Development of Free Radical Products during the Greening Reaction of Caffeic Acid Esters (or Chlorogenic Acid) and a Primary Amino Compound
ESR spectra were measured directly on a marked greening reaction mixture of Et-caffeate and a primary amino compound in alkali solution under aeration. A clear hyperfine structure was commonly detected early in the greening reaction with different amino compounds. Its hyperfine spectrum split into seven peaks was analyzed and found to be due to the oxidized free radical product of the Et-caffeate using an authentic sample system. Another type of hyperfine ESR spectrum was observed later in the reaction, and was altered with different amino compounds. The hyperfine structure for n-butylamine split into 12 lines. The latter type of free radical products were assumed to be a semiquinone type radical compounds of the trihydroxy benzacridine derivative, which was identified as the principal structure of the green and yellow pigments formed by this greening reaction system. A formation mechanism of the green pigment and related products involving these free radical products is proposed.
Characterization and modeling of the interactions between coffee storage proteins and phenolic compounds.
This study addresses the interactions of coffee storage proteins with coffee-specific phenolic compounds. Protein profiles of Coffea arabica and Coffea canephora (var. robusta) were compared. Major phenolic compounds were extracted and analyzed with appropriate methods. The polyphenol-protein interactions during protein extraction have been addressed by different analytical setups [reversed-phase high-performance liquid chromatography (RP-HPLC), sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), matrix-assisted laser desorption ionization-time of flight-mass spectrometry (MALDI-TOF-MS), and Trolox equivalent antioxidant capacity (TEAC) assays], with focus directed toward identification of covalent adduct formation. The results indicate that C. arabica proteins are more susceptible to these interactions and the polyphenol oxidase activity seems to be a crucial factor for the formation of these addition products. A tentative allocation of the modification type and site in the protein has been attempted. Thus, the first available in silico modeling of modified coffee proteins is reported. The extent of these modifications may contribute to the structure and function of "coffee melanoidins" and are discussed in the context of coffee flavor formation.
Gut immunity in Lepidopteran insects.
Lepidopteran insects constitute one of the largest fractions of animals on earth, but are considered pests in their relationship with man. Key to the success of this order of insects is its ability to digest food and absorb nutrition, which takes place in the midgut. Because environmental microorganisms can easily enter Lepidopteran guts during feeding, the innate immune response guards against pathogenic bacteria, virus and microsporidia that can be devoured with food. Gut immune responses are complicated by both resident gut microbiota and the surrounding peritrophic membrane and are distinct from immune responses in the body cavity, which depend on the function of the fat body and hemocytes. Due to their relevance to agricultural production, studies of Lepidopteran insect midgut and immunity are receiving more attention, and here we summarize gut structures and functions, and discuss how these confer immunity against different microorganisms. It is expected that increased knowledge of Lepidopteran gut immunity may be utilized for pest biological control in the future.