Qualitative and quantitative analysis of fish meal

The qualitative and quantitative analysis of fish meal involves many aspects, including sensory identification, chemical analysis, microscopic observation, etc. The following are some common methods for qualitative and quantitative analysis of fish meal:

1. Qualitative detection
Sensory identification
Color and morphology: Observe the color and morphology of fish meal. Normal fish meal is generally yellow-brown or yellow-brown, and may also be white, grayish-white, etc., depending on the fish species. Fish meals should contain basic components such as fish meat, fish bones, and fish scales, the color should be relatively uniform, and there should not be too many black and brown spots.
Smell: Smell the smell of fish meal. Normal fish meal has the aroma of roasted fish and a slight fishy smell. Spoiled fish meal may have bad odors such as fishy smell and ammonia.
Chemical reagent detection
Urea detection: Use the cresol red indicator to detect urea. After mixing fish meal with water, add the cresol red indicator and observe the color change. If the color changes to dark purple, urea may be mixed.
Plant material detection: Use iodine-potassium iodide reagent to detect plant materials (such as wheat bran, rice husks, etc.). After boiling fish meal with water, add iodine-potassium iodide reagent. If the solution turns blue, it may be mixed with plant materials.
Ammonium salt detection: Use sodium hydroxide solution to detect ammonium salt. After adding sodium hydroxide to fish meal, observe the color change of pH test paper. If the test paper turns blue quickly, it may contain ammonium salt.
Microscope observation
Observe foreign matter: Use a microscope to observe foreign matter in fish meal, such as feathers, hair, sand, and plant materials. The presence of these foreign matter may indicate that the fish meal is adulterated.
Comparative observation: Use standard fish meal samples for comparative observation, analyze the proportion and morphology of fish meat, fish bones, fish scales, and other components in fish meal, and judge the quality of fish meal.
2. Quantitative detection
Crude protein determination
Kjeldahl nitrogen determination method: Use the Kjeldahl nitrogen determination flask method to determine the crude protein content in fish meal. This method converts nitrogen into ammonia by digesting fish meal samples, then absorbs ammonia with boric acid and titrates with standard sulfuric acid or hydrochloric acid to calculate the nitrogen content, and then multiply it by a certain coefficient to obtain the crude protein content.
Water washing method: Take a certain amount of fish meal and place it in a beaker, add distilled water and stir it thoroughly, filter it, and then wash it with distilled water several times. Dry the washed fish meal and measure the crude protein content using the Kjeldahl nitrogen determination method. By comparing the changes in crude protein content before and after washing, it can be determined whether soluble nitrogen fertilizer is mixed in the fish meal.
Determination of pepsin digestibility
Accurately weigh a certain amount of dehydrated and defatted fish meal, put it in a triangular flask, add preheated pepsin solution, cover it and seal it, and digest it for a certain period of time while stirring under constant temperature conditions. After digestion, filter it with filter paper and wash the undigested matter on the filter paper with warm water. Transfer the undigested matter and the filter paper into a Kjeldahl flask for digestion, and then measure the amount of undigested crude protein. The pepsin digestibility of fish meal is equal to (crude protein in fish meal-amount of undigested crude protein)/crude protein×100%.
Determination of other components
Crude fat determination: Use the Soxhlet extractor and other methods to determine the crude fat content in fish meal. The crude fat content of fish meal should generally not be higher than 12%.
Crude fiber determination: Use acid-base digestion and other methods to determine the crude fiber content in fish meal. The crude fiber of fish meal should be almost zero. If it is too high, it is mixed with fibrous raw materials.
Ash determination: Burn the fish meal at a high temperature to constant weight, and measure the weight of the remaining material, which is the ash content. Too high ash content may indicate that the fish meal is mixed with minerals or other non-organic substances.
In summary, the qualitative and quantitative analysis and detection of fish meal involves multiple aspects and multiple methods. In actual operation, the appropriate detection method should be selected according to the specific situation, and the operation procedures should be strictly followed to ensure the accuracy and reliability of the test results.