Topic overview

Start with the big picture

Disaccharides are classified as reducing when one anomeric carbon remains free, or non-reducing when both are involved in the glycosidic bond. Lactose and maltose are reducing examples; sucrose and trehalose are non-reducing. Their structures, sources, and digestive enzymes differ: for example, lactase acts on lactose, while sucrase hydrolyzes sucrose. Brush-border disaccharidases break glycosidic bonds so the resulting monosaccharides can be absorbed. When digestion is incomplete, unabsorbed carbohydrate can contribute to osmotic diarrhea and flatulence. Reducing disaccharides can undergo mutarotation and give positive Benedict’s or Fehling’s tests. The deeper lesson connects these structural features with digestion, absorption, enzyme regulation, and selected biochemical and clinical properties.