Question Corner

Rice difference

QUESTION: What is the difference in energy content of raw and boiled rice?

- Ravi Mukundan, Chennai

ANSWER: The energy content of raw rice is 3620 cal/kg with 12 per cent water content whereas that of boiled (cooked) rice is 1098 cal/kg with 73 per cent water content. Another variety is known as parboiled rice. Parboiling is a hydrothermal treatment followed by drying before milling for the production of milled parboiled grain.

During parboiling, the B vitamins and minerals from hulls, bran and germ will be leached into endosperm and hence loss during polishing is minimised. The energy content of parboiled raw rice is 3703 cal/kg with 10 per cent water content whereas that of boiled (cooked) parboiled rice is 1057 cal/kg with 73 per cent water content .

- S. Kaleemullah, Tirupati

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Art of pasteurisation

QUESTION: What is Pasteurisation? Is it a process of sterilization?

- P. Sri Lakshmi, Vijayawada.

ANSWER 1: Pasteurisation is defined as the process of heating milk to a particular temperature and holding it at that temperature for a particular time till the pathogenic (disease causing) micro-organisms are destroyed causing minimum change in composition flavour and nutritive value of milk. High temperature short time (HTST) pasteurisation at 71.7{+o}C for 15 seconds is the most common method of pasteurisation. Pasteurisation conditions are not sufficient to destroy thermo-resistant spores (reproductive part of microorganisms). Pasteurised milk has to be refrigerated.

Sterilization is a more severe thermal process where milk is subjected to temperature of about 135{+o}C for few seconds followed by aseptic (free of micro-organisms) packaging. Milk processed in this manner is termed as `commercially sterile', but it is not necessarily free of micro-organisms.

These micro-organisms, which survive heat treatment, are unlikely to proliferate during storage and cause spoilage to the product. However, spores are destroyed during sterilisation. Sterilised milk has longer shelf-life even at room temperature. Nutritional losses in sterilisation are more compared to pasteurisation.

- Jino Chacko, Allahabad.

ANSWER 2: Pasteurisation is one of the methods of preservation of products such as milk, alcoholic beverages etc. at higher temperatures. The process of heating of the product (milk (or) beverage) to a controlled temperature (usually below 100{+o}C) to enhance the keeping quality and to destroy harmful microorganisms is known as pasteurisation.

There are two methods of pasteurisation (of milk) in general use. One is low temperature holding (LTH) method in which milk is heated to 62.8{+o}C (145F) for 30 minutes in commercial pasteurisers (or) large closed vats which are heated by steam coils, hot water jackets etc.

The other method (i.e.) high temperature short-time (HTST) method in which the milk is heated to 71.7{+o}C (161F) for 15 seconds. The heating is accomplished by electricity (or) hot water and requires a heat exchange system, which preheats raw, cold milk and cools the hot pasteurised milk.

Pasteurisation does not sterilise the products but kills those organisms that grow most readily at low temperatures. The surviving organisms must be kept from multiplying by constant refrigeration.

- G. Ramya, AP.

ANSWER 3: Pasteurisation is sterilisation interpolated with a subtle nuance in the process conditions and hence in the final result as well.

Pasteurisation is named after the great French chemist Louis Pasteur, is the process of partial sterilisation, confined only with the killing of pathogens.

The subject is heated to temperature below its boiling point (usually less than 100{+o}C) and held at that temperature for a particular time period, with the aim of killing only the pathogens.

The time-temperature combination is decided based on the heat resisting capability of the target micro-organism and the nature of the subject. For instance milk is heated to 73{+o}C & held for 15 seconds, to destroy Coxciella burnetti and Mycobacterium tuberculosis, which are the target micro-organism.

Sterilisation is extended pasteurisation where the subject is heated above the boiling point and held for a particular time period to destroy all the microorganisms. The temperature is usually above 100{+o}C.

- S. Anand Swaminathan, Coimbatore.

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