I. Production Raw Materials and Pretreatment
- Raw Material Selection
Corn starch, sucrose, or whey (a byproduct of dairy processing) are primarily used as carbon sources, requiring low cost, easy availability, and minimal impurities (heavy metals ≤10 ppm). - Saccharification Treatment
- Starch Liquefaction: Corn starch is degraded into dextrin by α-amylase at 70–90°C.
- Saccharification: Dextrin is further hydrolyzed into glucose by glucoamylase at 55–60°C, with concentration controlled at 15–20%.
II. Core Microbial Fermentation Process
Strain Selection and Fermentation Control
- Core Strains:
- Lactobacillus delbrueckii: Preferred for its acid tolerance and production of L-lactic acid (metabolizable by humans), with optical purity >95%.
- Streptococcus thermophilus: Often used synergistically with Lactobacillus bulgaricus to enhance efficiency but produces D/L mixed lactic acid requiring separation.
- Fermentation Parameters:
- Anaerobic Environment: Nitrogen displacement in fermenters to exclude oxygen.
- Temperature: Maintained at 50±2°C (optimal for L. delbrueckii).
- pH Control: Calcium carbonate (CaCO₃) neutralizes lactic acid to stabilize pH at 5.0–6.0, preventing strain inactivation.
- Product Concentration: Fed-batch techniques achieve lactic acid levels of 80–100 g/L.
III. Separation and Refinement Process
- Solid-Liquid Separation
Fermentation broth undergoes plate-frame filtration or centrifugation to remove cell residues and protein precipitates. - Acidification and Crystallization
- Reaction: Calcium lactate + Sulfuric acid → Lactic acid + Calcium sulfate↓ (precipitate removed).
- Byproduct reuse: Calcium sulfate can be recycled as building material.
- Refinement and Purification
- Decolorization: Activated carbon adsorbs pigments/organic impurities at 70°C for 30 minutes.
- Ion Exchange: Resins remove metal ions (e.g., Ca²⁺, Fe²⁺) with regeneration cycles ≤48 hours.
- Molecular Distillation: Purification to ≥80% concentration under vacuum ≤10 Pa, separating D/L isomers.
IV. Food-Grade Lactic Acid Quality Standards
According to Chinese National Standard GB 1886.173-2016:
- Optical Purity: L-lactic acid ≥95%, D-lactic acid ≤5%.
- Impurity Limits: Arsenic ≤1 ppm, heavy metals ≤10 ppm, cyanides undetectable.
- Acidity Requirement: Total acidity (as lactic acid) ≥85%.
V. Technological Development Trends
- Strain Engineering: CRISPR gene editing boosts L-lactic acid yield to 98%.
- Green Processes:
- Immobilized Cell Technology: 50% increase in strain reuse rate, reducing costs.
- Whey Recycling: Substitutes starch with cheese byproducts to conserve resources.
- Extended Applications: High-purity L-lactic acid synthesizes polylactic acid (PLA) for food-grade biodegradable packaging.
food grade lactic acid, Acidity regulators, Lactic acid food grade, Food Acidity Regulators Lactic Acid, Lactic Acid Liquid, L-Lactic acid, L lactic, food grade lactic acid powder, lactic acid powder, Lactic-acid-powder