Chemical and Antioxidant Activity Changes in Philippine Green Mussel (Perna viridis) during Fermentation at Varying Salt Concentrations

Abstract

Green mussel (Perna viridis) is an extensively cultured bivalve species in the Philippines and a cheap source of valuable nutrients such as essential amino acids and minerals. Experimental samples were prepared by mixing salt to varying mussel meat ratios (1:3, 1:5, 1:7, and 1:9) which were assessed for changes in pH, degree of hydrolysis, and antioxidant activities during fermentation for 30 d. The pH levels in treatments 1:3, 1:5, and 1:7 decreased to low-acid levels (< pH 4.6) as fermentation progressed. Meanwhile, treatment 1:9 did not significantly change from its initial pH level with a slight decrease noted during 15 d but significantly increased at slightly neutral pH level (at 7.22) on 30 d. Formaldehyde nitrogen (formol-N) and the simultaneous formation of ammonia-N significantly increased (p < 0.05) with prolonged fermentation time but were more pronounced in 1:7 and 1:9 treatments. The gradual increase in pH and formol-N in treatments 1:3 and 1:5 could be due to the high salt content at 23.63 ± 0.29 %, and 19.48 ± 0.88 %, respectively, which could have slowed down proteolytic enzyme activity. However, continuous increase in ammonia-N in treatment 1:9 significantly reduced (p < 0.05) amino-N content which lowers the nutritional quality of fermented products. The development of antioxidant activities such as 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activity, ferric reducing antioxidant power (FRAP), and total phenol content (TPC) as gallic acid equivalent (GAE) was highest in treatments 1:7 and 1:9. These findings could be attributed to the increasing degree of protein breakdown producing substances and reaction products with increased bioactivity. This is also supported by the significant positive linear correlation between formol-N and antioxidant system assays (DPPH, FRAP, and TPC) (p < 0.01)