Freeze-Dried vs. Spray-Dried Bovine Colostrum: A Technical Comparison

Bovine colostrum powder is the most common colostrum product form in the functional food and dietary supplement industry. Freeze-drying and spray-drying are the two mainstream dehydration technologies for colostrum, differing significantly in bioactive component retention, production cost, and product characteristics. This article presents a comparative analysis across five dimensions: processing principles, immunoglobulin retention, physicochemical properties, cost structure, and process selection, providing technical guidance for colostrum raw material sourcing and product development.

1. Differences in Drying Process Principles

1.1 Freeze-Drying (Lyophilization)

Freeze-drying (lyophilization) is a low-temperature dehydration technology. The process consists of three stages: first, liquid colostrum is rapidly frozen at -30 to -50 degrees C to form ice crystals; then, in a vacuum environment, ice sublimates directly from solid to gas, removing moisture; finally, a desorption drying step removes residual bound water [1]. Throughout the entire process, the material temperature remains below the freezing point, and proteins and other heat-sensitive components do not experience high-temperature treatment [2].

The core advantages of freeze-drying technology lie in low-temperature protection and the vacuum environment. Low temperatures prevent protein thermal denaturation, while the vacuum environment reduces oxidation reaction rates. Since moisture is removed through sublimation rather than evaporation, the microstructure of the material is preserved, forming a loose, porous, sponge-like powder [3]. This structure gives freeze-dried powder good rehydration and solubility properties.

1.2 Spray-Drying (Conventional Drying)

Spray-drying is currently the most dominant drying technology in the dairy industry. The process involves: liquid colostrum is dispersed into tiny droplets (typically 10-200 micrometers in diameter) through an atomizer, and these droplets rapidly evaporate and dry in a hot air stream (inlet temperature typically 125-180 degrees C), forming fine powder particles [4].

The core characteristics of spray-drying are high temperature and rapid processing. Although the residence time of droplets in the high-temperature air stream is very short (typically only several to tens of seconds), droplet surface temperatures can reach 80-100 degrees C, sufficient to cause partial thermal denaturation of proteins [5]. The advantages of spray-drying technology include high production efficiency, relatively low energy consumption, and suitability for large-scale continuous production [4].

2. Differences in Immunoglobulin Retention

2.1 Immunoglobulin G (IgG) Retention

Immunoglobulin G (IgG) is the most critical bioactive component in bovine colostrum and the core indicator for assessing colostrum product quality. The effects of different drying processes on IgG retention differ significantly. The following sections describe the impact of each drying process on IgG retention separately. Because different studies employ different experimental designs and measurement indicators, cross-literature numerical comparison of data is not appropriate.

IgG Retention in Freeze-Drying

Freeze-drying causes minimal thermal damage to IgG because it operates under low temperature (material temperature below freezing) and vacuum conditions throughout the process. A review by Riaz et al. notes that freeze-drying can retain 85-95% of original IgG activity [8]. The loss of IgG during freeze-drying primarily originates from mild thermal stress and mechanical stress during the desorption drying stage, rather than high-temperature denaturation.

IgG Retention in Spray-Drying

During spray-drying, droplets experience thermal stress in the high-temperature air stream, inevitably causing partial IgG denaturation. The study by Chatterton et al. systematically quantified the effects of different process combinations on IgG [7]. When liquid colostrum enters the spray-drying process without preheating, the IgG denaturation rate is 30-38%, and the total protein denaturation rate is 6-11%. If high-temperature short-time pasteurization (HTST, 72 degrees C, 15 seconds) is applied before spray-drying, the IgG denaturation rate rises to 40%. If low-temperature long-time pasteurization (LTLT, 63 degrees C, 30 minutes) is followed by spray-drying, the IgG denaturation rate can be controlled at 15-29% [7]. This study clearly demonstrates that in the spray-drying process chain, the preheating temperature before drying is the critical factor affecting IgG retention, and its importance exceeds that of spray-drying itself. Under optimized process conditions (low-temperature preheating + mild spray-drying parameters), spray-drying can retain 70-88% of immunoglobulin activity.

Process Comparison

Although the above two groups of studies cannot be directly compared for specific numerical values, they both point to the same conclusion: freeze-drying is superior to unoptimized spray-drying processes in terms of IgG retention. Spray-drying can significantly improve IgG retention through process optimization measures such as controlling preheating temperature, reducing inlet temperature, and shortening drying time, thereby narrowing the gap with freeze-drying.

2.2 Retention of Other Bioactive Proteins

In addition to IgG, colostrum contains lactoferrin, lactoperoxidase, growth factors, and other bioactive proteins, all of which are temperature-sensitive.

Lactoferrin retention during freeze-drying is superior to that during spray-drying [6]. During spray-drying, droplets experience surface temperatures of 80-100 degrees C, which may cause partial thermal denaturation of lactoferrin, reducing its iron-binding capacity and antimicrobial activity.

Lactoperoxidase is extremely heat-sensitive, and its activity is significantly affected during spray-drying. In contrast, freeze-drying, which operates at low temperatures throughout, better preserves the catalytic activity of lactoperoxidase.

Regarding growth factors, freeze-drying has been shown to better preserve the biological activity of insulin-like growth factors (IGF-1 and IGF-2) and transforming growth factor-beta (TGF-beta) [8]. These growth factors play important roles in intestinal epithelial cell proliferation, immune modulation, and antioxidant defense. Thermal exposure during spray-drying may cause conformational changes in some growth factors, affecting their receptor-binding capacity.

3. Differences in Physicochemical Properties

3.1 Protein Structure

Fourier transform infrared spectroscopy analysis shows that high-temperature spray-drying causes more significant damage to protein secondary structure, while low-temperature freeze-drying better maintains the native conformation of proteins [6]. The integrity of protein structure directly affects biological function, including receptor-binding capacity and immunological activity.

During spray-drying, proteins may aggregate and denature, forming insoluble aggregates. This not only reduces the bioactivity of the product but may also affect solubility and mouthfeel. Freeze-drying avoids thermal stress, allowing proteins to maintain their native conformation, and the functional properties of the product are more stable.

3.2 Antioxidant Activity

The effects of the two drying processes on colostrum antioxidant activity present different characteristics. DPPH radical scavenging capacity (reflecting direct free radical scavenging activity) is stronger in freeze-dried samples [6]. This is primarily because freeze-drying better preserves bioactive peptides and vitamins with antioxidant activity.

However, FRAP (ferric reducing antioxidant power), TPC (total phenolic content), and ABTS values are higher in spray-dried samples [6]. Researchers speculate that this may be related to the formation of Maillard reaction products during spray-drying, where high temperatures cause proteins and reducing sugars to react, generating intermediate products with reducing capacity [6]. It should be noted that these indicators primarily reflect the reducing capacity of Maillard reaction intermediates, not the retention advantage of natural antioxidant components. Although freeze-dried products have lower values on these indicators, their retention of natural antioxidant components is more complete.

3.3 Microbiological Safety

The high-temperature air stream in spray-drying has a significant microbial killing effect. Studies show that spray-dried colostrum powder exhibits lower microbial growth than freeze-dried samples [6]. This is because the temperature experienced by droplets during spray-drying far exceeds the tolerance limit of most bacteria.

Although freeze-drying has a less significant microbial killing effect than spray-drying, it can also inhibit microbial growth by reducing water activity (typically to below 0.2) [1]. A comparative study showed that both freeze-drying and spray-drying have significant effects on reducing standard plate count, E. coli, and total coliforms in colostrum, with freeze-drying being particularly effective in reducing microbial load. Staphylococcus aureus was not detected in colostrum after freeze-drying [9].

It is noteworthy that regardless of which drying process is used, the quality of colostrum raw materials and subsequent storage conditions have a greater impact on microbiological safety than the choice of drying process itself.

3.4 Sensory Characteristics

Products obtained from the two drying processes have different sensory characteristics. Freeze-dried colostrum powder, due to its formation of a loose and porous microstructure, is preferred in appearance, and its reconstituted texture is closer to that of liquid colostrum [6]. Spray-dried powder scores higher in flavor and aroma [6], which may be related to moderate Maillard reaction compounds generated during spray-drying.

In terms of solubility, spray-dried powder typically has smaller particle size and better instant solubility, while freeze-dried powder, although having fast rehydration speed, may require gentle stirring to dissolve completely [4].

4. Differences in Cost and Scalability

4.1 Production Cost

Spray-drying is the most economically efficient drying method in industry. It has high production efficiency, relatively low energy consumption, and significantly lower equipment investment and operating costs compared to freeze-drying [4]. Spray-drying can achieve continuous large-scale production, with single-unit daily processing capacity reaching several tons or even dozens of tons.

Freeze-drying is a high-cost processing technology. Vacuum systems and refrigeration systems require substantial energy input, drying cycles are long (typically 24-48 hours, while spray-drying takes only seconds), and equipment investment and maintenance costs are also higher [4].

4.2 Scalability and Industrialization

Spray-drying technology is highly mature in the dairy industry, and the vast majority of global milk powder and colostrum powder manufacturers use this process [4]. A well-established industrial chain, standardized equipment, and mature process parameters make spray-drying the preferred choice for large-scale commercial production.

Although freeze-drying is widely used in the pharmaceutical and biotechnology fields, its application in the dairy industry is relatively limited, mainly confined to high-value-added functional products and laboratory-grade products [8]. In recent years, with increasing market attention to bioactive component retention rates, market demand for freeze-dried colostrum products has grown, but total production volume remains far below that of spray-dried products.

5. Process Selection: Freeze-Dried or Spray-Dried

5.1 From the Perspective of Bioactivity

If product positioning emphasizes the highest immunoglobulin and bioactive protein retention rates, freeze-drying has a clear advantage. The freeze-drying process can retain 85-95% of IgG activity and better preserves the activity of heat-sensitive components such as growth factors and lactoferrin [8]. For products targeting the high-end functional food market or specific medical nutrition applications, freeze-drying is the more appropriate choice.

5.2 From the Perspective of Cost Structure

Spray-dried products have significant cost advantages in large-scale production and are suitable for high-volume product lines. Freeze-dried products, due to higher production costs, are more suitable as raw material choices for high-value-added product lines, targeting market segments with higher requirements for bioactive component retention rates.

5.3 From the Perspective of Storage and Transportation

The storage requirements for both products are basically the same: both need to be stored in a cool, dry place away from direct sunlight. Spray-dried powder typically has better stability at room temperature due to its denser particle structure and lower specific surface area [5]. Freeze-dried powder is more prone to moisture absorption and requires more stringent packaging (such as aluminum foil bags with nitrogen flushing) to maintain quality.

In terms of use, spray-dried powder usually dissolves more rapidly and is suitable for ready-to-drink products; freeze-dried powder also has good rehydration properties but may require gentle stirring. Both can be conveniently added to beverages, yogurt, or solid foods as functional ingredients.

6. Summary

Freeze-drying and spray-drying are two fundamentally different colostrum dehydration technologies, each with its own advantages and applicable scenarios. Freeze-drying is centered on low-temperature protection, maximizing the retention of immunoglobulins, growth factors, and other heat-sensitive bioactive components, but at higher cost and with limited production capacity. Spray-drying is characterized by high efficiency and speed, suitable for large-scale industrial production, with significant cost advantages.

For colostrum raw material purchasers and product developers, the choice of process should be based on a comprehensive assessment of product positioning, target market, cost budget, and quality requirements. In procurement decisions, it is recommended to focus on IgG content test reports, raw material source traceability systems, production process documentation, and third-party quality certification, rather than making judgments based solely on drying process type.

References

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[2] Denholm K. A review of bovine colostrum preservation techniques. J Dairy Res. 2022. doi:10.1017/S0022029922000711.

[3] El-Fattah AMA, Abd Rabo FH, El-Dieb SM, El-Kasheif MA. Preservation methods of buffalo and bovine colostrum as a source of bioactive components. Int Dairy J. 2014;39(1):24-27.

[4] Costa A, et al. Invited review: bovine colostrum, a promising ingredient for humans and animals - properties, processing technologies, and uses. J Dairy Sci. 2023;106(8):5197-5217. doi:10.3168/jds.2022-23013.

[5] Yu H, Zheng Y, Li Y. Shelf life and storage stability of spray-dried bovine colostrum powders under different storage conditions. J Food Sci Technol. 2015;52(2):944-951.

[6] Fatima M, et al. In vitro evaluation of spray and freeze-dried bovine colostrum powder and their effects on the nutritional and functional properties. Int J Food Prop. 2024;27:985-1002.

[7] Chatterton DEW, Aagaard S, Hansen TH, et al. Bioactive proteins in bovine colostrum and effects of heating, drying and irradiation. Food Funct. 2020;11:2309-2327.

[8] Riaz S, et al. Health benefits and value addition of bovine colostrum (BC): a comprehensive review of its nutritional and functional potential. Food Sci Anim Resour. 2026;46:55.

[9] Sotudeh Z, et al. Effects of spray-drying, freeze-drying and pasteurization on microbiological quality and IgG level of bovine colostrum. J Food Qual Hazards Control. 2018;5(2):47-53. doi:10.29252/jfqhc.5.2.5.

[10] Playford RJ, Weiser MJ. Bovine colostrum: its constituents and uses. Nutrients. 2021;13(1):265.

Disclaimer

The content herein is provided solely for the purpose of academic exchange and industry information reference, and does not constitute any claims regarding product efficacy. Products of Kangping Bio are food ingredients and do not possess disease prevention or treatment functions. The research data cited herein are sourced from published academic papers and do not represent the position or product statements of Kangping Bioengineering Co., Ltd.