Parboiling involves soaking paddy in water for a short time followed by heating once or twice in steam and drying before milling. Dehusking of parboiled rice is easy and the grain becomes tougher resulting in reduced losses during milling.
The nutritive value of rice increases after parboiling, because the water dissolves the vitamins and minerals present in the hull and brancoat carries them into the endosperm. So the loss of vitamin B1, riboflavin and niacin due to milling and polishing is comparatively low in the parboiled rice than raw rice. Parboiled rice will not turn into glutinous mass when cooked. Baking of leavened dough of wheat helps to make bread. Baking is done in an oven preheated to 204 degrees C. During the first 10-12 minutes of baking there is an increase in dough volume. This is called oven spring. This is caused by an expansion of gases owing to the high temperature of the oven and due to increased enzyme activity in the centre of the dough. As baking continues, gluten a constituent of wheat dough expands without breaking and finally forms a rigid structure due to coagulation.
This helps in the retention to the rapidly expanding gases. Excess gases, CO2, alcohol and water vapour help to gelatinize the starch and structure is established. This aerated and finely vesicated crumb is very helpful for easy mastication of bread.
Using heat to bring about desirable changes in foods is called cooking. Cooking improves flavour and appearance and makes the food more palatable and digestible. Legumes and cereal grains contain trypsin inhibitors and other toxic substances which affect the digestibility and availability of sulphur containing amino acids.
Cooking destroys these toxic proteins and favours easy digestion Starch molecules which are the main source of calories in many diets when in an aqueous or moist environment swell and rupture and this permits greater enzymatic digestion by enzymes like amylase. Cooking thus increases the digestibility of carbohydrates.