Maillard reactions cause browning in bean seed coats during ageing: Inhibition by aminoguanidine

Physiological ageing was studied in a white-seeded cultivar of snap bean (Phaseolus vulgaris). Seeds were aged by first equilibrating them at 70% relative humidity followed by incubation at 40 degrees C, removing samples at one-week increments up to 6 weeks. Standard germination tests revealed that non-aged seeds had 95% germination, and no seeds germinated after 6 weeks. Changes in seed coat colour were observed with ageing, and browning increased with duration of ageing. Light reflectance measurements were made with a Hunter Colorimeter, and 'L' readings (white = 100 and black = 0) were obtained from a sample of intact seeds. A slight decrease in L values was measured during the first 4 weeks of ageing, followed by a significant decline in the 5- and 6-week samples. Maillard reactions were proposed to be responsible for seed coat browning. Since chemical analysis of advanced glycosylation endproducts is problematic, a specific chemical inhibitor of Maillard chemistry was utilized. Application of this inhibitor, aminoguanidine, prior to ageing reduced the usual browning, and thus supported the proposition that Maillard reactions may be responsible for seed coat browning in snap beans.