Protein solubility in relation to pH
Crucifer SSPs are known for their distinct solubility characteristics with changing pH (Perera et al., 2016; Wanasundara et al., 2012; Wanasundara and McInstosh, 2013). The protein solubility of camelina meal was similar to that from other eudicot seeds, including crucifers, with high solubility at extremely alkaline (43.6% at pH 10) and acidic pHs (16.2% at pH 1.5) (Figure 2A). The lowest protein solubility (~5% of total meal protein) was at pH 4.5, which is typical for canola and mustards (Wanasundara et al., 2012). In the pH range between 1.5 and 6.5, soluble proteins were of lower molecular weight with the ~15 kDa proteins likely being napin (Figure 2B). Of the proteins soluble above pH 6.5 (Figure 2B), ~40-54 kDa and ~22-33 kDa proteins are most likely cruciferin-derived polypeptides. The more diffuse polypeptides of <31 kDa observed after extraction at pH 12 (Figure 2B) may be indicative of alkali-induced hydrolysis. The present study confirms that varying pHs can be used to selectively recover camelina proteins. Highly alkaline conditions can be used to recover mixtures of SSPs, while lower pH conditions can be used to solubilise lower molecular weight proteins as has been reported for otherBrassica species (Wanasundara and McIntosh, 2013). Although extreme alkaline pH allows for higher protein yields, products may be subject to alkali-induced denaturation.