Unified Sample Prep Protocol
Principle
A single extraction workflow that splits into three assay-specific aliquots, allowing salicylate, oxalate, and amine measurements from the same sample.
The three assays require different pH conditions:
- Salicylate: alkaline (~pH 10, NaOH extraction)
- Oxalate: mildly acidic to neutral (~pH 6-7)
- Amines/Histamine: acidic (HCl or perchloric acid)
These are incompatible in a single step, so we extract in hot neutral water then adjust pH per tube.
Equipment
- Kitchen scale (0.1g resolution minimum)
- Mortar and pestle or small blender
- Saucepan or electric kettle
- 3x small plastic tubes or glass vials (avoid glass for histamine — it adsorbs)
- Coffee filters or filter paper
- Pipettes or droppers (1ml)
- pH strips or pH meter
Reagents Required
- Distilled water
- NaOH solution (0.25M) — for salicylate extraction and Tube A adjustment
- HCl solution (dilute) — for Tube C adjustment
- See Bill of Materials for sourcing
Procedure
Step 1 — Sample Preparation
Fresh produce:
- Weigh 0.5g of sample
- Chop finely, then grind with mortar and pestle
Dry meat (jerky, cured meat):
- Weigh 0.5g
- Rehydrate in 1ml distilled water for 5 minutes
- Grind thoroughly
Fresh meat:
- Weigh 0.5g
- Mince finely
Step 2 — Hot Water Extraction
- Add ground sample to 5ml distilled water
- Heat to near-boiling (90°C+), hold for 5 minutes
- This step is validated for histamine extraction (Kikkoman protocol) and works for salicylates and oxalates
- Cool to room temperature (~5 min)
Step 3 — Filtration
- Filter through coffee filter into a clean container
- For fatty meat samples: centrifuge or let settle before filtering
- Hand centrifuge useful here for clarity
Step 4 — Split
Divide filtrate equally into 3 labeled tubes:
| Tube | Volume | Purpose |
|---|---|---|
| A | ~1.5ml | Salicylate assay |
| B | ~1.5ml | Oxalate assay |
| C | ~1.5ml | Total amine screen |
Step 5 — pH Adjustment
- Tube A: Add 2-3 drops 0.25M NaOH → target pH ~10
- Tube B: Check pH, adjust to 6-7 if needed (small drop of HCl or NaOH)
- Tube C: Add 2-3 drops dilute HCl → target pH ~3-4
Proceed immediately to assays. See:
Notes
- Use plastic tubes for amine/histamine samples — histamine adsorbs to glass
- Hot water extraction step validated by Kikkoman histamine kit protocol
- Consistent sample weight (0.5g) and extraction volume (5ml) critical for cross-user comparability
- Record sample metadata: food type, variety if known, source (store/homegrown), storage time, preparation method