Cleaning fish oil with steam makes some bad smells worse in some oils, and doesn’t get rid of all the fishy odor.
Scientific Claim
The deodorization step in refining increases levels of volatile aldehydes (e.g., 2,4-decadienal, 2,4-nonadienal) in seabass and gilthead seabream by-product oils, while reducing fishy-smelling alcohols like 1-penten-3-ol, but fails to fully eliminate odor-causing compounds compared to commercial cod liver oil.
Original Statement
“The amount of 2,4-decadienal (from the n-6 fatty acids) increased after the distillation, especially in seabass and seabream oil... The composition and proportion of volatile compounds changed significantly during the refining process and only in tuna by-product oil the total sum of volatile compounds was reduced during refining.”
Evidence Quality Assessment
Claim Status
appropriately stated
Study Design Support
Design supports claim
Appropriate Language Strength
definitive
Can make definitive causal claims
Assessment Explanation
Volatile compounds were quantified in mg/kg using validated HS-SPME/GC-FID methods with calibration curves. The definitive language is justified by direct, precise measurements of specific compounds.
Gold Standard Evidence Needed
According to GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this specific claim, ordered from strongest to weakest evidence.
Randomized Controlled TrialLevel 1bWhether modified deodorization protocols (e.g., higher temperature, shorter time) reduce sensory off-flavors in refined fish by-product oils.
Whether modified deodorization protocols (e.g., higher temperature, shorter time) reduce sensory off-flavors in refined fish by-product oils.
What This Would Prove
Whether modified deodorization protocols (e.g., higher temperature, shorter time) reduce sensory off-flavors in refined fish by-product oils.
Ideal Study Design
Double-blind RCT testing 3 deodorization protocols (160°C/1h, 180°C/30min, 200°C/15min) on 100 batches of seabream by-product oil, with sensory panels (n=30) rating odor intensity and acceptability, and GC quantifying key aldehydes as primary endpoints.
Limitation: Does not assess impact on PUFA integrity or long-term stability.
In Vitro Chemical AnalysisLevel 4In EvidenceThe specific volatile profile changes during deodorization.
The specific volatile profile changes during deodorization.
What This Would Prove
The specific volatile profile changes during deodorization.
Ideal Study Design
The current study design — HS-SPME/GC-FID quantification of volatiles pre- and post-deodorization — is the ideal in vitro evidence for this claim.
Limitation: Cannot assess human sensory perception or consumer acceptability.
Evidence from Studies
Supporting (1)
Production and Refinement of Omega-3 Rich Oils from Processing By-Products of Farmed Fish Species
The study found that cleaning fish oil from seabass and seabream leftovers makes some smelly chemicals stronger (like 2,4-decadienal) and doesn’t get rid of all bad smells — just like commercial cod liver oil, which also still smells a bit fishy after cleaning.