Microbiological and Chemical Quality of Keropok Lekor during Processing And Storage
Keropok lekor is an important fish product in Malaysia. The customers’ demands for keropok lekor have been increasing. This study was conducted to analyze the microbiological and chemical quality of keropok lekor in every stage of its processing, namely mincing, mixing, kneading, boiling and cool...
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| Format: | Thesis |
| Language: | English English |
| Published: |
2008
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/5336/1/FSTM_2008_3.pdf |
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| Summary: | Keropok lekor is an important fish product in Malaysia. The customers’ demands
for keropok lekor have been increasing. This study was conducted to analyze the
microbiological and chemical quality of keropok lekor in every stage of its
processing, namely mincing, mixing, kneading, boiling and cooling.
Subsequently, this study was also undertaken in an attempt to determine the
effectiveness of post processing treatment on keropok lekor in order to prolong its
shelf life. The method used to analyze the microbiological quality is known as
the direct plate counts for the total plate counts (TPC), psychrotrophic, yeasts and
molds, mesophilic sporeformer, Staphylococcus aureus, total coliform and fecal
coliform counts. Simple biochemical test was carried out to identify the
presumptive bacteria present in keropok lekor processing. Chemical quality was
analyzed on the total volatile bases (TVB) and trimethylamine (TMA), using
Conway microdiffusion method, and biogenic amines was done using the High
Performance Liquid Chromatography (HPLC). The post-processing treatments
on keropok lekor were exposing keropok lekor to UV light for 15 or 30 min,
either coated with different concentrations of ascorbic acid (500, 1000 or 1500 ppm) or dipped in hot oil for 3, 6 or 9 s, and stored at the room temperature for 7
d or at chill temperature (4±1°C) for 14 d. When processing keropok lekor, the
boiling of keropok lekor at 100°C for 10 min reduced the TPC (4.38±0.47 log10
cfu/g), psychrotrophic counts (2.00 ± 0.00 log10 cfu/g), mesophilic sporeformer
counts (1.26 ± 0.34 log10 cfu/g) and total coliform counts (1.71±0.51 log MPN/g)
significantly (p>0.05). However, the microbial counts were found to increase
significantly (p<0.05) after the cooling process, except for the yeast and mold
counts and S. aureus counts. The presumptive predominant microorganisms,
isolated before the boiling stage, were members of the Enterobacteriaceae family
and those belonging to Pseudomonas, Vibrio, Staphylococcus, Bacillus and
Micrococcus genus. After the boiling stage, the presumptive predominant
microorganisms were members of Enterobacteriace family and those belonging
to Micrococcus, Bacillus, Staphylococcus and Aerococcus genus. As for the
chemical quality, TVB and TMA levels were indicated to significantly decrease
(p<0/05) after boiling from 7.29 to 4.68 mg/ 100g and 3.38 to 1.81 mg/ 100g,
respectively, but not for the putrescine, cadaverine and histamine levels. Before
the boiling stage, presumptive microorganisms producing putrescine, cadaverine
and histamine were members of the Enterobacteriaceae family, as well as
members of Staphylococcus, Pseudomonas and Micrococcus genus. Members of
the genus Pseudomonas, which produce biogenic amines, were not isolated from
keropok lekor after the boiling stage. The post-processing treatment which was
applied on keropok lekor was found to enhance both its quality and shelf life.
The results showed that exposing keropok lekor to UV light for 15 min and
dipping it in hot oil for 9 s had extended the shelf life of this snack for 5 d when
v
stored at the room temperature, and for 14 d when stored at 4±1°C. This post
processing treatment had also caused a significant reduction in TPC,
psychrotrophic count, yeasts and molds count, TVB, as well as TMA and
putrescine, cadaverine and histamine level. On the contrary, ascorbic acid was
not as effective in increasing the shelf life of keropok lekor or in reducing TVB,
TMA and putrescine, cadaverine and histamine level, as compared to dipping it in
hot oil. |
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