Influence of maturity on volatile production and chemical composition of fruits of six apricot cultivars

Abstract

The fruits of six apricot cultivars were chemically analysed at two distinct stages of maturity, first when ready for picking by conventional commercial criteria, and again after another 6 days of maturation on the tree. Firmness, levels of soluble solids (SS), organic acids (citric and malic acid), sugars (sucrose, fructose and glucose), respiration rates and the production of ethylene and other volatile compounds were measured. Forty-five volatile compounds, including 12 alcohols, 10 aldehydes. 2 ketones, 10 esters, 7 terpenes, 3 lactones and I hydrocarbon were sampled by head space SPME and identified by GC-MS. The chemical composition of the non-volatile fraction (soluble solids and organic acids) exhibited only minor differences. insufficient to differentiate between the apricot cultivars or to make any meaningful judgement of the degree of maturity. Some variation between the cultivars in the respiration rate and production of ethylene was observed. However, using a stepwise logistic regression analysis, chemicals were identified among the volatile compounds which allowed the differentiation of fruits at the two different stages of maturity. In addition to the results of physical tests of firmness using standard penetration methods, differences in the degree of fruit maturation were clearly indicated by the levels of volatiles such as trans-2-hexen-1-ol, 2-methylbutylacetate, butyl-2-methylbutyrate, 6-methyl-5-heptene-2-one, acetophenone and γ-octalactone. Principal component analysis (PCA) confirmed the development of significant differences between each of the 6 apricot cultivars over the six day period of extra maturation on the tree, as each cultivar developed its own specific chemical signature. Moreover, this varietal character, which plays such an important part in determining overall attractiveness to the consumer, was only seen in fruits picked at the later stage of maturity.