质,水解 氧化,1. Hydrolysis and saponification,动物脂肪 不利 有利 植物油 鱼脂 水解性质的应用构造脂质,2、氧化(酸败),自动氧化 光敏氧化 酶促氧化 热氧化 辐射氧化,Flavor Quality Loss Rancid flavor Changes of color and texture Consumer Acceptance

4、Economic loss Nutritional Quality LossEssential Fatty Acids Vitamins Health Risks Growth Retardation Heart Diseases,2.1 氧化机制,酶与非酶氧化两种机制 自催化机制的与分子氧的反应是脂类氧化变质的主要反应 光敏氧化触发了自动氧化,2.1.1 自动氧化的一般特性,遵循自由基机制，具有5个特点 干扰自由基反应的化学物质能显著抑制自动氧化 光和产生自由基的物质能促进自动氧化 产生大量的氢过氧化物 由光引发的氧化反应量子产额超过1 当原始物质为纯物质时存在一个相当长的诱导期,2.1.2

5、Mechanisms of Lipid Oxidation,Reactions Activation Energy Protein Denaturation 100 kcal/mol Nonenzymatic Browning Reaction 50 Enzyme Catalyzed Reaction 10-15 Lipid Oxidation 10-15,Activation Energy for Chemical Reaction,History of Oxygen,Oxygen - Scheele and Priestly in 1772. Triplet oxygen - Millik

6、an in 1928. Singlet oxygen - Herzberg in 1934.,Triplet Oxygen Oxidation,C,H,C,H,C,H,2,C,H,C,H,C,H,2,(,C,H,2,),6,C,O,O,H,C,H,2,(,C,H,2,),3,C,H,3,100,75,50,Bond Energy of Carbon and Hydrogen,kcal/mol,Stearic acid Oleic acid Linoleic acid Linolenic acid,C,H,3,(,C,H,2,),14,C,O,O,H,C,H,3,(,C,H,2,),6,C,H,

7、C,H,(,C,H,2,),7,C,O,O,H,C,H,3,(,C,H,2,),4,C,H,C,H,C,H,2,C,H,C,H,(,C,H,2,),7,C,O,O,H,C,H,3,C,H,2,C,H,C,H,C,H,2,C,H,C,H,C,H,2,C,H,C,H,(,C,H,2,),7,C,O,O,H,C,H,2,C,H,2,C,H,2,Initiation of Triplet Oxygen Oxidation,RH+引发剂,R,H,+,Initiation of autoxidation occurs when hydrogen atom at -methylene group in do

8、uble bonds of unsaturated fatty acids is removed to form an alkyl radical (R).,Propagation,ROO ,+,RH,ROOH,+,R,+,+,ROOH,+, OH,RO ,RH,RO ,ROH,R ,R,+,3O2,ROO ,Termination,2RO ,ROOR,+,+,+,ROOR,RO ,ROR,ROO ,ROOR,R ,+,R-R,R ,ROO ,+,R ,R ,ROO ,O2,Linoleic Acid Oxidation by Triplet Oxygen,14,13 12 11 10 9,1

9、2 11 10 9,- H,+ O,2,12 11 10 9,+ H,C,H,2,C,H,C,H,C,H,2,C,H,C,H,C,H,2,R,(,C,H,2,),3,C,H,3,INITIATION,(METAL),(,C,H,2,),4,C,H,3,C,H,C,H,C,H,C,H,C,H,2,R,C,H,(,C,H,2,),4,C,H,3,C,H,C,H,C,H,C,H,C,H,2,R,C,H,O,O,PROPAGATION,R = (CH2)6-COOH,12 11 10 9,HYDROPEROXIDE,DECOMPOSION,- OH,+ H,12 11 10 9,TERMINATION

10、,(PENTANE),C,H,C,H,C,H,C,H,C,H,C,H,2,R,(,C,H,2,),4,C,H,3,O,O,H,(,C,H,2,),4,C,H,3,C,H,C,H,C,H,C,H,C,H,2,R,C,H,O,C,H,3,(,C,H,2,),3,C,H,2,C,H,3,(,C,H,2,),3,C,H,3,O,C,H,C,H,C,H,C,H,C,H,C,H,2,R,+,R = (CH2)6-COOH,Singlet and Triplet Oxygen,Molecular Orbital of Triplet Oxygen,RH+O2自由基 35kcal/mol,Molecular

11、Orbital of Singlet Oxygen,Singlet Oxygen Formation,3O2 + Sensitizer,H2O2 + OCI-,H2O2 + O2 -,Ozone,Endoperoxides,OH- + O2 -,Enzymes,O2 - + Y+,1O2,O2 -,O2 - + O2 -,H2O2+ HO2 -,RCOO + RCOO,C,H,3,C,H,2,C,H,C,H,C,H,2,C,H,C,H,C,H,2,C,H,C,O,O,H,(,C,H,2,),6,C,H,2,C,H,O,C,H,3,C,H,2,C,H,C,H,C,H,2,C,H,C,H,C,H,

12、2,C,H,O,C,H,3,C,H,2,C,H,C,H,C,H,2,C,H,O,O,C,H,C,H,2,C,H,1O2,1O2,O,氢过氧化物形成：Reversion Flavor from Linolenic Acid by Singlet Oxygen Oxidation,O,2-(2-pentenyl)-furan,- H2O,C,H,3,C,H,2,C,H,C,H,C,H,2,C,H,O,O,C,H,C,H,2,C,H,C,H,3,C,H,2,C,H,C,H,C,H,2,C,C,H,2,O,C,H,2,C,H,O,C,H,3,C,H,2,C,H,C,H,C,H,2,C,C,H,C,H,

13、C,H,O,H,O,H,C,H,3,C,H,2,C,H,C,H,C,H,2,O,C,H,3,C,H,2,C,H,C,H,C,H,2,C,H,O,O,C,H,C,H,2,C,H,O,H,- OH,氢过氧化物裂解： Reversion Flavor Compounds from Soybean Oil,2-(2-pentenyl)-furan,C,H,3,C,H,2,C,H,C,H,C,H,2,O,C,H,3,C,H,2,C,H,C,H,C,H,O,2,2-(1-pentenyl)-furan,Reaction of 3O2 and 1O2 with Linoleic Acid,R,R,R,R,O

14、,O,H,3O2,Conjugated,Conjugated,R,R,R,R,R,R,HOO,3O2,- H,R,R,R,R,O,O,H,O,O,H,R,R,1O2,R,R,H,O,O,R,R,H,O,O,Conjugated,Nonconjugated,Reaction Rates of Lipid Oxidation,R+3O2K=109 M-1sec-1 ROO+Oleic AcidK=1 M-1sec-1 ROO+Linoleic AcidK=60 M-1sec-1 ROO+Linolenic AcidK=120 M-1sec-1 ROO+ROO K=105-107 M-1sec-1

15、R+AntioxidantsK= 107 M-1sec-1 RH+1O2K=105 M-1sec-1,Relative Reaction Rates of 3O2 and 1O2 with Oleic, Linoleic, and Linolenic Acids,Triplet oxygen 3 104 4 104 7 104,Singlet oxygen 12777,Oleic Linoleic Linolenic Acid Acid Acid,Formation of 1O2 by Sensitizers,Ground State,Excited State,hv,Fluorescence

16、 K= 2108/sec,1Sen,1Sen*,K=1- 20108/sec ISC,Phosphorescence,K=10- 104/sec,Singlet Oxygen, 1O2,K=1- 3109/sec,3Sen*,3O2,光敏氧化,Lipid,Free Radical,型,型,Photosensitizers in Foods,Chlorophyll Protoporphyrine Riboflavin Red No. 3,Enzymatic Oxidation（lipoxygenase,Lox）,Hydropeorxide at the -6 position of unsatu

17、rated fatty acid,Poly unsaturated fatty acids (a cis, cis-1,4-pentadiene unit),Lipoxygenase,热氧化,热分解 热聚合 热缩合,辐射氧化,过氧化脂质几乎可以与食品中的任何成分反应，降低品质 氢过氧化物几乎与人体内所有分子或细胞反应，破坏和细胞结构 脂质在常温或高温下氧化均产生有害物质,油脂氧化的安全性,影响自动氧化的因素,脂肪酸性质 氧与氧分压 温度 表面积 水分 过渡金属元素 光和射线 抗氧化剂 乳化,Control of Lipid Oxidation,Application of antioxidan

18、ts Elimination of oxygen by nitrogen flushing or vacuum packaging Elimination of photosensitizers Denaturation of lipoxygenase Low temperature and dark storage,Characteristics of Free Radicals in Oxidation,H : Hydrogen atom The simplest free radical O2 - : SuperoxideanionAn oxygen-centered radical.

19、Limited reactivity HO : HydroxylA highly reactive oxygen-centered radical. Indeed attacks all molecules in human body RO2: PeroxylOxygencentered radicals formed during the RO : Alkoxy breakdown of organic peroxides,Function of Antioxidant on Lipid Oxidation,Inhibits or slows the formation of free al

20、kyl radicals in the initiation step Interrupts the propagation of free radical chain Delays the start or slows the chemical reaction rate of lipid oxidation.,Types of Antioxidants,Hydrogen donating compounds Singlet oxygen quenchers Metal chelators Enzymes Oxygen scavengers and Reducing agents,Hydro

21、gen Donating Antioxidants,Standard One-Electron Reduction Potential,Compounds E (mV),HO , H+ / H2O 2310 RO , H+ / ROH1600 ROO , H+ / ROOH1000 PUFA , H+ / PUFA600 Catechol , H+ / Catechol530 - Tocopheroxyl , H+ / - Tocopherol500 Ascorbate- , H+ / Ascorbate282,Characteristics of Hydrogen Donating Anti

22、oxidants,The major hydrogen donating antioxidants are monohydroxy or polyhydroxy phenolic compounds with various ring substitutions. The antioxidant free radical does not initiate another free radical due to the stabilization of delocalization of radical.,Reaction of Antioxidants with Radicals,R + A

23、HRH +A,RO + AHROH+ A,ROO + AHROOH + A,Reaction of Antioxidants with Radicals,Effectiveness of Antioxidants,The difference of one-electron reduction potential between lipid radical and antioxidant radical. The stability of antioxidant radicals - The resonance delocalization - Further oxidation of ant

24、ioxidant radicals,Resonance of Antioxidant Radicals,O,H,C,(,C,H,3,),3,O,C,H,3,C,(,C,H,3,),3,O,C,H,3,O,.,O,C,H,3,C,(,C,H,3,),3,O,.,C,(,C,H,3,),3,O,C,H,3,O,.,O,C,H,3,C,(,C,H,3,),3,O,.,R , RO , ROO,RH , ROH , ROOH,Stability of Antioxidant Radical,O,C,C,H,3,C,H,3,C,H,3,O,C,H,3,Targets of Antioxidant,Ant

25、ioxidants can react with peroxyl radicals rather than alkoxyl radicals. The most prevalent radical is peroxyl (ROO) radical. Peroxyl radical has the lowest standard one electron reduction potential among alkyl, alkoxyl and peroxyl radicals,Synthetic Antioxidants,Butylatedhydroxyanisole (BHA),Butylat

26、edhydroxytoluene (BHT),Propyl gallate,Tertiary butylhydroquionone (TBHQ),Natural Antioxidants,Benefits Health implication Stability in food system Limits Characteristic flavor Safety test required,Tocotrienols,O,H,O,R,1,R,2,R,3,C,H,3,C,H,3,C,H,3,C,H,3,Trivial NameChemical NameR1R2R3 -Tocotrienol5,7,

27、8-TrimethyltocotrienolCH3CH3CH3 -Tocotrienol5,8-DimethyltocotrienolCH3HCH3 -Tocotrienol7,8-DimethyltocotrienolHCH3CH3 -Tocotrienol8-MethyltocotrienolHHCH3,Antioxidant Mechanism of Tocopherol,Transfer of phenolic hydrogen Scavenging of singlet oxygen Regeneration of tocopherol in the presence of asco

28、rbate,Tocopherol,A chain breaking antioxidant competes with polyunsaturated lipid for the lipid peroxyl radicals.,-Tocopherol -Tocopheryl semiquinone ,Lipid radicals,Lipid radicals,-Tocopheryl quinone,Resonance of - Tocopherol Radicals,O,O,C,H,3,H,3,C,C,H,3,C,16,H,33,C,H,3,R, RO , or ROO ,-Tocophero

29、l,O,H,O,C,H,3,H,3,C,C,H,3,C,H,3,C,H,3,C,H,3,C,H,3,O,C,H,3,C,H,3,H,3,C,C,H,3,C,16,H,33,O,O,C,H,3,H,3,C,O,C,16,H,33,C,H,3,C,H,3,O,C,H,3,H,3,C,O,C,16,H,33,C,H,3,C,H,3,RH , ROH , ROOH,R, RO , or ROO ,Effects of Diet Tocopherol on the Content of Tocopherol in Egg Yolk,Effects of Tocopherol on the Stabili

30、ty of Egg York,0,5,10,15,20,25,30,35,40,45,0,2,4,6,8,Time (Days),Total Headspace Volatiles ( 1000),25g Tocopherol / g yolk,45 g Tocopherol / g yolk,50 g Tocopherol / g yolk,75 g Tocopherol / g yolk,Control,Ascorbic Acid,Hydrogen donation to lipid radicals Quenching of singlet oxygen Removal of molec

31、ular oxygen Regenerate tocopherol radicals Prooxidant Reduce ferric iron to ferrous iron,Ascorbic Acid,O,O,O,H,O,H,C,H,C,H,2,O,H,O,H,O,O,O,O,H,C,H,C,H,2,O,H,O,H,L-Ascorbic acid,Dehydroascorbic acid,- H ,- H ,R, RO , ROO ,R , RO , ROO ,Ascorbic Acid and Related Compounds,L-Ascorbic Acid,O,O,H,O,H,C,H

32、,O,C,H,2,O,H,H,O,H,Erythorbic Acid,Ascorbic Palmitate,O,O,H,O,H,O,H,C,H,C,H,2,O,H,O,H,O,O,O,H,O,H,O,H,C,H,C,H,2,O,C,(,C,H,2,),14,C,H,3,O,H,Synergistic Effectof Tocopherol & Ascorbic Acid,Singlet Oxygen Quencher,Singlet Oxygen Quenching Mechanism,ISC,3O2,A,1Sen,1Sen*,3Sen*,1O2,AO2,Kq,Kox-Q,QO2,Kd,Q,Q

33、,1Sen,1Sen,3O2,3O2,hv,Carotenoids,C,H,O,b -,Carotene,Apo - 8- carotenal,O,Canthaxanthin,O,b -,Peroxide Value (meq/kg oil),Storage Time (hr),Effects of -Apo-8-Carotenal, -Carotene or Canthaxanthin on the Soybean Oil Oxidative Quality,Quenching Mechanism of b-Carotene on Singlet Oxygen Oxidation,1/ So

34、ybean Oil (1/ M),1/ Peroxide (1/ M),Singlet Oxygen Quenching Rates of Carotenoids,Carotenoids Number of Conjugated Quenching Rate Double Bonds Constants (M-1sec-1) -Apo-8- carotenal 10 2.86 109 - Carotene 11 4.60 109 Canthaxanthin 13 1.12 1010,Singlet Oxygen Quenching Rate of Carotenoids,Carotenoids

35、 Number of Conjugated Rate Constants Double Bonds (109 M-1sec-1) Astaxanthin 13 9.88 Isozeaxanthin 11 7.31 Zeaxanthin 11 7.03 Lycopene 11 6.89 Lutein 10 5.86,Singlet Oxygen Quenching Rates of Tocopherols,Singlet oxygen quenching ability: - Tocopherol,-Tocopherol: 2.70 107 (M-1sec-1),Singlet Oxygen Q

36、uenchers,Singlet Oxygen Quencher Quenching Rate (M-1sec-1) -Carotene 4.60 109 Ascorbic acid 1.08 108 -Tocopherol 2.70 107,Metal Chelators,Prooxidant Mechanisms of Metals,Hydroperoxide decomposition to form peroxyl radical and alkoxyl radical Fe3+ROOHFe2+ ROO + H+ Fe2+ROOHFe3+ RO + OH- Formations of

37、alkyl free radical by direct reaction Fe3+RH Fe2+ + R + H+ Activation of oxygen for singlet oxygen formation Fe2+3O2Fe3+ + O-2 1O2 Formation of hydroxyl radical Fe2+H2O2Fe3+ + OH- + OH,k1,k2,k2 k1 = 105,Reaction between Metal and Hydroperoxide,Rapid Exponential increase in oxidation during propagati

38、on step b-Scission of alkoxyl radical to low molecular weight compounds Copper is 50 faster than ferrous ion in decomposing hydrogen peroxide Ferrous is 100 faster than ferric iron in decomposing hydrogen peroxide Ferrous is 1015 times more soluble than ferric iron,Metal Chelators,Phosphoric acid Ci

39、tric acid Ascorbic acid Ethylene Diamine Tetra Acetate.(EDTA) Proteins such as Transferrin, Ovotransferrin Amino acids and Peptides,Mechanism of Metal Chelators,Formation of complex ions or coordination compounds with metals Prevention of metal redox cycling Occupation of all metal coordination site

40、s Formation of insoluble metal complexes Steric hindrance of interactions between metals and lipid intermediates,Phospholipids,Phosphatidyl ethanolamine,C,H,2,O,C,O,R,1,C,H,O,C,O,R,2,C,H,2,O,P,O,O,O,C,H,2,C,H,2,N,H,2,-,Phosphatic acid,-,C,H,2,O,C,O,R,1,C,H,O,C,O,R,2,C,H,2,O,P,O,O,O,-,M,O,C,O,C,H,2,O

41、,C,O,C,H,2,N,C,H,2,C,H,2,O,O,N,C,O,C,H,2,C,O,C,H,2,Ethylene Diamine Tetra Acetate (EDTA),Interaction of Chealator and Metal,Enzymatic Antioxidants,2 Glucose + 2O2 + 2H2O 2 Gluconic acid + 2H2O2,Glucose Oxidase/Catalase,2 Glucose + O2 2 Gluconic acid,2H2O2 2H2O + O2,Glucose Oxidase Catalase,Catalase,

42、Glucose Oxidase,Oxygen Scavenging,Superoxide Dismutase,2O,2,O,2,-,+,2H,+,+,Superoxide anion participates in oxidative reactions Maintaining transition metals in their reduced, active state Promoting the release of metals bound to proteins Producing singlet oxygen,Superoxide Dismutase,+,Catalase,2H,2

43、,O,2,O,2,2H,2,O,3,Glutathione Peroxidase,H2O2 + 2GSH 2H2O + GSSG LOOH + 2GSH LOH + H2O + GSSG,GSH: Reduced glutathione GSSH: Oxidized glutathione,Oxygen Scavengers,Oxygen Scavengers and Reducing Agents,Ascorbic acid Ascorbic palmitate Erythorbic acid Sodium erythorbate Sulfites,Oxygen Scavenger Mechanisms,C,H,3,S,H,C,H,3,S,S,C,H,3, O,2,+,O,O,O,O,H,C,H,C,H,2,O,H,O,H,H O,2,+, O,2,+,H O,+,H,O,S,O,H,O,H,O,S,O,H,O,O,O,2,2,Superoxide Dismutase,2O,2,O,2,-,+,2H,+,+,H,2,O,2,Superoxide Dismutase,+,Catalase,O,2,2H,2,O,3,2H,2,O,2,Producing triplet oxygen from superoxide anion,3,Multifun