In the soft packaging food sector, oxidation, moisture absorption, light exposure, and flavor loss are the four core factors that shorten the shelf life. High barrier films, as functional composite substrates, control the penetration of oxygen, water vapor, light, and aroma to delay lipid rancidity, microbial proliferation, and taste deterioration. They are the core solution for preserving products such as nuts, meat products, pet food, baking, and seasoning powder. Many purchasers and factories tend to fall into the misconception that "the higher the barrier, the better," blindly choosing ultra-high barrier materials to increase costs or having insufficient type matching, resulting in problems such as bloating, moisture absorption, layering, and non-compliance with shelf life standards. This article, from six dimensions including principles, indicators, material selection, structural design, process control, and detection verification, summarizes practical technical points that can be implemented for soft packaging professionals and food brand supply chains.
Food spoilage can be classified into three types: oxidation spoilage, moisture migration, and light-induced reactions. Oxygen contact with oil produces a rancid smell, damaging pigments and vitamins; dried products absorb moisture and become soft and lumpy, while high-humidity products lose moisture and become dry and hard; ultraviolet rays accelerate oxidation, causing fading and flavor attenuation. High barrier films do not completely block out, but control the oxygen transmission rate OTR and water vapor transmission rate WVTR within the product's tolerance threshold, combined with sealing, gas regulation, and deoxygenating agents, to achieve the preset shelf life. The two core determination indicators in the industry are oxygen transmission rate OTR, representing the speed of oxygen penetration; and water vapor transmission rate WVTR, representing the speed of water vapor penetration. All material selection must be based on these two data.
Mainstream high barrier substrates have their own advantages and disadvantages, and there is no universal material. Aluminum foil AL has the strongest barrier performance, while also blocking light and oxygen, suitable for long-term preservation pet food, cooked food, and sauce bags; its disadvantage is that it is opaque and prone to pinholes when bent, and the barrier will decrease after repeated rubbing. EVOH ethylene-ethylene oxide copolymer is transparent with high barrier oxygen and oil resistance, suitable for meat products, chilled meat, and seasoning foods, with the disadvantage of being sensitive to humidity, and the barrier significantly decreases in high-humidity environments. PVDC polyvinylidene chloride has balanced oxygen and water barrier, stable in moisture, and often used in ham sausages, cheese, and mooncakes; its disadvantage is a narrow processing window and difficult recycling. Aluminized film VMPET has a high cost-performance ratio, blocking light and oxygen, suitable for snacks and crispy foods, with a barrier weaker than aluminum foil, and the coating will fail if scratched. SiOx/AlOx ceramic coating is transparent with high barrier, resistant to boiling, and bendable, suitable for high-end foods that require visual display, but the cost is high and the composite process is strict. PA nylon mainly functions to resist punctures and has moderate barrier oxygen capacity, often used as an auxiliary structure on the outside, not as a barrier layer alone.
The design of material structure should follow the idea of layer division, with the outer layer providing printing, wear resistance, and UV protection; the middle layer bearing the barrier function; and the inner layer using PE and CPP to handle heat sealing. For products with high oil content and sensitivity to oxidation, such as nuts, freeze-dried products, and pet food, aluminum foil structure or ceramic coating is preferred, controlling low OTR; for high-humidity circulation environments and moist cooked foods, PVDC or properly protected EVOH structure is preferred; if the customer needs to see the contents, aluminum foil is abandoned and ceramic high-transparency barrier film is selected; for products that need to be protected from moisture, such as crackers and biscuits, the focus is on WVTR control. At the same time, it is necessary to match the storage conditions. In normal temperature, refrigeration, freezing, and steaming environments, the performance of the same barrier film can vary greatly. EVOH cannot directly apply the normal temperature parameters in high-temperature and high-humidity storage environments. The processes of compounding, slitting, and bag-making should avoid stretching and scratching the barrier coating. Once the aluminized or ceramic film is scratched, the barrier performance will drop sharply. The matching of heat sealing temperature, pressure, and time is crucial; micro-pores at the sealing edge are the hidden reason for many products to deteriorate prematurely. In bag design, the corners and folded corners are prone to cracking and pinholes. Aluminum foil bags especially need to avoid sharp corner structures. If accompanied by controlled atmosphere packaging and deoxygenating agents, the bag's internal headspace volume must be calculated simultaneously. The specifications of deoxygenating agents, nitrogen replacement rate, and OTR of the film need to match. Adding deoxygenating agents alone without matching the packaging barrier will still limit the preservation effect to a certain extent.
The barrier solution must undergo shelf validation and cannot only rely on the factory test report of the film material. The factory test of the film material is a separate film indicator. After making the composite bag or bag, the barrier will show attenuation. Common testing items include OTR, WVTR, pinhole detection, peel strength, heat seal strength; accelerated aging test is placed in a high-temperature and high-humidity environment, and regular detection of acid value, peroxide value, microorganisms, and sensory flavor is conducted to simulate long-distance transportation and storage; the circulation chain should be evaluated simultaneously. Sea transportation, southern rainy areas, and open storage are subject to much greater challenges from water vapor and temperature than constant-temperature warehouses.
The waste of many projects comes from excessive selection. Short-term refrigerated products do not require ultra-high barrier aluminum foil; ordinary biscuits do not need ceramic coating. The selection logic is: first clearly define the food type, fat content, water activity, target shelf life, and storage and circulation environment, then reverse lock the OTR and WVTR indicators, and then match the barrier material and composite structure. Finally, summarize that high-barrier film extension of shelf life is a complete system solution, and the substrate is only one part of it. Reasonable barrier indicators, suitable multi-layer structures, stable composite bag-making process, complementary preservation auxiliary means, and shelf validation are all indispensable. Purchasers and technicians should go beyond simple price comparison and take product stability, shelf life data as the core, balance preservation effect, cost, processing performance, compliance, and recycling requirements.
