Sinapine Leakage from Brassica Seeds

Abstract

The purpose of this project was to study factors that influence the leakage rate and develop methods to enhance leakage of sinapine from Brassica seeds. Six seedlots (two seedlots of one cultivar each of cabbage (Brassica oleracea L., Capitata group), broccoli, and cauliflower (B. oleracea L., Botrytis group) were studied. Leakage was quantified spectrophotometrically by measuring the absorbance of the soak water at 330 nm. The onset of sinapine leakage was determined from single seeds by the visual presence (yellow soak water) caused by soaking seeds in a biological buffer adjusted to pH 10. The leakage pattern from heat-killed seeds of all seedlots was sigmoidal with a distinct lag phase followed by a rapid efflux and final slower rate. The duration of the lag phase and the total amount of sinapine leaked after 24 hours was not the same for all seedlots after adjusting for seed count, seed weight, or sinapine content. Therefore, another factor was responsible for differences measured in leakage. Embryos or seeds with cracked testas leaked faster than intact seeds, and the leakage pattern without testa integrity was biphasic. From these studies, we conclude that the testa was a major factor regulating sinapine leakage. Pretreating heat killed seeds, with up to 1.0% NaOCl for 10 minutes, accelerated the onset of leakage. The time for 50 percent of the seeds to leak (T50) decreased as NaOCl concentration increased. Leakage uniformity, as measured by the standard deviation of the distribution, generally increased as NaOCl concentration increased. The sigmoidal leakage pattern from heat-killed Brassica seeds may be attributed to seedcoat cracking associated with imbibitional swelling. A NaOCl pretreatment may have increased the permeability of the testa and, thereby, enhanced the leakage rate.