FDSCI 501 - Enzymes

First genetically engineered food product approved for human consumption

Genetically engineered chymosin (rennin), approved by FDA in 1990; produced using recombinant bacteria and used in cheese making

What are the four requirements for polyphenol oxidase (PPO) activity?

Enzyme (PPO), substrate (phenolic compounds), oxygen (O2), and copper (Cu2+ cofactor)

How can the enzyme (PPO) be controlled to prevent browning?

Heat treatment (blanching) to denature the enzyme

How can the substrate be controlled to prevent browning?

Limit exposure of phenolic compounds by reducing cutting/damage or using protective processing methods

How can oxygen be controlled to prevent browning?

Exclude oxygen using vacuum packaging, water immersion, or heavy sugar syrups; can also remove O2 enzymatically (e.g., glucose oxidase)

How can copper (cofactor) be controlled to prevent browning?

Use chelating agents to bind Cu2+ and inactivate the enzyme

What are common reducing agents used to control enzymatic browning?

Ascorbic acid (vitamin C), erythorbic acid

What are common chelating agents used to control enzymatic browning?

Citric acid, EDTA

What are acidulants and how do they control browning?

Compounds that lower pH (below ~3) to inactivate PPO; examples include citric acid and acetic acid

What are sulfites and how do they control browning?

Sodium bisulfite (NaHSO3) and sulfur dioxide (SO2); inhibit PPO and prevent formation of brown pigments (regulated due to health concerns)

What is the general strategy for controlling enzymatic browning?

Remove or interfere with one or more of the four requirements (enzyme, substrate, oxygen, copper)

What is enzymatic browning?

Browning caused by polyphenol oxidase (PPO) reacting with phenolic compounds in the presence of oxygen to form brown pigments (melanins); occurs in cut fruits and vegetables

What is Maillard browning?

Non-enzymatic browning reaction between reducing sugars and amino acids/proteins, producing brown color and complex flavors; occurs during heating

Key difference between enzymatic and Maillard browning

Enzymatic browning requires enzymes and oxygen and occurs at mild conditions; Maillard browning is non-enzymatic, requires heat, and involves sugars and amino acids

Conditions required for enzymatic browning

Enzyme (PPO), phenolic substrate, oxygen, and copper cofactor

Conditions required for Maillard browning

Reducing sugar, amino group (amino acids/proteins), and heat (often enhanced by low moisture and higher pH)

What is α-amylase?

Endoenzyme that hydrolyzes internal α-1,4 glycosidic bonds in starch, producing dextrins, maltose, and some glucose; reduces viscosity (liquefying enzyme)

What is β-amylase?

Exoenzyme that cleaves α-1,4 bonds from the non-reducing ends of starch, producing maltose; cannot bypass α-1,6 branch points (blocked by them)

What is glucoamylase?

Exoenzyme that cleaves both α-1,4 and (more slowly) α-1,6 bonds from the non-reducing ends, producing glucose

Key difference between α-amylase, β-amylase, and glucoamylase

α-amylase acts randomly within the chain (endo) and reduces viscosity; β-amylase releases maltose from ends but cannot pass शाख points; glucoamylase releases glucose and can eventually break branch points

Which enzyme causes soft rot in fruits and vegetables?

Polygalacturonase (PG)

What bonds does polygalacturonase cleave?

α-1,4 glycosidic linkages between galacturonic acid units in pectin (pectic substances)