Laboratory grain analysis

Like any agricultural product, grain has its own quality characteristics, which determine how suitable it is for human use. These parameters are approved by GOST and are evaluated in special laboratories. Analysis of grain allows you to determine the quality, nutritional value, cost, safety and scope of use of a particular batch or variety.

The test results depend on three components:

• genetic characteristics of the crop with which the crop was harvested;
• growing conditions and transportation technology;
• storage.

The approved state quality assessment unit is a batch from which samples are taken for analysis.

Key analysis parameters

The parameters determined by laboratory analysis of grain are divided into 3 large groups:

• quality indicators - a set of physicochemical and biological properties characterizing the degree of usefulness and suitability of grain for technical and agricultural use;
• safety indicators - evaluate the presence of chemical impurities harmful to health, characterize the environmental friendliness of grain;
• GMO content (genetically modified samples).

The first group is the most extensive and is a mandatory component of the verification of grain lots. The quality assessment includes 2 types of indicators of grain analysis:

• organoleptic - are evaluated using the human senses;
• laboratory or physico-chemical - are determined using specific techniques and technical equipment.

Among the laboratory parameters, there are basic (mandatory for a particular culture) and additional. Each grain quality characteristic has a special name and determination method.

For wheat, grains for gluten and protein content are additionally analyzed.

Evaluation of grain quality is an integral part of the control of agricultural products and forms the basis of scientific research of the crop, which accompany the cultivation of new varieties or study the influence of various environmental factors on grain plants (fertilizers, soils, pests, phytohormones, etc.).

Additional parameters of the analysis of grain quality include the chemical composition, enzyme activity, the content of microorganisms, etc.

Features of the analysis of sowing grain

The abundance of the crop largely depends on the quality of the sown grain. The key characteristics are size (the larger the seed, the better the growth will go), purity (the absence of weed impurities and parasites of the culture) and the results of germination analysis.

For the analysis of grain for sowing qualities, 3 average samples are selected from the batch by the quartration method, which are used to determine different indicators:

• sample 1 - purity, germination, weight of 1000 seeds;
• sample 2 - moisture and pest infestation;
• sample 3 - the degree of damage to seeds by diseases.

Based on the results of the analysis, a conclusion is made about the sowing qualities of the seeds, which is included in the relevant inspection document.

Germination is determined by placing 100 grains in suitable conditions for germination for 3 days. At the same time, the number and uniformity of seedlings are evaluated. To quickly identify dead grains, the Lecon method is effective, which gives a result in a few hours. Living grains are determined by the color change that occurs when oxygen is absorbed from a solution of tetrazolium salt. In dead seeds, breathing is absent.

Organoleptic assessment

The main organoleptic indicators are color, luster, taste and smell, on the basis of which they conclude that the grain party is high-quality and fresh. The color should be uniform, the surface of the seeds should be smooth and shiny. The presence of extraneous odors (not characteristic of the culture) indicates corruption or a violation of storage technology.

On the eye are also evaluated:

• shape and size;
• party uniformity;
• weed;
• shell condition.

The color, smell and taste of the grains are checked for compliance with a particular biological variety. Organoleptic analysis is superficial and approximate, but can reveal serious abnormalities. The parameters of the test sample are compared with the standards available in the laboratory.

Assessment of weeds and infection

Impurities are divided into 2 large groups: grain and weed. The latter is divided into 4 types:

• mineral - particles of inorganic nature (pebbles, sand, dust, pebbles, etc.);
• organic - third-party particles of organic origin, mostly vegetable (pieces of spikelets, leaves, etc.);
• weed - seeds of foreign cultures;
• harmful - fruits or seeds, which contain substances that are poisonous to humans.

Grain impurity is called defective (different from normal) seeds of the batch. They can also be used for technological processing, although they give a lower quality product. To reduce the content of trash impurities, the grain is cleaned on production machines.

The weight of medium samples for analysis of grain weeds is 20-25 grams. The proportion of impurities is determined as a percentage.

Infection can be overt and covert. In the first case, the pests are separated from the sample using a sieve, and in the second case, each grain is cracked and inspected (sample size - 50).

Chemical analysis

This analysis belongs to the category of supplementary and involves the study of the chemical composition of grain. In this case, the percentage of the following components is determined:

• proteins;
• lipids;
• carbohydrates (including starch and fiber);
• vitamins;
• minerals (macro-, micro- and ultramicroelements).

Chemical analysis of grain also includes the determination of ash.

These parameters show the nutritional value of a particular variety, and sometimes technical utility. For example, a large amount of lipids in sunflower seed indicates a high suitability of raw materials for oil production.

Identification of some constituents is a key quality factor. So, when analyzing wheat grains, the percentage of protein is necessarily determined. This indicator characterizes not only nutritional value, but also baking properties, as it correlates with vitreous and gluten quality.

Equipment

There are a huge number of instruments for analyzing grain, among which there are specialized (developed for laboratory assessment of grain production) and general. The latter include instruments for physical and chemical measurements, equipment for working with reagents.

The standard laboratory kit for grain analysis includes:

• high precision scales;
• weights;
• devices for determining the properties of gluten;
• watch glasses and petri dishes;
• sieves with cells of different diameters;
• porcelain stupas;
• desiccator;
• mill;
• moisture meters;
• a device for measuring temperature;
• laboratory glassware (flasks, bottles, etc.);
• drying chamber;
• chemical reagents.

Narrow-profile devices may also be present in the kit, for example, peeling devices, with the help of which they determine the filminess. The presence of metallomagnetic impurities is detected using milliteslameters.

Some instruments replace manual methods for determining certain parameters. For example, vitreous can be set using a diaphanoscope. Automation of grain analysis significantly reduces the subjective factor and saves time.

There are also complex analysis devices that replace the multi-stage process of determining various parameters, requiring a whole set of devices and reagents. However, the functionality of such devices is still limited.

Currently, the assessment of the quality of grain products is a combination of manual and automated methods for analyzing grain, the ratio of which is determined by the technical support of a particular laboratory and a set of verifiable indicators.

Moisture determination

Humidity is one of the key parameters of grain quality, which determines not only its nutritional value, but also storage conditions.

There are 2 ways to analyze grain moisture:

• using an electric drying cabinet (SES) - consists in drying a ground grain sample and comparing the weight before and after the procedure;
• using an electric moisture meter - determining the degree of humidity by electrical conductivity, a sample of grain is placed in the device under a press.

The second method is economical in time, but it is less accurate. In case of too high humidity (more than 17%), the test sample is pre-dried.

Depending on the percentage of water, 4 degrees of grain moisture are distinguished:

• dry (less than 14%);
• average dryness (14-15.5%);
• wet - (15.5-17%);
• raw - (more than 17%).

The percentages given are acceptable for main crops (rye, oats, wheat, etc.).

Humidity of more than 14% is considered increased and undesirable, since it leads to a decrease in the quality and germination of grain. Each culture has its own water content standards, developed taking into account the characteristics of the chemical composition of the seeds.

Film

Assessment of filminess includes 2 stages:

• counting the number of shells or films;
• determination of the percentage mass fraction of shells.

The second indicator is the most important. To determine it, the grains are first freed from the shells using a scrubber or manually, and then the croup and film mass are separately weighed. At the end, the weight of the purified and untreated samples is compared.

Glassy

The degree of transparency depends on the ratio of protein to starch. The higher the content of the latter, the more mealy (starchy) and cloudy the grain. Conversely, a large amount of protein increases the transparency of the seed. Therefore, the value of glassiness reflects the nutritional value and baking quality of the grain. In addition, this indicator is associated with the mechanical and structural properties of the endosperm. The higher the vitreous, the grain is stronger and requires more energy costs for grinding.

There are 2 methods for determining this parameter: manual and automated. In the first case, transparency is evaluated by eye or using a diaphanoscope. A sample of 100 grains is analyzed. Each seed is cut in half and determined in one of three vitreous groups:

• mealy;
• partially vitreous;
• vitreous.

The total number of grains from the last two categories is the total vitreous (only half the number of partially vitreous seeds is included). The check is carried out 2 times (the discrepancy between the results should not exceed 5%).

There are also automated diaphanoscopes that simultaneously determine the vitreous nature of seeds placed in a cuvette. Some devices do not even require preliminary cutting of grains.

Fall number

The fall number is an indirect indicator of the degree of germination, determined on the basis of the level of autolytic activity of the grain. The latter is the result of the action of the enzyme alpha-amylase, which breaks down the starch of endosperm to simple sugars, which are necessary for the development of the seed germ. Naturally, this leads to a significant decrease in baking quality.

Autolytic activity is determined using special equipment (Falling Number, IPHI, PPP, etc.). The method is based on enzymatic liquefaction (under the influence of alpha-amylase) of a flour suspension, gelatinized in a boiling water bath.

GOST grain analysis

All components of product analysis are strictly regulated and spelled out in the relevant standards. GOST contains quality standards, equipment requirements and methods for determining each indicator. The results of grain analysis are considered reliable only if they are obtained in accordance with established instructions.

According to GOST, classes of grain crops are determined, for each of which corresponding values ​​of quality parameters (the so-called restrictive norms) are prescribed. Soft wheat has 5 classes.

The class determines the nature of processing and use, storage features and market value of grain.

Express grain analysis using IR spectroscopy

Using infrared spectroscopy, you can quickly and accurately determine:

• humidity;
• protein and gluten content;
• the amount of starch;
• nature;
• density;
• oil content;
• ash content.

For the main parameters of grain analysis, the error does not exceed 0.3%.

The work of complex analyzers is based on diffuse reflection of light with a wavelength within the near infrared region. This significantly saves time (analysis of several parameters is carried out within a minute). The main disadvantage of the express method is the high cost of equipment.

Gluten content and quality analysis

Gluten is a dense and viscous rubbery mass formed after leaching of water-soluble substances, starch and fiber from a crushed grain. The composition of gluten includes:

• gliadin and glutenin proteins (from 80 to 90% dry matter);
• complex carbohydrates (starch and fiber);
• simple carbohydrates;
• lipids;
• minerals.

Wheat contains from 7 to 50% crude gluten. Rates above 28% are considered high.

In addition to the percentage in the analysis of grain for gluten, four parameters are evaluated:

• elasticity;
• elongation;
• elasticity;
• viscosity.

The most important indicator is the elasticity, which characterizes the baking properties of wheat. To determine this parameter, a gluten deformation index (IDC) device is used. The sample for analysis is a ball, rolled up from 4 grams of the test substance and previously soaked in water for 15 minutes.

The quality of gluten is a hereditary characteristic of a particular variety and does not depend on growing conditions.

Analysis of wheat grains for gluten content is carried out strictly in accordance with the standard, since the slightest error can greatly distort the result. The essence of the method consists in washing the analyte out of the dough mixed with wheat meal (crushed and sifted grains). Washing is carried out under a weak water stream with a temperature of + 16-20 ° C.