Views: 568 Author: Site Editor Publish Time: 2025-01-13 Origin: Site
Yingtai: Application of Vacuum Freeze-Drying Technology in Insect Freeze-Drying
Vacuum freeze-drying is a stable material drying process that involves freezing water-containing substances into a solid state, then under certain vacuum conditions, directly sublimating the water from solid to gaseous state to remove moisture and preserve the material. Insect freeze-drying production is conducted using a freeze dryer. The insects are frozen into solid form at low temperatures according to their eutectic temperature requirements, then sublimated under vacuum conditions. The ice in the insects transitions directly from solid to gas without melting and is captured and removed by the condenser. This low-temperature and vacuum drying process preserves the original proteins, amino acids, vitamins, and other heat-sensitive substances. Oxidation and enzyme activity are almost nonexistent. As a result, freeze-dried insects processed with a freeze dryer retain their original color, aroma, taste, shape, and nutritional components, making them highly nutritious as feed.
1. Advantages of Insect Freeze-Drying
Using a freeze dryer for insect freeze-drying offers several advantages: it preserves nutritional components, provides excellent rehydration properties, and allows storage at room temperature for 1–3 years. In the feed processing industry, freeze dryers are widely used for freeze-drying high-nutrition, heat-sensitive materials such as probiotics, amino acids, proteases, and vitamins. This improves feed nutritional content and balance, promoting healthy development in aquaculture and livestock farming.
As food substitutes become a popular research topic to address food shortages, insects have gained attention due to their rich nutritional content. Processing is a key step in developing insect-based foods, but comprehensive reviews summarizing processing methods and their impacts are lacking. Thermal treatments like boiling and blanching negatively affect insect nutrition but are essential for food safety. High-pressure processing (HPP) and cold atmospheric pressure plasma (CAPP) achieve similar sterilization effects while retaining nutritional and sensory qualities.
2. Freeze-Drying Steps for Insect Foods
The edible insect industry is growing rapidly, with increasing demand for new products, including recognizable insect forms. Traditional processing methods may no longer suffice, necessitating an evaluation of technologies used during production. The process typically begins with harvesting insects and ends with the final product. Some byproducts generated during this process may be recovered and used as secondary products.
2.1 Raw Material Selection and Preprocessing
- Material Selection: Select fresh, pest-free, high-quality insects, such as mealworms or grasshoppers, ensuring they meet food safety standards.
- Cleaning: Wash the insects thoroughly with clean water to remove surface dirt, impurities, and any pesticide residues.
- Blanching: Place the cleaned insects in boiling water or steam for 1–5 minutes (depending on type and size) to deactivate enzymes and prevent chemical reactions like browning during further processing.
- Draining: After blanching, remove the insects and place them on a screen or filter cloth to drain excess water.
2.2 Freezing Process
- Pre-Freezing: Evenly place preprocessed insects on freezing trays and place them in pre-freezing equipment at -20°C to -40°C for 2–4 hours, allowing the water inside the insects to freeze into ice crystals.
- Quick Freezing: Transfer the pre-frozen insects to deep-freezing equipment at -60°C to -80°C for 1–2 hours to form small and uniform ice crystals, avoiding cellular damage from large crystals.
2.3 Drying Stage
Drying is another critical step in insect food production to extend shelf life. Drying methods range from traditional techniques (e.g., sun drying and oven drying) to modern ones (e.g., freeze-drying and microwave drying). Proper drying reduces moisture content and activity, which is vital for microbial inhibition when water activity is below 0.65.
Appropriate drying technologies significantly increase dry matter concentration without compromising the food's appearance or structure—desirable for innovative insect foods. Sun drying and oven drying are commonly used for whole insects, while freeze-drying, microwave drying, and other novel methods are preferred for producing insect powder.
- Traditional Methods: Sun drying is mainly used at the household level but offers limited control, exposing products to bacterial contamination from soil or air.
- Commercial Methods: Vacuum freeze-drying is the preferred method for commercial insect food production. Freeze-drying allows for continuous dehydration of frozen insects through sublimation without significant physical or color changes.
Freeze-drying suppresses microbial activity by combining low temperatures and the absence of liquid water. It has minimal impact on flavor, aroma, and nutritional value, making it ideal for producing high-quality insect foods.