Continuous Low-Temperature Defatting Process for Peanut Protein Powder

1. Overview of the Production Process

The production process of continuously extracting defatted peanut protein powder is illustrated in Figure 1. The process involves the following steps:

• Peanut Preparation: Raw peanuts undergo impurity removal and grading.
• Low-Temperature Drying: Peanuts are dried and cooled before dehulling.
• Dehulling: Removal of the peanut skin.
• Color Sorting: Optical sorting and manual inspection to eliminate impurities and off-color peanuts.
• Conditioning: Peanuts are conditioned before the pressing phase.

Once prepared, peanuts are subjected to a two-stage low-temperature pressing:

• First Press: Low-temperature pressing to extract cold-filtered peanut oil, yielding defatted peanut cake.
• Second Press: Further extraction of oil from the defatted cake, followed by crushing, grading, and packaging to produce defatted peanut protein powder.

2. Production Process Characteristics

The method for producing low-temperature defatted peanut protein powder is similar to traditional peanut oil extraction. Both use mechanical pressing to extract oil from the oil cells within the peanut cotyledons, resulting in defatted peanut cake. High-temperature pressing emphasizes the aromatic oil and yields well; however, it denatures the protein and significantly diminishes nutritional value, making the resultant cake suitable only for animal feed or fertilizer under strict quality requirements.

In contrast, low-temperature extraction produces a product intended for direct consumption or use as raw material in the food industry. This method imposes stringent quality criteria related not only to peanut morphology, fat, and protein content but also to the strict removal of aflatoxins and skins.

To achieve high-quality end products, peanuts must be thoroughly cleaned, dried, and cooled. It is recommended to use a continuous natural-gas oven for drying to ensure product quality and yield while reducing energy consumption. Efficient removal of skin can be achieved using an air dehulling machine. Moreover, implementing a color sorter during the preprocessing stage helps eliminate any moldy peanuts, addressing aflatoxin sources at the origin to ensure compliance with final product safety standards.

To optimize the quality and quantity of peanut protein, the raw materials should be handled to effectively control temperature, moisture, and particle size. It is vital to maintain the moisture content of peanuts at around 6% to 7% for hydraulic presses and at 3% to 5% for continuous screw presses. Key equipment for this low-temperature extraction includes specialized mechanical presses. Although hydraulic presses can be used, they are often limited to smaller production runs due to their higher labor intensity and batch-processing constraints.

Continuous screw presses are categorized as single-screw and double-screw. Traditional screw presses can achieve low-temperature extraction by adjusting the compression ratio and pressing temperature. Double-screw presses represent a new advancement for the continuous processing of low-temperature peanut protein powder. The term “low-temperature pressing” generally refers to temperatures lower than 120°C to 130°C. To ensure a high nitrogen solubility index (NSI) of the peanut protein powder produced, temperatures within hydraulic presses should not exceed 70°C. At the same time, the first stage of double-screw pressing should be kept below 60°C.

After cooling and crushing the first batch of defatted peanut cake, the second pressing should be maintained at a temperature below 75°C. Although peanuts are exposed to high temperatures during mechanical pressing, the actual exposure time is minimal (2-3 minutes), which minimizes heat-induced protein denaturation, provided that internal temperatures remain below 70°C and moisture content stays low. As a result, the NSI values of the ultrafine-ground protein powder can reach 65% to 70%.

Defatted peanuts undergo moderate crushing and moisture adjustment before being fed into the continuously rotating press. Under significant pressure, the compacted peanuts rupture the cell walls, and the heat generated by friction raises the temperature. At the same time, oil viscosity decreases, allowing subcellular oil droplets to merge into continuous peanut oil, which is then cold-filtered and refined. The resulting peanut oil is light in color and retains natural fat-soluble vitamins, making it an excellent source of nutrition.

Subsequent pressing of defatted peanut cake can further reduce the residual oil content to meet low-fat standards while maintaining high protein levels. The defatted cake can then be ground and refined into varying particle sizes for low-temperature peanut protein powder.

Table 1: Key Quality Indicators of Low-Temperature Defatted Peanut Protein Powder

Continuous Low-Temperature Defatting Process for Peanut Protein Powder

1. Overview of the Production Process

The production process of continuously extracting defatted peanut protein powder is illustrated in Figure 1. The process involves the following steps:

• Peanut Preparation: Raw peanuts undergo impurity removal and grading.
• Low-Temperature Drying: Peanuts are dried and cooled before dehulling.
• Dehulling: Removal of the peanut skin.
• Color Sorting: Optical sorting and manual inspection to eliminate impurities and off-color peanuts.
• Conditioning: Peanuts are conditioned before the pressing phase.

Once prepared, peanuts are subjected to a two-stage low-temperature pressing:

• First Press: Low-temperature pressing to extract cold-filtered peanut oil, yielding defatted peanut cake.
• Second Press: Further extraction of oil from the defatted cake, followed by crushing, grading, and packaging to produce defatted peanut protein powder.

2. Production Process Characteristics

The method for producing low-temperature defatted peanut protein powder is similar to traditional peanut oil extraction. Both use mechanical pressing to extract oil from the oil cells within the peanut cotyledons, resulting in defatted peanut cake. High-temperature pressing emphasizes the aromatic oil and yields well; however, it denatures the protein and significantly diminishes nutritional value, making the resultant cake suitable only for animal feed or fertilizer under strict quality requirements.

In contrast, low-temperature extraction produces a product intended for direct consumption or use as raw material in the food industry. This method imposes stringent quality criteria related not only to peanut morphology, fat, and protein content but also to the strict removal of aflatoxins and skins.

To achieve high-quality end products, peanuts must be thoroughly cleaned, dried, and cooled. It is recommended to use a continuous natural-gas oven for drying to ensure product quality and yield while reducing energy consumption. Efficient removal of skin can be achieved using an air dehulling machine. Moreover, implementing a color sorter during the preprocessing stage helps eliminate any moldy peanuts, addressing aflatoxin sources at the origin to ensure compliance with final product safety standards.

To optimize the quality and quantity of peanut protein, the raw materials should be handled to effectively control temperature, moisture, and particle size. It is vital to maintain the moisture content of peanuts at around 6% to 7% for hydraulic presses and at 3% to 5% for continuous screw presses. Key equipment for this low-temperature extraction includes specialized mechanical presses. Although hydraulic presses can be used, they are often limited to smaller production runs due to their higher labor intensity and batch-processing constraints.

Continuous screw presses are categorized as single-screw and double-screw. Traditional screw presses can achieve low-temperature extraction by adjusting the compression ratio and pressing temperature. Double-screw presses represent a new advancement for the continuous processing of low-temperature peanut protein powder. The term “low-temperature pressing” generally refers to temperatures lower than 120°C to 130°C. To ensure a high nitrogen solubility index (NSI) of the peanut protein powder produced, temperatures within hydraulic presses should not exceed 70°C. At the same time, the first stage of double-screw pressing should be kept below 60°C.

After cooling and crushing the first batch of defatted peanut cake, the second pressing should be maintained at a temperature below 75°C. Although peanuts are exposed to high temperatures during mechanical pressing, the actual exposure time is minimal (2-3 minutes), which minimizes heat-induced protein denaturation, provided that internal temperatures remain below 70°C and moisture content stays low. As a result, the NSI values of ultrafine-ground protein powder can reach 65% to 70%.

Defatted peanuts undergo moderate crushing and moisture adjustment before being fed into the continuously rotating press. Under significant pressure, the compacted peanuts rupture the cell walls, and the heat generated by friction raises the temperature. At the same time, oil viscosity decreases, allowing subcellular oil droplets to merge into continuous peanut oil, which is then cold-filtered and refined. The resulting peanut oil is light in color and retains natural fat-soluble vitamins, making it an excellent source of nutrition.

Subsequent pressing of defatted peanut cake can further reduce the residual oil content to meet low-fat standards while maintaining high protein levels. The defatted cake can then be ground and refined into varying particle sizes for low-temperature peanut protein powder.

Table 1: Key Quality Indicators of Low-Temperature Defatted Peanut Protein Powder