Sweet corn processing and vacuum packaging

Sweet corn introduction

Sweet corn is a naturally occurring genetic variant of field corn, and its kernels store more sugar than field corn. Fresh sweet corn has a genetic trait that inhibits the conversion of sugar into starch. Compared with ordinary corn, sweet corn has significant differences in the content of starch, sugar, protein, fat and vitamins. The protein content of fresh sweet corn kernels is above 13%, the sugar content is above 10%, and the crude fat content is around 9.9%. Every 100g of sweet corn contains 0.7mg vitamin C, 0.22mg niacin and vitamin B2, and 1.70mg riboflavin and vitamin B2. .In addition, sweet corn also contains a variety of volatile aromatic substances, minerals, dietary fiber, oryzanol, sterols and other ingredients.

Sweet corn cob processing and Vacuum Packaging process

The processing process of sweet corn can be summarized as follows: raw material harvesting → pretreatment → (removing husks and cobs → grading and sorting → cleaning → punching) → precooking → cooling → vacuum packaging → sterilization → shaping → cooling → insulation inspection → finished product

Raw material harvesting

Sweet corn in the milky stage (18-20 days after pollination) should be selected and harvested on a sunny morning, leaving (2~4) husks. After fresh sweet corn cobs are picked according to the harvesting standards, they must not be thrown on the ground at will, and they must not be violently collided or squeezed during loading and unloading and transportation. They must be handled carefully to reduce losses and increase yields. Corn cobs must be free of insects, with grains arranged neatly and plumply. Corn cobs with insects can still be used as raw materials after being trimmed to meet the requirements.

Pretreatment of sweet corn after harvest

Harvested sweet corn cobs should be protected from the sun and rain, and sent to the processing plant in time (within 12h) at low temperature.

Carefully remove the husks and silk. There are many models of automatic corn cob shelling Machines with different capacities and prices. You can try to search and choose according to your production scale.

Trim the corn cobs to a uniform length, manually or using an automatic corn cob trimmer.

Wash the corn cobs with clean water, manually or using a bubble washer.

Pre-cooking and blanching of sweet corn

Add 0.1% citric acid and 1% salt to the blanching water, the temperature is 95℃-100℃, the time is 5-12 minutes, so that the corn cob temperature reaches above 95℃. Steam blanching can also be used.

The main purpose of pre-cooking and blanching is:

Soften the tissue, remove the air in the tender corn tissue, reduce the pressure of ice crystal formation during freezing, and correspondingly reduce the oxidation degree of the raw materials, which helps to maintain the color and nutrition of the product.

Blanching destroys enzyme activity, stabilizes color, improves flavor and tissue, and prevents the destruction of nutrients in corn.

Blanching can remove some of the moisture in sweet corn and keep the solidified material stable.

Blanching can kill some microorganisms in the corn cob, reduce the number of pathogens, and lay the foundation for improving the sterilization effect.

Cooling and drying of sweet corn

The corn cobs must be cooled in time after blanching, otherwise the corn kernels will wrinkle due to high temperature water loss, affecting the appearance and quality of the corn. Generally, spray with clean water or soak in cold water for 3-5 minutes to reduce the surface temperature of the corn to ensure that the temperature of the corn cobs is around 50℃ during the next step of packaging. If the temperature of the corn cobs is too high, the water will evaporate and produce steam during the vacuum packaging process, which will have an adverse effect on the quality of the vacuum packaging.

Before entering the vacuum packaging step, the corn cobs should be blown dry on an automatic dryer to eliminate moisture.

Vacuum packaging of sweet corn cobs

According to the different packaging materials, the vacuum packaging machines for sweet corn cobs can be roughly divided into two categories:

Vacuum packaging machines using pre-made vacuum bags

Vacuum packaging machines using roll film automatic bag making.

Vacuum packaging machines using pre-made bags mainly include single double chamber vacuum packaging machines and continues vacuum packaging machines。

The vacuum packaging machine that uses roll film automatically is also called the commonly used fully automatic stretch film vacuum packaging machine, or thermoforming vacuum packaging machine.

So how should you choose the right sweet corn vacuum packaging machine?

It depends on which type of packaging you prefer, pre-made vacuum bags or thermoformed packaging.

If you choose pre-made bag packaging, the next consideration is the budget. Single-Chamber Vacuum packaging machines cost from a few thousand yuan to more than 10,000 yuan; double-chamber vacuum packaging machines cost more than 10,000 yuan to 40,000 to 50,000 yuan; rolling continuous vacuum packaging machines cost about 50,000 yuan. These 3 vacuum packaging machines are low-cost, but at least 1 staff member is required to operate the machine, and other staff members need to put the corn ears in the vacuum bag and be ready for vacuum packaging at any time

If your production is relatively large and the vacuum packaging speed required is high, the fully automatic stretch film vacuum packaging machine seems to be the best choice. According to your requirements, the mold is specially customized, and one package can contain 1, 2 or more corn ears, so as to achieve different packaging speeds, ranging from 1,500 bags per hour to 5,000 bags per hour. Depending on the size of the machine, the price of the fully automatic stretch film vacuum packaging machine may be around 250,000 yuan. Remember that you need compressed air for the machine to work properly. If you want to print date information on the package, you need a matching inkjet printer.

High temperature sterilization

Before high temperature sterilization, check whether the quality of vacuum packaging meets the standard requirements. Qualified packaged products are sent to the sterilizer for high temperature sterilization. The sterilization method is 15'-20'-20'/121℃, that is, the temperature in the sterilization tank reaches 121℃ in 15 minutes and the temperature is kept constant for 20 minutes. During this period, the pressure in the sterilization tank must be kept stable, otherwise the bag will break. Because the moisture in the packaging bag will expand when heated. To prevent the bag from breaking, back pressure cooling should be used, and the pressure should be 0.02-0.03 MPa higher than the sterilization pressure. The cooling time is 20 minutes, and the temperature drops to 40°C.

Cleaning, drying and storage of packaging

Use an automatic cleaning and drying line to clean and dry the packaging, and check the quality of the vacuum packaging to see if there is any leakage or bag breakage.

Store the vacuum-packed sweet corn cobs at room temperature, and the shelf life can reach 6-12 months.

Conclusion

There are several key points to pay attention to in the processing and vacuum packaging of pre-cooked sweet corn cobs, including:

The quality of sweet corn raw materials. The basic factors that determine the edible and processing quality of sweet corn are the sugar content and water-soluble polysaccharide content of the corn kernels. Polysaccharides are a multi-branched small molecule starch that is soluble in water and has a waxy taste. It is one of the main factors that make up the flavor of sweet corn. The tenderness of the peel is also one of the factors that affect the taste. Therefore, when the corn is harvested, it is necessary to determine that the above three factors of sweet corn are in the best state based on observation and research.

Precooking and blanching time. On the one hand, blanching can inactivate various enzymes in the sweet corn cobs, so that the nutrients in the corn are not destroyed, and can effectively prevent discoloration (corn kernels may turn purple if not properly cooked) and extend the storage period; on the other hand, pre-cooking can effectively kill microorganisms and insect eggs on the surface of corn cobs, ensuring the hygiene and food safety of processed foods; it can also squeeze out the air in the tender corn tissue, increase the anti-expansion pressure, and reduce the damage rate during sterilization; correspondingly reduce the oxidation of raw materials, which is beneficial to preserve the color and nutrition of the product to a certain extent, making the sweet corn cobs have a cooked feel.

The formation of corn sweetness mainly depends on the gelatinization degree of amylopectin in the endosperm during the pre-cooking stage. Only after full gelatinization can the sweet corn flavor be obtained, and the same flavor quality can be maintained after sterilization. However, if the gelatinization is not good, the amylopectin cannot be further gelatinized during the sterilization process. Make the product unsuitable for consumption. If the pre-cooking time is too long, the corn kernels will break and the flavor will decrease. Therefore, we use its flavor, palatability and grain cracking as comprehensive evaluation indicators to determine the blanching time.

High temperature sterilization. For most vacuum packaging, thorough and timely sterilization is the key to extending the shelf life.