Edible oil is a necessity in daily life, to which frequent food safety problems have occurred in recent years. From the quality of product, packaging safety to the shelf life, wave after wave of safety problems with edible oil were reported and caused the panic of the consumers, who become confused about how to choose among various edible oil products. As a special "additive" for food, packaging has a more or less impact on food safety. This article describes the impact of packaging on the safety of edible oils and how to solve those safety problems and promote the safety of edible oil.
Influences of Packaging on the Safety of Edible Oil
Plasticizer
Plasticizers can be used to increase the softness of materials or to liquefy materials, which are also widely used in the production of plastics, rubber and inks. Phthalates plasticizers are most common plasticizers for plastic food packaging materials. Because they do not form covalent bonds when mixed with plastics, they are likely to leach and volatilize into edible oils. During long-term storage's contacting with the packaging, the plasticizer in the edible oil continues to accumulate and after the accumulated exceed certain amount in the edible oil, it may affect human health. Moreover, the plasticizer's harm to the human body is not an acute poisoning reaction, but a similar effect of "environmental hormones" causing the body to secrete disorders, thereby impairing the function of the organism. Such damage is occult.
In order to avoid the threat of plasticizers to human health, China has issued corresponding national standards to guide the use of plasticizers. For example, in GB9685-2008, it is clearly stated that DBP and DEHP are only used in packaging for fat-free foods. And with the enhancement of public awareness of food safety and arising of the accidents caused by the plasticizers, plasticizers have become the focus of food packaging, and as a result, PVC materials that use plasticizers are gradually disappearing in the edible oil market.
Barrier Property
Most consumers know about the influence of plasticizers on the safety of edible oil, which will be taken into consideration by the manufacturers of edible oil when selecting packaging materials. But not many people know how the barrier property of packaging material can influence the safety of edible oil.
Edible oil contains a large amount of unsaturated fatty acids, which are likely to be oxidized automatically or by photosensitive reaction and hydrolyzed during the storage process being exposed to oxygen, heat, light, moisture and metal ions, etc., and then begin to decompose to form compounds such as aldehydes, ketones, alcohols, acids, etc., which have a special odor. Oxygen is the main factor that causes deterioration of edible oil. Therefore, antioxidants are usually added to the edible oil to ensure the stability of the oil. In order to reduce or avoid the use of antioxidants, it is required to improve the oxygen barrier property of the packaging material. Barrier property refers to the barrier ability of packaging materials to pass through water vapor, oxygen, and nitrogen, etc. The high-barrier packaging material can prevent the oxygen in the air from permeating through the package, so as to avoid the contact of the edible oil with oxygen and ensure the quality and safety of the edible oil.
Seal Performance
In addition to carrying edible oil, the packaging also protects the edible oil. If the seal performance of the package is poor, it will not only cause the oil leakage, but also create a passage for the oxygen to enter the package. According to the data, even the edible oil in glass packaging, if the bottle is not sealed after use, the peroxide value of soybean oil can reach more than 9mmol / kg, after 6 months of storage at room temperature, while for peanut oil and sunflower blending oil, this value may reach more than 10mmol/kg after three months of storage, all exceeding the national standard of 6.0mmol/kg or 7.5mmol/kg for edible oil quality standards. If the bottle mouth is resealed after opening, the oxidation rate of the edible oil can be effectively reduced, and the peroxide value of the edible oil can be kept within the required standard range within 12 months. Therefore, the seal performance of the bottle mouth is of great significance to the hygienic safety of edible oil.
Measures to take to ensure the safety of edible oil
Evaporation Residue Test
In addition to plasticizer, stabilizer, diluent and other additives of plastics are also liable to dissolve in oil, which may migrate from the packaging into the edible oil during storage. Evaporation residue is an indicator for detecting the mass of chemicals that may come out when food contact materials are exposed to water, acidic substances, alcohols and oils, etc. in use. The simulant materials are generally distilled water, 4% acetic acid, 20% or 65% ethanol and n-hexane. For edible oil packaging, the simulant can be n-hexane.
Today, we have special testing instrument for evaporation residue, which can avoid the manual operation errors. For example, Labthink’s ERT-01 Evaporation Residue Constant Weight Tester is a professional automatic testing instrument for evaporation residue of edible oil packaging. The testing accuracy of this instrument reaches 0.3mg and the test temperature can be controlled with the range of 100~130℃ so the weighing process can be performed at high temperature, which minimizes the interference to the testing accuracy in the cooling process.
The tests follow the test methods described in GB13113-91: Hygienic Standard for Polyethylene Terephthalate Products Used as Food Containers and Packaging Materials, and GB5009.60-03: Method for analysis of hygienic standard of products of polyethylene, polystyrene and polypropyrene for food packaging. Pour the simulant solution into the sample as required so as to contact with the inside of the sample. After soaking for 2 hours, take 200 ml of the soaked n-hexane and pour it into the test cup. At the same time, add 200 ml of the n-hexane stock solution into the test cup for blank test. Each test cup was placed in a constant temperature bath and heated until most of the water is evaporated, and then moved to ERT-01. Set the parameters and then start the test. In order to ensure the accuracy of the results, several samples and simulant solution can be taken for testing. The instrument can test 1~8 samples at a time, and the blank simulant solution can be tested simultaneously with the sample, which is labor-saving and improves the test accuracy.
Oxygen Transmission Rate Test
Edible oil is usually packed in bottles or bucket, the oxygen barrier property of which shall be tested with equal pressure method. By now, there is no standard for OTR test of packaging containers. In actual testing, the reference standard can be ASTM F1307-2014: Standard Test Method for Oxygen Transmission Rate Through Dry Packages Using a Coulometric Sensor. The testing instrument is Labthink’s C230 Oxygen Transmission Rate Test System. 
Seal Performance Test
The seal performance test of edible oil package follows negative pressure method in accordance with GB/T 15171-94: Test method for leaks in sealed flexible packages. This method can be used to detect the micro leak points of the package. Test should be performed in the following procedures.
Set the test sample inside the vacuum chamber of MFY-01 Leak Tester. Close the lid and set pressure to -90kPa. Turn on the vacuum pump to evacuate the vacuum chamber. Keep observing the test sample and there will be successive air bubbles coming out of the package from the leak points. Record the pressure when the leak occurs and the position where leak occurs.
Keep in dark place
Light has a catalytic effect on the oxidation reaction of edible oil. After 5 months of irradiation with sunlight or light, the peroxide value of edible oil can reach 6mmol/kg or more, which exceeds the limit specified by the national quality standard for edible oil. When kept in dark place, the peroxide value in the edible oil will only increase slightly and will not exceed the standard limit. Therefore, edible oil should be kept away from light. Especially for the edible oil supplemented with vitamin A, which is sensitive to light. After ultraviolet radiation in the sun, vitamin A will decompose and disappear. Therefore, opaque material is suggested to use when designing the package for edible oil.
Conclusion
To be summarized, glass or tinplate and other materials with superior barrier properties are optimal packaging materials for edible oil. Considering the weight of material, logistics cost and other cost, PET is the best choice of packaging material for edible oil for now.
How to guarantee the safety of edible oil is a question both for the consumer and the manufacturer. It is suggested to take measures from two aspects i.e. the product and the package. On one hand, the quality control of the oil should be strengthened. On the other hand, the consumer shall choose the product with package made of glass, tinplate or PET. The package made of PVC that contains large amount of plasticizer or PE with poor barrier property are not good choices for the package of edible oil. One more thing, it is recommended to choose small volume package of edible oil according to actual demand, otherwise the safety of the oil will be decreased in long-term storage.