A two-step method of cyclolinopeptide (linusorb) preparation from flaxseed cake via dry-screening.

Linusorbs (LO), cyclolinopeptides, are a group of cyclic hydrophobic peptides and considered a valuable by-product of flaxseed oil due to numerous health benefits. Currently applied acetone or methanol extraction could contaminate the feedstocks for further food-grade application. Using flaxseed cake as feedstock, this study established a practical method for preparing LO from pressed cake. Firstly, LO composition of 15 flaxseed cultivars was analyzed. Next, cold-pressed cake was milled and screened mechanically. The kernel and hull fractions were separated based on the disparity of their mechanical strength. Monitored by hyperspectral fluorescence, the LO-enriched kernel fraction separated from cold-pressed flaxseed cake was further used as feedstock for LO production. After ethanol extraction, partition, and precipitation, LOs were extracted from cold-pressed flaxseed cake with a purity of 91.4%. The proposed method could serve as feasible flaxseed cake valorization strategy and enable the preparation of other polar compounds such as flax lignan and mucilage.

Stability of tryptophan-containing LOs in flaxseed oil and their response towards γ-tocopherol.

Linusorbs (LOs), significantly influence oil quality and sensory properties of flaxseed oil. Trp-containing LOs exhibit distinct oxidative behavior when γ-tocopherol (γ-T) is present. Polar fractions of crude flaxseed oil were stripped via silica absorption, and reintroduced (LO and γ-T) separately into the oil matrix to investigate their interaction during storage. Compared with crude oil, LOs account for 18.49% reduction of p-anisidine value, while LOs with γ-T contributed to most of the endogenous antioxidant effect in crude oil. γ-T was found to suppress oxidation of Trp-containing LO at early stage (Met form), while facilitate oxidation while at their mid-stage (MetO form, Methionine sulfoxide). In vitro oxidation shows that CLD more likely cleaved into peptide fragments, while few products retain intact ring structures. LC-MS/MS analysis and silicon simulation revealed proximity between MetO and Trp residues, facilitating inter- or intra-molecular reactions and ring structure rupture. Remarkably, the presence of γ-T facilitate these phenomena.