Abstract
The industrial production of Tenebrio molitor L. requires optimized rearing and processing conditions to generate insect biomass with high nutritional value in large quantities. One of the problems arising from processing is a tremendous loss in mineral accessibility, affecting, amongst others, the essential trace element Zn. As a feasible strategy this study investigates Zn-enrichment of mealworms during rearing to meet the nutritional requirements for humans and animals. Following feeding ZnSO4-spiked wheat bran substrates late instar mealworm larvae were evaluated for essential micronutrients and human/animal toxic elements. In addition, growth rate and viability were assessed to select optimal conditions for future mass-rearing. Zn-feeding dose-dependently raised the total Zn content, yet the Znlarvae/Znwheat bran ratio decreased inversely related to its concentration, indicating an active Zn homeostasis within the mealworms. The Cu status remained stable, suggesting that, in contrast to mammals, the intestinal Cu absorption in mealworm larvae is not affected by Zn. Zn biofortification led to a moderate Fe and Mn reduction in mealworms, a problem that certainly can be overcome by Fe/Mn co-supplementation during rearing. Most importantly, Zn feeding massively reduced the levels of the human/animal toxicant Cd within the mealworm larvae, a technological novelty of outstanding importance to be implemented in the future production process to ensure the consumer safety of this edible insect species.
Highlights
The industrial production of Tenebrio molitor L. requires optimized rearing and processing conditions to generate insect biomass with high nutritional value in large quantities
L3–4) were fed with Zn-spiked wheat bran feed for 8 weeks; # see Table 2 for total Zn content of the wheat bran material. LWGtotal/ total live weight gain larvae; average larval weight; FC/ total feed consumption; ECI/ efficiency of ingested feed conversion; FCR/ feed conversion ratio; total feces release during rearing; FA/ feed assimilation; ECD/ efficiency of digested feed conversion; Data are shown as means ± SEM of 5 replicates
Mealworms grown in any of the Zn-enriched wheat bran materials remained highly viable until late instar, but were significantly lower in fresh weight at stage L9–10 (52.3 ± 1.6 mg Znbasal vs. 42.4 ± 1.8 mg Zn40; ANOVA with Dunnett’s post hoc test Z nbasal vs Zn40 p < 0.01), corresponding to a loss in biomass of around 20% (Table 1)
Summary
The industrial production of Tenebrio molitor L. requires optimized rearing and processing conditions to generate insect biomass with high nutritional value in large quantities. The yellow mealworm (Tenebrio molitor L., Coleoptera: Tenebrionidae) has received extensive attention because of its high macronutrient value (on a dry weight basis ∼ 55% protein, 30% lipids, 7% carbohydrate)[9] and its wide range of potential applications[10,11] This makes these mealworms ideal candidates for cultivation and processing on an industrial scale[12]. It was to be investigated to what extent this fortification impacts the larval composition in essential and toxic elements, respectively These results will be of utmost importance when aiming to improve T. molitor processing technologies, a basic prerequisite for utilizing mealworms as novel food or animal feed in the future
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