1. Starch Residue Detection Method

1-1. Purpose: To check if tableware or food containers are clean and free of starch residue.

1-2. Reagent:

• Starch Residue Test Solution (Iodine Solution: Dissolve 20g of potassium iodide in 100mL of water, then add 12.7g of iodine; after dissolution, take 1mL and dilute with water to 1000mL to obtain the iodine test solution).
• Our company sells a pre-formulated Starch Residue Test Solution in a ready-to-use spray bottle.

1-3. Inspection Method:

1. Take starch test solution

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2. Drip onto the tableware or container to be tested

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3. Rotate slowly to cover the entire surface with solution

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4. Starch residue will turn blue-purple

1-4. Suggestion:

1. Determination of starch residue is based on whether there are distinct blue-purple spots or streaks on the plate. Slight brownish-yellow or extremely faint blue tints should not be judged as starch residue.

2. Fat Residue Detection Method

2-1. Purpose: To check for oil/fat residue on tableware or food containers to determine if they are clean.

2-2. Reagent:

• Fat Residue Test Solution (Preparation of Oil-soluble Paprika reagent: Take 50 mg of oil-soluble paprika and dissolve it in ethanol to make a total of 100 mL).
• Our company sells a pre-formulated Fat Residue Test Solution in a ready-to-use spray bottle.

2-3. Inspection Method:

1. Drip the solution onto the item to be tested

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2. Rotate slowly to cover the entire surface

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3. Rinse gently with water

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4. Fat residue will appear as orange-brown spots (Note)

Note: Determination is based on spots. If plastic containers are stained with an orange background that cannot be removed by water after testing, medicinal alcohol can be used to restore the original state.

2-4. Suggestion:

1. Determination of fat residue is based on distinct orange-brown oil spots or clear orange-brown streaks. Slight orange-brown tints should not be judged as fat residue.

3. Protein Residue Detection Method

Ninhydrin

• Formula: C₉H₆O₄    Molecular Weight: 178.14
• CAS Registry Number: 485-47-2

• Chemical Structure:
  This structure is also available as a 2d Mol file.
• Other Names: 1H-Indene-1,3(2H)-dione, 2,2-dihydroxy-; 1,3-Indandione, 2,2-dihydroxy-; Ningidrin; Ninhydrin hydrate; Triketohydrindene hydrate; 2,2-Dihydroxy-1,3-indandione; 2,2-Dihydroxy-1H-indene-1,3(2H)-dione; 1,2,3-Indantrione, 2-hydrate; 1,2,3-Indantrione monohydrate; 1H-Indene-1,2,3-trione, 2-hydrate

3-1. Ninhydrin Test Solution (ninhydrin T.S.)

Dissolve 0.2g of ninhydrin in 95% alcohol to make a total volume of 100ml. This product should be prepared just before use. If using a pre-configured Ninhydrin solution, it should be stored refrigerated at 0~5°C, and tested every month on a standard sample to ensure the reagent still colors effectively.

3-2. Test Method:

Spray Ninhydrin test solution onto the tableware, then place it in a 100°C oven for 3~5 minutes. If blue-purple residue is found, it indicates protein residue on the tableware.

3-3. Note:

1. This reaction must be conducted in a slightly acidic or neutral solution (pH 5–7); it will fade if alkaline.
2. The blue-purple complex or CO₂ produced in this experiment can be used for the quantification of α-amino acids.
3. Proline and hydroxyproline lack an α-amino group and therefore will not produce a red-purple color.
4. Protein derivatives and non-protein compounds containing amino groups may also react, causing interference.
5. Saliva and sweat also produce positive reactions, so contamination should be avoided to prevent interference with judgment.