Glycine

Glycine is the sweet one. Its taste is documented as sweet (unlike the bitter BCAAs), which makes it a genuine flavour-system tool rather than something to be masked — it is used as a mild sweetener and flavour modifier in food manufacture, and it is the reason a glycine-heavy powder tastes better than an EAA blend.

It is also the smallest amino acid at 75.07 g/mol and the second most water-soluble in this range at 249 g/L at 25 °C, rising to 672 g/L at 100 °C. On a molar basis it dissolves further than anything else here, so it is never the limiting solubility.

It exists in three polymorphic forms — alpha, beta and gamma — which is unusual among the amino acids in this range and matters if you are crystallising, milling or granulating. Different polymorphs have different habit, flow and dissolution rate even at identical chemical purity. If your process is sensitive to crystal form, specify it.

The 0.2 molar solution sits at pH 4.0 with an isoelectric point of 5.97, which is why glycine is a standard buffer component in laboratory and biopharmaceutical work — it buffers usefully in both the acidic and the alkaline range. Expect it to contribute buffering capacity to your own product whether you designed for that or not.

It is almost insoluble in organic solvents — 0.06 g per 100 g of absolute ethanol — but soluble in pyridine (1 part in 164). Aqueous and dry formats only.

Thermally it starts to decompose at about 233 °C and is completely sintered by 290 °C, so extrusion and baking are safe, but the sintering behaviour is worth knowing if you are running a hot granulation.

The regulatory position in the US is the single most important thing to understand about this ingredient, and it is counterintuitive: glycine is explicitly NOT GRAS for human food under 21 CFR 170.50, while remaining GRAS for animal feed and authorised as a food additive for protein-quality improvement under 21 CFR 172.320. Any US food customer needs to be walked through that distinction before they formulate.