Abstract
Flavour is a key quality attribute of apples defined by volatile aroma compounds. Biosynthesis of aroma compounds involves metabolic pathways in which the main precursors are fatty and amino acids, and the main products are aldehydes, alcohols and esters. Some enzymes are crucial in the production of volatile compounds, such as lipoxygenase, alcohol dehydrogenase, and alcohol acyltransferase. Composition and concentration of volatiles in apples may be altered by pre- and postharvest factors that cause a decline in apple flavour. Addition of biosynthetic precursors of volatile compounds may be a strategy to promote aroma production in apples. The present manuscript compiles information regarding the biosynthesis of volatile aroma compounds, including metabolic pathways, enzymes and substrates involved, factors that may affect their production and also includes a wide number of studies focused on the addition of biosynthetic precursors in their production.
Highlights
Apple quality is determined by attributes such as appearance, firmness and flavour, as well as by the absence of physiological and pathological disorders
The present manuscript compiles information regarding the biosynthesis of volatile aroma compounds, including metabolic pathways, enzymes and substrates involved, factors that may affect their production and includes a wide number of studies focused on the addition of biosynthetic precursors in their production
Volatile compounds are synthesized from fatty acid metabolism, amino acid metabolism, and carbohydrate metabolism [5,63,64], through the following pathways [40]: (i) straight-chain aldehydes, alcohols and esters are synthesized from lipids, mainly linolenic and linoleic acids, through β-oxidation and lipoxygenase activity [8,16], (ii) branched-chain aldehydes, alcohols and esters are derived from isoleucine [17,65,66,67], (iii) terpenoids are synthesized via the mevalonate pathway [63,68] and deoxyxylulose phosphate pathway [69], and (iv) phenylpropanoids are synthesized from the phenylpropanoid pathway [70]
Summary
Flavour is a key quality attribute of apples defined by volatile aroma compounds. Biosynthesis of aroma compounds involves metabolic pathways in which the main precursors are fatty and amino acids, and the main products are aldehydes, alcohols and esters. Some enzymes are crucial in the production of volatile compounds, such as lipoxygenase, alcohol dehydrogenase, and alcohol acyltransferase. Composition and concentration of volatiles in apples may be altered by pre- and postharvest factors that cause a decline in apple flavour. Addition of biosynthetic precursors of volatile compounds may be a strategy to promote aroma production in apples. The present manuscript compiles information regarding the biosynthesis of volatile aroma compounds, including metabolic pathways, enzymes and substrates involved, factors that may affect their production and includes a wide number of studies focused on the addition of biosynthetic precursors in their production
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