Comparison of chemical composition of different agro-industrial by-products.
Agro-industrial by-products are processed materials that can have high protein content or other nutrients. The agro-industrial by-products are traditionally sold at low prices for animal feed consumption. These residues of the agro-industry have a high concentration of nutritional and bioactive compounds, which can be applied as fishmeal substitutes. In this chapter, it is shown how extrusion can be an alternative process for aquaculture feed production, increasing digestibility, and functional properties of the aquaculture feed, such as water stability and floatability. The thermal process during extrusion decreases the antinutritional factors present in legumes or other agro-industrial by-products, such as trypsin inhibitors and lectins. This chapter reviews research related to new protein sources that can potentially complement or substitute fishmeal for aquaculture feed. The use of bean (Phaseolus vulgaris) protein and cottonseed meal as a fishmeal substitute are shown, as well as the optimization of the extrusion process for aquaculture feed production. The incorporation of plant protein into the aquaculture production contributes to a more sustainable process. The effect of the extrusion parameters on the final product and quality are explained.
- cottonseed meal
- functional properties
The Food and Agriculture Organization (FAO) considers that about 16% of the consumed animal protein comes from fish proteins . With increasing population, demand for fish consumption will increase. Aquaculture is a good alternative for wild fish production. Aquaculture is a growing economic activity with estimated sales in the USA in 2013 of $1.3 billion dollars . About 43% of the world’s fish production has increased in farms and has been increasing in the past decade, especially in Asia and Africa . Worldwide the aquaculture production grew in 2013 to 97.2 million tons (live weight), with a value of 157 billion US dollars. Asia is the major aquaculture producer in the world. Aquaculture production, such as that of finfish and crustaceans, requires a high amount of fishmeal . Fishmeal represents about 60% of the cost of aquaculture feed and is also a limited resource. The world market consumes about 68% of fishmeal for aquaculture products, such as shrimp, trout, salmon, and other species , and it is expected to grow in the next decades. Several investigations have looked into the use of alternative protein sources that could either supplement or substitute for fishmeal. Agro-industrial by-products have been successfully used for animal feed , but can also be applied in aquaculture.
Soybean has been successful to a certain point as a substitute for fishmeal as a protein source for different aquaculture species. Reports show the use of soybean in feeding trout and shrimp. About 47% of world soybean production is GMO-soy . Up to 69% soybean in the global market is genetically modified, while 85% of the soy produced in the USA is genetically modified. Consumers are also looking for nonGMOs for consumption. Different legumes represent an alternative source of protein usable for aquaculture feed. Agro-industrial by-products have high protein concentration and are sold at low cost for animal feed. Bean (
Extrusion applies high-temperature in short processing times. Extrusion is an alternative for feed production, increasing digestibility, and functional properties of the aquaculture feed, such as water stability and floatability. The thermal process during extrusion decreases the antinutritional factors present in legumes or other agro-industrial by-products, such as trypsin inhibitors and lectins . The chapter reviews agro-industrial by-products than can substitute or complement fishmeal for aquaculture feed. The optimization of the extrusion process for aquaculture feed production is discussed.
2. Chemical composition and diet requirements in extruded aquaculture products
Agro-industrial by-products are processed materials, where some of the main compounds have been either extracted or are products that do not comply with certain quality requirements. The oil extraction industry produces by-products with high protein, while distillery by-products have less sugar after fermentation, but high protein concentrations. The bean (
The agro-industrial by-products are traditionally sold at low prices for animal feed consumption. These residues of the agro-industry have a higher concentration of nutritional and bioactive compounds, which can be either used as supplements in functional foods or extracted and used for nutraceuticals. After oil extraction, soybean meal, canola meal, and flax seed meal contain high concentrations of proteins, minerals, and fiber. The brewing and distillery industry also offers by-products with high protein concentration. Cottonseed meal is obtained after oil extraction from the cottonseed. Glandless cottonseed has a low concentration of gossypol and is suitable for consumption by humans as well as livestock and aquaculture products. The levels of gossypol present in glandless cottonseed meal are not toxic for monogastric animals. The concentration of protein in glandless cottonseed meal (GCSM) can be up to 55%, which is more than 100% protein increased, compared to the cottonseed. GCSM has more protein than canola meal and is comparable to soybean meal (Table 1). Soybean seeds can have 40% of protein , but its content increases after oil extraction. Cottonseed meal has low starch content and a high mineral content, which makes it an excellent complement for aquaculture feed. Small and cracked beans do not have the required quality for consumer acceptance, but have a high protein and starch content (Table 1). Although the protein content is lower than other agro-industrial by-products presented in Table 1, the high starch content makes it more suitable for extrusion than by-products with low starch content. The extruded bean flour can be used for human and animal consumption, as well as for the aquaculture feed industry. The extrusion process totally inactivates the trypsin inhibitors and lectins in the bean flour .
|Product||Fat (%)||Crude protein (%)||NFE (%)||Mineral content (%)||Crude fiber (%)|
|Flax seed meal4||2.2||38.9||46.6||7.0||5.3|
|Cottonseed meal2||12.6||41.03, 55.3||8.2||7.8||1.0|
Legumes have high protein content, and can potentially substitute for fishmeal. Bean flour can substitute for fishmeal in aquaculture feed. A balanced aquaculture feed should contain proteins and essential fatty acid, normally from fish oil, minerals, and vitamins. Aquaculture feed contains about 62% fishmeal, 20% wheat flour, 20% fish oil, 3.4% milk whey, 2.1% vitamins and minerals, and 0.5% choline chloride for cell function and structure (Table 2). The use of plant proteins should supply enough proteins to cover the nutritional requirements of the aquaculture products. Fishmeal is a limited resource, but alternative protein sources can substitute for fishmeal in aquaculture diets.
|Composition||Fish meal||Bean flour concentration||Soy protein concentrate|
|Soy protein concentrate||–||–||–||–||9.3||18.6||27.9|
|Vitamin and minerals||2.0||2.0||2.0||2.0||2.0||2.0||2.0|
3. Hardness and functional properties of extruded products
Hardness, Water Absorption Index, and Water Solubility Index are essential functional properties of aquaculture feed. The feed should have a certain hardness for the trout or shrimp to be able to eat it. The hardness of the extruded product depends on extrusion moisture and extrusion temperature. High extrusion temperature and high moisture content result in a hard extruded product. Softer products are the result of extruding at low temperatures and high moisture content (Figure 1). Aquaculture feed products need a specific Water Absorption Index (WAI) to facilitate consumption, while the Water Solubility Index (WSI) correlates well with the stability of the feed in an aqueous environment. The extruded products need to be stable in the water; a high WAI also produces a high WSI of the extrudates. Studies show that extruded products with lower WSI are obtained at low extrusion temperatures and low moisture content, which also produces harder extruded products. If we compare Figures 1 and 2, we can conclude that although crystallinity is lower in the product extruded at higher temperatures, the hardness tends to be high. The results indicate a probable high degree of denaturation, where proteins unfold, allowing protein to restructure into harder structure.
4. Extruded bean flour
Studies show that with a fishmeal substitution of 15, 30 and 45% bean flour or soy protein, there are no significant (
|Extruded diet||Fat (%)||Crude protein (%)||NFE* (%)||Mineral content (%)||Dry matter (%)|
|With fish meal1||16.9bc||48.7a||29.2a||12.9b||91.7b|
|With 15% bean flour1||18.8d||41.9a||27.8a||11.4b||91.6b|
|With 30% bean flour1||16.7ab||40.9a||24.1a||10.4b||91.9bc|
|With 45% bean flour1||16.4a||38.7a||35.0a||9.7a||92.5b|
|With 15% soy protein2||17.7c||40.9a||32.4a||8.9a||92.6a|
|With 30% soy protein2||15.9a||42.2a||32.2a||9.5a||92.4ac|
|With 45% soy protein2||16.0a||45.3a||29.5a||91.9a||92.3ac|
Another quality parameter in aquaculture feed is the sinking velocity of the product. The sinking velocity of the aquaculture feed is different for each aquaculture species. Some fish requires slow sinking feed that will resemble the movement of small fish or other living organisms. In the case of shrimp, the feed should sink to the bottom of the ponds for better use. Extrusion temperature affects (
The independent variables to be considered in aquaculture extrusion are temperature, moisture content, and screw speed. Based on the independent variables and the dependent variables (Expansion Index, bulk density, and sinking velocity), in which the EI should be between 0.88 and 1.11, the bulk density ranges between 0.55 and 0.97 g/cm3 and the sinking velocity is required to be between 2 and 6.2 cm/s. The best extrusion conditions with a single laboratory extruder (Brabender, Germany) are 120°C, 22% moisture content at a screw speed of 140 rpm with a diet formulation containing 62% fishmeal and no vegetable protein. Diets containing 15 and 30% bean flour require less moisture (18%), but the same temperature and screw speed, to obtain an optimum aquaculture feed. Diets containing 45% bean flour and 15% soy protein are best extruded at 120°C and 18% moisture at a lower screw speed (80 rpm). The lower mineral content appears to affect in this case the screw speed. A sharp increase in soy protein concentrate of 30 and 45% requires high extrusion temperatures of 135 and 150°C, respectively. Extrusion of 30% soy protein requires 20% moisture content and a screw speed of 110 rpm. The moisture requirements are also high (22%) as well as the screw speed (140 rpm) for extrudates with 45% soy protein concentrates.
The specific mechanical energy (SME) is the necessary energy in the form of work in the extrusion process. In aquaculture feed, the SME is affected (
5. Starch pregelatinization
Pregelatinized and not pregelatinized starch has been added to balanced aquaculture feed to study the effect of pregelatinization on the functional properties of the extrudates. The studies have shown that pregelatinization of starch before extrusion has a positive effect (
Nixtamalization can also be used to pregelatinize starch. Nixtamalization is a traditional thermal treatment used for corn products in North and Central America, where corn kernels are cooked with CaOH, resulting in a pregelatinized dough suitable for extrusion. Figure 7b shows pregelatinized corn kernels, where the center of the kernels appears to be enzymatically degraded during the steeping time of the process. Figure 7a shows a bean starch kernel before extrusion, while Figure 7c shows the structural matrix of extruded bean/corn flours. Again we observe the protein structure, but also partial gelatinization of the starch kernels. Different raw material influences the final product characteristics. Crystallinity represents the structure arrangement and is mostly related to the starch structure in the kernel. Although corn has a higher starch content (about 65.5%) , than bean flour (51.9%), bean flour shows a higher crystallinity than nixtamal (Figure 8). Extrusion decreases crystallinity because of the gelatinization of the starch kernels, but the temperature and moisture content during extrusion also affect the percentage of the crystallinity of the extruded product. The crystallinity of the extruded product is related to the retrogradation of the starch. Low extrusion temperatures produce the lowest crystallinity of the end-product probably because of the lower degree of gelatinization. High extrusion temperatures yield a low crystallinity because of starch dextrinization during extrusion and lower retrogradation.
6. Feeding trials of extruded aquaculture feed
Studies of extruded trout feed show a final weight decrease (
The condition factor or coefficient of condition
7. Color of extruded bean flour aquaculture feed
The L* values describe the lightness of the color of the sample on a scale of 0–100, where 0 = black and 100 = white. On the other hand, the a* values if positive (0–60) are related to a reddish color of the extruded product, if the a* values are negative (0–60), the feed tends to be greener. The closer the values are to zero the more the color tends to be neutral. The values with the highest (
8. Effect of extrusion on bioactive compounds
The effect of extrusion moisture and temperature on the antioxidative capacity and bioactive compounds in bean/corn extrudates is shown in Table 4. Neither extrusion temperature nor extrusion moisture had an effect (
|CUPRAC (µM Trolox equivalent/g)||−368.566||1.089||37.097||−2.83E–3||−1.060||−0.011||0.116|
|Flavonoids (mg Catechin equivalent/g)||−288.451||1.754||17.586||2.91E–3||−0266||−0.049||0.157|
|Polyphenols (mg Gallic acid equivalent/g)||−184.111||1.133||11.783||−2.07E–3||−0.209||−0.027||0.114|
9. Extruded cottonseed meal
The use of cottonseed meal (CSM) in extruded snacks can double the amount of protein with just an increase of 10% CSM . The protein concentration of an extruded snack can enhance from 6.4 to 12.8% when 10% CSM was added to the formulation. Table 1 shows the protein content of different agricultural by-products and their chemical composition.
The difference in chemical composition changes the chemical and physical structure, the extrusion properties, and the functional properties of the final product. Figure 12 shows two extruded samples. Figure 12a illustrates the structure of extruded corn masa, with a low protein content and a high starch content. It can be seen how layers of starch are built to provide expansion to the extruded product. On the other hand, Figure 12b shows the matrix of extruded cottonseed meal, which has 12.8% of protein. The flat, homogenous layers are gone, and a more irregular structure is present. It appears as if the protein breaks up the continuous starch structure and builds a less homogenous texture. The lower concentration of starch and the presence of more protein produce a more compact structure, which has a Lower Expansion Index and a harder crispier structure. The increase of protein content in extruded corn/cottonseed meal products reduces (
Extrusion shows restructuring of cottonseed meal. Figure 13a shows a heterogeneous structure before extrusion and a homogenous structure after extrusion (Figure 13b). Lambda scan microscopy of extruded products shows different scans between samples with and without cottonseed meal (Figure 14). The extruded samples with cottonseed meal show a second pick at about 670 nm (Figure 14b), which is not shown in the samples without cottonseed meal (Figure 14a).
This work was supported in part by the USDA National Institute of Food and Agriculture, Hatch project 1010849. This work was also supported in part by the Cotton Incorporated, USA project 126758.