Effect of cooking and malting on the content and bioaccessibility of zinc and folates in quinoa (Chenopodium quinoa) and amaranth (Amaranthus sp.)
Authors: Castanheira Isabel Palmira , Motta Carla , Delgado Inês Margarida , Nascimento Ana Claudia , Matos Ana Sofia , Gonzales Gerard Bryan , Santos Mariana Coelho , Martins Carla , Assunção Ricardo , De Alvito Paula Cristina 
Published: November 2023

Zinc (Zn) is an essential dietary mineral which has been reported to also affect the metabolism of water‐soluble vitamins. Intestinal folate conjugase enzyme is zinc‐dependent, such that Zn deficiency tends to reduce absorption of polyglutamylfolates. Hence, it is important to investigate the co‐occurrence and bioaccessibility of Zn and folates in diets.

Our objective was to study the effect of cooking and malting processes on the content and bioaccessibility of five folate vitamers and Zn in quinoa and amaranth. Folates were determined using a trienzymatic extraction method followed by liquid chromatography‐mass spectrometry (LC‐MS/MS) while Zn content was determined by inductively coupled plasma – optical emission spectrometry (ICP‐OES). Bioaccessibility studies were performed according to the harmonized static in vitro digestion model.

Total folate content ranged between 123 – 268 μg / 100 g fresh weight in boiled and raw quinoa respectively whereas in amaranth, ranged between 87,3 – 272 μg / 100 g fresh weight in boiled and malted respectively. In both pseudocereals, 5‐methyltetrahydrofolate (5‐MTHF) represents the predominant form of folate. Zn content ranged from 0.98 – 3.22 mg / 100 g fresh weight in boiled and malted quinoa compared to 1.24 – 3.68 / 100 g fresh weight in boiled and raw amaranth respectively. The effects of different processing methods on the folate and Zn contents were analysed using Tukey Kramer multiple comparison test. According to our results, cooking and malting did not influence the content of total folates for quinoa whereas boiling significantly decreased (p < 0.001) the amount of total folates in amaranth. In contrary, malting significantly increased the total folate content of amaranth compared to raw (p < 0.001). Zn content was also generally not affected by the processing methods in quinoa and amaranth except for malted amaranth where a significant decrease (p < 0.001) was observed. The bioacessibility of 5‐MTHF is approximately 100% in quinoa and amaranth. However bioaccesibility of 10‐formyltetrahydrofolate differed depending on the food matrix: below 27% in boiled quinoa, 36% in steamed amaranth, 100% in malted quinoa and amaranth. Bioaccessibility of Zn on the other hand presents the lowest values in steamed amaranth and quinoa (23–37%) and the highest in malted amaranth (58%) and boiled quinoa (40%). These data suggest that cooking and processing affect the contents and bioaccessibility of folates and Zn. While it is important to consider the contents of folate and Zn in the raw materials, the cooking procedure should be taken into account when assessing actual dietary folate and Zn intake. This information is especially beneficial for people with special dietary needs, such as celiac disease patients.

Support or Funding Information

The work was supported by the project PROMETROFOOD proposal number 739568 ‐ research and innovation action Horizon 2020 EU Programme