Organoleptic evaluation is typically performed by trained personnel under controlled conditions to ensure consistency and reliability. The process involves four main sensory assessments: appearance, smell, taste, and texture. Below are the detailed steps, precautions, and considerations for each.
1. Preparation for Organoleptic Evaluation
Trained Evaluators: Use personnel trained in sensory analysis to recognize normal and abnormal milk characteristics. Training should include exposure to fresh, spoiled, and adulterated milk samples.
Controlled Environment: Conduct evaluations in a clean, well-lit, odor-free room with a temperature of 20–25°C to avoid external sensory interference.
Sample Preparation:
Collect a representative sample (100–250 mL) using proper sampling techniques (e.g., single or composite sampling, as described in previous responses).
Store samples at 4–7°C and evaluate within 6 hours of collection to prevent spoilage.
Warm samples to 15–20°C before evaluation to enhance sensory perception (especially for smell and taste).
Equipment: Use clean, odor-free glass or stainless steel containers for sample presentation. Avoid plastic containers, which may impart odors.
Precautions:
Ensure evaluators avoid strong perfumes, smoking, or consuming spicy foods before testing to prevent sensory bias.
Cleanse the palate with water or plain crackers between samples to avoid carryover flavors.
2. Sensory Assessment Procedures
The organoleptic evaluation is conducted systematically, assessing each sensory attribute in sequence to detect deviations from expected milk quality.
a. Appearance (Visual Inspection)
Procedure:
Pour 50–100 mL of milk into a transparent glass container or hold the sample against a white background under good lighting (preferably natural or neutral light).
Observe for:
Color: Fresh cow milk should be creamy white; buffalo milk is slightly whiter. Abnormal colors (e.g., yellowish, bluish, or reddish tints) may indicate spoilage, adulteration, or contamination.
Clarity: Check for homogeneity and absence of foreign particles, clots, or sediments. Cloudy milk may indicate microbial growth or adulteration (e.g., starch).
Consistency: Note if the milk appears watery (possible water adulteration) or overly thick (possible additives like starch or flour).
Expected Characteristics:
Cow milk: Creamy white, opaque, no visible particles.
Buffalo milk: Slightly whiter, creamier texture.
Abnormalities:
Yellowish tint: Oxidation or bacterial growth.
Bluish hue: Water adulteration or Pseudomonas contamination.
Clots/Sediments: Microbial spoilage or physical contaminants.
Precautions:
Use clean containers to avoid false positives from container residues.
Avoid direct sunlight, which may alter perceived color.
b. Smell (Odor Assessment)
Procedure:
Pour 50 mL of milk into a clean glass or cup, warmed to 15–20°C for optimal odor release.
Gently swirl the sample to release volatiles, then sniff the headspace immediately above the milk surface.
Note the odor intensity and character:
Normal Odor: Fresh milk has a mild, slightly sweet, or creamy odor.
Abnormal Odors:
Sour/acidic: Lactic acid from bacterial fermentation (e.g., Lactobacillus).
Rancid: Lipolysis due to lipase activity or improper storage.
Chemical: Adulterants like detergents, formalin, or urea.
Burnt: Overheating during pasteurization.
Feed-like: Strong feed odors (e.g., silage) from cow diet.
Precautions:
Avoid prolonged exposure to air, which may mask odors or introduce external smells.
Evaluate each sample quickly (within 10–15 seconds) to capture initial impressions.
Use a separate container for each sample to prevent cross-contamination of odors.
c. Taste
Procedure:
Take a small sip (5–10 mL) of milk, warmed to 15–20°C, and roll it over the tongue for 5–10 seconds before swallowing or spitting out.
Assess the taste profile:
Normal Taste: Fresh milk is mildly sweet, creamy, and slightly rich, with no aftertaste.
Abnormal Tastes:
Sour: High acidity from microbial growth.
Bitter: Proteolysis or rancidity due to bacterial enzymes.
Salty: High mineral content or mastitis in cows.
Chemical: Adulterants like urea, neutralizers, or detergents.
Metallic: Contamination from equipment or oxidation.
Rinse the mouth with water between samples to reset the palate.
Precautions:
Taste testing is optional and should only be conducted if the milk is confirmed safe (e.g., free from pathogens or harmful adulterants) via prior microbiological or chemical tests.
Avoid taste testing in cases of suspected spoilage or chemical adulteration to prevent health risks.
Limit the number of samples per session (e.g., 5–10) to avoid sensory fatigue.
d. Texture (Mouthfeel)
Procedure:
During taste evaluation, assess the milk’s texture or mouthfeel by noting its consistency and smoothness.
Expected characteristics:
Normal Texture: Smooth, creamy, and slightly viscous (varies by fat content; buffalo milk is creamier than cow milk).
Abnormal Textures:
Watery: Dilution with water or low fat/SNF content.
Gritty: Presence of undissolved adulterants (e.g., starch, flour).
Slimy: Microbial growth (e.g., Pseudomonas or coliforms).
Curdled: High acidity or protein denaturation.
Precautions:
Ensure the sample is well-mixed to avoid false impressions of texture due to fat separation.
Combine texture assessment with visual inspection to confirm findings (e.g., watery texture with cloudy appearance).
3. Scoring and Interpretation
Scoring System:
Assign scores (e.g., 1–5 or 1–10) for each attribute based on intensity and acceptability:
Appearance: 1 (unacceptable, e.g., clots) to 5 (ideal, creamy white).
Smell: 1 (strong off-odor) to 5 (mild, creamy).
Taste: 1 (bitter/chemical) to 5 (sweet, creamy).
Texture: 1 (slimy/watery) to 5 (smooth, creamy).
Total scores can be used to classify milk as acceptable, borderline, or rejected.
Interpretation:
High scores (e.g., >80% of maximum) indicate fresh, high-quality milk.
Low scores or specific abnormalities (e.g., sour smell, watery texture) trigger further testing (e.g., microbiological for spoilage, chemical for adulteration).
Indian Context:
FSSAI’s Manual of Methods of Analysis of Foods: Milk and Milk Products (2025) recommends organoleptic evaluation as a preliminary step before advanced testing.
Common issues in India include watery appearance (water adulteration), chemical odors (urea, detergents), and sour tastes (poor cold chain).
4. Precautions and Considerations
Hygiene: Ensure all containers and tools are cleaned and sanitized to avoid introducing odors or contaminants.
Sample Integrity: Evaluate samples promptly after collection and maintain cold storage (4°C) to prevent spoilage before testing.
Evaluator Health: Exclude evaluators with colds, allergies, or other conditions that impair sensory perception.
Subjectivity: Use multiple evaluators (e.g., 3–5) to reduce bias and average scores for consistency.
Safety: Avoid taste testing if preliminary tests (e.g., visual, smell) suggest spoilage or adulteration, as per FSSAI guidelines.
Documentation: Record observations with details (e.g., sample ID, date, evaluator name) for traceability, as required by FSSAI.
Limitations: Organoleptic evaluation is subjective and should be complemented by objective tests (e.g., lactometer for adulteration, TPC for microbial load).
5. Applications in India
Milk Collection Centers: Used by cooperatives (e.g., Amul, Mother Dairy) to quickly screen raw milk for freshness and adulteration before acceptance.
Dairy Processing: Employed to check pasteurized or processed milk for off-flavors or processing defects (e.g., burnt flavor from overheating).
Regulatory Surveillance: FSSAI uses organoleptic evaluation during market surveys (e.g., 2018 National Milk Safety and Quality Survey) to identify substandard milk.
Consumer Protection: Helps detect adulteration (e.g., water, starch) and spoilage, addressing public health concerns in India’s dairy sector.