SEVERAL FACTORS will influence the nutritional content of the food we eat. Before food is acquired, the amount of control that consumers are able to directly apply in order to get the most from the food they eat is limited. Factors that apply during this period are: the species or breed of the plant or animal from which the food is derived; the soil in which plant foods are grown or the feed animals are given; whether or not fertiliser is used and the content of the fertiliser; prevailing weather; maturity at harvest or at slaughter; packaging/processing methods; cooking method and storage conditions before distribution and sale.
Consumers are more likely to have a choice in factors, such as food selection, storage and preparation method, which apply during and after the acquisition of food. In acquiring and preparing food, the consumer should take care that the nutrients in it, up to this point, are conserved.
The nutrients in foods, especially in fruits and vegetables, vary greatly in the extent to which they change over time. Some nutrients are not affected to any great extent by ordinary handling. For example, the mineral content of foods
are less likely to be affected by food handling than the macronutrient and vitamin
content.
The extent to which nutrients are retained depends on several conditions, such as the characteristics of the food item, for example, size, maturity and species; the amount of the nutrient in the food; the amount of heat applied; exposure to air and light; pH (acidity or alkalinity) of the storage or cooking medium.
Nutrients such as vitamin C, vitamin A, thiamine, folate, and potassium are more readily lost from some foods compared with others. For example, about 60 per cent of vitamin C is retained when green leafy vegetables such as spinach are cooked in water. Other vegetables such as broccoli will retain about 80 per cent vitamin C when cooked the same. Some nutrients such as vitamin D and niacin are usually stable to most food processing methods and storage.
EFFECT OF SOME PREPARATION METHODS
Heat Heating can be both beneficial and detrimental to nutrient content of foods. Heating generally improves the digestibility of foods, making some nutrients more available. A typical example is the protein in legumes, which is made more digestible by heating.
However, if the food contains reducing sugars such as glucose, fructose and lactose, there might be non-enzymatic (Maillard) browning, as the sugars react with certain amino acids to create a compound that is indigestible. This type of reaction produces, for example, the golden-brown colour of bread crusts. It can reduce the protein quality of the food. Lysine (an amino acid) content is most often affected by this type of reaction.
Some nutrients such as vitamin C are destroyed by heating. Losses of this and other nutrients that are sensitive to heat will depend on the extent of heating and the other prevailing conditions, such as pH.
Boiling can result in large losses of some nutrients into the cooking water. Losses of water-soluble vitamins are greater than for fat-soluble vitamins and minerals. Steaming and pressure cooking are known to result in greater mineral retention.
Drying Two processes occur during drying: the application of heat and the removal of moisture from the food. Nutritional losses during drying are more due to the application of heat than to the removal of moisture. Generally, except for thiamine (vitamin B1) which is very heat sensitive, removal of moisture results in increased concentration of nutrients. Nutrient losses during drying can be decreased by drying at a low temperature and reducing drying time.
Blanching Blanching is the exposure of vegetables to boiling water or steam for a brief period of time. This is often done before carrying out other treatments such as drying, or when preparing to store foods in the freezer. One of the major objectives of blanching is to destroy or inactivate enzymes that can affect the colour, texture, flavour and nutritive value of foods during storage. Blanching also reduces the number of micro-organisms on the food. However the process can sometimes result in significant nutrient losses. These losses will depend on several factors such as: the food item, surface area exposed, the method used (steam blanching or hot water blanching), contact time, amount of agitation or shaking.
Adding sodium bicarbonate (or another alkali) to the water when vegetables are blanched is a decision that should be weighed carefully. Although it has alkali, it preserves the colour, it also has the effect of softening the texture of the vegetable and increasing destruction of vitamin C and thiamine.
Salting Salting is most often used to preserve meat, fish and poultry. However, the process of salting causes liquid to ooze from the flesh of the food, taking with it some of the proteins, vitamins and minerals. Some proteins also become denatured, that is, experience structural changes during this process.
- Nyam News, Caribbean Food and Nutrition Institute
