Study On Lysinoalanine Formation And Control In Alkali-pickled Eggs

During alkali-pickling process, the presence of strong alkali causes a great dealof lysinoalanine (LAL) formation in preserved eggs, which may reduce thenutritional value of proteins in preserved eggs and result in potential hazard tohuman health. However, few studies on LAL formation in alkali-pickled (preserved)eggs have been reported and they are not systematic and in-depth. In this paper,alkali-pickled eggs were chosen as research object. Firstly, a method for LALanalysis was established. On this basis, effects of processing conditions and someadditives on LAL formation in preserved eggs were tested, then some of additiveswere picked out to minimize LAL formation while maintain the quality of preservedeggs. In additon, effects of alkali treatment on LAL formation in egg white andovalbumin as well as how mixed amino acids to form LAL were explored. Thepurpose of this paper was to effectively control LAL formation in preserved eggs,preliminary reval the LAL formation mechanism, and lay the foundation for thetheory on LAL. The main contents and results are as follows:1. The effects of N-methyl-N-(tert-butyldimethylsilyl)trifluoroacetamide(MTBSTFA) dosage, derivatisation temperature, and time on the formation ofN(O)-tert-butyldimethylsilyl derivative of LAL were investigated. Optimizedderivatisation conditions were100μL of MTBSTFA,75℃of derivatisationtemperature, and30minutes of derivatisation time. A method of gas chromatographyusing MTBSTFA as derivatisation reagent was developed to determine LAL inpreserved eggs.2. Preserved eggs were produced by controlling alkali-pickling and aging time,temperature, type and concentration of alkali as well as the amount of metal salts.The sensory quality of them was checked, and effects of proessing conditions onLAL formation in preserved eggs were explored by determining LAL level using gaschromatography method. The results show during the alkali-pickling process, theamount of LAL in preserved eggs was increased with the prolonged time, elevatedtemperature, increased alkali concentration; however, it was decreased first and then increased with the increase amount of heavy metal salts. The additon of NaCl andKCl across all these concentrations tested almost had no effect on the LAL formationin preserved eggs. When the temperature was20-25℃and the alkali-pickling timewas controlled as short as possible，4%of NaOH or5%-5.5%of KOH,0-8%ofNaCl or KCl,0.4%of CuSO4or ZnSO4or the mixture of CuSO4and ZnSO4wereused to produced preserved eggs, not only was the sensory quality of them good butalso the level of LAL was controlled lower than others.3.5-80mmol/L of glutathione, L-cysteine, sucrose, D-glucose, maltose,L-ascorbic acid, citric acid, DL-malic acid, lactic acid, and sodium sulfite wereindividually added to the alkali-pickling solution to produce preserved eggs. Thesensory quality of them was checked and the presence of LAL in the preserved eggwhite and yolk was determined to evaluate the effects of these additives on LALformation so that available additives were identified. The results indicate that theformation of LAL in preserved egg albumen and yolk was more or less inhibited bythe addition of glutathione, D-glucose, maltose, L-ascorbic acid, citric acid, lacticacid, and sodium sulfite across all concentrations tested in this study as well asL-cysteine at5-10and80mmol/L concentrations. Wherein,40-80mmol/L ofsodium sulfite,40-80mmol/L of D-glucose,40mmol/L of citric acid, and40mmol/L of L-ascorbic acid were individually added into the pickling solution, theLAL formation was minimized and normal sensory quality of preserved eggs wasensured.4. The egg white and ovalbumin were treated with alkali. The contents ofthreonine, serine, cysteine, lysine and arginine in egg white were remarkabledecreased after alkali treatment. LAL was formed and its amount was increased withincreasing pH and temperature, and it was increased at first, thereafter declined withtime extension. Under the same alkali treatment condition, the amount of LALformed in ovalbumin was50.51%-58.68%of it in egg white. Therefore, ovalbuminmay be the major protein involved in the formation of LAL in alkali-treated(preserved) egg white. Alkali-treated amino acids were also studied. The resultsshow LAL was formed, when L-serine, L-cysteine, and L-cystine were individuallymixed with L-lysine under alkali treatment. Serine, cysteine, cystine, and lysine may be regarded as precursor amino acids for LAL formation.