UC Davis

Basil, like most aromatic herbs, is typically marketed as a dried product, although demand for fresh basil has grown dramatically over the years due to its distinct sensory properties. However, unlike other culinary herbs, fresh basil is particularly sensitive to chilling temperatures which limits its transport and storage. Understanding the basis of chilling sensitivity is essential in designing storage regimes for quality maintenance after harvest. Since basil is a culinary herb valued for its unique aroma and flavor, preserving its sensory quality postharvest is also of utmost importance. I explored the biochemical basis of differential chilling sensitivity among genotypes and found that ‘Lemon’ and ‘Genovese’ were more sensitive to chilling than ‘Purple’, ‘Thai’, and ‘Holy’ basil. I also observed that different genotypes utilized various mechanisms to cope with postharvest chilling stress, as revealed by the dynamics between antioxidant enzymes and metabolites. Sensitive genotypes either had low activity of antioxidant enzymes such as catalase (CAT) and ascorbate peroxidase (APX), and/or the inability to recycle antioxidant metabolites such as ascorbic acid (AsA), which can result in the accumulation of reactive oxygen species (ROS) that damage cells and exacerbate chilling injury symptoms.

I also investigated whether controlled atmosphere storage can mitigate the impact of chilling temperatures on basil quality, particularly on the content of volatile compounds responsible for aroma and flavor. Storage at 5% CO2 alleviated the symptoms of chilling injury for up to 3 days in ‘Genovese’, but not in ‘Lemon’ basil. I identified potential volatile markers of chilling stress in both ‘Genovese’ and ‘Lemon’ which could play a significant role in early diagnosis of said stress. I also determined that the impact of atmosphere modulation on chilling injury is cultivar- or species-dependent, and its potential is hampered by relative sensitivity to CO2 injury. While both chilling temperatures and controlled atmospheres altered key volatile compounds implicated in basil aroma and flavor, we determined that temperature had a bigger influence on the changes in volatile profile.

The loss of volatile compounds in basil must be linked with sensory data to shed light on the effects on aroma and flavor as it relates to human perception. To determine impacts on sensory quality, I assessed changes in key flavor volatile compounds of ‘Genovese’ basil following storage at low temperature and controlled atmospheres and related these to descriptive sensory data based on perceived aroma and flavor. I found associations between major volatile compounds and basil sensory attributes involving aroma, mouthfeel, taste, and flavor-by-mouth. Storage at the chilling temperature of 5°C, regardless of atmosphere, resulted in a reduction in volatile constituents which impacted the perceived aroma and flavor, confirming the need for optimum handling and storage temperatures in order to preserve fresh basil external and internal qualities.