How is the shelf life of food currently determined? What is the expected shelf life for the company's new products? Can it meet the requirements? How to improve if the requirements are not met? What is the actual shelf life of old products? Everyone has countless thoughts, and even the quality department has no conclusion. Next, taking beverages as an example, we will discuss influencing factors, accelerated testing, and long-term testing.
The continuous advancement of beverage production and packaging technology has led to the extension of the shelf life of beverages. In addition, considering the increasing diversity of beverage categories and packaging forms, as well as the continuous expansion of sales scope, the shelf life of beverages needs to be determined through scientific methods. Therefore, how to predict and determine the shelf life of beverages uniformly, reasonably, accurately, and quickly has become an urgent task for beverage research and development personnel.
At present, the determination of the shelf life of beverages mostly relies on experience or simple testing, lacking scientific and standardized methods. With the globalization of beverage product marketing, the changes in shelf life of beverages under different climatic conditions have also received increasing attention. However, countries with vast territories such as China often span multiple climate zones, making it necessary to consider the shelf life of products sold only domestically in different climate zones. The international climate zones are shown in Table 1:
Table 1 International Climate Zones
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The temperate regions mainly include Russia, the United Kingdom, Canada, and Northern Europe; Subtropical regions include the United States, Western Europe (Portugal Greece), and Japan; Dry tropical regions include Sudan, Iran, and Iraq; Damp and hot regions include the Philippines, Indonesia, Brazil, Ghana, and Nicaragua. Most parts of China are subtropical, and some areas are humid tropical. Therefore, the long-term testing method for the shelf life of beverages can adopt the following experimental conditions: temperature of 25 ± 2 ℃, relative humidity of 60% ± 10%.
01
Main quality issues during the shelf life of beverages
At present, there are mainly two types of quality problems with beverages during their shelf life. One is biological, which refers to the spoilage, sedimentation, and turbidity of products caused by microorganisms themselves and their metabolites; The other type is non biological, which refers to product discoloration, bulging, leakage, layering, and sedimentation caused by physical or chemical changes in beverage ingredients. The common quality issues are detailed in Tables 2 and 3:
Table 2 Beverage quality issues caused by microorganisms during the shelf life
Table 3 Quality Problems of Beverages Caused by Non biological Factors within the Shelf Life
02
Experiment on influencing factors
The influencing factor experiment is conducted under more severe conditions than accelerated testing, such as light, temperature, humidity, acid, alkali, oxidation, etc., to understand the quality retention of beverages under the corresponding conditions, and provide reference information for beverage formula design, production process, packaging, storage conditions, etc. The experiment on the influencing factors of beverages generally only requires one batch of samples. If the experimental results are unclear, two additional batches of samples should be tested.
At present, the commonly conducted experiments on the influencing factors of beverage shelf life testing are high-temperature experiments, high humidity experiments, and strong light experiments.
① Method of high temperature test
Seal the beverage and place it in a clean commercial packaging or similar commercial packaging. Leave it at 60 ℃ for 10 days, and take samples on the 5th and last day for testing according to the beverage shelf life indicators. If the beverage has undergone unacceptable quality changes within 10 days of storage, continue the experiment at 40 ℃ according to the above time. If there is no unacceptable quality change at 60 ℃, the 40 ℃ experiment will no longer be conducted. This experiment can investigate the stability of beverage storage and transportation in tropical regions, as well as the stability of beverage logistics during summer.
② Method of high humidity experiment
Seal the beverage and place it in a clean commercial packaging or similar commercial packaging. Place it at 25 ℃ and relative humidity of 90% ± 5% for 10 days. Samples will be taken on the 5th and last day, and tested according to the indicators of the beverage's shelf life. This high humidity experiment is generally only applicable to solid beverages. Constant humidity conditions can be achieved using a constant temperature and humidity experimental chamber. During the logistics process, beverages in the sea transportation stage can also be tested for their corrosion resistance using salt spray test boxes. This experiment is of great significance for beverages using semi transparent PET plastic bottles or metal containers. While examining the shelf life of the beverage itself, the stability and corrosion resistance of the container can also be evaluated.
③ Method of strong light irradiation experiment
Place beverages sealed in commercial packaging or similar commercial packaging in a lighting test chamber or other suitable lighting device equipped with fluorescent lamps (simulating shelf lighting) or xenon lamps (simulating sunlight exposure), and place them in an illumination condition of 4500 ± 500xl for 10 days. On the middle and last day, perform testing according to the beverage shelf life assessment indicators, with a focus on checking the sensory changes of the beverage. Any light source with an output similar to the D65/ID65 emission standard can be selected. This experiment mainly examines the stability of beverages during the shelf sales period.
In addition, acid, alkali, and oxidation experiments can be designed as needed to explore the impact of these factors on the shelf life and quality of beverages, and to study and analyze the mutual influence of various components in beverages.
03
Accelerated destructive testing
Accelerated destructive testing is a quality destructive test conducted under specific conditions, with the aim of understanding the physical, chemical, and biological changes in beverages in a relatively short period of time, providing experimental basis for beverage formulation design, quality evaluation, packaging, transportation, storage conditions, and predicting the stability of samples preliminarily.
Accelerated destructive testing is usually conducted using samples from three or more batches, placed in packaging containers that are the same or similar to commercially available products. The general placement conditions refer to the experimental conditions of chemical drugs (preparations), which are 40 ± 2 ℃, relative humidity of 75% ± 5%, and a placement time of six months.
The detection generally includes three time points: initial, intermediate, and final. Based on research and development experience, if it is predicted that the results of accelerated destructive testing may approach the critical point of quality change during the shelf life of beverages, then increasing the detection frequency should be considered in the experimental design. If there are obvious abnormalities in the sensory or indicators of the beverage, that is, if the quality of the beverage has changed significantly during the shelf life, the test can be terminated.
In addition, for some beverages that require refrigeration storage (5 ℃± 3 ℃), the accelerated destructive test conditions are 25 ± 2 ℃ and relative humidity of 60% ± 5%. If there is a significant change in quality during the first 3 months of the accelerated test, manifested as obvious sensory or indicator abnormalities, the impact of storage conditions on their quality during transportation or handling should be evaluated; If necessary, an additional batch of samples can be tested, the frequency of sampling and testing can be increased, and experiments can be conducted within 3 months; If there have been significant unacceptable changes in sensory or indicators in the first 3 months, the accelerated destructive test can be terminated. There is currently no reference for the placement conditions for accelerated testing of frozen stored beverages.
The most widely and effectively used method for predicting food shelf life is the Arrhenius model, which is used to describe the effect of different temperatures on the rate of chemical reactions related to food. The Arrhenius model equation is:
In the formula, k is the velocity constant; K0 is a constant in the relationship equation; E is the activation energy; R is the gas constant; T is the absolute temperature.
In the above equation, the degree of influence of temperature on chemical reactions is represented by Q10. In general chemical reactions, the reaction rate doubles for every 10 ℃ increase in temperature, and Q10 is usually 2. The ratio of shelf life Q10 at any temperature difference of 10 ℃ has the following formula:
Q10=shelf life at T temperature/shelf life at (T+10) temperature
Normally, Q10 for beverage shelf life is calculated by selecting two temperatures for the ratio, and the frequency of experiments at these two temperatures must also be determined. The formula is as follows:
In the formula, Δ T is the temperature difference between two experimental temperatures T1 and T2, and f1 is the time interval between tests at temperature T1; F2 is the time interval between tests at temperature T2. For Q10 with a temperature difference of not 10 ℃, the above formula becomes:
In the formula, Δ T is the temperature difference between T1 and T2, and θ s (T1) is the shelf life at a specific temperature T1; θ s (T2) is the shelf life at a specific temperature T2.
04
Long term experiment
The purpose of long-term testing of beverages is to study the stability of their quality under specified storage conditions, while also providing reference for the packaging, storage environment, and shelf life of beverages. In general, long-term experiments need to be conducted under conditions close to the actual storage conditions of the beverage.
The long-term testing of beverages generally involves sealing the beverage in clean commercial packaging or similar commercial packaging, and then placing it in an environment with a temperature of 25 ± 2 ℃ and a relative humidity of 60% ± 5%, or a temperature of 30 ± 2 ℃ and a relative humidity of 65% ± 5%. The experimental time is the shelf life of the sample, usually 12 months. This is based on the differences in climate between the southern and northern regions of our country, while beverages sold in other countries should be considered based on their climate zones.
Samples for long-term testing are generally selected from three batches, with samples taken every three months at the beginning of storage, three months, six months, nine months, and twelve months, and tested according to the quality inspection indicators for beverage shelf life.
Considering the dispersion of detection data in practical experiments, data statistical analysis should generally be organized according to a 95% confidence limit to obtain an effective shelf life.
If the statistical analysis results of three batches of beverages have a small difference, the average value is taken as the shelf life of the beverage. If the statistical analysis results of the three batches of beverages have a large difference (P value ≤ 0.25), the shortest batch time is taken as the shelf life of the beverage. If the data shows that there is little change in the measurement results, indicating that the beverage is very stable, then no statistical analysis will be conducted.
In special circumstances, some beverages may require refrigeration or freezing. The long-term experimental conditions for storing beverages in refrigeration are 5 ± 3 ℃. If unacceptable quality changes occur between 3 and 6 months during accelerated destructive testing, the shelf life should be determined based on the stability data of the actual inspection time. The long-term test conditions for certain beverages that require freezing storage are -20 ℃± 5 ℃, and their shelf life should be determined based on the stability data of the actual inspection time under long-term experimental storage conditions.
05
Key inspection items for shelf life test
The key inspection items for the shelf life test of beverages can be divided into sensory indicators, physicochemical indicators, and microbiological indicators, which are the three main aspects for evaluating whether a beverage has spoiled. Sensory indicators are the most direct basis for judging the quality or taste of food. Physical and chemical indicators specify the ingredient content that beverages should reach, while microbiological indicators measure the degree of microbial or other contamination of beverages.
For different beverages, the evaluation criteria are not completely the same. For example, vitamin drinks should focus on physical and chemical indicators, while carbonated drinks should focus on the carbon dioxide gas capacity; Microbial indicators involve food safety, and while paying attention to pathogenic bacteria indicators, indicators of indicator bacteria should also be considered.
Table 4 Reference Table for Key Inspection Projects
Note: Unstable substances refer to key components in beverages with unstable properties, such as the vitamin content in vitamin drinks, the fruit and vegetable juice content in fruit and vegetable juice drinks, and the carbon dioxide gas capacity in carbonated drinks.
Example: Key inspection project for solid beverages of plants and tea - Study on clumping rate
Plant based solid beverages are processed solid beverages made primarily from plants and their extracts (excluding fruits, vegetables, tea, and coffee), with or without the addition of other food ingredients and additives. Tea solid beverage is a solid beverage made by processing tea extract or its extract, or directly using tea powder (including instant tea powder, ground tea powder) as raw material, with or without adding other food raw materials and food additives.
The key inspection items for the clumping rate test of solid beverages can be divided into sensory indicators, physicochemical indicators, and microbiological indicators, which are the three main aspects for evaluating whether the beverage has spoiled. Sensory indicators are the most direct basis for judging the quality or taste of food, physical and chemical indicators specify the ingredient content that beverages should reach, and microbiological indicators measure the degree of microbial or other contamination of beverages.
For different beverages, the evaluation criteria are not completely the same. For example, vitamin drinks should focus on physical and chemical indicators, while carbonated drinks should focus on the carbon dioxide gas capacity; Microbial indicators involve food safety, and while paying attention to pathogenic bacteria indicators, indicator bacteria indicators should also be considered.
The product characteristics of solid beverages generally focus on the clumping situation of the product. For plant solid beverages and tea solid beverages, the clumping rate is an important indicator of shelf life. It is also a major indicator, and this article only studied the agglomeration rate. Although it only studied a part of the shelf life, enterprises can use this as a basis to determine the shelf life of their products.
At present, there is no unified regulation on the clumping rate of plant solid beverages and tea solid beverages, and there is no fixed method for quickly determining the clumping rate. According to the Arrhenius model, taking plant solid beverages and tea solid beverages as examples, accelerated testing can be used to calculate the approximate clumping rate of the company's products and compare it with the target clumping rate. If the target clumping rate is not reached, process improvement can be immediately carried out, including product formula, process parameters, packaging materials or packaging methods, providing new ideas and experimental basis for the rapid determination of clumping rate in the development process of such new products.
The experimental results of Liu Jianwen et al. showed that the time for the true agglomeration rate to reach 5% is about 5% longer than the approximate agglomeration rate under accelerated experimental conditions. The experimental results are accurate and reliable. If the agglomeration rate of the product does not meet the specified requirements, it can be extended by improving the production process, formulation, and packaging materials of the product.
06
Evaluation of shelf life test research results
The prediction research on the stability of beverage shelf life is of great significance to the development of the beverage industry. It is based on the experimental results of influencing factors, accelerated destructive tests, and long-term tests, and combined with the systematic analysis and judgment of the situations that may be encountered in the actual production and transportation process of beverages. Beverage shelf life testing can provide information on the changes in the quality of beverages over time under various environmental factors, and can scientifically and rigorously predict and determine the storage conditions, packaging, and shelf life of beverages; Thus, establish the shelf life and recommended storage conditions for beverages to ensure stable quality during the shelf life.
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