Citric Acid-1

Production of Citric Acid

  • Citric acid can be produced via three methods:

    • Extraction from Citrus Fruits: Low yields, high costs, rarely used.

    • Synthesis: Chemical methods; not preferred.

    • Fermentation: Predominant method using Aspergillus niger, efficient at low pH without toxic by-products.

  • Citric Acid: Weak acid (C6H8O7), found in citrus fruits, exists as monohydrate or anhydrous form, and is tribasic.

The Krebs Cycle

  • Also known as the citric acid cycle or TCA cycle, it releases energy from nutrients through acetyl-CoA oxidation.

  • Steps of the Cycle:

    1. Citrate Synthase

    2. Aconitase

    3. Isocitrate Dehydrogenase

    4. α-Ketoglutarate Dehydrogenase

    5. Succinyl-CoA Synthetase

    6. Succinate Dehydrogenase

    7. Fumarase

    8. Malate Dehydrogenase

Historical Developments

  • First isolated by Karls Scheels in 1874 from lemon juice.

  • Initial production monopoly by Italian manufacturers led to significant research for alternatives.

  • Significant advancements in fermentation methods made in 1917 by Currie, leading to the commercial use of Aspergillus niger.

  • In the 1950s, the biochemical basis of the fermentation processes was established, leading to improved yields.

Applications of Citric Acid

  • Primarily used in food industry for flavor and preservation.

  • Pharmaceutical and cosmetic industries account for 10% of citric acid use.

  • Also utilized in beverages, confectionery, frozen fruit, dairy products, and various industrial applications.

Micro-organisms Used for Production

  • Various micro-organisms have been tried, but A. niger and certain yeasts are most effective for commercial production.

  • Advantages of A. niger:

    • Easy to handle

    • Effective fermentation of low-cost raw materials

    • High yields

Production Techniques and Raw Materials

  • Mainly produced from starch or sucrose-based mediums.

  • Raw materials divided into two groups:

    • Low-ash content (e.g., cane sugar, dextrose)

    • High-ash content (e.g., molasses, unfiltered starch hydrolysates)

  • Various agro-industrial residues are also investigated for use in citric acid production.

Types of Fermentation

  • Submerged Fermentation (SmF): Most common, yielding about 80% of world production.

    • Advantages: Higher yields, lower labor costs.

    • Requires aeration for optimal yeast growth.

  • Surface Fermentation (LSC): Earlier method, easier operation but less commonly used now.

  • Solid-State Fermentation (SSF): Uses agro-industrial residues and can be beneficial due to less sensitivity to trace elements.

Recovery of Citric Acid

  • Recovery involves:

    • Precipitation, extraction, and adsorption processes.

    • Common classical method uses calcium oxide hydrate to precipitate tri-calcium citrate.

    • Further processed to obtain citric acid monohydrate or anhydrous form through crystallization.

Conclusions and Perspectives

  • Continued research for alternative raw materials and methods to meet the growing demand.

  • Focus on efficient pre-treatment processes and continuous culture techniques for better yields.

Uses of Citric Acid

  • Food: Flavoring, preservation, enhances taste and prevents bacterial growth.

  • Pharmaceutical: Anticoagulant, preservative, and used in many drugs.

  • Industrial: Used in detergents, soap manufacturing, and as a chelating agent.

Benefits of Citric Acid

  • Improves health, acts as a preservative, used in cosmetics, aids in water softening, and has industrial applications.

  • Benefits in kidney health and skin treatments.

Side Effects of Citric Acid

  • Excess exposure may lead to stomach issues, tooth decay, and skin irritation.

  • Can cause mood changes, nausea, and convulsions in severe cases.