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A friend recently asked: Someone gave me some freeze-dried fruit snacks, and my child instantly fell for them. People always say fruits should be eaten fresh—once processed, they lose most of their nutrients. Even dried fruits retain dietary fiber and minerals, but at least vitamins and health benefits are lost. Is this freeze-dried fruit just a 'tax on intelligence'? Are they really nutritious given their high price? And when you give such snacks as New Year gifts, do they even qualify as healthy food?
In reality, if fresh fruits are inconvenient to consume, insufficient in quantity, or pose other concerns, freeze-dried fruits can serve as a nutritious alternative. They also make for tasty snacks. Today, we'll explore the growing popularity of freeze-dried fruits in recent years and examine whether they truly qualify as healthy food.
How is freeze-dried fruit made and why is it more expensive?
Freeze-dried fruits are produced through vacuum freeze-drying technology. Unlike regular drying methods that require heating, this process achieves dehydration while maintaining the frozen state. As physics students know, water follows a three-phase curve. During freezing, a small amount of water vapor sublimates directly from ice crystals.
The vacuum freezing process first cools the fruit to-30°C or-40°C, creating a dense network of microscopic ice crystals throughout the food. Subsequently, the air is evacuated to reduce atmospheric pressure. As the ice sublimates into water vapor, this vapor is continuously extracted, maintaining a vapor-water equilibrium that promotes the formation of liquid water.
As a result, the ice crystals in the food gradually turn into water vapor at low temperatures. After several dozen hours, the food becomes dry.
Since the ice crystals transform directly into vapor without passing through the liquid phase, they silently detach from the food matrix, leaving numerous voids within the food. This results in a crisp and crunchy texture when consumed.
The process requires both freezing and vacuum extraction, making it highly energy-intensive and more costly than other dehydration methods such as sun-drying, hot-air drying, infrared drying, microwave drying, or low-temperature oil frying.
But there are costs and benefits.
Nutrient preservation of freeze-dried fruits: vacuum to prevent oxidation, low temperature to prevent heat-sensitive vitamins
Vacuum extraction effectively prevents the oxidation of nutrients and antioxidants during processing. For instance, vitamin C, vitamin A, vitamin E, folic acid, and antioxidants like anthocyanins, flavonoids, and carotenoids are highly susceptible to oxidative damage.
Low-temperature freezing also solves the problem that some vitamins and phytochemicals are heat-sensitive. It is well known that vitamins such as vitamin C, vitamin B1, and folic acid are heat-sensitive, as are health-promoting components like anthocyanins and sulforaphane.
Since it is not boiled, there is no loss of water-soluble health components such as vitamin C, various B vitamins, anthocyanins, flavonoids, and chlorogenic acid.
Since it is not fried, there is no loss of oil-soluble healthy components such as carotenoids and vitamin K.
Because it is sufficiently dry to inhibit microbial growth, preservatives are not required.
Note that freeze-dried fruits are prone to moisture and should not be confused with low-temperature fried fruits and vegetables or candied dried products.
However, due to the numerous pores, vacuum freeze-dried foods are highly susceptible to moisture absorption. Similarly, porous foods exposed to oxygen at room temperature will oxidize rapidly.
Therefore, freeze-dried foods are typically stored in vacuum-sealed, nitrogen-filled packaging that prevents light and oxygen exposure. Once opened, they should be consumed immediately.
It's also worth noting that many people mistake low-temperature fried crisp fruits and vegetables for freeze-dried versions. In reality, they are entirely different.
Low-temperature fried fruit and vegetable chips are produced under vacuum conditions. The vacuum reduces pressure, and according to thermodynamic laws, the oil's boiling point drops significantly, sometimes below 100°C.
This low-temperature frying method can significantly reduce the oxidation and polymerization of oils, preventing the formation of carcinogens like benzopyrene. It also slows down the Maillard reaction, effectively preserving the original color of fruits and vegetables while minimizing heat-induced aroma loss.
However, this heating method still raises the temperature, inevitably causing vitamin loss. The high fat content also leads to the loss of some carotenoids and chlorophyll.
Most importantly, deep-frying at low temperatures significantly increases the fat content in fruit and vegetable foods.
It's common knowledge that fruits and vegetables are classic low-fat foods, with most containing less than 1% fat. However, when processed into low-temperature fried' fruit chips,' their fat content can soar to over 10%, sometimes even reaching 30%—turning them into high-calorie, high-fat products! So when buying dried fruits and vegetables, always keep your eyes peeled and check the ingredient list and nutrition facts carefully.
Crispy fruit and vegetable slices aren't necessarily freeze-dried products. If the ingredient list includes' vegetable oil 'or the nutrition facts show high fat content, it's definitely not freeze-dried fruit but low-temperature fried products.
Additionally, check the ingredient list for any added sugars or sweeteners. Unless certain highly acidic fruits (such as sea buckthorn, hawthorn, lemon, or cranberry) require a small amount of sugar for flavor, the freeze-dried fruit should list only 'a certain fruit' as its main ingredient. These products boast the highest nutrient density.
This food is suitable for people with gastrointestinal issues or diabetes, and also ideal for those with limited appetite or busy schedules.
Who should eat freeze-dried fruit?
First, people with poor stomachs
Vacuum freeze-dried fruits are more stomach-friendly, solving the problems of eating fruits before meals, eating fruits in the morning, and eating fruits that hurt the stomach. At the same time, it also avoids the loss of nutrients and the extra sugar caused by cooking fruits.