How to process pumpkin seed protein powder

Abstract: Pumpkin seed protein powder is rich in nutritional value and belongs to a high-quality health-care plant protein resource, which is currently a hot research and development topic. Based on the traditional meal protein extraction process, this paper designs a new process that integrates two traditional methods: cold pressing and solvent extraction. The temperature during the production process is strictly controlled to prevent protein denaturation and preserve biological activity and nutritional value, thereby enabling factory-scale production.

Keywords: Pumpkin seed protein powder; Extraction process; Cold pressing followed by extraction

Pumpkin seeds are the main by-product of mature pumpkins, rich in nutritional value, containing 35%–50% oil, up to more than 60%, and protein content of 30%–40%. In addition to being directly edible, pumpkin seeds have two main application values: pumpkin seed oil and pumpkin seed protein. In recent years, research on pumpkin seeds in China has become increasingly in-depth. Studies show that pumpkin seed oil is rich in various unsaturated fatty acids, with effects including lowering blood lipids, anti-thrombotic activity, lowering blood pressure, preventing myocardial infarction, inhibiting cancer, reducing excessive linoleic acid intake, and preventing and treating prostate diseases. Pumpkin seed protein is rich in about 20 amino acids, including the 8 essential amino acids for humans and histidine, which is essential for children, making it a high-quality plant protein source. Therefore, pumpkin seeds have become a plant-derived raw material with significant development prospects in healthcare.

In China, pumpkins are mostly produced in Shaanxi, Xinjiang, Inner Mongolia, and other regions. With advances in cultivation technology, the yield and quality of pumpkins in China have improved, and pumpkin seed yield has also increased. Currently, pumpkin seeds are mostly used for oil extraction, and the by-product after oil extraction—pumpkin seed meal—is also a high-quality plant protein source. According to experimental measurements, pumpkin seed meal has a protein content exceeding 60%, and its amino acid composition is highly rich, with high nutritional value. Pumpkin seed protein powder processed from pumpkin seed meal has gradually appeared on the market. Some people directly add pumpkin seed protein powder to milk, soy milk, juice, or breakfast cereals for consumption; others add it to bread and other baked goods; still others consume meal replacement or milkshake products made from pumpkin seed protein powder. At the same time, some processing plants incorporate pumpkin seed protein as an auxiliary material or additive in products such as soy sauce, beverages, ham sausages, flour, and biscuits, with favorable results. This indicates that the market prospects for pumpkin seed protein powder are very promising, thereby driving the need to achieve large-scale production as soon as possible.

1 Traditional Processing Techniques for Pumpkin Seed Protein

Currently, factory-scale production methods for pumpkin seed protein are broadly classified into pressing, solvent extraction, and supercritical fluid extraction.

1.1 Pressing Method

The pressing method is a traditional oil-extraction method that separates oil from oilseeds by external pressure, thereby yielding defatted pumpkin seed protein powder. Depending on the oil-extraction temperature, pressing methods are classified as hot pressing and cold pressing. Hot pressing involves steaming and roasting pumpkin seed kernels at 120°C, with moisture controlled at 1.0%–1.5%, before pressing. The obtained oil has a rich taste, but high-temperature heating causes severe denaturation of pumpkin seed cake protein. Cold pressing involves mechanically pressing unsteamed oilseeds at temperatures below 60°C. Compared with hot pressing, cold pressing better preserves biological activity and yields a cake protein that is largely undenatured; however, oil yield is low.

1.2 Solvent Extraction Method

The solvent extraction method is widely used in large-scale industrial production, leveraging the mutual solubility of oil and organic solvents for extraction. Commonly used organic solvents include n-hexane. Compared with traditional pressing methods, the solvent extraction method yields a higher oil extraction rate and lower protein denaturation in the meal, thereby improving the meal’s value. However, the organic solvent used as the oil-extraction medium is toxic, flammable, and explosive, thereby increasing the requirements for production management.

1.3 Supercritical Fluid Extraction Method

Using CO₂ fluid to extract pumpkin seed oil, the extraction temperature is low, which can protect the biological activity of pumpkin seed meal protein, and the extraction rate is high with no organic solvent residue. However, because the entire extraction process must operate under high pressure, the pressure resistance requirements for equipment and pipelines are relatively stringent, making the extraction equipment expensive and limiting the promotion and application of this method. Based on the three methods described above, this paper optimizes the extraction of pumpkin seed protein powder by combining cold pressing and solvent extraction, aiming to establish an optimal process scheme for factory-scale production.

2 New Processes for Pumpkin Seed Protein Powder Extraction

2.1 Process Flow

The preparation process of pumpkin seed protein powder is as follows:

Pumpkin seeds → Cleaning → Crushing → Low-temperature conditioning → Pressing → Extraction → Low-temperature desolventizing → Defatted pumpkin seed meal → Drying → Crushing → Sterilization → Defatted pumpkin seed protein powder

After cleaning, pumpkin seeds are transported by conveying equipment, first through a roller crusher to reduce particle size to below 5 mm, then into a low-temperature conditioning pot. Hot water is passed through the jacket at the bottom of the low-temperature conditioning pot to heat the material. At a temperature of 50°C–70°C, the moisture content of the material is reduced to 5%–7%, thereby achieving optimal pressing conditions while maintaining pumpkin seed protein in a largely undenatured state. The conditioned pumpkin seeds are fed into a dedicated screw oil press. For oilseeds with high oil content, such as pumpkin seeds, pressing can be performed directly. Control the cold pressing pressure at 3.5–4.0 MPa, screw speed at 36 r/min, with part of the pressed cake being re-pressed to increase the pressing chamber pressure and improve oil yield. The remaining cold-pressed cake enters the extraction workshop. Throughout the pressing process, the cake temperature does not exceed 60°C, keeping the protein basically undenatured.

After entering the extraction workshop, pumpkin seed cake is first stored in a temporary storage box, then quantitatively conveyed to the extractor via a sealed screw conveyor for oil extraction. A traditional rotary extractor is used, employing n-hexane to extract oil from the material, with the extraction temperature maintained at approximately 55°C. The pumpkin seed meal after oil extraction contains a high solvent (n-hexane) content and requires desolventizing treatment. The traditional desolventizing process uses high-temperature desolventizing, removing the solvent with direct steam. However, to ensure protein denaturation is avoided, a low-temperature desolventizing process should be employed. A two-stage horizontal low-temperature desolventizing device is used. Pumpkin seed meal first enters cylinder A, where the solvent is vaporized (about 69°C). The solvent vapor then directly contacts the tumbling pumpkin seed meal material, quickly evaporating and removing the solvent from the material surface. The solvent gas is purified through a cyclone, and the clean solvent gas is sent partly to the condensation system via a fan, and partly back to the solvent heater. After heating, it returns to cylinder A to remove the solvent from the material. Since the solvent boiling point is only about 69°C, the material temperature is always kept below 70°C. After surface solvent removal, the material enters cylinder B, which is designed to operate at a specified vacuum. The remaining solvent is evaporated and removed through vacuum, and the solvent gas is finally purified through a trap before going to the vacuum system. The defatted pumpkin seed meal is dried, crushed, and sterilized to produce defatted pumpkin seed protein powder, which is then conveyed to the packaging workshop.

2.2 Technical Key Points

The key technical point of this scheme is the combination of traditional cold pressing and solvent extraction. In this way, after pumpkin seeds undergo cold pressing followed by extraction, not only can the extraction rate of pumpkin seed oil be greatly improved, resulting in less residual oil in the pumpkin seed meal and increasing the protein proportion of the meal, but also the temperature throughout the processing is controlled below 80°C, greatly reducing the denaturation degree of the meal protein, better preserving the biological activity of the protein, and thereby improving the nutritional value of pumpkin seed protein powder.

3 Conclusion

With improvements in living standards, the pursuit of healthy eating is also increasing. Pumpkin seed protein powder is a plant-based protein powder with diverse functions, rich nutrition, and safe without side effects. It is suitable not only for vegetarians and health-conscious consumers but also for individuals seeking to improve their quality of life and prevent chronic diseases. Therefore, pumpkin seed protein powder has gradually become a focus of current research. The process scheme proposed in this paper combines the advantages of cold pressing and solvent extraction, making it suitable for large-scale industrial production. With technological development and continuous in-depth research by scientific researchers, the application of pumpkin seed protein powder in the food and health product industries is becoming more extensive, and the demand for large-scale production of pumpkin seed protein powder in factories will gradually increase.