FAYETTEVILLE, Ark. — University of Arkansas researchers have found that spinach grown in different seasons varies in its antioxidant capacity, a discovery that could allow commercial growers to maximize the content of these health-beneficial compounds in their products by altering the plants’ growing season.

Food scientists Luke Howard, N. Pandjaitan, Teddy Morelock and M.I. Gil of CEBAS-CSIC in Spain reported their findings in a recent issue of the Journal of Agricultural and Food Chemistry.

The researchers grew 11 commercial cultivars and 15 advanced breeding lines of spinach in Kibler, Ark., over two growing seasons to determine their antioxidant capacity. Previous research has shown that spinach antioxidants called flavonols have anti-cancer, anti-inflammatory and other properties that may prevent disease and enhance health.

"Spinach appears to be a powerhouse in terms of nutrition," Howard, University of Arkansas professor of food science, said. The antioxidants in spinach and other fruits and vegetables tie up free radicals that cause oxidation of body tissue. This oxidation has been linked to degenerative diseases including cancer, stroke and Alzheimer’s.

"An analogy is to say that our bodies are rusting, and antioxidants stop the rusting," he said.

So in the interest of maximizing the healthful properties of spinach, the researchers wanted to determine the genetic variation of antioxidant capacity and the influence of breeding season on that capacity.

The researchers used two measurements to determine antioxidant levels; the concentration of phenolics, themselves antioxidants, and the oxygen radical absorbing capacity (ORAC) of the cultivars. The concentration of phenolics is easier and less expensive to monitor, and since it is linked to ORAC, can be used by breeders to determine the relative levels of antioxidants.

They planted the fall crop of spinach in early September and harvested the crop in early December. The spring spinach crop was planted in mid-October and harvested in March.

They found that the overall means of ORAC were 17.1 in the spring and 13.5 in the fall; the phenolic concentrations were 3,633 in the spring and 1,932 in the fall.

"It appears that different cultivars respond differently to stressful growing conditions," Howard said.

The spinach harvested in the spring faced higher temperatures, greater light intensity, more disease and susceptibility to bolting than spinach grown in fall, the researchers contend.

"The effect of the growing season is quite dramatic. You can’t just screen the cultivar for one season" and predict its antioxidant levels from that screening, Howard said.

Further, the researchers’ results indicated that the strength of the seasonal change varied with the plant cultivar. This finding emphasizes the need for breeders and researchers to raise cultivars over multiple years and growing seasons to get a full picture of a plant’s antioxidant capacity.