Carotenol fatty acid esters: easy substrates for digestive enzymes?

To study the specificity of gastric lipases on carotenoid mono- and diesters, an enzymatic assay was applied. Digestions were carried out in phosphate buffer at pH 7.4 and 37 degrees C. As substrates we employed oleoresins from marigold (Tagetes erecta L.; lutein diesters), red paprika (Capsicum annuum L., mainly capsanthin diesters), papaya (Carica papaya L.; beta-cryptoxanthin esters), and loquat (Eriobotrya japonica Lindl.; beta-cryptoxanthin esters) as well as retinyl palmitate. These were reacted with porcine pancreatic lipase, porcine pancreatin, porcine cholesterol esterase, and human pancreatic lipase. As reference enzyme a yeast lipase from Candida rugosa was applied. A high turnover could be observed with porcine pancreatic lipase and porcine cholesterol esterase, indicating cholesterol esterase to be a plausible candidate for generation of free carotenoids in the gut. Human pancreatic lipase accepted only retinyl palmitate as substrate, carotenoid mono- and diesters were not hydrolyzed. The assay permits an approach for calculation of enzymatic activities towards carotenoid esters as substrates for the first time, which is based on the amount of enzyme formulation, present in the assay (U/mg solid). Furthermore, these studies provide deeper insight into carotenoid ester bioaccessibility.