Changes in volatile compounds, ATP-related compounds and antioxidative properties of Kapi, produced from Acetes vulgaris, during processing and fermentation

During salting, drying and fermentation for making Kapi (salted shrimp paste of Thailand), from Acetes vulgaris, Maillard reaction products (MRPs), adenosine triphosphate (ATP)-related compounds, antioxidative activities and volatile compounds were monitored. Varying colors were observed during processing. The results of the study showed that L* and b*-value decreased, while a*-value increased as fermentation time increased (p < 0.05). This was correlated well with the increase in browning intensity (A₄₂₀) (p < 0.05). ATP was not detected in raw material, whereas adenosine diphosphate (ADP) and adenosine monophosphate (AMP) disappeared after salting and drying, respectively. After 30 days of fermentation, Kapi contained hypoxanthine (Hx) (112.49 mg/ 100 g dry sample) as the most abundant ATP-related compound. Aldehydes, ketones as well as N-containing compounds increased as fermentation time increased (p < 0.05). N-containing compounds, mainly pyrazine derivatives, were prevalent volatiles in Kapi. Moreover, antioxidative activities increased, particularly when fermentation proceeded, as evidenced by the increases in 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2-azino-bis (3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) radical scavenging activities, and ferric reducing antioxidant power (FRAP) (p < 0.05). According to these results, several changes of Kapi took place throughout all processes. However, odorous compounds and flavorants were mainly formed during fermentation process. Those compounds were plausibly involved in the unique flavor/taste of Kapi.