Pigments In Animal And Plant Tissue PDF

PIGMENTS IN ANIMAL AND PLANT Thus, myoglobin is a complex of TISSUE globin and heme. The heme porphyrin is present within 1. HEME COMPOUNDS...

PIGMENTS IN ANIMAL AND PLANT Thus, myoglobin is a complex of TISSUE globin and heme. The heme porphyrin is present within 1. HEME COMPOUNDS a hydrophobic pocket of the globin - Responsible for the red pigments in protein and bound to a histidine meat residue - Water-soluble The centrally located iron atom - Heme associates with a protein shown possesses six coordination forming a complex sites, four of which are occupied by - Myoglobin in muscle tissue the nitrogen atoms within the - Hemoglobin in red blood cells tetrapyrrole ring. - The color of meat is mainly due to The fifth coordination site is bound by myoglobin the histidine residue of globin, leaving the sixth site available to complex 1. HEME COMPOUNDS with electronegative atoms donated a) Myoglobin/hemoglobin by various ligands. Hemoglobin consists of four Structure of Heme Compounds: myoglobins linked together as a Myoglobin is a globular protein tetramer. consisting of a single polypeptide Hemoglobin, a component of red chain. blood cells, forms reversible Its molecular mass is 16.8 kD complexes with oxygen in the lung. and it is comprised of 153 amino This complex is distributed via the acids. blood to various tissues throughout This protein portion of the molecule is the animal where oxygen is known as globin. absorbed. It is the heme group that binds molecular oxygen. Myoglobin within the cellular tissue acts in a similar fashion, accepting the oxygen carried by hemoglobin. Myoglobin thus stores oxygen within the tissues, making it available for metabolism Chemistry and Color - Oxidation Meat color is determined by the - chemistry of myoglobin, - its state of oxidation, The chromophore component - type of ligands bounds to responsible for light absorption and heme, and color is a porphyrin known as heme. - state of the globin protein. Within the porphyrin ring, a centrally The heme iron within the porphyrin located iron atom is complexed with ring may exist in two forms: either four tetrapyrrole nitrogen atoms.  reduced ferrous (+2) or oxidized - It is thought that hydrogen peroxide ferric (+3). and/or hydrogen sulfide arise from This state of oxidation for the iron bacterial growth. A third mechanisms atom within heme should be for green pigmentation occurs in distinguished form oxygenation of cured meats and is mentioned later. myoglobin. When molecular oxygen binds to 1. Chlorophyll myoglobin, oxymyoglobin (MbO₂) is - Fat-soluble pigments in all green formed and this is referred to as plants Fruits (particularly when it is oxygenation. unripe) Vegetables (peas, broccoli, When oxidation of myoglobin occurs, spinach) the iron atom is converted to the ferric (+3) state, forming metmyoglobin (MMb). Heme iron in the +2 (ferrous) state, which lacks a bound ligand in the sixth position, is called myoglobin. Meat tissue that contains primarily myoglobin (also referred to as deoxymyoglobin) is purplish- red in color. Binding of molecular oxygen at the sixth ligand yields oxymyoglobin (MbO2) and the color of the tissue a. Chlorophyll a - Bluish green changes to the customary bright red. b. Chlorophyll b - Yellowish green Color reactions in fresh meat are dynamic and determined by conditions in the muscle and the resulting ratios of myoglobin (Mb), metmyoglobin (MMb), and oxymyoglobin (MbO2). Interconversion among these forms can occur readily Chemistry and Color - Discoloration Two different reactions can cause green discoloration of myoglobin. 1. Hydrogen peroxide - react with either the 2. Carotenoids ferrous or ferric site of heme, resulting in A group of fat-soluble pigments red, choleglobin (a green-colored pigment). orange, and yellow. 2. Presence of hydrogen sulfide and oxygen, The most widespread natural can form green sulfomyoglobin. pigments Abundant in yellow/orange fruits and vegetables  All green leafy vegetables contain carotenoids but their color is masked with green chlorophylls in animal tissue, eggyolk, salmon, shrimp 3. Flavonoids and other Phenols A. B-carotene - The most abundant carotenoids in plants. (carrot, orange, pumpkin, sweet potato, squash) B. Lycopene - Red color (tomato, watermelon) C. Capsaicin - Red pepper D. Lutein (xanthopyll) - Yellow pigment (mango, papaya, cabbage, kale, kiwi) E. Bixin - Orange yellow very stable (annatto seed)