As in other agriculture industry, the olive and olive oil industry produce large number of by-products. One of the solutions to fully utilized olive oil by-products is by using it as an ingredient in animal feed including fish. This review was done to look into the opportunities and challenges of using olive oil by-products in the aquafeed industry.
Olive oil sources
In order to get olive oil, oil extraction was carried out by an extraction process conditions using an oleodosor system. Conventionally, the method of extraction involves three major steps; crushing, malaxation and centrifugation.
Malaxation process involved wide range of temperature from cold to high temperature. There are five types of olive oil produced from different phase of olive fruits and temperature which namely extra virgin olive oil (EVOO), virgin olive oil (VOO), refined olive oil (ROO), pure olive oil (POO) and olive pomace oil (OPO). Different types of olive oil have different content of composition.
Effects on the carcass composition
In fish, besides geographic location, age, sex and maturity, the feed it consumed is regarded as one of the primary factors that influence its carcass composition. By formulating and establishing feed with certain ingredients and nutrients, farmers can produce fish with desirable and better carcass composition to fulfil human consumption needs.
Overall, olive oil by-products have different effects on fish carcass composition depending on the type of by-products and fish species. Most of the study reported on fatty acid composition compared to carcass/ muscle proximate analysis.
In terms of proximate analysis, it was found that the muscle of juvenile African catfish fed with feed containing 9% and 3% olive pomace oil with and without L-carnitine has higher lipid content compared to controls.
Mixed results were also seen in the FA analysis of fish fed with olive oil by-products. Among all olive oil by-products, olive pomace has shown to have impacted the FA amount in the fish species tested.
For olive pomace oil (OPO), it was found that it decreases most FA in the muscle/fillet of African catfish. In gilthead seabream, OPO seems to only significantly increase only one FA (saturated FA (16:0)). Compared to other olive oil by-products, olive leaf powder (OLP) is the least tested product in terms of studying the impacts on fish carcass/muscle.
Effects on the growth performance
Several previous studies reported that the antioxidant content on olive oil extract can affect the growth performances of sea bream. The growth rate a performances of fish is normally related with improvement in humoral, mucosal immune parameters and antioxidant enzymes activities.
Improvement in growth performance parameters is recited to be attributed of immune nutritional constituent such as polysaccharides as complex sugar.
However, since an olive product is categorized as herbal plant, the higher herbal extract inclusion level has been reported to give a negative effect on the fish growth performances because of the higher concentration of antinutritional factors (ANFs).
Thus, to make the olive product more acceptable in aqua feed, more research was needed to be highlight on ANFs compound to reduce the negative effect on growth and health performances of fish.
Effects on the feed utilization
When oil is extracted from olives, a waste product called waste olive cake is generated. It is composed of olive pulp, skin, stones, and water. The olive pomace may be an effective protein source for feed formulation, especially nowadays with the increased of focus on cost reduction and value added of agroindustrial waste.
Furthermore, in addition to its high phenolic content, olive pomace also contains vitamins such as tocopherol, hydrocarbons such as squalene, and sterol compounds such as sitosterol, all of which have significant nutritional and physiological benefits for animals.
“A study conducted by Serra et al. (2017) revealed that inclusion of olive pomace in swine diets had potentially reduced the lipid oxidation in the sausage which also improved the fatty acid composition.”
As the olive pomace meal is utilized as a feed component in tilapia diets, it has the potential to aid in the development of more cost-effective feedstuffs.
Nutritional olive pomace meals are natural by-products that are available at a low cost and are not genetically modified. It was determined that substituting wheat bran with olive waste at a level of more than 25% in tilapia diets considerably affected their growth performance as well as their efficiency in utiliszng their feed.
The poor development performance of tilapia found with increasing amounts of olive pomace in their diets could be attributed to a combination of factors, including high dietary fiber content as well as deficiency in certain amino acids, specifically methionine.
“A previous study found that utilizing olive pomace meal and olive waste oil in sea bass diets instead of fish meal and oil resulted in significantly lower feed conversion ratios (FCR) and lowered specific growth rates.”
The low growth performance of sea bass could be linked to the species’ limited metabolic capabilities. Additionally, Nasopoulou et al. (2011) revealed that olive pomace as a partial substitute for fish oil in gilthead sea bream, reported that feeding olive pomace to the fish leads to an enhancement in the fish’s potential to suppress atherogenesis.
These improvements may indicate that the fish’s immune system is being strengthened, with positive effects against various diseases and long-term stressful pressures.
Effects on the intestinal health and microbial diversity
Olive oil by-products have been used as partial replacement of fish oil in aquafeed due to its benefits on intestinal health and microbial diversity. Moreover, olive oil by-products or extra virgin olive oil diet also have shown anti-inflammatory activity where its derivatives such as hydroxytyrosol, tyrosol and oleuropein were mostly found in the lumen of the intestine.
“The olive extract was previously used to produce digestible biofilm which demonstrated antibacterial properties against Escherichia coli and Staphylococcus aureus. Apart from that, olive oil by-products could stimulate the growth of fish gut microbiota such as Lactobacillus acidophilus which has been reported as good candidate as probiotics.”
Aside from anti-inflammatory properties, bioactive compounds such as oleuropein and hydroxytyrosol are also known as potential candidates that could balance the gut microbiota diversity. The gastrointestinal microbiota composition is vital for gut health and nutrient absorption in improving fish growth performance.
Effects on the immune response
The fatty acids from refined olive pomace oil such as oleic, linoleic, stearic, palmitic, palmitoleic acids and other bioactive compounds are beneficial for immune modulation and can be used as prophylaxis against infection when added into diet.
High composition of antioxidants in the olive oil by-products might contribute to the improvement of immune status of fish by reducing the oxidative stress. Oxidative stress is known to reduce the efficiency of innate immune response in fish that make fish more susceptible to diseases.
Effects on the antioxidative capacity
For a food safety perspective, the use of natural antioxidants in fish feeds is increasing in recent years. To avoid undesirable side effects from the use of synthetic antioxidants, researchers are focusing on several natural compounds.
It has been the fruit, leaves and oil of olive trees are significant sources of polyphenols. Olive leaves contain important natural phytonutrients like oleuropein and oleanolic acid.
Many beneficial effects have been noticed due to the presence of antioxidant properties of olives, olive oil and olive mill vegetation water. In addition, it was observed that pomace olive extract had an excellent antimicrobial character, which was in consistence with its total phenolic, flavonoid and antioxidant activities.
Moreover, its extract consisted highly of bioactive components that reduced toxigenic fungal growth and mycotoxins.
Effects on the disease resistance
As aquaculture industry is heading toward to intensification, the industry development was hindering with fish diseases problem. The recent studies and findings revealed olive leaf extract (OLE) have huge potential as immunostimulant agent for aquaculture uses.
“These findings showed olive by-products extract possess immunostimulant property where can increase immune system of commercial farmed fish to resistant various diseases infection.”
Olive leaf is olive oil by-products and considered as cost less raw material for medical and nutritional uses. Hence, methanol solvent can be widely used in preparing OLE for aquaculture uses in the commercial scale. There is huge potential of olive by-products can be used in fish health management.
This statement was supported by several recent studies and findings. Further study need to be carried out in order to upscale recent findings for mass production before it can come to a commercial sense.
Conclusion and future perspectives
Each of olive by-productswhich include olive cake, olive leaves and branches, or vegetative waters, offers a nutritious value that, while minor, should not be overlooked. These by-products can and should be employed in animal feed to a greater extent. The antioxidant, antibacterial, antimicrobial, antioxidant, antifungal and anti-oxygenic properties were discovered in the olive by-products, which improved the intestinal health and immune response of fish.
The presence of olive by-products in the fish feed also had no deleterious impact on the growth performance. Taking into account the benefits reported here, olive by-products have the potential to be employed in aquafeed, albeit a system for purifying and extracting important polyphenols remains to be developed.
More research is required to improve the quality of animal products by incorporating olive by-products into their diets.
This is a summarized version developed by the editorial team of Aquaculture Magazine based on the review article titled “OLIVE OIL BY-PRODUCTS IN AQUAFEEDS: OPPORTUNITIES AND CHALLENGES” developed by: MOHD KHALID HAZREEN-NITA, University Malaysia Kelantan, Malaysia, ZULHISYAM ABDUL KARI, University Malaysia Kelantan, Malaysia, KHAIRIYAH MAT, University Malaysia Kelantan, Malaysia, NOR DINI RUSLIA, University Malaysia Kelantan, Malaysia, SUNIZA ANIS MOHAMAD SUKRI University Malaysia Kelantan, Malaysia, HASNITA CHE HARUN, University Malaysia Kelantan, Malaysia, SEONG WEI LEE, University Malaysia Kelantan, Malaysia, MOHAMMAD MIJANUR RAHMANA, University Malaysia Kelantan, Malaysia, N.H. NORAZMI-LOKMAN, University of Tasmania, Taroona, Tasmania, Australia, Universiti Malaysia Terengganu, Kuala Terengganu, Terengganu, Malaysia, MANSOR NUR-NAZIFAH, International Islamic University Malaysia, Bandar Indera Mahkota, MOHD FIRDAUS-NAWI, International Islamic University Malaysia, Bandar Indera Mahkota, MAHMOUD A.O. DAWOOD Kafrelsheikh University, Egypt, The American University in Cairo, Egypt.
The original article was published on DECEMBER 2021, through AQUACULTURE REPORTS under the use of a creative commons open access license.
The full version can be accessed freely online through this link: https://doi.org/10.1016/j.aqrep.2021.100998