A team of researchers conducted two experiments to understand the impact of pre-gelatinized (PG) taro and broken rice for manufacturing higher quality floating fish feed pellets.
The study concluded that the use of PG taro and broken rice results in greater flexibility to fish nutritionists to produce a variety of lower cost floating pellets with less starch restriction.
The study demonstrated that relatively low levels of PG taro and broken rice had several important benefits to the characteristics of the pellets which included high floatability, durability and integrity during water immersion as well as a relatively low moisture content. These are all important considerations when producing pellets since these can reduce product wastage, transportation costs as well as improving hygiene during storage.
Further studies need to be conducted to investigate the effects of carbohydrate utilisation and digestibility in fish using PG taro and broken rice in extruded pellets.
Research
Most of the studies examined the physical quality of the fish pellets and are limited to native starch from corn, tapioca, wheat, potato, barley, taro, broken rice and sago. Although native starches have unique properties, they lack versatility to function properly in the production of floating pellets which is likely due to various interactions with the other ingredient types (protein, fiber and lipid) and their levels but also the moisture content and extrusion processing parameters.
Due to these many complex interactions, the production of floating or sinking aquafeeds requires optimization and it is crucial to understand the relationship between the ingredients, processing parameters, and equipment design and operation to develop new and quality fish pellets.
The first experiment was conducted to evaluate the effects of PG taro and extruder die head temperature(125, 140, 155 and 170 °C) and a subsequent experiment was conducted using PG broken rice instead on the physical properties of the pellets included floatability, expansion ratio, bulk density, pellet durability, water absorption and solubility, moisture content and pellet microstructure.
The fresh taro corms (Colocasia esculenta) had been purchased from a local market in Malaysia. It was washed, peeled, sliced and steamed (99 ± 2 °C, 10 min) then cooled to room temperature. It was oven dried in an electric convection oven (60 °C, 48 hours) and subsequently, grounded using a hammer mill and sieved to obtain the flour. Similarly, broken rice (Oryza sativa) was finely ground to flour.
Taro and broken rice flour were modified using a pre-gelatinization method whereby 1:1 flour solutions (1 kg flour + 1 kg deionized water) were autoclaved for 10 min (121 °C, 15 PSI). The gelatinized flour was dried in an electric convection oven (60 °C) for 48 hours and then grounded in powder using a hammer mill.
Six balanced isocaloric diets (14.65 kJ/g) were formulated to make an isonitrogenous targeted net protein of 30% with appropriate amounts of fishmeal, soybean meal, corn meal, rice bran, vegetable oil, vitamin and mineral premix, alpha-cellulose, and then using three different levels of PG taro and broken rice (15, 20 and 25% as fed basis). For each blend, the ingredients were groundand mixed using a dough mixer.
All the blends were pre-conditioned to 40% moisture content and extruded using a single screw extruder, with the barrel divided into 3 temperature zones 70,90 and 100 °C and then extruded pellets were dried in an electric convection oven (60 °C, 16 hours).
The findings showed that PG taro and broken rice inclusion levels and die temperature had significant effects on most of the physical properties of the pellets except for pellet durability index.
Changing the inclusion rate of PG taro and broken rice from 15 to 25% significantly increased the expansion ratio and floatability of the extruded pellets. Similarly, as the die temperature was elevated in both experiment, the floatability of the extruded pellets in diet containing PG taro and broken rice increased by 114.62% and 21.88%, respectively.
It was also noted that use of PG taro and broken rice resulted in highly durable pellets in all treatments.
Further, microstructure analysis of the extruded pellets revealed that using PG taro and broken rice, the surface of the extruded pellets became coarser when the die temperature was elevated from 125 to 170 °C and the PG taro and broken rice inclusion level was at 15%.
In conclusion, pre-gelatinized taro and broken rice could be used to manufacture higher quality floating pellets.
Source: Animal Feed Science and Technology
