Determining the shelf life of processed foods is o\^ of the main problems faced by food companies when launching a product to market, or when modifying some of its ingredients. This problem is especially considerable when it comes to non-perishable products, where food needs many months, or even years, to deteriorate. That is why it is very important to employ methods that correctly estimate the shelf life of products.
We understand shelf life to be the time during which a food maintains characteristics and a level of quality thai is suitable for human consumption. In the food industry, the shelf life of a food is the time between the production or packaging of the product and the time when it becomes unacceptable under certain environmental conditions and when the consumption of said food implies a risk to consumer health.

4. DESCRIPTION (Description shall start from next stage)
From the point of view of food safety, the shelf life of the food depends on four main factors:
formulation, processing, packaging and storage, which we will explain later. In countries such as Spain, each marketing company is responsible for establishing and guaranteeing the shelf life of the food it places on the market given the importance and impact on consumers' health; making a mistake on the guarantee of the shelf life of the food carries serious consequences such as product recall, consumer complaints, market mistrust and brand reputation problems.
The expiration date and best by dates of foods
Prior to understanding the methods to determine the shelf life of foods, we must take into accotmt two elementary concepts: the expiration date and the best by date.
The expiration date is indicated on perishable products with biological risk(s), meaning its consumption after that date can generate some degree of food poisoning. This date depends largely ox\ factors such as optimal storage conditions, water activity, microbiological criteria or oxidation.
On the other hand, the best by date, which is applicable to more durable and stable products, indicates when a product begins to lose its physical qualities such as colour, smell or taste, but its consumption remains safe and presents no microbiological risk for the consumer. The use of antioxidants can help delay the best by date of a product.
Factors that influence food shelf life
There are several factors involved in the deterioration.or loss of the original quality of a food. These factors can be divided into two types: intrinsic (inherent to the nature of the food itself) or extrinsic (external conditions facing food), and are determined by different quality parameters: organoleptic, nutritional, hygienic, physical, chemical or microbiological.
. The intrinsic factors that affect shelf life are those that respond to the formulation of the food. In the food industry, it is imperative that the manufacturer has the following knowledge about its products:
• Raw materials
• Composition and formulation of the product (additives used)
• Water activity
• Total-acidity and pH value
• Potential Redox
• Available oxygen
Taking all this information into account, the producer can choose the systems that maximise the life of a product according to the needs that it may have. For example, the oxidation of edible oils is a significant problem for the food industry due to the considerable increase in tjie use of fat and polyunsaturated oils (Frankel, 2010), so it is important to know the nutritional quality and the possible processes that the different raw materials have gone though, and to determine what antioxidants can slow down the oxidation process.

The extrinsic factors that affect the shelf life of the food are those that are present in.the process, packaging and storage of the product. Mainly they are:
• Exposure to sunlight
• Temperature
• Humidity
• Damage to packaging
• Distribution and places of sale
During the different manipulation processes of the product, it is necessary to control its interaction with the components of the external system. To control of the process used every detail counts: the light permeability of the packaging, the distribution of humidity and the relative temperature, both in storage and in transportation, are the main external factors to be monitored and optimised.
Methodologies to determine foods' shelf life
The methods most used today to estimate the shelf life of foods are:
Direct method: These are real-time studies that consist of storing the product under conditions similar to those that it will actually face, to monitor its evolution in regular intervals of time. The main advantage of this method is that it creates a very accurate estimation of the time it takes for a product to deteriorate; however, they are studies that usually take a long time and do not consider the fact that storage conditions of a product are not always stable over time.
Challenge Test: This method consists of experimentally introducing pathogens or,microorganisms into the food during the production process, so that the product is exposed to the real conditions it will suffer in real life. The main disadvantage of this type of test is that the effects caused by the studied parameters are the only things analysed, and the fact that the product can be faced with multiple factors at the same time is not addressed. In addition, they are studies that are quite complex and difficult to implement.
Predictive microbiology: This methodology studies the different microbial responses of foods to varying environmental conditions, based on mathematical and statistical models, m order to predict the behaviour of the microorganisms in the product. This type of stuil\. widely used when developing a new product, does consider the possible changing conditions of a product, however, its major limitation is that it implies greater complexity for the manufacturer and that the results correspond to a simulation, which may not be accurate.
Accelerate shelf life tests: In these tests, conditions such as temperature, oxygen pressure or moisture content are modified to accelerate spoilage reactions of a food. These predictions allow one to predict the behaviour of foods in certain conditions and to estimate how the\ will evolve under certain storage conditions. Accelerated tests allow the inclusion of changing environmental conditions and concentration variations of the ingredients that they are composed of. These studies are very versatile, low cost for the manufacturer and allow for the comparison of different scenarios. Obviously, since it is not an exact representation of reality, there is some margin of error in the obtained results.
Survival method: It is a type of study that is based on the opinion of the consumer about the physical characteristics of the product. It consists in knowing the attitude of people towards the same product with different dates of manufacture, to determine if they would consume it or not. This method seeks to establish a relationship between the shelf life and the perceived quality of the product. Although it is not a method to accurately estimate the shelf life, it is important to do it in a complementary way to establish the best by date of a product.

The interest in preserving food goes very far back in lime. Salting, pickling or drying in the .sun and air were the first attempts to extend the shelf life of food. Today, thanks to food industrialisation, companies have the responsibility to determine the shelf life of their products and to provide good quality food. The search for this quality leads producers to conduct studies and to learn the factors that cause the deterioration of their products in order to have a sustainable basis for decision making, from the type of packaging, distribution or use of antioxidants to protect food against oxidation. .

5. CLAIMS
1. The shelf-life study can be initiated due to development of a new product, a formulation
change, or an alternate package evaluation.
2. According to claim 1, it is prescribed as Identify mode of deterioration. End of shelf life is specific to different food commodities. For chilled foods, the end of shelf life is attributed to elevated spoilage microbial levels. Other modes of deterioration may be oxidation of fats as in fried snack foods, vitamin degradation as in fruit juices and starch retrogradation or staling of breads.
3. According to claim 1, it is prescribed as Define key attributes to monitor. Microbial examination, chemical analysis (e.g. lipid oxidation and vitamin .degradation), physical testing (e.g. color and viscosity) or sensory evaluation can be monitored throughout the shelf-life study. Note that a key part of establishing the usefulness of any analytical measurement is the correlation with sensorial changes.
4. According to claim 19 it is prescribed as Select test methods. For chemical analysis, lipid oxidation could be monitored by measuring peroxide, free fatty acid, or thiobarbituric acid 4 reactive substances formation. Sensory evaluation could be determined by various methods such as discrimination and descriptive or acceptance testing. . •
5. According to claim 1, it is prescribed as Set storage conditions. Select the variables such as temperature, relative humidity, and lighting conditions. Product storage conditions can be optimal, typical or average, or worst-case scenario. The variables can also be fixed or fluctuating to simulate real-life product exposure during storage, distribution, and the retail environment. •
6. According to claim 1, it is prescribed as Set target end point and testing frequency. For product with a short shelf life (seven to 10 days), evaluation can be performed daily or every two days. For moderate shelf life (three weeks) and long shelf life (one year),, testing can be done at the initial point, end point, two to three occasions in between, and one point beyond the end point.
7. According to claim 7, it is prescribed as Determine appropriate test and control samples. Set the ingredients, process, and packaging for the shelf-life study. Test samples should be from the same batch to minimize variation and enough samples should be stored for duplicate or triplicate testing. Select the appropriate sensory control; if the product deteriorates oyer time, use freshly manufactured product or chill or freeze samples to ensure
. minimal deterioration and perform shelf-life study. Store the samples under conditions outlined in the study and test at the selected intervals.
8. According to claim 1, it is prescribed as Analyze results. In the absence of standards (legal or voluntary), manufacturers must set their own end point based on microbiological, chemical, or sensory criteria. The shelf-life date is usually assigned as die last day of an acceptable sensory score or analytical results. The preliminary shelf-life date can be conservative and based on the worst-case manufacturing and storage scenario.
9. According to claim 1, it is prescribed as Monitor and confirms shelf life. Once the product has been introduced into the market, sample at the distribution and retail levels and adjust the shelf-life date accordingly.