Effects of Methanol on Physical Properties of α-and β-Lactose

Abstract

Crystalline .alpha.-lactose monohydrate and crystalline .beta.-lactose were treated with absolute methanol at room temperature and at reflux temperature. Methanol also was added to fresh aqueous solutions of .alpha.- and .beta.-lactose to initiate crystallization. For each of the dried products of these methanol treatments melting point, heat of fusion and heat capacity (all 3 by differential scanning calorimetry), density and crystalline habit were determined. The same measurements were made on the untreated crystalline materials and the stable, anhydrous .alpha.-lactose obtained by heat treatment. The anhydrous .alpha.-lactose .alpha.M, produced by methanol treatment of crystalline .alpha.-monohydrate, was different from the stable anhydrous .alpha.-lactose .alpha.s formed by heat. The melting point of .alpha.M was lower by 5.8.degree. C, heat of fusion higher by 33%, heat capacity lower by .027 cal g-1 deg-1, and density higher by .025 g cm-3. The various physical measurements offered evidence of several other distinct forms of lactose, a species of .beta.-lactose, .beta.M, prepared by refluxing in methanol, another .beta.-lactose form .beta.M'', crystallized by methanol, and another anhydrous .alpha.-lactose form, .alpha.M'', also crystallized by methanol. Each of these 3 forms had a unique melting point, heat capacity and density. [This study relates to milk chemistry.].