Extracting Tenebrio molitor protein while preventing browning: effect of pH and NaCl on protein yield

The potential of insects as an alternative protein source for food applications was investigated by studying the effect of pH and NaCl on extraction yield of water-soluble proteins from Tenebrio molitor, while preventing browning due to polyphenol oxidation. Minimum protein solubility (29.6%) was at pH=4-6 and maximum (68.6%) at pH=11. Protein extraction at 0.1 M NaCl, pH=10 gave a recovery of 100%. The observed increase in browning at pH=8-11 corresponded to a lower monomeric phenol content. Sodium bisulphite (studied from 0.5-4%) could prevent browning, whereas ascorbic acid (studied in the range 0.01-0.04%) could not prevent as strong as sodium bisulphite. After acid precipitation (pH=4) an isolate with a protein content of 74% (yield of 22% of total protein) was obtained. It was observed that proteins from T. molitor behave more or less the same as proteins from meat and fish with respect to aqueous extraction, which is of relevance for food industry when using T. molitor protein as an ingredient in food products.