Potassium Bioaccessibility in Uncooked and Cooked Plant Foods: Results from a Static In Vitro Digestion Methodology

Abstract

Hyperkalemia is a major concern in chronic kidney disease and in end-stage renal disease, representing a predictor of hospitalization and mortality. To prevent and treat hyperkalemia, dietary management is of great clinical interest. Currently, the growing use of plant-based diets causes an increasing concern about potassium load in renal patients. The aim of this study was to assess the bioaccessibility of potassium in vegetables, concerning all aspects of the plants (fruit, flower, root, tuber, leaf and seed) and to what extent different boiling techniques affect potassium content and bioaccessibility of plant-based foods. Bioaccessibility was evaluated by an in vitro digestion methodology, resembling human gastro-intestinal tract. Potassium content was higher in seeds and leaves, despite it not being possible to define a common "rule" according to the type of organ, namely seed, leaf or fruit. Boiling reduced potassium content in all vegetables excluding carrot, zucchini, and cauliflower; boiling starting from cold water contributed to a greater reduction of the potassium content in potato, peas, and beans. Bioaccessibility after in vitro digestion ranged from 12 (peas) to 93% (tomato) regardless of species and organs. Higher bioaccessibility was found in spinach, chicory, zucchini, tomato, kiwi, and cauliflower, and lower bioaccessibility in peas. Potassium from leaf resulted in the highest bioaccessibility after digestion; as a whole potassium bioaccessibility in the fruits and vegetables studied was 67% on average, with differences in relation to the different organs and species. Further, considering the method of boiling to reduce potassium content, these data indicate that the effective potassium load from plant-based foods may be lower than originally expected. This supports the clinical advices to maintain a wide use of plant-based food in the management of renal patients.

Keywords: CKD; ESKD; food boiling; hyperkalemia; in vitro food digestion; plant-based diet; potassium bioaccessibility; potassium intake.

Figure 1

Potassium content in 100 g of raw samples of fruits (white columns), vegetables (grey columns) and legumes (black columns). Data were statistically analyzed following one-way ANOVA using the species as the variability factors and separated by Fisher’s least significant difference (LSD) post-hoc test (p < 0.05).

Figure 2

Percentage reduction of potassium content in samples when boiled starting from cold water (full columns) and when boiled starting from hot water (empty columns), in respect to potassium content in raw samples. Considering each sample singularly, means were statistically analyzed by Student’s t test, comparing different boiling procedures. * p < 0.05; ** p < 0.01; *** p < 0.001.

Figure 3

Percentage (%) of bioaccessible potassium in digested raw samples of fruits (white columns), vegetables (grey columns) and legumes (black columns). Means were statistically analyzed following one-way ANOVA using the species as the variability factors and separated by Fisher’s least significant difference (LSD) post hoc test (p < 0.05).

Figure 4

Percentage variation of bioaccessible potassium in samples analyzed when boiled starting from cold water (full columns) and when boiled starting from hot water (empty columns), when compared with potassium content in raw samples. Considering each sample singularly, means were statistically analyzed by Student’s t test, comparing different boiling procedures. *** p < 0.001.