Blueberry Feeding in Pigs: Effects of Dose and Duration on Physiological Parameters

W. Kalt et al.

Despite an abundance of in vitro evidence supporting a role for berry flavonoids in human health, there is a paucity of evidence related to the in vivo bioavailability of these compounds. Until information on the quantities and forms of absorbed flavonoids is available, it will be difficult to develop hypotheses related to the mode of action of fruit flavonoids and to assess the significance of in vitro results with respect to human health functionality. 

            In addition to a lack of information on berry flavonoid bioavailability, little is know about the effects of long term berry feeding in normal, healthy animals. Most studies have focused on the effects of  flavonoid intervention in conjunction with an acute treatment or have used animals that are genetically predisposed to a condition of interest.

            Compared to many berry crops, blueberries (Vaccinium sp., including V.angustifolium, V. corymbosum and V. myrtillus) contain a high concentration of phenolic compounds and, in particular, anthocyanins.  Studies conducted in vitro provide evidence to suggest that blueberries possess antioxidant and other beneficial bioactivities. While in vivo studies using various animal models have demonstrated that blueberry diet supplementation can be neuroprotective, very little is known about the bioavailability of blueberry flavonoids to the brain and other tissues, or about the transport mechanisms involved

To assess the potential role of blueberries on various aspects of health maintenance, we have studied the effects of long-term feeding of blueberries in healthy pigs. Pigs were chosen for this study because of their similarity to humans with respect to digestive absorption, and cardiovascular physiology. A major aim of the study was to assess anthocyanin bioavailability, since these compounds are present in blueberries at a high level, and may contribute to the beneficial effects of blueberries on health-related parameters.

            In the first year of a two year study, diets of pigs were supplemented with 0, 1, 2 and 4% powdered whole freeze dried blueberries (V. corymbosum). Blood was collected on all pigs at 0,  4 and 8 weeks. Pigs in each diet group (n=5) were killed after 4 and 8 weeks to determine the  bioavailability of anthocyanins in tissues and fluids. Materials collected included: liver, kidney, large and small intestine, 3 brain regions, eyes, muscles, urine, plasma, and feces.

            Methods developed for the extraction of anthocyanins from tissues were a modification of those published by Tsuda et al. (1998). The level of recovery of anthocyanins spiked into tissues before extraction was between about 65 and 100%. Liquid chromatography with both electrochemical (EC) and mass spectrometric (MS) detection was necessary to separate and detect anthocyanins in tissues. EC detection was substantially more sensitive (up to 5 X) than MS detection for most of the anthocyanins analyzed. Although only limited results are available at this time, at least two anthocyanins have been detected in extracts of pig brain cortex.

            Plasma lipids were affected by blueberry supplementation. Pigs supplemented with either 1, 2 and 4% blueberries had a significantly lower total cholesterol, LDL-cholesterol, and HDL cholesterol than pigs that not receive blueberries. Compared to controls (0%), pigs receiving 2% blueberries had 12% lower total cholesterol, 19% lower LDL cholesterol, and 9% lower HDL cholesterol. Plasma triglycerides were not affected by blueberry supplementation.

            Blood platelet activity was evaluated using an automated platelet function analyzer which simulated normal blood flow and used, in this case, collagen/epinephrine as a platelet agonist . There was no effect of blueberry supplementation on platelet activity or on other factors related to blood clotting (e.g. prothrombin time, activated partial prothrombin time). 

            Results from this study indicate that blueberry anthocyanins cross the blood brain barrier, and can be identified at least in the cortex. Also, flavonoid supplementation may provide beneficial effects to plasma lipid profiles. Finally, contrary to published reports using other methods, flavonoid supplementation does not affect blood platelet activity.  

Key words: blueberry; anthocyanins, pigs, bioavailability, lipids