Measuring Seafood Quality

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Measuring Seafood Quality

• Chuck Crapo
• Marine Advisory Program
• Fishery Industrial Technology Center
• Kodiak

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Measuring Quality

• Everyone wants to know the quality of the fish
  they are buying
• Need reassurance that it is acceptable
• Want quantitative measures

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Methods

• Testing Quality By
• 1. Sensory
• 2. Chemical
• 3. Physical
• 4. Microbiological

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Sensory Tests

• Using senses to evaluate the quality of seafoods
• Typical sensory tests includes the evaluation of
• appearance
• texture
• odor
• flavor
• other attributes

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Sensory Tests

• This method is very subjective since everyone has
  their own likes and dislikes. This can be
  minimized by 'training' people to taste.
• Most convenient method for testing seafood
  quality.

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Chemical Tests

• Measuring compounds that appear during
  post-mortem deterioration.
• Proximate composition
• Measures water, protein, lipid and ash content
• Rough estimate of quality, but not really useful.
  Fish to fish variation can be great.

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Chemical Tests

• TMA - Trimethylamine
• Measured as an indicator of bacterial spoilage.
  Not used as a measure for freshness.
• Limitations because TMA is low during edible
  storage and only goes up rapidly when fish is
  close to spoilage.

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Chemical Tests

• TVB - Total Volatile Bases
• Measuring all volatile compounds that result from
  bacterial spoilage
• Same problems as TMA

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Chemical Tests

• Nucleotides Measuring hypoxanthine and inosine
  created from degradation of ATP.
• Used as relative measure of fish freshness and
  correlates with sensory evaluation.
• Limits - Dark muscles are higher in these
  compounds and there are variations in ATP
  degradation

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Chemical Tests

• Oxidative Rancidity -
• Measuring compounds that result from the
  oxidation of fats. Include free fatty acids,
  peroxide value and TBA test.
• Free fatty acids - useful to measure hydrolysis
  by enzymes and useful for stored, fresh fish

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Chemical Tests

• Peroxide value - measures peroxides from first
  stage of lipid oxidation.
• TBA (thiobarbuturic acid) - measures compounds
  from second stage of oxidation.
• Neither of these methods are useful in fresh
  fish, but a good indicator of frozen fish
  degradation. But do not correlate with sensory
  evaluation.

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Physical Methods

• Electrical Properties of the Skin
• Measuring conductance has been a method for
  assessing quality. Performed By Torrymeter.
• Difficult in correlating this type of information
  with other signs of degradation.

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Physical Tests

• Texture Measurements
• Instrumental method trying to mimic the action of
  chewing to get an objective measurement.
• Methods measure compression, shear and tensile
  properties of fish muscle

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Physical Methods

• Water Binding Capacity
• Determining the amount of water that could be
  removed from fish muscle has been used as an
  indication of protein degradation.
• Consists of forcing water out of muscle using a
  steady force.

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Microbiological Methods

• Not used to assess freshness or eating quality,
  but rather the hygienic quality of the fish,
  hygiene during processing and the
  presence/absence of public health risks.

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Microbiological Methods

• Total Plate Counts (TPC)
• Measures Number of Bacteria and Often Used as
  Quality Index
• Many Quality Specifications Include TPC

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Measuring Quality

• Many ways to measure, some give conflicting
  information.
• Always striving to find the one method that works
• But in the end our senses are probably the best