पोषक तत्वों की गुणवत्ता बनाए रखने के लिए गेहूं कटाई की उपयुक्‍त अवस्‍था 

structure of wheat grainThe nutritional value of wheat is extremely important as it is the second most important staple food crop of India. The importance of wheat is mainly due to the fact that its grain can be ground into flour, semolina, etc., which form the basic ingredients of bread and other bakery products, as well as pastas, and thus it presents the main source of nutrients to the most of the world population. These end products of wheat are mainly dependent up on the nutritional quality of the wheat grains. The wheat grain (Fig. 1) contains 2-3% germ, 13-17% bran and 80-85% mealy endosperm. The wheat bran, is mainly rich in fiber (53%), vitamin B complex and minerals which are lost from the starchy endosperm during the first stage of milling. The endosperm mainly contains energy-yielding starch. The germ lies at one end of the grain which is rich in proteins (25%) and lipids (8-13%). The detailed nutritional profile of wheat is given in the table 1. Wheat is grown every where in India. It is of prime importance to preserve the nutritional quality of wheat grain by selecting proper stage of harvesting wheat.

 

Fig 1:The structure and nutritional composition of wheat grain

 Nutrient

Availability

Carbohydrate

1.

Total carbohydrate

72.5 g

2.

Dietary fiber

12.1 g

Protein

1.

Protein

13.6 g

Fats

1.

Total fat

1.8 g

2.

Saturated fatty acid

0.3 g

3.

Monounsaturated fatty acid

0.25 g

4.

Polyunsaturated fatty acid

0.75 g

5.

Omega-3-fatty acid

38 mg

6.

Omega-6-fatty acid

738 mg

Vitamins

1.

Vitamin A

91 IU

2.

Vitamin E

0.8 mg

3.

Thiamine (B1)

0.41 mg

4.

Riboflavin (B2)

0.25 mg

5.

Niacin (B3)

6.3 mg

6.

Pantothenic acid (B5)

1.0 mg

7.

Pyridoxine (B6)

0.3 mg

8.

Folate (B7)

44 (µg)

Minerals

1.

Calcium

34 mg

2.

Iron

3.9 mg

3.

Magnesium

138 mg

4.

Phosphorus

345.8 mg

5.

Potassium

405 mg

6.

Sodium

5 mg

7.

Zinc

2.9 mg

8.

Copper

0.4 mg

9.

Manganese

3.8 mg

10.

Selenium

70.6  µg

Others

1.

Water

10.25 g

2.

Energy

1420  kJ

3.

Ash

1.58 g

Table 1: Nutritional profile of wheat grains (amount /100g grain)

Effect of immature grain harvesting on wheat quality

There are several parameters which define the wheat quality viz. grain color, grain size, weight, hardness, grain protein, flour color, dough properties, sedimentation value, bread quality, biscuit quality etc. Almost all the wheat-based end products require a set of standard grain quality parameter. Any fluctuation in the standard parameters will lead to deterioration of grain quality and therefore end products. Harvesting wheat at premature stage as well as at over maturity stage leads to significant loss of nutritional quality including grain color, grain size, weight, hardness, grain protein, flour color, dough properties.  Therefore, for a maximum return, farmers have to identify the suitable stage of wheat harvesting.

What is physiological maturity of wheat?

The term physiological maturity is defined as the stage of maximum dry weight of the kernels, which indicate the readiness of the crop for harvest. This is an important stage, which determines yield potential of a cultivar with maximum nutritional composition.

Selecting suitable physiological maturity stage for what harvesting

There are numerous set parameters including visual parameters to identify the physiological maturity (stage of harvesting) of the wheat crop. Moisture percentage is not a good parameter to detect the physiological maturity because it depends on varieties and prevailing environments. About 20-40% moisture content is considered to prevail at physiological maturity. To determine physiological maturity, visual indicators are quick and easy to use. Among all visual indices, appearance of a dark layer of cells is the most accurate indicator, which varies with the crops.  For instance, it is seen at the base of the corn kernels (black layer) and along the crease of the wheat kernel (pigment strand). Although this pigment strand is the most accurate visual indicator of physiological maturity, it is not always the most useful as kernels in the same spike and especially different spikes reach physiological maturity at different times. In addition, loss of green color from the preduncle, kernel (including crease) and glumes is also used as visual indicators. In this, glumes at the bottom of the spike are the last to lose green color. The loss of green color from glumes is a good predictor of physiological maturity that is easily observed across the field. Complete loss of green color from the flag leaf could be used as an indicator of the commencement of rapid decrease in grain dry weight and final stage of grain filling which ends when the glumes have lost the whole of their green color. Complete loss of green color from glumes is a suitable stage for maximum grain recovery with highest grain quality.  Six weeks post anthesis (WPA) is a perfect stage for grain harvesting followed by air-drying to preserve maximum nutrients.

 


Authors:

Om Prakash Gupta*1, R.K. Gupta1 and I. Sharma2

1Quality and Basic Sciences, 2Project Director,

 Directorate of Wheat Research, Karnal-132001

*Corresponding author email: This email address is being protected from spambots. You need JavaScript enabled to view it.