The quality of fresh fruits can be defined in terms of factors such as appearance, firmness, color, flavor, and nutritional value. Modified atmospheres (MA) containing 10–20 kPa CO2 have been applied commercially for many years to reduce decay incidence and to preserve quality attributes of strawberries (Harvey, 1982). However, not all quality characteristics can be preserved to the same extent. Flavor tends to decline before changes in appearance signal the end of acceptable postharvest life (Pelayo et al., 2003).
Sugars and acids together with aroma compounds are the primary constituents determining strawberry (Fragaria ×ananassa Dutch.) flavor. Strawberries stored in CO2-enriched controlled atmospheres (CAs) (Holcroft and Kader, 1999a) and those stored in MAs (Sanz et al., 1999) had reduced sucrose concentration with a concomitant increase in the levels of glucose and fructose over time. Also, decreased levels of citric and malic acids in ‘Selva’ strawberries stored at 5 °C in air were greater in strawberries stored in CO2-enriched atmospheres (Holcroft and Kader, 1999a). Thus, pH increases during storage were greater in CO2-stored strawberries than in those kept in air, and a corresponding change was observed in titratable acidity (TA). Similarly, Fernandez-Trujillo et al. (1999) found that malate concentrations were 22% lower in 20 kPa CO2- stored than in air-stored fruit of seven strawberry cultivars, but the level of citric acid was unaffected by the CO2 treatment.
Among aroma compounds, esters are apparently the volatiles most affected by CO2-enriched atmospheres. The levels of ethyl acetate and ethyl butyrate increased over isopropyl, propyl, and butyl acetates in ‘Chandler’ strawberries at 5 °C in 50 kPa CO2-enriched atmospheres (Ke et al., 1994). The authors hypothesized that, under these conditions, the synthesis of ethyl esters predominates over other alkyl esters and the synthesis of other acyl esters predominates over acetates. Larsen and Watkins (1995a) reported an increase in ethyl butyrate and ethyl hexanoate in ‘Pajaro’ strawberries stored at 0 °C in 20 kPa CO2. Watkins et al. (1999) found that the increase in acetaldehyde, ethanol, and ethyl acetate in strawberries stored at 2 °C in 20 kPa CO2 was cultivar dependent. However, no information is available about the effect of CA on branched esters, which apparently are important contributors to the aroma of strawberries (Schieberle and Hofmann, 1997).
In addition to flavor components, CO2-enriched atmospheres slow the softening rate of strawberries (Kader, 1986; Ke et al., 1991) or increase the fruit flesh firmness (Harker et al., 2000). Strawberries stored in CO2-enriched atmospheres were lighter and less red than air-stored fruit (Gil et al., 1997; Holcroft and Kader, 1999b; Watkins et al., 1999). Strawberries contain 580 to 2100 mg·kg−1 of total phenolic compounds (Kader, 1991), and these compounds play a role in the astringency perception of strawberries (Perkins-Veazie, 1995). The total content of phenolic compounds increased with time in storage at 5 °C but was unaffected by storage atmosphere (in air or in air + 10–20 kPa CO2) in ‘Selva’ strawberries (Holcroft and Kader, 1999b).
The objectives of the present work were to evaluate changes of the primary flavor components of ‘Camarosa’ strawberries in response to a 20 kPa CO2-enriched atmospheres and to elucidate the possible factors contributing to the loss of flavor during storage.
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