Family and Consumer Sciences

Agglutinating compounds are commonly used to improve the physical quality of aquafeeds. An evaluation was done of the effect of the agglutinating compound sodium alginate on the functional properties of aquaculture fish feed produced by extrusion. Meals containing one of four sodium alginate concentrations (0,0.5, 1.5 and 2%) were extruded in a simple-screw extruder at 120 °C, 20% moisture content and a 1:1 compression ratio, extruding each treatment in duplicate. Expansion index values ranged from 1.11 to 1.12 with no differences (P > 0.05) between the diets containing sodium alginate. In contrast, the different sodium alginate levels had positive (P < 0.05) effects on water absorption index values (2.24 to 2.79 g/g), water
solubility index values (10 to 12.94%), sinking velocity (6 to 8.56 cm/s) and hardness (1.98 to 3.31 N). Maximum hardness (3.31 N) was produced in the 2% sodium alginate diet. The highest sodium alginate level tested (2%) had the most appropriate physical and functional properties for an extruded fish meal-based (62%) aquaculture fish feed.

This study aimed to analyze the calorimetric, rheological, and structural characteristics of an extruded shrimp feed mainly made out of glandless cottonseed meal as protein source and nixtamalized maize a binder to understand its behavior under extrusion processing conditions to ensure proper structure and water stability. An optimal extruded shrimp diet was formulated using 44% of glandless cottonseed meal as the main protein source. Extruded shrimp diet showed the following composition: dry matter: 95.1%, total digestible nutrients: 81.0%, crude protein: 50.5%, crude fat: 8.8%, ash: 8.9%, digestible energy: 4.0 Mcal/kg, and metabolizable energy: 3.6 Mcal/kg. The rheological analyzes showed an increase in the viscosity of non-extruded optimal shrimp feed and a decrease in the viscosity of extruded optimal shrimp feed. Scanning electron microscopy showed that starch granules were present in the optimal treatment before and after extrusion processing. Different geometries can be appreciated, but mostly spherical and ellipsoidal starch granules of ~50 μm and flat and round particles that could be proteins from glandless cottonseed meal of ~150 μm of length and ~50 μm of thickness. Confocal microscopy showed the presence of chlorophylls and significant amounts of carotenoids. Fluorescence microscopy showed darker sections of the samples that made most contact with the inner surface of the extruder’s barrel due to the Millard reaction and caramelization of carbohydrates. Differential scanning calorimetry suggests that due to an exothermic transition observed, covalent cross-links are formed in these systems, along with a swelling of starch granules and the formation of physical entanglements. The obtained results suggest that using glandless cottonseed meal as the main protein source in extruded shrimp might be a reasonable option to decrease feeding costs while showing an appropriate structure, stability, and high protein content.