The Preharvest Application of Stress Response Elicitors Improves the Content of Bioactive Compounds without Modifying the Sensory Attributes of Butterhead Lettuce (Lactuca sativa var. capitata).

Using stress elicitors in fruits and vegetables is considered a good strategy to increase the content of bioactive compounds in plant foods. However, bioactive compounds can affect the sensory characteristics of food products, and little is known about their shelf-life stability in fresh produce treated with elicitors. In the present work, carotenoids and polyphenols were quantified by spectrophotometric methods in red and green butterhead lettuce treated with elicitors that had previously been demonstrated to increase bioactive compounds: arachidonic acid (AA), methyl jasmonate (MJ), and Harpin protein (HP). The bioactive compounds were determined immediately and during three weeks after harvest. A descriptive sensory analysis was carried out, which included odor, taste, tactile, and visual attributes of control and elicitor-treated lettuce. Carotenoids showed greater shelf-life stability than polyphenols, and both were more stable in red than in green lettuce during the first two weeks of storage. The best elicitor was MJ, which increased phenolic compounds (red and green lettuce), anthocyanins, and carotenoids (red lettuce) through the storage period. Color intensity, crispness, wettability, and bitter taste were some of the primary sensory attributes in butterhead lettuce and were not affected by any treatment. Other organoleptic properties were also not affected by the elicitors. These results suggest that elicitation could improve the content of bioactive compounds, which is stable through the shelf-life of butterhead lettuce, without any adverse effect on the sensory properties.

Effect of Elicitation on Polyphenol and Carotenoid Metabolism in Butterhead Lettuce (Lactuca sativa var. capitata).

The effect of elicitation in butterhead lettuce on carotenoid and polyphenol metabolism was evaluated. Different concentrations of arachidonic acid (AA), salicylic acid (SA), methyl jasmonate (MJ) (15, 45, and 90 µM) and Harpin protein (HP) (30, 60, and 120 mg/L) were applied on red and green butterhead lettuces. Total phenolic and flavonoid content were incremented by MJ (90 µM) in green and red lettuce. Carotenoids were increased in red lettuce (AA; 45 µM). Green lettuce modifies their phenolic acid profile after elicitation with AA and MJ; meanwhile, red lettuce incremented mainly in hydroxycinnamic acids and flavonols, MJ being the elicitor with the highest effect. There was an impact on secondary metabolite enzyme gene transcript concentration. Phenylalanine ammonia-lyase (PAL) and lycopene beta cyclase (LBC) increased in both varieties after elicitation. A relationship between phytochemical increase and the activation of the metabolic pathways after elicitation in butterhead lettuce was observed.

Effect of Different Elicitors and Preharvest Day Application on the Content of Phytochemicals and Antioxidant Activity of Butterhead Lettuce (Lactuca sativa var. capitata) Produced under Hydroponic Conditions.

The effect of four elicitors on phytochemical content in two varieties of lettuce was evaluated. The best preharvest day for application of each elicitor was chosen. Solutions of arachidonic acid (AA), salicylic acid (SA), methyl jasmonate (MJ), and Harpin protein (HP) were applied by foliar aspersion on lettuce leaves while cultivating under hydroponic conditions. Application of elicitors was done at 15, 7, 5, 3, or 1 day before harvest. Green lettuce showed the highest increase in phytochemical content when elicitors (AA, SA, and HP) were applied on day 7 before harvest. Similarly, antioxidant activity rose in all treatments on day 7. In red lettuce, the highest content of bioactive molecules occurred in samples treated on day 15. AA, SA, and HP were the elicitors with the highest effect on phytochemical content for both varieties, mainly on polyphenol content. Antioxidant activity also increased in response to elicitation. HPLC-MS showed an increase in the content of phenolic acids in green and red lettuce, especially after elicitation with SA, suggesting activation of the caffeic acid pathway due to elicitation.

Effect of the smoking process and firewood type in the phytochemical content and antioxidant capacity of red Jalapeño pepper during its transformation to chipotle pepper.

Chipotle pepper is a dry smoked red Jalapeño pepper well appreciated in the Mexican and American cuisines. Phytochemical content and antioxidant activity of red Jalapeño pepper has been previously reported, however, the effect of the smoking process in the content of phytochemicals, antioxidant capacity and capsaicinoids has not been previously reported. In the present study we found that the smoking process had a significant effect on the content of polyphenolic compounds and antioxidant capacity of red Jalapeño pepper. It induced a nearly 50% increase in total phenols and 15% increase in antioxidant capacity in chipotle pepper compared to fresh samples (in dry weight basis). Capsaicinoids and ascorbic acid content decreased in smoked samples, while carotenoids remained practically unchanged. The strongest effect of smoking was observed in the content of total flavonoids and catechin determined by HPLC. Therefore we can conclude that smoking process has a positive effect in the fruit because it raises its phytochemical properties. The type of wood used in the smoking process also had an effect on the phytochemical content and antioxidant capacity with traditional pecan wood being the best.