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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.
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