Abstract:
The objective of this study is to extend the shelf life of fish balls by using modified atmosphere packaging (MAP) technique. The study was devided into 2 parts. Firstly, the qualities and spoilage characteristics of fish balls sold in local markets were determined. Secondly, MAP technique was applied in order to extend shelf life of the products. For the first part, 22 samples of fish balls were sampling from the local markets in Bangkok. The results showed that the hardness of fish balls ranged from 5417.33?76.96 to 10341.92?505.43 g while the gel strength was within the range of 204.16?8.87 to 921.99?2.21 g/cm. The hardness
and gel strength of fish balls were decreased as the storage time increased. For the microbiological results, the fish balls contained total viable count and Staphylococcus aureus ranged from 3.4 x 104 2.11x108 cfu/g and 1x 102 2.5 x104 cfu/g, respectively while the MPN of Esherichia coli was less than 3-15 MPN/g. The number of microorganism was increased rapidly after storing
the samples at 4?2?C for 3-5 days with the range of 1.26 x105 4.5 x 109 cfu/g. Spoilage characteristics of fish balls (slimy appearance and sour odor) were related with total bactrial counts and pH value of the sample. Those characteristics could be observed when the total count was more than 106cfu/g whereas the pH value was less than 6.0. For the second part, two polymeric films (nylon/PE and PET/PE) and four gaseous compositions (100% CO2, 80% CO2+ 20%N2, 60% CO2+ 40% N2 and 40% CO2+ 60% N2) were used. For the
fish balls packed in nylon/PE bags, the hardness of fish balls packed under 100% CO2, 80% CO2+20% N2, 60% CO2+ 40% N2 and 40% CO2+ 60% N2 increased from 6034.43?442.17 g to11289.14?301.10, 11190.80?345.30, 10449.11?354.90 and 8347.55?273.47 g whereas the springiness increased from 0.565?0.006 to 0.622?0.004, 0.615?0.004, 0.612?0.01 and 0.609?0.003, respectively. The hardness and springiness of fish balls packed under MAP were
higher than those of atmospheric condition which the values decreased from initial 6034.43? 442.17 g to 5469.90?295.30 g and from 0.611?0.01 to 0.579?0.005, respectively. Chemical results indicated that pH of all samples were decreased during storage period which ranged from 5.65?0.03 to 5.91?0.05. The microbiological results elucidated that total bacteria of the fish balls
packed under MAP had increasd as the storage time increased. Nevertheless fish balls packed under 100% CO2 could be kept for 24 days while fish balls packed under 80% CO2+ 20% N2 , 60% CO2+ 40% N2 and 40% CO2+ 60% N2 could keep for 21 days and 18 days, respectively. The results elucidated that fish balls packed under 60% CO2+ 40% N2 were still accepted by the panelists until 18 days of storage. For the fish balls in PET/PE bags, the hardness of fish balls packed under 100% CO2, 80% CO2+ 20%N2, 60% CO2+ 40% N2 and 40% CO2+ 60% N2 increased from 5606.54?195.74 g to 12557.50?225.40, 10366.93?855.07, 10806.29?201.43 and 7724.03?488.47 g whereas the springiness increased from 0.585?0.003 to 0.634?0.003, 0.636?0.011, 0.629?0.004 and
0.615?0.005, respectively. The hardness and springiness of fish balls packed under MAP were higher than those of atmospheric condition which the values decreased from initial 5606.54?195.74 g to 12557.50?225.40, 10366.93?855.07, 10806.29?201.43 and 7724.03?488.47 g, respectively.Chemical results indicated that pH of all samples were decreased during storage period which
ranged from 5.82?0.098 to 5.91?0.02. The microbiological results elucidated that total bacteria of the fish balls packed under MAP had increased as the storage time increased. Nevertheless fish balls packed under 100% CO2 and 80% CO2+ 20% N2 could be kept for 18 days while fish balls packed under 60% CO2+ 40% N2 and 40% CO2+ 60% N2 could keep for 15 days. The results elucidated that fish balls packed under 80% CO2+ 20% N2 were still accepted by the panelists
until 15 days of storage. All the results from this experiments revealed that the most suitable condition for extending shelf life of food balls was 60% CO2+ 40% N2 (nylon/PE). After storing for 18 days, the fish balls kept in aforementioned condition had the hardness and springiness of 10465.64?288.45 g. and
0.619?0.005, respectively. While the pH of the products decreased to 6.17?0.03. The products contained total bacterial of 5.82?0.01 log cfu/g.