The Measurement Uncertainty Evaluation of proximate and elemental composition of Wheat Flour

Abstract

: Wheat is the main cereal crop in India. It is valuable commodity on a global market as one of the most consumed cereals because of its nutritional value and cost effectiveness. Wheat grain is today the most important source of food on earth. It contains 75–80% carbohydrates, 9–18% protein, fiber, many vitamins (especially B vitamins), calcium, iron and many macro- and micro-nutrients. Its world trade is higher than all the other crops combined. Therefore, it become important to analyze wheat for its quality. There are different parameters to check the quality of wheat flour such as proximate composition and elemental composition. The sample is analyzed for proximate composition in accordance with IS 1155(1968) and for elemental composition with reference of NIST standards. Proximate composition such as moisture, gluten, ash, acidity analyzed in accordance with Indian Standard. All of these parameters decide the quality of the wheat flour sample. Two zones of sample have been analyzed for which results are shown in Table1. Sample A is from Madhya pardesh and sample B is from Haryana.

S.No.

Parameter

Sample A

Sample B

   1

Moisture Content

9.83 ± 0.1966

11.13 ± 0.11

   2

Ash Content

1.81 ± 0.0034

1.80 ± 0.02

   3

Acid Soluble Ash

0.05 ± 0.002

0.1 ± 0.016

   4

Gluten

8.28 ± 0.03

10.37 ± 0.06

   5

Alcoholic Acidity

0.172

0.123

Table 1

 Moisture content is determined by keeping sample in moisture analyzer until it gets a constant weight. It is important parameter to check the grain quality and storability. High moisture content holds bacteria and molds. The result for moisture is less than 14 % which means that samples are within the permissible limits for moisture. Ash test is done by igniting the samples at very high temperature. The result shows that ash content is less than 2.5% which means that ash is also under the permissible limits. Ash determines the amount and type of mineral present in the flour. It also indicates milling performance by indirectly revealing the amount of bran contamination in flour.  Acid insoluble ash value is determined by digesting ash in conc. HCl and its value must be less than 0.1% according to IS 1155(1968). Result shows that sampleA sample is within the acid insoluble ash limits of IS standard but not sample B. Acid insoluble ash indicates siliceous impurities which affects the quality of flour. Samples are analysed for its gluten content by mixing wheat flour with water to make a dough and when this dough is washed thoroughly to remove all the starch, gluten is left behind. It determines the strength and elasticity of the dough and also the protein present in the flour. Results shows that sample B has more protein content than sample A. For both of samples, alcoholic acidity is determined which indicates the acidity of germ oil in the flour. Acidity is greater than 0.1% for both of the samples. Therefore, it is not in the limits of IS standards. The multi-element contents of wheat grain are the result of many factors such as agricultural practices, genetic factors, soil characteristics, seasonal influences and contamination from anthropogenic sources. Therefore, it becomes important to analyze wheat for its elemental composition. The analytical technique employed is Inductively Coupled Plasma Optical Emission Spectrometry (ICP OES). The method validation (including digestion and determination) was performed using a certified reference material of wheat flour furnished by National Institute of Standards & Technology (NIST). The samples were digested using nitric acid and hydrogen peroxide in open system. The results obtained are described in Table 2. The elements determined were: mercury, lead, arsenic, copper, iron.

Elements

Hg

Pb

As

Fe

Cu

Conc.(mg/Kg)

0.00036 ±7.7 ×10^-6

0.0096 ± 1.9 ×10^-5

< -0.008 ± 1.6 ×10^-6

10.04 ± 0.2

2.1±0.01

                                                          Table 2

Inductively coupled plasma optical emission spectrometry (ICP OES) is employed for metal and metalloid determination in food due to the wide linear response, low limits of detection (LODs), multi elemental capability, fast analysis, good precision, and accuracy. The accuracy of the method used for determination of the elements in wheat flour samples was confirmed by analysis of certified reference material, furnished by National Institute of Standard and Technology (Gaithersburg, MD, USA), wheat flour NIST 1567a.