Department of Food Science and Nutrition, University of Minnesota, St. Paul, Minnesota 55108, United States.
Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455, United States.
J Agric Food Chem. 2020 Jun 10;68(23):6395-6402. doi: 10.1021/acs.jafc.0c01925. Epub 2020 May 26.
The formation of covalent bonds between 47 flavor compounds belonging to 13 different classes of functional groups and β-lactoglobulin (BLG) has been evaluated using electrospray ionization protein mass spectrometry. Covalent bond formation was determined by the appearance of ions in the mass spectra corresponding to BLG + flavor molecule(s). The observed processes for covalent bond formation were Schiff base, Michael addition, and disulfide linkages. Some reactions resulted in protein cross-linking. Aldehydes, sulfur-containing molecules (especially thiols), and functional group-containing furans were the most reactive flavor components. The thiol-containing compounds cleaved one or both electrophilic disulfide linkages in BLG to form disulfide linkages and the sulfides formed covalent bonds with the free cysteine group. Ketones were generally stable, but α-diketones (e.g., diacetyl) were reactive. Some bases (e.g., pyrazines and pyridines) were interactive, while the nucleophilic allylamine was reactive. Hydrocarbons, alcohols, acids, esters, lactones, and pyrans did not give observable levels of adduct formation within the period studied. The formation of covalent bonding (flavor protein) is potentially responsible for the loss of flavor, limiting the shelf-life of many foods.
采用电喷雾质谱法评价了 47 种风味化合物（属于 13 种不同官能团类别）与β-乳球蛋白（BLG）之间形成共价键的情况。通过质谱中对应于 BLG+风味分子（s）的离子出现来确定共价键的形成。观察到的共价键形成过程为希夫碱、迈克尔加成和二硫键。一些反应导致蛋白质交联。醛、含硫分子（特别是硫醇）和含官能团的呋喃是最具反应性的风味成分。含巯基的化合物将 BLG 中的一个或两个亲电二硫键切断，形成二硫键，而形成的硫化合物与游离半胱氨酸基团形成共价键。酮通常是稳定的，但α-二酮（如二乙酰）具有反应性。一些碱（如吡嗪和吡啶）具有交互作用，而亲核烯丙胺具有反应性。在研究期间，未观察到烃类、醇类、酸类、酯类、内酯类和吡喃类形成可观察到水平的加合物。共价键（风味蛋白）的形成可能是导致风味损失的原因，从而限制了许多食品的货架期。
