LAB SPOILAGE

Management of LAB and MLF can go astray at any juncture in the winemaking process. The following section addresses the chemical and physical manifestations of mismanagement. Use of preservatives or chem-ical/physical sterilization will be considered along with bottling in Chapter 6. 

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Protein swell is an unusual type of LAB spoilage, because it raises the pH of the spoiled product. This type of LAB spoilage was first reported by Meyer in 1956 in canned fish marinades (Schillinger and Holzapfel 2006). He called it protein swell ... 

Most native LAB species are relatively sensitive to the low pH and increasing alcohol environs of juice and fermenting wine. The point at which LAB spoilage may become increasingly apparent is pH >3.5. Below this, strains of Leuconostoc oenos typically represent the dominant flora, whereas at higher pH levels, the lactobacilli and pediococci may also develop. 

Unfortunately, uncontrolled MLF also presents a risk of wine spoilage by compounds that can produce off-flavours (including acetic acid, volatile phenols and mousiness) or that may be hazardous to human health (such as ethyl carbamate and biogenic amines). The most important aspects of the development of LAB and MLF in wines are dealt with in this chapter. 

Besides carrying out MLF, under certain conditions LAB can also cause undesirable changes in wine flavour which render the wine undrinkable. Many species of LAB do not conduct MLF and their growth in wine can cause some serious wine spoilage. The nature and extent of this spoilage depend on several factors such as the type of bacteria, composition of the wine and vinification practices specific types of spoilage are associated with a restricted number of lactobacilli. 

When alcoholic fermentation is too slow or when it stops, conditions are favourable for bacterial development. LAB ferment different quantities of sugars that have not been totally fermented by yeasts and produce acetic acid and D-lactic acid. This alteration is called Lactic disease" (piqure lactique) and is characterised by a high volatile acidity that depreciates the wine. If this volatile acidity exceeds the limit of 1 g/L, the wine is unmarketable (Lonvaud-Funel 1999). This spoilage also occurs in fortified wine where O. oeni, L. hilgardii, L. fructivorans and L. plantarum are active in spite of very high ethanol contents. 

Several strains of LAB isolated from wine were tested for their abilities to metabolize ferulic and p-coumaric acids. Cavin et al. (1993) showed that these acids were strongly decarboxylated by growing cultures of Lactobacillus brevis, Lactobacillus plantarum, and Pediococcus when decarboxylation was observed, volatile phenols (4-ethylguaiacol and 4-ethylphenol) were detected, indicating the possibility of reduction of the side chain before or after decarboxylation. Couto et al. (2006) reported L. collinoides as a producer of volatile phenols, although strain specificity concerning this capacity was observed. L. mali, L. sake, L. viridescens, and P. acidi-lactici were also found to be able to produce volatile compounds but they only perform the decarboxylation step. Volatile phenols cause animal taints such as horse sweat, wet animal and urine that are usually attributed to Brettanomyces spoilage. 

However, some LAB can be associated with spoilage problems including stuck alcoholic fermentations (Edwards et al., 1999 Huang et al., 1996), production of off-flavors or off-odors (Costello and Henschke, 2002 Drysdale and Fleet, 1989a Sponholz, 1993), excessive volatile acidity (VA) (Drysdale and Fleet, 1989a Huang et al., 1996), synthesis of polysaccharides responsible for ropiness (Manca de Nadra and Strasser de Saad, 1995), or other defects. 

The primary contributions of the LAB to a food product are to preserve the nutritive qualities of the raw material, by extending the shelf life and also by controlling the growth of spoilage and pathogenic bacteria. This is achieved by production of the inhibitory substances and by competing for nutrients (O Sullivan et al., 2002). They occur naturally in foods and as such, have traditionally been used as natural biopreservatives of... 

The lactic acid accumulated during the production of fermented milks and cheeses, besides the related pH drop, represents the key component for the antimicrobial effect of dairy LAB against many spoilage and/or pathogenic bacteria. On the other hand, in some dairy products, and mainly in vegetable-based fermented foods or in intermediate food products such as sourdough, acetic acid released by facultatively or obli-gately heterofermentative LAB can account for an additive preservative effect related to fermentation. 

The potential for L plantarum to prolong the shelf life of fresh vegetables was studied by Sathe, Nawani, Dhakephalkar, and Kapadnis (2007). To show the antifungal activity of this LAB, cucumbers were wounded, inoculated with L plantarum, and challenged with several spoilage molds, such as Aspergillus flavus, F graminearum, Rhizopus stolonifer, and Botrytis cinerea. The size of the lesions were evaluated after 9 days of incubation (20°C and 85% relative humidity), and results indicated that L plantarum was able to reduce up to 95% the diameter of the lesions caused by R. stolonifer and 88-93% the size of the ones caused by the other molds tested (Table 14.2). 

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