Sulphur compounds in alliums in relation to flavour quality.

Abstract

Although it is realized that flavour is the result of a multifaceted interaction among many different compounds, this chapter reviews the sulfur compounds that give alliums their characteristic flavours and odours.

Pungency of Spring Onion as Affected by Inoculation with Arbuscular Mycorrhizal Fungi and Sulfur Supply

“…The EPY value, shoot and root TSC, and S content of shoots and roots of spring onion all increased with increasing S supply level in the substrate (Table 3). These results were expected and similar results have been reported for onion plants by other investigators (Randle and Lancaster, 2002). Shoot total sulfur concentrations in spring onion ranged from 0.15 to 0.44 %, which falls within the range of S concentrations in onion leaves and bulbs as reported by Randle (1992).…”

“…Therefore, it is suggested that effects other than the enhanced sulfur nutritional level due to mycorrhizal colonization may also play a role. The flavor precursors have been generally regarded to be involved in the defense reaction of plants against micro-organisms ( Randle and Lancaster, 2002). Wounded plants deliver available sulfur to synthesize defense-related substances by activating genes involved in the metabolism of sulfur (Harada et al, 2000).…”

“…After disruption the enzyme alliinase acts upon the ACSOs in the cytoplasm, giving rise to the volatile compounds responsible for the characteristic flavor and aroma of the plants (Lancaster and Collin, 1981) with the formation of pyruvic acid and ammonia as by-products. The composition and total concentrations of ACSOs determine the flavor profile of the plants, differ among Allium species and cultivars (Yoo and Pike, 1998), and vary with the external environment (Randle and Lancaster, 2002). As the direct measurement of the flavor precursors or the active flavor compounds is laborious, technically demanding and costly for large scale routine agronomic or breeding studies (McCallum et al, 2005), enzymatically generated pyruvic acid (EPY) has been used to determine the gross pungency of Allium plants due to the simplicity of the measurement.…”

Interactions among genotype, environment and agronomic practices on production and quality of storage onion (Allium cepa L.) - A review

“…In particular, sulphur is absorbed by the plant as sulphate, successively reduced and incorporated into cysteine, which is used for the synthesis of methionine and glutathione in the pathway of flavour biosynthesis (Anderson 1990;Randle, Lancaster 2002). Glutathione is the key metabolite for the biosynthesis of all ACSOs, starting from cysteine, glutamic acid, and glycine (Lancaster, Shaw 1989), and it serves as sulphur vehicle through several peptide pathways terminating in the synthesis of any flavour precursors (Randle, Lancaster 2002).…”

“…In particular, sulphur is absorbed by the plant as sulphate, successively reduced and incorporated into cysteine, which is used for the synthesis of methionine and glutathione in the pathway of flavour biosynthesis (Anderson 1990;Randle, Lancaster 2002). Glutathione is the key metabolite for the biosynthesis of all ACSOs, starting from cysteine, glutamic acid, and glycine (Lancaster, Shaw 1989), and it serves as sulphur vehicle through several peptide pathways terminating in the synthesis of any flavour precursors (Randle, Lancaster 2002). Notably, amino acids are also included in the flavour determinants and during maturation they are translocated from the senescing foliage to the bulb (Nilsson 1980); arginine and glutamine are the most abundant in onions (Hansen 2001), accounting for over 40% of the total free amino acids.…”