Hydroperoxide Lyase Activity Necessary for Normal Aroma Volatile Biosynthesis of Tomato Fruit, Impacting Sensory Perception and Preference

Abstract

<jats:p>The aldehydes cis-3-hexenal, hexanal, and trans-2-hexenal; the alcohols 1-hexanol, and cis-3-hexenol; and the ketone 1-penten-3-one are produced as a consequence of lipid degradation following tissue disruption and are among the most important volatile compounds in tomato (<jats:italic>Lycopersicon esculentum</jats:italic> Mill.) aroma. The biosynthesis of cis-3-hexenal and other volatiles noted involves the action of a sequence of enzymes including lipase, lipoxygenase (LOX), hydroperoxide lyase (HPL), isomerase, and alcohol dehydrogenase (ADH) on glycerolipids containing the fatty acids, linoleic acid (18:2) and linolenic acid (18:3), via the LOX pathway. In the current work, the formation and sensory perception of volatile compounds was studied in tomato plant lines where HPL activity was genetically altered. LeHPL co-suppression dramatically reduced the production of lipid-derived C6-volatiles in leaves, but in fruits, only unsaturated C6-volatile production was affected, suggesting LeHPL-independent formation of hexanal occurs in fruits, but not in leaves. Increased production of 5-carbon volatiles is proposed as an alternative way to metabolize 13-hydroperoxy linolenic acid in plants with reduced LeHPL activity. Changes in the volatile profile of leaves and fruits of tomato lines in which LeHPL activity is reduced markedly are readily detected by nontrained sensory panels. The studies demonstrate that a marked reduction in the activity of one of the most critical steps in the LOX pathway can markedly impact sensory perception. Efforts to improve total volatile formation may require the modification of LOX pathway at several steps simultaneously, including precursor formation, and LOX and HPL activities.</jats:p>

Effect of methyl salicylate and methyl jasmonate pre-treatment on the volatile profile in tomato fruit subjected to chilling temperature

“…In tomato fruit, C6-aldehydes are synthesized from 13-hydroperoxide lyase (13-HPL) pathway, starting with C18 fatty acids, LA or LnA (Canoles et al, 2005) (Table 2). C18 fatty acids are initially acted upon by TomloxC to produce 13-hydroperoxides (13-HPOs).…”

Responses of volatile compounds in inner tissues on refrigeration in full ripe tomatoes

“…Hexanal was reported to be positively correlated with sweetness and ripe tomato ratings (Maul et al, ). In tomato fruit, the key enzyme for their synthesis is hydroperoxide lyase (HPL) (Canoles, Soto, & Beaudry, ), which is sensitive to low temperature stress (Bai et al, ). So in our study the reduction of all three C6 aldehydes by refrigeration might be due to down‐regulation of 13‐HPL mRNA, and subsequent reduction of HPL enzyme activities in the oxylipin pathway.…”

Compuestos Volátiles Responsables Del Sabor Del Tomate

“…ADH es otra enzima considerada de gran importancia en el desarrollo del sabor del tomate (Baldwin et al, 2000), cuya mayor actividad se observa cuando el fruto está completamente maduro y de color rojo (Yilmaz et al, 2001c). La ADH es responsable de convertir el compuesto 3-metilbutanal formado por el ácido cetoisocaproico, en el alcohol 3-metilbutanol (Canoles et al, 2005).…”

“…Por ejemplo, se considera que los volátiles del aroma de tomate, 6-metil-5-hepten-2-ona, geranil acetona y farnesil acetona, son resultado del rompimiento oxidativo de carotenoides acíclicos. De manera similar, α-ionona, β-ionona y β-damascenona son productos probables del rompimiento oxidativo de los carotenoides cíclicos y al parecer de otros terpenoides que pueden existir en el tejido vegetal enlazados a carbohidratos (Canoles et al, 2005). En este caso (Cuadro 1), cuando las cadenas de los carotenoides 9, 10, 9´ y 10´ se rompen, pueden formar dos mono-aldehídos y un di-aldehído central (Lalel et al, 2004).…”