3.1. The TVB analysis
The TVB test was one of the methods used notably to determine fish freshness. It is based on volatile bases
found in fish flesh. The TVB value higher than 30 mg N % indicates that the fish flesh quality was reduced.
Fig. 2 .Total Volatile Base (TVB) analysis of freshly caught wild young YFT. Values shown were the average of duplicates. Details regarding
samples’ code (A1B0 - A2B1) can be referred in Figure 1.
Prior to storage (T0), the TVB number indicated the fresh condition of the samples used, varied from 13 mg to 15
mg N % (Fig. 2). Samples immersed in 1 % nano-chitosan solution made by both types of water (A1B0-A2B1)
indicated an increase in TVB number after 6 h of storage, but still below the freshness threshold of international
standard. This was maintained until the end of the storage period, where TVB numbers ranged between 18 and 24.
Only one sample immersed in DW at 28 °C (A1B1) that showed consistent increase of TVB number, from 15 mg N
% to 28 mg N %.
On the other hand, after six hours of storage, negative control incubated at 28 °C (A0B1) showed decrease in
freshness, with TVB number peaked at 30 mg N %. The sharp increase was possibly caused by the autolysis process
and bacterial activity during the storage period. Despite the evisceration phase prior to storage, the bacteria existing
internally and externally worked actively to convert the existing protein and/or its derivative compounds in the
samples’ flesh tissues into volatile bases such as ammoniac, histamine, hydrogen sulfide (H2S) and trimetilamine
(Karungi et al. 2003) which produced the rotten-egg-like odor. The TVB number was decreased at 12 h of storage
and stabilized at 26 mg N % 6 h after. This activity was confirmed by the TPC result and the organoleptic
assessment (cf. section 3.2 and 3.3), where the bacterial total number reached 7.9 × 105 CFU · g–1 at 6 h of storage
and organoleptic assessment indicated changes in samples appearance in all four parameters (eyes, flesh, texture and
odor) below the acceptable limit (7). The sample without nano-chitosan treatment stored at 4 °C (A0B0) had TVB
number that started to increase only after 12 h of storage, but did not trespass the freshness threshold. The overall
TVB data indicated that fish sample immersed in WW based 1 % nano-chitosan and stored at 4 °C (A2B0) gave the
optimal result, with TVB number only as high as 19 mg N % during the experiment.
The ANOVA test indicated that there was no statistically difference of treatments’ effect on TVB results
(p = 0.116), but there were significant effects of temperature and storage time on these results (p < 0.05). However
there was a statistically significant interaction between the effect of treatments and temperature on TVB result
(p < 0.05).