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Influence of different freezing regimes on bioelectrical properties of Atlantic chub mackerel (Scomber colias) PowerPoint Presentation
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Influence of different freezing regimes on bioelectrical properties of Atlantic chub mackerel (Scomber colias)

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IntroductionIn recent years, bioelectrical properties of frozen-thawed fish have attracted much attention as possible indicators of freezing history. In our previous studies, the resistance and reactance of frozen-thawed sea bass and rainbow trout in a frequency range 100 Hz-1 MHz were measured. The results revealed that the reactance higher than 500 kHz could differentiate the fish with different freezing history. In this work we assessed whether frozen-thawed, commercially important wild fish Atlantic chub mackerel had similar bioelectrical properties as farmed species.

Influence of different freezing regimes on bioelectrical properties of Atlantic chub mackerel (Scomber colias)

Results

Materials and Methods

EXPERIMENTAL PLAN

Thirty (30) samples of Atlantic chub mackerel

a

CLEANING, FILLETING

CHILLING (+4 C,12 hours)

CUTTING THE EPAXIAL MUSCLE (10 x 2 x 1 cm)

DIVIDING THE SAMPES

2. group of samples

UNFROZEN (CHILLED)

  • group of samples
  • UNFROZEN (CHILLED)

b

Bioelectrical measurements

Resistance (R) and Reactance (X) measured by HPLCR Meter

at 19 frequencies from 0.1-1000 kHz; constant current method

Physical and chemical measurements

Water holding capacity (WHC), water content, pH

-

SLOW FREEZING (AIR,-18C)

FAST FREEZING (LIQUID N2)

Figure 1Resistance (R) and reactance (X) spectra of slow frozen (a) and fast frozen (b) groups of Atlantic chub mackerel

FROZEN STORAGE (-18 C, 14 days)

Table 1Differences between slow and fast frozen samples after one and two freezing cycles (Mann Whitney U test)

THAWING BY AIR (+4 C,12–16 hours)

Sanja Vidacek, Helga Medic, Nives Marusic, Božena Surić and Tomislav Petrak

Faculty of Food Technology and Biotechnology, University of Zagreb, Pierottijeva 6, Zagreb, Croatia

corresponding author:svidacek@pbf.hr

SLOW FROZEN-THAWED SAMPLES

FAST FROZEN-THAWED SAMPLES

Repeated bioelectrical, physical and chemical measurements

Legend

Sf-slow frozen

SfII-double Sf

Ff – fast frozen

FfII--double Ff

SLOW FREEZING (AIR,-18C)

FAST FREEZING (LIQUID N2)

FROZEN STORAGE (-18 C, 14 days)

THAWING BY AIR (+4 C,12–16 hours)

DOUBLE FAST FROZEN-THAWED SAMPLES

DOUBLE SLOW FROZEN-THAWED SAMPLES

Table 2.ANOVA among unfrozen, frozen and double frozen samples

Repeated bioelectrical, physical and chemical measurements

STATISTICAL ANALYSIS (SPSS, 12.0)

Kolmogorov Smirnov test

Confirmation of the normality of data

Testing the difference between

-fast and slow frozen samples

Mann Whitney U test

-double fast and double slow frozen samples

-unfrozen, frozen and double frozen samples

ANOVA

ConclusionsThe relationship between frequency and bioelectrical parameters follows the same pattern for all the fish species studied previously. Mann-Whitney U test shows that that the reactance is the only parameter that can differentiate fast frozen from slow frozen fish and double fast frozen from double slow frozen fish. The results of testing the differences among unfrozen, frozen and double frozen samples (ANOVA) show that the resistance measured at 500 and 1000 kHz, reactance measured between 0.1 and 15 kHz, moisture content and WHC are significantly different for different tissue conditions. Therefore, the reactance is the only variable that can distinguish fast frozen from slow frozen fish samples (at higher frequencies) and that may differentiate between double and single freezing cycle (at low frequencies) which supports our previous results on farmed fish.