Text 18

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Citric acid by a gypsum-free process

Introduction

Citric acid is used mainly in beverages and food and as a detergent in wash­ing agents. Almost all citric acid is produced by fungi or yeasts in fermen­tation processes followed by a purifica­tion process. The quality of the citric acid ranges from food to pharmaceuti­cal grade.

Conventional citric acid process

The conventional citric acid purifica­tion process comprises the following steps:

- Precipitation of citric acid by addition of lime

- Separation of the calcium citrate by filtration

- Resolution to citric acid by adding sulphuric acid

- Removal of gypsum, followed by waste disposal

- Purification of the citric acid solution

- Concentration and crystallization.

The disadvantages of this purification process are the use of lime for the citrate precipitation, the use of sulphu­ric acid for resolution to citric acid and the contaminated gypsum for waste disposal.

Process description

Substrate preparation

The substrate consists of the glucose or saccharose solution and salts for the microorganisms.

The sugar solution is fed into a cation exchanger and subse­quently sterilized in a continuous sterilizer,

Fermentation

The citric acid is produced batchwise in high-yield submerged fermentation by aspergillus niger.

Bubble columns are used as reactors.

Answer the questions:

1. Where is citric acid used?

2. How is almost all citric acid produced?

3. What does the substrate consist of?

Text 19

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SUGAR

The term sugar to most people means cane or beet sugar which is sucrose. However this is only the most common of the several sugars responsible for sweet taste of certain foods.

Sugar is called by the chemists "carbohydrates". People have known ordinary sugar from ancient times. The first sugar was produced from sugar cane.

There are only two kinds of sugar that we are primerily concerned with in sugar refining namely" sucrose" the white sugar that is used by us in food and drink and invert sugar that we find in fruits and honey.

Sucrose is easily absorbed by our digestive organs. It is a necessary part of the diet of growing children. Sucrose is widely distributed in vegetables, roots and stems of all grasses. Sucrose will turn into invert sugar very easily but it is impossible to turn invert sugar into sucrose.

Answer the questions:

1. What does the term sugar to most people mean?

2. How is sugar called by the chemists?

3. How many kinds of sugar are there?

4. What is invert sugar?

Text 20

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Sugars and non-sugar sweeteners

Sugars are sources of energy and sweetness. But also they are used in jam-making, canning and freezing as pre­servatives. In biscuits, cakes, soft drinks and some other foods they help to provide their characteristic texture.

Besides there are some other substances which also taste sweet, Sorbitol and mannitol, which are made from glucose or sucrose, are sometimes used in diabetic foods because they are absorbed slowly. However, their energy value is as large as that of glucose. In contrast, saccharin has no che­mical or nutritional relationship to sugars and provides no energy.

Non-sugar sweeteners do not rank as foods, but they may be used as sweetening agents when it is necessary to make the amount of sugars in the diet smaller.

Answer the questions:

1. Where are sugars used as preservatives?

2. What are the other substances which taste sweet?

3. What sweetener does not provide energy?