《食品化学》课程教学资源（课件讲稿）第五章 蛋白质 第八节 食品蛋白质

第八节食品蛋白质

第八节 食品蛋白质

肌肉蛋白·骨骼肌蛋白质含量16-22%·肌浆蛋白水或稀盐溶液色泽一肌红蛋白/血红蛋白·肌纤维蛋白（占1/2）高浓度盐溶液一生理条件下不溶·基质蛋白质水不溶一组织骨架

肌肉蛋白 • 骨骼肌蛋白质含量 16-22% • 肌浆蛋白 水或稀盐溶液 – 肌红蛋白/血红蛋白 色泽 • 肌纤维蛋白（占1/2） 高浓度盐溶液 – 生理条件下不溶 • 基质蛋白质 水不溶 – 组织骨架

Composition of Muscle Tissue (%)LipidAshWaterProteinSpecies1Beef70-734-820-22Pork9-1168-701.419-2073.74.71Chicken20-237320Lamb5-61.681.20.3Cod17.61.2641.3Salmon13-1520-22

Milk Protein

Milk Protein

MilkMilk isatrue solutionfor salts,lactose,water-solublevitaminsmilk isa colloidal dispersion for proteins and someCa phosphatea dilute emulsion for fat globules

Milk  Milk is  a true solution for salts, lactose, water-soluble vitamins  milk is a colloidal dispersion for proteins and some Ca phosphate  a dilute emulsion for fat globules

MilkpH of milk: 6.6 at 25oC-whenheated,pHdecreases,H+areliberatedwhenCaphosphateprecipitatesComponentsofmilkvarieswiththefeed,breednutrition & the physiological condition of the cow

Milk • pH of milk: 6.6 at 25oC – when heated, pH decreases, H+ are liberated when Ca phosphate precipitates • Components of milk varies with the feed, breed, nutrition & the physiological condition of the cow

CompositionofMilkSolidsCompositionofWholeMilkAsh/Minerals6%Fat30%WaterProteinSolids87%27%13%Lactose37%WheyProtein20%Casein80%CompositionofMilkProtein

ConcentrationsoftheMajorProteins inMilkpercentageProteinConcentration(g/L)802428Caseins4215-19a,-Caseins12-1534 a.s1834as2259-11β-Caseins93-4K-Caseins124-Caseins5720Wheyproteins92-4β-Lactoglobulins411.5α-Lactalbumin40.61.8Proteose-peptonesBlood proteins10.10.4Serumalbumin20.61.0Immunoglobulins

Milk Proteins - Caseins Phosphoproteins, account for 8o% of totalmilk proteins Four groups: αs1~, αs2~, β-, K-caseinsPresent in milk as micelles, stabilized by k-caseins & Ca phosphate: Easily precipitated by adding acid to pH 4.6

Milk Proteins - Caseins • Phosphoproteins, account for 80% of total milk proteins • Four groups: αs1-, αs2-, β-, κ-caseins • Present in milk as micelles, stabilized by κ- caseins & Ca phosphate • Easily precipitated by adding acid to pH 4.6

Milk Proteins - CaseinsAcidprecipitates caseinsRennin casein: enzyme rennin coagulates caseins,when Kappa-casein is destroyed by rennin (enzymefrom the stomach lining of calves), other caseinsreact with Ca to form a coagulum Caseinates: salts of caseins, highly soluble, used asemulsifier, binder, thickening, foaming & gelling

Milk Proteins - Caseins • Acid precipitates caseins • Rennin casein: enzyme rennin coagulates caseins, when Kappa-casein is destroyed by rennin (enzyme from the stomach lining of calves), other caseins react with Ca to form a coagulum • Caseinates: salts of caseins, highly soluble, used as emulsifier, binder, thickening, foaming & gelling