Understanding the Free Fatty Acid Value
The free fatty acid (FFA) value, or acid value, is a standard parameter used to assess the quality of fats and oils, including ghee. It measures the amount of free fatty acids that have been liberated from their parent triglyceride molecules through hydrolysis. This liberation can be caused by heat, light, moisture, or enzymatic activity (lipase). Higher FFA levels indicate poorer quality, as these free acids contribute to unpleasant, rancid flavors and odors. For pure ghee, the acid value should typically be low, often less than 2.0 mg KOH/g.
The Principle of Titration
The most common and practical method for determining the FFA value is titration. The principle involves dissolving a known weight of the ghee sample in a neutral solvent and then titrating it with a standard alkaline solution, such as potassium hydroxide (KOH) or sodium hydroxide (NaOH). A color indicator, like phenolphthalein, is used to signal the endpoint of the reaction. The volume of the alkali solution needed to neutralize the free fatty acids is then used to calculate the acid value.
Required Apparatus and Reagents
Before beginning the titration, ensure all glassware is clean and dry. You will need the following:
-
Apparatus:
- 250 mL conical flask
- Burette and stand
- Pipette
- Analytical balance
- Heating bath or hot plate
- Measuring cylinders
-
Reagents:
- Ghee sample
- Neutralized ethanol (95% v/v)
- 0.1N standard Sodium Hydroxide (NaOH) or Potassium Hydroxide (KOH) solution
- 1% phenolphthalein indicator solution in ethanol
Step-by-Step Titration Procedure
Follow these steps for accurate determination of the FFA value:
- Prepare the Solvent: Pour 50 mL of 95% ethanol into a conical flask. Add 1-2 mL of phenolphthalein indicator. Gently heat the solvent to around 70°C and neutralize it by adding 0.1N NaOH solution dropwise until a faint pink color persists for about 15 seconds.
- Prepare the Ghee Sample: Melt the ghee sample and mix it thoroughly. Filter it through a dry filter paper (e.g., Whatman No. 1) to remove any solid impurities. Weigh an appropriate amount of molten ghee (typically 5–10g, depending on expected FFA) into a clean 250 mL conical flask. Record the exact weight (W).
- Mix and Heat: Add the previously neutralized, hot ethanol to the flask containing the ghee. Mix the contents well to dissolve the free fatty acids completely. Gently boil the mixture for about five minutes to ensure complete dissolution.
- Titrate: While the mixture is still hot, titrate it with the standard 0.1N NaOH solution, shaking vigorously throughout the process. Continue until a faint pink color appears and persists for at least 15 seconds. Record the volume of NaOH used (V).
Calculation of the Free Fatty Acid Value
The acid value, expressed as mg of KOH required to neutralize one gram of fat, is calculated using the following formula:
$$ \text{Acid Value} = \frac{V \times N \times 56.1}{W} $$
- V: Volume of standard alkali solution (NaOH or KOH) used in the titration (in mL).
- N: Normality of the standard alkali solution (e.g., 0.1 N).
- 56.1: Molecular weight of KOH.
- W: Weight of the ghee sample (in grams).
To express the FFA as a percentage of oleic acid, a common standard for fats, use this formula:
$$ \text{% FFA (as Oleic Acid)} = \frac{V \times N imes 282.5 imes 100}{W} $$
- 282.5: Equivalent weight of oleic acid.
Comparison of FFA Testing Methods
While titration is a reliable and cost-effective method for routine FFA testing, advanced techniques offer greater specificity and accuracy. Here is a comparison of different methods:
| Feature | Titration (Standard Method) | Gas Chromatography (GC) | Nuclear Magnetic Resonance (NMR) | Fourier Transform Infrared (FTIR) Spectroscopy |
|---|---|---|---|---|
| Principle | Neutralization reaction with a strong alkali | Separates fatty acids after derivatization | Analyzes molecular structure without derivatization | Identifies FFAs based on characteristic absorption bands |
| Cost | Low | High (instrumentation and reagents) | Very High (advanced equipment) | Medium (FTIR Spectrometer) |
| Speed | Moderate | Long (requires derivatization and analysis) | Rapid (no sample pretreatment) | Rapid (non-destructive) |
| Accuracy | Good for total FFA content | High; identifies specific FFA profiles | High; detects even minor components | High, especially with ATR-FTIR |
| Sample Preparation | Simple; melting and filtration | Complex; requires derivatization | Simple; no pretreatment needed | Minimal |
| Information | Total acid value (sum of FFAs) | Specific composition of fatty acids | Detailed profile of all molecules | Identification of functional groups associated with FFAs |
How Results Reflect Ghee Quality
The free fatty acid value directly correlates with the quality of ghee. A lower FFA value indicates a fresh, high-quality product, as the triglycerides have not yet significantly broken down. Conversely, a high FFA value suggests that the ghee has undergone hydrolysis, potentially due to poor storage conditions, age, or microbial action. This is a key indicator of rancidity, which not only affects the flavor and aroma but can also diminish the ghee's nutritional value.
Conclusion
Determining the free fatty acid value of ghee is a straightforward yet crucial process for quality control and assurance. While advanced analytical methods provide detailed insights into the specific fatty acid profile, the classic titration method remains a robust, cost-effective, and reliable approach for routinely measuring the overall acid value. By performing this test, producers and consumers can confidently assess the freshness, purity, and edibility of ghee, ensuring it meets the expected standards of quality.
FSSAI - Revised method for determination of acid value in oils and fats
