Food Preservative

Abstract

Food preservatives are employed to ensure safety and avoid quality loss derived from microbial, physical–chemical, or enzymatic reactions. There are different types of antimicrobial and antioxidant agents, each one with particular modes of action. Acidulants, organic acids, and parabens are widely used antimicrobials, though the use of natural alternatives is increasing. Antioxidants are another very important group of food additives. This article provides an overview of current industry applications of food preservatives, modes of action, limitations, and international regulations. A clear market trend for the adoption of natural alternatives is observed and discussed, with special focus in herbs, spices, and their derivatives.

Publisher Summary

Food preservatives are substances added to foods to inhibit the growth of micro-organisms. This action usually requires that the preservative be absorbed by the organism in question and thus the chemical structure must be such as to allow passage through the microbial cell wall. Foods are multi-phase systems where one of the phases is often oil. Numerous surfactants are also likely to be present. A wide variety of surfactants may also be added to foods; these are generally non-ionic. The known tendency for solutes that are sparingly soluble in water to become associated with surfactant micelles or aggregates leads one to expect that food preservatives may also be found associated with micellar structures in foods; this has undoubted consequences for the activity (and reactivity) of these solutes. This chapter describes a stage in the development of a model for the distribution of food preservatives in multi-phase foods; it considers the quaternary system water + surfactant + oil + preservative to gain understanding of the affinity of surfactants for benzoic and sorbic acids. The implications of preservative-surfactant interactions are considered in the chapter for the specific case of the reaction between sorbic acid and thiols. The latter is potentially the most reactive species toward sorbic acid in foods.

4.2.1 Sensing Preservatives

Food preservatives like benzoates and taste-intensifying additives, such as, glutamates have been checked for their isolation and isotachophoresis zonal electrophoresis detection on a microfluidic poly(methylmethacrylate) chip. The method is very sensitive, with low limits of detection (μM/L) with no interference from food (Bodor et al., 2001). Concentrations of benzoic acid and its salt added as food preservatives are dictated by law, as well as, controlled by regulatory agencies (European Union Law, 1995). Nanomaterial made of glassy carbon electrodes can detect benzoic acid in yogurt and other nonalcoholic beverages. Benzoic acid inhibits the biocatalytic activity of tyrosinase and polyphenol oxidase. Concentrations of benzoic acid up to 0.03 μM could be proportionally detected by catalytic inhibition of tyrosinase entrapped in titania gel modified with multiwalled carbon nanotubes and Nafion in nonalcoholic beverages. The results obtained were consistent with those obtained with HPLC method but with a better sensitivity of 1.06 μA/μM (Kochana et al., 2012). Amperometric quantitation of monosodium glutamate in food seasonings, sauces, and soups using glutamate oxidase anchored to a screen-printed electrode was in the range of 1–20 mg/dL detected within 2 min (Basu et al., 2006).

Background

Food preservatives constitute a group of compounds of widely different molecular structures; they are organic and inorganic substances with different functional groups and tendencies to form ions. There are no procedures that are generally applicable to the analysis of preservatives as a class of food additive; the procedures are specific to the preservative being analyzed. The lowest concentrations of commonly used preservatives are of the order of a few milligrams per kilogram of food, and, with few exceptions, recommended or statutory methods of analysis are designed to give a good accuracy at levels of 10 to  > 1000 mg of preservative per kilogram of food. The question of the lower limit of detection is rarely an issue, unless it is desired to use small sample sizes, e.g., < 1 g, or to determine whether or not a food or its ingredients had been treated with a preservative. For solid foods, small sample sizes often lead to nonrepresentative sampling and should be avoided. Not all the procedures described constitute official methods of analysis. Frequently, for routine analysis, a food manufacturer would use a rapid or cheap analytical technique standardized against an official method. The official status of given procedures varies from country to country.

Organic and inorganic acid preservatives may be added in the form of the undissociated acid or a variety of salts. In food, the ionic composition is determined largely by concentration and pH, but it is generally impossible to predict this accurately for any given situation. In order to avoid complications with the specification of the amount of preservative in a food, this is usually referred to as the weight-for-weight concentration of the undissociated acid, e.g., benzoic acid, sorbic acid, or sulfur dioxide. Nitrite and nitrate levels are expressed in terms of the weight of the sodium salt.

There are, of course, a very large number of possible analytical procedures available for each preservative. Those given here represent a selection to illustrate the variety of methods recommended for use on food samples.

6.5.2 Preservatives in Processed Foods

Food preservatives are specific additives to prevent deterioration from enzymes, microorganisms, and exposure to oxygen. All chemical preservatives must be nontoxic and readily soluble, not impart off-flavors, exhibit antimicrobial properties over the pH range of the food, and be economical and practical.

Sugar, salt, nitrites, butylated hydroxy anisol (BHA), butylated hydroxyl toluene (BHT), tert-butylhydroquinone (TBHQ), vinegar, citric acid, and calcium propionate are all chemicals that preserve foods. Salt, sodium nitrite, spices, vinegar, and alcohol have been used to preserve foods for centuries. Sodium benzoate, calcium propionate, and potassium sorbate are used to prevent microbial growth that causes spoilage and to slow changes in color, texture, and flavor. Potassium sorbate and sodium benzoate both prevent spoilage by inhibiting mold and yeast. Sodium benzoate may be in foods such as salad dressings, soft drinks, canned tuna, and mixed dried fruit. Potassium sorbate is found in cheese, wine, and dried meats. BHA and BHT are antioxidants that prevent rancidity of fats and are added to shortening, margarine, and fried snacks such as potato chips.

Consumers have raised concerns about the use of preservatives in foods that have complicated chemical names that make them seem more appropriate for a chemistry experiment than a meal. Sodium benzoate, BHA, BHT, and TBHQ have especially been targets of consumer apprehension. These compounds have been approved for their safe use in foods and have not been linked to any human illness or complications for the general public. As is the nature of scientific inquiry, reports of adverse effects of these compounds can be found in the literature. The abundance of evidence suggests that the risks of these compounds, which are used in small amounts, to human health are insignificant. And, in contrast to having a negative impact on health, BHA and BHT have been linked with having a positive effect due to their antioxidant capacity. Weighing the risk/benefits of using these chemicals in foods is an ongoing debate and the FDA, food companies, and consumers must all participate. No food, additive, or ingredient will be 100% safe for 100% of the people. Using scientific thinking to consider these complicated decisions is essential to avoid emotional reactions based on misinformation.

Mechanism of Antimicrobial Action

The given formula is considered to be the basis for studying the action of preservatives in foods. This rule is valid, however, only for relatively high dosages of preservatives and a genetically uniform cell material. A preservative added to a food when microbial counts are low inhibits microorganisms in the initial lag phase; the dosage of preservatives necessary in practice to inhibit microorganisms in the exponential log phase would be too high. Preservatives are not designed to kill microorganisms in substrates already supporting a massive germ population. In general, the action of preservatives includes physical as well as physicochemical mechanisms, especially the inhibitory action on enzymes.

The partial dissociation of weakly lipophilic acid food preservatives plays an important role in the inhibition of microbial growth. The undissociated lipophilic acid molecules are capable of moving freely through the membrane. They pass from an external environment of low pH (where the equilibrium favors the undissociated molecules) to the cytoplasm, which is of high pH (where the equilibrium favors the dissociated molecules). At the high pH level, the acid ionizes to produce protons, which in turn acidify the cytoplasm and break down the pH component of the proton motive force. To maintain the internal pH, the cell then tries to expel the protons entering it. In doing so, it diverts the energy from growth-related functions and hence both the growth rate and yield of the cell fall. If the external pH is low and the extracellular concentration of the acid is high, then the cytoplasmic pH drops to a level at which growth is no longer possible and the cell eventually dies. Some preservatives also exert specific effects on metabolic enzymes. Sorbic acid is reported to react with the sulfhydryl groups of enzymes, such as fumarase, aspartase, succinic dehydrogenase, catalase, and peroxidases in bacteria, molds, and yeasts. Antimicrobial activity of organic acids increases with chain length, but the limited water solubility of long-chain acids restricts their use.

Benzoic acid is effective only in acid foods. It inhibits enzymes of acetic acid metabolism, oxidative phosphorylation, amino acid uptake, and various stages in the tricarboxylic acid cycle. It also alters membrane permeability of the microbial cell. Transport inhibition is the primary mode of action of parabens. Respiration of microbial cells also is inhibited.

Antimicrobial action of propionic acid is due to inhibition of nutrient transport and growth by competing with substances like alanine and other amino acids required by microorganisms. Antimicrobial action of formic acid is similar to any acidulant. Additionally, formic acid inhibits decarboxylase and heme enzymes, especially catalase. The antimicrobial effect of other acids (e.g., lactic, tartaric, phosphoric, and succinic acids) is due to acidification of the microbial cell and inhibiting nutrient transport.

Sulfur dioxide is highly reactive, and therefore it interacts with many cell components. The sulfite ion acts as a powerful nucleophile, cleaving the disulfide bonds of proteins, which changes the molecular configuration of enzymes, thus modifying active sites. It reacts with coenzymes (nicotinamide adenine dinucleotide (NAD⁺)), cofactors, and prosthetic groups such as flavin, thiamin, heme, folic acid, and pyridoxyl. In the case of yeast, the blocking of the oxidation of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate is the salient feature. Sulfite treatment of yeast cells results in a rapid decrease in adenosine triphosphate (ATP) content prior to cell death. This is attributed to inactivation of the enzyme glyceraldehyde-3-phosphate dehydrogenase. Sulfite also reacts with carbonyl constituents of the metabolic pool to form hydroxysulfonates. Yeasts when treated with sublethal concentrations of sulfite tend to excrete increased amounts of acetaldehyde. This is due to the trapping of this metabolic intermediate as the stable hydroxysulfonate, thereby preventing its conversion to ethanol so that the reaction equilibrium shifts. Glycerol is formed instead of ethanol by reduction of glyceraldehyde-3-phosphate to glycerol-3-phosphate, which subsequently is dephosphorylated. In Escherichia coli NAD-dependent formation of oxalacetate from malate is inhibited. Sulfite destroys the activity of thiamin by breaking the bond between the pyrimidine and thiazole portion of the molecule.

The antimicrobial action of nitrite is based mainly on the release of nitrous acid and oxides of nitrogen. Nitrite inhibits active transport of proline in E. coli and aldolase from E. coli, Enterococcus faecalis, and Pseudomonas aeruginosa. Reaction between nitric oxide from the nitrite and iron of a cidophore compound involved in electron transport in clostridia accounts for the anticlostridial action. Nitrite reacts with heme proteins such as cytochromes and sulfhydryl enzymes, resulting in the formation of S-nitroso products.

Preservatives

Food preservatives can be extrinsic (intentionally added), intrinsic (normal constituent of food), or developed (produced during fermentation) (Potter and Hotchkiss, 1995; Jay, 1996). Factors affecting preservative effectiveness include: (1) concentration of inhibitor, (2) kind, number, and age of microorganisms (older cells more resistant), (3) temperature, (4) time of exposure (if long enough. some microbes can adapt and overcome inhibition), and (5) chemical and physical characteristics of food (water activity, pH, solutes, etc.). Preservatives that are cidal are able to kill microorganisms when large concentrations of the substances are used. Static activity results when sublethal concentrations inhibit microbial growth.

Some examples of inorganic preservatives are sodium chloride (NaCl), nitrate and nitrite salts, sulfites, and sulfur dioxide (SO₂). NaCl lowers water activity and causes plasmolysis by withdrawing water from cells. Nitrites and nitrates are curing agents for meats (hams, bacons, sausages, etc.) to inhibit C. botulinum under vacuum packaging conditions. Sulfur dioxide (SO₂), sulfites (SO₃), bisulfite (HSO₃), and metabisulfites (S₂O₅) form sulfurous acid in aqueous solutions, which is the antimicrobial agent. Sulfites are widely used in the wine industry to sanitize equipment and reduce competing microorganisms. Wine yeasts are resistant to sulfites. Sulfites are also used in dried fruits and some fruit juices. Sulfites have been used to prevent enzymatic and nonenzymatic browning in some fruits and vegetables (cut potatoes).

Nitrites can react with secondary and tertiary amines to form potentially carcinogenic nitrosamines during cooking; however, current formulations greatly reduce this risk. Nitrates in high concentrations can result in red blood cell functional impairment; however, at approved usage levels they are safe (Nitrite Safety Council, 1980; Hotchkiss and Cassens, 1987). Sulfiting agents likewise can cause adverse respiratory effects to susceptible consumers, particularly asthmatics (Stevenson and Simon, 1981; Schwartz, 1983). Therefore, use of these two classes of agents is strictly regulated.

A number of organic acids and their salts are used as preservatives. These include lactic acid and lactates, propionic acid and propionates, citric acid, acetic acid, sorbic acid, and sorbates, benzoic acid and benzoates, and methyl and propyl parabens (benzoic acid derivatives). Benzoates are most effective when undissociated; therefore, they require low pH values for activity (2.5–4.0). The sodium salt of benzoate is used to improve solubility in foods. When esterified as parabens, benzoates are active at higher pH values. Benzoates are primarily used in high-acid foods (jams, jellies, juices, soft drinks, ketchup, salad dressings, and margarine). They are active against yeast and molds, but minimally so against bacteria. They can be used at levels up to 0.1%.

Sorbic acid and sorbate salts (potassium most effective) are effective at pH values less than 6.5 but at a higher pH than benzoates. Sorbates are used in cheeses, baked or nonyeast goods, beverages, jellies, jams, salad dressings, dried fruits, pickles, and margarine. They inhibit yeasts and molds, but few bacteria except C. botulinum. They prevent yeast growth during vegetable fermentations and can be used at levels up to 0.3%.

Propionic acid and propionate salts (calcium most common) are active against molds at pH values less than 6. They have limited activity against yeasts and bacteria. They are widely used in baked products and cheeses. Propionic acid is found naturally in Swiss cheese at levels up to 1%. Propionates can be added to foods at levels up to 0.3%.

Acetic acid is found in vinegar at levels up to 4–5%. It is used in mayonnaise, pickles, and ketchup, primarily as a flavoring agent. Acetic acid is most active against bacteria, but has some yeast and mold activity, though less active than sorbates or propionates. Lactic acid, citric acid, and their salts can be added as preservatives, to lower pH, and as flavorants. They are also developed during fermentation. These organic acids are most effective against bacteria.

Some antibiotics may be found in foods, although medical compounds are not allowed in human food, trace amounts used for animal therapy may occasionally be found. Bacteriocins, which are antimicrobial peptides produced by microorganisms, can be found in foods. An example of an approved bacteriocin is nisin, which is allowed in process cheese food as an additive. Some naturally occurring enzymes (lysozyme and lactoferrin) can be used as preservatives in limited applications where denaturation is not an issue. Some spices, herbs, and essential oils have antimicrobial activity, but such high levels are needed that the food becomes unpalatable. Ethanol has excellent preservative ability but is underutilized because of social stigma. Wood smoke, whether natural or added in liquid form, contains several phenolic antimicrobial compounds in addition to formaldehyde. Wood smoke is most active against vegetative bacteria and some fungi. Bacterial endospores are resistant. Activity is correlated with phenolic content. Carbon dioxide gas can dissolve in food tissues to lower pH and inhibit microbes. Developed preservatives produced during fermentation include organic acids (primarily lactic, acetic, and propionic), ethanol, and bacteriocins. All added preservatives must meet government standards for direct addition to foods. All preservatives added to foods are GRAS.

9.3.2 Antimicrobial peptides

Chemical food preservatives are widely used in the food industry and are invariably cheap ingredients that are effective against a wide range of spoilage organisms. Chemical food preservatives include compounds such as sodium benzoate, benzoic acid, nitrites, sulfites, sodium sorbate and potassium sorbate. Forced by public opinion the demand for natural or label-friendly alternatives has increased.

Specific proteins, such as lactoferrin, are known for their natural antimicrobial properties whereas others, such as lactoperoxidase and myeloperoxidase, produce antimicrobial compounds in the presence of hydrogen peroxide (Klebanoff et al. 1984; Boots and Floris 2006). The activity of lactoferrin against microorganisms is twofold (Recio and Visser 2000, and references therein). First, the iron-sequestering capabilities of the positively charged molecule have been described. More recently a second mechanism has been described based on the fact that antimicrobial peptides can be generated from the N-terminal part of lactoferrin. In this second mechanism the binding of lactoferrin to the bacterial surface plays a crucial role. The most active peptide obtained from lactoferrin is lactoferricin, which displays an activity 40 times higher than that of lactoferrin. Despite this higher activity, the estimated cost in use of this specific hydrolysate is the major drawback for its application as a natural or clean label preservative.

Abstract

The use of food preservatives has increased enormously over the past several decades. Intuitively, constant ingestion of food preservatives (antimicrobials) could have a profound effect on the oral flora. Preservatives used range from antibiotics to the more commonly used weak acids, for example benzoates, propionates and sorbates. Weak acids reduce the acid tolerance of microorganisms, damage the properties of their cell membranes and exert their antimicrobial effect in a manner similar to that of fluoride. Results from laboratory- and animal-based investigations support the concept that food preservatives alone or in combination with fluoride could reduce the prevalence of dental caries and possibly other plaque related diseases of the mouth.

Abstract

An ideal food preservative should ensure that foods and food products remain safe and unspoiled. Essential oil as whole or its components can contribute in the prevention of food spoilage. The potency of naturally occurring antimicrobial agents or essential oil from plants varies from species to species. To achieve the goal of preservation using natural compounds/extracts/essential oils can be done by combining essential oil or its components from various species. Since an ideal agent should ensure the complete protection from food spoilage, mode of action, synergistic and antagonistic effects of the agent have to be considered. In this chapter, the potential value of jasmine essential oil for its antibacterial, antifungal, and antioxidant action is discussed for food preservation. Apart from other uses of jasmine essential oil, it has been found to be active against various gram-negative, gram-positive bacteria and fungi. This property of jasmine oil allows it to be used in food preservation. It also possesses antioxidant activity. The major components of jasmine essential oil are linalool, benzyl acetate, and benzyl benzoate. The linalool is a monoterpeniod alcohol also found in other antimicrobial essential oils. The antimicrobial activity of most terpenoids is linked to their functional groups, and it has been shown that the hydroxyl group of phenolic terpenoids and the presence of delocalized electrons are important for the antimicrobial activity. The mode of action of linalool is associated with membrane expansion, increased membrane fluidity and permeability, disturbance of membrane-embedded proteins, inhibition of respiration, and alteration of ion transport processes of microorganisms. Synergistic antimicrobial effect has been observed for linalool when combined with other groups of monoterpenoids, that is, phenolic monoterpenoid. Various regulatory bodies such as the European commission and US Food and Drug Administration have registered linalool to be a safe flavoring agent used for food products.