Lipid digestion in turbot (Scophthalmus maximus): In-vivo and in-vitro studies of the lipolytic activity in various segments of the digestive tract

In-vivo and in-vitro studies were carried out to evaluate lipolytic activity in the gut of juvenile turbot. The in-vivo study examined total lipid (% DW digesta), neutral and phospholipid classes (% total lipid, mg g(-1) DW digesta) and the fatty acid composition of the neutral lipid classes (% wt. of lipid class), as a function of hydrolysis, in the digesta of the stomach, foregut, hindgut and rectum of 50-60 g juvenile turbot. In contrast with earlier investigations, this study found the highest lipolytic activity and absorption occurring in the hindgut and rectum. In addition, various fatty acid groups showed differential uptake in this region which can be expressed, in order of increasing absorption, as saturates < monoenes < polyunsaturates. The in-vitro study investigated the lipolytic ability of digesta from different segments of the C-14-labelled lipid substrates: triacylglycerol (TAG), turbot digestive tract to hydrolyse the cholesterol ester (CE) and phosphatidylcholine (PC). Consistent with findings in the in-vivo analysis, the pattern of hydrolysis was repeated in all substrates tested and can be expressed in order of increasing hydrolytic activity as stomach < foregut < hindgut < rectum, Moreover, both studies suggested a non-specific lipolysis and phospholipid hydrolysis occurring in the posterior region of the gut particularly the rectum. The combined results of these studies concluded that the major site for lipolysis and absorption in juvenile turbot resides in the hindgut-rectum region. Future research should focus on the potential contribution of highly lipolytic bacteria in the posterior gut, such as Vibrio spp., which have been shown to effectively hydrolyse fish oils. (C) 1997 Elsevier Science B.V.