I. Rapid Sensory Identification Methods

1. Water Solubility and Turbidity Test
   • Soak 10g of feed in 200ml of room-temperature clean water and let stand for 10 minutes.
   • Qualified standard: Slightly turbid water (transparency reduction ≤30%) with no flocculent suspensions.
   • Unqualified performance: Water rapidly becomes cloudy like rice water, with white flocculent substances (indicating leaching of ungelatinized starch).
2. Expansion Structure Observation
   • Measure volume change after soaking for 5 minutes.
   • Qualified standard: Uniform expansion (volume increases by 1.5–2 times), with a fine honeycomb-like pore structure on the surface.
   • Unqualified performance: Insufficient expansion (<1.2 times) or excessive cracking (>2.5 times).
3. Cross-Section Structure Analysis
   • Break open a soaked pellet and observe the cross-section.
   • Qualified characteristics: Uniform honeycomb pores throughout, with no hard core layer.
   • Unqualified characteristics: Presence of a white hard core (raw starch area) or uneven pore distribution.

II. Professional Testing Method (Iodine Staining)

1. Procedure
   • Grind the feed into powder, mix with distilled water at a 1:5 ratio, and boil for 3 minutes.
   • After cooling, add Lugol's iodine solution and observe the color reaction.
2. Judgment Criteria
   • Dark blue/purple-black: Gelatinization degree <70% (starch not fully denatured).
   • Light blue/pale purple: Gelatinization degree 70%–85% (basically qualified).
   • Brown-yellow/colorless: Gelatinization degree >85% (ideal condition).

III. Feeding Behavior Verification

1. Feeding Response Observation
   • Qualified performance: Koi actively compete for food, eat smoothly, and pellets soften within 5–10 seconds in the mouth.
   • Problematic performance: Frequent spitting of food, filtering debris through gills, or white paste-like residues floating on the water surface after feeding.
2. Fecal Form Monitoring
   • Qualified indicator: Feces are short, cylindrical, sink, and have a compact structure.
   • Risk signal: Feces are loose, float, contain undigested particles, or are accompanied by bubbles.

IV. Indirect Verification Through Process Parameters

1. Extrusion temperature: Should be stable at 125–135°C (insufficient temperature reduces gelatinization rate).
2. Conditioning moisture: Should be controlled at 18%–22% (moisture deviation affects starch gelatinization).
3. Screw speed: Compatibility with die head pressure (pressure fluctuations >10% may cause uneven gelatinization).

V. Long-Term Breeding Performance Tracking

1. Reduced digestibility: Apparent protein digestibility <80% (normal should be >90%).
2. Accelerated water quality deterioration: Leachates from uneaten feed increase COD by over 30%.
3. Decreased growth efficiency: Feed conversion ratio (FCR) >1.5 (high-quality feed can achieve 1.1–1.3).

VI. Industry Reference Standards

1. International General Thresholds
   • Ornamental fish extruded feed: Gelatinization degree ≥85%.
   • Aquaculture feed: Gelatinization degree ≥80% (cold-water species require ≥85%).
2. Allowable Error Ranges
   • Coefficient of variation in gelatinization degree for the same batch should be <5%.
   • Difference in gelatinization degree between particles of different sizes should be <3%.