Nonproteinaceous Antimicrobial Compounds

The assessment of cheese spoilage by yeast and molds can be done considering the action of antifungal properties of LAB (lactic acid bacteria) ( Delavenne et al., 2015).

Fungal activity during ripening may be either needed or detrimental to product quality, depending of the quality of cheese and microorganisms. Spoilage of cheese due to fungal activity is caused by the volatile compounds, leading to off-flavors and by myco- toxins production (Delavenne et al., 2015).

Penicillium spp. and Aspergillus spp. are the main responsible of spoilage in preservative free-hard, semi-hard, and soft cheese. Candida spp and Kluyromyces marxianus are the main contaminants in unripened soft cheese.

The control of spoilage yeasts and molds is usually done by determination of chemical additives such as sorbic, propionic, benzoic acid and their salts, which have a broad activity of spectrum.

Among antifungal compounds produced by Lactobacillus casei SM20 and Propionibacterium jensenii SM11, during fermentation in whey-medium, there are: 2- pyrrolidone-5 carboxylic acid, 3-phenyllatic acid, hydroxyphenil-lactic acid, succinic acid.

Lactobacillus rhamnosus LC 705 is also able to produce 2-pyrrolidone-5 carboxylic acid.

A study by Delavenne et al. (2015) showed that Lactobacillus harbinensis K.V9.3.1 Np, has a great antifungal activity on yogurt during the storage, maintaining and preserving its organoleptic properties.

Once L. harbinensis K.V9.3.1 Np reached a population of about 2.5 x 106 cfu/g of yogurt at the time of contamination, total inhibition of the yeast was achieved. Then by an inoculation rate of 5 x 106 cfu/mL in milk, no detrimental effect on yogurt organoleptic properties was observed.

It has also been suggested that several antimicrobial compounds may be controlled by quorum- sensing regulatory mechanism. This regulatory system is well documented for bacteriocins production by LAB (Gobetti et al., 2007), but much less for production of antifungal compounds.

Furthermore, compounds like acetic, caproic, formic, propionic, butyric, n-valeric, and benzoic acids, as well as 3-hydroxy fatty acids, can be considered as antifungal compounds.

Probiotic cultures can also improve the food technological properties, contributing to inhibit the harmful microflora of the dairy products. A publication by Marek Aljewicz et al. (2015) reported the influence of three probiotic cultures L. rhamnosus HN001, L. acidophilus NCFM and L. paracasei LPC37 on the average counts of starter cultures and harmful bacteria such as Enterococcus sp., Clostridium perfrigens, Clostridium tirobuliricum, and other undesired microorganisms and their impact on the quality and microbiological safety of industrially produced Dutch-type cheese-like products. In this study, experimental cheese-like products and ripened cheeses were prepared. The average counts of coliform bacteria, yeasts, and molds were significantly influenced by Lactobacillus sp. counts and processing temperature.

Although the decrease in the average size of yeast and mold populations can probably be attributed to elevated concentrations of acetic acid and dyacetil, which are products of lactose, lactate, and citrate metabolism by starter lactic acid bacteria (8-9 log cfu/g) and Lactobacillus sp. strains used in the production process, yeast and mold counts were also influenced by the concentrations of lactones and hydrogen peroxide, a potent antifungal substance (Tharmaraj et al., 2009). The quantity of metabolites produced by Lactobacillus genus is related to ripening/storage temperature.

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