Content of nitrate and nitrite in commercial and self-made beetroot juices and the effect of storage temperature

Abstract

Popularity of beetroot juice (BJ) is growing due to its high inorganic nitrate content $\left({\mathrm{NO}}_3^{-}\right)$ and its potential physiological benefits. However, the content of ${\mathrm{NO}}_3^{-}$ is not indicated in most commercial BJs and it can be affected by seasonal changes and storage conditions. This study analyzed the content of ${\mathrm{NO}}_3^{-}$ and nitrite $\left({\mathrm{NO}}_2^{-}\right)$ in five and two commercial and self-made BJs, respectively, that were purchased in the summer and winter periods. The effect of storage temperature (20°C, 4°C, and -20°C) and pH was also analyzed. In nonconcentrated BJs, the ${\mathrm{NO}}_3^{-}$ content was 34 ± 20% (p = .075) in the winter than in the summer. ${\mathrm{NO}}_3^{-}$ was fully degraded in self-made BJ after 3 days at 20°C. This effect was attenuated by 78% and 82% when it was kept at 4°C and -20°C, respectively. The addition of lemon juice (5%) to self-made BJ was another useful approach to avoid ${\mathrm{NO}}_3^{-}$ degradation for 3 days when it was kept at 20°C. Regarding ${\mathrm{NO}}_2^{-}$, self-made BJ had higher concentration (0.097 ± 0.01 mg/mL) compared to commercial BJs (<0.1 mg/mL; p = .001). The pH of self-made BJ was higher (6.3 ± 0.1) compared to commercial BJs (4.5 ± 0.3; p = .001). These results suggest that the content of ${\mathrm{NO}}_3^{-}$ in nonconcentrated BJs can substantially differ across the year and this is an important factor to take into account when recommending BJs to promote some of its potential physiological benefits.

Keywords: beet; nitrate; nitric oxide; nitrite; nitrogen.