Effect of season and processing steps in nutritional components and bioactivities of blue mussels (Mytilus edulis)

Blue mussels (Mytilus edulis) from Tongyeong, South Korea were evaluated for seasonal variation in terms of proximate composition, fatty acid (FA) profile, antioxidant activities (DPPH radical scavenging, superoxide anion radical scavenging, and reducing power), and alcohol dehydrogenase (ADH) activity. The effect of different processing steps on blue mussels (from harvest to market) was also assessed. Samples were taken from late autumn to early spring (November 2015 - April 2016). Moisture (79.4 - 82.9%), lipid (1.3 - 2.2%), and protein (8.9 - 10.5%) components varied significantly according to season and processing stage; while ash content remained relative (2.1 - 2.4%). The lowest glycogen (34.2 - 36.7 mg/g) content was found in mussels sampled in January, signifying its usage to generate energy and combat cold stress in winter. Meanwhile, an inverse relationship was observed in mussel lipid (highest, 2.0 - 2.1%) and protein (lowest, 8.9 - 9.3%) contents in April, signifying the conversion of protein to lipid in preparation for spawning in summer. The main FA from lipid class profiling were n-3 polyunsaturated FAs (PUFA, 39.0 - 45.1%), and primarily DHA (14.8 - 16.9%). Atherogenic (AI), thrombogenic (TI), and hypocholesterolaemic/hypercholesterolaemic (h/H) indices, as well as PUFA/SFA and DHA/EPA ratios remained relative throughout the duration of the study. Freshly-harvested mussels exhibited significantly greater radical scavenging and ADH activities than the marketed mussels which emphasise the importance of keeping the bivalve’s freshness. April was determined as the most suitable time for utilising blue mussels as food, food ingredient, and/or for pharmaceutical development. This is because it is during its harvest season where the proximate composition is neither too high nor too low, and omega-3 PUFA content (28.7 - 30.9%) and omega-3/omega-6 PUFA ratio (6.5 - 7.2) are at their peak which support better antioxidant benefits.