The Nature And Dynamics Of Ripening

It has been repeatedly confirmed that safety, stability, and sensory quality of fermented sausages are the result of a complex and interacting set of microbiological, physical, and (bio-)chemical changes (4,11,13,14). Within this complexity, most attention has been directed to the role of bacteria in relation to both safety and flavor: a ''Web of Science'' search for ''fermented sausage'' in April 2002 shows 194 papers published since 1977 (0.00075% of all documents !), 100 of which were published since 1997, containing 62 dealing exclusively with the behavior of desirable or undesirable microorganisms. Safety has been the subject of excellent reviews describing the ''hurdle concept'' (34) as well as focusing on the potential of bacteriocinogenic lactic acid bacteria (52) and will not be further discussed here. Besides an adequate redox-potential and the presence of nitrite and competitive desirable bacteria, major hurdles ensuring bacteriological safety are considered to be either the rate and extent of acidulation (10) or the extent of drying (lowered aw) (9) for NP and MP, respectively.

A. The Dynamics of Acidulation and Drying

Both the rates and extents of acidulation and drying can be quantified using simple exponential models (13) allowing demonstration of effects of processing factors such as the use of back slopping and starter cultures, sausage diameter, as well as the use of additives such as spices and soy protein (13,53-55). The same models allow for the quantitative evaluation of the relations between rates of acidulation and those of drying and texture development (19). Predicted changes of DM content are assumed to be determined by water loss (drying) only, and thus can be used to predict weight losses (55), for the calculation of empirical or ''effective'' diffusion rates (13,56) and, together with data for salt content, for the prediction of aw values with acceptable precision (57,58).

B. The Nature and Dynamics of Sausage Metabolism

The carbohydrate, protein, and lipid fractions of the sausage are subject to changes brought about by chemical as well as biochemical changes, and the latter are mediated by microbial as well as by muscle and fat tissue enzymes. Multifactorial effects involving raw materials, additives, and starter cultures as well as processing determine the relative intensities of these changes, mainly reflected in the rate and extent of acidulation and the development of sensory quality characteristics.

1. Sausage Metabolism and Acidulation

It is now clear that acidulation of the sausage matrix is induced by the interaction of salt-solubilized muscle proteins with both lactic acid and ammonia formed during fermentation (33,59). Molar amounts of lactate and ammonia present (59) as well as produced (54) during sausage ripening have indeed been related to pH and pH changes, respectively. Lactate is mainly produced from (added) carbohydrates but may also be formed during microbial fermentation of glycerol, liberated in lipolysis, and, together with ammonia, from fermentation of amino acids. Besides lactic acid, variable amounts of acetic acid are produced, determined by the nature of the bacteria and their metabolism, both affected by the processing conditions. Finally, considerable amounts of oxygen are consumed during ''fermentation,'' therefore better referred to as metabolism (60). This overall ''sausage metabolism" affects the relationship between the amounts of carbohydrate ''fermented'' and lactate produced and has been described in a simplified stoichiometric model (61,14), represented in Fig. 1.

Such a model ignores the complexity of bacterial amino acid metabolism (11), representing it by either deamination to ammonia or decarboxylation to amines. Nevertheless, it has been supported by experimental data, within experimental error (60). Together with simple exponential analytical models, stoichiometry can be used to characterize the respective rates and relative importance of carbohydrate and protein oxidation (respiration) and fermentation, as well as the nature of fermentation (lactate/ acetate) (14). In contrast to the kinetic and analytical models, referred to under Sec III.A, models for metabolism are mechanistic, require more analytical data, and are therefore better suited for comprehensive rather than predicting purposes (62). For example, they have been used to illustrate effects of the processing factors mentioned earlier (Sec. III.A) as well as chopping intensity (63) on the relative importance of respiration and protein fermentation. Table 2 shows that in a series of experiments characterizing ripening metabolism of NP, carbohydrate disappearance accounted for between 82% and 94% of pyruvate equivalents metabolized.

An increase of diameter was shown to increase the relative contribution of protein fermentation as well as the accumulation of free amino acids, buffering the increased rate of lactate production. The relative importance of protein (amino acid) fermentation with ammonia production was lowered by addition of active lactic acid bacteria. When the latter were added during backslopping, however, or as isolates from fermented sausages, proteolytic activity is apparent—an important effect for flavor, as recently confirmed (47).

Amines

Figure 1 Reaction scheme underlying the stoichiometric model of sausage metabolism.

Acetate

Amines

Figure 1 Reaction scheme underlying the stoichiometric model of sausage metabolism.

Table 2 Effect of Processing Conditions on the Pattern of Sausage Metabolism During Ripening of NP (21 days) (% of Pyruvate Equivalents Derived from Carbohydrate and Protein and Utilized in Fermentation to Lactate and Acetate and in Respiration.)

Added starters3 Sausage diameterb Chopping timec (min)

Table 2 Effect of Processing Conditions on the Pattern of Sausage Metabolism During Ripening of NP (21 days) (% of Pyruvate Equivalents Derived from Carbohydrate and Protein and Utilized in Fermentation to Lactate and Acetate and in Respiration.)

Added starters3 Sausage diameterb Chopping timec (min)

Effect of

None

Was this article helpful?

0 0
Bread Making

Bread Making

Discover How To Surprise Family and Friends With Homemade Bread? Is Your Bread Coming Out Doughy Or Crumbly? Well, you don't have to be frustrated anymore by baking bread that doesnt rise all of the way or just doesn't have that special taste.

Get My Free Ebook


Post a comment