BROWNING:

NON ENZYMATIC BROWNING REACTIONS:

CHEMICAL REACTION:

• Change of a substance into a new one with a different chemical identity

  • Bonds are broken → new bonds are rated

  • Can be observed by

    • Color change, heat emission, precipitate formation, gas production, etc.

  • Particles must collide + come into contact for reaction to occur

    • Heat increases kinetic energy → increases particle movement → increased number of collisions → increase rate of reaction

      • (add heat → increased reaction rate)

      • (decrease heat —> decreased reaction rate)

• Energy threshold must be met → activation energy (for any reaction to happen)

• Lactase → biological catalysts (enzymes)

  • Catalysts = decrease activation energy for reaction

  • Enzymes → make things happen

TYPES OF BROWNING REACTIONS IN FOOD:

• Nonenzymatic browning

  • Maillard reaction

    • Louis camile maillard

    • Family of reactions

    • Creates many flavors, aromas, colors

    • Requires

      • Reducing sugar (glucose, fructose, not sucrose)

      • Amino acid

      • Heat

    • End products = melanoidins

      • Complex molecules

      • Not all have been identified

    • 20 different amino acids + 8 reactive sugars = form many products

      • Variety of flavors, aromas, colors

    • EX: coffee roasting

    • Factors affecting

      • Temperature

        • Increase in temp → increase rate of reaction → faster browning

        • Can occur at room temp → too slow to observe

        • Portions of food that touch grill grate → brown faster than surrounding areas

      • pH

        • Amino acids = more reactive in alkaline (higher pH)

        • Higher pH = quicker browning

        • Adding baking soda to a batter of fried food → achieve desired browning in less time to present overcooking 

      • Acrylamide

        • Class 2 carcinogen

          • Classification based on strength of evidence → not unlikelihood of cancer occurring

          • Probable human carcinogen 

        • Maillard reaction product of asparagine → 120 + celsius (284 + fahrenheit) 

        • Not too much of concern

        • In CA = warning

        • To prevent = add enzyme asparaginase

          • Cleaves asparagine

          • Use genetically modified potatoes → have less asparagine in it (innate potato)

  • Caramelization

    • Does Not involve amino acids/proteins

    • Involves sugars

    • Higher staring temp (320-365 fahrenheit) (160-180 celsius)

    • Maillard reaction + caramelization usually happen concurrently in foods

      • Caramelization occurs primarily in starchy veggies + sucrose

    • Class I - Plain caramel color

      • Distilled alcohol (whiskey)

    • Class II - Caustic Sulphite Caramel Color

      • Beer, sherry, malt vinegars

    • Class III - Ammonia Caramel Color

      • Beer, sugar candies, soy sauce

    • Class IV - Ammonia Sulfite Caramel Color

      • Acidic solutions like soft drinks (cola, dr. pepper, etc.)

    • 4- methylimidazole (in Caramel IV)

      • Used in sodas

      • Class 2B carcinogen (possible carcinogen)

      • Dose makes the poison

• Enzymatic browning

WHY DO WE WANT BROWNING/WHY DON'T WE:

• Why we want

  • Creates aromas + flavors

    • Chemical reactions → new compounds

      • New compounds → new flavors + aromas

        • Bread vs. toast

        • Raw vs. grilled steak

  • Color makes food appetizing

• Why we don't want

  • Nonenzymatic browning can create carcinogenic compounds

  • Makes food unappetizing

  • Enzymatic browning → decrease nutritional content

    • EX: leaving avocados out = ew

ENZYMATIC BROWNING REACTIONS:

WHAT IS IT:

• Major source of food waste

• Composition of fruits

  • Organic acids

  • Pectic substances

  • Phenolic compounds

    • Found in plants + kept in separate compartment from PPO (enzyme)

    • One cells are damaged → substrate comes into contact with PPO → browning occurs

    • Responsible for browning + bruising that occurs in ripening fruit

REACTANTS, PRODUCTS, EFFECTS OF ENZYMATIC BROWNING:

• Presence of three substances:

  • Phenolic compounds

  • Enzymes (PPO)

  • Oxygen

• Dark compounds ford are called: melanin

5 WAY TO CONTROL ENZYMATIC BROWNING:

• Enzymatic browning in fruit is catalyzed (caused) by enzyme (polyphenol oxidase) 

  • Blanching: boiling (salt water to cook it faster to keep from going soft) vegetables (cooking) and immediately putting them in freezing water

    • Freezing point depression + melting point

    • Denatures the PPO (enzyme) b/c it’s a protein → no more browning

  • Lowering pH

    • Inhibit activity of PPO enzyme in presence of acid

    • Coating by citric acetic acid or vinegar

    • EX: adding lemon or lime juice can delay browning

  • Reducing Temperature

    • Freezing: cold temp → reduce rate of enzyme activity

  • Dehydration

    • Removing water molecule from product

    • Inhibit PPO enzyme

  • Adding antioxidant

    • Such as ascorbic acid (vitamin C) + sulfur compounds

    • Make oxygen unavailable