Environmental and Varietal Effects on Niacin and Folate Contents in Raw and Roasted Peanuts

Abstract

Peanuts (Arachis hypogaea L.) are known to be sources of several important B-vitamins, including niacin and folate. Recent research has shown that therapeutic doses of niacin are beneficial for vascular health; therefore, determination of the concentrations found in current varieties in production and potential breeding lines is needed. Folate is a term for a related group of compounds with vitamin activity important in DNA biosynthesis. Adequate levels of folate intake have been found to reduce the risk of a variety of syndromes, most notably fetal neural disorders. Current information about the concentrations and the specific types of folates present may position peanuts as an important source of this nutrient.

For the niacin assay, a series of raw and roasted samples from the 2007 and 2008 Uniform Peanut Performance Trials (UPPT) and the 2008 Core of the Core peanut germplasm collection were analyzed to compare levels of niacin across 10 growing locations. Thirty-nine total UPPT Florunner (medium grade size) and NC7 (extra large kernel {ELK} grade size) samples were analyzed using the AOAC non cereal foods method. Thirteen selected samples from the Core of the Core were also analyzed. Niacin concentration (mg/100g) of raw UPPT samples ranged from 8.20 to 25.8 with an average of 16.1 for the 2007 UPPT, 17.7 for the 2008 UPPT, and 16.8 for the Core of the Core samples. The average niacin concentration in raw Florunner and NC7 samples increased from 14.6 and 17.4 in 2007 to 16.4 and 18.9 in 2008, respectively. There was a significant difference between niacin concentration and peanut variety, growing location and year of production. These differences are a result of slowed metabolic processes during dark respiration caused by cooler night temperatures. For the roasted UPPT samples, niacin concentration (mg/100g) ranged from 12.2 to 22.4. There was not a significant difference between raw and roasted samples, due to the stability of niacin to light and heat. For the folate assay, a series of raw and roasted samples from the 2008 UPPT and the 2006 and 2008 Core of the Core were analyzed to compare total folate and individual folate vitamers across varying locations. Twenty-four Core of the Core and 12 UPPT samples were analyzed using a tri-enzyme method of extraction. Total folate content (μg/100g) for Core of the Core samples ranged from 207.7 to 378.3 in 2006 and 116.0 to 257.9 in 2008. The average total folate content (μg/100g) for raw Florunner and NC7 samples was 176.2 and 136.5, respectively, and for the roasted Florunner and NC7 samples was 78.9 and 72.0, respectively. Raw UPPT samples had significantly higher folate contents than roasted UPPT samples, regardless of variety. This is a result of the instability of folate at high temperatures. There was also a significant difference between Florunner and NC7 varieties, but no difference among growing locations. Of the individual folate vitamers, 5-methyl-tetrahydrofolate (THF) and 5-formyl-THF were in the highest amounts regardless of peanut collection, variety or condition. This is noteworthy since these vitamers are absorbed and used most readily by humans.

Environmental effects, including differences in light, temperature and moisture, and plant genetics play a role in the amount of vitamins produced and utilized. Environment, genetics, and the interaction between environment and genetics may be responsible for the outcomes observed. These results suggest that germplasm/varietal differences may be sufficient for increases in niacin and folate levels through conventional breeding.