*Dr. Pravin M. Ganorkar and Dr. Anil S. Nandane
Edible salt (sodium chloride) is having important place since ancient human life. Salt was used as one of the currency for trades in antique era. Egyptians referred salt as ‘natron’ (divine). The latin word ‘salarium’ derived from salt and referred to the amount of salt that used to give a worker as job payment. It is combination of sodium and chloride ions in the ration of 1:1. Salt also known as table salt. Salt in earlier centuries, had the economic importance as crude oil in the present era. Before the invention of electricity and refrigeration, salt was used to preserve food.Salt influences food palatability due to its unique flavor and pleasantness. It makes bland food pleasurable and perceivable in terms of taste and natural flavor. Moreover, salt is emerged as most impacting ingredient in food processing and food flavor enhancement. Salt is employed in food processing as solid (food additive) and liquid as brine solution (cleaning agent or heating medium). Beyond doubt, salt is widely explored as additive or processing aid. Henceforth, the important roles of salt in food processing are briefly discussed.
1. Salt as food preservative
From ancient days, salt is being used as food preservative specifically for meat, fish, dairy products and other food products. Commonly this preservation is referred as salt curing. Common salt does not show much antimicrobial action. But it reduces water activity of foods. This slows or interfere with important microbial metabolic processes. At higher concentration, osmotic microbial cell dehydration occurs and eventually leads to microbial cells death. Salt is acting as preservative through combined or individual mechanism responsible for microbial growth inhibition include enzyme hindarance vide by reducing their catalytic activities and by altering their cofactors; inhibiting respiration; O-nitrophenyl-β-galactoside hydrolysis; depletion of cell energy source (ATP molecule); cellular plasmolysis; deterrence of substrate transport into the cells across cell membranes; restricted oxygen solubility. Clostridium perfringens and Clostridium botulinum are majorly inhibited by salt, but Staphylococcus aureus and Listeria monocytogenes are comparatively halotolerant. Salt helps to prolong freshness, making food safer for long time. Inspite of development of refrigeration system, this is vital for maintaining food hygiene.Simultaneously, osmotic effect can negatively affect the nutritional value preserved foods through riddance of water soluble vitamins and minerals. Moreover, the salt curing on its own is insufficient as a exclusive preservation method in many food products, requiring its combination with other preservation techniques (drying, osmotic dehydration, etc.).
2. Salt as binding agent
Salt can act as binding and emulsifying agent. Salt and proteins interact to provide an essential water-binding function. This property is affected by pore and capillary size, the charges of the protein matrix (hydrophobic interactions, hydrogen bonds, S–S bonds), van der Waals forces protein ionic strength, ion species, pH, temperature, equilibrium between protein and water and the presence of low molecular weight substances. The increase in the water-binding capacity of meat proteins upon the addition of salt may be attributed to preferential anion binding (Cl–) by protein molecules. Salt helps to form protein gels. These gels can be used as a binding agent. When salt is added to foods such as sausage or other processed meats, it causes proteins gel formations which then hold the product together. Consequently, it reduces the cooking losses particularly moisture, water soluble nutrients and fat.
3. Salt as Fermentation Regulator
Salt is one of the four essential ingredients in bread (flour, salt, yeast and water). Salt inhibit or controls fermentation rate by decreasing the rate of gas production which result in the longer proof times. This appears to be the result of increased osmotic pressure and the sodium and chloride ions on the membrane of yeast cells. The growth of yeast cell is then retarded; hence the fermentation and dough development is controlled. If dough is made without salt, the yeast ferments excessively resulting in gassy and sour dough. The dough with these properties when baked may result in products with open grain and poor texture. The salt also contributes towards the gas production, dough without salt has higher gas production of 67.8 GU and was significantly different compared to dough treated with sodium chloride which had 61.8 GU. In addition, salt with different cations has lower gas production than sodium chloride except for potassium chloride. This study does not indicate whether it is acceptable to reduce salt from the formulation without posing any effect on gas production. Reducing salt content in processed food especially for bread based products is one of the greatest ongoing challenges facing food manufactures.
4. Salt as Texture Aid
Salt plays an important role in cheese making particularly in deciding the final texture of cheese. Salt especially enhances the hydration of proteins and combining of proteins to fats. Salt also affects the solubility of proteins and the moisture content of cheese, which in turn determine the rheology, texture, and changes that occur during cooking. Low contents of NaCl (5-6%, w/w) increases the solubility of casein or para-casein in natural cheeses. NaCl exerts several important effects on the textural aspects of cheese. For example, it affects casein hydration, and thus affects the water binding capacity of the casein gel. Adding NaCl to cheese initially results in enhanced protein hydration. However, at higher concentrations, it is associated with a decrease in casein hydration; therefore, increased NaCl concentrations cause the cheese matrix to become firmer and stiffer. Typical Gouda/Cheddar-type cheeses with considerably reduced NaCl levels may develop undesired softness, leading to problems in maintaining their shape. The softening that occurs upon salt reduction enhances the mobility of caseins in the cheese matrix. This makes the cheese less viscous, and more extensible, and contributes to desirable cooking properties.
Salt increases the strength of gluten in bread dough. It has conditioning effect on the dough. Moreover, salt is used to enhance the handling properties of the dough by reducing stickiness. It delays gluten formation during dough mixing. Salt helps to expand the dough without break. Moreover, it helps to provide uniform grain, crumb and crust texture.
5. Salt color developer or controller
Salt used with sugar and nitrate or nitrite produces a colour in processed meats. This color is very well liked by consumers. In bakery products like bread, crust color is important. Salt can act as color controller in bread. When salt is employed in bread dough, it slows down fermentation process and fewer amounts of acids are produced from sugar. It leads to higher dough pH which ultimately contributes to dark crust color. Salt enhances the golden color in bread crust by reducing sugar destruction in the dough and increasing caramelisation. If salt is not employed in bread dough, more sugar is utilized by yeast to more acid which contributes to lower pH. This leads to lighter bread crust color.
*Department of Food Processing Technology, A.D. Patel Institute of Technology, New Vallabh Vidya Nagar, Anand-388121, Gujarat, India