The origin and mechanism of formation of the volatile fatty acids (VFA) present in budu were investigated. The acids did not appear t o derive from the breakdown of the fish lipid. When the fish was allowed to spoil, a single bacterial species predominated, and as the fermentation progressed, the appropriate VFA were formed.Using (U-lJC)-protein hydrolysate it was shown that amino acids are the precursors of the n-butanoic and 17-pentanoic acid and also contributed to the formation of other acids. The bacterium did not use glucose as a carbon source nor did any particular combination of unlabelled amino acids produce the fatty acids. The metabolic route by which the fatty acids are produced from the amino acids is not known. An experiment that allowed spoilage to occur, prior to salting, in the normal environment involved in the preparation of budu, showed that the VFA were produced.
The changes that occur during the commercial production of budu, a Malaysian fish sauce were examined. It was shown that the maximum volume of liquid was produced after 140 days and that proteolysis continued to occur until 200 days when 56 % of the insoluble fish protein had been hydrolysed into soluble form. The colour was produced early during the fermentation. The aroma constituents, ammonia and trimethylamine, were produced early in the fermentation process, but the volatile fatty acids did not appear when fresh fish (Stolephorus) was used for the fermentation. In the commercial production, n-butanoic acid concentration remained constant during the fermentation but ethanoic acid did increase during the period. The salt concentration and the pH were approximately constant throughout, at 26 % and 5.65, respectively.
The production of a fish hydrolysate, using plant proteases, which could be added to traditionally fermented fish sauce to increase the total volume without affecting the overall nutritional quality was investigated.The effect of adding bromelain, papain or ficin, on the rate of hydrolysis and the extent of the conversion of insoluble fish protein, to soluble nitrogen was examined. The conditions employed were similar to those used in traditional fish sauce manufacture but both whole and minced Ikanbilis (Stolephorus sp.) were investigated. Measurement of the extent of hydrolysis after 1,2,4,7, 14, 27,28 and 35 days at 33°C showed that bromelain tended to give slightly better results with some 65 % of the protein being hydrolysed. The effect of temperature enzyme, co-enzyme and salt concentrations for the hydrolysis by bromelain were investigated and the optimum conditions established at the pH normally found in fish sauce production. The hydrolysate produced in 18-21 days was comparable to traditional fish sauce in the distribution and concentrations of nitrogenous compounds and had very little aroma. The product could be added to the traditional sauce without affecting its quality.
When batches of Ikanbilis were acidified using hydrochloric acid to pH 2.0-3.5 at 30°C, the rate and extent of hydrolysis of the fish protein and the rate of formation of supernatant liquor were increased.The effect of pH and salt concentration was invqtigated. Although the presence of salt generally decreased the extent of proteolysis, it made the mixtures easier to filter. The optimum conditions were either p H 2.0 and 10% salt (w/w) or pH 3.0 and 15% salt (w/w). The extent of fish protein hydrolysed was comparable to the natural fermentation and the concentrations and distribution of soluble nitrogen were very similar to those obtained in the traditionally produced sauces. This liquor was produced within 6 days. The natural fermentation takes 4-9 months.The use of formic acid was investigated and showed no particular advantage.When the pH of the acid ensiled mixtures was adjusted above 4.2, calcium phosphate precipitated; this was removed by filtration. The effect of adding alkaline ensiled fish to acid ensiled fish mixtures (the p H of which had been re-adjusted) was investigated. The amount of insoluble protein hydrolysed increased to a limited extent.As the solutions produced by acid ensilation had very little aroma or taste but had a high soluble nitrogen content, they could be used to add to traditionally prepared fish sauce in order to increase the net volume which would increase the rate of production.
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