Advances in the Determination of the Groat Content in the Oat Kernels through NIRS
Agronomic Engineer: Elena R. Molfese
Barrow Integrated Experimental Station (M.A.A.-I.N.T.A.)
Agreement. C.C. 216 - Tel./FAX 54-0983-31081 (7500)
Tres Arroyos - Province of Buenos Aires

When we talk about the quality of oats, there are various aspects that must be taken into account:  agronomical quality, nutritional quality, milling quality and the quality required by the consumers.  The prerequisites will be different for each one of these cases.

The characteristics that the industry takes into account for the milling oats are the following: size of the kernel, weight of a thousand kernels, relationship of kernel to husk, absence of tertiary kernels, acidity, protein percentage, adherence of husk/groat, grain colour, and pubescence of thegroat.

The industry prefers oats with higher protein and groat content.  A high percentage of husk means a serious obstacle for the industries. The quality parameters established in the Barrow Station Laboratory are: hectolitric weight, grain size, the weight of a thousand grains, the absence of tertiary kernels, protein and groat percentage.

The first objective that the industry has on buying oats is to make sure this can produce a high quality end product. The second objective is to have the kind of oats that has good milling yield.

When we talk about quality in the milling industry of the oats, we refer basically to the milling yield, which will be affected by the percentage of groat, hectolitric weight, and the weight of 1000grains. These are characteristics which are affected mostly by inheritance but also by the environment and storage conditions.

The relationship between groat and husk and the chemical composition of the grain are topics which have received the most attention for improvement during the last few years. Traditionally the industries have paid more attention to protein content in the kernel than to other chemical components.  According to some authors, there is enough genetical diversity in the oat cultivars to improve these components.

An understanding of the relationship between groat and husk will have a good chance of successs in improving milling yield. The husk has low energy and nutritious value.  Reducing its content will be beneficial for both human consumption and animal feed.  The husk has a hard consistency, no taste, and is not palatable. Its principal function is to maintain the ripening karyopsis  free from fungi and to protect it from the environment. It is desirable that a variety of oats with a low content of husk but with similar kernel yield will soon be developed.  However, there are studies which show negative correlation between groat percentage and grain yield.  Results of these studies suggest not to put so much pressure in making the selection of the earliest generations for this characteristic.  The desirable values reported in the literature range between 68 and 72% of groat, reaching in some environments to 78-80%. These percentages can be adversely affected by diseases (royas), and by adverse climatic conditions as well as by poor handling .


In our Laboratory we have made several attempts to determine the percentage of groat in samples coming from advanced material (F7 onward).  During 1978 to 1981, we evaluated the groat percentage in the oat samples for each year by separating the husks from the oat kernels in a boiling solution of sodium hypochlorite. The implementation of this method was very slow, because we had to work with toxic substances. The average percentage of groat in 352 samples analysed using this method was 65.2.  The average percentage of groat protein was 18.7%.  Graph 1 shows the distribution of these values.

Graph Nº1: Distribution of the protein and  groat percentages, crop 1979 to 1981.


Due to the many inconveniences, the sodium hypochlorite method was abandoned. From 1986 to 1990 the Quaker Laboratory in Buenos Aires made the analyses. The percentage of groat in the samples sent was about 62.6%. Trying to find a quick non-polluting  and economic method, they began in 1993 to deploy NIRS technology, using an Infralyzer 400 (Technicon,New York), to determine the content of groat in the oat grains. This technique has been used in our laboratory for several years to determine protein and moisture content in wheat with very good results.

To calibrate the NIR instrument, we used 44 samples taken from 6 trials of advanced material. The groat contents of the samples varied from 58.6 to 77.2%. We alsoe dehusked the seed samples manually. The reflected energy values, measured at 19 different wave lengths in the infrared spectrum (log1/R), were red  in the Infralyzer.  For selection of the variables we used the statistical analysis Stepwise (SAS). We obtained an equation of calibration for the instrument in which only
six of the considered variables intervened. The model resulted with a R²=0,88.


The results obtained during the 94/95 and 95/96 crops were very satisfactory with average values of groat percentages of 71% and 69.7% respectively.  The level of protein content in the grain was also determined in each case. The average value ranged from 16.3% to 15.1%. The total number of samples analysed was close to the 280.  The results are shown  graphs 2 and 3.

Graph Nº2: Distribution of the protein and groat percentages, crop 1994/95.

Graph Nº3: Distribution of the protein and groat percentages, crop 1995/96.

At the beginning of each year, we took random samples and determined the percentages of groat by NIR and also by dehusking the grains manually.

During the 96/97 period, we repeated the methodology of the calibration control.  As we began to process the samples, we found that a great number of kernels were discolored grains.  In several cases, the kernels were also shown to have low percentages of groat (manually determined).  Poor weather conditions (due to excessive rainfall and high wind) had adversely affected the experimental plots at the time of harvest.

As the calibration range for the groat percentage was not wide enough to accommodate weathered samples. some of the samples were completely out of the spectral range.  Several NIR tests gave groat values, which were completely atypical. The differences between these values and results from other crop years were very noticeable.

We decided that the NIR unit had to be recalibrated; 32 items which were more representative for the 1996/97 crop year were included in the calibration.  This recalibration resulted in increasing the range of the percentage of the groat, from 52,8% till 77,2%. We used the same statistical  procedure as in the previous tests.  The new calibration equation  took 7 of the considered variables (log1/R); all of them were significant up to the 0.15 level.  The model resulted with a R²=0.81.

The 1996/97 oat samples were retested after recalibration of the NIR unit.  We obtained average values of  67.1% for groat and 15.7% for protein for all the samples that we tested.  We found that the oat samples in these tests had lower groat and protein contents than those from the other crop years.  Results of the oat samples from the 1996/97 crop year are shown in Graph 4.
Graph 4: Distribution of the protein and groat percentages in the crop year1996/97.


We confirmed the need of performing the calibration annually, by comparing the values obtained by manual peeling with the NIRS values.  The results were influenced by variations in the cultivation cycles. In the future we shall have to consider using a larger sample lot for calibration.  We should also include materials coming from other regions grown under different growing conditions. This will ensure a better coverage of most possible situations.  We also plan to determine how the different types of oats and how the size of the grains will influence groat percentage in future studies.


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