The scientists, Witkowska and Woltering, at Wageningen University (The Netherlands) have investigated the impact of the time and the storage conditions of lettuce heads occurring between harvest and processing on the quality of both the intact heads and of the fresh-cut lettuce prepared from the stored heads.
For the study, three genotypes of Lactuca sativa (butterhead lettuce) were used: two green varieties (GB, green butterhead) and one red variety (RB, red butterhead).
After harvesting, lettuce heads were stored testing three situations:
- heads were stored at 12°C in darkness for 17 days with and without roots to investigate the effect of root system on head senescence during storage;
- heads were stored at 12°C in darkness for 5 days with and without roots to investigate the effect of prior storage conditions of the heads on the subsequent performance of fresh-cut product;
- heads were stored at 12°C in darkness and under continuous light for 5 days with roots to investigate the effect of light during prior storage of heads on quality of fresh-cut product.
The scientists have evaluated the overall visual quality using a scale from 9 to 1, where 9 was excellent and 1 was extremely poor, the pigments content (chlorophyll and carotenoids), the soluble sugars content (glucose and fructose), and the electrolyte leakage.
Despite the relatively high storage temperature of 12 °C, regardless of roots presence, the heads still looked fresh after 17 days of storage; however, the researchers found that with the advancing the storage days the content of soluble sugar and chlorophyll decreased and the electrolyte leakage increased.
After 15 days of storage, the glucose content decreased by 60% and 95% in RB and GB, respectively; while the content of chlorophyll and carotenoids decreased by 15% and 45% in GB and RB, respectively.
These physiological processes occurring in the heads during storage prior to processing affect severely the quality retention of fresh-cut lettuce prepared from these heads. Furthermore, storing the heads with roots and using light during storage prior to processing do not reduce the negative impact due to the prolonged storage of intact heads on quality of fresh-cut lettuce.
According to the results, the scientists suggest that the lettuce heads for fresh-cut chain should be minimally processed immediately after harvest.
