Textbook Notes (368,060)
Canada (161,608)
Food Science (205)
FOOD 2010 (197)
Chapter 6

Chapter 6 summary.docx

6 Pages
110 Views
Unlock Document

Department
Food Science
Course
FOOD 2010
Professor
Massimo Marcone
Semester
Winter

Description
Chapter 6: Food Chemistry III, Color, Flavor and Texture 6.1 Food Color Chemistry What is color?  color is a perception of a physical attribute of food arising from a collection of sensations  Food object is either absorbed, reflected or transmitted  Reflected light determines the color of a food  Surface color of food objects can be characterized by 3 qualities: 1. Hue: actual color name (red, blue, green) 2. Saturation or chroma: clarity and purity of the color 3. Intensity: the range from lightness to darkness of color o Surface appearance characteristics: (1) shinny, (2) glossy, (3) cloudy and (4) translucent Pigment molecules  Red color of ground beef= presence of special molecules in beef called pigment molecules  Chromophoretic (pigment): compounds in foods constitute a structurally diverse group and posses extremely complex chemical and physical properties The color chemistry of red meat  Myoglobin: single polypeptide, a globular protein containing the globin protein part and a prosthetic group called heme - globin= polypeptide: composed of amino acids (attached to heme) - has the ability to bind oxygen because of its globin polypeptide tertiary structure and heme (iron porphyrin ring complex; composed of 4 pyrrole units that are connected by methane bridges and has 4 nitrogen atoms in corners) - oxidation of iron causes the color  Oxymyoglobin: myoglobin derivative responsible for a bright red color th - oxygenation: Fe 2+ myoglobin binds oxygen at 6 binding site and oxygen becomes part of pigment complex  Metmyoglobin: myoglobin derivative associated with aged meat exposed to air, producing a grayish of brown meat color - iron in metmyoglobin changes from the reduced Fe2+ to Fe 3+ which alters the color  Nitric oxide myoglobin: bright pink-red myoglobin reacted with nitric oxide  Other types: choleglobin and sulfmyoglobin: result form bacterial action on contaminated meat to yield green colors (oxidation of porphyrin ring) The color chemistry of fruits and vegetables  Appealing color of fruits + vegetables is due to occurring plant pigments that absorb and reflect light at certain wavelengths  Conjugated double bonds: all plant pigments are composed of these. These are alternating single and double carbon to carbon bonds: C = C – C = C  color is result of resonance within the ring structures in porphyrin rings and conjugated carbon chains (resonance electron spread across atoms contain single and double bonds; movement across carbon-carbon bonds = color 3 GROUPS OF PLANT PIGMENT MOLECULES: 1. Phenolic based pigments Anthocyanins: are water-soluble flavonoid compounds that range in color from deep purple to orange-red - flavonoid: chemically related phytochemicals, contains 2 phenol rings and intermediate ring of variable structure - pigment color is pH sensitive - chemical structure  combination of aglycone molecule attaché to sugar molecule by glycosidic bond - anthocyanidin: anthocyanin broken apart into sugar and free aglycone (e.g. pelargonidin, cyanidin, delphinidin) Anthoxanthins: colorless or white pigments that can become yellow. Contribute slightly to food color. (found in animal) Betalains: group of 2 types of water-soluble plant pigments (betacyanins: 50 violet-red pigments. Betaxanthins: series of 20 yellow pigments) (e.g. betanin, betanidin, vulgaxanthin) 2. Carotenoids: class of fat-soluble plant pigments that consists of carotenes (hydrocarbon, polymers of isoprene) and xanthophylls (oxygenated carotenoids) (example of carotenes: beta-carotene and lycopene) (example of xanthophylls: lutein) red, orange, yellow, easily oxidized 3. Chlorophylls: green-lipid soluble plant pigments that contain a porphyrin ring complexed to magnesium, fat soluble - chlorophylls a and b with acid, heat, Mg2+  produce pheophytin: gray- green and olive-green degradation product - pheophytin + heat + CO2CH3= pyropheophytin - chlorophyll + chlorophyllase (enzyme) = chlorophyllide - chlorophyllide + acid + heat Mg2+ = Pheophorbide - chlorophyllide heat + CO2CH3 = pyropheophorbide The color chemistry of food colorants  Colorant: pigments used to impart color to a food or beverage (1) natural colorants (naturally derived) (2) synthetic colorants FD&C colorants - all color ingredients are additives - certified as safe by FDA for use in food, drugs and cosmetics. - all contain phenolic ring having double bonds and various functional groups - dyes: water soluble chemicals that are used to color entire food products - lake: insoluble powder formed by precipitation of a water-soluble food colorant. They are derived from dyes and used to color the surface of foods or fat-based products, including chocolates. Exempt colorants  Cochineal extract: derived form dried bodies of cochineal insects. Is a anthraquinone, major pigment is carminic acid  Caramel color: coloring agent used at low concentrations in foods and beverages. Formation of caramel is through nonenzymatic thermal: caramelization 6.2 Food flavor chemistry Flavor: property of food material and the receptor mechanisms of human body (taste + aroma) Chemical structure and taste - substance to produce taste has to be water soluble  pungency - sensation of spicy heat, due to specific chemicals from cruciferous veggies and chili peppers - causes warming sensation in the mouth and lips - endorphins are released, causing pleasure amongst pain - Capsaicinoids: pungent alkaloid compounds that occur in chiles (capsaicin, dihydricaosaicin) - Scoville heat unit: unit of measure of hotness in chiles  cooling sensation - due to methanol and its isomers causing a minty flavor and aroma - coolness sensation in the mouth - can also be due to sugar alcohols - Polyols: are polyhydric alcohol counterparts of the sugars maltose, sucrose and xylose; maltitol, mannitol, sorbitol (has humectant properties; prevent products rom drying out) and xylitol Process and reaction flavors - Nonenzymatic browning: duration and temperature of thermal processing affect flavor of cooked foods (e.g. caramelization of sugar) - e.g. in baking of bread the Maillard reaction generates dicarbonyl compounds such as glyoxal. These can react with amino acids through a series of steps called Strecker degradation to produce pyrazine. These contribute to flavor and aroma of bread  Producing food flavors - Food flavorists isolate and develop flavoring ingredients; flavor compounds or additives (see table 6.9 on p.165) - process flavor substances are obtained by heating a variety of substances (including at least one nitrogen and a reducing sugar) - reaction technology can produce reaction flavors - reaction flavors are produced by chemical reactions under c
More Less

Related notes for FOOD 2010

Log In


OR

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.


Submit