The Effect of Soaking Almonds and Hazelnuts on Phytate and Mineral Concentrations

Abstract

Background: Nuts are important sources of macronutrients, in particular cis-unsaturated fats; micronutrients; and phytonutrients, which are all important components of a cardioprotective diet. However, one phytonutrient, phytate, has been associated with reduced bioavailability of some minerals, including zinc, iron, calcium and magnesium. Recently, the general public has been bombarded with messages advocating soaking (or “activating”) nuts in order to enhance their health benefits. However, there is currently no scientific evidence to support or refute such claims. Research on grains and legumes has shown reductions in phytate concentrations with soaking, particularly when particle size is reduced. Therefore, the overall aim of this study is to assess the effects of different soaking regimes on phytate and mineral concentrations of whole and chopped almonds and hazelnuts to inform messages around soaking nuts. Methods: Two nut types, almonds and hazelnuts were analysed in this study in two different forms (whole and chopped). Three different soaking treatments were used to assess the importance of soaking time and the addition to salt to the soaking solution: 1. soaking for 12 hours in salt solution (12hrs+salt), 2. soaking for 4 hours in salt solution (4hrs+salt), and 3. soaking for 12 hours in water with no added salt (12hrs-salt). These were compared to unsoaked whole nuts. All samples were analysed for phytate (sum of inositol hexa-phosphate (IP6) and inositol penta-phosphate (IP5)), calcium, magnesium, phosphorous, potassium, iron, sodium, and zinc. Phytate concentrations were analysed using high-performance liquid chromatography (HPLC) and minerals by inductively coupled plasma mass spectrometry (ICP-MS). Results: No statistically significant differences in phytate concentrations were observed between any of the treatments for whole almonds and whole hazelnuts. However, for chopped nuts, the soaking process generally resulted in statistically significant decreases in phytate concentrations, with reductions around 10% in hazelnuts (all p<0.001). In addition, statistically significant reductions were also observed for most minerals (calcium, iron, magnesium, phosphorus, potassium and zinc) following soaking in chopped nut. The reductions in phytate concentrations in the chopped nuts were accompanied by a reduction in mineral content which attenuated reductions in the phytate:mineral molar ratios. Hence, the changes in the phytate:mineral molar ratios suggest that soaking both whole or chopped nuts had no meaningful effect on the bioavailability of minerals. Changing the soaking duration, and addition of salt to the soaking solution, generally had little effect on mineral concentrations, with a few exceptions. However, an increase in sodium content was seen for whole (around 200-300 fold) and chopped (around 600-800 fold) in both almonds and hazelnuts when soaked in salt solutions compared to unsoaked nuts and nuts soaked without salt (all p≤0.002). Conclusion: It is evident from the current research that soaking almonds and hazelnuts in the whole form was not effective in reducing phytate concentration. While soaking chopped nuts led to reductions in phytate, the mineral content was also compromised, with no overall improvements observed in the phytate:mineral molar ratios. Therefore, there is no evidence to support claims that activating nuts reduces phytate content to the extent which allows for greater nutrient bioavailability.