Assessment of Digestion Methods to Assist Mineral Analysis of Purple Corn, Quinoa, Amaranth and Buckwheat by ICP-OES

Nascimento, Ana Cláudia; Santiago, Susana; Santos, Mariana; Coelho, Inês; Gueifão, Sandra; Castanheira, Isabel; Samman, Norma; Calhau, Maria Antónia

http://hdl.handle.net/10400.18/1776

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ASSESSMENT OF DIGESTION METHODS TO ASSIST MINERAL ANALYSIS OF PURPLE CORN, QUINOA, AMARANTH AND BUCKWHEAT BY ICP-OES.pdf		792.59 KB	Adobe PDF	Download

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Authors

Nascimento, Ana Cláudia

Calhau, Maria Antónia

Abstract(s)

Purple corn (Zea mays L.), quinoa (Chenopodium Quinoa) and amaranth (Amaranthus caudatus) are a cereal and pseudocereals of Andean origin, largely consumed in North of Argentina. Buckwheat (Fagopyrum esculentum) is a pseudocereal with an important role in food diets around the world, especially in Asia and Eastern Europe. They gained increasing attention of scientific community, specially due to their high nutritional value and health benefits. Mineral concentrations in cereals and pseudocereals can differ with genotype, type of soil, fertilizer application, region’s mineral composition and treatments applied, that can even cause the loss of some minerals. Analytical values must be obtained by applying high quality criteria, such as criteria on sample handling, appropriate sample preparation and subsequent analytical method and, an effective internal and external quality control program. Inductively Couple Plasma Atomic Emission Spectrometry – ICP-OES is a high specific technique which allows a rapid and simultaneous multi-elemental analysis of several elements, in a numerous and wide scale of sample matrices, with good detection limits. A previous sample decomposition through its dissolution is required which can be undertaken by different methods, namely microwave digestion, dry-ashing, wet digestion. The destruction of organic matter is a slow step of overall analytical process largely dependent on the content of major components. The purpose of this work was to compare the performances of microwave and dry-ashing digestion procedures, including the optimization of microwave conditions to assist ICP-OES analysis. The optimized digestion method was applied on determination, of copper, manganese, iron, zinc, magnesium, calcium, phosphorus, sodium and potassium contents in purple corn, quinoa, amaranth, buckwheat and rice. Samples were dry ashed within platinum capsules in a furnace at 470 ºC during 40 h and microwave digested using a closed-vessel system digestion with a mixture of concentrated acid nitric, hydrogen peroxide and deionised water. The accuracy of analytical procedure was verified by analyzing a NIST 1548a reference material. Mineral profiles of purple corn, pseudocereals and rice were compared. Copper ranged from 0.07 mg/100g (rice) to 0.59 mg/100g (quinoa), manganese ranged from 0.64 mg/100g (purple corn) to 1.73 mg/100g (quinoa), iron ranged from 0.2 mg/100g (rice) to 8.8 mg/100g (amaranth), zinc ranged from 1 mg/100g (rice) to 5.1 mg/100g (amaranth), magnesium ranged from 27 mg/100g (rice) to 211 mg/100g (amaranth), calcium ranged from < 10 mg/100g (rice) to 154 mg/100g (amaranth), phosphorus ranged from 105 mg/100g (rice) to 480 mg/100g (amaranth), potassium ranged from 90 mg/100g (rice) to 587 mg/100g (quinoa). By comparing purple corn and pseudocereals with rice, pseudocereals presented the highest mineral content as expected. Also, for almost all minerals, purple corn showed higher mineral amounts than rice. These results showed that purple corn and pseudocereals understudy can be added to diets, with already known improved nutritional benefits. Statistically there was no evidence that the two different digestion methods applied have influenced final results, as P value was considered to be not significant (P > 0.05). However, microwave digestion enabled a more effective control of contamination or losses than dry-ashing, with less time consuming dispended.