Elicitation of the Proline-Linked Pentose Phosphate Pathway Metabolites and Antioxidant Enzyme Response by Ascorbic Acid in Dark Germinated Fava Bean Sprouts

Abstract

Elicitation by ascorbic acid stimulated higher phenolic content in late stages of germination and higher antioxidant activity during early and late germination in fava bean sprouts. The high free radical scavenging‐linked antioxidant activity on day 1 coincided with high levo‐dihydroxy phenylalanine and total phenolics. A positive correlation between the stimulation of phenolic synthesis and glucose‐6‐phosphate dehydrogenase (G6PDH) activity was also observed, indicating its likely role in carbohydrate mobilization. Improved guaiacol peroxidase (GPX) activity in response to elicitation indicated the likely polymerization of soluble phenolics. Higher GPX, superoxide dismutase and catalase linked antioxidant enzyme response correlated to increase in proline and phenolics. A proline‐linked stimulation likely provided nicotinamide adenine dinucleotidephosphate from pentose phosphate pathway (PPP) as indicated by an increase in G6PDH, the first committed step of PPP, which then supported phenolic synthesis and antioxidant enzyme response. PRACTICAL APPLICATIONS This research indicates that ascorbic acid is an effective elicitor of the pentose phosphate pathway (PPP) in dark germinated fava bean sprouts. It increases synthesis of health‐relevant phenolics and levo‐dihydroxy phenylalanine relevant to Parkinson's disease management. The stimulation of PPPwas linked to accumulation of free proline thereby supporting the proline‐linked pentose phosphate pathway model. It provides an understanding of the role of phenolic antioxidants on redox modulation in the cell by being effective free radical scavengers and also by inducing the antioxidant enzyme responses through providing the reducing equivalents required for their activity. This knowledge can be used as a biochemical strategy to design seed sprouts for functional food applications.

Impact of Elicitation on Antioxidant and Potential Antihypertensive Properties of Lentil Sprouts

“…However, the application of ascorbic acid, folic acid or chitosan/glutamic acid enhanced significantly (P ≤0.05) the phenolic content in sprouted lentils (3.6-3.9 mg GAE/g d.w.) and no significant differences (P>0.05) among these elicitors were found. Our results are in agreement with those reported for sprouted peas, fava beans and kidney beans [14][15][16]19]. The increased TPC concentration found in elicited sprouted lentils could be attributed to de novo synthesis of phenolic compounds since previous studies observed that chitosan and ascorbic and folic acids stimulate the pentose phosphate and phenylpropanoid pathways in legumes [14,16].…”

“…This statement is supported by the positive correlation (r=0.75) found between TPC content and ORAC values. Our results are consistent with previous studies indicating that abiotic elicitors increased the phenolic content and, consequently, the antioxidant activity of vegetable sprouts [14][15][16]. Ascorbic acid is a potent natural antioxidant that might also contribute to the enhancement of ORAC values in lentil sprouts treated with this elicitor, as it has been previously observed in pea sprouts [14].…”

“…However, little has been reported about the application of chemical elicitors or precursors of GABA and phenolic compounds to enhance the nutritional and nutraceutical properties of legume sprouts. For instance, some studies have shown that the addition of polyphenol precursors and H 2 O 2 as well as ascorbic and folic acid solutions improved the content of phenolic compounds and antioxidant activity of lentil, pea and fava bean sprouts [14][15][16][17][18], whilst glutamic acid feeding promoted the accumulation of GABA and phenolic compounds in germinated kidney beans [19]. Other studies supported the role of chitosan in stimulating the growth and productivity of soybean sprouts, as well as their vitamin C content [20,21].…”

Biostimulant prevents yield loss and reduces oxidative damage in tomato plants grown on reduced NPK nutrition

“…authors have indicated the positive correlation between phenol synthesis and activities of glucose 6-phosphate dehydrogenase which stimulates mobilization of sugars to phenylpropanoid pathway (Randhir & Shetty 2007). Our results showed that biostimulant in conditions of reduced NPK nutrition can affect the ratio of total sugars and acids, but the change of these two parameters is specific for particular genotype (Figure 1).…”

“…The obtained results in our research showed positive correlation between increase of fruit ascorbic acid content, TPC in the leaves, as well as TAC (Figure 1(c) and Figure 2) and a similar trend was obtained in some other research studies (Parađiković et al 2011; Zodape et al 2011). According to literature data, increased content of ascorbic acid is closely associated with phenol concentration due to stimulation of phenylpropanoid pathway, whereby antioxidative capacity also increases (Randhir & Shetty 2007).…”