Let's talk seriously about the "continuation of life" of food|Earth Knowledge Bureau

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NO.2415-What is shelf life

Author: Douyun

Proofreader: Gu Hanyi / Editor: Chestnut

In the past, due to the lack of materials, people made various foods such as pickles and bacon in order to preserve food for a long time.

Nowadays, with the increase in productivity, there is a variety of food in various supermarkets, and consumers also tend to buy fresh food. For food manufacturers, it is more inclined to extend the shelf life of food to meet storage, transportation and other requirements.

The food section is full of shelves

It is the epitome of today's development of food preservation technology

(Photo: Shutterstock)

It is generally believed that "fresh" foods have a shorter shelf life, and foods with a long shelf life are not "fresh". So, what kind of food is considered "fresh"? Is "fresh" food necessarily better?

"Freshness" and shelf life

There is no clear definition of freshness. From different perspectives, the definition of "fresh" is also different.

A chemist might say that "fresh" is that the food has not yet oxidized; A rheologist might say that "freshness" is when food has not lost moisture; A nutritionist might say that "freshness" makes food better retained in nutrients; A microbiologist might say that "fresh" means that the food has not gone spoiled; Farmers might say "fresh" when food has just been picked or slaughtered.

In a sense, all these statements are true. In conclusion, it is considered an attribute associated with raw or natural products.

The development of the modern food industry has made the concept of freshness more ambiguous, and "fresh" does not fully represent better quality of food. Apples that look "fresh" in supermarkets may have been stored in warehouses for half a year; Freshly slaughtered meat is post-ripened and left for a while before it becomes more tender.

"Retreat" in cold storage for several months

The value doubles in the next season

(Photo: Figureworm Creative)▼

At present, some emerging technologies are also used in food, such as irradiation, high voltage, pulsed electric field, ultrasonic and ultraviolet treatment, which have a small degree of processing on food and can make food look "fresh".

These emerging non-thermal processing technologies are sterilized at the same time

There is also less damage to the flavor, color and nutritional value of the food

(Apple in the Cobalt-60 irradiation device Photo: OneImage) ▼

But people are not receptive to these new technologies, especially when they know that what looks "fresh" uses new technology that they are unfamiliar with or not accepting, can they buy with peace of mind?

Although the definition of "freshness" is vague, the definition of "food shelf life" is clear: that is, the period of time that food maintains quality under the established storage environment parameters such as temperature, humidity, and light.

The "lifespan" of each food item is determined when it leaves the factory

(Photo: Figureworm Creative)▼

That is, during the shelf life, food should maintain its desired organoleptic, chemical, physical, functional or microbiological characteristics, and when stored under normal conditions, the nutritional content should also comply with the label instructions on the package.

Even advent food

It should have no less nutrients

(Photo: Figureworm Creative)▼

Food shelf life is divided into microbial shelf, chemical shelf, and sensory shelf. Food shelf life reflects the overall effect of these different aspects, so the study of food shelf life involves a variety of disciplines.

In addition, the study of food shelf life is unlikely to have particularly clear results, and cannot be truly accurate to a certain month, month and day of a certain year. This is mainly because food is a very complex, active system.

It's like Schrödinger's cat

Whether the food that is close to the expiration date is bad or not, you will not know until you open it

(Whether the advent milk has deteriorated is even more elusive Picture: Tuworm Creative) ▼

So, what is the research related to the shelf life of food being studied?

Food quality, what is the guarantee?

Convenience stores are crowded, freezers are often opened and closed, and the ice cream inside may melt and deform over time. Although the melted ice cream is still within its shelf life and probably won't get food poisoning after eating, we still think that the ice cream is not of good quality. This deterioration is caused by improper storage of food and repeated rise and fall of temperature.

Especially when you first enter the summer, it is easy to buy

"Old popsicles" who have been "out of shape" for a long time

(But let's still eat it Picture: Tuworm Creative) ▼

All foods spoil, and the way they go bad is complex, often by multiple mechanisms. It is basically impossible to prevent food spoilage, and the purpose of understanding the mechanism of food spoilage is to predict or extend the shelf life of food as much as possible.

There are five common mechanisms of deterioration in food.

First, food deterioration caused by water transfer. In many foods, water is the most important ingredient. Therefore, many foods are sensitive to water transfer, such as vegetable salads in salads that absorb water and become thinner, and biscuits that absorb water and lose their brittleness.

Desiccants that can often be seen in food packaging

It is the "hero" of extending the shelf life of food

(Photo: Shutterstock)

Moreover, as long as there is a moisture gradient, water transfer occurs between adjacent components in the composite product, even at freezing temperatures. For example, to prevent moisture transfer, people apply a layer of chocolate and other grease coatings to the inside of the ice cream roll to delay the water absorption and softening of the egg roll.

Humans really spend a lot of brains trying to eat

(Photo: Figureworm Creative)▼

The second is food deterioration caused by microorganisms. Microorganisms are currently the most important factor leading to food spoilage, and they are also the type of food spoilage that people are most concerned about every day. The primary goal of many food technologies is to minimize microbial growth. A good understanding of the various preservation techniques that give food microbiological safety and stability can also help to select the most appropriate method to extend shelf life.

Microbes are everywhere

If you are not careful, good food will become a "culture medium"

(Photo: Figureworm Creative)▼

The main preservation techniques work by inactivating microorganisms (pasteurization, sterilization, irradiation, autoclaving), preventing or inhibiting microbial growth (refrigeration, freezing, drying, vacuum packaging, acidification, fermentation, addition of preservatives), restricting the entry of microorganisms into the product (aseptic processing, purification, packaging).

Food in the process of production, packaging and storage

We must always be wary of all kinds of microorganisms that "grab food" with us

(Pasteurization Photo: Shutterstock) ▼

The third is the deterioration of food caused by the transfer of substances other than moisture, such as oxygen, odor or spices. For example, carbon dioxide in carbonated beverages packaged in PET bottles will gradually be lost and bubbles will disappear, and a 500ml bottle of carbonated drinks packaged in PET can lose up to 60% of carbon dioxide. Heavy metals in packaging materials migrate to food, which can lead to food spoilage.

Freshly produced carbonated drinks should taste more "strong"

(Photo: Shutterstock)

The fourth is the deterioration caused by chemical reactions. Food is made up of chemicals, and most of the raw materials used to make food are biological, so it is inevitable that these in food will react with each other. These major chemical reactions include oxidation (oil oxidation, food color oxidation, vitamin oxidation), hydrolysis, non-enzymatic browning, enzymatic browning, and interactions between food and packaging.

Cut apples will change color when left for a long time

It is enzymatic browning

(Photo: Shutterstock)

For example, the oxidation of oils and fats can lead to undesirable "odors" (rancidity) and odor production. Myoglobin oxidation in fresh meat will make the color of the meat dull, making people feel that the meat is not fresh. The sweetener aspartame is often used in "sugar-free" beverages, and at the right temperature and pH, it also hydrolyzes slowly, resulting in a gradual decrease in the sweetness of the product.

Oxidized darkened meat, "polished" under a red light

All turned into "small fresh meat"

(Photo: Figureworm Creative)▼

Fifth, light-induced changes, that is, food deterioration caused by exposure to sunlight and artificial light. Ascorbic acid decomposes rapidly in the presence of oxygen and light, and the decomposition increases with increasing light. Many natural pigments (e.g., riboflavin, chlorophyll) are sensitive to light, and light can cause fading.

Carrots are rich in B vitamins and vitamin C

Storage away from light can effectively prevent nutrient loss

(This pile of radishes is not sunscreen at first glance Photo: Shutterstock) ▼

Among the above five mechanisms of food spoilage, temperature is the most critical influencing factor, affecting all of the above mechanisms that lead to food spoilage, so the influence of temperature will be evaluated in all shelf life studies.

How to predict food shelf life

Knowing the types of food spoilage, developers have to find ways to predict the shelf life of food. The shelf life of food can be determined by test method, literature method, and reference method.

The literature method and the reference method are better understood, that is, to determine the shelf life of food according to the existing literature and similar products. The test method is based on the mechanism introduced above to determine the shelf life of food through food stability tests, which can be divided into long-term stability tests and accelerated destructive tests (ASLT).

The two test methods have different suitability

However, long-term stability tests are more universal▼

As the name implies, long-term stability test refers to a research method that analyzes the degree and law of physical, chemical and microbiological status changes over time in the entire life cycle of food to determine or verify the shelf life of food under real or simulated real temperature, humidity, light and other storage environmental parameters. Its defect is also obvious, that is, the test time is too long, and it is not suitable for high-speed product replacement.

Selection of test parameters and setting of test conditions

It directly affects the accuracy of shelf life prediction

(Experiment Variable Condition Setting Reference)▼

Accelerated destructive testing results in a shorter-than-normal deterioration time by exposing food samples to higher-than-normal levels of external factors such as temperature, humidity, air pressure, and light. In short, accelerated destructive testing uses harsher storage conditions than the actual storage environment parameters.

Accelerated destructive testing is generally appropriate for specific food types

Frozen food is not suitable for this test method▼

In the process of accelerated destruction test, it is also necessary to regularly test and collect various data of the sample in the process of deterioration, and after analysis and calculation, the shelf life of the food under the expected storage environment parameters is calculated. Normally, for every 10°C increase in temperature, the rate of deterioration reaction doubles.

Temperature is often the key factor, or even the only factor, when designing accelerated destructive tests. Due to the calculations involved, more complex accelerated destructive tests, such as multi-temperature test methods, may also require higher mathematical requirements for the tester.

However, multivariate accelerated testing was used

It will be more accurate and reliable than univariate accelerated testing

(Postharvest shelf life prediction model of shiitake mushrooms Photo: Yanjie Li).

However, accelerated destructive testing also has some limitations. Due to the complexity of food components, as the temperature increases, food components may interact with each other, such as changes in physical state (melting of solid fats), which in turn affects the rate of certain reactions.

Extending the shelf life of food is mostly considered from a commercial perspective. In many cases, manufacturers mostly want food shelf life to be extended. However, the approach to extending shelf life must be based on our understanding of the various mechanisms by which food goes bad. The ability to extend the shelf life of food also reflects how well we know about the mechanisms by which they spoil.

In the process of finding ways to extend shelf life

It has also produced many unique flavors

(Photo: Shutterstock)

From a business perspective, extending shelf life typically brings the following benefits: eliminating peaks and troughs in food production, providing consumers with a wider range of options, inventory for seasonal sales increases or special promotions, expanding sales territories, and reducing product waste due to physical product failures or lack of time on retail shelves.

Foods with a long shelf life can also be used as a reserve food for emergencies

(Photo: Shutterstock)

Science and technology is a double-edged sword, perhaps in order to achieve a long shelf life, some nutrients will be lost, but objectively improve the quality of life of our consumers. For example, the extension of the shelf life of food enriches our choices: we can eat fruits from all over the world and all year round at any time; Imported food is still safe to eat after months of sea freight.

Almost all of the food we eat today is inseparable from the support of food technology

(In short, I will show off the tribute Photo: Tuworm Creative) ▼

Nutrients lost due to over-processing, which can be obtained from fresh food; After sticking to the vegetable salad for a while, you can occasionally choose "fat house happy water" to indulge.

The ancients said that fish and bear's paw cannot have both, but now we can achieve both nutrition and deliciousness with rich food choices.

Resources:

[1] LIU Ling. Theory and technology for determining the shelf life of food[J]. Dairy Science and Technology, 2004(4):4.

Qiang Wanli, Xie Tian, Li Hui, et al. Overview analysis of food shelf life[J]. Cereals, Oils and Food Science and Technology, 2020, 28(4):5.

[3] LI Huan, PENG Rong. T/CNFIA 001-2017 General Guidelines for Food Shelf Life[J]. Standard Life, 2018(4):4.

[4] Persis Subramaniam,David Kilcast.Food and Beverage Stability and Shelf Life[M]. Woodhead Publishing Series in Food Science,Technology and Nutrition, 2011

[5] (Dominic Man). Food Industry Briefing Series Shelf Life[M]. ACS, 2001

*The content of this article is provided by the author and does not represent the position of the Earth Knowledge Bureau

Cover: OneImage.com

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