Food Proteins
Role of Proteins in Foods
B. Pam Ismail
bismailm@umn.edu
FScN 146
612 625 0147
Role of Proteins in Foods
Functional Property
Representative Food Systems
Solubility
Beverages, protein concentrates/shakes
Water-holding capacity
Meat and poultry products, cheese, yogurt, surimi
Gelation
Meat and poultry products, custard, scrambled eggs,
yogurt, gelatin, tofu, baked goods, surimi
Emulsification
Mayonnaise, salad dressing, gravies, ice cream,
frozen desserts
Foaming
Whipped toppings, meringues, angel cakes, sponge
cakes, marshmallows, yeast-leavened breads
Role of Proteins in Foods
 Protein functionality in food systems can be affected by
A. Denaturation state of the protein
B. R groups of the amino acids
C. Number of free thiol groups
D. A & B
E. B & C
F. A & C
G.All of the above
H. None of the above
Role of Proteins in Foods
 The following is always true:
A. A good emulsifier is a good foaming agent
B. A protein that forms a strong gel is also a good emulsifier
C. A protein with low surface hydrophobicity is a good emulsifier
D. A & B
E. B & C
F. A & C
G.All of the above
H. None of the above
Global Protein Demand
 The global protein demand for a population of 7.8 billion exceeds
200 million tons
 The global demand for protein ingredients, including plant and
animal sources, is expected to reach 7 million tons by 2025
 The global protein ingredient market revenues are expected to
reach 70 billion dollars by 2025, growing at rate of ~8% from 2014
to 2025
 Plant protein ingredients account for ~ 40% of the global protein
market
http://nutritionsuccess.org/blog/2013/04/homemade‐protein‐boost‐powder/
Global Protein Demand
 The demand is on the rise---why?
Global Protein Demand
 Reasons behind increased interest in plant proteins
 From consumers perspective
 Growing interest in sustainable and environment friendly sources
 Animal Welfare
 Increased traction to plant‐based and healthy diet
 Vegetarians and flexitarians
 Rising incidences of allergenicity
Population
growth (10
billion by 2050)
 From producers’ perspective
 Addressing consumer demand
 seeking lower cost compared to traditional protein ingredients
 Finding a unique and competitive place in the market
 Valorizing by‐products
 Replacing chemical ingredients with functional proteins (clean label)
Trendy Applications
 Meat analogues
 Protein beverages
 Dairy analogues
“According to market research, the plant-based meat
sector is set to reach $5.2 billion by 2020 and could
make up one-third of the market by 2050. This move
away from meat is largely due to consumers’ rising
concerns about animal welfare, personal health, and
importantly, sustainability.”
http://www.onegreenplanet.org
 Protein bars
 Extruded products
Seeking
alternatives to soy
protein and gluten!
https://www.statista.com/statistics
Protein Ingredients
 What are the most common protein ingredients?
 Their uses?
 New and emerging protein ingredients?
 Advantages and disadvantages?
Role of Proteins in Foods
Role of Proteins in Foods
 Nutritional contributions is a function of protein quality and quantity
o Essential amino acids and daily requirements
(50g/day or 1g of protein/1 kg of body weight)
o Ease of digestion
70%
http://foodsafety.merieuxnutrisciences.com
Role of Proteins in Foods
 Physiological functionality
 Muscle growth/re-generation
 Other benefits – reduce muscle
deterioration in aging population,
weight loss and metabolic health
 Bioactive peptides: reduce
hypertension, antidepressant, promote
satiety
Chocolate Temptation Bar
INGREDIENTS: Soy Protein Blend [Soy
Protein Nugget (Non-GMO Soy Protein
Isolate, Rice Flour, Tapioca Starch, Malt,
Salt, Non-GMO Soy Protein Concentrate],
Chocolate Flavored Coating (Sugar,
Fractionated Palm Kernel Oil, Cocoa,
Whey Powder, Nonfat Dry Milk, Soy
Lecithin, Natural Flavor), ...
o “25 g of soy protein a day, as part of a
diet low in saturated fat and cholesterol,
may reduce the risk of heart disease”
Food and Drug Administration (1999)
o Association of bioactive components –
isoflavones and soy proteins
Isoflavone
Role of Proteins in Foods
 Physical functional properties
 Color
o Light scattering – e.g. casein micelle
o Chromaphores – e. g. myoglobin in meat, betalains in red beets
o Browning (non-enzymatic and enzymatic)
 Flavor
Ripened Cheese
MSG
o Hydrophobic a.a. – bitter
o Acidic a.a. – sour
o Cysteine – sulfur taste
o Glutamate MSG – Umami flavor
o Proteolysis
o Sweetness
Aspartame
Role of Proteins in Foods
 Physical functional properties
 Texture
o Water-binding
o Gelation/Coagulation
o Solubility
o Emulsifying
o Foaming
o Viscosity
o Elasticity
Chemical and physical interaction with other
food components – other proteins, lipids,
saccarides and water – through:
 Ionic
 H-bonds
 Hydrophopic interactions
 Covalent Cross-linking
Thus forming different structures
Anti-nutritional Factors and Toxic
components
 Enzyme inhibitors
o Protease inhibitor (trypsin inhibitor found in legumes)
o Amylase inhibitor (mainly found in cereals)
 Allergenic proteins (“Big 8”)
o
o
o
o
o
Milk – casein and whey proteins
Soybean - glycinin and conglycinin
Wheat – gluten forming proteins
Peanut proteins
Egg proteins
 Toxic components
o Some a.a. can be precursors of toxins such as the carcinogenic N-nitrosocompounds – cured meat; heterocyclic amines
o Lectins (mainly found in seeds)
 Other
o Avidin (found in eggs) binds to biotin
o Histamine (found in fish products) – vasoactive amine
Protein Structure/Function Relationship:
Impact on Final Product
Native
Intrinsic Factors:
- Protein source (e.g. milk, soy)
- Composition
- Amino acid sequence
- Ionizable and reactive groups
- Hydrophobicity
- Conformation
- Molecular interactions
Protein
Structure
Denatured/
Modified
Extrinsic Factors:
- Environmental
- pH
- Temperature
- Ionic strength
- Processing and Handling
- Drying/heating/extrusion
- Extraction solvent and conditions
- Storage conditions
- Protein Modification
- Enzymatic
- Chemical
- Physical
- Natural reactions
- Biotechnology
Protein
Function
Functional Properties:
- Organoleptic
- Taste/aroma
- Color
- Hydration
- Solubility
- Water holding
- Surface Properties
- Emulsification
- Foaming
- Structural Properties
- Viscosity
- Gelation
- Viscoelasticity
 Protein functional property: any
physicochemical property which affects
processing and behavior of food
systems, as judged by the quality
attributes of the final product
Role of Proteins in Foods
 A soft drink manufacturer wishes to fortify their
beverages with protein. The pH of their beverage is
typically pH 2.5 to 3. Which dairy protein would you
recommend they work with and why?
Role of Proteins in Foods
 A muffin ingredient declaration list sodium caseinate.
Why was sodium caseinate chosen?
Protein Structure/Function Relationship:
Impact on Final Product
Intrinsic Factors:
- Protein source (e.g. milk, soy)
- Composition
- Amino acid sequence
- Ionizable and reactive groups
- Hydrophobicity
- Conformation
- Molecular interactions
Protein
Structure
Protein
Function
 Protein functional property: any
physicochemical property which affects
processing and behavior of food
systems, as judged by the quality
attributes of the final product
Intrinsic Factors
 Proteins differ in:
 Amino acid composition and sequence
 Structural configuration (conformation)
 Molecular interactions
 Chemical/biochemical properties
o Hydrophobicity
o Net charge
 Thus they vary in functional contributions
Basic Protein Structure
Amino Acids: Structure and Properties
 The pKa of the side chain (R group) of the following amino acid(s)
is lower than 6
A. Lysine
B. Arginine
C. Histidine
D. A & B
E. B & C
F. A & C
G.All of the above
H. None of the above
Basic Protein Structure
Amino Acids: Structure and Properties
Basic Structure
Neutral pH
H
H
O
C
C
H2N
O
Cα C
R
OH
Chiral
+H N
3
Basic
O-
R
Acidic
L - Configuration
Buffer
Determines polarity, hydrophobicity,
structure, reactions/interactions and
functionality
Basic Protein Structure
Amino Acids: Structure and Properties
Hydrophobic (Non-polar)
Aromatic
Ionizes at alkaline pH
Absorb in UV
region
(280 nm)
Molar Extinction Coefficient =
1340 cm-1 mol-1
Molar Extinction Coefficient =
5500 cm-1 mol-1
Basic Protein Structure
Amino Acids: Structure and Properties
Hydrophobic (Non-polar)
Aliphatic
Chiral Cβ
Unique structure;
secondary amine
Hydroxyproline
Basic Protein Structure
Amino Acids: Structure and Properties
Hydrophilic (Polar)
Positively charged
(basic)
With Charged
Side Chain
Hydroxylysine
Negatively charged
(acidic)
Basic Protein Structure
Amino Acids: Structure and Properties
Maillard browning
+ Reducing sugar
Nutritional loss
Heat, slight
alkaline, low
moisture
Basic Protein Structure
Amino Acids: Structure and Properties
Hydrophilic (Polar)
With uncharged
side chain
Unique, Cα is
not chiral
Acid or alkaline
hydrolysis - NH3
Glutamic acid
Aspartic acid
Basic Protein Structure
Amino Acids: Structure and Properties
OO
Phosphate
group
P
Phosphrylation
e.g. α- & β- casein
O-
O-
N-acetylglucoseamine
Gylcosylation
e.g. κ- casein
Basic Protein Structure
Amino Acids: Structure and Properties
Hydrophilic (Polar)
With uncharged
side chain
Unique, Cα is
S-S linkages
not chiral
Acid or alkaline
hydrolysis - NH3
Glutamic acid
Aspartic acid
Basic Protein Structure
Amino Acids: Structure and Properties
+
Oxidation
Reducing agent
(free thiol group)
2
Cystine
Basic Protein Structure
Amino Acids: Structure and Properties
Hydrophilic (Polar)
With uncharged
side chain
Unique, Cα is
S-S linkages
not chiral
Acid or alkaline
hydrolysis - NH3
Glutamic acid
Aspartic acid
Basic Protein Structure
Amino Acids: Structure and Properties

Bread making quality
Transglutaminase
Amine group of a lysine residue with the
carboxyamide group of glutamine residue
Rice Bread
Basic Protein Structure
Amino Acids: Structure and Properties
 Acid-Base properties
For amino acids with no charged side chain
For acidic amino acids pI = (pKa1 +pKa3)/2
For basic amino acids pI = (pKa2 +pKa3)/2
Basic Protein Structure
Amino Acids: Structure and Properties
Basic Protein Structure
Amino Acids: Structure and Properties
 Acid-Base properties
For amino acids with no charged side chain
For acidic amino acids pI = (pKa1 +pKa3)/2
For basic amino acids pI = (pKa2 +pKa3)/2
Basic Protein Structure
Amino Acids: Structure and Properties

Acid-Base properties
Henderson-Hasselbach equation
pH = pKa + log [A-]
[HA]
Food Proteins
Role of Proteins in Foods
B. Pam Ismail
bismailm@umn.edu
FScN 146
612 625 0147