Addition of calcium compounds to reduce soluble oxalate in a high oxalate food system

•Spinach leaf contains high levels of total and soluble oxalates.•Addition of soluble calcium salts makes small changes to the pH of the homogenate.•Calcium salts significantly reduce the soluble oxalate content of spinach homogenates.•Calcium carbonate was the least effective at reducing soluble oxalate content.

Spinach (Spinacia oleracea L.) is often used as a base vegetable to make green juices that are promoted as healthy dietary alternatives. Spinach is known to contain significant amounts of oxalates, which are toxic and, if consumed regularly, can lead to the development of kidney stones. This research investigates adding 50-500 mg increments of calcium carbonate, calcium chloride, calcium citrate and calcium sulphate to 100 g of raw homogenates of spinach to determine whether calcium would combine with the soluble oxalate present in the spinach. Calcium chloride was the most effective additive while calcium carbonate was the least effective. The formation of insoluble oxalate after incubation at 25 °C for 30 min is a simple practical step that can be incorporated into the juicing process. This would make the juice considerably safer to consume on a regular basis.