Changes in antioxidant activities and physicochemical properties of Kapi, a fermented shrimp paste, during fermentation

Abstract

Changes in chemical composition, physical properties and antioxidant activities of Kapi were monitored during fermentation for 12 months. DPPH (2, 2-diphenyl-1-picryl hydrazyl), ABTS (2, 2 – azino-bis (3-ethylbenzothiazoline-6-sulfonic acid)) radical scavenging activity as well as ferric reducing antioxidant power (FRAP) gradually increased as the fermentation time increased, particularly during the first 8 months (P < 0.05). Thereafter, the decreases in DPPH and ABTS radical scavenging activities were observed (P < 0.05), whereas FRAP remained constant (P > 0.05). The continuous increases in ammonia nitrogen, formaldehyde nitrogen and amino nitrogen contents were noticeable within the first 8 months (P < 0.05), indicating the formation of peptides and free amino acids via the hydrolysis of protein by both microbial and indigenous proteases. Browning intensity most likely caused by the formation of Maillard reaction products (MRPs) were concomitantly observed throughout fermentation, as evidenced by the decreases in lightness (L*-value), but the increases in redness (a*-value) and yellowness (b*-value). Low level of thiobarbituric acid reactive substances in Kapi was found during 12 months. Antioxidant activities of Kapi were more likely governed by the low molecular weight peptides, amino acids as well as Maillard reaction products generated during fermentation.