Step 1: Understanding the Concept:
Cereal proteins are historically classified into four groups based on their solubility (the Osborne classification):
1. Albumins (soluble in water).
2. Globulins (soluble in dilute saline).
3. Prolamines (soluble in aqueous alcohol).
4. Glutelins (soluble in dilute acids or bases).
Detailed Explanation:
Zein is the primary storage protein found in the endosperm of maize (Zea mays), accounting for approximately $50\text{ to }60\%$ of its total protein content.
Based on its solubility properties:
- Zein is insoluble in water or anhydrous alcohol but soluble in aqueous alcohol solutions (typically $70\text{ to }80\%$ ethanol).
- Due to these solubility characteristics, it is classified as a prolamine (C).
- Prolamines are rich in proline and glutamic acid residues and are deficient in essential amino acids like lysine and tryptophan.
- Similar prolamines in other cereals include gliadin in wheat, hordein in barley, and secalin in rye.
Step 2: Final Answer:
The predominant maize protein, zein, belongs to the class of Prolamine.