Crunchy carrots and fluffy bread – It’s all about the structure

By Li Day

3 October 2013



It’s a food’s structure that gives a carrot its crunch and a loaf of bread its fluffiness, and researchers increasingly believe that many of a food’s key properties relate to its structure.

Nature is able to assemble sophisticated structures and food is no exception, even right down to the microscopic scale. Food components such as protein, carbohydrate, fat and minor ingredients, when mixed, organise into a range of structures, and its becoming clear that many properties key to a food’s processability, nutritional and sensory qualities, and safety are related to its structure.

Plants are structured like honeycomb, called ‘cell wall’ structure. The video below clearly shows the defined cell walls in raw carrot – that’s why it’s crunchy!

[wpvideo oj5U7qZz]A scanning laser confocal microscope video in 3D showing the defined cell wall structure of raw carrot (Video: Sofia Oeseth)

Most foods have a ‘fluffy’ foam structure that forms when air bubbles are incorporated into a liquid, like bread, ice cream and meringue. The microscopic image below shows dough with air bubbles (black), gluten (yellow), starch granules (green) and protein (red).

Dough under the microscope.

Dough’s foam structure is full of air.

Then there are suspensions, which are a bit like oceans, with a sea of solid particles (the ingredients) suspended within a major component that is a liquid (quite often water).  Think tomato paste, fruit juices and some sauces and soups.

Cooked pumpkin in water under the microscope.

Cooked pumpkin cells suspended in water.

The next microscopic image shows a suspension in 3D of cooked pumpkin in water. Notice how round the pumpkin cells are – that’s why pumpkin soup feels so smooth and creamy when we’re eating it.

Colloids, which have microscopic particles dispersed through another substance, are another type of structure. Milk is an emulsified colloid of liquid butterfat dispersed in a water-based solution. The third microscopic image is of milk, and the red dots are drops of fat dispersed throughout the liquid whey (black).

Microscopic image of breast milk

Milk has a colloid structure.

There are other structure types as well – solutions, emulsions and gels, which all behave differently to each other.

The structure of a food affects the way we chew it, how it breaks down in our mouths and our perception of its texture and flavour.  And because each structure also breaks down differently in our digestive system, the release and bioavailability of small molecules such as minerals, vitamins and polyphenols is also different.

Because of all these factors, food structures are increasingly being recognised as important in technology innovation for the development of healthier foods.

And as there is increasing awareness that structure has a significant effect on the bio-availability of nutrients, the focus of developing nutritional guidelines is shifting away from the traditional approach of simply assessing the nutrient composition of foods.

We are hosting the Food Structures, Digestion and Health Conference on 24 – 27 October, which will discuss the role of structure in designing foods for nutrition and wellbeing.