Help! Who said that putting garlic on watermelon can keep it fresher? Please share this with your parents!

Food is not easy to preserve in summer, so wrapping it in plastic wrap and putting it in the refrigerator is a common way to preserve food. Recently, I saw some amazing operations on preserving watermelons. The unfinished watermelons were not only wrapped in plastic wrap, but also two cloves of garlic were put in them. The reason is that garlic can help sterilize the watermelon, which can extend the shelf life of the watermelon.

Can putting garlic on watermelon really achieve better preservation effect? ​​How to use plastic wrap properly? Plastic wrap can't be used to wrap everything, so you must be rational.

Can putting garlic on watermelon kill bacteria?

Garlic contains allicin, a volatile organic sulfide. It is not only the biologically active substance of garlic, but also the main ingredient for seasoning dishes with a pungent smell.

Allicin has a significant inhibitory effect on bacteria, fungi, viruses and parasites . [1] However, it is only after the garlic is squeezed or cut that allicin is rapidly produced under the action of alliinase, which gives it a spicy taste .

Just peeling a few cloves of garlic and putting them directly on the watermelon will not have any antibacterial effect, let alone two or three cloves of garlic. Even if you spread the garlic all over the watermelon, it will be useless (don't even think about cutting it into garlic paste and spreading it on it), and the garlic smell will affect the taste of the watermelon itself.

It’s really difficult to do this, so I’d better add “garlic”. Not only will it not help sterilize the watermelon, it will also turn the watermelon into a “garlic-flavored watermelon” that is difficult to swallow .

Regarding the preservation of watermelons, if you can't finish eating watermelons, just wrap them in food-grade plastic wrap and put them in the refrigerator. If the watermelon is in good condition and has no odor the next day, you can cut off 1~2cm of the surface before eating. The premise is to ensure that the knife and cutting board for cutting the watermelon are clean. It is best not to store the unfinished watermelon in the refrigerator for more than 24 hours.

There are different types of cling film, so you must pay attention to the scope of application

Compared with ordinary plastic bags, plastic wrap is a thin film produced by single-layer extrusion or multi-layer co-extrusion processes and has self-adhesive properties. [2] Plastic wrap can adhere well to containers and has good sealing properties. It can isolate the food to be stored from the outside environment and play a role in food preservation and cleaning.

Using plastic wrap to store food on a daily basis can also prevent odors from crossing over, moisturize and prevent dryness, prevent nutrient loss, and inhibit oxidation.

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How many people think that there is only one kind of cling film? In fact, there are many kinds of cling films on the market. Although they are all self-adhesive and feel similar to use, they are made of different materials and cannot be used randomly.

The materials of cling film include: polyethylene (PE), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), polymethylpentene (PMP), ethylene-vinyl acetate copolymer (EVA), polybutylene terephthalate-adipate (PBAT), among which the first four are the most common. Let's mainly talk about them.

Polyethylene (PE) : Commercially available cling film is generally made of PE, which is relatively safe and has a certain degree of air permeability. Films made from it can still maintain flexibility at -40°C. [3]

However, PE is easily soluble in oils and fats . When in contact with oily foods for a long time, the amount of non-volatile substances released will increase significantly. [4] If PE plastic barrels are used to store cooking oil, low molecular weight polyethylene may migrate into them and give them a waxy smell. [3] It is relatively safe to contact with acidic foods at room temperature, but if heated, the amount of non-volatile substances released will increase. [4]

PE plastic wrap is more suitable for sealing fresh fruits and vegetables and oil-free frozen foods .

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Let me emphasize again here that the most common plastic wrap we see is made of PE material , and we can take note of its characteristics.

Polyvinyl chloride (PVC) : This material is easy to decompose and age. Due to the production process requirements of PVC cling film, plasticizers need to be added during the production process to enhance flexibility and transparency.

Its biggest problem is safety. When in contact with oil or at high temperatures, plasticizers can migrate into food. Excessive intake of plasticizers by humans can cause harm to health, leading to hormonal imbalance and endocrine disorders, and even inducing cancer or mental illness . [5]

PVC plastic wrap should not be used to preserve meat, cooked food, hot food and other foods containing fat, but it can be used to preserve fruits and vegetables .

Polyvinylidene chloride (PVDC) : This material has high transparency, heat resistance above 140°C [6], acid and alkali resistance, insoluble in oil, and has high barrier properties, especially against oxygen, carbon dioxide and water vapor. It can ensure that the sealed food is relatively isolated from the outside world, and can better preserve the taste and moisture, preventing the evaporation of food moisture and preventing the entry of external moisture. [5]

It is suitable for preserving foods that are afraid of moisture, such as seaweed, dried mushrooms, nuts, and noodles. It can also preserve foods containing fat, such as meat and seafood.

Polymethylpentene (PMP) : It has strong heat resistance and can withstand high temperatures of 180°C. It does not contain plasticizers and is very suitable for heating food.

Collect these six things to note when using plastic wrap!

As a common material for extending the shelf life of food, food wrap is very popular. Proper use of cling film can not only extend the shelf life of food, but also improve the quality of life. However, if used incorrectly, it is harmful to health. Therefore, the following suggestions on the use of cling film cannot be ignored.

When purchasing: check whether the packaging is marked with "for food contact" or "for food use". If the plastic wrap claims to be microwaveable, it should be labeled with "microwaveable", heating method and maximum temperature resistance .

To preserve fruits and vegetables, such as leafy greens, eggplants, beans, apples, pears, strawberries, and leftover watermelons, PE and PVC plastic wrap can be used. In this regard, PVC plastic wrap has a better preservation effect,[7] but is more suitable for use in supermarkets. PE plastic wrap is more recommended for home use because it has good air permeability and is safer .

To preserve meat and fatty foods: you can use PVDC or PMP plastic wrap without worrying about the migration of harmful substances after contact with oil.

To prevent food from getting damp, for example, dried mushrooms, seaweed, peanuts, cashews, melon seeds, etc., it is recommended to choose PVDC plastic wrap, which has good preservation effect and can prevent moisture.

Heating food: If you need to heat dishes, the most recommended are PVDC and PMP cling films, which can also be used in microwaves and are safer. Although some PE cling films are marked "microwaveable" on their packaging, they are only suitable for short-term microwave heating and are not recommended for long-term heating.

Figure: PMP cling film

Figure: PE cling film (microwaveable)

A reminder: No matter what kind of plastic wrap you use to heat food, it is best not to directly contact the food. You can put the food in a heat-resistant container and keep a certain distance from the sealed plastic wrap . If it is wrapped tightly, it is recommended to poke a few small holes for ventilation when heating. In addition, no matter what kind of plastic wrap you use, it cannot be used in the oven .

Summary: Cling film is not a panacea, so don't wrap everything with it . Generally, you can keep two types of cling film at home: PE cling film and PVDC cling film. PVC is not very safe, so don't keep it.

References

[1] Pu Chuan, Hu Haibo, Kuang Haixue, Peng Jinnian, Tan Ying, Huang Hao, Hu Bin. Research progress on the anti-pathogenic effects of garlic and its active ingredients[J]. Chinese Herbal Drugs, 2022, 53(07): 2174-2183.

[2] GB/T 10457-2021 General rules for quality of plastic self-adhesive cling film for food

[3] Sun Changhao. Nutrition and Food Hygiene 7th Edition[M]. People's Medical Publishing House. 2017:45

[4] Zhang Guohui, Chen Haifeng, Dou Chengying. Study on the hygienic properties of polyethylene cling film[J]. Popular Standardization, 2019, No.309(16):80-81.

[5] Zuo Tianming, Cheng Cheng. Research on the application and characteristics comparison of mainstream packaging materials in food cling film[J]. Modern Food, 2022, 28(15): 12-15. DOI: 10.16736/j.cnki.cn41-1434/ts.2022.15.004.

[6] GB/T 24334-2009 Polyvinylidene chloride (PVDC) self-adhesive food packaging film

[7] Gong Qiling, Zhou Yu, Li Danyang, et al. Effects of different plastic wraps on the preservation of fresh-cut loquat pulp[J]. Food Research and Development, 2019, 40(20): 27-30.

Author: Xue Qingxin, one of the first nutrition instructors of the National Health Commission, and a registered nutritionist in China

Review丨Zhong Kai, Director of Kexin Food and Health Information Exchange Center