Postharvest Biology and Technology 71 (2012) 41–50 Contents lists available at SciVerse ScienceDirect Postharvest Biology and Technology jou rnal h omepa g e: www.elsevier.com/locate/postharvbio Influence of maturity and ripening on aroma volatiles and flavor in ‘Hass’ avocado David Obenland a,∗ , Sue Collin b , James Sievert b , Fayek Negm b , Mary Lu Arpaia b a San Joaquin Valley Agricultural Sciences Center, USDA-ARS, Parlier, CA 93648, United States b Department of Botany and Plant Sciences, University of California, Riverside, CA 92521, United States a r t i c l e i n f o Article history: Received 30 September 2011 Accepted 26 March 2012 Keywords: Dry weight Minimum maturity Sensory Grassy Carbohydrates a b s t r a c t Changes in aroma volatiles were determined using solid phase microextraction (SPME) and gas chro- matography/mass spectrometry in ripe avocados (Persea americana Mill., cv. Hass) throughout an eight-month maturation period and related to the sensory properties of the fruit. As maturation pro- gressed sensory panelists found the likeability of the fruit to increase, coinciding with the fruit becoming creamier and less watery in texture, and the flavor richer and less grassy. During this maturation time the concentration of hexanal, (E)-2-hexenal and 2,4-hexadienal, three of the most abundant volatiles, greatly declined in amount. These volatiles all have a grass-like aroma, and it is likely that the loss in amount was responsible for the decline in grassy flavor during maturation. Acetaldehyde, methyl acetate, pen- tanal, and -myrcene were at higher concentrations in mature than non-mature fruit and may also have contributed to the overall flavor. Avocados of an intermediate maturity were ripened at 20 ◦ C and fruit of different ripeness levels (firmnesses) measured for ethylene production, rate of respiration and aroma volatile content. A sharp increase in the rates of respiration and ethylene production marked a rapid increase in softening and the beginning of the climacteric. Twenty-five volatiles were identified in the ripening avocados of which three (pentanol, hexanol, and 2-nonenal) were not detectable in fully-ripe fruit. Of particular interest was an 85% decline in the amount of hexanal in a comparison of firm to fully ripe (4 N firmness) fruit. Aroma volatiles have in the past been little-studied in avocados but appear to have a role in determining the flavor of the fruit. Published by Elsevier B.V. 1. Introduction Avocados (Persea americana, Mill.) picked prematurely at an immature stage can have an eating quality that has been associ- ated with a green or grassy aftertaste, lack of flavor and a rubbery or watery texture (Harding, 1954). As an early response to this problem, California growers in 1925 established a state maturity standard that required a minimum oil content of 8% before avoca- dos could be harvested in California (Anon., 1925). This was based on the fact that oil accumulates in avocados in large amounts as they mature and was thought to provide a reasonable estimate of maturity (Church and Chance, 1920–1921). Although oil content was shown to relate to flavor and eating quality (Hodgkin, 1939), fruit-to-fruit variability in oil content and varietal differences in accumulation rate (Hatton et al., 1957a; Stahl, 1933) make per- cent oil an imperfect threshold for maturity. An extensive study in California on the relationship of maturity, eating quality and dry weight accumulation (Lee et al., 1983) led to the adoption of dry matter in conjunction with release dates as the basis for minimum ∗ Corresponding author. Tel.: +1 559 596 2801; fax: +1 559 596 2803. E-mail address: david.obenland@ars.usda.gov (D. Obenland). maturity in 1983, replacing oil content. Dry matter and oil accu- mulation are closely related, but measurement of dry matter is far simpler to perform and is now the standard maturity measurement used throughout most of the world. Nonetheless, it is recognized in the avocado industry that neither dry matter nor percent oil are adequate in themselves to fully explain the differences in the eating quality of avocados and that additional means of assessing eating quality would be desirable. Volatiles have a well-established role in helping to determine flavor in a wide variety of fruits, but have not been studied exten- sively in avocado. This may have been largely due to the strong emphasis that other flavor influencing factors in avocado, such as oil content and texture, have received. Also, the high lipid content may make some types of flavor volatile analysis more problematic. In an early study, Yamaguchi et al. (1983) utilized vacuum distil- lation and solvent extraction to identify 96 compounds, the major constituents being n-hexanol, cis-3-hexanol and trans-2-hexenol which made up over 80% of the extract on a peak area basis. Sim- ilar extraction techniques were later used to identify a number of compounds in avocado extracts, with terpenes and aldehydes being some of the most predominant compounds present (Pino et al., 2000, 2004; Sinyinda and Gramshaw, 1998). Extracts that were stored rather than being processed immediately were found to have a greater number of compounds, some being products of lipid 0925-5214/$ – see front matter. Published by Elsevier B.V. http://dx.doi.org/10.1016/j.postharvbio.2012.03.006