In accordance with EU regulations, 100% fruit juice (100%FJ) has nothing added or taken away, which is why it reflects the nutrient content of the fruit from which it is made1 . The nutrient composition of 100% orange juice (100%OJ) is shown below per 100 g. Values in red represent official ‘source’ claims that can be made on pack.
Are nutrients in 100%FJ bioavailable?
The bioavailability of 100%OJ polyphenols was measured in 12 adults who ate a low polyphenol diet for 2 days before being given 250 ml pulp-enriched 100%OJ or a placebo drink, following a 2-week washout. The 100%OJ contained 584 mmol of polyphenols, mostly as flavanones.
24-hour urine sampling showed that metabolites of flavanone were appearing 2-10 hours after consumption which is consistent with the accepted view that flavanones are absorbed in both the small and large intestines. Flavanone catabolites (produced during breakdown) were seen in large quantities, equivalent to 88% of what had been consumed. These findings suggest that polyphenols in 100%OJ appear to be more bioavailable than previously believed.
A longer term study examined the bioavailability of nutrients and bioactive substances in 100%OJ. For 3 weeks, 13 healthy, normal weight adults drank 236 ml juice daily which provided 256 mg vitamin C, 229 mg hesperidin, 6 mg carotenoids, and 160 µg folate.
Compared with baseline, blood sampling revealed a significant increase in nutrient levels i.e. vitamin C and folate levels increased by around 50% while flavanone levels rose by 8-times. Carotenoid levels increased by 22%. Urine results confirmed a 9-times higher excretion of flavanones which returned to baseline levels within 2 weeks of stopping the juice consumption.
Interestingly, subjects’ weight did not change during the study and the participants reported a lower intake of snacks and smaller portion sizes of meals.
How do juices compare with whole fruit?
Aschoff et al. (2015) compared the bioavailability of ß-cryptoxanthin, lutein, zeaxanthin and zeinoxanthin from fresh oranges (400 g) versus pasteurized 100%OJ (719 g). Using a randomised cross-over design in 12 participants, a known amount of ß-cryptoxanthin was provided in both test conditions. Blood samples were taken hourly for the next 10 hours.
The results showed that ß-cryptoxanthin was 1.8-times more bioavailable in 100%OJ than in whole oranges. Based on a separate in vitro method, ß-cryptoxanthin was 5-times more bioaccessible in 100%OJ versus whole oranges (see chart on the left for ß-cryptoxanthin; there was also a similar although non-statistically significant trend for lutein).
The differences may be due to high pectin levels in the whole fruit inhibiting absorption, or the disruption of cell walls in 100%OJ leading to a greater release of ß-cryptoxanthin. Other work has found that more of the carotenoids in 100%OJ are present in droplet form which may explain why absorption from juice is greater than from whole fruits.
A second similar study examined the bioavailability of the flavanones, hesperidin and narirutin, in 100%OJ versus whole oranges. This was done by tracking the excretion of a known amount of flavanones in urine. Despite the hesperidin content of whole oranges being 2.3-times higher than 100%OJ, 24-hour urine excretion of hesperitin (the metabolite) was similar.
This could mean that absorption and metabolism of dietary flavanones is saturated when intake exceeds a certain limit, perhaps due to poor solubility or limitations of transport mechanisms in the gut. Or, it could mean that flavanones in the whole fruit are not very bioavailable due to the fibre content. Dietary fibre in oranges is 16-times higher than in 100%OJ.
Fresh juice versus processed juice
As commercially-produced juice often contains lower levels of vitamins, due to the impact of shelf life, there is an assumption that it is less useful nutritionally than freshly squeezed juice.
This was investigated for 100%OJ in a randomised crossover trial in 24 adults where the two types of juice were given for 2 days each separated by a 30-day washout. Blood and urine sampling revealed no statistical differences in the metabolism of the flavanones, hesperidin and narirutin coming from processed or fresh 100%OJ. However, due to differences in the flavanone content (58 mg processed vs. 16 mg fresh), gut absorption and urinary excretion were significantly higher following consumption of the processed 100%OJ. Overall, this resulted in an increased 1.6-times bioavailability (see diagram on the right).
Flavanones are known to be soluble compounds which sit within the juice cloud, rather than in the cell wall material. The authors proposed that the rich flavonoid content of 100%OJ may be responsible for some of the health effects seen in studies, i.e. antioxidative and anti-inflammatory responses.
In other work, the focus on vitamin C degradation in heat-treated foodstuffs may be rather narrow as health outcomes could be driven by complex mixtures of phytochemicals rather than a single antioxidant. As one example, vitamin C provides only 0.4% of the total antioxidant activity of apples with the remaining activity driven by phenolics, flavonoids, and anthocyanins. Therefore, a broad spectrum of bioactive substances in food should be considered in future studies, as well as the water content which can influence the concentration of nutrients.
Role of bioactives in the body
Various studies have confirmed the potential health impact of the bioactives found in 100%FJ. In a controlled trial in diabetic participants, hesperidin lowered oxidative DNA damage and lipid peroxidation. In another trial ß-cryptoxanthin lowered total, LDL and HDL cholesterol and positively modified bone turnover markers. Lutein and zeaxanthin have been found to partially restore vision in people with age-related macular degeneration, while citrus flavonoids may lower the risk of neurodegenerative diseases. No EU health claims have yet been authorised for citrus flavonoids but claims exist for olive polyphenols (blood lipid oxidation) and cocoa flavanols (vascular health).
Bioavailability and ageing
The availability and metabolism of nutrients is affected by ageing. An observational study of 2118 women from six European countries examined blood levels of carotenoids and tocopherol (a form of vitamin E). Older women had lower levels of carotenoids but higher levels of tocopherol. As older women had higher intakes of fruit and fruit juice (both sources of carotenoids), it is likely that the age-related differences were due to a lower bioavailability or different storage patterns in the body. If this were the case, higher intakes of fruit and fruit juice could be an important way to prevent a significant decline in carotenoid status in older people.