HUMIDIFICATION OF GREEN CANOLA SEED LEADS TO PIGMENT DEGRADATION IN THE ABSENCE OF GERMINATION

Mature canola seeds (Brassica napus cv. Westar) exposed to frost durin g development frequently contain green pigments that discolor extracte d canola oil. The green pigments must be removed from the oil by bleac hing, which significantly reduces the oil yield. The quantity of pigme nt remaining in the oil prior to bleaching is a function of the amount of pigment and the proportion of phytylated pigments in the seeds. Th e objective of this study was to determine whether the quantity and ch emistry of the pigments could be altered by seed humidification after harvest without leading to germination. Intact plants with seed moistu re in the range of 700 to 500 g kg(-1) were exposed to -5 degrees C fo r 3 h. The seeds were harvested at maturity, and analysed for moisture content, pigment content, storage protein, and triacylglycerol before and after exposure to 97% relative humidity for 10 d that increased s eed moisture content to 230 g kg(-1). This treatment led to a 25% redu ction in total pigment content and a 35% increase in the percentage of dephytylated pigments. In vitro measurements indicated this was the r esult of chlorophyllase activity. Neither storage proteins nor triacyl glycerols were mobilized during humidification. In comparison, unrestr icted water imbibition led to changes associated with seed storage pro tein reserve mobilization within 24 h of initial imbibition. Apparentl y, humidification treatment has the potential to decrease canola oil p igment content without decreasing seed oil or meal quality and quantit y. The recommended humidification procedure attains a seed moisture co ntent of 200 g kg(-1), which can be achieved by a 7-d exposure to 97% RH.