Refractive index is a physical property of matter. It is a commonly used process control index in food production. Measuring the refractive index of liquid food by a refractometer can identify the composition of the food, determine the concentration of the food, and judge the purity and quality of the food.
The refractive index of sucrose solution increases with increasing concentration. Refractometer measurement of refractive index can determine the concentration of sugar liquid and the sugar content of beverages, canned sugar water and other foods.
Various oils are composed of certain fatty acids, and each fatty acid has its own specific refractive index. When the number of carbon atoms is the same, the refractive index of unsaturated fatty acids is much larger than that of saturated fatty acids; the greater the molecular weight of unsaturated fatty acids, the greater the refractive index; oils with high acidity have a lower refractive index. Therefore, the composition and quality of grease can be identified by measuring the refractive index with a refractometer.
Under normal circumstances, the refractive index of some liquid foods has a certain range. For example, the refractive index of normal milk whey is between positive 1.34199 and 1.34275. When the quality of the material changes, the refractive index often changes. Therefore, measuring the refractive index with a refractometer can preliminarily determine whether certain foods are normal. If milk is mixed with water, the refractive index of whey will decrease. Therefore, by measuring the refractive index of milk whey, we can know the content of lactose and judge whether milk is mixed with water.