House cricket (Acheta Domesticus) processing for food applications : focusing on drying and milling

Edible insects, such as house crickets (Acheta domesticus) are environmentally friendly, nutritious and safe alternative to meat, when special details such as allergenic potential and antinutrients are considered. The goal of this Master’s thesis is to study the processing methods and parameters of house cricket in creating flour for food applications that is safe and of optimal quality. The thesis hopes to provide a reference for parameters used in house cricket drying and milling, with the equipment available. Furthermore, the goal is to study the optimal time to get below critical value in water content of 10 % and within critical values in water activity of 0,25-0,45 with an oven and a freeze-dryer. The samples within the critical safety values with minimal drying time are then milled with centrifugal mill with two different sieve-sizes and particle size distribution is measured and compared between oven-drying and freeze-drying, the two sieve-sizes and to reference flours. Particle size range of 45-150 μm was used as a goal. Optimal measured drying time at T=70 °C for oven-drying was 5 hours. For Freeze-drying at Tp=25 °C, Tc=-87 °C, p=1 mbar was 6 hours. Of the optimally dried samples, Oven-dried sample milled with 0,5 mm sieve size had the lowest mean and median particle size followed by Freeze-dried sample milled with 0,5 mm sieve size. The 5-hour Oven-dried sample milled with 0,5 mm sieve size was thus the closest to the optimal product, because it had the smallest particle size from all the samples with minimal drying time. Samples milled with 1 mm sieve size had coarser mean and median particle size similar to that of the reference samples obtained from the industry. Furthermore, it can be concluded that compared to reference flours, finer house cricket flour can be milled with 0,5 mm sieve size. On the other hand, 1 mm sieve size with the particular centrifugal mill used yields a flour with similar coarse particle size than those used in the industry today. However, Oven-dried samples caused smearing during milling and thus the relationship between drying method and smearing should be studied further. All of the milled samples showed narrower particle size distribution compared to the Reference samples, which indicates a more homogenous flour and thus is considered a desirable trait in this study, when the specific food application is not known. Furthermore, all samples including the Reference samples showed negative skeweness in terms of their particle size distribution.