Food Quality and Design, Wageningen University and Research, PO Box 17, 6700 AA, Wageningen, The Netherlands.
Laboratory of Food Chemistry, Wageningen University and Research, PO Box 17, 6700 AA, Wageningen, The Netherlands.
Sci Rep. 2019 Feb 27;9(1):2967. doi: 10.1038/s41598-019-38923-x.
Insects are a promising alternative protein source. One of the bottlenecks in applying insects in food is the fast darkening initiated during grinding. Besides enzymatic browning, non-enzymatic factors can cause off-colour formation, which differs between species. This study investigates the impact of iron, phenoloxidase, and polyphenols on off-colour formation in insect larvae. Hermetia illucens showed a blackish colour, whereas Tenebrio molitor turned brown and Alphitobius diaperinus remained the lightest. This off-colour formation appeared correlated with the iron content in the larvae, which was 61 ± 9.71, 54 ± 1.72 and 221 ± 6.07 mg/kg dw for T. molitor, A. diaperinus and H. illucens, respectively. In model systems, the formation of iron-L-3,4-dihydroxyphenylalanine (L-DOPA) bis- and tris-complexes were evidenced by direct injection into ESI-TOF-MS, based on their charges combined with iron isotope patterns. The reversibility of the binding of iron to phenolics, and thereby loss of blackening, was confirmed by EDTA addition. Besides complex formation, oxidation of L-DOPA by redox reactions with iron occurred mainly at low pH, whereas auto-oxidation of L-DOPA mainly occurred at pH 10. Tyrosinase (i.e. phenoloxidase) activity did not change complex formation. The similarity in off-colour formation between the model system and insects indicated an important role for iron-phenolic complexation in blackening.
昆虫是一种很有前途的替代蛋白质来源。在将昆虫应用于食品中时，一个瓶颈是在研磨过程中快速变黑。除了酶促褐变外，非酶因素也会导致颜色变深，不同物种之间的形成机制不同。本研究调查了铁、酚氧化酶和多酚对昆虫幼虫变色形成的影响。Hermetia illucens 呈现出黑色，而 Tenebrio molitor 变成棕色，而 Alphitobius diaperinus 保持最浅的颜色。这种变色形成似乎与幼虫中的铁含量有关，T. molitor、A. diaperinus 和 H. illucens 中的铁含量分别为 61±9.71、54±1.72 和 221±6.07mg/kg dw。在模型系统中，通过直接注入 ESI-TOF-MS，根据其电荷与铁同位素模式，证明了铁与 L-3,4-二羟基苯丙氨酸（L-DOPA）双和三配合物的形成。通过添加 EDTA 证实了铁与酚类物质结合的可逆性，从而失去了变黑的能力。除了配合物形成外，L-DOPA 还主要在低 pH 值下通过与铁的氧化还原反应而发生氧化，而 L-DOPA 的自动氧化主要发生在 pH 10 时。酪氨酸酶（即酚氧化酶）活性没有改变配合物的形成。模型系统和昆虫之间变色形成的相似性表明，铁-酚类配合物在变黑中起着重要作用。
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