Wheat germ: not only a by-product

Abstract

The wheat germ (embryonic axis and scutellum) represents about 2.5–3.8% of total seed weight and is an important by-product of the flour milling industry. The germ contains about 10–15% lipids, 26–35% proteins, 17% sugars, 1.5–4.5% fibre and 4% minerals, as well as significant quantities of bioactive compounds such as tocopherols [300–740 mg/kg dry matter (DM)], phytosterols (24–50 mg/kg), policosanols (10 mg/kg), carotenoids (4–38 mg/kg), thiamin (15–23 mg/kg) and riboflavin (6–10 mg/kg). Oil recovery is achieved by mechanical pressing or solvent extraction, which retrieve about 50% or 90% lipids, respectively; innovative approaches, such as supercritical carbon dioxide extraction, are also proposed. The oil is rich in triglycerides (57% of total lipids), mainly linoleic (18:2), palmitic (16:0) and oleic (18:1) acids, but relevant amounts of sterols, mono- and diglycerides, phospho- and glycolipids are present. The lypophilic antioxidants tocopherols and carotenoids are also abundant. The main by-product of oil extraction is defatted germ meal, which has high protein content (30–32%), is rich in albumin (34.5% of total protein) and globulin (15.6%), and thus presents a well-balanced amino acid profile. Its principal mineral constituents are potassium, magnesium, calcium, zinc and manganese, in decreasing order. Total flavonoid content is about 0.35 g rutin equivalent/100 g DM. The wheat germ is therefore a unique source of concentrated nutrients, highly valued as food supplement. While the oil is widely appreciated for its pharmaceutical and nutritional value, the defatted germ meal is a promising source of high-quality vegetable proteins. Better nutrient separation from the kernel and improved fractioning techniques could also provide high-purity molecules with positive health benefits.