The connection between buckwheat grain quality and the changes of the acid number of fat (AN) and grain acidity after eight months of storage has been investigated. Parameters of buckwheat with different content of moisture, germinated grains, and spoiled grains were determined. The studies performed have shown that oxidative damage to buckwheat grain increases concomitantly to the increase of humidity and content of germinated and spoiled seeds. All three defects of grain (increased humidity and increased content of germinated and spoiled seeds) accelerate the hydrolysis of grain lipids, and this leads to an increase of the acid number of fat. AN can be considered an indicator of grain freshness and should be introduced as an indicator of buckwheat quality for inward inspection of grain.
Acidity, acid number of fat, spoiled grain, sprouted grains, humidity, buckwheat
INTRODUCTION
Buckwheat is the second most popular grain (after rice) on the Russian market. It accounts for over 20% of total consumption. All buckwheat on the Russian market is produced domestically.
Buckwheat (Fagopyrum esculentum Moench.) is the most common cereal crop in the Altai region: in 2012, buckwheat cultivation area occupied more than 420 thousand hectares in this region, this amounting to almost half of the total cultivation area of buckwheat in Russia. Altai region ranks first in the production of buckwheat in Russia. Grain from this region is supplied to all regions of Russia, and the volume of production amounted to 119 thousand tons in 2012 [1].
However, deterioration of the quality of incoming grain was observed during the recent years. Operational experience at OAO “Biiskii elevator” showed that the harvested buckwheat grain often remained in floor storage for several months prior to the post-harvest treatment and contained large amounts of moisture, spoiled, and sprouted grains upon submission for processing [2].
This is due to the deterioration of farming conditions and standards and the lack of post-harvest processing resulting in spoilage of grain and changes in its technological properties [3, 4].
Quality of the raw grain has a considerable effect on the storage ability of buckwheat. Deterioration of grain quality due to adverse environmental influences resulting in germination, spoilage, or frost damage, decreases the storage ability of the grain and makes the cereals produced from this grain more prone to spoilage upon storage.
In contrast to grain, which is alive and therefore capable of active resistance to various adverse influences, cereal is more vulnerable to microorganisms, moisture and heat, and therefore it becomes spoiled much easier and faster than grain. Biochemical processes occurring during storage of cereals are primarily manifested as lipid changes.
The content of lipids in buckwheat reportedly varies from 1.5 to 4.0 % [5], being maximal in the embryo (7–14 %) and minimal in the shell (0.4–0.9 %) [6]. Analysis of the neutral lipid fraction revealed the predomination of palmitic (16:0), oleic (18:1), and linolenic acid (18:2) residues in the triglycerides (16, 42, and 32%, respectively) [7]. The rate of oxidation for linolenic acid is twice higher than that for oleic acid, and 20 times higher than that for palmitic acid [8]. Lipid oxidation impairs the organoleptic characteristics of grain.
Rancidification is caused by the hydrolysis of lipids; the extent of this process depends on such parameters as grain humidity and the content of sprouted and spoiled grains, in which the process of hydrolysis had already started. Organoleptic detection of the beginning of cereal spoilage is impossible, since distinctive and easily identifiable changes in appearance and odor do not occur during the initial stage. Measurements of the acid number of fat (AN) reported by L.G. Priezzheva included the investigation of rice groats, millet, peeled rye flour, and top grade wheat flour; changes in the AN during the guaranteed shelf life of Gercules oat flakes were reported in [9].
The aim of the present work was to investigate the effect of humidity and the proportion of sprouted and spoiled buckwheat grains on the changes of acid number (AN) of the fat and grain acidity.
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