Microbiology and Spoilage Trail in Nile Perch (Lates niloticus), Lake ...

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4.3.2.4 Establishment E4 – chilled fillets (5 days iced whole Nile perch) Chilled Nile perch fillets were processed from a lot of whole Nile perch stored in ice for 5 days. Changes for spoilage bacteria on chilled fillets were constant up to 13 storage days (figure 24 and 25). The trend was characterised by an increase for both SSO and TVC in parralel and reached a stationary phase after 13-15 storage days. The changes in TVB-N showed moderate increase from the beginning up to 13 days and then very rapid increase between days 13-15. The SSO and TVC increased from 3-7log10cfu/g in the first 10 days of storage and to 9 log10 cfu/g after 15 days while the Enterobacteriaceae counts gave only a slight increase from 2.5-3.7 log10 cfu/g. Again these results indicate that the SSO counts are closely equals to TVC counts between 13-15 storage days. The chemical (TVB-N) changes during 15 days storage of chilled Nile perch fillets show an increase from about 5- 13mgN/100g up to 15 storage days (figure 25 and 26). The changes in pH shifted from 6.5- 6.9 units during 15 storage days. Figure 24: Changes of specific spoilage organism (SSO), total viable counts (TVC) and Enterobacteriaceae (Ent.) on chilled fillets. 55 Figure 25: Changes of TVB-N on chilled fillets. Figure 26: Changes of specific spoilage organism (SSO), total viable counts (TVC), Enterobacteriaceae (Ent.) and TVB-N on chilled fillets.
The results from chilled fillets (figure 27) from all four establishments show similar trends on both spoilage microflora and TVB-N. Changes in the spoilage micro flora on all chilled fillets during storage, initially were 3-4log10cfu/g and at the end of storage time were ≥8- 9log10cfu/g (5 and 6 days in ice) and ≥10log10cfu/g (10 and 17 days in ice) respectively. The changes in total volatile base nitrogen (TVB-N) were from 10-21mgN/100g, the values were well below the maximum limits of 30-35mgN/100g of acceptability of fresh fish. The trends in SSO and TVC counts are better than Enterobacteriaceae and TVB-N implying that are good indicators for making decision of freshness quality of chilled fillets stored at low temperatures (0-3 o C). Figure 27: Chilled fillets from establishments 4.4 PRESUMPTIVE SSOs At the end of storage time for whole Nile perch and chilled fillets, few colonies from plates of IA and VRBGA were confirmed. Most colonies results were Gram-negative, rod shaped, oxidase positive, catalase positive, and Hugh and Leifson (O/F – fermentative in glucose). Few colonies were oxidase/catalase negative and non fermentative in glucose. The Enterobacteriaceae colonies from VRBGA also were Gram-negative, rod shaped, oxidase negative, catalase positive, and Hugh and Leifson (O/F – fermentative in glucose). These results imply that the main SSO (H2S) on iced whole Nile perch and chilled fillets may be caused by Shewanella putrefaciens, Pseudomonas, Vibrios/Aeromonas and Enterobactericeae (figure 28). 56
Page 1 and 2:
1 Microbiology and Spoilage Trail i
Page 3 and 4:
i DECLARATION I wish to declare tha
Page 5 and 6:
iii ABSTRACT The microbiological sp
Page 7 and 8:
4 RESULTS..........................
Page 9 and 10:
vii LIST OF TABLES TABLE 1: NILE PE
Page 11 and 12:
East Africa. The lake produces a fi
Page 13 and 14: Table 1: Nile perch export processi
Page 15 and 16: 1.2.1.3 Output from the study The i
Page 17 and 18: eservoir i.e. Salmonella, Shigella,
Page 19 and 20: Spoilage of food means to deprive i
Page 21 and 22: • Pseudomonas and Shewanella putr
Page 23 and 24: NH3 Ammonia amino acids and urea Ac
Page 25 and 26: According to Cornell, (1975), the p
Page 27 and 28: as well as indices of fish spoilage
Page 29 and 30: Table 6: Cardinal temperature for m
Page 31 and 32: is insufficient for good quality an
Page 33 and 34: which are posing difficulties in de
Page 35 and 36: Vibrionaceae at higher temperatures
Page 37 and 38: 3 MATERIALS AND METHODS 3.1 STUDY A
Page 39 and 40: 3.2.1.2 Phase I- trial 2: Sediments
Page 41 and 42: 3.2.3.2 Phase III - trial 2: Shelf
Page 43 and 44: • Total viable counts (TVC): Volu
Page 45 and 46: 3.3.2.1.3 Phase I - Trial 3: Whole
Page 47 and 48: 3.3.2.2.2 Phase II trial 2: Shelf l
Page 49 and 50: 4 RESULTS 4.1 PHASE I: MICROBIOLOGY
Page 51 and 52: Table 15: Pathogenic microorganisms
Page 53 and 54: The excellent freshness fish grade
Page 55 and 56: Figure 7: Changes of specific spoil
Page 57 and 58: 4.2.2.2 Chemical analysis Changes o
Page 59 and 60: Figure 14: Whole Nile perch in stai
Page 61 and 62: 21mgN/100g from days 12-15 which co
Page 63: 4.3.2.3 Establishment E3 - chilled
Page 67 and 68: 5 DISCUSSION 5.1 PHASE I: NATURAL M
Page 69 and 70: etween 15-20 days (2-3 weeks). Henc
Page 71 and 72: the components contributing to TVB-
Page 73 and 74: ice there was only a small margin (
Page 75 and 76: (around 6 log10 cfu/g) after 12 sto
Page 77 and 78: 5.4 PRESUMPTIVE SSO There are two t
Page 79 and 80: 6.2 RECOMMENDATION 1. Similar shelf
Page 81 and 82: REFERENCES Adams M. R. and Moss, M.
Page 83 and 84: Doyle M. P., (1990): Pathogenic Esc
Page 85 and 86: Huss, H. H. and Larsen A., (1980):
Page 87 and 88: Liston J, (1992): Bacterial spoilag
Page 89 and 90: Ozogul, F. and Ozugul, Y., (2000):
Page 91 and 92: Zeng, Q. Z., Thorarinsdottir K.A.,
Page 93 and 94: Appendix II: Iron agar (IA) for tot
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Microbiology and Spoilage Trail in Nile Perch (Lates niloticus), Lake ...

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