Studies on tender wheatgrass: estimation of elemental content, bioaccessibility of essential elements and antioxidant activity

Tender wheatgrass is being consumed by human beings in juice form or as it is due to its antioxidant potential and medicinal value. Systematic studies were carried out to (i) estimate elemental profiles as a function of growth period and conditions, bioaccessibility of different elements and the antioxidant potential of the tender wheatgrass, (ii) determine the optimum growth period for obtaining maximum benefit and (iii) examine the possible correlation between antioxidant potential and mineral content. Wheatgrass was grown in four different conditions namely (i) tap water, (ii) tap water with nutrients, (iii) soil and tap water and (iv) soil with nutrient solution. The studies were carried out on the wheatgrass of 5-20 days old. For comparison with laboratory grown wheatgrass, a set of commercially available wheatgrass tablets and wheat seeds were also studied. Instrumental neutron activation analysis (INAA) was used for concentration determination of elements in the wheatgrass, wheat seeds and wheatgrass tablets. A total of 15 elements like Na, K, Ca, Mg, Mn, Br, Fe and Zn were determined in the samples of shoots and roots of tender wheatgrass. A comparison with the recommended dietary allowance (RDA) of different essential elements with that in tender wheatgrass revealed that wheatgrass is a good source of minerals for health benefits rather than a food supplement. Bioaccessible fractions of various elements were estimated by a chemical NAA method by subjecting the samples to in vitro gastric and gastro-intestinal digestion followed by NAA. The bioaccessibility concentrations by both the measurements were in the range of 9-60%. It was found that bioaccessibility of the elements studied was the highest from fresh wheatgrass and the lowest from wheat seeds. Accuracy of the NAA method was evaluated by analyzing two biological reference materials, SRM 1573a (Tomato leaves) from NIST, USA and ICHTJ CTA-vtl-2 (Tobacco leaves) from INCT, Poland. The antioxidant activity of wheatgrass at different levels of protection was studied. The methods employed include FRAP (ferric reducing antioxidant power), ABTS (2,2'-azobis-3-ethylbenzthiazoline-6-sulfonic acid) and DPPH (1,1'-diphenyl-2-picrylhydrazyl) assays. Lipid peroxidation and oxygen radical absorbance capacity (ORAC) were also used. Antioxidant potential for the wheatgrass grown in all the conditions reached optimum values around 6 to 10 days and was also found higher than the wheatgrass tablet and wheat seeds. These studies suggested that the mineral contents, bioaccessibility of the elements and antioxidant potential were optimum around 6-10 day old wheatgrass. (author)