Purple-fleshed sweet potato P40 has been shown to prevent colorectal cancer in a murine model. This study is to identify anthocyanins by using HPLC/MS-MS and assess the stability during various cooking conditions. P40 possesses a high content of anthocyanins up to 14 mg/g dry matter. Total 12 acylated anthocyanins are identified. Top three anthocyanins, e.g., cyanidin 3-caffeoyl-p-hydroxybenzoyl sophoroside-5-glucoside, peonidin 3-caffeoyl sophoroside-5-glucoside, and cyanidin 3-(6"-caffeoyl-6"-feruloylsophoroside)-5-glucoside, account for half of the anthocyanin contents. Over 80% of anthocyanins measured by acid hydrolysis were cyanidin derivatives, indicating P40 is unique when compared with other purple-fleshed sweet potatoes that usually contain more peonidin than cyanidin. Steaming, pressure cooking, microwaving, and frying but not baking significantly reduced 8-16% of total anthocyanin contents. Mono-acylated anthocyanins showed a higher resistance against heat than di- and non-acylated. Among of which, cyanidin 3-p-hydroxybenzoylsophoroside-5-glucoside exhibited the best thermal stability. The stable acylated and cyanidin-predominated anthocyanins in P40 may provide extra benefits for cancer prevention.

In a growth chamber study, lettuce ( Lactuca sativa ) plants were used to evaluate the effects of water deficits on health-promoting phytochemicals with antioxidant properties. Lettuce plants were treated with water stress by withholding water once at 6 weeks after sowing for 2 days or multiple times at 4 weeks for 4 days, at 5 weeks for 3 days, and at 6 weeks for 2 days. Water stress increased the total phenolic concentration and antioxidant capacity in lettuce. Young seedlings, 7 days after germination, had the highest total phenolic concentration and antioxidant capacity, and also, younger plants were typically more responsive to water stress treatments in accumulating the antioxidants than older plants. Phenylalanine ammonia lyase and γ-tocopherol methyltransferase genes, involved in the biosynthesis of phenolic compounds and vitamin E, respectively, were activated in response to water stress, although no activation of L-galactose dehydrogenase was detected. Lettuce plants subjected to multiple water stress treatments accumulated significant amounts of chicoric acid compared with the control plants. Although the increase in antioxidant activity in water stress-treated plants at harvest was not as great as in young seedlings, it was significantly higher than the control. One-time water stress treatment of lettuce at the time of harvest did not result in any adverse effect on plant growth. Thus, these results show that mild water stress in lettuce applied just before harvest can enhance its crop quality with regard to its phytochemical concentration without any significant adverse effect on its growth or yield.