meat fermentation

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Chapter 13

Meat

The curing of meat pre-dates the Romans as an exercise in enhancing meat

quality and preserving it.

It comprises lactic fermentation of mixtures of meat, fat, salt, curing agents

(either nitrate or nitrite), reducing agents, spices and sugar. Frequently the

meat is encased in a tubular form as sausage.

The role of components of the curing mixture

Salt solubilises the proteins of the muscle as well as increasing the osmotic

pressure such that spoilage by bacteria is suppressed. Naturally it enhances

flavour. Levels may range from 2% to 3% to as high as 6% to 8%.

The key component is sodium nitrite, which promotes the typical colour

of preserved meats through the formation of nitric oxide compounds by reac-

tion with the haem of myoglobin (Fig. 13.1). Furthermore, it contributes to

flavour as well as inhibiting the development of pathogens such as Clostridium

botulinum. The downside is the production of the potentially carcinogenic

nitrosamines and so there are legal limits on how much may be used (e.g.

120 ppm for US bacon). Meat typically has a pH of between 5.5 and 6 after

rigor mortis is complete. At this pH, nitrite is converted to N2O, which also

features in curing. Nitrate may replace nitrite, in which case it is converted to

nitrite through the action of bacteria.

Sodium phosphate increases the water-binding capacity of the protein,

leading to a stabilisation of the myofibrils. It also binds heavy metals and

thus helps protect against the microbes that need those metals.Sugar is added to counter the salt flavour-wise and is also the carbon and

energy source for any microbes necessary for fermentation, for example, those

organisms involved in the reduction of nitrate. This sugar will react during

any heating stages in Maillard reaction to impact colour and flavour.

Reducing agents, notably ascorbate, reduce nitrite to the nitric oxide

that reacts with myoglobin and also helps to suppress the development of

nitrosamines.

Binding agents and emulsifiers may be used to improve stability. They may

include soy (or hydrolysed soy) starches and carrageenan.Finally, antioxidants such as BHT and propyl gallate may be added to

counter the development of rancidity through lipid oxidation.

Food, Fermentation and Micro-organisms

Charles W. Bamforth

Copyright 2005 by Blackwell Publishing Ltd


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Meat 183

Globin binds

COO

CH2 CH2

CH2 CH2

H3C

H2C

CH3 CH2

C CH

C

C

C C

CC C

C

C C

C CH3

CH3

C

C CH

CH C

CH

C

HC CH

N

Fe

N N

N

COO

Remaining

chelation site

Fig. 13.1 The interaction of nitrite with haem. The sixth binding site, occupied by nitrite, is the

one otherwise occupied by oxygen, carbon monoxide, cyanide, etc.

Table 13.1 Classifications of fermented sausage.

Type Aw

Fermentation

time (weeks)

Surface

mould

growth

Smoked/

not smoked Example Origin

Dry 4 Yes No Salami Italy

Dry 4 Yes Yes Salami Hungary

Dry 4 No Either Dauerwurst Germany

Semi-dry 0.90.95


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184 Food, Fermentation and Micro-organisms

If no starter culture is used, then the pH reaches only 4.65. Fermentation

here is dependent upon endogenous organisms such as Lactobacillus sakeiand

Lb. curvatus.

In the production of fermented sausages, the comminuted lean and fatty

tissue is mixed with salt, spice, sugar, curing agent and starter cultures and

put into casings. The Aw of a starting semi-dry sausage mix is achieved by

employing some 3035% of fatty tissue and 2.53% salt. Nitrite is added in

the range of 100150 mg kg1, and ascorbic acid is also generally included at

300500 mg kg1. For dry sausages, nitrate may replace nitrite and the fer-

mentation temperature is likely to be lower. Mixes incorporate 0.3% glucose

to act as substrate for lactic acid bacteria. The oxygen is rapidly consumed

by endogenous meat enzymes. The acid produced in fermentation promotes

the reaction of nitrite with metmyoglobin to produce NO-myoglobin. Any

residual nitrite is reduced by the microflora. The temperature is lowered to

approximately 15

C and the relative humidity in the chamber is brought downto 7580%. Much of the flavour and aroma that develops is due to the degrada-

tion of lipids, notably through autoxidation and the microbial transformation

of the products generated by lipid degradation (Fig. 13.2). Additionally, pro-

teinases produce peptides that are converted by the microflora to amino acids

and volatile fatty acids.

The sausage may be aged (dried) and smoked. A surface growth may

be allowed to develop and this comprises inter alia salt-tolerant yeasts (e.g.

Debaromyces hansenii) and moulds. Where smoking is performed, surface

microflora are eliminated. The flora may also be reinforced by starters ofPeni-

cillium nalgiovense or Penicillium chrysogenum. The surface moulds scavenge

oxygen and assist the drying process.

LH

L

LO2

LO2H

Carbonyls

I

IH

O2

LH

LH = unsaturated fatty acidI = initiator radical,

e.g. hydroxyl, perhyxdroxylL = alkyl radicalL = peroxyradicalLO2H = hydroperoxide

Fig. 13.2 The fundamental route for autoxidation of unsaturated fatty acids.


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Meat 185

The pH of unground meat must be below 5.8 to prevent the growth of

undesirable organisms (pathogens). It is also important that the raw material

should not be oxidised (i.e. it should have a low peroxide value). To this end,

the meat may first be chilled or frozen to prevent oxidation. Furthermore,

the access of oxygen to the meat will be minimised at all stages. To ferment

unground meat, salt is first rubbed into the surface, or the meat is dipped in

brine, or it is injected with the salt. The meat is then kept at 10C to allow the

salt to become evenly distributed throughout thepiece. The meat is then shifted

to 1530C to allow for water loss and the action of endogenous proteinases

in the meat, which degrade the protein structure and increase tenderness and

improve the flavour. During this time, a surface bloom of cocci, moulds and

yeasts may develop. The meat may be smoked and then dried to the target Aw.

Bibliography

Campbell-Platt, C.H. & Cook, P.E. (1994) Fermented Meats. London: Blackie.

Lcke, F.-K. (2003) Fermented meat products. In Encyclopedia of Food Sciences and

Nutrition (eds B. Caballero, L.C. Trugo & P.M. Finglas), pp. 23382344. Oxford:

Academic Press.

Varnam, A.H. & Sutherland, J.P. (1995) Meat and Meat Products. London:

Chapman & Hall.

meat fermentation

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