Abstract: In today's society, "green" and "environmental protection" have become the most concerned topics. Pollution-free green materials, chlorine-free green refrigerators, especially pollution-free green foods are increasingly favored by people. How to process green food raw materials into green cooking products that can be eaten directly, and how to control the safety of things in the cooking process have become issues of general concern and discussion in the cooking field.
Key words: cooking process, harmful substances, high temperature heating, N- nitrite compounds, polycyclic aromatic hydrocarbons, carcinogens, pollution.
"Food is the most important thing for people", the degree of food safety and hygiene is directly related to people's health, and the degree of food safety and hygiene is closely related to the science of cooking. It is not enough for people to have "green ingredients" in order to have scientific and reasonable dietary nutrition. Green food must be cooked scientifically. Because when cooking, if the method is proper, it is easy to mix or produce some harmful substances to pollute the so-called green raw materials. Moreover, there are many links that produce harmful substances in the next process, such as: low processing temperature of raw materials, time course, excessive cooking in protein, high oil temperature or improper food preparation, improper use of spices and seasonings, improper use of pigments, etc. Therefore, the author believes that in order to let people eat real green food, chefs should focus on the following work to ensure the safety and hygiene of food during cooking.
1. Cooking, 2. Control the safety of things, 3. The most important point is to control the heating temperature and time properly. Cooking temperature is too high or too low, 5. The heating time is too short or too long. It may affect food safety.
As we all know, an important purpose of cooking is to sterilize cooking materials, so that food materials are hygienic and safe from raw to cooked, and are easily digested and absorbed by the human body. Although cooking producers all understand the cooking purpose of "ensuring the safety of cooked food and getting sick from the mouth", they may not be able to meet the hygiene requirements of every cooked food. You may have heard of big fish pieces, meat, sausages, patties and so on. Boiled or fried; Everyone has heard that some people sometimes have stomach pain, diarrhea and other adverse reactions because of eating immature eggs, chicken, seafood and other foods; And you may have seen those dishes that are served while frying and sliding, with the blood of animal raw materials next to them. There are many similar phenomena mentioned above among chefs. In order to ensure food safety, chefs should always be vigilant and do a good job of sterilization and disinfection.
Understand the influence of temperature on microorganisms. According to the related literature, when the temperature is 50℃, the general corrupt microorganisms stop growing. When the temperature is higher than 60℃, microorganisms gradually die; 30 minutes at 63 ~ 65℃ or 5 ~10 minutes at 70℃ or 3 minutes at 85 ~ 90℃; After 100℃ 1 min, microbial cells will be killed, but the spores of bacteria and molds can only be killed under high temperature and high pressure. If you are familiar with the influence of temperature on microorganisms, you can flexibly choose the heating temperature and time according to different cooking materials. For example, you know that eggs are easily contaminated by Salmonella. You can heat eggs to a temperature of 70℃~80℃ which can kill Salmonella for 8~ 10 minutes.
Avoid heating too high or too long.
Cooking food with proper heat can not only sterilize, but also ensure food nutrition, so that the product has good color, fragrance and taste. If the temperature is too high or the machine time is too long, many harmful components may be produced.
According to the analysis, it is generally believed that the harmful substances produced by high temperature and long-term heating mainly come from two aspects:
The object of heating-raw materials. Under the condition of high temperature for a long time, protein and carbohydrates in raw materials are easy to transform and produce harmful substances. Usually, the protein of raw materials is in a normal thermal denaturation state in the temperature range of 45℃~ 120℃, and begins to denature at 45℃; 55℃~ 60℃- thermal denaturation accelerates and condensation begins; 60℃ ~120℃-gradually becomes completely condensed. This moderate denaturation of protein is beneficial to human digestion and absorption. However, with the increase of heating temperature and time, the denaturation of protein is further deepened, and protein molecules are gradually dehydrated, broken or thermally degraded, so that protein is deaminated, and may combine with carbonyl groups of carbohydrates to form pigment complexes, leading to non-enzymatic browning and deepening the color of food. When the surface temperature of raw materials is continuously raised above 200℃ and heated continuously, amino acids and protein in raw materials are completely decomposed and coked into substances harmful to human body, especially the-aminomethyl derivatives produced by tryptophan in coked protein have a strong carcinogenic effect. Not long ago, an authoritative research result of ophthalmology pointed out to people that too much cooking and smoking of food in protein will cause calcium deficiency in the body. A large number of clinical data and animal experiments have proved that myopia is related to the lack of trace elements such as calcium and chromium in the body. Eating too much cooked and smoked protein food will cause calcium deficiency in the body. Thereby causing myopia in the eyes. In addition, with the increase of heating temperature and the extension of heating time, other substances of sugar are also decomposed and carbonized, and with the extension of heating time, the process of chromium coking is from the outside to the inside, which is also the reason why things we see are carbonized because of too much cooking. Therefore, the high temperature should be strictly controlled in the cooking process, and the raw materials should not be burnt or burnt.
Body grease from heating
The heating temperature of edible oil should not be too high, because the temperature range of oil is very wide (generally from 0℃ to 240℃).
Grease commonly used in cooking is the medium of heat transfer, which forms different flavor and texture of cooking products. When cooking producers heat oil, they often know through practice that if the oil temperature is not high and the heating time is short, the color and transparency of oil will not change much. However, if the grease is too high or heated repeatedly, the change of grease will gradually become obvious. Usually, when the fresh refined vegetable oil is heated for the first time, with the heating of the oil, the oil surface gradually changes from a calm state to a slightly bubbling state with a large amount of foam. Later, the foam disappeared, and then it became a slightly bubbling smoke. The oil surface is always transparent and clear, and the heated raw materials are also transparent and pale yellow or golden yellow. The oil that is used repeatedly at high temperature gradually becomes darker and turbid with the increase of usage times, and the viscosity of the oil also increases greatly. When heated, a large number of fine and thick foams are produced on the surface of oil, which is difficult to dissipate and quickly produces lampblack, and the surface color of raw materials put into heating immediately deepens and darkens, which is commonly called thermal denaturation of oil. It is the result of complex physical and chemical changes such as polymerization, hydrolysis, condensation and decomposition of oil at high temperature. Specifically, at high temperature, oils and fats begin to partially hydrolyze to form glycerol brown fatty acids. When the oil temperature rises above 300℃, fatty acid molecules begin to dehydrate and condense into ether compounds with large molecular weight. When the temperature rises to 350℃~360℃, fatty acid molecules (especially unsaturated fatty acids, such as linolenic acid, linolenic acid and arachidonic acid) are decomposed into low molecular weight ketones and aldehydes. In addition, glycerol after high temperature hydrolysis of oil is further dehydrated to produce acrolein, which is the main component of oil and has a strong stimulating effect on people's nose and eyes. When cooking practitioners see smoke on the heated oil surface, it means that the oil temperature has reached the smoke point of oil at this time, and some acrolein has been produced. Of course, the smoke point of oil is slightly different with the refining degree, type and use of oil. If the unrefined vegetable oil contains more low molecular substances, the smoke point is mostly160℃ ~180℃; The smoke point of refined vegetable oil is about 240℃. Another example is that the smoke point of soybean oil is 18 1℃~256℃, vegetable oil is 186℃~227℃, and cotton oil is 2 16℃~229℃. In addition, with the increase of service time, the smoke point of grease also shows a downward trend, which is also the reason why the repeatedly used grease smokes quickly after heating.
Many interesting experiments have proved that after repeated use of oil at high temperature, the substances produced are quite toxic to people and animals after various complex reactions mentioned above. Some people raised animals with high-temperature heating oil for a period of time and found that their growth was stagnant and their livers were swollen. At first, it was thought that high temperature heating destroyed the oil, which was caused by nutrients. However, some people can't improve the adverse effects of this swelling after adding vitamin E to their feed. Therefore, it is considered that it may be caused by harmful substances produced after high temperature heating. It was also found that after feeding rats with high temperature oil for several months, papilloma, liver tumor, lung adenoma and breast adenoma were common.
What are the harmful substances formed by high temperature heating of oil? Experts generally believe that unsaturated fatty acids are various polymers produced by heating. Among them, trimer is not easy to be absorbed by human body because of its large molecular weight, and its toxicity is small; However, cyclic mono-and dimers with small molecular weight and easy absorption by human body are highly toxic, which can make the growth of animals stagnate, the liver swell and even lead to cancer. In addition, the thermal polymerization of oil at high temperature can form polycyclic aromatic hydrocarbons with strong carcinogenicity, which deserves our attention.
In order to prevent oil poisoning caused by high temperature heating, the following points should be done when heating with oil:
(1) Try to avoid frying food at high temperature continuously. In general, the temperature of edible oil should be controlled below 200℃.
(2) When lubricating grease is used repeatedly, new oil should be added at any time, and floating impurities should be discharged at any time.
(3) According to the variety of raw materials and the requirements of finished products, correctly select oils with different decomposition temperatures. For example, if squirrel fish and pineapple fish require molding at a temperature above 230℃, cottonseed oil and high-grade refined oil with high decomposition temperature should be selected.
Secondly, in the cooking process, in order to control the safety of food, it is necessary to prevent the pollution of N- nitroso compounds to food.
The content of naturally occurring N- nitroso compounds in food is very small, generally below 10pg/kg. The contents of pickled fish, meat products, pickles and fermented foods are higher.
Some foods contain precursors of N- nitroso compounds, such as secondary amines and nitrites, which can form nitrosamines or nitrosamides if cooked improperly or under the action of microorganisms.
The main factors affecting the synthesis of N- nitroso compounds are PH value, reactant concentration, amine type and the presence of catalyst.
Nitrosamines and their formation reactions need acidic conditions, for example, the optimum PH for nitrosation of secondary amines is 3.4. Under neutral and alkaline conditions, nitrosamines can also be generated if the reaction concentration is increased, the reaction time is prolonged or carboxyl compounds such as catalyst halide ions and formaldehyde exist.
The reactants of nitrosamine synthesis include amine and nitrite. All compounds with -N= structure can participate in the synthesis reaction, such as amine, amide, ethyl carbamate, amino acid guanidine and so on. Primary amine, secondary amine and tertiary amine can all be nitrosated, but secondary amine is fast and tertiary amine is about 200 times slower than secondary amine.
Nitrate-reducing bacteria such as Escherichia coli and Proteus vulgaris can also synthesize nitrosamines from secondary amines and nitrates. But this often happens in people's stomachs and during food fermentation.
In the process of making sausages, bacon and crystal hooves, dried salted fish with nitrate or nitrite as color fixative will also contain N- nitroso compounds. Seasoning for curing sausages: Mix black pepper, Chili powder and other seasonings with crude salt and nitrite in advance, and then detect nitrite-based biroline and nitrosopyridine in sausages. Therefore, it is forbidden to marinate sausages with pre-mixed marinating seasonings, and the marinated seasonings should be packaged separately.
Smoked meat and fish, fried bacon slices and direct baking exposed to air can also form some nitrosamines.
Third, in the cooking process, to control the safety of things, we must pay attention to prevent polycyclic aromatic hydrocarbons from polluting food.
Polycyclic aromatic hydrocarbons are the most harmful chemicals in cooking. Polycyclic aromatic hydrocarbons (PAHs) refer to a series of aromatic compounds and their derivatives bonded by more than two benzene rings. They are carcinogenic to human beings, especially benzopyrene (B(a)P) with five benzene rings fused together. According to research, one of the main ways to produce polycyclic aromatic hydrocarbons during cooking is that the above oils are polymerized at high temperature to produce polycyclic aromatic hydrocarbons-benzopyrene; Secondly, it mainly comes from smoking and baking food. When people use coal, gasoline, charcoal, firewood and other organic substances to smoke and bake food at high temperature, incomplete combustion of organic substances will produce a large number of polycyclic aromatic hydrocarbons. However, the raw materials of smoked food are often in direct contact with fire and smoke, and are directly polluted by polycyclic aromatic hydrocarbons. With the extension of smoking and baking time, polycyclic aromatic hydrocarbons (PAHs) continue to penetrate into the raw materials from the surface. Especially, when foods containing more oil and cholesterol are smoked and baked, benzopyrene can also be produced due to thermal polymerization of the oil contained in them, which contains more benzopyrene. According to relevant statistics, the content of benzopyrene in smoked food is about 0. 17~0.63 g/kg in general barbecued pork and sausage, and the amount of (b (a) p) in Guangdong barbecued pork and sausage increases the most, followed by coal stove and charcoal stove, and the amount of (B(a)P) in electric stove is the most. The content of roasted mutton in Xinjiang is 4.7~95.5g/kg, with an average of 3.9g/kg. As for smoking, barbecue foods contain more polycyclic aromatic hydrocarbons and have a strong carcinogenic effect, which has been proved by a series of facts. According to the survey, the incidence of gastric cancer in western Hungary is obviously high, which is related to the fact that residents in this area often eat homemade bacon. The high incidence of gastric cancer in Latvia-coastal areas of the former Soviet Union is due to eating more smoked fish. The high mortality rate of gastric cancer in Iceland is due to eating more smoked fish; The mortality rate of gastric cancer in Iceland is the third, one of the reasons is that Icelandic residents like to eat smoked mutton, and feeding local smoked mutton to mice has induced malignant tumors.
In order to prevent polycyclic hydrocarbons from polluting food, the above measures can be taken:
(1) When smoking and baking food, (2) don't (3) stay too close to the fire, (4) avoid direct contact between food and charcoal fire, (5) the temperature should not be (6) higher than 400℃.
(7) Don't (8) let the smoked food grease drip into the furnace because the oil discharged during smoking contains 3.4- benzopyrene, (9) it is highly carcinogenic (10) Don't use this oil.
(1 1) Try to improve the cooking technology of smoke baking, (12) switch to electric stove, (13) improve food fumigant or use cold fumigant, etc. 、
Four, effectively reduce or eliminate the adverse ingredients in raw materials, to ensure food safety.
For example, people often remove organic acids from spinach, vegetables, eggplant and other raw materials by flying water, which can prevent them from forming stone-like organic substances with other high-calcium or high-protein foods ingested by the human body, such as tannins, calcium oxalate and other substances that cannot be absorbed in the body. Another example is: boiling colchicine in fresh yellow flowers; When processing germinated potatoes, we should not only clean the tissues around the epidermis and buds, but also pay attention to cooking, and add appropriate amount of vinegar to destroy luteolin harmful to human body. When boiling green beans, boil them for a long time and heat them thoroughly to destroy the harmful components-saponin and glycinin; When cooking ginkgo biloba, full heating can avoid the toxicity of ginkgolic acid to human body; Cooking cassava, bitter almond, peach kernel, etc. Harmful to cyanosis, if thoroughly heated and cooked without cover, the growing hydrocyanic acid will volatilize; When heating the food contaminated by parasite eggs such as tapeworm, liver fluke and ascaris lumbricoides, the heating time should be a little longer, so that the parasites can be completely killed when the central temperature inside the raw materials reaches the sterilization temperature.
Appropriate use of spices, spices, pigments and other auxiliary materials for seasoning and color matching to prevent artificial addition of harmful ingredients in food. It is best not to use spices such as pepper, pepper, cinnamon and fennel, inferior or counterfeit seasonings such as soy sauce, rice vinegar, cooking wine and salt, preservatives and colorants such as nitrite, and food pigments such as sunset yellow, cabbage red and lemon yellow. According to analysis, "lutein" contained in pepper, pepper, cinnamon and fennel has carcinogenic effect; Inferior or counterfeit soy sauce, rice vinegar, salt, etc. Contains aflatoxin, methanol, heavy metals and other harmful components. At the same time, the products are bright red and rose red colorants. Nitrite, nitrate and amine easily contain carcinogenic nitrosamines in human body or outside human body; Other edible pigments may also be mixed with heavy metals such as potassium and lead in the production process. Bad for people. Therefore, in the case of using pigment or chromogenic agent, the dosage should be strictly controlled. Usually the amount of carmine and carmine is 0.05 g/kg; Lemon yellow and indigo are 0. 1 g/kg; Nitrite does not exceed 0.5g/kg；; ; Nitrate shall not exceed 0. 15g/kg.
5. In the cooking process, special attention should be paid to the proper release of monosodium glutamate (the main component of monosodium glutamate). In weak acid or neutral solution, the use effect is the best when the temperature is 70~90 degrees. If the temperature is too high, sodium glutamate will be converted into sodium pyroglutamate at high temperature, which is not only tasteless, but also may cause poisoning symptoms such as nausea, dizziness and rapid heartbeat.
6. When cooking, 7. Control food safety, 8. Cooks should be in good health.
Because the practitioners engaged in cooking production are one of the important ways to spread food pollution diseases, they need to do personal hygiene well. There are also provisions in the Food Hygiene Law; Food production and marketing personnel must have a health examination every year, and new and temporary food production personnel must obtain health certificates before they can take part in the work. Anyone suffering from dysentery, trauma, viral hepatitis, active tuberculosis or purulent exudative dermatosis shall not participate in the preparation of direct food. All patients or carriers of infectious diseases should immediately stop working and receive treatment, and only after three positive tests can they return to work. In short, in order to realize the ideal of modern "green cooking food", cooks should pay close attention to the influence of each link in the cooking process on food, accumulate and master various measures to control food safety in the cooking process, and explore more scientific and reasonable cooking methods.
References:
Encyclopedia of Family Kitchen, Shanghai Culture Publishing House, 199 1, 1.
Knowledge of Cooking Chemistry Wuhan Business Press.
Cooking technology, edited by Zhu, Commercial Press.
Fundamentals of Cooking, edited by Lin Zepu, China Business Press.
Dietary Nutrition and Hygiene, edited by Liu, China Commercial Press.
Cooking Nutrition, edited by Peng Jing, China Light Industry Press.
Basic Chemistry of Cooking, edited by Zhu, China Business Press.
Cooking Hygiene, edited by Jiang, China Light Industry Press.
Food Microbiology China Business Press.
Food Toxicology People's Health Publishing House.