From waste to resource: Potential of tomato peels for Tenebrio molitor rearing

Steady population growth and the global increase in demand for protein, both for human consumption and for animal husbandry, have necessitated the search for alternative protein sources to traditional ones. In this context, insect farming is often considered one of the most promising options. Moreover, from the perspective of a circular economy, the possibility of using waste substrates for insect growth represents an important opportunity. Tomato production and processing are among the most significant agribusinesses in Italy. In fact, our country is the third largest producer in the world, after the United States and China. In 2024, the production of processing tomatoes in Italy is estimated at 5.3 million tons. During processing, by-products and waste are generated, accounting for about 10-30% of the input mass. One of the by-products is tomato peels, composed of peels and seeds that have good nutritional properties, with a mean protein content of 16% and mean lipid content of 7%, in addition to the presence of fiber and numerous antioxidants. In this project, the use of this by-product as a growth substrate for Tenebrio molitor L. (Coleptera, Tenebrionidae), a species already approved for human and animal consumption in the EU, was evaluated. In detail, a mixture of dried tomato peels and wheat bran (1:1 ratio) was tested as a growth substrate for the larvae and compared with wheat bran alone as control. One hundred four-week-old larvae were used for each replicate, for a total of three replicates per substrate. Development time, weight gain, larval biomass, survival and substrate conversion indices were evaluated. No significant differences were shown between the two substrates in terms of survival (~95%), weight of larval biomass collected, and development time (34 days until the appearance of the first pupa). However, individual mean larval weight was greater (F(1,118)=87.24; p<0.001) with the tomato mixture (0.144±0.004g), compared with the control diet (0.096±0.003g). The conversion indices (feed conversion rate and substrate reduction) showed no significant differences between the two experimental diets. The results obtained indicate tomato peels as a possible substrate to be incorporated into the mass rearing of T. molitor. However, it is necessary to evaluate the influence of this substrate on the reproductive performance of adults. In fact, deformities have been observed in the late larval age and pupal stage, which prevented the emergence of adults or lead to deformed specimens. This could be due to the presence of pesticide residues, or the presence of anti-nutritional factors in the by-product considered. Therefore, it is crucial to pay special attention to the origin of the by-products and the possible presence of pesticide residues. This work is funded by PRIN 2022 Project InProFarm (Insect Probiotic-assisted Farming: a promising tool to enhance edible insect health and performances), grant number 2022L4NJMK, funded by the European Union - Next Generation EU.