Introduction of Wheat Germ Proteins/Peptides
In the contemporary era, wheat germ stands as a cornerstone of healthy diets, deemed crucial in "correct" and "healthy" nutrition systems. Comprising 2%-3% of the total weight of wheat, wheat germ harbors vital nutrients, including 26%-35% protein, 10%-15% lipids, ~10%-14% dietary fiber, and ~4% minerals. Despite its nutritional richness, during flour production, wheat germ is often discarded due to its impact on flour quality and shelf life. Wheat germ houses up to 30% wheat germ protein/peptides (WGPs), which boast eight essential amino acids, particularly high in lysine, isoleucine, valine, and leucine. With less glutenin than whole wheat, WGPs emerge as an excellent choice for gluten-intolerant individuals. Rich in non-protein nitrogen, including choline and glutathione, WGPs contribute to various physiological processes and cellular protection. So the extraction, characterization, and utilization of WGPs have gained considerable attention in recent years.
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Extraction Methods for Wheat Germ Proteins/Peptides
WGPs are extracted from defatted wheat germ using various advanced technologies, including chemical and microbial methods. These extraction methods play a crucial role in obtaining WGPs while maintaining their bioactive properties.
Fig. 1 The extraction methods of wheat germ protein/peptides from (defatted) wheat germ (Zhang Z., et al. 2023).
Alkali Extraction and Chemical Methods
Traditionally, alkali extraction has been a widely used method for obtaining WGPs. However, this method has drawbacks such as low extraction rates and the generation of large amounts of alkaline wastewater, posing environmental concerns. Additionally, WGPs extracted through alkali methods often face denaturation, resulting in unstable peptides with low functional activity.
Microwave- and Ultrasonic-Assisted Alkaline Extraction
To overcome the limitations of traditional methods, microwave- and ultrasonic-assisted extraction has been introduced. These methods enhance extraction efficiency and reduce extraction time. The use of ultrasonic power and specific pH conditions has shown a significant improvement in the extraction rate of WGPs. However, these techniques require expensive equipment and may impact protein properties, affecting foam stability and emulsifying properties.
Subcritical Water Extraction
Subcritical water extraction involves placing water in a subcritical state under certain pressure and temperature conditions. This method offers a shorter extraction time and higher extraction rates compared to conventional alkaline methods. WGPs obtained through subcritical water extraction exhibit favorable characteristics, including high emulsion and foam stability.
Reverse Micelle Extraction
Reverse micelle extraction, involving nano-sized aggregates of surfactant molecules, has become a promising method for protein extraction. This technique includes forward and reverse extraction steps, leading to improved extraction efficiency. Ultrasonic-assisted reverse micelle extraction has shown notable progress, enhancing the forward extraction efficiency of WGPs. Despite its advantages, the total extraction efficiency of this method remains lower than some traditional alternatives.
Enzymatic Extraction
Enzymatic extraction of WGPs employs alkaline protease under mild conditions, yielding specific target peptide segments with defined biological activities. This method offers controlled hydrolysis, ensuring high-quality proteins/peptides. Enzymatic extraction enhances the solubility and biological activity of WGPs, making it a favorable choice for industrial production.
Microbial Fermentation
Microbial fermentation emerges as an effective method for obtaining biologically active peptides, especially from natural sources like wheat germ. Fermentation by strains like Bacillus subtilis, lactic acid bacteria, and fungi releases various peptides with bioactive properties. This method enhances the physiological characteristics of WGPs due to their mild conditions. Antioxidant peptides obtained through microbial fermentation show promising potential against free radicals.
Bioactive Functions of Wheat Germ Proteins/Peptides
Anti-aging Properties
WGPs exhibit significant anti-aging properties, primarily attributed to their antioxidant activity. Oxidative stress is a major factor in aging metabolism, and WGPs, rich in peptides with antioxidant capabilities, scavenge free radicals, inhibit lipid peroxidation, and chelate metals. Studies on aging models, including D-galactose-induced cognitive impairment and alcoholic liver injury, have shown that WGPs can enhance antioxidant enzyme activities and delay the aging process.
Anti-inflammatory and Immune-Protective Activities
Inflammation is a common factor in aging, and WGPs demonstrate anti-inflammatory and immune-protective activities. By modulating inflammatory factors, WGPs help regulate immune responses, stimulate lymphocyte proliferation, and enhance macrophage phagocytosis. These properties make WGPs valuable in preventing chronic inflammation associated with aging.
Intestinal Protection and Microbial Regulation
Maintaining intestinal flora homeostasis is crucial for overall health. WGPs promote the growth of beneficial bacteria and inhibit potentially harmful species, contributing to intestinal health. In inflammatory bowel disease models, WGPs have shown the ability to shift the balance of intestinal flora and reverse gut dysbiosis. The potential applications of WGPs extend to regulating microbial composition and promoting intestinal health.
Other Bioactive Functions
Beyond anti-aging, anti-inflammatory, and intestinal protection, WGPs exhibit various other bioactive functions. These include anti-diabetic activity by inhibiting α-glucosidase, preventing the adhesion of Helicobacter pylori on gastric epithelial cells, and improving the oxidation stability of emulsified sausages. The versatility of WGPs positions them as promising candidates for preventing or treating different chronic diseases.
Application of WGPs in the Food Industry
The high nutritional and functional characteristics of WGPs render them valuable additives in the food industry, contributing to improved nutritional profiles and enhanced food properties. The applications of WGPs in various food products are diverse and include:
Flour Products
WGPs are frequently employed as additives in flour products, particularly in bread. The addition of WGPs enhances the emulsion stability, uniformity, taste, and texture of bread. Flour products with added WGPs not only improve nutritional value but also extend storage periods by reducing easily oxidized fat content.
Beverages
WGPs find application in beverages, contributing to a refreshing flavor and stable qualities. Healthy drinks incorporating WGPs, along with other natural ingredients, offer a comprehensive composition of proteins and functional components. The solubility, foaming, and emulsion properties of WGPs make them valuable in beverage formulations.
Mayonnaise
Research has explored the addition of WGPs to mayonnaise, demonstrating improvements in stability, viscosity, and tissue properties. The low cholesterol content of WGPs makes wheat germ mayonnaise a healthier alternative with high consumer acceptance.
Meat Products
WGPs play a role in meat products by addressing water retention issues during cooking. The water retention capacity of WGPs contributes to reduced fat content and cooking loss in meat products, positively impacting product stability and quality.
Food Packaging
WGPs extend their application to food packaging, where they can be used as a coating for films. The resulting films exhibit antioxidant and antibacterial properties, showcasing potential benefits for enhancing the shelf life and safety of packaged foods.
Healthy Food
The health food industry has witnessed the application of WGPs, with extracted peptides featuring in various health foods. These natural, cost-effective nutrients present promising avenues for developing functional foods or even novel drugs.
Conclusion
The extraction, bioactive function, and application of WGPs represent a dynamic field of research with promising implications for human health and the food industry. As innovative extraction methods continue to evolve, the multifaceted bioactive functions of WGPs offer opportunities for addressing aging-related issues, and inflammation and promoting overall well-being. The diverse applications in various food products underscore the versatility of WGPs as valuable additives with the potential to revolutionize the nutritional landscape.
References
- Zhang Z., et al. Extraction, bioactive function and application of wheat germ protein/peptides: A review. Current Research in Food Science. 2023, 6:100512.
- Mahmoud A. A., et al. Wheat germ: an overview on nutritional value, antioxidant potential and antibacterial characteristics. Food and Nutrition Sciences. 2015, 6(02): 265.
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