Use of rice by-products for production of the Tenebrio molitor larvae: emphasis on the fatty acid profile

The objectives of this study were to assess the ability of Tenebrio molitor larvae to biotransform by-products from rice processing enriched with 1% flaxseed oil into high-nutritional value food and to obtain oil from T. molitor larvae with a fatty acid profile suitable for future application in animal nutrition. Larvae of T. molitor were cultured on seven experimental diets, including four diets composed of rice processing by-products enriched with 1% flaxseed oil (rice husk, rice cleaning residue, whole rice bran, and defatted rice bran), and three control diets (chicken feed, wheat bran in combination with yeast (in a 9:1 ratio) with the addition of 1% flaxseed oil, and wheat bran in combination with yeast (in a 9:1 ratio) without flaxseed oil). The addition of 1% flaxseed oil aimed to improve the larvae’s fatty acid profile. Growth and larval survival were assessed during the experimental period. The larvae were analyzed for dry matter, ash, protein, fat levels, and fatty acid profiles. Larvae fed diets containing wheat bran with oil (111.9 ± 5.2 mg) and wheat bran without oil (111.6 ± 1.9 mg) exhibited significantly higher final weights than the rest of the dietary treatments, followed by larvae fed diets composed of rice cleaning residue (75.8 ± 2.2 mg) and chicken feed (67.8 ± 7.0 mg). The remaining treatments showed significantly lower weights. Survival rates were similar among treatments, being equal to or greater than 90%. Protein content ranged from 39.3% to 49.1%, while lipid levels varied from 23.3% to 39.4%. The fatty acid profile differed significantly among treatments. Linoleic acid (C18:2n-6) was the predominant polyunsaturated fatty acid (PUFA), with the highest concentration observed in larvae fed chicken feed. Higher levels of polyunsaturated fatty acids (PUFAs) were found in larvae raised on whole rice bran. The highest omega-6 content was found in the larvae reared with chicken feed (24.1%), while the highest omega-3 content was found in the treatment with whole rice bran (6.1%). The omega-6/omega-3 ratio varied significantly among the treatments, reaching 42.9 in the treatment with rice cleaning residue, while in the whole rice bran treatment, the ratio was 3.5. Moreover, in wheat bran treatments, the addition of 1% flaxseed oil reduced the omega 6/omega-3 ratio from 29.1 to 8.9. The growth results of the current study demonstrate that among the tested rice by-products, the best outcomes were obtained with rice cleaning residue. However, the most favorable fatty acid profile for future application in animal nutrition was achieved with whole rice bran enriched with 1% flaxseed oil.