Cutin composition of five Finnish berries

The raw cutin (i.e., extractive-free isolated cuticular membrane) fraction from Finnish berries, sea buckthorn (Hippophae rhamnoides), black currant (Ribes nigrum), cranberry (Vaccinium oxycoccos), lingonberry (Vaccinium vitis-idaea), and bilberry (Vaccinium myrtillus), was depolymerized by NaOMe-catalyzed methanolysis. The composition of cutin monomers was determined by GC-(EI)MS analysis either as methyl esters or as TMSi esters, with OH groups derivatized to TMSi ethers. There was a notable difference in the degree of depolymerization, ranging from 6 to 47%. The extractive-free berry cuticle, that is, raw cutin, thus contains < 50% polyester polymer cutin. The predominant cutin monomers were C-16 and C-18 omega-hydroxy acids with midchain functionalities, mainly epoxy and hydroxyl groups. Typically, the major compounds were 9,10-epoxy-18-hydroxyoctadecanoic acid, 10,16-dihydroxyhexadecanoic acid, 9,10,18-trihydroxyoctadecanoic acid, 9,10-epoxy-18-hydroxyoctadec-12-enoic acid, and 18-hydroxyoctadec-9-enoic acid. The amount of epoxyacids was rather high in sea buckthorn (similar to 70%) and cranberry (similar to 60%), compared with the other berries. The black currant cutin differed from that of the other berries with a significant portion of hydroxyoxohexadecanoic acid (similar to 12% of total monomers). This investigation of the cuticular hydroxy acids of five Finnish berries is part of the exploitation of the northern natural resources related to the chemical composition, nutritional value, and sensory properties.