TEMPERATURE EFFECT ON OXIDATIVE STRESS AND DEPURATION EFFICIENCY OF DIFFERENT BIVALVE SPECIES PRODUCED IN AQUACULTURE

Consumption of bivalve mollusks may represent a risk to human health. Depending on the microbiological load, bivalves require depuration before commercialization, to ensure food safety. Production areas (e.g. in EU countries) can be classified in A, B or C, based on Escherichia coli load, which must not exceed 230, 4600 and 46000 most probable number (MPN) of E. coli per 100 g of flesh and intravalvular liquid, respectively. Usually, depuration last for 24 h in recirculating systems (equipped with filters, UV sterilizers and temperature control systems - water chillers), using the same water parameters for all purified species. However, due to physiological specificities, it might be relevant to adapt water parameters, namely temperature, to the physiological requirements of each species, in order to optimize the depuration process. We aimed to test the effect of temperature on depuration efficiency, cellular energy allocation and oxidative stress and damage of clams (Ruditapes decussatus) and razor clams (Solen marginatus) produced in class C areas.

Bivalves, harvested in Algarve, south Portugal, were depurated during 24 h in 250 L modular depuration systems equipped with a filtration system and a UV-c unit (25W UV-c, 6.000 µW.s/cm²), testing 4 temperatures: 10, 15, 20 and 25 ºC. Samples for microbiological and biochemical analyses were performed at 0 h (arrival) and 24 h (depuration period). Microbiological load, antioxidant defenses (catalase, glutathione S- transferases, and total glutathione), oxidative damage (lipid peroxidation and DNA damage) and cellular energy allocation were evaluated.

Bivalve 24 h depuration process (diminution of E. coli levels to legal commercialization values) was successful in  all tested temperatures.  However,  R. decussatus performed better at 20 ºC (<18 E. coli/100  g) and  S. marginatus between 10 and 15 ºC ( 69 and 62 E. coli/100 g, respectively).

No changes were observed on antioxidant defenses.  R. decussatus seemed to have a higher range of temperature tolerance, with DNA damage increasing only at 25 ºC, whereas temperatures above 20 ºC caused increase in  S. marginatus  DNA strain breaks. Regarding energy consumption,  R. decussatus presented a higher activity of electron transport system  than  S. marginatus , although no significant changes in energy consumption were observed due to water temperature (Fig. 1). This study highlighted the relevance of considering species-specific requirements to improve  bivalve  depuration  process and food safety.