Characterization of concentrated agave saps and storage effects on browning, antioxidant capacity and amino acid content

• Furosine, browning and antioxidant capacity were positively correlated.
• Serine, phenylalanine and lysine were related to browning and antioxidant capacity.
• Sugar and saponin concentration remained stable during storage.

Sap from agave plants (“aguamiel”) is traditionally consumed in Mexico as a fresh beverage, fermented or concentrated. Concentrated agave sap (CAS) is used as a sweetener but, due to heating, a brown color develops and intensifies during storage. Browning varies among CAS batches and this work was focused on its correlation with the chemical composition changes observed during 20 weeks of storage. The browning index (BI), measured as the optical density at 490 nm (OD490 nm) per gram of sample, increased 54.4% in the batch that initially had 57 OD490 nm/g but in the other two batches that had a lower BI, the increase was less than 26.1%. Antioxidant capacity only increased in the batch with the highest BI going from 18 to 23 Trolox equivalent μmol/g dry weight. Saponin content was different in the three batches (224.2–434.7 protodioscin equivalents/gram dry weight) but did not change after 20 weeks of storage. Browning index and antioxidant capacity were negatively correlated with free amino acid concentration, particularly serine, phenylalanine and lysine decreased 29.4, 50 and 30%, respectively. Browning was positively correlated to furosine, an early Maillard reaction derivative of lysine previously reported as a free radical scavenger.