food preservation techniques using salt and sugar

Question: Explain the mechanism of food preservation by sugar and common salt.

Sugar and Salt:

Both sugar and salt exert adverse effects on microorganisms. In food preservation, a concentration of above 15% NaCl (common salt) is used. The process of preserving food using NaCl is called Curing. On the other hand, the higher the concentration of sugar (usually 40% – 60%), the more effective it becomes as a food preservative. In jams, pickles, and jellies, the sugar concentration is maintained around 65% – 70%. A concentrated solution of sugar acts as a poison for microorganisms.

Mechanism of Food Preservation by Sugar and Salt:

When sugar and salt are used to preserve food, they absorb the free water present in the food material and turn it into a solution. Due to this absence of moisture, microorganisms can neither grow nor multiply, thus preventing food spoilage.

Furthermore, both sugar and salt exert high Osmotic Pressure on the cell walls of bacteria, which damages or destroys their cell walls. As a result, it becomes extremely difficult for microorganisms to survive or reproduce.

In addition, sugar and salt work together to significantly enhance the taste and quality of food. They also create a favorable environment for the growth of certain beneficial microorganisms. For instance, in winemaking, sugar is converted into ethanol by yeast, and sugar is turned into beneficial organic acids by lactic acid bacteria. Salt builds up an effective defense against molds and yeasts.

The sugar used in jams, jellies, pickles, preserves (Morabba), and various condiments acts as an active food preservative.

Spices themselves cannot directly destroy microorganisms; however, they create a favorable condition for other antimicrobial agents. Various spices such as turmeric, cloves, garlic, and mustard oil play vital roles. Among these, turmeric acts as an Antioxidant, which hinders the decomposition process. Mustard oil forms a protective layer that prevents bacteria from coming into direct contact with the food items.

Question 3: Sugar is a natural food preservative – Explain. [Chattogram Board, 2022]

Chemical substances that prevent the spoilage and decomposition of food items are known as food preservatives. When these substances are obtained from nature, they are called Natural Food Preservatives.

Sugar is a natural food preservative because it is derived directly from natural sources such as sugarcane, date palm sap, palmyra palm sap, etc. Sugar is extensively used as a preservative to protect and extend the shelf life of food items like jams, jellies, pickles, Kasundi, preserves (Morabba), and orange pickles. Therefore, sugar is rightfully recognized as a natural food preservative.