Drought stress enhances nutritional and bioactive compounds, phenolic acids and antioxidant capacity of Amaranthus leafy vegetable

Abstract

Background: Bioactive compounds, vitamins, phenolic acids, flavonoids of A. tricolor are the sources of natural antioxidant that had a great importance for the food industry as these detoxify ROS in the human body. These natural antioxidants protect human from many diseases such as cancer, arthritis, emphysema, retinopathy, neuro-degenerative cardiovascular diseases, atherosclerosis and cataracts. Moreover, previous literature has shown that drought stress elevated bioactive compounds, vitamins, phenolics, flavonoids and antioxidant activity in many leafy vegetables. Hence, we study the nutritional and bioactive compounds, phenolic acids, flavonoids and antioxidant capacity of amaranth under drought stress for evaluation of the significant contribution of these compounds in the human diet.

Results: The genotype VA3 was assessed at four drought stress levels that significantly affected nutritional and bioactive compounds, phenolic acids, flavonoids and antioxidant capacity. Protein, ash, energy, dietary fiber, Ca, K, Cu, S, Mg, Mn, Mo, Na, B content, total carotenoids, TFC, vitamin C, TPC, TAC (DPPH), betacarotene, TAC (ABTS⁺), sixteen phenolic acids and flavonoids were remarkably increased with the severity of drought stress. At moderate and severe drought stress conditions, the increments of all these components were more preponderant. Trans-cinnamic acid was newly identified phenolic acid in A. tricolor. Salicylic acid, vanilic acid, gallic acid, chlorogenic acid, Trans-cinnamic acid, rutin, isoquercetin, m-coumaric acid and p-hydroxybenzoic acid were the most abundant phenolic compounds in this genotype.

Conclusions: In A. tricolor, drought stress enhanced the quantitative and qualitative improvement of nutritional and bioactive compounds, phenolic acids, flavonoids and antioxidants. Hence, farmers of semi-arid and dry areas of the world could be able to grow amaranth as a substitute crop.

Keywords: ABTS+; Amaranthus tricolor; Antioxidant activity; DPPH; Drought; Flavonoids; HPLC-UV; LC-MS-ESI; Nutritional and bioactive compounds; Phenolics.

Fig. 1

Changes of proximate compositions (g 100 g^− 1) at four drought levels: Control (100% FC), LDS (90% FC), MDS (60% FC), and SDS (30% FC) in a selected A. tricolor genotype; (n = 3), letters mentioned in the bars are significantly varied by DMRT (P < 0.01)

Fig. 2

Effect of proximate composition (g 100 g^− 1) (% to the value of control) at four drought levels: Control (100% FC), LDS (90% FC), MDS (60% FC), and SDS (30% FC) in a selected A. tricolor genotype

Fig. 3

Response of mineral content (Macro elements mg g^− 1) at four drought levels: Control (100% FC), LDS (90% FC), MDS (60% FC), and SDS (30% FC) in a selected A. tricolor genotype; (n = 3), letters mentioned in the bars are significantly varied by DMRT (P < 0.01)

Fig. 4

Impact of mineral content (Micro elements μg g^− 1) at four drought levels: Control (100% FC), LDS (90% FC), MDS (60% FC), and SDS (30% FC) in a selected A. tricolor genotype; (n = 3), letters mentioned in the bars are significantly varied by DMRT (P < 0.01)

Fig. 5

Assessment of mineral contents (Macro and microelements, mg g^− 1 and μg g^− 1, respectively) (% to the value of control) at four drought levels: Control (100% FC), LDS (90% FC), MDS (60% FC), and SDS (30% FC) in a selected A. tricolor genotype

Fig. 6

Influence of Leaf pigments at four drought levels: Control (100% FC), LDS (90% FC), MDS (60% FC), and SDS (30% FC) in a selected A. tricolor genotype; Betacyanin (ng g^− 1 FW), Betaxanthin (ng g^− 1 FW), Betalain (ng g^− 1 FW), Chlorophyll a (μg g^− 1 FW), Chlorophyll b (μg g^− 1 FW), Chlorophyll ab (μg g^− 1 FW), Total carotenoids (mg 100 g^− 1 FW); (n = 3), letters mentioned in the bars are significantly varied by DMRT (P < 0.01)

Fig. 7

Comparison of leaf pigments (% to the value of control) at four drought levels: Control (100% FC), LDS (90% FC), MDS (60% FC), and SDS (30% FC) in a selected A. tricolor genotype; Betacyanin (ng g^− 1 FW), Betaxanthin (ng g^− 1 FW), Betalain (ng g^− 1 FW), Chlorophyll a (μg g^− 1 FW), Chlorophyll b (μg g^− 1 FW), Chlorophyll ab (μg g^− 1 FW),Total carotenoids (mg 100 g^− 1 FW)

Fig. 8

Response of Betacarotene, Vitamin C, TPC, TFC and TAC at four drought levels: Control (100% FC), LDS (90% FC), MDS (60% FC), and SDS (30% FC) in a selected A. tricolor genotype; AsA, Vitamin C (mg 100 g^− 1); Betacarotene (mg g^− 1), TFC, Total flavonoid content (RE μg g^− 1 dw); TPC, Total polyphenol content (GAE μg g^− 1 dw); TAC (ABTS⁺), Total antioxidant capacity (ABTS⁺) (TEAC μg g^− 1 dw); TAC (DPPH), Total antioxidant capacity (DPPH) (TEAC μg g^− 1 dw); (n = 3), letters mentioned in the bars are significantly varied by DMRT (P < 0.01)

Fig. 9

Response of Vitamins, TFC, TPC and TAC, (% to the value of control) at four drought levels: Control (100% FC), LDS (90% FC), MDS (60% FC), and SDS (30% FC) in a selected A. tricolor genotype; AsA, Vitamin C (mg 100 g^− 1); Betacarotene (mg g^− 1), TFC, Total flavonoid content (RE μg g^− 1 dw); TPC, Total polyphenol content (GAE μg g^− 1 dw); TAC (ABTS⁺), Total antioxidant capacity (ABTS⁺) (TEAC μg g^− 1 dw) TAC (DPPH), Total antioxidant capacity (DPPH) (TEAC μg g^− 1 dw)

Fig. 10

Changes of hydroxybenzoic acid compositions (μg g^− 1FW) (% to the value of control) at four drought levels: Control (100% FC), LDS (90% FC), MDS (60% FC), and SDS (30% FC) in a selected A. tricolor genotype

Fig. 11

Changes of hydroxycinnamic acid and flavonoid compositions (μg g^− 1FW) (% to the value of control) at four drought levels: Control (100% FC), LDS (90% FC), MDS (60% FC), and SDS (30% FC) in a selected A. tricolor genotype