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Abstract: Pre-storage at 20°C before cold storage was used to improve volatile compound emissions of ‘Big Top’ nectarine and ‘Early Rich’ peach fruit without negatively affecting quality measures and sensory attributes. Commercially harvested fruit were subjected to pre-storage at 20°C for 0, 10, 24, or 36h and then stored at −0.5°C for 10, 20, or 40 d. After cold storage, the fruit were kept at 20°C for up to three days. ‘Big Top’ nectarines given 10h pre-storage followed by 10 and 20 d cold storage were perceived as more flavourful, juicy, and sweet, had higher soluble solid contents, and contained more butyl propanoate, 2-methybutyl-2-methylpropanoate, and 2-methyl-1-butanol than control fruit. ‘Early Rich’ peaches given 36h pre-storage followed by 20 d cold storage were perceived as sweeter and had more propyl acetate, pentyl acetate, and 2-methyl-1-butanol than control fruit. [Copyright &y& Elsevier]

Abstract: Standard quality parameters, consumer acceptance, and volatile compound emission of ‘Pink Lady®’ apples (Malus × domestica Borkh.) were measured at harvest and after 14 and 25 weeks of cold storage in three different atmospheres. After storage, fruit were left to ripen for 1 and 7 days at 20°C before instrumental and sensory measurements were performed. Data were subjected to principal component analysis (PCA) and partial least square regression (PLSR). PLSR results indicated that the parameters positively influencing acceptability were soluble solid content, titratable acidity, background colour, and emission of hexyl 2-methylbutanoate, hexyl hexanoate, hexyl propanoate, butyl 2-methylbutanoate, 2-methylbutyl acetate and butyl propanoate. Results of sensory analyses revealed the treatments considered in this work could be split into two levels of acceptability. [Copyright &y& Elsevier]

Abstract: Emission of aroma volatile compounds and some related enzyme activities (LOX, PDC, ADH, and AAT) were assessed in ‘Fuji’ apples (Malus × domestica Borkh.) during shelf life at 20°C following cold storage under air or under three different CA conditions (3kPa O2:2kPa CO2; 1kPa O2:1kPa CO2; or 1kPa O2:2kPa CO2). Data were used for principal component analysis (PCA) and partial least-square regression (PLSR) analysis of results. LOX activity was partly inhibited by hypoxic conditions, and thus could have contributed to differentiation between air- and CA-stored fruit. Accordingly, emission of straight-chain esters was also higher in air- than in CA-stored fruit. In contrast, PDC activity was responsible for part of the differences between low (3kPa) and ultra-low (1kPa) O2 storage conditions, probably by providing substrates for AAT action. AAT activity afforded no satisfactory differentiation between samples, and therefore it is suggested that substrate availability is a more decisive factor than enzyme activity for volatile production after storage. The PCA and PLSR models developed in this work were not useful for discrimination between the two studied ultra-low O2 conditions. [Copyright &y& Elsevier]

Production of volatile aroma compounds, and quality parameters, were monitored in relation to the activity of lipoxygenase, pyruvate decarboxylase, alcohol dehydrogenase and alcohol o-acyltransferase during maturation of ‘Fuji’ apples. Acetate esters increased during maturation and were quantitatively the most significant compounds contributing to ‘Fuji’ aroma. Increase in acetate ester production was associated with the availability of the necessary alcohol precursors. Principal component analysis revealed a clear separation according to sampling date, which accounted for up to 67% of total variance, and allowed ‘Fuji’ apples used in this study to be classified into three ripeness stages. Overall the results suggest that precursor availability for the related enzymes is a more significant factor than enzyme activity for the development of aroma during on-tree maturation of ‘Fuji’ apples. [Copyright &y& Elsevier]

Standard quality parameters, consumer acceptability, emission of volatile compounds and ethylene production of ‘Mondial Gala®’ apples (Malus × domestica Borkh.) were determined in relation to storage atmosphere, storage period and shelf-life period. Fruit were harvested at the commercial date and stored in AIR (21kPa O2:0.03kPa CO2) or under three different controlled atmospheres (CAs): LO (2kPa O2:2kPa CO2), ULO1 (1kPa O2:1kPa CO2), or ULO2 (1kPa O2:2kPa CO2). Fruit samples were analysed after 12 and 26 weeks of storage plus 1 or 7d at 20°C. Apples stored in CA maintained better standard quality parameters than AIR-stored fruit. The volatile compounds that contributed most to the characteristic aroma of ‘Mondial Gala®’ apples after storage were butyl, hexyl and 2-methylbutyl acetate, hexyl propanoate, ethyl butanoate, ethyl hexanoate, ethyl, butyl and hexyl 2-methylbutanoate. Data obtained from fruit analysis were subjected to principal component analysis (PCA). The apples most accepted by consumers showed the highest emission of ethyl 2-methylbutanoate, ethyl hexanoate, tert-butyl propanoate and ethyl acetate, in addition to the highest titratable acidity and firmness values. [Copyright &y& Elsevier]

The production of aroma volatile compounds and standard quality attributes, in addition to lipoxygenase (LOX), hydroperoxide lyase (HPL), pyruvate decarboxylase (PDC), alcohol dehydrogenase (ADH) and alcohol o-acyltransferase (AAT) activities, were assessed during maturation of ‘Pink Lady®’ apples. Low production of aroma volatiles was observed in early harvested fruit, which gradually increased as ripeness approached. Hexyl acetate, hexyl 2-methylbutanoate, hexyl hexanoate, hexyl butanoate, 2-methylbutyl acetate and butyl acetate were prominent within the blend of volatiles produced by fruit throughout maturation. Multivariate analysis showed these compounds had the highest influence on differentiation of maturity stages, indicating that aroma volatile emission is an important factor for definition of fruit ripeness, which suggests production of these esters might be useful as an index of maturity. No large variations in AAT activity were found throughout the experimental period despite increasing ester emission, suggesting the enhancement of ester production by ‘Pink Lady®’ apples at ripening arises mainly from greater availability of substrates. Increased LOX activity was observed at later stages of fruit development, and the possible role of this enzyme activity on enhanced capacity for aroma volatile biosynthesis in more mature fruit is discussed. [Copyright &y& Elsevier]

The production of butyl and hexyl acetates and the contents of ethanol and acetaldehyde in relation to the activity of some related enzymes (lipoxygenase, pyruvate decarboxylase, alcohol dehydrogenase and alcohol o-acyltransferase) was studied in ‘Doyenne du Comice’ pears during ripening at 20 °C, following long-term cold storage under different conditions: air, or CA in 2 kPa O2 with various CO2 partial pressures (0.7, 2 or 5 kPa). A decrease in volatile production was found for fruit stored under low O2 upon return to ambient conditions. Results suggest that inhibition of volatile biosynthesis by CA storage is caused mainly by limited precursor/substrate supply to the related enzymes rather than by enzyme degradation or inactivation. Ethanol production by the fruit did not correlate well with ADH activity. The possibilities of a feedback inhibition of enzyme activity by excess product and of oxidation into acetaldehyde upon return to air are discussed. Hypoxic conditions caused a decrease in LOX activity after 5 months storage, possibly leading to shortage of lipid precursors for ester biosynthesis. [Copyright &y& Elsevier]