low tryptophan levels. Apparently tryptophan 

 is released into the soluble phase more slowly 

 than other amino acids during the earlier stages 

 of hydrolysis. 



The nutritive values of two samples of "liq- 

 uefied fish protein" (LFP) were reported by 

 Higashi et al. (1965). Experiments were con- 

 ducted with jack mackerel, and the nutritive 

 values were determined by rat feeding tests. 

 Sample 1, prepared by digesting the cooked ma- 

 terial with commercial proteolytic enzyme iso- 

 lated from Bacillus subtilis, showed very low 

 nutritive value and an imbalance of essential 

 amino acids. Sample 2 of LFP, prepared by di- 

 gesting the raw material with a commercial en- 

 zyme isolated from streptomyces, showed high 

 nutritive value and its biological value was high- 

 er than that of milk casein. 



March et al. (1961) determined the nutritive 

 value of "liquid herring" preparations which 

 had been prepared by enzymatic hydrolysis with 

 pepsin and by high-pressure acid treatment 

 (McBride et al., 1961) . In chick feeding studies 

 both liquid preparations gave a growth response 

 intermediate between that obtained with her- 

 ring meal and with condensed herring solubles. 



Acid/alkaline hydrolysis. — An estimated 30 

 million pounds of hydrolysed protein are con- 

 sumed annually in the United States, and nearly 

 all of it is prepared by acid hydrolysis (Connell, 

 1966). Most is prepared from cheap vegetable 

 sources and is used in relatively small concen- 

 trations as a flavoring agent for meat products, 

 soup mixes, snack items, crackers, and other food 

 products. The poor nutritive value of the acid 

 hydrolysates is of little or no concern in most 

 of these food products. 



Several processes have been proposed for the 

 acid or alkaline hydrolysis of fish although nu- 

 tritive value is reduced either through trypto- 

 phan destruction by acid or racemization of ami- 

 no acids by alkali. A process for the acid hydrol- 

 ysis of whole fish or fish waste under pressure 

 was described in a patent by Ryan and Wilson 

 (1952). Takahashi (1941) has described the 

 hydrolysis of codfish meal with HCl and subse- 

 quent treatment of the product. 



A mild alkaline hydrolysis was used by Mo- 

 hanty and Roy (1955) to improve the functional 

 properties of an acid-washed fish protein. An 

 alkaline process has also been used to solubilize 



solvent extracted FPC (Tannenbaum, Ahern, 

 and Bates, 1970) . Use of the solubilized FPC in 

 several food products was also described (Tan- 

 nenbaum, Bates, and Brodfeld, 1970). 



The preservation and digestion of oily fish ma- 

 terial in cold aqueous alkali has been described 

 in a patent by Lovern and Hansen (1954). Hy- 

 drolysis may be completed at a convenient time 

 by raising the temperature of the digest. A pro- 

 teinaceous precipitate, removed from the aqueous 

 phase after acidification, may be stabilized by 

 water and acetone washes. The unprecipitated 

 solids may be concentrated by evaporation. 



A patent by Libenson and Pirosky (1968) de- 

 scribes the acid precipitation of lipoproteins from 

 an alkali solubilized fish slurry. The "lipid-free" 

 hydrolysate is then deodorized with hydrogen 

 peroxide and neutralized prior to concentration. 



Fish fermentation — Modification of fish pro- 

 tein through fermentation is a biological method 

 of preservation which has been used for thou- 

 sands of years. Fermented fish pastes and 

 sauces form a very important part of the diet in 

 South East Asia today. Fermentation proce- 

 dures vary locally but the more popular processes 

 and products have been described by Amano 

 (1961) and by Van Veen (1965). In some pro- 

 cesses salt is added to whole fish as a preservative 

 and the fish are liquefied by autolysis (e.g., nuoc- 

 mam produced in Viet-Nam). Other processes 

 may start with gutted fish, and the production 

 of proteases or acids by growing microbial cul- 

 tures is of prime importance. Although fermen- 

 tation does not improve the nutritive value of 

 the protein, the keeping quality of fermented fish 

 is greatly increased and organoleptic character- 

 istics are generally improved (Van Veen and 

 Steinkraus, 1970). 



Nuoc-mam traditionally contains 20% NaCl 

 and requires 6 months to a year to ferment. The 

 high salt content limits the amount that may be 

 consumed by individuals and, of course, the 

 long period of fermentation is expensive. Over 

 40 years ago a patent was issued (Kahn, 1927) 

 for the production of fish sauce in 1 to 5 days 

 using less than 10% salt. Obviously this product 

 did not have the desired flavor as the traditional 

 method is still the one in use. 



The microbiology and chemistry of Nam-pla, 

 a fermented fish sauce of Thailand, has been 

 studied by Saisithi et al. (1966). Total viable 



