Temperature abuses during lettuce posharvest: impact on color and chlorophyll

AGÜERO MARÍA VICTORIA; BEVILACQUA ALICIA; ROURA SARA INES

Mar del Plata

Congreso; AIC 2010 Color and Food from farm to table; 2010

UNMDP

The appearance of fresh vegetables strongly affects the purchase decision. Color is an appearance component and a transcendental property, since it impacts directly on consumer visual perception. Lettuce is a highly perishable vegetable whose quality and shelf life are limited by the temperature. High temperature is recurrent during transport from farm towards distribution centers. The first hours after harvest are crucial because quality losses at these earlier stages can not be recovered. The objective was to describe chlorophyll and color changes during lettuce exposure to three isothermal conditions during the first 24 hours after harvest. For this purpose, heads of butterhead lettuce (Lactuca sativa var. ?Lores?) were harvested at optimal maturity and were stored during 24 hours in environmental chambers at 0-2ºC (optimal), 10-12ºC (abusive refrigeration) or 20-22°C (warm room), maintaining the relative humidity levels in 97-99%. Parameters were measured in three different lettuce sections: external (outer and older leaves), middle (mid leaves) and internal (inner leaves), to evaluate the colorlability of lettuce related to leaf age. Correlations between greenness indices were investigated in each section.The chlorophyll (C) content was determined following the methodology described by Moreira et al. (2003). Color was measured using a Minolta colorimeter, by L* (lightness), a* (redness/greenness parameter) and b* (blueness/yellowness parameter) chromaticity co-ordinates of the CIELAB scale. Leaf age had a significant effect on the initial values of greenness indices. Older and senescent leaves (external section) showed higher C and lower L*, a* and b* values, than younger leaves (internal section) characterized by a clearest color. Each lettuce section showed a particular C behavior during 24h. While the external section exhibited C degradation at any assayed temperature (more pronounced at higher temperatures), the middle and internal sections showed no C changes. Significant increases in a* were observed in the three sections and the three temperatures. The highest increment was observed in inner leaves at 20-22ºC. Increases of a* are usually associated with chlorophyll degradation. However, decreases in C were not detected in internal section while changes in a* parameter were detected. This fact could be associated with highest susceptibility of these leaves to browning. No changes were registered in b* or L* values as time advanced at any temperature and section. A high correlation (R2 = 0.93) was found between chlorophyll content and a* in external section at the three assayed temperatures.The knowledge of the effect of leaf age and temperature on the evolution of color quality indices is of fundamental importance for producers because they can take decisions based on this differential behavior related to the degree of tissue development.