Pet food has been one of keen competitive industries along with countless new pet foods introduced into the market. Same as human being food, pet food should conform to strict standards to ensure pet safety and health. In America, pet food is supervised by AAFCO (Association of American Feed Control Officials), USDA (United States Department of Agriculture) and FTC (Federal Trade Community). AAFCO establishes the nutritional standards for complete and balanced pet foods, and it is the pet food company’s responsibility to formulate and maintain their products according to the appropriate AAFCO standard. In many countries, like China, there aren’t special regulations or standards related to pet food quality control, so they usually also apply to AAFCO standards.

Like human being food, pet food also has a certain shelf life. Manufacturers and suppliers must ensure the pet food won’t be stale or lost nutrition during the shelf life. To enhance and keep the competitions, more and more manufacturers are trying to have a full consideration on factors affecting shelf life, in order to prolong their products shelf life

Factors Affecting Shelf Life

Many factors affect pet food shelf life, like additives (preservatives), packages, maintenance environment (temperature, lights). Maintenance environment, which is the conditions during the pet food delivery and maintenance, is a human factor and can be controlled by us.

Preservatives can also affect pet food shelf life. Basically, pet food added with artificial preservatives has as longer as months shelf life than those with natural preservatives. But artificial preservatives can change the original taste of food and perhaps release some toxic substance. Therefore, there are very strict restrictions on preservatives usage.

Complying with AAFCO, pet food must have primary nutrition including protein (more than 18%), fat and additional nutrition like amino acids, mineral substance, crude fiber, calcium, iron, vitamins and so on. All these nutrition aims to ensure the necessities of pet growth, living and make their fur sleek. Meanwhile, it also provides a good medium for growth of microorganisms. These microorganisms can reduce protein to organic amines and mercaptans, which stink and decay pet food, reduce fat to smelly ketone and aldehyde and other spoilage substance. All these low molecular will not only change the taste of pet food, but also make protein and fact lost their nutrition. Therefore, it is essentially important to restrain microorganisms no matter on production lines or shelves.

As we all know, growth and living of microorganisms need proper environment. The most three important factors are temperature, oxygen and water. Oxygen is primary factor that cause food decay. The less oxygen in food package, the less possibility food gets decay. While water also provides a living environment for microorganisms, it can speed up the reduction of fat; shorten shelf life of pet food. During shelf life, volumes of oxygen and water vapor in the packages mainly depend on package integrity and permeability of packaging materials.

1. I. Package Integrity

Packages commonly used in pet food industry include plastic flexible packages, laminated plastic packages, paper-plastic packages, aluminum-plastic packages and so on. No matter what kind of package is used, package integrity is the first primary requirement for quality control. Oxygen and water vapor will transmit into package through even a tiny opening. Basically, package integrity issues always occur on the places of sealing and joint.

a)        Package Entirety

Oxygen and water vapor in air will definitely transmit into food packages if the packages are not sealed. Pet food will be easily decayed and nutrition will also lose.

b)        Peel Strength and Seal Strength of Pet Food Packages

The most commonly used packages are stand up pouches with zipper and Aluminum-plastic packages for pet food. These kinds of laminated packages can improve the force resistance and permeability of the whole packages.

If the peel strength is too low, it means the layers of materials are not laminated well, and then the packages cannot achieve the expected purpose on force resistance and permeability. When packages drop from a height, it will be broken more easily.

Seal Strength also affects package integrity to a large degree. If the seal strength is not strong enough, packages will split open at the seams, which may result in contents spilled out or let oxygen and water vapor in air permeate into the packages.

c)        Resistance of Puncture and Tearing

Puncture strength is generally strength that a material is ruptured by a probe or other type of device. It is used in food processing industry to determine the texture of ripeness of packaging. If puncture strength is not strong enough, pet food package can be broken down during delivery and maintenance.

Tearing strength is force required to rupture a pre-slit packaging materials, like paper, plastic films. It should not be too high, which results in worse consumer experiences or too low, which results in packages opening during the transportation or maintenance.

1. II. Permeability of Packaging Materials

Permeability is a measure of the ability of a barrier material to allow gases (O2, N2, CO2 and water vapor etc.) to permeate through it in a specific time. It usually depends on the type of material, pressure, temperature and thickness of materials. During pet food shelf life, oxygen and water vapor in the packages should maintain the prefilled volumes, which reply heavily on pet food packages. In Labthink laboratory, we did oxygen transmission rate and water vapor transmission rate testes, analysis and comparison of seven commonly used pet food packaging PET, PET+CPP, Bopp/CPP, BOPET/PE, OPP/PE/CPP, BOPET/VMPET/LDPE. Higher oxygen transmission rate, lower oxygen permeability of materials; high water vapor transmission rate, lower water vapor permeability of materials.

Oxygen Transmission Testing Use Labthink OX2/230 Oxygen Transmission Rate Test System and equal pressure testing method.

Before testing, place the specimen in a standard environment (23±2℃、50%RH) for 48h to make a air balance of specimen surface.

• Select the smooth without wrinkle specimen and cut it into round shape
• Mount the conditioned specimen on OX2/230 Oxygen Transmission Rate Test System. In this way, the test chamber is divided into an upper chamber and a lower chamber by the specimen. Close and fix the test chamber
• Pour high-purity oxygen into upper chamber, high-purity nitrogen into lower chamber
• Because of concentration difference, oxygen will be in solution diffuses from upper chamber to lower chamber, through the specimen, then these oxygen will be taken to the oxygen sensor by flowing Nitrogen in lower chamber
• Oxygen concentration in lower chamber will be obtained using oxygen sensor, and then oxygen transmission rate can be calculated through the specimen.

Water Vapor Transmission Rate Test Use Labthink W3/030 Water Vapor Transmission Rate Tester and traditional cup method.

• Pre condition specimen as oxygen testing and cut the specimen into round shape
• Fill the test cup with certain quantity of double distilled water. Mount the specimen into the test cup so that the test cup is divided into two part
• Set the test environment at 38 ℃ and 90%RH
• WVTR could be obtained through period-measuring the reductive weight of test cup during the testing process

OTR and WVTR test results of these 7 packaging materials as follow:

Table 1 Test Data of Pet Food Packaging Permeability

Analyzing the test results of these 7 kinds of packaging materials, we can find that materials laminated with different layers can have a significant difference in oxygen permeability. From Table 1, aluminum-plastic materials, BOPET/VMPET/LDPE, PET/CPP has a relative lower oxygen transmission rate (better oxygen barrier property). According to our research, pet food with these kinds of packaging usually has longer shelf life。

Laminated films have a good performance in barrier of water vapor. Referring to the chart below, PET has high water vapor transmission rate, which means it has a poor performance in barrier of water vapor and not suitable for pet food packaging, as it will shorten the shelf life of pet food.

Solutions

According to the tests we conducted in Labthink laboratory, choosing proper packaging for pet food is helpful in prolonging pet food shelf life, decreasing the addition of preservatives, saving production cost as well as pet health. Therefore, we have advices for manufacturers and suppliers of pet food packaging as follows:

ü  Choose laminated plastic, aluminum-plastic materials and metal materials as pet food packages, because all these materials have a good barrier properties to oxygen and water vapor. Besides consideration of oxygen and water vapor permeation properties of materials, we should know that the environment also have some impacts on these properties of materials. Such as EVOH and PA, they are very sensitive about humidity. In Room temperature and relative lower humidity, both of them have a good barrier to water vapor, while in high humidity environment, their water vapor permeability would decrease. So if there is high humidity environment during pet food delivery and maintenance, EVOH and PA are not suitable for packaging.

Choose materials with good peel strength, seal strength and puncture strength and other physical properties. The mechanical properties of material can help to improve the integrity of pet food packages, decrease the contacting of pet food and air, and prolong the shelf life of pet food.