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Lecture 4

week 4

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Food Science
FOOD 2010
Massimo Marcone

Week 4 Readings -what is colour? -rods are sensitive to lightness and darkness, while the cones are sensitive to red and green or blue colour -380nm to 780nm -hue, which is the actual colour name -saturation or chroma -intensity, the range from lightness to darkness of colour -pigment molecules -pigment or chromophoretic compounds in foods constitute a structurally diverse group and posses extremely complex chemical and physical properties -in some fish tissue such as salmon, the bright orange is due to carotenoid pigments, although these are not biosynthesized by the fish but derived from plant sources -the colour chemistry of red meat -myoglobin is a single polypeptide, a globular protein containing the globin protein part and a prosthetic group called heme -oxidation and reduction of the iron atom in myoglobin are linked are linked to colour changes in meat -myoglobin's functional property is to bind oxygen .in nitrate-cured meats myoglobin reacts with nitric oxide to produce nitric oxide myoglobin, or nitrosylmyoglobin, which is bright pink-red -when cured meats are cooked, they retain the pinkish or reddish colour, due to the formation of nitrisohemochrome from denatured, coagulated nitrosylmyoglobin -the colour chemistry of fruits and vegetables -all plant pigment molecules contain conjugated double bonds, which are alternating single and double carbon-to-carbon bonds -resonance electrons are spread across the atoms containing alternating single and double bonds, and their movement across carbon-to-carbon bonds gives colour -anthocyanins -are water soluble flavonoid compounds that range in colour deep purple to orange-red -anthoxanthins -are colourless or white pigments that can become yellow, they contribute only slightly to food colour -Betalains -represent a group of two types of water soluble plant pigments -carotenoids -are a class of fat soluble plant pigments that consist of carotennes and xanthophylls -carotenes are hydrocarbons, while xanthophylls are oxygenated carotenoids containing alcohol, carbonyl, or other functional groups -chlorophylls -are green lipid soluble plant pigments that contain a porphyrin ring complexed to magnesium -such situations can alter their colour -chlorophylls a and b are degraded to produce a substance called pheophytin -in the process, acid and heat cause removal of the Mg++ atom of chlorophyll, which is replaced in the pheophytin structure by hydrogen -an enzyme called chlorophyllase catalyzes the degradation of chlorophyll -this enzyme cleaves the phytol group, producing a compound called chlorophyllide -the colour chemistry of food colourants -a colourant is a pigment used to import colour to a food or beverage -natural colourants or those naturally derived -synthetic colourants -FD&C Colourants -FDA does not recognise any of today's colourants as "natural" -dyes are water soluble chemicals that are used to colour entire food products, for example lollipops, throughout -a lake is an insoluble powder formed by precipitation of a water soluble food -exampt colourants -these range from annatto to caramel, and from cochineal and grape skin extract to paprika -caramel colour is not a flavour but is a simple colouring agent used at low concentrations in foods and beverages -Flavour chemistry -flavour is a property of food material and the receptor mechanisms of the humans body -flavour involves both taste and aroma -sour and bitter -umami and astringency -chemical structure and taste -pungency -the sensation, identifiable as a warming or not sensation in the mouth and lips is termed pungency -capsaicinoids are pungent alkaloid compounds that occur is chiles -cooling sensation -are menthol and isomers of menthol -polyols are polyhydric alcohol counterparts of the sugars maltose, mannose, sucrose, and xylose and the corresponding polyols are maltitol, mannitol, sorbitol and xyl
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