Changes in free amino acid, protein, flavonoids, and phenolic content in jujube (Ziziphus jujube) fruit during eight stages of growth and antioxidative and cancer cell inhibitory effects by extracts

Authors: CHOI,, SUK-HYUN - Seowon University, Korea; AHN, JUN-BAE - Seowon University, Korea; KIM, HYUN-JEONG - Keimyung University; IM, NAM-KYUNG - Keimyung University; KOZUKUE, NOBUYUKI - Seowon University, Korea; Levin, Carol; Friedman, Mendel

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/26/2012
Publication Date: 10/9/2012
Citation: Choi,, S., Ahn, J., Kim, H., Im, N., Kozukue, N., Levin, C.E., Friedman, M. 2012. Changes in free amino acid, protein, flavonoids, and phenolic content in jujube (Ziziphus jujube) fruit during eight stages of growth and antioxidative and cancer cell inhibitory effects by extracts. Journal of Agricultural and Food Chemistry. 60(41):10245-10255. doi:10.1021/jf302848u.

Interpretive Summary: The jujube fruit is widely cultivated from southwest Europe to China, including India and the Middle East. In addition to their food uses, jujubes have been used in many traditional medicines and have been shown to exhibit numerous health-promoting effects. Jujubes may therefore be considered as a so-called functional food, having nutritional as well as medicinal uses. In the United States, jujube products are available at health food stores. In the present study, the widely consumed Korean Boeun-deachu variety of jujube was analyzed by HPLC, MS, and MS-MS for changes in the content of crude protein, free amino acids, and individual flavonoids at eight stages (S1-S8) of ripeness. Extracts were also analyzed by colorimetry for total phenolics, total flavonoids, for antioxidative activities by three methods and for their ability to inhibit human cancer cells. Flavonoid content and the antioxidant levels decrease rapidly during ripening, indicating that fruits should be eaten at the earliest time of palatability. However, this may also need to be balanced against the high levels of free asparagine, a precursor of acrylamide, found in mid-maturity fruits. These results might help guide the optimization of harvesting jujube fruit at different stages of maturity to optimize beneficial nutritional and health effects. Because individual jujube flavonoids are reported to exhibit different health promoting effects, knowledge of both composition and concentrations of bioactive compounds of jujube as a function of fruit ripeness can benefit consumers.

Technical Abstract: The widely consumed Korean Boeun-deachu variety of jujube (Ziziphus jujube) was analyzed by HPLC, MS, and MS-MS for changes in the content of crude protein, free amino acids, and individual flavonoids at eight stages (S1-S8) of ripeness. They were also analyzed by colorimetry for total phenolics, total flavonoids, and for antioxidative activities by three methods. The FRAP antioxidant assay was well correlated with colorimetrically determined total flavonoids and total phenolics, but the DPPH and ABTS antioxidant methods were not. Total flavonoid levels were much lower when determined by colorimetry than by HPLC, and they did not correlate with each other except when epicatechin, the predominant flavonoid, was deducted. Levels of epicatechin, which were not correlated with any other parameter, increased from S1 to S6 and then decreased. The MTT assay measuring cell viability showed that the jujube extracts dose-dependently inhibited the growth of HeLa cervical cancer cells similarly at all jujube growth stages. This inhibition was highly correlated with the DPPH antioxidant value. The dose-dependent inhibition of Hel299 normal lung and A549 lung cancer cells decreased as the fruit matured, and was well correlated with the FRAP value, total polyphenols, and total flavonoids. Chang normal liver cells were dose dependently inhibited by only the S5 extract. U937 lymphoma cells were unaffected by the extracts. The maturity of the fruit is inversely correlated with total polyphenolics, flavonoids, and crude protein content, and the three antioxidative tests as well as activity against Hel299, HeLa, and A549. Total free amino acid content was relatively consistent throughout the stages, except that it peaked at S5, mostly owing to an increase in free asparagine, a precursor to potentially carcinogenic acrylamide. These results might help guide the optimization of harvesting jujube fruit at different stages of maturity to optimize beneficial nutritional and health effects.