Cereals and pulses — Specifications and test methods — Part 1: Rice
1. Scope
This document specifies minimum requirements and test methods for rice (Oryza sativa L.).
It is applicable to husked rice, husked parboiled rice, milled rice and milled parboiled rice, suitable for human consumption, directly or after reconditioning.
It is not applicable to cooked rice products.
2. Normative References
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 712 Cereals and cereal products — Determination of moisture content — Reference method
ISO 6646 Rice — Determination of the potential milling yield from paddy and from husked rice
ISO 8351-1: 1994 Packaging — Method of specification for sacks — Part 1: Paper sacks
ISO 8351-2 Packaging — Method of specification for sacks — Part 2: Sacks made from thermoplastic flexible film
ISO 16634: -- Cereals, pulses, milled cereal products, oilseeds and animal feeding stuffs — Determination of the total nitrogen content by combustion according to the Dumas principle and calculation of the crude protein content
ISO 20483: 2013 Cereals and pulses — Determination of the nitrogen content and calculation of the crude protein content — Kjeldahl method
ISO 24333: 2009 Cereals and cereal products — Sampling
3. Terms and Definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
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ISO Online browsing platform: available at http://www.iso.org/obp
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IEC Electropedia: available at http://www.electropedia.org
3.1
paddy
paddy rice
rough rice
rice retaining its husk after threshing
[SOURCE: ISO 7301, Section 3.1]
3.2
husked rice
DEPRECATED: cargo rice
paddy (3.1) from which the husk only has been removed
[SOURCE: ISO 7301, Section 3.2, modified — The term "cargo rice" is shown as deprecated, and Note 1 to entry is not included here]
3.3
milled rice
white rice
husked rice (3.2) from which almost all of the bran and embryo have been removed by milling
[SOURCE: ISO 7301, Section 3.3]
3.4
parboiled rice
rice whose starch has been fully gelatinized by soaking paddy (3.1) rice or husked rice (3.2) in water followed by a heat treatment and a drying process
3.5
waxy rice
variety of rice whose kernels have a white and opaque appearance
Note 1 to entry: The starch of waxy rice consists almost entirely of amylopectin. The kernels have a tendency to stick together after cooking.
3.6
extraneous matter
EM
<rice> organic and inorganic components other than whole or broken kernels
EXAMPLE: Foreign seeds, husks, bran, sand, dust.
3.7
HDK
heat-damaged kernel
kernel, whole or broken, which has changed its normal colour as a result of heating
Note 1 to entry: This category includes whole or broken kernels that are yellow due to alteration. Parboiled rice in a batch of non-parboiled rice is also included in this category.
3.8
damaged kernel
kernel, whole or broken, showing obvious deterioration due to moisture, pests, disease or other causes, but excluding HDK (3.7)
3.9
immature kernel
unripe kernel
kernel, whole or broken, which is unripe and/or underdeveloped
3.10
husked rice yield
amount of husked rice obtained from paddy
[SOURCE: ISO 6646, Section 3.1]
3.11
nitrogen content
quantity of nitrogen determined after application of the procedure described
Note 1 to entry: It is expressed as a mass fraction of dry product, as a percentage.
[SOURCE: ISO 20483, Section 3.1]
3.12
crude protein content
quantity of crude protein obtained from the nitrogen content as determined by applying the specified method, calculated by multiplying this content by an appropriate factor depending on the type of cereal or pulse
Note 1 to entry: It is expressed as a mass fraction of dry product, as a percentage.
[SOURCE: ISO 20483, Section 3.2]
3.13
gelatinization
hydration process conferring the jelly-like state typical of the coagulated colloids, which are named gels, on kernels
Note 1 to entry: See Figure C.1.
[SOURCE: ISO 14864, Section 3.1]
3.14
gel state
condition reached as a consequence of gelatinization (3.13), when the kernel is fully transparent and absolutely free from whitish and opaque granules after being pressed between two glass sheets
[SOURCE: ISO 14864, Section 3.2]
3.15
gelatinization time
time necessary for 90 % of the kernels to pass from their natural state to the gel state (3.14)
[SOURCE: ISO 14864, Section 3.3]
4. Specifications
4.1. General, organoleptic and health characteristics
Kernels of rice, whether parboiled, husked or milled, and whether whole or broken, shall be sound, clean and free from foreign odours or odour which indicates deterioration.
The levels of additives and pesticide residues and other contaminants shall not exceed the maximum limits permitted in the country of destination.
The presence of living insects which are visible to the naked eye is not permitted. This should be determined before separating the bulk sample into test samples.
4.2. Physical and chemical characteristics
4.2.1.
The mass fraction of moisture, determined in accordance with ISO 712, using an oven complying with the requirements of IEC 61010-2:1998, shall not be greater than 15 %.
The mass fraction of extraneous matter and defective kernels in husked and milled rice, whether or not parboiled, determined in accordance with Annex A, shall not be greater than the values specified in Table 1.
NOTE Lower mass fractions of moisture are sometimes needed for certain destinations depending on the climate, duration of transport and storage. For further details, see ISO 6322-1, ISO 6322-2 and ISO 6322-3.
4.2.2.
The defect tolerance for the categories considered, and determined in accordance with the method given in Annex A, shall not exceed the limits given in Table 1.
Table 1 — Maximum permissible mass fraction of defects
| Defect | Maximum permissible mass fraction of defects in husked rice | |||
|---|---|---|---|---|
| in husked rice | in milled rice (non-glutinous) | in husked parboiled rice | in milled parboiled rice | |
| Extraneous matter: organica | 1,0 | 0,5 | 1,0 | 0,5 |
| Extraneous matter: inorganicb | 0,5 | 0,5 | 0,5 | 0,5 |
| Paddy | 2,5 | 0,3 | 2,5 | 0,3 |
| Husked rice, non-parboiled | Not applicable | 1,0 | 1,0 | 1,0 |
| Milled rice, non-parboiled | 1,0 | Not applicable | 1,0 | 1,0 |
| Husked rice, parboiled | 1,0 | 1,0 | Not applicable | 1,0 |
| Milled rice, parboiled | 1,0 | 1,0 | 1,0 | Not applicable |
| Chips | 0,1 | 0,1 | 0,1 | 0,1 |
| HDK | 2,0c | 2,0 | 2,0c | 2,0 |
| Damaged kernels | 4,0 | 3,0 | 4,0 | 3,0 |
| Immature and/or malformed kernels | 8,0 | 2,0 | 8,0 | 2,0 |
| Chalky kernels | 5,0c | 5,0 | Not applicable | Not applicable |
| Red kernels and red-streaked kernels | 12,0 | 12,0 | 12,0c | 12,0 |
| Partly gelatinized kernels | Not applicable | Not applicable | 11,0c | 11,0 |
| Pecks | Not applicable | Not applicable | 4,0 | 2,0 |
| Waxy rice | 1,0c | 1,0 | 1,0c | 1,0 |
|
Live insects shall not be present. Dead insects shall be included in extraneous matter. | ||||
NOTE 1 This table is based on ISO 7301, Table 1. NOTE 2 Some commercial contracts require information in addition to that provided in this table. NOTE 3 Only full red husked (cargo) rice is considered in this table. a Organic extraneous matter includes foreign seeds, husks, bran, parts of straw, etc. b Inorganic extraneous matter includes stones, sand, dust, etc. c The maximum permissible mass fraction of defects shall be determined with respect to the mass fraction obtained after milling. | ||||
5. Sampling
Sampling shall be carried out in accordance with ISO 24333, Clause 5.
6. Test methods
6.1. Moisture content
Determine the mass fraction of moisture in accordance with the method specified in ISO 712.
6.2. Waxy rice content
Determine the mass fraction of waxy rice. Annex B gives an example of a suitable method.
6.3. Nitrogen content and crude protein content
Determine the nitrogen content and crude protein content in accordance with either ISO 16634, Clause 9, or ISO 20483. For details on the determination of protein content using the Kjeldahl method, see Reference [12] in the Bibliography. For details concerning the use of the Dumas method, see References [10] and [16].
Calculate the crude protein content of the dry product by multiplying the value of the nitrogen content by the conversion factor specified in ISO 20483, Annex C and Table C.1, that is adapted to the type of cereals or pulses [13][14] and to their use.
6.4. Gelatinization time
Determine the gelatinization time,
Report the results as specified in Clause 7.
6.5. Husked rice yield
6.5.1. Determination
CAUTION—Only use paddy or parboiled rice for the determination of husked rice yield.
Determine the husked rice yield in accordance with ISO 6646.
6.5.2. Precision
6.5.2.1. Interlaboratory test
The results of an interlaboratory test are given in Annex D for information
6.5.2.2. Repeatability
The absolute difference between two independent single test results, obtained using the same method on identical test material in the same laboratory by the same operator using the same equipment within a short interval of time, shall not exceed the arithmetic mean of the values for
where
-
-
is the repeatability limit.
6.5.2.3. Reproducibility
The absolute difference between two single test results, obtained using the same method on identical test material in different laboratories by different operators using different equipment, shall not exceed the arithmetic mean of the values for
where
-
-
is the reproducibility limit.
7. Test report
For each test method, the test report shall specify the following:
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all information necessary for the complete identification of the sample;
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a reference to this document (i.e. ISO 17301-1);
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the sampling method used;
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the test method used;
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the test result(s) obtained or, if the repeatability has been checked, the final quoted result obtained;
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all operating details not specified in this document, or regarded as optional, together with details of any incidents which may have influenced the test result(s);
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any unusual features (anomalies) observed during the test;
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the date of the test.
8. Packaging
The packaging shall not transmit any odour or flavour to the product and shall not contain substances which may damage the product or constitute a health risk.
If bags are used, they shall comply with the requirements of ISO8531-1, Clause 9, or ISO 8351-2, as appropriate.
9. Marking
The packages shall be marked or labelled as required by the country of destination.
Annex A
(Normative)
Determination of defects
A.1. Principle
Extraneous matter, broken kernels, damaged kernels and other kinds of rice are separated manually according to the following types: husked rice, milled rice, husked parboiled rice and milled parboiled rice. Each type is then weighed.
A.2. Apparatus
The usual laboratory apparatus and, in particular, the following.
A.2.1. Sample divider, consisting of a conical sample divider or multiple-slot sample divider with a distribution system, e.g. "Split-it-right" sample divider, such as that shown in Figure A.1.
A.2.2. Sieve, with round perforations of diameter 1,4 mm.
A.2.6. Steel bowls, of diameter 100 mm ± 5 mm; seven per test sample.
A.2.7. Balance, which can be read to the nearest 0,01 g.
A.3. Sampling See Clause 5.
A.4.1. Preparation of test sample
Carefully mix the laboratory sample to make it as uniform as possible, then proceed to reduce it, using a divider (A.2.1), until a quantity of about 30 g is obtained.
All parts of kernels which get stuck in the perforations of a sieve should be considered to be retained by the sieve.
Figure A.1 — Split-it-right sample divider
A.5. Determination
Weigh, to the nearest 0,1 g, one of the test samples obtained in accordance with A.4.1 and separate the different defects into the bowls (A.2.6). When a kernel has several defects, classify it in the defect category for which the maximum permissible value is the lowest (see Table 1).
Weigh, to the nearest 0,01 g, the fractions so obtained.
A.6. Calculation
Express the mass fraction of each defect using Formula (Formula A.1):
where
-
-
is the mass fraction of grains with a particular defect in the test sample;
-
-
is the mass, in grams, of grains with that defect;
-
-
is the mass, in grams, of the test sample.
A.7. Test report
Report the results as specified in Clause 7.
Annex B
(Informative)
Determination of the waxy rice content of parboiled rice
B.1. Principle
Waxy rice kernels have a reddish brown colour when stained in an iodine solution, while non-waxy rice kernels show a dark blue colour.
B.2. Apparatus
The usual laboratory apparatus and, in particular, the following.
B.2.1. Balance, capable of weighing to the nearest 0,01 g.
B.2.2. Glass beaker, of capacity 250 ml.
B.2.3. Small white colour bowls, or any white colour container of a suitable size.
B.2.4. Wire sieve, with long rounded apertures of (1 mm
B.3. Reagents
WARNING—Direct contact of iodine with skin can cause lesions so care should be taken in handling iodine. Iodine vapour is very irritating to eyes and mucous membranes.
B.3.1. Deionized water, Grade 3 quality as specified in ISO 3696.
B.4. Sampling
Sampling shall be carried out in accordance with Clause 5.
B.5. Determination
B.5.1.
Weigh a portion of about 100 g of milled rice and put it into a glass beaker (B.2.2).
B.5.2.
Add enough iodine working solution (B.3.3) to soak the kernels, and stir (B.2.5) until all the kernels are submerged under the solution. Let the kernels soak in the solution for 30 s.
B.5.3.
Pour the rice and solution into a wire sieve (B.2.4), and shake the basket slightly in order to drain out the solution. Then place the wire sieve on a piece of tissue paper (B.2.7) to absorb the excess liquid.
B.5.4.
Pour the stained kernels into a bowl (B.2.3). Using tweezers or forceps (B.2.6), separate the reddish brown kernels of waxy rice from the dark blue kernels of non-waxy rice.
B.5.5.
Weigh the waxy rice portion (
B.6. Calculation
Calculate the mass fraction, expressed as a percentage, of the waxy rice,
where
-
-
is the mass, expressed in grams, of the waxy rice portion;
-
-
is the mass, expressed in grams, of the non-waxy rice portion.
B.7. Test report
Report the results as specified in Clause 7, giving the results calculated using Formula (Formula B.1).
Annex C
(Informative)
Gelatinization
Figure C.1 gives an example of a typical gelatinization curve. Figure C.2 shows the three stages of gelatinization.
Key
-
-
mass fraction of gelatinized kernels, expressed in per cent
-
-
cooking time, expressed in minutes
-
-
time required to gelatinize 90 % of the kernels
P
-
point of the curve corresponding to a cooking time of
- a
The time
NOTE These results are based on a study carried out on three different types of kernel.
Figure C.1 — Typical gelatinization curve
Figure C.2-1 — Initial stages: No grains are fully gelatinized (ungelatinized starch granules are visible inside the kernels)
Figure C.2-2 — Intermediate stages: Some fully gelatinized kernels are visible
Figure C.2-3 — Final stages: All kernels are fully gelatinized
Annex D
(Informative)
Results of interlaboratory test for husked rice yields
An interlaboratory test [15] was carried out by the ENR [Rice Research Centre (Italy)] in accordance with ISO 5725-1 and ISO 5725-2, with the participation of 15 laboratories. Each laboratory carried out three determinations on four different types of kernel. The statistical results are shown in Table D.1.
Table D.1 — Repeatability and reproducibility of husked rice yield
| Description | Rice sample | |||
| Arborio | Dragoa | Balilla | Thaibonnet | |
| Number of laboratories retained after eliminating outliers | 13 | 11 | 13 | 13 |
| Mean value, g/100 g | 81,2 | 82,0 | 81,8 | 77,7 |
| Standard deviation of repeatability, |
0,41 | 0,15 | 0,31 | 0,53 |
| Coefficient of variation of repeatability, % | 0,5 | 0,2 | 0,4 | 0,7 |
| Repeatability limit, |
1,16 | 0,42 | 0,88 | 1,50 |
| Standard deviation of reproducibility, |
1,02 | 0,20 | 0,80 | 2,14 |
| Coefficient of variation of reproducibility, % | 1,3 | 0,2 | 1,0 | 2,7 |
| Reproducibility limit, |
2,89 | 0,57 | 2,26 | 6,06 |
a Parboiled rice. | ||||
Bibliography
[1] ISO 3696, Water for analytical laboratory use — Specification and test methods
[2] ISO 5725-1, Accuracy (trueness and precision) of measurement methods and results — Part 1: General principles and definitions
[3] ISO 5725-2, Accuracy (trueness and precision) of measurement methods and results — Part 2: Basic method for the determination of repeatability and reproducibility of a standard measurement method
[4] ISO 6322-1, Storage of cereals and pulses — Part 1: General recommendations for the keeping of cereals
[5] ISO 6322-2, Storage of cereals and pulses — Part 2: Practical recommendations
[6] ISO 6322-3, Storage of cereals and pulses — Part 3: Control of attack by pests
[7] ISO 7301: 2011, Rice — Specification
[8] ISO 14864: 1998, Rice — Evaluation of gelatinization time of kernels during cooking
[9] IEC 61010-2:1998, Safety requirements for electric equipment for measurement, control, and laboratory use — Part 2: Particular requirements for laboratory equipment for the heating of material
[10] Standard No I.C.C 167. Determination of the protein content in cereal and cereal products for food and animal feeding stuffs according to the Dumas combustion method (see http://www.icc.or.at)
[11] Nitrogen-ammonia-protein modified Kjeldahl method — Titanium oxide and copper sulfate catalyst. Official Methods and Recommended Practices of the AOCS (ed. Firestone, D.E.), AOCS Official Method Ba Ai 4-91, 1997, AOCS Press, Champaign, IL
[12] Berner D.L., & Brown J. Protein nitrogen combustion method collaborative study I. Comparison with Smalley total Kjeldahl nitrogen and combustion results. J. Am. Oil Chem. Soc. 1994, 71 (11) pp 1291-1293
[13] Buckee G.K. Determination of total nitrogen in barley, malt and beer by Kjeldahl procedures and the Dumas combustion method — Collaborative trial. J. Inst. Brew. 1994, 100 (2) pp 57-64
[14] Frister H. Direct determination of nitrogen content by Dumas analysis; Interlaboratory study on precision characteristics. AOAC International, Europe Section 4th International Symposium, Nyon, Switzerland, 1994, 33 pp
[15] Ranghino F. Evaluation of rice resistance to cooking, based on the gelatinization time of kernels. Il Riso. 1966, XV pp 117-127
[16] Tkachuk R. Nitrogen-to-protein conversion factors for cereals and oilseed meals. Cereal Chem. 1969, 46 (4) pp 419-423