PROCESSING OF TILAPIA WASTE PROTEIN HYDROLYSATES AND DIGESTIBILITY OF NUTRIENTS AND ENERGY AT DIFFERENT TIMES OF HYDROLYSIS  

The aim of this work was to study the processing to optimize the use of Nile tilapia waste in different hydrolysis methods, acid (A) or fermented (F) with different raw material, viscera (V) or total waste (T - head, viscera, fins and spine), and to evaluate the apparent digestibility coefficient of crude protein, lysine, methionine and gross energy in different times of hydrolysis. The acid hydrolysates were produced with the addition of 3% phosphoric acid and 2% acetic acid and the fermented with the addition of 15% (w/w) sugar cane molasses, and 5% (w/w) of Lactobacillus sp, to produce lactic acid. A reference diet was formulated and pelletized reaching the nutritional requirements for Nile tilapia. Twelve test diets were produced containing 69.5% of the reference diet, 0.5% of chromium oxide III (Cr₂O₃) and 30% of protein hydrolysate in three different times (VA 24, 72 and 144; VF 24, 48 and 120; TA and TF 24, 96 and 192 hours).

Three hundred eighty four juveniles (15±1,3g) were distributed in 32 tanks with total capacity of 150 liters each. Fish received the test diets until apparent satiation three times per day. On the morning of collecting period (after one hour of the first feeding) fish were transferred to the feces collectors. The fish feces were collected every 30 minutes. The chromium III oxide concentrations in the diet and feces were determined by nitro-perchloric digestion. Means of ADC values were subjected to one-way ANOVA and Tukey multiple range test (p<0.05) analysis. The results of the protein hydrolysates ADC of crude protein, lysine, methionine and gross energy are shown in Table 1.

The apparent digestibility coefficients of crude protein, lysine, methionine and gross energy tend to decrease with time hydrolysis. These low results on digestibility may be due to the high proportion of free amino acid.