Production of fish powder by acid hydrolysis.

HapLochromis spp. is an underutilized fish stock abundant in L. Victoria and occurring in many African lakes. Its small size and boniness make it unpopular as human food. A process for producing fish powder for human consumption from whole HapLochromis by partial acid hydrolysis was developed. Whole fish was minced and mixed with hydrochloric acid in the ratio. 30:100 v/wo The mixture was continuously stirred for 30 minutes, neutralised with NaOH to the original pH of the mince, homogenized and drum dried or spray dried. The effect of varying temperature, acid concentration and using cooked or uncooked fish as raw material on hydrolysis were investigated by determining changes in TCA-soluble N of the hydrolysate over the 30 minute period. Seven temperatures between 25 and 84cC and four acid concentrations (2.5M, 5M, 7.5M and 1l.3M) were investigated. The overall extent of hydro lysis for each run was determined by calculating the nett increase in TCA-soluble N expressed as % of total N, and it ranged between 0.8% and 10.4% and 6.7% and 34.1% for cooked and uncooked fish respectively. The extent of hydrolysis was greater in uncooked than cooked fish due to the synergistic effect of the endogenous proteolytic enzymes in uncooked fish and its absence in cooked fish. Cooking had destroyed the enzymes. Eight different products were produced. Data for crude protein, true protein, amino acid profiles, total lipid, ash, NaCl, aw, in vitro digestibility, colour, particle size distribution and sensory evaluation of the products were obtained. The data indicated the products had a high nutritional value and would be micrcbiologically stable for several months but susceptible to oxidative rancidity unless antioxidant were added. Using the data a process in which uncooked fish would be partially hydrolysed with 2.5M HCl at 48oC (approximately) for 30 minutes and the hydrolysate spray dried was proposed