Sausage is a traditional Chinese cured meat product. It is mainly made of lean pork and pork back fat, supplemented with salt, nitrite (or nitrate), Chinese liquor, sugar and other accessories. The finished product is obtained through stirring, pickling, casing filling, drying and hanging curing.
In industrial production, traditional natural drying is replaced by baking at 45～55℃ for 40 to 60 hours. This method shortens production cycles, cuts costs and improves economic benefits, yet brings multiple quality defects including surface oil leakage, greasy taste, bland flavor, oxidative rancidity and discoloration. Souring stands out as the most prominent problem. Fat rancidity not only causes an unpleasant stale odor, but also generates substances harmful to human health. This paper analyzes the causes of sausage souring and corresponding preventive measures.
1. Process of Fat Rancidity
Fat accounts for 20% to 40% of raw meat, which is prone to deterioration and leads to product souring. Fat rancidity falls into two categories.
1.1 Hydrolytic Rancidity
Hydrolytic rancidity refers to the decomposition of triglycerides into diglycerides, glycerol and free fatty acids under high temperature, acid, alkali or microbial lipase, accompanied by increased acid value. It commonly occurs when oil is stored under high temperature, humid and impure conditions. The optimal temperature of lipase is 25-35℃. Without enzymatic action, only one fatty acid chain of triglyceride will break down. Fat hydrolysis barely reduces nutritional value. Nevertheless, when free fatty acid content reaches 0.75%, further hydrolysis will be accelerated. Strong offensive odor will emerge once the content exceeds 2%.
1.2 Oxidative Rancidity
Fat undergoes spontaneous oxidation when exposed to air. Oxidative rancidity results from complex chemical reactions triggered by oxygen, heat, light, enzymes and microorganisms. Continuous fat hydrolysis produces abundant free fatty acids and raises the acid value. Partial unsaturated fatty acids are oxidized mostly via autoxidation, forming hydroperoxides and increasing peroxide value. These unstable primary oxidation products further decompose into low-molecular compounds such as aldehydes, ketones, alcohols and hydroxymethyl substances, producing typical sour rancid smell. The TBA value indicates fat oxidation degree, reflecting the content of malondialdehyde, a secondary oxidation product.
Sausage has low moisture content of 15%~20% and water activity ranging from 0.6 to 0.9. Autoxidation serves as the main cause of souring, with thermal oxidation and photo-oxidation being major inducing factors.
2. Analysis on Causes of Souring in Cured Sausage
2.1 Raw Material Factors
Stale or excessively crushed back fat easily triggers fat oxidation. Poultry fat is softer and more susceptible to oxidation than pork fat. Mechanically deboned chicken meat raises material temperature during processing, accelerating microbial reproduction as well as fat hydrolysis and oxidation. Soy protein powder rich in carbohydrates and white sugar are decomposed into acidic substances by microorganisms, aggravating fat hydrolytic rancidity.
2.2 Technological Factors
2.2.1 Blanching Temperature of Fat
Traditional blanching temperature is 50～60℃, designed to remove free oil from damaged fat particles and avoid gelatinization and oil exudation. Modern processing adopts 100℃ blanching. Though lipase loses activity at this temperature, the rinsing process mostly stays at 30～50℃. Unused fat after blanching is highly vulnerable to hydrolytic deterioration.
2.2.2 Stuffing Technology
Insufficient vacuum degree or excessive stuffing speed traps abundant air bubbles inside semi-finished products, facilitating fat oxidation.
2.2.3 Drying Technology
Excessively high temperature and inadequate moisture exhaust create a hot and humid environment, speeding up fat hydrolysis and raising acid value.
2.2.4 Packaging Materials
Oxygen, moisture and light promote fat rancidity. Packaging films with low oxygen permeability, low moisture permeability and good light barrier performance can effectively inhibit fat deterioration.
2.2.5 Circulation and Storage
Temperature fluctuation and prolonged exposure to hot humid surroundings shall be avoided. Temperature change condenses water on sausage surface and creates conditions for fat hydrolysis.
3. Preventive Measures against Fat Rancidity
3.1 Production Control
Adopt fresh raw meat and firm back fat instead of belly fat and broken fat. Strictly control blanching temperature and duration, and process fat immediately after blanching without overnight storage. Avoid overmixing and control stuffing speed properly.
3.2 Packaging Control
3.2.1 Vacuum Packaging
Air is extracted to form an oxygen-free environment and prevent fat oxidation. Packaging materials with low oxygen permeability are preferred.
3.2.2 Modified Atmosphere Packaging
The package is filled with inert mixed gas such as 70% CO₂ and 30% N₂ after air removal for fresh-keeping effect. This technology is widely applied overseas but rarely used domestically due to high cost.
3.2.3 Oxygen Absorber Application
Independent oxygen absorber sachets eliminate free and penetrating oxygen inside packages to extend shelf life, with no toxic effect on human body.
3.2.4 Antioxidant Addition
Antioxidants are divided into synthetic and natural types. Natural antioxidants are more acceptable, mainly phenolic compounds including tea polyphenols, tocopherol, rosemary extract and sesamol, which effectively restrain fat oxidation with strong reducibility.
The combined application of vacuum packaging and antioxidants is the mainstream prevention method. Common antioxidants include TBH, BHT and BHA, which exert better effects when used in compound formulas.
In industrial production, traditional natural drying is replaced by baking at 45～55℃ for 40 to 60 hours. This method shortens production cycles, cuts costs and improves economic benefits, yet brings multiple quality defects including surface oil leakage, greasy taste, bland flavor, oxidative rancidity and discoloration. Souring stands out as the most prominent problem. Fat rancidity not only causes an unpleasant stale odor, but also generates substances harmful to human health. This paper analyzes the causes of sausage souring and corresponding preventive measures.
1. Process of Fat Rancidity
Fat accounts for 20% to 40% of raw meat, which is prone to deterioration and leads to product souring. Fat rancidity falls into two categories.
1.1 Hydrolytic Rancidity
Hydrolytic rancidity refers to the decomposition of triglycerides into diglycerides, glycerol and free fatty acids under high temperature, acid, alkali or microbial lipase, accompanied by increased acid value. It commonly occurs when oil is stored under high temperature, humid and impure conditions. The optimal temperature of lipase is 25-35℃. Without enzymatic action, only one fatty acid chain of triglyceride will break down. Fat hydrolysis barely reduces nutritional value. Nevertheless, when free fatty acid content reaches 0.75%, further hydrolysis will be accelerated. Strong offensive odor will emerge once the content exceeds 2%.
1.2 Oxidative Rancidity
Fat undergoes spontaneous oxidation when exposed to air. Oxidative rancidity results from complex chemical reactions triggered by oxygen, heat, light, enzymes and microorganisms. Continuous fat hydrolysis produces abundant free fatty acids and raises the acid value. Partial unsaturated fatty acids are oxidized mostly via autoxidation, forming hydroperoxides and increasing peroxide value. These unstable primary oxidation products further decompose into low-molecular compounds such as aldehydes, ketones, alcohols and hydroxymethyl substances, producing typical sour rancid smell. The TBA value indicates fat oxidation degree, reflecting the content of malondialdehyde, a secondary oxidation product.
Sausage has low moisture content of 15%~20% and water activity ranging from 0.6 to 0.9. Autoxidation serves as the main cause of souring, with thermal oxidation and photo-oxidation being major inducing factors.
2. Analysis on Causes of Souring in Cured Sausage
2.1 Raw Material Factors
Stale or excessively crushed back fat easily triggers fat oxidation. Poultry fat is softer and more susceptible to oxidation than pork fat. Mechanically deboned chicken meat raises material temperature during processing, accelerating microbial reproduction as well as fat hydrolysis and oxidation. Soy protein powder rich in carbohydrates and white sugar are decomposed into acidic substances by microorganisms, aggravating fat hydrolytic rancidity.
2.2 Technological Factors
2.2.1 Blanching Temperature of Fat
Traditional blanching temperature is 50～60℃, designed to remove free oil from damaged fat particles and avoid gelatinization and oil exudation. Modern processing adopts 100℃ blanching. Though lipase loses activity at this temperature, the rinsing process mostly stays at 30～50℃. Unused fat after blanching is highly vulnerable to hydrolytic deterioration.
2.2.2 Stuffing Technology
Insufficient vacuum degree or excessive stuffing speed traps abundant air bubbles inside semi-finished products, facilitating fat oxidation.
2.2.3 Drying Technology
Excessively high temperature and inadequate moisture exhaust create a hot and humid environment, speeding up fat hydrolysis and raising acid value.
2.2.4 Packaging Materials
Oxygen, moisture and light promote fat rancidity. Packaging films with low oxygen permeability, low moisture permeability and good light barrier performance can effectively inhibit fat deterioration.
2.2.5 Circulation and Storage
Temperature fluctuation and prolonged exposure to hot humid surroundings shall be avoided. Temperature change condenses water on sausage surface and creates conditions for fat hydrolysis.
3. Preventive Measures against Fat Rancidity
3.1 Production Control
Adopt fresh raw meat and firm back fat instead of belly fat and broken fat. Strictly control blanching temperature and duration, and process fat immediately after blanching without overnight storage. Avoid overmixing and control stuffing speed properly.
3.2 Packaging Control
3.2.1 Vacuum Packaging
Air is extracted to form an oxygen-free environment and prevent fat oxidation. Packaging materials with low oxygen permeability are preferred.
3.2.2 Modified Atmosphere Packaging
The package is filled with inert mixed gas such as 70% CO₂ and 30% N₂ after air removal for fresh-keeping effect. This technology is widely applied overseas but rarely used domestically due to high cost.
3.2.3 Oxygen Absorber Application
Independent oxygen absorber sachets eliminate free and penetrating oxygen inside packages to extend shelf life, with no toxic effect on human body.
3.2.4 Antioxidant Addition
Antioxidants are divided into synthetic and natural types. Natural antioxidants are more acceptable, mainly phenolic compounds including tea polyphenols, tocopherol, rosemary extract and sesamol, which effectively restrain fat oxidation with strong reducibility.
The combined application of vacuum packaging and antioxidants is the mainstream prevention method. Common antioxidants include TBH, BHT and BHA, which exert better effects when used in compound formulas.
