[Advances in separation and analysis of aromatic amino acids in food]

Amino acids are important building blocks of proteins in the human body, which are involved in many metabolic pathways. Patients with metabolic diseases such as phenylketonuria, tyrosinemia, and hepatic encephalopathy are genetically defective and cannot metabolize aromatic amino acids (AAA) in food; hence, a regular diet may lead to permanent physiological damage. For this reason, it is necessary to restrict the intake of AAA in their daily diet by limiting natural protein intake, while ensuring normal intake of low protein foods and supplementation with low-AAA protein equivalents. Sources of low-AAA protein equivalents currently rely on free amino acid complex mixtures and low-AAA peptides (also known as high-Fischer-ratio peptides), which have better absorption availability and palatability. AAA separation and analysis techniques are essential for the preparation and detection of low-AAA peptides. Researchers in this field have explored a variety of efficient adsorption materials to selectively remove AAA from complex protein hydrolysates and thus prepare low-AAA peptide foods, or to establish analysis strategies for AAA. Covering more than 70 publications on AAA removal and separation in the last decade from Web of Science Core Collection and China National Knowledge Infrastructure, this review analyzes the structural characteristics and physicochemical properties of AAA, and summarizes the technological progress of AAA removal based on adsorbents such as activated carbon and resin. The applications of two-dimensional nanomaterials, molecular imprinting, cyclodextrins, and metal-organic frameworks in AAA adsorption and analysis from three dimensions, i. e., sample pretreatment, chiral separation and adsorption sensing, are also reviewed. The mainstream adsorbents for AAA removal, such as activated carbon, still suffer from poor specificity and cause environmental pollution during post-use treatment. Existing AAA separating materials show impressive selective adsorption capability in food samples and chiral mixtures as well as high sensitivity in adsorption sensing. The development of an efficient detection technology for AAA may help in detecting trace AAA in food and in evaluating chiral AAA adulteration in food samples. By exploring the advantages and disadvantages of each type of technology, we provide support for the advancement of the removal and analysis techniques for AAA.

Synthesis, Characteristics and Application of Novel Non-Ionic Gemini Surfactants as Reverse Micellar Systems for Encapsulation of Some Aromatic α-Amino Acids in n-Hexane

Non-ionic carbohydrate based gemini surfactants with rigid aromatic spacer CH2-Ar-CH2, which carry two hydrophobic tails of different tail lengths (C12, C14 and C16) and two sugar moiety polar head groups were synthesized and their reverse micellar behavior for solubilization of some aromatic α-amino acids viz. histidine (His), phenylalanine (Phy), tyrosine (Tyr) and tryptophan (Trp) in n-hexane were studied by spectroscopic analysis. The head group of these gemini surfactants consists of sugar moiety connected to C-6 of tertiary amines. Amino acids form complexes in order of His > Phy > Tyr > Trp, and in all cases it was found that the D-enantiomers solubilize better in comparison to the L-enantiomers. Moreover, more hydrophobic surfactants i.-e. surfactants with longer hydrocarbon tails show greater complex formation tendency towards D- and L-enantiomers of aromatic α-amino acids.