Accelerated Shelf-life Testing- A basic understanding

Food and Agriculture Organization has defined Shelf-life as “The period during which the product maintains its microbiological safety, regulatory Compliance and sensory qualities at specific storage temperature.” Shelf-life of a product can be determined by taking Microbial conditions (Usually followed for Meat and meat products) or Sensorial attributes (Most of the food products) and analytical parameters like Vitamins or bioactive (In any foods with vitamin and bioactive compounds also claimed).

Shelf-life assessment can be done by two different methods. They are Direct Method and Indirect Method. The direct method is having the assessment in real-time study, i.e. we keep the sample in ambient condition and take sample at respective intervals and have the sensory evaluation and the analysis. Whereas the Indirect Method has Predictive Modelling and Accelerated Shelf-life Test (ASLT).

Accelerated Shelf-life Test

Real Time assessment is usually time and resource consuming. The food industry has a great need to have a shelf-life test in the minimum time possible because of the fierce competition, sudden shortage of agricultural inputs, opportunity loss and low unit value of the commodity. ASLT is a form Shelf-life assessment in which the stability or quality of the product is found out by keeping the sample in elevated conditions. By this, the deterioration rate is increased which effectively reduced the time of assessment. The ASLT method was first introduced to the pharmaceutical product which was later adopted in food. Moreover, the use of ASLT can help to reformulate the product in-house to check the shelf-life extension. Or even the change of process and its effect on the shelf-life can be explored. ASLT can be applied to any deterioration that follows any order of the kinetic model. The process can be Chemical, Biochemical, Microbiological and Physical deterioration.

ASLT can be classified as two, based on the number factors used. They are Single factor ASLT and Multiple factor ASLT. Factor means any condition like temperature, pH or RH. In Single factor ASLT, we follow any one condition.

Here we are discussing Single factor ASLT. It is characterized by deliberately increasing the temperature or pH or Humidity to increase the deterioration rate. In ASLT, ‘For every 10 °C rise, the rate of reaction is doubled’- this concept is called Q10 which is derived from Arrhenius equation. Arrhenius equation relates to the temperature dependence of reactions.

Where K₀ is constant, E_a the energy of activation, R the gas constant, K rate of reaction and T absolute temperature. As this model is utilized in most of the case, the value of activation energy is readily available. To simplify the calculation process, one can get over the need to find the K₀ by taking a ratio for any arbitrary value. But usually, it is done for 10 °C, thus the Q₁₀.

Where K₁ is the initial reaction rate, K₂ the reaction rate of 10 °C elevated temperature, ΔT is the difference of elevated temperature and desired storage temperature.

DRT is desired real time or shelf-life of the product under normal storage condition, AATD is Accelerated Aging Time Duration is the number of days where the product is stable at the elevated condition (ASLT).

Guidelines to perform ASLT:

Pre-requisites for ASLT:

• Define the critical Analytical parameter (like Vitamin C, Moisture content etc- Based on product the parameters vary), key Sensory attributes and Microbial specifications.
• Obtain a required amount of representative sample for the test.
• Keep some samples for Real Time study (Keeping samples at normal conditions- just to compare)
• Set up the frequency of sample collection.
• Run the Test.

Stage 1: Determining the basic data of unpacked product

1. Find out the Initial Moisture content (IMC) of the product by using the Oven Drying Method. IMC is nothing but the actual moisture content of the product
2. Expose the product to Accelerated conditions in the humidity cabinet to determine the Critical Moisture Content (CMC) of the product. (Note: Accelerated condition means Temperature usually 10-13 °C above the normal storage temperature of the product and RH 90% because microbial growth is maximum observed, CMC is the moisture content at which the product is unacceptable)
3. By using IMC & CMC we can find the maximum permissible moisture in the product. Based on this data we can select suitable packaging material for the product.

Stage 2: Determine the AATD (Accelerated Aging Time Duration) of the packaged product

As mentioned before, AATD is the number of days where the product is stable at the elevated condition (ASLT).

1. Load the representative sample into a humidity cabinet.
2. Collect the sample based on the frequency determined earlier.
3. Simultaneously conduct all the defined analytical tests, Microbial enumeration as well as sensory evaluation (Test parameters varies from product to product) along with the reaction rate (K₂) to determine the Q₁₀
4. Record all the observations.
5. Now continue the same till the product fails (It can be due to sensorial attributes or Microbial load or any other parameter)
6. Now get the average of all the Q₁₀.
7. Now calculate AAR from Q₁₀
8. Now AATD is determined.
9. Desired Real Time is also determined from the equation as mentioned above. This will be the number of days.
10. Conclusion of ASLT.