ISO 17646:2025

Rapid detection of moisture content in fresh meat - Low-field nuclear magnetic resonance (LF-NMR) method

This document specifies requirements for rapid determination of moisture of fresh meat based on low-field nuclear magnetic resonance (LF-NMR) technology. This document is applicable to the rapid detection of moisture in fresh meat.

Détection rapide de la teneur en humidité dans la viande fraîche — Méthode par résonance magnétique nucléaire à champ faible

General Information

• Status: Published
• Publication Date: 07-May-2025
• ICS: 67.120.10 - Meat and meat products
• Technical Committee: ISO/TC 34/SC 6 - Meat, poultry, fish, eggs and their products
• Drafting Committee: ISO/TC 34/SC 6 - Meat, poultry, fish, eggs and their products
• Current Stage: 6060 - International Standard published
• Start Date: 08-May-2025
• Due Date: 23-Aug-2025
• Completion Date: 08-May-2025

Overview

ISO 17646:2025 - Rapid detection of moisture content in fresh meat - Low-field nuclear magnetic resonance (LF‑NMR) method defines a rapid, LF‑NMR‑based procedure for determining moisture in fresh meat. The standard specifies sample preparation, instrument settings, calibration and data-processing steps to obtain quantitative moisture estimates and to resolve water fractions by transverse relaxation time (T2). It was prepared by ISO/TC 34/SC 6 (Meat, poultry, fish, eggs and their products).

Key topics and technical requirements

• Scope: Rapid determination of moisture in fresh meat (fresh meat defined per ISO 23722).
• Principle: LF‑NMR measures 1H NMR signals from water; signal amplitude is used to estimate moisture mass. T2 relaxation is used to distinguish water states.
• Sample preparation:
  • Remove skin, connective tissue and fat.
  • Cut along muscle fiber into 1 cm thick slices, then into 1 × 1 × 2 cm cuboids; at least three cuboids per sample.
  • Sample temperature: 22 °C ± 2 °C.
• Instrument and environment:
  • LF‑NMR analyser (universal), field strength ≈ 0.5–1.0 T, spectrometer frequency ≈ 20–23 MHz.
  • Instrument chamber ambient: 32–35 °C.
• Measurement sequences: Use FID for calibration and CPMG for determination to obtain relaxation attenuation curves and inversion spectra.
• Key parameter ranges (examples from the standard):
  • Sampling bandwidth (SW): ≈100–200 kHz
  • Regulate first data (RFD): ≈0.002–0.5 ms (recommended 0.08 ms at SW = 100 kHz)
  • Time wait (TW): calibration ≈1 000–4 000 ms, determination ≈4 000–8 000 ms
  • Echo time (TE): pork ≈ 0.3 ms, beef ≈ 0.5 ms, chicken ≈ 0.2–0.3 ms
  • Echo number (NECH): ≈2 000–5 000
• Standard curve procedure: Use freeze‑dried meat, add water increments (1%, 5%, 10%, 30%, 50%, 70%) with ≥5 repeats per group to build calibration curves (Annex A).
• Data processing: Convert CPMG decay to T2 inversion spectra (SIRT method), extract peak areas A(T2b), A(T21), A(T22) corresponding to bound, immobilized and free water (T2 ranges given in the standard).

Practical applications and users

Who uses ISO 17646:2025:

• Food testing laboratories performing routine moisture analysis of fresh meat
• Meat processors and quality assurance teams for production control
• Instrument manufacturers and service providers for LF‑NMR systems
• Research labs studying water distribution in muscle tissues
• Regulatory or inspection bodies needing standardized rapid moisture tests

Practical applications:

• Rapid moisture quantification in production and QC workflows
• Generating reproducible standard curves for LF‑NMR moisture calibration
• Differentiating bound, immobilized and free water fractions for product characterization

Related standards

• ISO 23722 (definition of fresh meat) - cited in ISO 17646:2025
• Prepared by ISO/TC 34/SC 6 (Meat, poultry, fish, eggs and their products) - consult national bodies for implementation guidance

Keywords: ISO 17646:2025, LF‑NMR, low‑field nuclear magnetic resonance, rapid detection, moisture content, fresh meat, T2 relaxation, CPMG, FID, standard curve, food testing.

Standards Content (Sample)

International
Standard
ISO 17646
First edition
Rapid detection of moisture
2025-05
content in fresh meat — Low-field
nuclear magnetic resonance
(LF-NMR) method
Détection rapide de la teneur en humidité dans la viande fraîche —
Méthode par résonance magnétique nucléaire à champ faible
Reference number
© ISO 2025
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 3
5 Materials and apparatus . 3
6 Preparation of sample . 3
6.1 Preparation of testing sample .3
6.2 Preparation of standard sample .3
7 Low-field nuclear magnetic resonance determination . 3
7.1 General parameters .3
7.2 Calibration parameters setting .4
7.3 Determination parameters setting .4
7.4 Determination of blank substrate .5
7.5 Determination of testing sample .5
7.6 Determination of standard sample and establishment of standard curve .5
8 Data processing and moisture content calculation . 5
8.1 Data processing.5
8.2 Standard curve fitting .5
8.3 Expression of results .6
9 Test report . 6
Annex A (informative) Preparation of standard sample and standard curve . 8
Annex B (informative) Interlaboratory test report . 10
Bibliography .20

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 6, Meat,
poultry, fish, eggs and their products.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
International Standard ISO 17646:2025(en)
Rapid detection of moisture content in fresh meat — Low-
field nuclear magnetic resonance (LF-NMR) method
1 Scope
This document specifies requirements for rapid determination of moisture of fresh meat based on low-field
nuclear magnetic resonance (LF-NMR) technology.
This document is applicable to the rapid detection of moisture in fresh meat.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
fresh meat
meat that retains its original compositional and structural properties, and has not been subjected to heating,
canning, salting or drying, etc.
[SOURCE: ISO 23722:2021, 3.22]
3.2
transverse relaxation time
T
spin-spin relaxation time
time constant when the transverse magnetization vector decreases to 37 % of the maximum value that
characterizes the speed of signal attenuation
Note 1 to entry: The relaxation process is the process of the spinning hydrogen nucleus in the static magnetic field
returning from the excited state to the equilibrium state. The time required for the relaxation process is called the
“relaxation time”.
3.3
free induction decay
FID
nuclear magnetic resonance (NMR) signal received, resulting from using a single 90° radio frequency pulse
to activate the sample
3.4
Carr-Purcell-Meiboom-Gill
CPMG
pulse sequence that involves applying multiple 180° radio frequency pulses after applying a 90° radio
frequency pulse
Note 1 to entry: Each 180° radio frequency pulse applied will delay the signal attenuation caused by the uneven
magnetic field, and data that are not affected by magnetic field uniformity can be sampled at the echo peak of the signal.
3.5
sampling bandwidth
SW
frequency range of the nuclear magnetic resonance (NMR) signal received by the receiver coil when the
signal is collected
3.6
regulate first data
RFD
control parameter for the starting time of nuclear magnetic resonance (NMR) signal acquisition
3.7
pre-amp regulate gain
PRG
parameter used to show that the nuclear magnetic resonance (NMR) signal from the receiver coil is pre-
amplified to levels in a low-noise pre-amplifier
3.8
regulate analogue gain 1
RG1
parameter used to show that the nuclear magnetic resonance (NMR) signal is further amplified to levels in a
pre-amplifier following the pre-amplification
3.9
regulate digital gain 1
DRG1
parameter used to show that the nuclear magnetic resonance (NMR) signal is amplified to levels after
converted to digital signals for averaging and computer processing
3.10
inversion curve
frequency-domain spectrum converted from the attenuation curve composed of several points through the
inversion method
3.11
bound water
T
2b
water in meat that is closely bound to the polar groups of protein by hydrogen bonds
Note 1 to entry: The transverse relaxation time (3.2) of bound water is shorter than that of immobilized water (3.12)
and free water (3.13).
3.12
immobilized water
T
water trapped within the myofibrils that cannot move freely
Note 1 to entry: The transverse relaxation time (3.2) of immobilized water is between that of bound water (3.11) and
free water (3.13).
3.13
free water
T
water outside the myofibrillar lattice and also outside the muscle cell that can move freely
Note 1 to entry: The transverse relaxation time (3.2) of free water is more than that of immobilized water (3.12) and
bound water (3.11).
4 Principle
The meat system contains atomic nuclei (1H protons) with fixed magnetic moments, which can absorb radio
frequency energy and generate NMR signals of the water hydrogen when stimulated by radio frequency
pulses of specific frequencies under a constant magnetic field. When a meat sample is put in a uniform static
magnetic field, a specific nuclear magnetic pulse sequence is used to motivate the 1H protons of moisture
in the meat sample. After the sample absorbs the excitation energy, an NMR signal is produced, which is
proportional to the water mass of the sample. As the transverse relaxation process occurs, the moisture
content of the meat sample is obtained by estimating the functional relationship between the moisture mass
and the received signal amplitude of controls and samples.
5 Materials and apparatus
5.1 Meat samples, which should be fresh meat, with a temperature of 22 °C ± 2 °C.
5.2 Sharp knife, e.g. double bladed (spacing 1,0 cm), ceramic knife.
5.3 Nuclear magnetic tube (inner diameter 25 mm).
5.4 Analytical balance, capable of weighing the samples with an accuracy of 0,000 1 g.
5.5 LF-NMR instrument, a universal LF-NMR analyser shall be used. The chamber should accommodate
the test sample. The field strength should be approximately 0,5 T to 1,0 T. The spectrometer frequency
should be approximately 20 MHz to 23 MHz. The ambient temperature inside the instrument should be
approximately 32 °C to 35 °C.
6 Preparation of sample
6.1 Preparation of testing sample
Visible skin, connective tissue and fat shall be removed. The meat shall be cut into 1 cm thick pieces along
the natural direction of muscle fibre with a double-bladed knife. The meat pieces shall be further cut into
1 cm × 1 cm × 2 cm meat cuboids with a ceramic knife. At least three meat cuboids shall be prepared for each
sample. Visible connective tissue, blood vessels and other defects shall be avoided in the process of cutting
the meat samples.
6.2 Preparation of standard sample
See Annex A.
7 Low-field nuclear magnetic resonance determination
7.1 General parameters
The sequences of FID and CPMG, which have been widely recognized in the field of nuclear magnetic
resonance testing, shall be selected. The appropriate parameters for calibration and determination shall

be selected from a meat moisture nuclear magnetic test sequence database. The parameters can be set
according to the actual situation of the sample to ensure complete signal attenuation.
7.2 Calibration parameters setting
The instrument shall be calibrated using the sequences of FID to automatically find the centre frequency
and pulse width.
Calibration parameter settings as follows:
— sampling bandwidth: SW = approximately 100 kHz to 200 kHz;
— spectrometer frequency: SF = approximately 20 MHz to 24 MHz;
— regulate first data: RFD = approximately 0,002 ms to 0,5 ms (should be modified in conjunction with SW,
and it is recommended to have an RFD of 0,08 ms at SW = 100 kHz);
— time wait: TW = approximately 1 000 ms to 4 000 ms (long enough to ensure complete echo);
— regulate analogue gain 1: RG1 = 10 db to 20 db;
— regulate digital gain 1: DRG1 = 3;
— pre-amp regulate gain: PRG = 0,1,2,3 (it is generally recommended to be 0 or 1 to avoid excessive gain,
while if the signal is weak, it can be increased appropriately);
n
— number sampling: NS = 2 ;
— data radius: DR = 1.
7.3 Determination parameters setting
The sequences of CPMG shall be selected for determination parameters settings.
Determination parameters settings:
— sampling bandwidth: SW = approximately 100 kHz to 200 kHz;
— spectrometer frequency: SF = approximately 20 MHz to 24 MHz;
— regulate first data: RFD = approximately 0,002 ms to 0,5 ms (should be modified in conjunction with SW,
and it is recommended to have an RFD of 0,08 ms at SW = 100 kHz);
— time wait: TW = approximately 4 000 ms to 8 000 ms (long enough to ensure complete echo);
— regulate analogue gain 1: RG1 = approximately 10 db to 20 db;
— time data: TD = 1 024;
— regulate digital gain 1: DRG1 = 3;
— pre-amp regulate gain: PRG = 0,1,2,3 (it is generally recommended to be 0 or 1 to avoid excessive gain,
while if the signal is weak, it can be increased appropriately);
n
— number sampling: NS = 2 ;
— data radius: DR = 1;
— echo time: TE = approximately 0,2 ms to 0,6 ms (there are slight differences in different types of raw
meat and different parts of the meat, and it is recommended to use 0,3 ms for pork, 0,5 ms for beef and
0,2 ms to 0,3 ms for chicken);

— echo number: NECH = approximately 2 000 to 5 000 (the value of NECH*TE is horizontal ordinate value
of the relaxation spectrum, and it is recommended that the decaying area of the relaxation spectrum be
approximately 1/3 to 2/3 of the total relaxation time).
7.4 Determination of blank substrate
The empty sample tube shall be put into the sample measuring chamber of the NMR instrument, and then the
test shall be conducted according to the determination parameters setting in 7.3 to obtain blank substrate signal.
7.5 Determination of testing sample
The testing samples after preparation (see 6.1) shall be put into the measuring tubes and calibrated to
22 °C prior to putting into the sample measuring chamber of the NMR instrument to collect LF-NMR signals
according to the determination parameters setting in 7.3 (one rectangular specimen is placed per tube).
Then the peak areas of T , T , and T are obtained by deducting the blank substrate signal (see 7.4).
2b 21 22
7.6 Determination of standard sample and establishment of standard curve
The standard freeze-dried meat sample shall be put into nuclear magnetic tube, and then shall be put into
the sample measuring chamber of the nuclear magnetic instrument to collect basic data. Then water shall
be added by 1 %,5 %,10 %,30 %,50 % and 70 % (no less than five repeats for each group) on the basis of
the meat's mass. After 30 min, the meat samples with different water contents shall be put into the nuclear
magnetic tubes, then into the sample measuring chamber for data collection (see Annex A) and then the
standard curve shall be created.
8 Data processing and moisture content calculation
8.1 Data processing
The nuclear magnetic signals of standard and testing samples shall be arranged according to X as sampling
time (ms) and Y as signal intensity to obtain the T relaxation inversion curve from relaxation attenuation
curve (CPMG curve) of continuous sample distribution. The method used to create the inversion curve is
SIRT (simultaneous iterative-reconstruction techniques). According to the transverse relaxation time of the
spectrum peak, it can be divided into:
— T = approximately 1 ms to 10 ms is bound water;
2b
— T = approximately 10 ms to 100 ms is immobilized water;
— T ≥ 100 ms is free water.
According to the corresponding inversion curve of water, the corresponding nuclear magnetic signals are
calculated respectively, including A (bound water peak area), A (immobilized water peak area) and A
2b 21 22
(free water peak area).
8.2 Standard curve fitting
Standard samples shall be tested according to the parameter set in 6.1, and the actual added water mass
shall be denoted as (m , m , .). The sum of inversion peak areas of three kinds of water (bound water,
1 2
immobilized water and free water) in N standard samples shall be recorded as S , S , ., respectively. The
1 2
linear model between moisture mass and nuclear magnetic signal intensity (sum of peak areas) shall be
established as shown by Formula (1):
Y = K × X + B (1)
where
X is the moisture mass (g);
K is the fitting slope;
B is the fitting intercept;
Y is the nuclear magnetic signal intensity (sum of peak areas) in the sample inversion curve.
8.3 Expression of results
The mass of the meat sample to be measured shall be recorded as M, and the test shall be carried out
according to the same parameters and procedures of the standard sample in 7.3. The T relaxation signal
intensity of the samples (the sum of the area of the inversion curve) shall be obtained and recorded as S. Then
the calculation of the moisture content (C) in the meat sample shall be calculated as shown by Formula (2):
()S
...