ABSTRACT
Vacuum pre-cooling has become one of the most widely used techniques for
keeping vegetables fresh because of its fast and clean,etc. Chinese little greens was
easy to lose its commercial value because of its tender texture and easy to rot.
Therefore, there is a very important practical significance to research the pretreatment
and storage physiology of Chinese little greens to extend its storage and preservation.
In this paper, The quality variations of Chinese little greens, affected by different
vacuum pre-cooling treatment conditions have been studied. Some experimental
parameters such as pressure and temperature have been analyzed during vacuum
cooling process. Moreover, the effect of vacuum pre-cooling on the keeping freshness
of Chinese little greens during storage were studied and the variations of mass, texture,
chromatic aberration, POD activity and microbiological indicators (total bacteria and
E.coli) were detected.
The results showed that: when the pre-cooling temperature was lower, the mass
loss and hardness loss were greater after the vacuum pre-cooling treatment. In the
storage period, the pre-cooling temperature of 4 ℃made the quality, hardness,
chromatic aberration change of the lowest, while 8℃made the highest rate of change.
When the pre-cooling pressure was lower, the mass loss and hardness loss were greater.
In the storage period, the pre-cooling pressure of 1000Pa made the lowest loss rate of
quality and hardness. The chromatic aberration change of Chinese little greens which
were vacuum pre-cooled was less than the control group during the storage. The
vacuum pre-cooling could delay the Chinese little greens turning yellow and maintain
the POD activity at a high level. The micro-structure and appearance of quality was
also better during the storage. As a conclusion, compared with the control group,
vacuum pre-cooling did a positive role to keep Chinese little greens fresh.
The growth of microorganisms in Chinese little greens was effectively suppressed
after the vacuum pre-cooling treatment. Pre-cooling at the same pressure, the
inhibitory effect was better with the lower temperature. Pre-cooling at the same
temperature, different pre-cooling pressures effected on the growth of microorganisms
significantly. The lower pre-cooling pressure made the more obviously role in
inhibiting the growth of microorganisms. The best pre-cooling pressure is 800Pa.
Vacuum pre-cooling was proved to be effective to extend of Chinese little greens’