Are freeze-dried foods really nutritious?

Preserving activity and locking in nutrients, freeze-drying technology has some serious benefits!

Freeze-dried fruits and vegetables, freeze-dried yogurt bites, probiotic freeze-dried powder, freeze-dried face masks… In recent years, the application of “freeze-drying technology” has expanded into more and more areas of everyday life, becoming a hallmark of quality and convenience in products.

As these products gain more attention, people are not only amazed by the premium experience “freeze-drying magic” brings but also have more questions about this cutting-edge technology. Let’s dive into the secrets of freeze-drying with a closer look!

What is freeze-drying technology?

Freeze-drying technology, also known as vacuum freeze-drying, involves quickly freezing water-containing raw materials into a solid, then using the sublimation properties of water to remove the moisture in the form of vapor under vacuum conditions. This achieves the drying process [1].

Throughout the freeze-drying process, which occurs in a low-temperature, vacuum, and low-oxygen environment, the reproduction of aerobic microorganisms and the activity of certain biological enzymes are greatly inhibited. This allows for the preservation of the bioactive and heat-sensitive components of the raw materials. For these reasons, freeze-drying has unique advantages in modern food processing and is widely applied [2].

The versatile applications of freeze-drying technology

As the technology matures, freeze-drying has found applications in a wide variety of food products.

1. Fruit and vegetable crisps

Fruits and vegetables are rich in nutrients, providing vitamins, minerals, and dietary fiber [3]. However, due to their high water content, they spoil easily and are difficult to store long-term, requiring processing to remove excess moisture [4].

Studies have shown that freeze-drying better preserves the nutrients of fruits and vegetables, and the texture is superior to other drying methods. For example, in the case of mushrooms, research indicates that freeze-dried mushrooms have better rehydration and retain more vitamins than those dried by hot air, with less shape distortion and browning [5].

Freeze-drying not only makes fruits and vegetables easier to store and transport but also retains their original color, nutrients, and flavor. As a result, freeze-dried fruit and veggie crisps are gaining popularity as a healthy and convenient snack option.

2. Coffee drinks

Coffee, the go-to pick-me-up for many, benefits from freeze-drying technology’s ability to enhance both its quality and nutrition.

Freeze-drying retains the color, aroma, flavor, and shape of coffee while minimizing the loss of its nutrients and unstable compounds. Because freeze-dried coffee has a more stable structure, the resulting product is porous and sponge-like, which improves its solubility and rehydration [6].

Compared to other drying methods, freeze-dried coffee is more thoroughly dehydrated, has a longer shelf life, and is more stable during storage [7]. This type of coffee, with its low level of processing and enhanced aroma, has become increasingly popular with consumers [8].

3. Dietary supplements

Freeze-drying technology offers dual benefits: it protects heat-sensitive substances and prevents oxidation of functional ingredients, aligning with the trend toward high-quality health foods. As a result, more and more freeze-dried supplements, such as probiotic freeze-dried powders, are appearing on the market.

Traditional liquid and semi-solid preservation methods often cause a significant loss of live bacteria and require strict temperature controls, limiting product distribution [9]. Vacuum freeze-drying, which transforms probiotic fermentation liquids into live bacterial preparations, is considered an ideal preservation method [10].

Freeze-drying not only facilitates the transport, sale, and use of probiotics [11] but also helps protect the bacteria during storage, maintaining the stability of both the probiotic powder’s appearance and the number of live bacteria, thereby enhancing the effectiveness of the probiotics [12].

Do freeze-dried probiotics stay “alive and kicking”? — Decoding probiotic freeze-drying technology

Freeze-drying does not render probiotics “inactive” but instead puts them in a dormant state.

Probiotic freeze-drying combines freezing and drying technologies, subjecting the bacteria to extreme conditions during the process. Most of the moisture is removed, leading to changes in the physical condition of the cell membranes or sensitive protein structures, which lowers bacterial activity [13]. This effectively slows or inhibits bacterial growth.

However, mechanical damage to the bacteria during freeze-drying is inevitable [14], and their ability to regulate their own metabolism is affected. This is where freeze-drying protectants come in.

Freeze-drying protectants can alter the environment in which probiotics are dried, minimizing damage to the cells during the process, and preserving their physiological, biochemical, and biological properties as much as possible [15], providing effective protection.

Commonly used protectants include sugars (such as lactose, glucose, xylan, and trehalose), amino acids (such as alanine, L-serine, and glycine), and compounds (such as skimmed milk and gelatin). Each plays a role in protecting the bacteria during freeze-drying.

For example, glycerol can reduce the damage to active substances in the bacteria during freeze-drying; xylan has a noticeable effect on promoting probiotic growth and offers protection; skimmed milk powder forms a protective membrane around the bacteria, shielding them from harsh environmental factors [16].

With the aid of freeze-drying protectants, the overall structure and appearance of freeze-dried probiotics are well preserved, and they rehydrate quickly, restoring their pre-dried state [17]. This solves the issues of probiotics being sensitive to storage and having low survival rates after entering the body.

Are you feeling more familiar with freeze-drying technology now?

Currently, the scope of freeze-drying technology’s applications continues to expand. It has brought technological breakthroughs to the food industry, provided quality assurance for end products, and created new possibilities to meet our nutritional and health needs. We are likely to see freeze-drying technology play an even bigger role in the future of food!

References

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4. Journal of Food Safety and Quality Detection, 2016, 7(09):3470-3476.
5. Research on the Freeze-Drying Process of Mushrooms [D]. Anhui Agricultural University, 2007.
6. Brand and Standardization, 2018(06):71-74.
7. Beverage Industry, 2019, 22(06):71-74.
8. Food Science and Technology Industry: 1-11 [2023-05-14].
9. Trends in Food Science & Technology. 1999;10(12):387-392.
10. Research on Plant Lactobacillus Culture and Freeze-Drying Technology [D]. Shaanxi University of Science and Technology, 2016.
11. Journal of Microbiological Methods. 2006;66(2):183-193.
12. Cryo Letters. 2004;25(6):425-434.
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14. Cryobiology. 2004;48(1):8-21.
15. Transactions of the Chinese Society of Agricultural Engineering, 2015, 31(21):285-294.
16. Journal of Food Safety and Quality Detection, 2021, 12(15):6208-6212.
17. China Dairy Industry, 2010, 38(03):47-50.