3.3. Textural profile analysis
All textural parameters for fresh muscle of controls and HPP treated
samples were affected by freezing and frozen storage.
Hardness of fresh mackerel muscle was 33.3 N, increased to 87.1 N
after freezing, and then decreased to 65.1 N after 3 month of frozen
storage. Adhesiveness of the frozen muscles (around 60 g s) was
lower than that of fresh samples (98.8 g s) while springiness
and cohesiveness were less affected and in the narrow range of
0.20e0.30 and 0.17e0.22 for the springiness and cohesiveness of
fresh and frozen muscles, respectively. Chewiness of fresh muscle
was 1.33 N, increasing to 6.12 N after freezing and frozen storage for
1 month, and then decreasing to only 2.84 N after 3 months.
Table 2 shows the results of HPP as pre-treatment on frozen
mackerel texture profile analysis of raw muscle. The effect of HPP
pre-treatment and frozen storage on the hardness of raw fish was
evaluated by multifactor ANOVA. A significant (p < 0.0001) model
was obtained. Evaluation of F-values of the three variables
confirmed that hardness was highly affected by pressure level (Fvalue
¼ 18.46), pressure holding time (F-value ¼ 8.34) and pressure
level-pressure holding time interaction (F-value score ¼ 21.83).
However, the effect of frozen storage time on the hardness of
muscle after HPP pre-treatment was negligible.
Prediction of the model (r2 ¼ 0.67) for the effect of the two
variables that exerted a higher influence on hardness, i.e., pressure level and pressure holding time, is shown in Fig. 3. Pre-treatments
at high-pressure levels caused a significant increase in hardness.
However, HPP treatments at 150 MPa yielded hardness values
below 78 N, maintaining hardness levels similar to frozen muscle
without HPP pre-treatment but with the beneficial effect of lipid
oxidation inhibition observed in previous reports (Vázquez et al.,
2012). The HPP influence on hardness has also been observed for
other fish species like cod (Gadus morhua). An increase in hardness
was observed due to pressure while only minor changes in hardness
were observed during frozen storage The multifactor ANOVA of the effect of HPP pre-treatment and
frozen storage on adhesiveness of rawmuscle produced a significant
model (p < 0.0001). The evaluation of the F-values for the three
variables confirmed that adhesiveness was highly affected by the
pressure level (F-value ¼ 140.78), frozen storage time (Fvalue
¼ 27.78) and the pressure level-frozen storage time interaction
(F-value score ¼ 22.04). This analysis implies that when an HPP pretreatment
is applied, the effect of pressure holding time on the
adhesiveness of muscle is negligible. The prediction of the model
(r2¼0.83) obtained for the effect of pressure level and frozen storage
on adhesiveness is shown in Fig. 4. HPP pre-treatments caused a
significant adhesiveness increase when high-pressure levels and
long storage timewere selected. However, lowpressure levels (150e
175MPa) yielded values close to 100 g s, i.e., an adhesiveness similar
to that of fresh muscle. This result is in accordance with the negative
effect on adhesiveness found during freezing of salmon before
smoking