Effects of preservation methods and geosmin content on off-flavor in Nile tilapia (Oreochromis niloticus) | |
| Author | Jirawan Yamprayoon |
| Call Number | AIT Diss. no.AE-98-03 |
| Subject(s) | Food--Preservation Nile tilapia |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Technical Science, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. AE-98-03 |
| Abstract | In this study, the masking of reduction of off-flavor in tilapia was investigated on various preservation methods including salting, drying, smoking, frying, microwave heating, marinating and fermentation with carbohydrate mixture. The concentrations of geosmin (1,10-trans-dimethl-trans-9-decaol) in fresh and processed tilapia were analyzed by applying high-vacuum distillation, extraction and gas chromatography techniques. the relationship between geosmin content and intensity of muddy flavor was also evaluated by sensory methods the distribution of geosmin in tissues from various parts of tilapia were also examined along with the rated of geosmin absorption and purging. Analysis showed that 51 to 89% of geosmin, that was added to the flesh at concentrations ranging from 2.8 to 390 ug/kg was recovered. A linear relationship exists between the logarithm of geosmin concentration (ug/kg) and score from sensory evaluation of muddy flavor intensity, Muddy flavor was detected in freshwater tilapia with a geosmin content ranging from 7.55 to 9.85 ug/kg of fish flesh. However, panelists failed to detect a muddy flavor in brackishwater tilapia that contained geosmin only in the range of 1.5 to 2.6 ug/kg. Among various tissues of the fish, the intestines contain the highest geosmin concentration, and appeared in descending order in the abdominal, skin and muscle tissues. After holding for 2 h in water with 5 and 50 ug/ geosmin, tilapia absorbed 17.6 and 42.2 ug/kg geosmin in the flesh, respectively. Holding the fish over longer periods in water with higher geosmin content resulted in a greater amount of absorption. In contrast, transferring muddy-flavored fish to static clean water was able to purge geosmin but it required at least 16 days to eliminate the muddy flavor. Muddy-flavored fish treated by brining and dry salting and then dried by either hot air at 50'c or sun-drying only slightly reduced the geosmin content of the product. Deep-fry treatment reduced the muddy flavor intensity and geosmin content in both fresh muddy-flavored tilapia and salted dried tilapia. Pretreatment of tilapia fullest with acidified brine before smoking reduced geosmin content and marked the cuddy flavor in the smoked product. Microwave cooking of fresh muddy flavored tilapia showed no effect on its geosmin content nor its off-flavor. Marinating tilapia in an acetic acid solution resulted in decreased muddy flavor, and longer marinating period led to a lower geosmin content in the products. After storage, for at least 14 days, sensory evaluation revealed the preference for samples that were fried before miniating compared to other samples that were either cold (raw) or cooked before marinating. Tilapia was also prepared by a traditional Thai process involving lactic acid fermentation of minced tilapia flesh mixed with cooked rice, garlic and salt to produce som fak. No significant differences were observed in som fak produced from either non off-flavor or muddy tilapia and the taste panelists preferred the som fak fermented for 3 days. |
| Year | 1998 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. AE-98-03 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Agricultural and Food Engineering (AE) |
| Chairperson(s) | Athapol Noomhorm; |
| Examination Committee(s) | Lin, Chang Kwei;Jindal, Vinod K.;Lovell, R.T.,; |
| Scholarship Donor(s) | Royal Thai Government; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 1998 |