Lingcod (Ophiodon elongates) is a fish sourced from the West coast of the United States – from Alaska to California. It is a good source of protein and vitamin B12 but is very low in fat, including healthy omega-3 fatty acids.
Fish, which is susceptible to microbiological and chemical degradation, is typically preserved by cold storage and freezing. However Yungyang Zao and colleagues note in an article accepted for publication in the journal Food Chemistry that these methods do not totally stop the quality of the fish from deteriorating.
Previous studies have used chitosan, derived from shellfish, as an edible, invisible coating on Atlantic cod and herring fillets; it has also been use to as an anti-microbial for fruits, vegetables, cheeses and meat.
However Zao and his team noted that chitosan’s polymer structure means it can be used as a carrier for other substances, such as nutraceuticals and antioxidants. They set out to see chitosan coatings incorporating fish oil could improve physicochemical and microbial qualities of lingcod fillets during cold and frozen storage, and enhance omega-3.
Chitosan plus omega-3
The researchers used 3 per cent chitosan solutions with 10 per cent fish oil, with and without the addition of vitamin E at 0.8 per cent. The lingcod fillets were then vacuum-impregnated in the coating solution at 100mmHg for 10 minutes, followed by atmospheric restoration for 15 minutes.
After drying the fillets were stored at 2ºc for 3 weeks, or -20ºc for three months.
The coating was seen to increase total lipid and omega-3 content three-fold, and to reduce TBARS (thiobarbituric acid reactive substances) values in both the fresh and the frozen samples.
Drip loss in the frozen samples also reduced by between 14.1 and 27.6 per cent. The coatings inhibited the growth of total and psychotropic bacteria, which thrive in a cold environment, by 0.37-1.19 log CFU/g in the cold stored fish and 0.27-1.55 log CFU/g in the frozen.
“Chitosan-fish oil coatings may be used to extend shelf-life and fortify omega-3 fatty acid in lean fish,” concluded the researchers. The coatings could be applied to fish packaging.
The colour of the fish filet was seen to be unaffected, but the pH and moisture content was lowered. The addition of vitamin E did not contribute any more to the antioxidant effect of the chitosan.
The researchers said that the sensory characteristics and consumer acceptance of the treated fillets will be assessed in a separate study.
The sensory properties of the fish fillets were not assessed, and will be investigated in a further study.
Food Chemistry (published online ahead of print)
“Quality enhancement in fresh and frozen lingcod (Ophiodon elongates) fillets by employment of fish oil incorporated chitosan coatings”
Authors: Jingyun Duan, Gita Cherian, Yanyun Zhao