Enhancing bioactive compounds accumulation in red beet (Beta Vulgaris L.) plants by managing N nutrition. The identification of the 'critical' zone as a cultivation technique.

The increasing interest in natural health-promoting compounds, which are mostly plant secondary metabolites, inspired attempts to stimulate mechanisms strengthening their bioaccumulation in crop plants via abiotic stress while maintaining the yield potential. This study investigates the long-term effects of limiting nitrogen (N) supply on the concentration of total phenolics, free radical activity of natural antioxidants, betacyanin content, biomass production, net photosynthetic rate, total chlorophyll content, and plant water relations in red beetroot plants (Beta vulgaris L.) grown hydroponically. Depending on fertilization, the range of N supply for evaporative demand comprises two contrasted nutrient zones, in which N is limiting (zone-1) or non-limiting (zone-2). Based on the carbon-nutrient-balance hypothesis, at the transition from 1st-zone to 2nd-zone, there is a narrow transition zone in which the plant nutrient status is considered 'critical'. Herein, to determine the 'critical' zone, a modified Michaelis-Menten (M-M) model was used using a piecewise linear regression on two indexes: net photosynthetic rates and free radical-scavenging capacity of phenolic antioxidants. The model showed that the 'critical' transition points of net photosynthetic rate and phenolic free radical content are located in a narrow zone ranging between 196.70 ± 8.75 and 271.54 ± 75.50 ppm NO3-, while the cropping season appears to affect slightly the range of 'critical' (transition) zone. Thus, supplying N to red beetroot plants to levels ranging within this 'critical' zone may be an efficient, profitable and sustainable way to increase the accumulation of health-promoting plant bioactive compounds (total phenolic compounds with radical activity and betacyanins) in hydroponically cultivated reed beetroot plants.

Cowpea fresh pods - a new legume for the market: assessment of their quality and dietary characteristics of 37 cowpea accessions grown in southern Europe.

BACKGROUND: Cowpea is traditionally cultivated in some regions of southern Europe for its dried seeds; however, there is a scarcity of information on the quality and dietary characteristics of fresh pods, which are occasionally used in folk diets. This paper aims at covering this gap in knowledge, thereby contributing to the dissemination of fresh cowpea pods as a novel product for the market. The quality and dietary characteristics of pods from 37 accessions (Vigna unguiculata ssp. unguiculata and ssp. sesquipedalis) grown in southern Europe were assessed in an attempt to provide information on pod quality and nutritional properties and to identify relationships between quality traits and accession origin. RESULTS: Pods from the sesquipedalis accessions were heavier and larger, and reached commercial maturity 2 days later, than those from the unguiculata accessions. There were also large differences in the quality and dietary characteristics of the accessions. The pods of most accessions were rich in proteins, chlorophylls, carotenoids and phenolics, and showed high antioxidant activity and low concentrations of nitrates and raffinose-family oligosaccharides. Cluster analysis based on quality, dietary or antinutritional traits did not reveal any apparent grouping among the accessions. All the quality characteristics were independent of accession origin and subspecies. CONCLUSION: Most of the accessions produced fresh pods of good quality and high dietary value, suitable for introduction in the market and/or for use as valuable genetic material for the development of new improved varieties. © 2017 Society of Chemical Industry.