FAQs

Black Spots in Hydrocolloids Powder: Causes, Inspection, and Acceptance Criteria

1. Definition and Sources of Black Spots

Black spots refer to visible dark or black impurity particles in white or light-colored hydrophilic colloid powder. They primarily originate from two categories:

• Process-related black spots (endogenous)

  Caused by localized overheating or scorching during production.

  Common stages: drying (e.g., wall scorching in spray dryers), grinding (friction-induced carbonization), or extrusion.

• Foreign black spots (exogenous)

  Result from wear and tear of equipment or packaging materials.

  Common sources: worn plastic/rubber seals, blade fragments, packaging debris, or environmental contaminants.

2. Standard Inspection Method

Method: White paper spreading with backlight visual inspection.

• Equipment: Analytical balance (0.01g accuracy), A5 white paper, glass plate, LED inspection light, magnifier (5–10×), tweezers, petri dish.

• Procedure:

  1. Weigh 10.00g of sample.

  2. Spread evenly on A5 paper (layer thickness ~1–2 mm).

  3. Place under uniform backlight and scan systematically with a magnifier.

  4. Pick out and count all visually distinct dark spots.

• Acceptance limit: Typically ≤5–10 black spots per 10g sample (subject to customer specifications).

3. Composition Analysis and Disposition

• Quick screening (solubility test):

  Place individual black spots in hot water (>80°C).

  • Completely soluble → Likely scorched colloid (process-related).

  • Insoluble → Likely foreign material (e.g., plastic, metal).

• Definitive analysis:

  Techniques like FTIR or microscopy can identify materials (e.g., plastic, rubber, carbonized organics).

4. Acceptance Criteria and Corrective Actions

• Acceptable:

  • Process-related spots within quantity limit (e.g., ≤10/10g).

• Reject:

  • Black spots exceed limit, or

  • Any confirmed non-colloid foreign material (plastic, metal, etc.).

• Preventive measures for suppliers:

  • Optimize drying/grinding to avoid overheating.

  • Replace wear-prone parts with food-grade alternatives.

  • Implement sieving, metal detection, or X-ray inspection