2-FIF_Reader_Proteins

Introduction to Protein Ingredients

• Commercial protein ingredients are available in powdered form (typically produced via spray drying) and categorized based on purity:

  • Protein Isolates: Contain greater than $90\%$ protein.

  • Protein Concentrates: Contain $35\%$ to $80\%$ protein.

• Agricultural sources and side-streams for protein extraction:

  • Plant Sources: Legumes (peas, soybeans, faba beans, lupins, lentils), cereals (wheat, corn, barley, oats, rice), edible seeds (quinoa, buckwheat), pseudocereals (amaranth, chia), tubers (potatoes), oilseeds (rapeseed, cottonseed, peanut, sunflower, hemp seed), and algae.

  • Animal Sources: Milk, muscle tissue, insects, eggs, and blood.

  • Production Side-Streams: Liquid whey from cheese production and defatted soybean press cake from oil extraction.

  • Fungal Sources: Mycoproteins.

Interactions Between Proteins

• Protein functionality (solubility, emulsification, foaming, and gelling) is dictated by non-covalent forces (Van der Waals interactions, hydrogen bonds, hydrophobic interactions, electrostatic interactions) and covalent bonds (disulphide bridges).

• Surface Charge Density and Zeta Potential:

  • Surface Charge Density: Defined as the number of positive or negative charges per unit surface area of a protein particle.

  • Zeta Potential ($\zeta$, measured in $mV$): Electrostatic potential measured at the slipping layer boundary surrounding the protein particle.

  • Zeta potential varies continuously with pH: negative at pH above the isoelectric point ($pI$), positive below $pI$, and net zero at $pH = pI$.

Solubility of Proteins

• Solubility Profile Characteristics:

  • Simple crystalline salts like $\text{NaCl}$ show linear dissolution up to a sharp thermodynamic saturation limit ($\sim 350\,g/L$ at $20\,^\circ\text{C}$), beyond which added salt remains solid.

  • Protein solubility curves are non-linear over a broad range, only slowly approaching a saturation plateau, and are strongly concentration-dependent.

Sources, Isolation, and Molecular Properties of Protein Ingredients

• Milk Composition and Fractionation Overview:

  • Bovine milk dry matter composition ($\sim 12.5\%$ total solids in whole milk):

  • Proteins: $26\%$ w/w of dry matter ($80\%$ Caseins, $20\%$ Whey proteins).

  • Lipids: $27\%$ w/w of dry matter (Fat globules, size $> 1000\,nm$).

  • Carbohydrates: $39\%$ w/w of dry matter ($> 99\%$ lactose, size $< 3\,nm$, MW $342\,Da$).

  • Ash/Minerals: $8\%$ w/w of dry matter ($\text{Ca}$, $\text{P}$, $\text{Na}$, $\text{K}$, $\text{Cl}$).

• Size Distribution of Milk Components:

  • Fat Globules: $1\,\mu m$ to $20\,\mu m$ ($1000\,nm$ to $20000\,nm$).

  • Casein Micelles: $50\,nm$ to $500\,nm$ (average $120\,nm$).

  • Whey Proteins: $2\,nm$ to $6\,nm$ ($\alpha$-lactalbumin $1.8\,nm$, $\beta$-lactoglobulin dimer $3.5\,nm$, BSA $4\,nm$, IgG $6\,nm$).

  • Lactose and Minerals: $\sim 0.1\,nm$ to $1\,nm$.