Legume Antioxidant Activity Rocha-Guzman, Nuria E., Gonzalez-Laredo,

Legume Antioxidant Activity

Rocha-Guzman, Nuria E., Gonzalez-Laredo, Ruben F., Ibarra-Perez, Francisco J., Nava-Berumen, Cynthia A., and Gallegos-Infante, Jose-Alberto. (2007). Effect of pressure cooking on the antioxidant activity of extracts from three common bean (Paseolus vulgaris L.) cultivars. Food Chemistry, 100(1), 31-35.

Summary of background, methods, and findings.

The above authors were interested in understanding both the anti-nutritional and antioxidant activity of dried beans when consumed. The anti-nutritional components include enzyme inhibitors, lectins, phytates, cyanoglycosides, and polyphenols. The authors chose to focus on polyphenols because many of these compounds also exhibit antioxidant activity.

Prior research has shown uncooked beans have significant levels of polyphenols and antioxidants, but the effects of food processing on the concentration of these compounds had yet to be determined. The authors therefore assessed total phenol content and antioxidant activity after commercial-style processing of three different cultivars: Flor De Mayo M38, Bayo Victoria, and Pinto Villa.

The beans were cooked in an autoclave (high temperature), allowed to cool, and then seed coat separated from the cotyledon. This approach allowed independent testing of the cooking water, seed coat, and cotyledon. The aqueous phase of the cooking water was removed through lyophilization. Organic compounds were extracted from these three different preparations using 70% acetone. The extracts were then dried in a lyophylizer at a low temperature. Equal weight samples, at different dilutions, were then tested for total phenol content using a spectrophotometer. Free radical scavenging activity was assessed using DPPH (2,2-diphenyl-1-picrylhydracyl).

Most of the phenol content in dried beans is contained in the seed coat and the majority of this is lost during cooking to the water and cotyledon tissue. Overall phenol content in the cooked beans was reduced by 90% or more. In contrast, antioxidant activity increased significantly in all three cultivars and the evidence supported the conclusion that the increase in cotyledon antioxidant activity came from the seed coat via the cooking water.

Section II: Critique of methods and interpretations

The authors chose to compare total extracted phenolic compounds and antioxidant activity from the seed coat and cotyledon, before and after cooking. This is a straight forward approach that minimized the impact of potential confounding factors. The primary difference between the two approaches, aside from the cooking, is that the uncooked cotyledon and seed coat were ground into flour prior to the acetone extraction. The authors do not mention whether the cooked beans were also ground into a paste before extraction with acetone, or whether whole cotyledons were extracted. If the results do represent a comparison between extracts prepared from flour and whole cotyledons, this could affect efficiency of the extraction process.

There may be another flaw in the methods. Both uncooked and cooked seed coat and cotyledon preparations were extracted with acetone, but the lyophilized cooking water residue wasn't. It's possible this deviation in the protocol may have introduced an artifact that prevented accurate, direct comparisons between cooking water, seed coat, and cotyledon samples.