The expert visited several ports in Thailand, particularly those in the south of the country, to observe fish handling and processing and to collect samples of products. He also visited inland areas to observe the marketing and processing of freshwater fish. The expert paid a visit to Cochin, India, to study the technical and administrative aspects of the quality control of shrimp exports practised there.
The expert visited three of the seven shrimp processing factories in Bangkok, and the two factories in Songkla. A more detailed examination of two of the Bangkok factories was made, including investigations into the performances of their freezers.
The expert found that the quality of the shrimp used in the Bangkok factories was not very high. The material usually was brought from ports in the south and not purchased in the Bangkok market. The shrimp was not very well handled on-board the trawlers and the further packing in the large boxes for distribution also contributed to the spoilage. The quality of the shrimp in the Songkla factories was better because they were obtained locally.
The processing was carried out reasonably efficiently and the fish was kept cooled by ice. The standard of hygiene in the factories was generally low but the expert did not make a detailed investigation into this as it will be included in the terms of reference of his successor.
The weighing and grading of the shrimp was carelessly carried out and about half of the final packs examined in the laboratory were underweight or had unacceptably wide ranges of individual sizes.
In collaboration with the counterpart, the expert measured the temperatures of packs during freezing, using thermocouples. In one of the factories the freezing times were longer than is recommended for good quality products. In the other factory two types of freezers were in use; one type gave acceptable values for freezing times but the other gave slightly longer than recommended times. Reports of this work on the freezers were prepared along with suggestions for improvement and sent from the Fisheries Technology Laboratory to the managers of the respective factories.
Laboratory work was carried out by the expert to get information about the quality of the products, train the staff and initiate research projects.
Shrimp was iced under good conditions in the laboratory and its spoilage measured during storage up to 21 days. It was found that Total Volatile Basic Nitrogen content which is an index of bacterial spoilage did not rise until the shrimp was about ten days in ice. This is appreciably later than when shrimp are caught in temperate waters.
The bacterial counts ranged on average from 1 × 106 organisms per g after one day in ice to 1 × 108 after 20 days.
It appears from this that the shrimp carry a heavy bacterial load on catch but the growth rate at 0°C is slow.
The expert did not make any analyses of fermented fish sauce himself but he collected samples at various stages of preparation from factories in Cholburi and sent them for amino acid analysis to Torry Research Station, Aberdeen, Scotland.
The expert analysed the nitrogenous compounds and volatile acid of some samples of fermented fish (pla-ra), purchased from the retail market. The full processing history of these was not available but there was a big difference in the analyses and there appears to be an increase in both non protein nitrogen and volatile acid contents during fermentation.
A batch of fermented fish was prepared at the laboratory and this will be analysed at regular intervals during fermentation according to the analytical scheme devised by the expert.
Samples of frozen chub mackerel ranging from one to twelve months storage time were selected from the Cold Storage Organization store in Chumpon and sent in the frozen state to the Fisheries Technology Laboratory where they were analysed and tasted to determine their quality. Judging from the trimethylamine content of the flesh some of the samples were not completely fresh when frozen and judging from the peroxide value of the extracted lipids the temperature of storage was too high. Tasting showed that all the samples had rancid oil and cold storage off-flavours and even the one month sample was of poor eating quality. It is therefore apparent that the store temperatures are not low enough for storage of chub mackerel.
On average between 50 percent and 60 percent of the trawl catch is trash fish which is used for reduction to fish meal or fed to animals directly. The expert considered possible an alternative way of utilizing this high proportion of the catch.
He obtained data on the species composition of trash fish landed in the Songkla area from the Marine Laboratory in Songkla. This laboratory had sampled trash fish monthly between February and September 1970, a total of 258 kg, 2.9 percent of the total trash fish landings being examined, and most of the species identified. Over 50 species were recognized though many were represented by only a few members and a summary of these data grouped into genera is given below.
| Composition of Trash Fish from Songkla District | |
| Genus | % by Weight in Sample |
| Leiognathus | 19.6 |
| Balistes | 9.1 |
| Upenus | 6.0 |
| Nemipterus | 5.3 |
| Scolopsis | 4.6 |
| Caesio | 4.1 |
| Priacanthus | 3.5 |
| 52.2 | |
| Other named species | 35.3 |
| Unidentified fish | 12.5 |
All the named genera are of edible species but the fish are too small to be marketable. It is possible that the Leiognathus species are in sufficient amounts to be worth sorting for further processing but their small size. (between five and ten grammes) would make exploitation very difficult.
As an alternative to reduction to fish meal the expert converted some trash fish to fish silage by adding formic acid to a final concentration of three percent. The fish liquified readily within a few days at laboratory temperatures, about 30°C, and the liquefaction of whole fish was only a little slower than that of minced fish. The final mixture had a protein content, (N × 6.25), of 14.7 percent, lipid content of 3.7 percent, and ash content 2.6 percent. The cost of this product on a nitrogen basis will be similar to that of fish meal but its biological value may be greater because there is no heat treatment.
The Torry kiln in the laboratory was used to demonstrate and investigate the mechanical drying of fish. Though the kiln is designed for smoking fish it can also be used as a drying tunnel without modification. The expert used a rapid drying schedule where the tunnel air temperature is raised as the product dries.
Shrimp was dried in collaboration with a commercial firm which wanted to produce shrimp powder for export. The shrimp meat was shelled, deveined and split before spreading evenly on perforated trays. The trays were loaded into the kiln and drying started at 40°C. Every half hour the temperature was raised by 10°C up to 100°C and maintained there until drying was complete; a total of three half-hours. The product had a good strong flavour of shrimp with only slight caramelized flavour and was easily powdered.
Threadfin (Nemipterus spp.) was also successfully dried. The fish was split from the dorsal side, gut and gills removed and laid on perforated trays. After a few trials a suitable programme was to start drying at 50°C and raise the temperature by 10°C every hour up to 100°C and maintain it there. Drying was complete in a total of 12 or 13 hours. Some of this product was stored in airtight containers and there was no sign of mould growth at six weeks when the expert left Thailand. The flavour was pleasant with a noticeable caramelized and meaty flavour.
The expert made one trial to dry chub mackerel and freshwater cat fish (Clarias sp.) by this schedule but because of their high fat contents, these fish dried more slowly than the threadfin and cooked before drying. Oily fish of this type should have a lower starting temperature and a slower temperature increase at least in the early stages.
A small amount of fish, both marine and freshwater, is smoked in Thailand but it is later completely dried in the sun. The expert investigated the manufacture of smoked fish produced in the European style as a new product, using the Torry kiln in the laboratory.
Chub mackerel was smoked as split fish or headless whole fish. The split fish was prepared as for the British kipper and the final product was almost identical with it except in size. Several batches of them were prepared and distributed among many people, both within and outside the laboratory for comment. All reports were highly favourable and this type of smoked product would be readily acceptable within Thailand. This kippered mackerel would also be acceptable to Europeans or Americans and could be frozen and exported.
The nobbed (headed and gutted) mackerel were prepared as a hot-smoked product similar to the European buckling and this too was very favourably received by those who tasted it. It could be frozen and exported or processed as a canned pack.
Spanish mackerel (Scomberomus commersoni) fillets were smoked like British smoked cod fillets and gave a very attractive looking and finely flavoured product. Once again they were completely acceptable to the staff of the laboratory who tasted them. Since Spanish mackerel is a fairly expensive fish and the yield of smoked fillet is only 40 percent, this product may be more suitable for the catering or export trade.
Bonito (Euthynnus affinis) fillets were smoked but the dark muscle was too bitter in taste for the fillets to be left whole. Apart from this, the flesh had a good rich flavour and the fillet had a pleasant deep red/brown colour. Bonito is quite cheap on the wholesale market though the landings are small and smoking could be used to raise its value. It is possible that this fish could be prepared in the same way as smoked salmon to give a delicatessen product.
The expert assisted generally in the work of the laboratory and introduced new or modified methods of analysis and investigation.
He also advised on and trained some of the staff in the statistical interpretation of experimental data.
