Importance of Gas Sensors in Storage of Fruits & Vegetables

According to the Analysis Report of Market Research and Investment Forecast of Cold-Chain Logistic Industry in 2013 – 2017, in China, the loss ratio of agricultural products astonishingly reaches up to 25~30% per year in logistic processes including picking, transportation and storage, and this is the key factor for the high prices of fruits and vegetables.
The concept of refrigeration may have been known to all, but the concept of CA cold storage may not be the case. CA cold storage is the abbreviation of controlled atmosphere cold storage for fresh agricultural products, which is one of the most advanced, effective and widespread preservation technologies.
However, different from its scale development abroad, the popularity of CA cold storage remain sluggish in China due to various reasons. Statistically, among over 30 thousand agricultural fresh-keeping storehouses in China, only 5~7% of them adopts CA technology. In developed countries, over 80% of edible agricultural products are of modified atmosphere packaging, while in China there are only 2%.

CA cold storage, or say modified atmosphere storage, adds gas component adjustment to refrigeration. By controlling conditions like temperature, humidity, concentration of CO2, O2 and ethylene, the respiration of fruits and vegetables is restrained, the metabolism of them is suspended, so that the freshness and commodity of these products can be better preserved, and their storage period and refreshing time can be extended.
The storage period in CA cold storage can be nearly double than it in common refrigeration. After being taken out of the CA cold storage, the fruits and vegetables “awake” from their “dormancy”, so their length for preservation (shelf lives) are prolonged by 21~28 days, which triple or even quadruple that of fruits from common refrigeration storage.
The reason for CA cold storage to be capable of prolonging refreshing time is that it is particularly strict on controlling dehydration of fresh agricultural products. Instead, common refrigeration storage depends only on cooling system which can do nothing on product dehydration, not to mention extending length of preservation.
Compared with common refrigeration storage, a CA cold storage makes higher profits while takes higher construction cost. The extra cost goes to a whole set of air modifying equipment and airtight construction. Though the initial outlay of a CA cold storage is relatively high, in long term it can make large economic benefit after coming into service, especially when used for those out-of-season species with high additional value, like kiwi fruits and large cherries. It is proved by facts that the high investment in CA preservation will surely bring about high market return. That’s why CA cold storage is widespread in western countries.

It takes only two steps to transform a common refrigeration storage into a CA cold storage. First, enhance airtightness of the storage. Usually atmospheric modifying is to add CO2 and N2 to prolong refresh time, which means gas leakage from both inside and outside should be prevented. Second, add atmospheric controlling equipment. The main equipment for modified atmosphere packaging includes CO2 maker, N2 maker, ethylene removing machine and O2 removing machine, etc.
Fruits and vegetables are still animated after collected. In storage they keep on metabolic activities, mainly respiration, normally, showed as consuming oxygen and releasing carbon dioxide and some heat. Thus, control on concentration of O2 and CO2 in the whole storage environment can significantly increase the storage lives of fruits and vegetables in it.

The design purpose of SST O2 sensor Lox-02 and CO2 sensor MINIR is to modify the atmospheric environment in the whole storage through accurate measurement on concentration of O2 and CO2, so as to extend the expiration date of perishable foods.

Low Power Carbon Dioxide Sensor (NDIR CO2 Sensor) MinIR

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Perishable products, like fruits and vegetables, will keep on metabolic activities after collected, which means that they will consume oxygen (O2) while generate heat, CO2, moisture and probably ethylene. In this period the plants will gradually be mature and resolved into undesirable status.
Therefore, it’s a challenge to guarantee the integrity of products in transportation and storage of perishable foods. During transport process, four essential factors need to be considered — quality, temperature, relative humidity and gas concentration. Quality — the initial fine quality of fruits and vegetables shall be kept; temperature — with temperature lowered by 10℃, the metabolic rate will decrease by half; relative humidity — the quality of products will be severely affected if they are dehydrated by 2%; atmospheric environment control — if O2 concentration decrease from 21% to 2%, the metabolic rate will decrease by 30%.

The graph below shows the effect after adding an atmospheric control system.

In the places where these factors are appropriately arranged, the storage life of fresh agricultural products can be apparently extended by controlling and altering the environment. By slowing down the metabolic rate of these products, their natural maturity can be delayed while their taste and flavor remain unchanged. Therefore, in the storage process of fruits and vegetables, atmospheric control becomes the most crucial part in the design of a CA cold storage.