Influence of geographic location, emergence season and degutting method on quality of gonimbrasia belina

Abstract

Edible insects such as Gonimbrasia belina (mopane worm) consumption contributes to the sustainable supply of protein and other nutrients (iron and zinc) for low socio-economic communities. Moreover, mopane worms are a potential source of bioactive compounds such as phenolic compounds, which have antioxidant properties. However, the nutritional composition of foods of animal and plant origin is affected by different factors, including processing method, emergence season and sourcing geographical area though the above factors are cited as affecting the nutritional composition of edible insects, and there is limited information about their specific effects on mopane worm for full utilization of the resource. Mopane worms are bivoltine, producing two generations per rainy season which is also postulated to affect their nutritional value. Effects of emergence season, geographic location, and pre-processing techniques on their nutritional composition are relevant for dependable usage of mopane worm. The acceptance of mopane worm by consumers and its contribution to food security is well studied. However, there is still a knowledge gap in terms of food safety and anti-oxidant properties associated with this edible insect. Finding an answer to these areas has many implications; from enhancing the productivity of mopane worm and to developing better strategies of utilization of this important natural resource. In this study, the influence of geolocation and emergence season on mopane worms' nutritional composition was investigated. Proximate, mineral composition and fatty acid profile were analysed on degutted mopane worm samples collected over two mopane worm emergence seasons (November to December 2020 and 2021, April to May 2021, from three locations in Gwanda district, Zimbabwe. A further analysis on the effect of degutting method on the mopane worm's proximate composition, antioxidant capabilities, chemical, and microbial safety was conducted. Natural degutting process is when mature mopane worm remove their gut contents before they burrowing in the soil. Manual degutting process is when actively feeding mopane worm’s gut is pressed outside in order to remove the gut contents. Crude protein was determined by Kjeldahl method, crude fat by Soxhlet extraction, ash by incineration in a muffle furnace and crude fibre by chemical digestion followed by ashing. Mineral and heavy metal content was determined on an Atomic absorption spectrophotometer after wet ashing. Phosphorus was determined calorimetrically on a UV-visible spectrophotometer. Total phenolic content was determined by the folin-ciocalteau assay whilst the total flavonoid content was determined by the aluminium chloride assay. The crude protein content of mopane worms ranged between 52.5±0.21 v

and 59.9±0.18 % DM and differed significantly (Bonferroni-correction α < 0.002) (p<0.05) between seasons, location and degutting method. Naturally degutted mopane worms had higher crude protein than manually degutted samples. Depending on the season, location, and degutting method, mopane worms' fat content varied considerably (Bonferroni-correction α < 0.002) (p<0.05) between 12.1±0.06 and 19.0±0.05 % DM. Season, location, and degutting technique all had a significant (Bonferroni-correction α < 0.002) (p<0.05) impact on the mineral content of mopane worms. Potassium (1195.3±0.4 – 1759.9±0.2), magnesium (104.6±0.3 – 225.5±0.3) and calcium (51.2±0.4 – 145.5±0.3) were the most abundant macro-elements (mg/100g DM), whilst iron (10.6±0.2 – 21.6±0.2) and zinc (12.7±0.1 – 17.9±0.4) were the most abundant micro-elements (mg/100g DM). Manually degutted samples had significantly higher (p<0.05) concentrations of zinc (16.1±0.3 mg/100g) and phosphorus (610.0±3.4 mg/100g). Mopane worm fat was found to contain high concentrations of oleic (ω-9) and linoleic (ω-6) and palmitoleic (ω-7) fatty acids using an Attenuated Total Reflectance Fourier-Transform Infrared Spectroscopy (ATR-FTIR). The antioxidant activity against the DPPH radical (53.8±1.4 %), ABTS radical (97.8±0.18 %), Fe2+ metal chelating activity (56.6±0.01 %), PFRAP (0.25±0.01), total phenolic content (740±2.4 mg gallic acid eq/100 g) was high for naturally degutted samples, whilst total flavonoid content was high in manually degutted (16.8±0.02 mg QE/100g). However, samples that were naturally degutted exhibited a larger microbial load (TBC, coliforms, E. coli, as well as yeast and moulds) than samples that were manually degutted (p<0.05). S. aureus, Salmonella spp and heavy metals were not detected in naturally and manually degutted samples. The results showed that mopane worms can be used as an alternative protein source and a strong source of antioxidants. Harvesting mature mopane worm (naturally degutted) has an advantage of ensured high levels of macro and micro-nutrients and antioxidants but poses a great risk in terms of microbial safety. These results also suggest that mopane worm, could have a substantial role in reducing protein, zinc, and iron deficiencies in target communities.