Physical characteristics of vegetable foodstuffs that could influence bowel function

Abstract

Abstract There is a need to explore physical characteristics of dietary vegetable fibre that can be tested in nutritional studies. This paper describes two properties of the fibre of commonly eaten vegetables and fruit, namely water‐holding capacity (w.h.c.) and ion exchange capacity. Twenty‐six different fruit and vegetables were dried to a powder. The capacity of the powder to hold water was estimated. Lettuce, carrot, cucumber, celery and aubergine had the greatest w.h.c. whereas maize, oatmeal, potato, banana, wheat and bran had the least. The water‐adsorptive capacity of any dietary plant is determined by its fibre content and the water‐holding capacity of the fibre. Estimations of the fibre content of the original plant and the w.h.c. of that fibre suggest that in their natural state, bran (447 g of water holding/100 g of original material), mango (312 g), carrot (208 g), apple (177 g) and brussels sprouts (168 g) are better as hydrophilic laxatives than bananas (68 g), cauliflower (68 g), potatoes (49 g) and turnip (37 g). Most of the fibre acts as a monofunctional weak cation exchange resin; lettuce (3.1 mequiv./g), cabbage, carrot, orange, turnip (2.4 mequiv./g) are in the range of commercially available weak cation exchange resin. When a diet is changed to one with a high fibre content then these physical characteristics may influence the choice of vegetables and fruit which are included in the diet.