Agriculture Reference
In-Depth Information
way for the oxidation of lipid stores and, conse-
quently, deterioration in the quality of the prod-
uct, as the triglycerides are altered. Whether
the seed is destined to be sown or sold as a
foodstuff, the quality demands are similar. The
quality control standards require close control
of all stages of harvesting, drying, storage and
conditioning. Evaluation of the quality of the
hemp seed can be established simply by meas-
uring germination following storage for a few
months at ambient temperature.
A more objective criterion that is used as a
basis for commercial transactions is the meas-
urement of the acidity index (oleic acidity, OA)
and/or the oil peroxide index of the sample to
be evaluated. The maximum oleic acidity per-
mitted for alimentary oils is 2% (measured on
the final product). The minimal OA of hemp
seed that has been optimally collected is already
0.3%. Drying will then increase the index by
0.1% and storage will increase it by 0.05% per
month. The objective is to commercialize a
hemp seed with an OA below 1%. In com-
merce, this is the value commonly accepted
as determining that hemp seed is food grade
(Box 6.1).
Hemp, though it has been cultivated for
thousands of years, has preserved the charac-
teristics of wild plants: not all the seeds reach
maturity at the same time. We will not revisit
the traditional methods of harvesting seeds by
hand, though these are still used in certain
areas to collect seedstock for resowing.
An antiquated harvest method that would
fall between harvesting manually and modern
practices employed two stages. First, hemp
was cut and placed in sheafs according to a
characteristic pattern that regrouped and
crossed the heads of the plants in the centre of
the sheaf. Reaping was undertaken just as
the first seeds arrived at maturity. A period of
1 week to 10 days was then required before
the seeds could be collected. In this way, the
hemp seed continued to mature while the hurds
were drying. The major inconvenience of this
technique lies in its vulnerability to climatic
conditions (in 1984, for example, a lot of hemp
seed actually germinated within the sheafs).
The development of combine harvesters
for hemp dates back to the 1980s and the
arrival of axial flow combine harvesters that
used the principle of centrifugal seed collec-
tion. Today, the majority of combine har-
vesters can be adapted for the harvesting of
hemp (Fig. 6.2). Given the amount of material
that must pass through the machine, only the
heads are cut and combined, with the cutting
undertaken as high as possible on the stalk.
This capability represents significant progress,
as the farmer is now much less dependent
on weather conditions. The farmer must,
however, determine the optimal time for
harvest. This is a compromise between the
yield of mature hemp seed and the weather
conditions, which, were they to deteriorate,
could result in shelling at best and germination
Box 6.1.
Sampling method for the validation of the quality of oleic acid in hemp seed.
Each batch received at the silos is sampled in order to determine the acidity index and oleic index. The
acidity index reflects the extent of fatty acid hydrolysis. These characteristics are useful indicators of
the quality of raw (or virgin) oil and allow the refining process and its efficacy to be monitored carefully
(measure of residual acidity).
Two methods are used to verify these indices: the titration method and the potentiometer method.
These measurements concern all the fatty substances, whether they are of plant or animal origin, as
determined by the European standard NF EN ISO 660.199 (approved in France in July 1999).
The sampling and tests conducted at the silos allow the peroxide index to be verified. This index
reflects the formation of primary compounds of oxidation. This test is easy to conduct and is therefore
widely used in units that do not possess sophisticated laboratory equipment.
Finally, it should be noted that in order to comply with alimentary standards, the oleic acidity level
must be below 2% where the product is intended for human consumption. In concrete terms, taking into
account the manipulations that the product undergoes after harvesting and in the factory, the processor
will ensure that this level stays below 1%.
In this way, the end product can be offered for human consumption.