Transcript Document
Chemistry 106 University of Nebraska Spring 2009 MONDAY 30 March 2009 What do Additives do? • They improve or maintain the quality of foods • Functions of food additives – antioxidants – Colorings/dyes – Flavorings – Preservatives – Emulsifiers (keeps from seperating) – Stabilizers and Thickeners (adds quality) Additives – Free-radicals atom or molecule with an unpaired electron – Fat or oil (or any type of compound) + oxygen free radicals + other products (responsible for rancidity) – **fats and oils particularly susceptible due to double bonds Additives • Antioxidants – Compounds that prevent packaged, processed foods from becoming rancid due to oxidation of fats and oils which form harmful free radicals – Two most common: **recognize for test Butylated hydroxytoluene (BHT) Butylated hydroxyanisole (BHA) - interrupt free-radical oxidative reactions by contributing hydrogen from the phenolic hydroxyl groups - BHT & BHA become STABLE free radicals which do not initiate or propagate further oxidation of lipids. Additives • Another important antioxidant: EDTA (ethylenediaminetetraacetic acid) – removes small amounts of metal ions from food (these ions cause catalytic oxidation – leading to food spoilage and “off flavors”) – EDTA molecule wraps itself around metal ions like a crab (the combination of the compound with the metal ion is called a chelate (from the Greek word meaning crab’s claw)) – In the act of holding the metal the chelating agent becomes a sequestrant (to remove or set apart) – EDTA (and like compounds) used in fats and oils, for protection of vitamins, and to reduce discoloration (browning) of many foods **recognize for test!!! EDTA uses: -textiles-prevent dyes from being oxidized -cosmetics-keep fats and oils from oxidizing -food -paper-prevent white paper from discoloring Additives • Colorings – Most foods are unlikely to reach grocery shelves at their peak in color – In 1900 more than 80 different synthetic dyes were used in foods to enhance natural colors – In recent years, more natural coloring compounds such as carotenoids (yellow-red) and anthocyanins (red-blue) are being used (about 30 today) – Beta-Carotene (a carotenoid) provides color as well as being an antioxidant and converted to vitamin A – Natural food colors are listed as “artificial color” while synthetic dyes are listed as an F, D, & C colorant. Additives • Flavorings – Many used today are synthetic versions of natural flavorings (aldehydes, ketones, esters) – Some flavorings are simple with only a few components – others are very complex (tarragon contains over 80 different chemicals) – Why aren’t some man-made flavorings as “good” as their natural counterparts? – synthetics have only the essential compound(s) – Synthetic vanilla flavoring contains the aldehyde vanillin, natural vanilla contains the aldehyde along with several other compounds. Additives • Flavorings – Many fruit flavorings are esters – banana, pear, pineapple, – Some are very strong (capasaicin-habanera pepper) – Some actually can cause cancer (safrole-found in tree that provides flavor for rootbeer) **don’t need to recognize for test! Additives • Flavor enhancement – Flavor enhancer mode of action • Synergistic: cooperative action of two different substances such that the total effect is greater that the sum of each effect alone • potentiation: substance that does not have an effect by itself but exaggerates the effects of other chemicals Additives • Flavor enhancement – Monodoium glutamate (MSG) • A new taste (sweet, sour, salty, bitter) – savory taste • A synergistic compound – Table salt (NaCl) • Used for centuries to enhance flavor • A synergistic compound – Nucleotides • Acts as a potentiator (have no taste, but enhance taste of other compounds) • Commonly used on meats Additives • Preservatives – Most are synthetic and have very low toxicity to humans – Most are used to inhibit growth of mold and other microorganisms • • • • Sodium or calcium propionate – baked goods Sodium benzoate – canned goods Sodium nitrite – cold meats Sorbic acid - cheese Additives • Stabilizers • Humectants – keeps foods moist by attracting atmospheric water – glycerine (used in coconut) – Glyceryl monostearate (used in marshmallows) • Anticaking agents– keep finely powdered food dry and free flowing (added to hygroscopic (foods that tend to absorb water by themselves) foods) – Silicon dioxide and calcium silicates (used in salt, baking powder, etc) Additives • Thickeners – Used in liquids to give a thicker texture and feel (pudding, salad dressing, etc) – Examples • Gum arabic – from the acacia tree • Starch – isolated from corn • Xanthan gum – complex carbohydrate from corn Additives • Emulsifiers – Compounds that allow polar and nonpolar mixtures to remain mixed without separating – Examples • Xanthan gum – used in many salad dressings (thousand island) • Mono and diglycerides– used in peanut butter Additives • pH Control – Weak organic acids (such as acetic acid) – Acid salts (Na2HPO4) – Enhance flavor and preserve – Buffers added to adjust pH (potassium tartrate) Sodium Nitrite – a preservative • Risk of use in cold meats: may cause cancer – Steps • NaNO2 Na+ + NO2• NO2- + HCl HNO2 + Cl• HNO2 + protein (forming amines during digestion) nitrosamine – Nitrosamines are carcinogenic Sodium Nitrite – a preservative • Benefits: effective in preventing growth of Clostridium botulinum which produces the botulinum toxin • Botulinum toxin is the worlds most potent toxin, natural or manmade Sodium Nitrite – a preservative • Only about 1/3 of nitrite salts in our stomach come from the additive if we eat cold meat • Bacteria in stomach convert sodium nitrate in fresh fruits and vegetables into nitrites • So, eliminating it from the diet doesn’t mean eliminating it altogether • Some fresh fruits and vegetables also contain compounds that react with nitrous acid to inhibit formation of amines.