Use of edible insects' chitosan to improve shelf-life and safety of bread
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Chitosan is a natural fiber with antimicrobial properties and has been used as an ingredient in food products. However, information on the extraction of quality chitosan from edible insects, its application as a natural preservative and its impact on nutritional value of bread has received limited research attention. This study evaluated extraction and characterization of chitosan from desert locusts (Schistocerca gregaria), house crickets (Acheta domesticus) and appendages of the long-horned grasshoppers (Ruspolia differens). The effect of chitosan extracted from appendages of the long-horned grasshoppers on the nutritional values, shelf life and safety of bread was evaluated. The shelf-stability, proximate analysis, and consumer acceptability of bread fortified with chitosan compared to bread without chitosan “control” were determined. The results from this study showed that desert locusts had the highest chitin yield (30.6%) followed by the appendages of long-horned grasshoppers (27.6%) and house crickets (5.9%). The moisture content of chitin from long-horned grasshoppers’ appendages, house crickets and desert locusts was 6.3%, 4.0% and 2.3% respectively. The ash content of extracted chitin was 0.3%, 0.6% and 0.4% for desert locusts, house crickets and long-horned grasshoppers’ appendages respectively. However, the chitosan yield of the long-horned grasshoppers’ appendages (47.3%) was higher than that of the desert locusts (37.0%) and house crickets’ chitosan (27.4%). The solubility in 1% acetic acid of chitosan was 91.3% for house crickets compared to 100.0% for both the desert locusts and appendages of long-horned grasshoppers. The degree of deacetylation of extracted chitosan was recorded 81.5%, 81.3% and 81.2% from the appendages of long-horned grasshoppers, desert locusts and house crickets respectively. The pH value of house crickets’ chitosan was (pH = 8.9) and (pH= 8.8) for both the desert locusts and long-horned grasshoppers’ appendages. The inclusion of chitosan extracted from the appendages of the long-horned grasshopper to bread significantly (p<0.05) increased the amount of crude protein (from 9.5% to 10.7%) and fiber (from 2.7% to 10.0%) content, and reduced the moisture (from 34.7% to 31.5%) and carbohydrate (from 83.5% to 75.2%) as chitosan concentration increased. The shelf life of bread enriched with 3% of chitosan indicated a significant decrease in the total plate count and total yeasts and molds in both room (25 oC) and refrigerated (4 oC) temperature conditions at day one and day 5 after baking. After one day of storage of bread, at both 25 oC and 4 oC, total plate counts decreased from 1.4 log cfu/g for bread without preservative to 0.0 log cfu/g for bread with 3% chitosan and from 0.8 log cfu/g for bread without preservative to 0.0 log cfu/g for bread with 3% chitosan respectively. Total yeasts and molds were not detected at both temperature storages. At day 5 of storage, total plate count was decreased from 6.4 log cfu/g for bread without preservative to 5.8 log cfu/g for bread with 3% chitosan at 25 oC and from 2.0 log cfu/g for bread without preservative to 0.4 log cfu/g for bread with 3% chitosan at 4 oC. Total yeasts and molds was decreased from 0.9 log cfu/g for bread without preservative to 0.0 log cfu/g for bread with 3% chitosan at 25 oC and from 1.3 log cfu/g for bread without preservative to 0.0 log cfu/g for bread with 3% chitosan at 4 oC. Sensory testing results further revealed that the 3% chitosan enriched bread had lower preference for color (from 7.9 to 5.9), texture (from 7.1 to 6.1) and overall acceptability (from 7.3 to 6.3) compared to the bread without chitosan. The findings of this study demonstrate that insects are potential and promising natural source of chitosan, and it inclusion to bread does not negatively affects the sensory preference and acceptability of consumers but extends the shelf life, improves nutritional value and safety of bread. The role of insect-based chitosan in bread justify the opportunities for future investments and engagement with policy makers, public private partnership that would lead to enhanced sustainability in the production of natural preservatives for the food industry, particularly in low- and middle-income countries.