Antimicrobial Agents of Chemical Origin

In cheese the most common problem is the development of molds and yeasts. In addition to an economic problem, mold growth on cheese is a potential health hazard. Certain molds produce toxic substances called mycotoxins, which may cause acute or chronic disease conditions in humans. These molds are able to produce mycotoxins not only in cheese but also on a variety of dairy products.

The number of chemical preservatives approved to counteract the microbial problem in dairy foods is remarkably small. Good milk and dairy products chemical preservatives must be nontoxic, easy removable, leave no detectable residues, and be inexpensive and easy to apply. The efficiency of chemical preservatives depends primarily on the concentration of preservative, the composition of food and the type of microorganism to be inhibited. Widely used chemical preservatives are benzoic and sorbic acids and their salts (sodium benzoate and potassium sorbate) (Tfouni and Toledo, 2002), calcium lactate, and calcium ascorbate. They are generally used to inhibit mold and yeast growth and are also effective against many bacteria (Can et al., 2011). Benzoic acid is manufactured from toluene, a petroleum byproduct. It is classified as a carboxylic acid, weakly acidic, with a pH of 2.8. Both benzoic acid and sodium benzoate have inhibitory effects on yeast growth. Due to the fact that benzoic acid is toxic, the amount of benzoates that can be added to foods is carefully controlled. Codex Alimentarius, an international treaty dictating food safety standard, limits the amount of benzoic acid to 0-5 mg/kg of the body weight (WHO, 1996). Sodium benzoate, which is the sodium salt of benzoic acid, is preferred compared to benzoic acid since its solubility in water is higher than that of benzoic acid (Pylypiw and Grether, 2000). Akpan et al. (2007) compared the effect of sodium benzoate and potassium metabisulphates on soya beans yogurt shelf life. They found that the addition of sodium benzoate at a concentration of 20 mg/mL combined with refrigeration storage, improved yogurt shelf life for 21 days thus proving better than potassium metabisulphates. In another study, Gul and Dervisoglu (2013) revealed that the use of sodium benzoate and potassium sorbate improved the microbiological quality of Kashar cheese that is a typical semi-hard Turkish cheese, only if combined with milk pasteurization and hygienic production conditions. Lucera et al. (2014) elaborated an active sodium alginate coating with different chemical preservatives: potassium sorbate, sodium benzoate, calcium lactate, and calcium ascorbate in order to choose the best chemical preservative for Fior di latte cheese, that is a typical Mediterranean pasta filata cheese. Only potassium sorbate and sodium benzoate showed good results, delaying Pseudomonas spp. and Enterobacteriaceae growth without affecting sensory characteristics. Faccia et al. (2013) studied the effect of calcium lactate added in the brine of Fior di latte cheese with the final results that 1.2% (w/v) of calcium lactate exerted an antimicrobial action against Pseudomonas and Enterobacteriaceae. Sorbic acid and its salts have less harmful effect than benzoic acid since they are metabolized rapidly like some fatty acids (as butyric, caproic acid) in human and animals (Koyuncu and Uylaser, 2009). The acceptable daily intake (ADI) value of sorbic acid and its salts is 0-25 mg/kg body weight as established by the JECFA (WHO, 1974). Sorbate preservatives are effective inhibitors of most common microorganism that can attack foods, without affecting sensory quality. Oksuztepe et al. (2010) studied the addition of potassium sorbate on microbiological quality of Cokelek, that is a typical Turkish dairy product. The addition of potassium sorbate at

Table 3.1.2.1 Antimicrobial Effects of Sugar Esters.

Sugar Esters

Microorganism

Effect

Reference

Sucrose monolaurate

E.coli 0157:H7

Strong inhibition with sodium hypochlorite

Xiao 2011

Sucrose and fructose palmitate and laurate

Bacillus cereus and E. coli K12

Inhibition of Bacillus with 1% w/v of sucrose laurate, limited inhibition against E. coli

Habulin 2008

Erythritol and xylitol

esters

Gram-positive and negative

Inhibition of xylitol Monolaurate against Bacillus cereus

Piao 2006

Synthetic sugar esters

Gram-positive and -negative

Sucrose and maltose laurate inhibited Bacillus and E.coli

Ferrer 2005

Maltose laurate, Maltotriose laurate and Sucrose laurate

Streptococcus

mutans

All esters suppressed the growth at 0.05% to 2% w/v

Devulapalle

2004

0.1% w/v revealed a strong antimicrobial activity against molds and yeast. Potassium sorbate proved to be effective also in improving yogurt microbial quality as demonstrated by Rajapaksha et al. (2013), which have added potassium sorbate at 0.1% (w/v) during the inoculation of milk with starter cultures, with a final result of no contamination by coliforms, E. coli, Salmonella, and molds. Mastromatteo et al. (2015) studied the combination of MAP and an active sodium alginate coating with 3% of potassium sorb- ate on Fior di latte shelf life, finding that the treatment reduced physiological changes and microbial growth increasing the shelf life of 157%. The study of Azza and Ahmed (2010) used in conjunction bio and chemical preservation to improve the microbiological quality of soft cheese. Specifically, they used Bifidobacterium longum and potassium sorbate during the production process of soft cheese with the final result of a strong inhibition of the main deteriorative microorganism of cheese, preserving at the same time its organoleptic quality. Another class of chemical substances used in dairy sector are sucrose esters which have shown antimicrobial property against Gram-positive bacteria and Gram-negative bacteria as described in Table З.1.2.1. Wagh (2013) explored the antimicrobial properties of synthesized lactose monolaurate against four Grampositive and Gram-negative bacteria in milk. The study confirmed the antimicrobial activity of lactose monolaurate against the Gram-positive bacteria but no activity was found against Gram-negative bacteria.

 
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