SOP: Determination of Extraneous Material in Shelled and Unshelled Nuts
GIFSQ — Global Institute for Food Safety & Quality
1. Principle
Shelled and unshelled nuts, whole or in pieces, are sampled from a lot and examined for insect infestation, mould, rancidity, shrivelling and other extraneous material such as sand and soil. Shelled nuts are inspected on the outer surface with an illuminator and a magnifying lens, cut open and examined inside, with questionable areas confirmed under the stereoscopic or compound microscope. Unshelled nuts are cracked gently so the kernel comes out undamaged and the kernel is examined the same way. Each nut is classified into defect categories, and the percent of defectives is calculated for each analytical unit, to determine compliance with Sections 4, 5 and 7 of the Food and Drugs Act. The method covers, among others, almonds, Brazil nuts, cashews, chestnuts, filberts, pecans, peanuts, pistachios and walnuts.
2. Apparatus required
- Sharp knife
- Illuminator
- Magnifying lens (3–5x)
- Stereoscopic microscope (10–30x)
- Compound microscope (100x)
- Nutcrackers
3. Definition of a lot
A lot is that amount (volume, weight, etc.) of the food which is produced, stored and/or shipped under conditions as nearly uniform as possible, preferably designated by a common container code or marking, and, in any event, consisting of not more than one variety, grade or type of product from a single identifiable source.
4. Collection of samples
- Scrutinize the whole lot for live infestation; if live infestation is found, do not sample until after fumigation or other effective treatment
- Obtain eight sample units selected at random from the lot, each of at least 100 nuts, using appropriate sampling equipment and containers — eight sample units constitute a sample
- Keep each sample unit separate and label them 1, 2, 3, etc.
- Record full information respecting the lot: lot size, weight of individual containers, country of origin, exporter, importer, and product and lot identification — this record accompanies the sample
5. Procedure
If appropriate, freeze the samples before analysis to minimize the possibility of a live infestation of the laboratory
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Prepare the analytical units: from each of the eight sample units, take 100 whole nuts at random — or, if the sample unit is pieces of nuts, take 100 pieces. Each 100 whole nuts or pieces constitute one analytical unit. If the nuts are mixed, separate them into their various kinds before examination and report the results for each kind separately. Repeat for the remaining seven sample units
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Examine the shelled nuts: examine the outer surface of each shelled whole nut or piece using an illuminator and a magnifying lens (3–5x) for insects and/or their damage and mould as classified in step below. With a sharp knife, cut whole nuts in half and examine the interior of the nut for insects and/or their damage and mould. Use the stereoscopic microscope (10–30x) only to confirm questionable areas. Confirm mould filaments by transferring the questionable particles to a glass slide and observing them with the compound microscope (100x). Repeat the examination for the seven remaining analytical units
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Classify each shelled nut into one defect category below. If a shelled nut shows more than one defect, classify it only as a multiple defective:
- (a) Insect damaged — shelled nuts containing insects or their parts, insect tunnels, excreta, eggs or webbing. Report the kind and approximate number of insects present. Also classify as insect damaged any nut showing brown spot or kernel spot (see nut-specific defects below) where the single or combined spots exceed 10 mm in diameter
- (b) Mouldy — nuts with mouldy or rotten areas ≥ 5 mm in diameter, either singly or in aggregate
- (c) Rancid — rancid nuts are frequently soft and have a yellow, dark or oily appearance; light is detrimental to nuts and promotes oxidative rancidity in the oil in the outer layers
- (d) Otherwise decomposed — any nut kernel not classified as mouldy or rancid but otherwise decomposed due to: (i) embryo rot, if the discoloration extends more than two-thirds of the length of the centre ridge of the pecan; (ii) scabby blight, bacterial blight or sunburn, if the discoloration or growth shows a single or combined area exceeding 13 mm (add the diameters of the smaller areas); (iii) gumminess, if the resinous glaze coats more than one-half of the kernel surface
- (e) Dirty — nuts containing areas of dirt, excrement or excreta (bird, rodent or other mammalian) which are > 5 mm in length, either singly or in aggregate
- (f) Shrivelled — a nut whose kernel is less than one-half of its apparent normal size
- (g) Multiple defectives — nuts showing more than one of the above defects
Shelled nuts showing none of the above defects, but which may show other quality-related defects, are acceptable shelled nuts
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For shelled nuts of the kinds below, recognize the defectives characteristic of each kind:
- Brown spot — slightly depressed brown spots caused by the insertion of the mouth parts of the boxelder bug; characteristic of almonds
- Kernel spot — caused by sucking insects feeding on the immature nut; beneath the dark surface the meat is white and pithy; characteristic of pecans
- Pink rot — caused by the mould Trichothecium roseum; the shell becomes oily, the kernel rancid, and eventually the kernel is digested and replaced by a pink powder; characteristic of pecans
- Scabby blight — a hard and woody ashen-gray or brownish scale growth on the kernel skin; characteristic of almonds
- Gumminess — associated with injury from an organism such as an insect or from a mechanical source; gives almonds a sweeter taste, and the condition is objectionable when the resinous glaze heavily coats more than one half the kernel surface; characteristic of almonds
- Embryo rot — due to pre-harvest germination; dark grey to bluish-black or jet-black discoloration where the kernel halves join; characteristic of pecans
- Bacterial blight — black spots of various sizes on the nut meat; characteristic of walnuts
- Sunburn — causes the nut meat to turn dark; characteristic of walnuts
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Examine the unshelled nuts: crack the shell gently with a nutcracker and remove the kernel without damaging it, then examine the kernel as for shelled nuts above
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Classify each unshelled nut kernel into one of the defect categories (a) to (g) above. If a kernel shows more than one defect, classify it only as a multiple defective. Unshelled nuts showing none of the defects, but which may show other quality-related defects, are acceptable unshelled nuts
6. Calculation
Record the percent of each category of defectives, separately for each analytical unit, to the nearest 1%:
- category (a) = % insect damaged defectives only = (total number of insect damaged nuts ÷ total number of nuts examined) × 100
- category (b) = % mouldy defectives only
- category (c) = % rancid defectives only
- category (d) = % otherwise decomposed defectives only
- category (e) = % dirty defectives only
- category (f) = % shrivelled defectives only
- category (g) = % multiple defectives
Combine the percent by number of each category to obtain the total percent defectives for each separate analytical unit:
total percent defectives = (a₁ + b₁ + c₁ + d₁ + e₁ + f₁ + g₁) % — for analytical unit 1
total percent defectives = (a₂ + b₂ + c₂ + d₂ + e₂ + f₂ + g₂) % — for analytical unit 2, and so on
- Where:
- a, b, c, d, e, f, g = the percent defectives of categories (a) to (g) in the analytical unit
- the subscripts 1, 2, etc. = the analytical unit numbers
7. Precautions
- Do not sample a lot showing live infestation until after fumigation or other effective treatment
- If appropriate, freeze the samples before analysis so a live infestation does not establish itself in the laboratory
- Crack unshelled nuts gently so the kernel is removed without damage
- Use the stereoscopic microscope only to confirm questionable areas — it is not the primary examination tool
8. References
- Health Canada, Compendium of Analytical Methods, Volume 4 — Laboratory Procedure ExFLP-09: Determination of Extraneous Material in Shelled and Unshelled Nuts (January 2019; replaces ExFLP-09, September 1995)
- Pietrzak, E. 2009. Guidelines for the General Cleanliness of Food — An Overview. In: Volume 1. Compendium of Analytical Methods