10-10-2014, 11:33 AM
ELECTRONIC NOSE IN
FOOD INDUSTRY
[attachment=68965]
ABSTRACT
The main motivation for electronic nose is the development of qualitative, low cost, real-time and portable method performs reliable objective and reproducible measure of volatile compounds and odours. Odour is one of the most important indicators of food quality. Electronic nose mimics the human olfactory system. Two main components of our system and pattern recognition system. The sensing can be an array of sensors. There are different types sensors. Data processing is mainly done by Artificial Neural Network System. The application of electronic system in food analysis are freshness evaluation of fruits and vegetablesShelf life investigation ,quality analysis,maturity evaluation, detection of contamination, spoilage, adulteration etc. Some researches shows electronic nose system is very effective for monitory the maturity and shelf life of tomatoes. And it is also used for the detection of TVB-N content in egg which is one of the factor responsible for the shelf life of egg.
INTRODUCTION
In the food industry, flavours are important, from the raw ingredients to the final product. Flavour is a major criterion for consumers to accept or reject a product, and greatly influences decision on repeat-purchases. There are two components of flavour perception: taste and aroma. Taste occurs from the presence of non-volatile, the flavour cannot be defined by taste alone.
Many volatile compounds are responsible for the aroma of foods, and play an important role in flavour. These volatiles contribute to the nature of food, its product identify, and consumer preferences. They may also be responsible for the occurrence of off- flavour and taints, due to biochemical, chemical or microbial changes, or contamination (HODDINS, 1997).
Humans can detect a minimum of 10,000 odours, but the number of identifiable odours is about 50 (BARTLETT et al., 1997). A molecule can have a distinct odour. However, most natural smells or flavours are a complex mixture of chemicals, and contain hundreds of constituents(DODD et al.,1992).
Odour molecules can be detected by humans below 1ppb. Gas chromatography /Mass Spectrometry is used to detect odours at low levels, but the sample must be separated into its components before identification. However, true aroma is related to the complex interaction of all volatile compounds within foods. For example, using a gas chromatograph with a sniffer port, none of the individual aromatic compounds present in cocoa smelled like cocoa to humans; however, when all of these compounds combined, the overall aroma was that of cocoa (HODGINS and SIMMONDS, 1995; HODGINS, 1997). In addition, gas Chromatography/Mass Spectrometry is expensive, and requires a technician for operation and interpretation of the results
Due to these constraints, sensory analysis has been used for a long time for odour evaluation. However, sensory panel responses have potential problems (reproducibility, difficulties of expression, and stability).
These make it hard to compare results between different panels (BARTLETT et al. ,1997; HODGINS and SIMMONDS, 1995). There is a need for an instrument that can mimic our sense of smell, and provide rapid sensory information at low cost and without sample preparation. Electronic nose can be an alternative in this respect.
ELECTRONIC NOSE SYSTEM
The two main components of the system are the sensing system and the pattern recognition system. The combination of broadly tuned sensors coupled with sophisticated information processing makes the e-nose a powerful instrument for odour analysis application. The sensing system can be an array of chemical sensors where each the sensor measures a different property of the sensed chemical. Depending upon the type of the sensor used in the system, absorption and desorption of volatile compound cause a change in either the electrical resistance or frequency shift of each sensor. This information is recorded; and pattern recognition by neutral network is used to discriminate volatile compounds from different sources.[Bhat,K.K 2005]
3. Sample cell:
The goal of sampling is to collect the volatile compounds that represent the real condition of an analytical problem and to provide adequate concentration of compounds to the sensors for detection. Static headspace sampling methods are commonly used in measuring low molecular weight volatile compounds with low boiling points such as hydrogen sulphide, dimethyl sulphide and amine.
The e-nose sampling procedure included a wash cycle consist of a 30 second, 3% butanol wash to remove all of the odourant from the sensors before sampling. A 270-second reference cycle was then performed using air that had both humidity and organicvapors removed by a gas purification filter. Thus, the sensors reached a reference value before sample testing small syringe was attached to the opening of the purge inlet of the electronic node system. The syringe was filled with about 3 gram of dielectric and dry cotton balls. Atmospheric air used for purging the sensors passed through the syringe filled with drierite and cotton. They helped to remove any moisture and unnecessary odour from atmospheric air.
During the 60 second sampling cycle, volatile compounds are transferred as rapidly as possible to the measurement cell through tubing, which must be entirely composed of inert materials to avoid the adsorption or chemical modification of the compounds[Dodd,T.H,et al.2004
ARTIFICIAL NEURAL NETWORK MODEL
The back propagation model is commonly used. This model is known for its ability to generalize well on a wide variety of problems. This network is generally robust, although on of drawback is that the traing is slow. Typically there layers are sufficient for the vast majority of problems and each layer is connected to the immediately previous layer.
Formal ANN is made from artificial neurons. The most widespread variant is the MacCullob and Pitts neuron, representing the elementary model of the biological neuron. For the effective decision of the quantitative substance analysis, ANN should pass a traing stage. In addition, the adjustment of topology, weight factor etc. are carried out by specially formed training section.
At traing, the artificial neutral network should have the correct output signals. To achieve it, the traing is considered to be complete, when the criterion of the traing is stabilized at some level. By the way of such criterion residual dispersion is applied.
CONCLUSION
The e-nose system to be an excellent system for general-purpose application. Electronic nose is being used as an effective tool for rapid determination of aroma quality at various stages of designing and formulation of food products. Depending upon the products parameters will vary. The sensitivity and accuracy of e-nose can be further improved by adopting a combination of sensors. Food designing requires a quick analysis of food aroma at the developmental stage. Because of its versatility and case of operation e-nose is proving to the immense value in the field of product development, in processing quality control and life studies of packaged food.
FOOD INDUSTRY
[attachment=68965]
ABSTRACT
The main motivation for electronic nose is the development of qualitative, low cost, real-time and portable method performs reliable objective and reproducible measure of volatile compounds and odours. Odour is one of the most important indicators of food quality. Electronic nose mimics the human olfactory system. Two main components of our system and pattern recognition system. The sensing can be an array of sensors. There are different types sensors. Data processing is mainly done by Artificial Neural Network System. The application of electronic system in food analysis are freshness evaluation of fruits and vegetablesShelf life investigation ,quality analysis,maturity evaluation, detection of contamination, spoilage, adulteration etc. Some researches shows electronic nose system is very effective for monitory the maturity and shelf life of tomatoes. And it is also used for the detection of TVB-N content in egg which is one of the factor responsible for the shelf life of egg.
INTRODUCTION
In the food industry, flavours are important, from the raw ingredients to the final product. Flavour is a major criterion for consumers to accept or reject a product, and greatly influences decision on repeat-purchases. There are two components of flavour perception: taste and aroma. Taste occurs from the presence of non-volatile, the flavour cannot be defined by taste alone.
Many volatile compounds are responsible for the aroma of foods, and play an important role in flavour. These volatiles contribute to the nature of food, its product identify, and consumer preferences. They may also be responsible for the occurrence of off- flavour and taints, due to biochemical, chemical or microbial changes, or contamination (HODDINS, 1997).
Humans can detect a minimum of 10,000 odours, but the number of identifiable odours is about 50 (BARTLETT et al., 1997). A molecule can have a distinct odour. However, most natural smells or flavours are a complex mixture of chemicals, and contain hundreds of constituents(DODD et al.,1992).
Odour molecules can be detected by humans below 1ppb. Gas chromatography /Mass Spectrometry is used to detect odours at low levels, but the sample must be separated into its components before identification. However, true aroma is related to the complex interaction of all volatile compounds within foods. For example, using a gas chromatograph with a sniffer port, none of the individual aromatic compounds present in cocoa smelled like cocoa to humans; however, when all of these compounds combined, the overall aroma was that of cocoa (HODGINS and SIMMONDS, 1995; HODGINS, 1997). In addition, gas Chromatography/Mass Spectrometry is expensive, and requires a technician for operation and interpretation of the results
Due to these constraints, sensory analysis has been used for a long time for odour evaluation. However, sensory panel responses have potential problems (reproducibility, difficulties of expression, and stability).
These make it hard to compare results between different panels (BARTLETT et al. ,1997; HODGINS and SIMMONDS, 1995). There is a need for an instrument that can mimic our sense of smell, and provide rapid sensory information at low cost and without sample preparation. Electronic nose can be an alternative in this respect.
ELECTRONIC NOSE SYSTEM
The two main components of the system are the sensing system and the pattern recognition system. The combination of broadly tuned sensors coupled with sophisticated information processing makes the e-nose a powerful instrument for odour analysis application. The sensing system can be an array of chemical sensors where each the sensor measures a different property of the sensed chemical. Depending upon the type of the sensor used in the system, absorption and desorption of volatile compound cause a change in either the electrical resistance or frequency shift of each sensor. This information is recorded; and pattern recognition by neutral network is used to discriminate volatile compounds from different sources.[Bhat,K.K 2005]
3. Sample cell:
The goal of sampling is to collect the volatile compounds that represent the real condition of an analytical problem and to provide adequate concentration of compounds to the sensors for detection. Static headspace sampling methods are commonly used in measuring low molecular weight volatile compounds with low boiling points such as hydrogen sulphide, dimethyl sulphide and amine.
The e-nose sampling procedure included a wash cycle consist of a 30 second, 3% butanol wash to remove all of the odourant from the sensors before sampling. A 270-second reference cycle was then performed using air that had both humidity and organicvapors removed by a gas purification filter. Thus, the sensors reached a reference value before sample testing small syringe was attached to the opening of the purge inlet of the electronic node system. The syringe was filled with about 3 gram of dielectric and dry cotton balls. Atmospheric air used for purging the sensors passed through the syringe filled with drierite and cotton. They helped to remove any moisture and unnecessary odour from atmospheric air.
During the 60 second sampling cycle, volatile compounds are transferred as rapidly as possible to the measurement cell through tubing, which must be entirely composed of inert materials to avoid the adsorption or chemical modification of the compounds[Dodd,T.H,et al.2004
ARTIFICIAL NEURAL NETWORK MODEL
The back propagation model is commonly used. This model is known for its ability to generalize well on a wide variety of problems. This network is generally robust, although on of drawback is that the traing is slow. Typically there layers are sufficient for the vast majority of problems and each layer is connected to the immediately previous layer.
Formal ANN is made from artificial neurons. The most widespread variant is the MacCullob and Pitts neuron, representing the elementary model of the biological neuron. For the effective decision of the quantitative substance analysis, ANN should pass a traing stage. In addition, the adjustment of topology, weight factor etc. are carried out by specially formed training section.
At traing, the artificial neutral network should have the correct output signals. To achieve it, the traing is considered to be complete, when the criterion of the traing is stabilized at some level. By the way of such criterion residual dispersion is applied.
CONCLUSION
The e-nose system to be an excellent system for general-purpose application. Electronic nose is being used as an effective tool for rapid determination of aroma quality at various stages of designing and formulation of food products. Depending upon the products parameters will vary. The sensitivity and accuracy of e-nose can be further improved by adopting a combination of sensors. Food designing requires a quick analysis of food aroma at the developmental stage. Because of its versatility and case of operation e-nose is proving to the immense value in the field of product development, in processing quality control and life studies of packaged food.