Defects and spoilage

Olives are, generally, more susceptible to microbial spoilage than other fermented vegetables. Initially there is a diverse microflora present in raw olives and that flora is well maintained during the early stages of the fermentation. Reflective of this heterogenous mix, spoilage organisms include aerobic bacteria and fungi, facultative bacteria and yeasts, strict anaerobes, as well as sporeforming bacteria. If the lactic fermentation is delayed due to residual lye or limiting glucose, or if the pH remains high (i.e., above 4.5), organisms capable of causing spoilage may be given ample opportunity for growth and production of spoilage products.

Several of the spoilage defects that occur in olives are not unlike those that occur in pickles and other fermented vegetables (Table 7-4). Excessive gas production and tissue softening are major problems in olives, just as they are for pickles. In olive production, for example, gas produced by coliforms early in the fermentation can accumulate as gas pockets inside the olive surface, causing an unsightly blister-like appearance called "fish-eyes." Likewise, pectin hydrolysis by pectinolytic Pénicillium, Fusarium, Aspergillus, and other fungi or, less frequently, by coliforms, results in a soft tissue defect.

Another defect that is mostly specific for olives is termed zapatera spoilage.This occurs late in the fermentation and is characterized by foul, fecal, cheesy-like odors. It is caused by Clostridium sporogenes, Clostridium bu-tyricum, and other putrefactive clostridia whose presence in fermented foods is never a good thing. These bacteria, along with other anaerobes, produce butyric acid, sulfur dioxide, and other sulfur-containing compounds. Putrescine, cadaverine, and other putrefactive and malodorous end products may also be produced. Propionibacterium sp. also are associated with zapatera spoilage, although they may be indirectly involved. Growth of Propionibacterium zeae and other related species can occur at low salt concentrations (<5%), which leads to an increase in the brine pH (as lactic acid is consumed). If the pH is high enough, clostridia are no longer inhibited.

Control of spoilage organisms can be accomplished by making sure the salt concentration is sufficiently high (>7.5%) and the pH is sufficiently low (<4.0). Olives can be given a quick heat treatment or partially acidified with lactic acid (prior to fermentation) to reduce and control the background flora.Although seldom practiced, the addition of a lactic starter culture can provide additional assurance that a prompt fermentation will occur.

Fermented Vegetables and Biogenic Amines

Nearly all fermented foods can potentially contain biogenic amines, and fermented vegetables are no exception. This is because the series of events that culminate in biogenic amine formation are essentially the same for fermented vegetables as they are for other fermented foods. Specifically, accumulation of amines occurs whenever there is an available pool of free amino acids and a source of amino acid decar-boxylase enzymes.The amino acids are formed from protein in the food by the action of mi-crobial proteinases and peptidases. The decar-boxylases are also produced by microorganisms, including lactobacilli that may be present in fermented vegetables. Thus, the amount of biogenic amines that are actually produced depends on both the concentration of the amino acid substrates and the expression and activity of the relevant decarboxylases. The biogenic amines that have been found in fermented vegetables (mainly sauerkraut, kimchi, and fermented olives) include histamine (from histi-dine), tyramine (from tyrosine), and putrescine and cadaverine (from lysine, arginine, and gluta-mine). In most cases, however, the concentrations that have been reported were less than the level ordinarily thought to cause food disease symptoms (1 g/Kg).

Bibliography

Ayres,J.C.,J.O. Mundt, and W.E. Sandine. 1980. Microbiology of Foods. Chapter 9, Lactic fermentations, p. 198-230. W.H. Freeman and Company, San Francisco. Fernández,A.G., M.J.F. Díez, and M.R.Adams. 1997. Table Olives: Production and Processing. Chapman and Hall, London. Harris, L.J. 1998.The microbiology of vegetable fermentations, p. 45-72. In B.J.B.Wood (ed.) Microbiology of Fermented Foods, Volume 1, Blackie Academic and Professional (Chapman and Hall). Nout, M.R.J., and F.M. Rombouts. 1992. Fermentative preservation of plant foods. J. Appl. Bacteriol. Symp. Supple. 73:136S-147S. Nychas, G.-J.E., E.Z. Panagou, M.L. Parker, K.W.Wal-dron, and C.C. Tassou. 2002. Microbial colonization of naturally black olives during fermentation and associated biochemical activities in the cover brine. Lett.Appl. Microbiol. 34:173-177. Pederson, C.S. 1960. Sauerkraut. In C.O. Chichester, E.M. Mrak, and G.F. Stewart (ed.), Advances in Food Research. 10:233-291. Randazzo, C.L., C. Restuccia, A. D. Romano, and C. Caggia. 2004. Lactobacillus casei, dominant species in naturally fermented Sicilian green olives. Int. J. Food Microbiol. 90:9-14. Romero, C., M. Brenes, K.Yousfi, I? García,A. García, and A. Garrido. 2004. Effect of cultivar and processing method on the contents of polyphenols in table olives.J.Agri. Food Chem. 52:479-484.

Bread Fermentation

"... cut for yourself, if you will, a slice of bread that you have seen mysteriously rise and redouble and fall and fold under your hands. It will smell better, and taste better, than you remembered anything could possibly taste or smell, and it will make you feel, for a time at least, newborn into a better world than this one often seems."

From How to Rise Up Like New Bread by M.F.K. Fisher 1942

Introduction

The fermentation that occurs during bread manufacturing is different from most other food fermentations in that the purpose is not to extend the shelf-life of the raw materials, per se, but rather is a means of converting the grain or wheat into a more functional and consumable form. In fact, in contrast to dairy, meat, vegetable, or wine fermentations, where the starting material is much more perishable than the finished product, the raw material for bread-making, i.e., cereal grains, are better preserved than the bread that is ultimately produced. It is also interesting to note that in the bread fermentation, again in contrast to other lactic acid or ethanolic fermentations, essentially none of the primary fermentation end products actually remain in the food product.

In the United States, bread manufacturing is a $16 billion industry. Despite its commercial and dietary importance, however, consumption of bread was substantially higher a century ago than it is currently.At the end of the nineteenth century, for example, Americans consumed more than 100 Kg of wheat flour (used mostly for bread) per person per year. Consumption of wheat, however, then began to decline steadily for nearly a hundred years, reaching an all-time low of just 50 Kg per person per year in the

1960s. During the next thirty years, per capita grain consumption slowly increased, to nearly 70 Kg (Figure 8-1), only to fall back slightly in 2000 to just under 65 Kg,presumably as a result of the popularity of low-carbohydrate diets (more than one-third of Americans think that bread is "fattening").

Given the recommendations made in the USDA's revised Food Pyramid and 2005 Dietary Guidelines, one might expect that consumption of bread (and whole grain breads, in particular) will begin to increase. Still, some countries already have much higher per capita consumption of bread, compared to the United States (Figure 8-2), with annual consumption of more than 140 Kg per person (more than 0.8 pounds per day). Compared to European and other high bread-consuming countries, the United States ranks near the bottom for bread consumption, at only 25 Kg per person per year (less than 2.5 ounces per day).

History

It is impossible to know exactly when humans first made and ate bread. Ancient artifacts and writings discovered in the Middle East suggest that bread-making had its origins in the eightieth century B.C.E., but it is possible that bread may have been produced even

Figure 8-1. Wheat flour consumption (per person per year) in the United States. Adapted from the USDA Economic Research Service.

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