Ammonium nitrate fertility levels influence flavour development in hydroponically grown ‘Granex 33’ onion

Abstract

High levels of nitrogen (N) fertility have been shown to influence bulb flavour characteristics in onion (Allium cepa L). To test the effects of lower levels of N fertility on onion bulb flavour, 'Granex 33' onions were grown hydroponically in a greenhouse with varying solution N levels. Eleven levels were tested by increasing the concentration of NH 4 NO 3 in solutions from 20 to 140 mg l −1 N. Mature plants were harvested and evaluated for plant leaf and bulb fresh weights (FWs), bulb soluble solids content (SSC), bulb total pyruvic acid, bulb total sulphur (S), and bulb sulphate (SO 4 2− ). To determine the effect of N on the flavour biosynthetic pathway of onion, total and individual S-alk(en)yl cysteine sulphoxides and related peptide intermediates were also tested. Leaf and bulb FWs responded quadratically to N concentration, as did total bulb S. Bulb SO 4 2− and SSC, though significantly influenced by N concentration, did not respond with a meaningful trend. Bulb pyruvic acid increased linearly with N level increases, as did (+)-S-propyl-L-cysteine sulphoxide. Total precursors, (+)-S-methyl-Lcysteine sulphoxide, and trans-(+)-S-1-propenyl-L-cysteine sulphoxide responded quadratically to N levels. At lower N levels, trans-(+)-S-1-propenyl-L-cysteine sulphoxide content was highest relative to the other precursors. However, at elevated N levels, (+)-S-methyl-L-cysteine sulphoxide accumulated in the highest concentrations. Peptide intermediates 2-carboxypropyl glutathione and γ -glutamyl propenyl cysteine sulphoxide responded linearly and quadratically respectively to increasing N fertility levels. Nitrogen fertility levels can influence flavour intensity and quality and should be considered when growing onions for flavour attributes.

Sulfur and nitrogen fertility affects flavour of field-grown onions

“…In addition, we observed significant effects of N nutrition on composition, as previously reported only in glasshouse studies (Randle, 2000;Coolong and Randle, 2003). In these earlier studies, N and S treatments, particularly at the lowest levels, significantly affected bulb fresh weight.…”

“…Glasshouse studies have demonstrated that sulfate supply is the major environmental factor determining pungency (Randle, 1992;Randle and Bussard, 1993) and therefore mild onion production is conducted on light soils where S fertility can be readily controlled. In addition, hydroponic studies have also shown that nitrogen supply can affect flavour precursor levels (Coolong and Randle, 2003;Randle, 2000). However, surprisingly few field-based studies have demonstrated effects of S (or N) nutrition on pungency (Bakr and Gawish, 1998;Kumar and Sahay, 1954).…”

Assessment of the flavour of fresh uncooked onions by taste‐panels and analysis of flavour precursors, pyruvate and sugars

“…Measurement of the level of the flavour precursor compounds or one of their products (usually pyruvate) in onion bulbs is frequently taken to be equivalent to measurement of the flavour, or pungency, of onions 11, 17, 22. Very few studies have been reported of the relationship between these measurements and the perception of onion flavour by consumers, particularly over the wide range of onion varieties for sale in the UK.…”

Qualidade De Cebola Em Função De Doses De Nitrogênio E Épocas De Plantio

“…Morsy et al (2012) também obtiveram incrementos nos sólidos solúveis e na massa seca de bulbo com a aplicação de nitrogênio. A pungência do bulbo foi afetada pela aplicação de altas doses de nitrogênio (COOLONG;RANDLE, 2003).…”