Fermentation: A Biological Path to Calcium Lactate
Since the 19th century, a primary source for industrial calcium lactate has been the fermentation of carbohydrates. This biological process uses microorganisms, such as certain species of Lactobacillus, to consume a carbohydrate source and produce lactic acid. A calcium source is introduced during or after this fermentation to neutralize the lactic acid, forming the calcium lactate salt.
Fermentation Process Steps
- Preparation of Substrate: Carbohydrate-rich raw materials, such as corn, potatoes, molasses, or whey, are prepared for fermentation. This often involves liquefying and saccharifying the starch into simple sugars for the bacteria to use.
- Inoculation and Fermentation: The prepared substrate is inoculated with lactic acid-producing bacteria. The bacteria convert the sugars into lactic acid under carefully controlled conditions of temperature and pH.
- Neutralization: As lactic acid is produced, a calcium mineral source like calcium carbonate ($CaCO_3$) or calcium hydroxide ($Ca(OH)_2$) is added to the fermentation broth. This neutralizes the acid, preventing it from inhibiting bacterial growth, and forms the calcium lactate.
- Purification and Crystallization: The fermentation broth containing calcium lactate is purified to remove residual solids and impurities. The solution is then concentrated and cooled to crystallize the calcium lactate. The resulting crystals are filtered, washed, and dried to obtain the final product.
Chemical Synthesis: A Direct Manufacturing Route
In addition to fermentation, calcium lactate can be produced directly through a chemical synthesis process. This method bypasses the biological fermentation step and involves a straightforward neutralization reaction.
The fundamental chemical reaction involves combining lactic acid with a calcium-containing compound, most commonly calcium carbonate or calcium hydroxide. The reaction is as follows:
$2 C_3H_6O_3(aq) + CaCO_3(s) \to Ca(C_3H_5O_3)_2(aq) + H_2O(l) + CO_2(g)$
Or with calcium hydroxide:
$2 C_3H_6O_3(aq) + Ca(OH)_2(s) \to Ca(C_3H_5O_3)_2(aq) + 2 H_2O(l)$
This method is highly efficient and can yield a very pure, white crystalline product. Advancements in this area have even explored alternative raw materials, such as the direct catalytic conversion of biomass-derived glycerol, which offers a more sustainable approach.
Comparison of Production Methods
| Feature | Fermentation Method | Chemical Synthesis Method |
|---|---|---|
| Raw Materials | Carbohydrates (corn, molasses, starch), bacteria, calcium source ($CaCO_3$ or $Ca(OH)_2$) | Lactic acid, calcium source ($CaCO_3$ or $Ca(OH)_2$) |
| Process | Biological process involving microorganisms to convert sugar into lactic acid, followed by neutralization with a calcium source. | Direct chemical reaction between pre-made lactic acid and a calcium compound. |
| Purity | Can achieve high purity through crystallization, but requires more extensive purification to remove biological byproducts. | Can produce very high purity levels with fewer impurities to remove. |
| Control | Requires careful control of temperature and pH to manage bacterial activity and fermentation yield. | Straightforward chemical reaction with precise control over reactant ratios and reaction conditions. |
| Cost | Cost is dependent on the price of renewable carbohydrate sources and the efficiency of the bacterial strains. | Dependent on the cost and purity of the starting lactic acid and calcium compounds. |
Calcium Lactate as a Byproduct of Food Production
Beyond industrial manufacturing, calcium lactate can also appear as a natural byproduct during the aging of certain cheeses. In this process, lactic acid bacteria convert lactose (milk sugar) into lactic acid. The lactic acid then combines with the naturally present calcium in the milk, forming calcium lactate crystals. These harmless, flavorless crystals can sometimes be seen on the surface of aged cheeses like cheddar, which is why calcium lactate is sometimes referred to as 'cheese lactate'.
Conclusion
Calcium lactate has two primary origins: a multi-step biological fermentation process using carbohydrates and bacteria, and a more direct chemical synthesis method involving lactic acid and a calcium compound. It can also form as a natural byproduct during the cheesemaking process. The choice between fermentation and chemical synthesis depends on factors such as desired purity, cost, and raw material availability. Regardless of its origin, the final product is a highly soluble and bioavailable calcium salt with widespread applications in the food, pharmaceutical, and nutritional industries.
