“Temperatura abuses during lettuce postharvest: impact on color and chlorophyll”

BEVILACQUA, ALICIA, AGUERO, M. VICTORIA, ROURA, SARA I.

Color in Food

Taylor and Francis Group. CRC Press

Año: 2011;

Lettuce is one of the most consumed leafy vegetables in the world (Martín- Diana et al. 2007). There are different varieties of lettuce each with particular morphological characteristics (Di Benedetto 2005). Among them, butterhead lettuce is one of the most spread varieties all over the world. The lettuce head is an assemblage of heterogenic morphological leaves that are packed together over the growing point of the plant. Its formation results from the accumulation of young leaves under the layers of leaves covering the growing point (Wien 1997). This growth pattern determines that leaves formed by different tissues, not only with different maturity degree, but also with different metabolic and physiological activities, and exposed to different environmental conditions coexist within a plant. So the lettuce plant is an interesting biological model where it is possible to evaluate these factors simultaneously in each unit. In Argentine farms, lettuce is harvested using hand collection techniques, and as it is harvested, it is placed in package units, wooden crates, for its transportation to market. These crates are stacked on trucks and they are usually exposed to inadequate field conditions (usually high temperature) while they are waiting to be transported from the field to distribution centers (Mondino et al. 2007). Product exposed to sunlight could rapidly raise a temperature 4°C–6°C more than air temperature (Thompson et al. 2001). In the field, the combination between the heat of the sun and the respiration of the produce provokes the heat up of the produce, reducing its postharvest life. So the knowledge of the events occurring within the plant when temperature is uncontrolled during first hours after harvest is of fundamental importance to improve and optimize lettuce management. However, few researches have been developed to investigate the first few hours after harvest. Moreira et al. (2006) studied the effect of abusive temperatures after harvest over lettuce leaves and found that the first hours after harvest are crucial for vegetable shelf life because quality losses in this early stage could not been recovered. Jedermann and Lang (2007) proposed that the effect of short exposure of some few hours to inadequate conditions (too high or too low temperature and/or relative humidity) is sufficient to favor quality losses in the product. 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. The color of green leafy vegetables is determined by the chlorophyll concentration, which is the principal pigment of these photosynthetic tissues. Butterhead lettuce is characterized by light green color in outer leaves and yellow color in inner leaves. The objective of the present research was to describe the response of lettuce color to the exposure at three isothermal conditions (0°C–2°C, 10°C–12°C, and 20°C–22°C), all at optimal relative humidity (RH) during the first 24 h after harvest. Leaf color behavior was evaluated through total chlorophyll content and L*a*b* color coordinates. Additionally, parameters were measured in three different lettuce sections: external (outer and older leaves), middle (mid leaves), and internal (inner and younger leaves) to evaluate the colorability of lettuce related to leaf age and position. Correlations between greenness indices were investigated in each section. in three different lettuce sections: external (outer and older leaves), middle (mid leaves), and internal (inner and younger leaves) to evaluate the colorability of lettuce related to leaf age and position. Correlations between greenness indices were investigated in each section. accumulation of young leaves under the layers of leaves covering the growing point (Wien 1997). This growth pattern determines that leaves formed by different tissues, not only with different maturity degree, but also with different metabolic and physiological activities, and exposed to different environmental conditions coexist within a plant. So the lettuce plant is an interesting biological model where it is possible to evaluate these factors simultaneously in each unit. In Argentine farms, lettuce is harvested using hand collection techniques, and as it is harvested, it is placed in package units, wooden crates, for its transportation to market. These crates are stacked on trucks and they are usually exposed to inadequate field conditions (usually high temperature) while they are waiting to be transported from the field to distribution centers (Mondino et al. 2007). Product exposed to sunlight could rapidly raise a temperature 4°C–6°C more than air temperature (Thompson et al. 2001). In the field, the combination between the heat of the sun and the respiration of the produce provokes the heat up of the produce, reducing its postharvest life. So the knowledge of the events occurring within the plant when temperature is uncontrolled during first hours after harvest is of fundamental importance to improve and optimize lettuce management. However, few researches have been developed to investigate the first few hours after harvest. Moreira et al. (2006) studied the effect of abusive temperatures after harvest over lettuce leaves and found that the first hours after harvest are crucial for vegetable shelf life because quality losses in this early stage could not been recovered. Jedermann and Lang (2007) proposed that the effect of short exposure of some few hours to inadequate conditions (too high or too low temperature and/or relative humidity) is sufficient to favor quality losses in the product. 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. The color of green leafy vegetables is determined by the chlorophyll concentration, which is the principal pigment of these photosynthetic tissues. Butterhead lettuce is characterized by light green color in outer leaves and yellow color in inner leaves. The objective of the present research was to describe the response of lettuce color to the exposure at three isothermal conditions (0°C–2°C, 10°C–12°C, and 20°C–22°C), all at optimal relative humidity (RH) during the first 24 h after harvest. Leaf color behavior was evaluated through total chlorophyll content and L*a*b* color coordinates. Additionally, parameters were measured in three different lettuce sections: external (outer and older leaves), middle (mid leaves), and internal (inner and younger leaves) to evaluate the colorability of lettuce related to leaf age and position. Correlations between greenness indices were investigated in each section. in three different lettuce sections: external (outer and older leaves), middle (mid leaves), and internal (inner and younger leaves) to evaluate the colorability of lettuce related to leaf age and position. Correlations between greenness indices were investigated in each section. accumulation of young leaves under the layers of leaves covering the growing point (Wien 1997). This growth pattern determines that leaves formed by different tissues, not only with different maturity degree, but also with different metabolic and physiological activities, and exposed to different environmental conditions coexist within a plant. So the lettuce plant is an interesting biological model where it is possible to evaluate these factors simultaneously in each unit. In Argentine farms, lettuce is harvested using hand collection techniques, and as it is harvested, it is placed in package units, wooden crates, for its transportation to market. These crates are stacked on trucks and they are usually exposed to inadequate field conditions (usually high temperature) while they are waiting to be transported from the field to distribution centers (Mondino et al. 2007). Product exposed to sunlight could rapidly raise a temperature 4°C–6°C more than air temperature (Thompson et al. 2001). In the field, the combination between the heat of the sun and the respiration of the produce provokes the heat up of the produce, reducing its postharvest life. So the knowledge of the events occurring within the plant when temperature is uncontrolled during first hours after harvest is of fundamental importance to improve and optimize lettuce management. However, few researches have been developed to investigate the first few hours after harvest. Moreira et al. (2006) studied the effect of abusive temperatures after harvest over lettuce leaves and found that the first hours after harvest are crucial for vegetable shelf life because quality losses in this early stage could not been recovered. Jedermann and Lang (2007) proposed that the effect of short exposure of some few hours to inadequate conditions (too high or too low temperature and/or relative humidity) is sufficient to favor quality losses in the product. 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. The color of green leafy vegetables is determined by the chlorophyll concentration, which is the principal pigment of these photosynthetic tissues. Butterhead lettuce is characterized by light green color in outer leaves and yellow color in inner leaves. The objective of the present research was to describe the response of lettuce color to the exposure at three isothermal conditions (0°C–2°C, 10°C–12°C, and 20°C–22°C), all at optimal relative humidity (RH) during the first 24 h after harvest. Leaf color behavior was evaluated through total chlorophyll content and L*a*b* color coordinates. Additionally, parameters were measured in three different lettuce sections: external (outer and older leaves), middle (mid leaves), and internal (inner and younger leaves) to evaluate the colorability of lettuce related to leaf age and position. Correlations between greenness indices were investigated in each section. in three different lettuce sections: external (outer and older leaves), middle (mid leaves), and internal (inner and younger leaves) to evaluate the colorability of lettuce related to leaf age and position. Correlations between greenness indices were investigated in each section. in three different lettuce sections: external (outer and older leaves), middle (mid leaves), and internal (inner and younger leaves) to evaluate the colorability of lettuce related to leaf age and position. Correlations between greenness indices were investigated in each section.