Mendel Friedman

Chemistry, biochemistry, and safety of acrylamide. A review.

Acrylamide (CH2=CH-CONH2), an industrially produced alpha,beta-unsaturated (conjugated) reactive molecule, is used worldwide to synthesize polyacrylamide. Polyacrylamide has found numerous applications as a soil conditioner, in wastewater treatment, in the cosmetic, paper, and textile industries, and in the laboratory as a solid support for the separation of proteins by electrophoresis. Because of the potential of exposure to acrylamide, effects of acrylamide in cells, tissues, animals, and humans have been extensively studied. Reports that acrylamide is present in foods formed during their processing under conditions that also induce the formation of Maillard browning products heightened interest in the chemistry, biochemistry, and safety of this vinyl compound. Because exposure of humans to acrylamide can come from both external sources and the diet, a need exists to develop a better understanding of its formation and distribution in food and its role in human health. To contribute to this effort, this integrated review presents data on the chemistry, analysis, metabolism, pharmacology, and toxicology of acrylamide. Specifically covered are the following aspects: nonfood and food sources; exposure from the environment and the diet; mechanism of formation in food from asparagine and glucose; asparagine-asparaginase relationships; Maillard browning-acrylamide relationships; quenching of protein fluorescence; biological alkylation of amino acids, peptides, proteins, and DNA by acrylamide and its epoxide metabolite glycidamide; risk assessment; neurotoxicity, reproductive toxicity, and carcinogenicity; protection against adverse effects; and possible approaches to reducing levels in food. Further research needs in each of these areas are suggested. Neurotoxicity appears to be the only documented effect of acrylamide in human epidemiological studies; reproductive toxicity, genotoxicity/clastogenicity, and carcinogenicity are potential human health risks on the basis of only animal studies. A better understanding of the chemistry and biology of pure acrylamide in general and its impact in a food matrix in particular can lead to the development of improved food processes to decrease the acrylamide content of the diet.

Chemistry, biochemistry, nutrition, and microbiology of lysinoalanine, lanthionine, and histidinoalanine in food and other proteins.

Heat and alkali treatments of foods, widely used in food processing, result in the formation of dehydro and cross-linked amino acids such as dehydroalanine, methyldehydroalanine, beta-aminoalanine, lysinoalanine (LAL), ornithinoalanine, histidinoalanine (HAL), phenylethylaminoalanine, lanthionine (LAN), and methyl-lanthionine present in proteins and are frequently accompanied by concurrent racemization of L-amino acid isomers to D-analogues. The mechanism of LAL formation is a two-step process: first, hydroxide ion-catalyzed elimination of H(2)S from cystine and H(2)O, phosphate, and glycosidic moieties from serine residues to yield a dehydroalanine intermediate; second, reaction of the double bond of dehydroalanine with the epsilon-NH(2) group of lysine to form LAL. Analogous elimination-addition reactions are postulated to produce the other unusual amino acids. Processing conditions that favor these transformations include high pH, temperature, and exposure time. Factors that minimize LAL formation include the presence of SH-containing amino acids, sodium sulfite, ammonia, biogenic amines, ascorbic acid, citric acid, malic acid, and glucose; dephosphorylation of O-phosphoryl esters; and acylation of epsilon-NH(2) groups of lysine. The presence of LAL residues along a protein chain decreases digestibility and nutritional quality in rodents and primates but enhances nutritional quality in ruminants. LAL has a strong affinity for copper and other metal ions and is reported to induce enlargement of nuclei of rats and mice but not of primate kidney cells. LAL, LAN, and HAL also occur naturally in certain peptide and protein antibiotics (cinnamycin, duramycin, epidermin, nisin, and subtilin) and in body organs and tissues (aorta, bone, collagen, dentin, and eye cataracts), where their formation may be a function of the aging process. These findings are not only of theoretical interest but also have practical implications for nutrition, food safety, and health. Further research needs are suggested for each of these categories. These overlapping aspects are discussed in terms of general concepts for a better understanding of the impact of LAL and related compounds in the diet. Such an understanding can lead to improvement in food quality and safety, nutrition, microbiology, and human health.

Review of Methods for the Reduction of Dietary Content and Toxicity of Acrylamide

Potentially toxic acrylamide is largely derived from heat-induced reactions between the amino group of the free amino acid asparagine and carbonyl groups of glucose and fructose in cereals, potatoes, and other plant-derived foods. This overview surveys and consolidates the following dietary aspects of acrylamide: distribution in food originating from different sources; consumption by diverse populations; reduction of the acrylamide content in the diet; and suppression of adverse effects in vivo. Methods to reduce adverse effects of dietary acrylamide include (a) selecting potato, cereal, and other plant varieties for dietary use that contain low levels of the acrylamide precursors, namely, asparagine and glucose; (b) removing precursors before processing; (c) using the enzyme asparaginase to hydrolyze asparagine to aspartic acid; (d) selecting processing conditions (pH, temperature, time, processing and storage atmosphere) that minimize acrylamide formation; (e) adding food ingredients (acidulants, amino acids, antioxidants, nonreducing carbohydrates, chitosan, garlic compounds, protein hydrolysates, proteins, metal salts) that have been reported to prevent acrylamide formation; (f) removing/trapping acrylamide after it is formed with the aid of chromatography, evaporation, polymerization, or reaction with other food ingredients; and (g) reducing in vivo toxicity. Research needs are suggested that may further facilitate reducing the acrylamide burden of the diet. Researchers are challenged to (a) apply the available methods and to minimize the acrylamide content of the diet without adversely affecting the nutritional quality, safety, and sensory attributes, including color and flavor, while maintaining consumer acceptance; and (b) educate commercial and home food processors and the public about available approaches to mitigating undesirable effects of dietary acrylamide.

Review of antimicrobial and antioxidative activities of chitosans in food.

Interest in chitosan, a biodegradable, nontoxic, non-antigenic, and biocompatible biopolymer isolated from shellfish, arises from the fact that chitosans are reported to exhibit numerous health-related beneficial effects, including strong antimicrobial and antioxidative activities in foods. The extraordinary interest in the chemistry and application in agriculture, horticulture, environmental science, industry, microbiology, and medicine is attested by about 17,000 citations on this subject in the Scopus database. A special need exists to develop a better understanding of the role of chitosans in ameliorating foodborne illness. To contribute to this effort, this overview surveys and interprets our present knowledge of the chemistry and antimicrobial activities of chitosan in solution, as powders, and in edible films and coating against foodborne pathogens, spoilage bacteria, and pathogenic viruses and fungi in several food categories. These include produce, fruit juices, eggs and dairy, cereal, meat, and seafood products. Also covered are antimicrobial activities of chemically modified and nanochitosans, therapeutic properties, and possible mechanisms of the antimicrobial, antioxidative, and metal chelating effects. Further research is suggested in each of these categories. The widely scattered data on the multifaceted aspects of chitosan microbiology, summarized in the text and in 10 tables and 8 representative figures, suggest that low-molecular-weight chitosans at a pH below 6.0 presents optimal conditions for achieving desirable antimicrobial and antioxidative-preservative effects in liquid and solid foods. We are very hopeful that the described findings will be a valuable record and resource for further progress to improve microbial food safety and food quality.

An internal standard for amino acid analyses: S-β-(4-pyridylethyl)-l-cysteine

The new amino acid, S-β-(4-pyridylethyl)-l-cysteine (PEC), was prepared by treating l-cysteine with 4-vinylpyridine in an aqueous medium containing triethylamine. The postulated structure for PEC was confirmed by infrared, nuclear magnetic resonance, and mass spectroscopic analyses. PEC is stable to acid under conditions used for protein hydrolysis, it elutes on a basic column as a discrete peak before arginine, and its ninhydrin color is linear with concentration. The new amino acid has been evaluated as a internal standard for amino acid analyses. Equally excellent results were obtained when PEC was added to the protein either before or after hydrolysis. Addition of PEC before hydrolysis eliminates the need for nitrogen analysis of the hydrolysate and for accurate sample application to the column.

Origin, Microbiology, Nutrition, and Pharmacology of D-Amino Acids†

Exposure of food proteins to certain processing conditions induces two major chemical changes: racemization of all L‐amino acids (LAAs) to D‐amino acids (DAAs) and concurrent formation of cross‐linked amino acids such as lysinoalanine (LAL). The diet contains both processing‐induced and naturally‐formed DAA. The latter include those found in microorganisms, plants, and marine invertebrates. Racemization impairs digestibility and nutritional quality. Racemization of LAA residues to their D‐isomers in food and other proteins is pH‐, time‐, and temperature‐dependent. Although racemization rates of LAA residues in a protein vary, relative rates in different proteins are similar. The nutritional utilization of different DAAs varies widely in animals and humans. Some DAAs may exert both adverse and beneficial biological effects. Thus, although D‐Phe is utilized as a nutritional source of L‐Phe, high concentrations of D‐Tyr in such diets inhibit the growth of mice. Both D‐Ser and LAL induce histological changes in the rat kidney. The wide variation in the utilization of DAAs is illustrated by the fact that, whereas D‐Meth is largely utilized as a nutritional source of the L‐isomer, D‐Lys is not. Similarly, although L‐CysSH has a sparing effect on L‐Meth when fed to mice, D‐CysSH does not. Since DAAs are consumed as part of their normal diet, a need exists to develop a better understanding of their roles in foods, microbiology, nutrition, and medicine. To contribute to this effort, this overview surveys our present knowledge of the chemistry, nutrition, safety, microbiology, and pharmacology of DAAs. Also covered are the origin and distribution of DAAs in food and possible roles of DAAs in human physiology, aging, and the etiology and therapy of human diseases.

Effects of Allspice, Cinnamon, and Clove Bud Essential Oils in Edible Apple Films on Physical Properties and Antimicrobial Activities

Essential oils (EOs) derived from plants are rich sources of volatile terpenoids and phenolic compounds. Such compounds have the potential to inactivate pathogenic bacteria on contact and in the vapor phase. Edible films made from fruits or vegetables containing EOs can be used commercially to protect food against contamination by pathogenic bacteria. EOs from cinnamon, allspice, and clove bud plants are compatible with the sensory characteristics of apple-based edible films. These films could extend product shelf life and reduce risk of pathogen growth on food surfaces. This study evaluated physical properties (water vapor permeability, color, tensile properties) and antimicrobial activities against Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes of allspice, cinnamon, and clove bud oils in apple puree film-forming solutions formulated into edible films at 0.5% to 3% (w/w) concentrations. Antimicrobial activities were determined by 2 independent methods: overlay of the film on top of the bacteria and vapor phase diffusion of the antimicrobial from the film to the bacteria. The antimicrobial activities against the 3 pathogens were in the following order: cinnamon oil > clove bud oil > allspice oil. The antimicrobial films were more effective against L. monocytogenes than against the S. enterica. The oils reduced the viscosity of the apple solutions and increased elongation and darkened the colors of the films. They did not affect water vapor permeability. The results show that apple-based films with allspice, cinnamon, or clove bud oils were active against 3 foodborne pathogens by both direct contact with the bacteria and indirectly by vapors emanating from the films.

Analysis of phenolic compounds by high-performance liquid chromatography and liquid chromatography/mass spectrometry in potato plant flowers, leaves, stems, and tubers and in home-processed potatoes.

Potato plants synthesize phenolic compounds as protection against bruising and injury from bacteria, fungi, viruses, and insects. Because antioxidative phenolic compounds are also reported to participate in enzymatic browning reactions and to exhibit health-promoting effects in humans, a need exists for accurate methods to measure their content in fresh and processed potatoes. To contribute to our knowledge about the levels of phenolic compounds in potatoes, we validated and used high-performance liquid chromatography and liquid chromatography/mass spectrometry to measure levels of chlorogenic acid, a chlorogenic isomer, and caffeic acid in flowers, leaves, stems, and tubers of the potato plant and in home-processed potatoes. The total phenolic acid content of flowers (626 mg/100 g fresh wt) was 21 and 59 times greater than that of leaves and stems, respectively. For all samples, chlorogenic acid and its isomer contributed 96-98% to the total. Total phenolic acid levels (in g/100 g fresh wt) of peels of five potato varieties grown in Korea ranged from 6.5 to 42.1 and of the flesh (pulp) from 0.5 to 16.5, with peel/pulp ratios ranging from 2.6 to 21.1. The total phenolic acid content for 25 American potatoes ranged from 1.0 to 172. The highest amounts were present in red and purple potatoes. Home processing of pulp with various forms of heat induced reductions in the phenolic content. The described methodology should facilitate future studies on the role of potato phenolic compounds in the plant and the diet.

Storage Stability and Antibacterial Activity against Escherichia coli O157:H7 of Carvacrol in Edible Apple Films Made by Two Different Casting Methods

The antimicrobial activities against Escherichia coli O157:H7 as well as the stability of carvacrol, the main constituent of oregano oil, were evaluated during the preparation and storage of apple-based edible films made by two different casting methods, continuous casting and batch casting. Antimicrobial assays of films and high-performance liquid chromatography (HPLC) analysis of film extracts following storage up to 49 days at 5 and 25 degrees C revealed that (a) optimum antimicrobial effects were apparent with carvacrol levels of approximately 1.0% added to the purees prior to film preparation, (b) carvacrol in the films and film weights remained unchanged over the storage period of up to 7 weeks, and (c) casting methods affected carvacrol concentration, bactericidal activity, physicochemical properties, and colors of the apple films. Carvacrol addition to the purees used to prepare the films reduced water vapor and oxygen permeability of apple films. The results indicate that carvacrol has a dual benefit. It can be used to both impart antimicrobial activities and enhance barrier properties of edible films. The cited observations facilitate relating compositional and physicochemical properties of apple puree films containing volatile plant antimicrobials to their use in foods.

Molecular binding of catechins to biomembranes: relationship to biological activity.

Molecular dynamics simulations were used to study the interactions of four green tea catechin compounds with lipid bilayers. Reported studies have shown that catechins are linked to beneficial health effects, specifically those related to interactions with the cell membrane. To better understand the molecular interaction of catechins with membranes, simulations were carried out of interactions of four catechin molecules [epicatechin (EC), epigallocatechin (EGC), epicatechin gallate (ECG), and epigallocatechin gallate (EGCG)] with a 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) lipid bilayer. The simulations show that catechins possess a strong affinity for the lipid bilayer. Some are absorbed into the bilayer. The molecular structure and aggregated condition of the catechins significantly influences their absorption, as well as their ability to form hydrogen bonds with the lipid headgroups. Insight into these molecular interactions helps to distinguish the structure-function relationship of the catechins with lipid bilayers and provides a foundation for a better understanding of the role of catechins in biological processes.