LOW PH ENHANCES THE TRANSFER OF CAROTENE FROM CARROT JUICE TO OLIVE OIL

A current model for carotenoid transport and absorption in the gut pro poses an initial solubilization in the oil phase of dietary emulsions followed by incorporation of the carotenoids in mixed bile salt micell es. To assess the relevance of the first stage of this model to what i s observed in vivo we have examined the transfer of carotene from carr ot juice to olive oil. Increased acidity enhanced the transfer from bo th whole juice and carotene crystals isolated from carrot chromoplasts . The transfer was significantly slower from whole juice. By using exo genous P-carotene and measuring its transfer to oil in the presence an d absence of carrot juice we have demonstrated that the inhibition of the transfer in juice arises, at least in part, from soluble juice fac tors. The inhibition is relieved by a fall in pH, which leads to lower ing of the electric potential at the oil/aqueous phase interface and a ggregation of carrot tissue including crystalline carotene. Under cond itions of low pH, oil droplets adhere to the tissue aggregates, allowi ng carotene to pass into the oil. Our results provide an explanation f or why carotene absorption in vivo is depressed by conditions of low g astric acidity.