BIOSENSOR - Chapter Notes, Biotechnology, Engineering, Semester Biotechnology Engineering (BT) Notes | EduRev

Biotechnology Engineering (BT) : BIOSENSOR - Chapter Notes, Biotechnology, Engineering, Semester Biotechnology Engineering (BT) Notes | EduRev

 Page 1


BIOSENSOR 
 
Biosensor is an analytical device for the detection of an analyte that 
combines a biological component with a physicochemical detector component 
It consists of 3 parts: 
? The sensitive biological element (biological material (eg. tissue, microorganisms, 
organelles, cell receptors, enzymes, antibodies, nucleic acids, etc), a 
biologically derived material or biomimic) the sensitive elements can be 
created by biological engineering. 
? The transducer or the detector element (works in a physicochemical way; optical, 
piezoelectric, electrochemical, etc.) that transforms the signal resulting from 
the interaction of the analyte with the biological element into another signal 
(i.e., transducers) that can be more easily measured and quantified; 
? Associated electronics or signal processors that are primarily responsible for the 
display of the results in a user-friendly way. This sometimes accounts for the 
most expensive part of the sensor device, however it is possible to generate a 
user friendly display that includes transducer and sensitive element (see 
Holographic Sensor). 
A common example of a commercial biosensor is the blood glucose biosensor, which 
uses the enzyme glucose oxidase to break blood glucose down. In doing so it first 
oxidizes glucose and uses two electrons to reduce the FAD (a component of the 
enzyme) to FADH2. This in turn is oxidized by the electrode (accepting two electrons 
from the electrode) in a number of steps. The resulting current is a measure of the 
concentration of glucose. In this case, the electrode is the transducer and the 
enzyme is the biologically active component. 
Recently, arrays of many different detector molecules have been applied in so called 
electronic nose devices; where the pattern of response from the detectors is used to 
fingerprint substance. Current commercial electronic noses, however, do not use 
biological elements. 
Principles of Detection 
Analytical chemistry plays an important role in food quality parameters 
because almost every sector of industry and public service relies on quality control. A 
food quality biosensor is a device, which can respond to some property or properties 
Page 2


BIOSENSOR 
 
Biosensor is an analytical device for the detection of an analyte that 
combines a biological component with a physicochemical detector component 
It consists of 3 parts: 
? The sensitive biological element (biological material (eg. tissue, microorganisms, 
organelles, cell receptors, enzymes, antibodies, nucleic acids, etc), a 
biologically derived material or biomimic) the sensitive elements can be 
created by biological engineering. 
? The transducer or the detector element (works in a physicochemical way; optical, 
piezoelectric, electrochemical, etc.) that transforms the signal resulting from 
the interaction of the analyte with the biological element into another signal 
(i.e., transducers) that can be more easily measured and quantified; 
? Associated electronics or signal processors that are primarily responsible for the 
display of the results in a user-friendly way. This sometimes accounts for the 
most expensive part of the sensor device, however it is possible to generate a 
user friendly display that includes transducer and sensitive element (see 
Holographic Sensor). 
A common example of a commercial biosensor is the blood glucose biosensor, which 
uses the enzyme glucose oxidase to break blood glucose down. In doing so it first 
oxidizes glucose and uses two electrons to reduce the FAD (a component of the 
enzyme) to FADH2. This in turn is oxidized by the electrode (accepting two electrons 
from the electrode) in a number of steps. The resulting current is a measure of the 
concentration of glucose. In this case, the electrode is the transducer and the 
enzyme is the biologically active component. 
Recently, arrays of many different detector molecules have been applied in so called 
electronic nose devices; where the pattern of response from the detectors is used to 
fingerprint substance. Current commercial electronic noses, however, do not use 
biological elements. 
Principles of Detection 
Analytical chemistry plays an important role in food quality parameters 
because almost every sector of industry and public service relies on quality control. A 
food quality biosensor is a device, which can respond to some property or properties 
of food and transform the response(s) into a detectable signal, often an electric 
signal. This signal may provide direct information about the quality factor(s) to be 
measured or may have a known relation to the quality factor. There are various kinds 
of biosensors most of which work on the principle of one of the following: 
Electrochemical Biosensors 
Electrochemical biosensors are based on monitoring electroactive species 
that are either produced or consumed by the action of the biological components 
(e.g., enzymes and cells). Transduction of the produced signal can be performed 
using one of several methods under two broad headings: 
? Potentiometric Biosensors 
? Amperometric Biosensors 
 
Potentiometric Biosensors 
These are based on monitoring the potential of a system at a working 
electrode, with respect to an accurate reference electrode, under conditions of 
essentially zero current flow. In process, potentiometric measurements are related to 
the analyte activity (of a target species) in the test sample. Potentiometric biosensors 
can operate over a wide range (usually several orders of magnitude) of 
concentrations. The use of potentiometric biosensors for food quality analysis has 
not been as widely reported as for amperometric sensors. However, some of the 
examples where this approach has been used for food quality analysis include 
estimating monophenolase activity in apple juice, determining the concentration of 
sucrose in soft drinks, measuring isocitrate concentrations in fruit juices, and 
determining urea levels in milk. 
 
Amperometric Biosensors 
The use of amperometric biosensors in signal transduction has proved to be 
the most widely reported using an electrochemical approach. Both “one-shot” 
(disposable) sensors and on-line (multi measurement) devices are commercially 
available, monitoring a wide range of target analytes. In contrast to potentiometric 
devices, the principle operation of amperometric biosensors is defined by a constant 
potential applied between a working and a reference electrode. The applied potential 
results in redox reactions, causing a net current to flow. The magnitude of this 
current is proportional to the concentration of electro active species present in test 
Page 3


BIOSENSOR 
 
Biosensor is an analytical device for the detection of an analyte that 
combines a biological component with a physicochemical detector component 
It consists of 3 parts: 
? The sensitive biological element (biological material (eg. tissue, microorganisms, 
organelles, cell receptors, enzymes, antibodies, nucleic acids, etc), a 
biologically derived material or biomimic) the sensitive elements can be 
created by biological engineering. 
? The transducer or the detector element (works in a physicochemical way; optical, 
piezoelectric, electrochemical, etc.) that transforms the signal resulting from 
the interaction of the analyte with the biological element into another signal 
(i.e., transducers) that can be more easily measured and quantified; 
? Associated electronics or signal processors that are primarily responsible for the 
display of the results in a user-friendly way. This sometimes accounts for the 
most expensive part of the sensor device, however it is possible to generate a 
user friendly display that includes transducer and sensitive element (see 
Holographic Sensor). 
A common example of a commercial biosensor is the blood glucose biosensor, which 
uses the enzyme glucose oxidase to break blood glucose down. In doing so it first 
oxidizes glucose and uses two electrons to reduce the FAD (a component of the 
enzyme) to FADH2. This in turn is oxidized by the electrode (accepting two electrons 
from the electrode) in a number of steps. The resulting current is a measure of the 
concentration of glucose. In this case, the electrode is the transducer and the 
enzyme is the biologically active component. 
Recently, arrays of many different detector molecules have been applied in so called 
electronic nose devices; where the pattern of response from the detectors is used to 
fingerprint substance. Current commercial electronic noses, however, do not use 
biological elements. 
Principles of Detection 
Analytical chemistry plays an important role in food quality parameters 
because almost every sector of industry and public service relies on quality control. A 
food quality biosensor is a device, which can respond to some property or properties 
of food and transform the response(s) into a detectable signal, often an electric 
signal. This signal may provide direct information about the quality factor(s) to be 
measured or may have a known relation to the quality factor. There are various kinds 
of biosensors most of which work on the principle of one of the following: 
Electrochemical Biosensors 
Electrochemical biosensors are based on monitoring electroactive species 
that are either produced or consumed by the action of the biological components 
(e.g., enzymes and cells). Transduction of the produced signal can be performed 
using one of several methods under two broad headings: 
? Potentiometric Biosensors 
? Amperometric Biosensors 
 
Potentiometric Biosensors 
These are based on monitoring the potential of a system at a working 
electrode, with respect to an accurate reference electrode, under conditions of 
essentially zero current flow. In process, potentiometric measurements are related to 
the analyte activity (of a target species) in the test sample. Potentiometric biosensors 
can operate over a wide range (usually several orders of magnitude) of 
concentrations. The use of potentiometric biosensors for food quality analysis has 
not been as widely reported as for amperometric sensors. However, some of the 
examples where this approach has been used for food quality analysis include 
estimating monophenolase activity in apple juice, determining the concentration of 
sucrose in soft drinks, measuring isocitrate concentrations in fruit juices, and 
determining urea levels in milk. 
 
Amperometric Biosensors 
The use of amperometric biosensors in signal transduction has proved to be 
the most widely reported using an electrochemical approach. Both “one-shot” 
(disposable) sensors and on-line (multi measurement) devices are commercially 
available, monitoring a wide range of target analytes. In contrast to potentiometric 
devices, the principle operation of amperometric biosensors is defined by a constant 
potential applied between a working and a reference electrode. The applied potential 
results in redox reactions, causing a net current to flow. The magnitude of this 
current is proportional to the concentration of electro active species present in test 
solution and both cathodic (reducing) and anodic (oxidizing) reactions can be 
monitored amperometrically. Most of the amperometric biosensors described use 
enzymes as the biorecognition element. Typically, oxidase and dehydrogenase 
enzymes have been the most frequently exploited catalysts used for these biosensor 
formats. 
Calorimetric Biosensors 
Most of the biochemical reactions are accompanied by either heat absorption 
or production. Sensors based on calorimetric transduction are designed to detect 
heat generated or consumed during a biological reaction; by using sensitive heat 
detection devices. Various biosensors for specific target analytes have been 
constructed. In the field of food quality analysis, uses of such biosensors to detect 
metabolites have been described. 
Optical Biosensors 
These sensors are based on measuring responses to illumination or to light 
emission. Optical biosensors can employ a number of techniques to detect the 
presence of a target analyte and are based on well-founded methods including 
chemiluminescence, fluorescence, light absorbance, phosphoresence, photothermal 
techniques, surface plasmon resonance (SPR), light polarization and rotation, and 
total internal reflectance. For example the use of this technique has been 
demonstrated to detect the presence of allergens, in particular peanuts, during food 
production. 
Acoustic Biosensors 
Piezoelectric quartz crystals can be affected by a change of mass at the 
crystal surface; this phenomenon has been successfully exploited and used to 
develop acoustic biosensors. For practical applications, the surface of the crystal can 
be modified with recognition elements (e.g., antibodies) that can bind specifically to a 
target analyte. 
Immunosensors 
Immunosensors are based on exploiting the specific interaction of antibodies 
with antigens. Typically, immunoassays (such as the enzyme-linked immunosorbent 
assay technique) employ a label (e.g., enzyme, antibody, fluorescent marker) to 
detect the immunological reaction. The use of biosensor platforms, linked to an 
immunoassay format, offers a route to rapid and accurate quantitative measurements 
of target analytes. 
Page 4


BIOSENSOR 
 
Biosensor is an analytical device for the detection of an analyte that 
combines a biological component with a physicochemical detector component 
It consists of 3 parts: 
? The sensitive biological element (biological material (eg. tissue, microorganisms, 
organelles, cell receptors, enzymes, antibodies, nucleic acids, etc), a 
biologically derived material or biomimic) the sensitive elements can be 
created by biological engineering. 
? The transducer or the detector element (works in a physicochemical way; optical, 
piezoelectric, electrochemical, etc.) that transforms the signal resulting from 
the interaction of the analyte with the biological element into another signal 
(i.e., transducers) that can be more easily measured and quantified; 
? Associated electronics or signal processors that are primarily responsible for the 
display of the results in a user-friendly way. This sometimes accounts for the 
most expensive part of the sensor device, however it is possible to generate a 
user friendly display that includes transducer and sensitive element (see 
Holographic Sensor). 
A common example of a commercial biosensor is the blood glucose biosensor, which 
uses the enzyme glucose oxidase to break blood glucose down. In doing so it first 
oxidizes glucose and uses two electrons to reduce the FAD (a component of the 
enzyme) to FADH2. This in turn is oxidized by the electrode (accepting two electrons 
from the electrode) in a number of steps. The resulting current is a measure of the 
concentration of glucose. In this case, the electrode is the transducer and the 
enzyme is the biologically active component. 
Recently, arrays of many different detector molecules have been applied in so called 
electronic nose devices; where the pattern of response from the detectors is used to 
fingerprint substance. Current commercial electronic noses, however, do not use 
biological elements. 
Principles of Detection 
Analytical chemistry plays an important role in food quality parameters 
because almost every sector of industry and public service relies on quality control. A 
food quality biosensor is a device, which can respond to some property or properties 
of food and transform the response(s) into a detectable signal, often an electric 
signal. This signal may provide direct information about the quality factor(s) to be 
measured or may have a known relation to the quality factor. There are various kinds 
of biosensors most of which work on the principle of one of the following: 
Electrochemical Biosensors 
Electrochemical biosensors are based on monitoring electroactive species 
that are either produced or consumed by the action of the biological components 
(e.g., enzymes and cells). Transduction of the produced signal can be performed 
using one of several methods under two broad headings: 
? Potentiometric Biosensors 
? Amperometric Biosensors 
 
Potentiometric Biosensors 
These are based on monitoring the potential of a system at a working 
electrode, with respect to an accurate reference electrode, under conditions of 
essentially zero current flow. In process, potentiometric measurements are related to 
the analyte activity (of a target species) in the test sample. Potentiometric biosensors 
can operate over a wide range (usually several orders of magnitude) of 
concentrations. The use of potentiometric biosensors for food quality analysis has 
not been as widely reported as for amperometric sensors. However, some of the 
examples where this approach has been used for food quality analysis include 
estimating monophenolase activity in apple juice, determining the concentration of 
sucrose in soft drinks, measuring isocitrate concentrations in fruit juices, and 
determining urea levels in milk. 
 
Amperometric Biosensors 
The use of amperometric biosensors in signal transduction has proved to be 
the most widely reported using an electrochemical approach. Both “one-shot” 
(disposable) sensors and on-line (multi measurement) devices are commercially 
available, monitoring a wide range of target analytes. In contrast to potentiometric 
devices, the principle operation of amperometric biosensors is defined by a constant 
potential applied between a working and a reference electrode. The applied potential 
results in redox reactions, causing a net current to flow. The magnitude of this 
current is proportional to the concentration of electro active species present in test 
solution and both cathodic (reducing) and anodic (oxidizing) reactions can be 
monitored amperometrically. Most of the amperometric biosensors described use 
enzymes as the biorecognition element. Typically, oxidase and dehydrogenase 
enzymes have been the most frequently exploited catalysts used for these biosensor 
formats. 
Calorimetric Biosensors 
Most of the biochemical reactions are accompanied by either heat absorption 
or production. Sensors based on calorimetric transduction are designed to detect 
heat generated or consumed during a biological reaction; by using sensitive heat 
detection devices. Various biosensors for specific target analytes have been 
constructed. In the field of food quality analysis, uses of such biosensors to detect 
metabolites have been described. 
Optical Biosensors 
These sensors are based on measuring responses to illumination or to light 
emission. Optical biosensors can employ a number of techniques to detect the 
presence of a target analyte and are based on well-founded methods including 
chemiluminescence, fluorescence, light absorbance, phosphoresence, photothermal 
techniques, surface plasmon resonance (SPR), light polarization and rotation, and 
total internal reflectance. For example the use of this technique has been 
demonstrated to detect the presence of allergens, in particular peanuts, during food 
production. 
Acoustic Biosensors 
Piezoelectric quartz crystals can be affected by a change of mass at the 
crystal surface; this phenomenon has been successfully exploited and used to 
develop acoustic biosensors. For practical applications, the surface of the crystal can 
be modified with recognition elements (e.g., antibodies) that can bind specifically to a 
target analyte. 
Immunosensors 
Immunosensors are based on exploiting the specific interaction of antibodies 
with antigens. Typically, immunoassays (such as the enzyme-linked immunosorbent 
assay technique) employ a label (e.g., enzyme, antibody, fluorescent marker) to 
detect the immunological reaction. The use of biosensor platforms, linked to an 
immunoassay format, offers a route to rapid and accurate quantitative measurements 
of target analytes. 
 
Applications of Biosensors 
There are many potential applications of biosensors of various types. The 
main requirements for a biosensor approach to be valuable in terms of research and 
commercial applications are the identification of a target molecule, availability of a 
suitable biological recognition element, and the potential for disposable portable 
detection systems to be preferred to sensitive laboratory-based techniques in some 
situations. Some examples are given below: 
? Glucose monitoring in diabetes patients ?historical market driver 
? Other medical health related targets 
? Environmental applications e.g. the detection of pesticides and river water 
contaminants 
? Remote sensing of airborne bacteria e.g. in counter-bioterrorist activities 
? Detection of pathogens 
? Determining levels of toxic substances before and after bioremediation 
? Detection and determining of organophosphate 
? Routine analytical measurement of folic acid, biotin, vitamin B12 and pantothenic 
acid as an alternative to microbiological assay 
? Determination of drug residues in food, such as antibiotics and growth promoters, 
particularly meat and honey. 
? Drug discovery and evaluation of biological activity of new compounds. 
? Protein engineering in biosensors  
? Detection of toxic metabolites such as mycotoxins 
Utility Biosensors for applications in Agriculture in Food/ Fruit Quality Control 
Quality control is the essential part of a food industry and efficient quality 
assurance is becoming increasingly important. Consumers expect good quality and 
healthy food at a given price; with good shelf life and high safety while food 
inspections require good manufacturing practices, safety, labelling and compliance 
with the regulations. Further, food producers are increasingly asking for efficient 
control methods, in particular through on-line or at-line quality sensors. Their main 
aim is to satisfy the consumer and regulatory requirements and to improve the 
Page 5


BIOSENSOR 
 
Biosensor is an analytical device for the detection of an analyte that 
combines a biological component with a physicochemical detector component 
It consists of 3 parts: 
? The sensitive biological element (biological material (eg. tissue, microorganisms, 
organelles, cell receptors, enzymes, antibodies, nucleic acids, etc), a 
biologically derived material or biomimic) the sensitive elements can be 
created by biological engineering. 
? The transducer or the detector element (works in a physicochemical way; optical, 
piezoelectric, electrochemical, etc.) that transforms the signal resulting from 
the interaction of the analyte with the biological element into another signal 
(i.e., transducers) that can be more easily measured and quantified; 
? Associated electronics or signal processors that are primarily responsible for the 
display of the results in a user-friendly way. This sometimes accounts for the 
most expensive part of the sensor device, however it is possible to generate a 
user friendly display that includes transducer and sensitive element (see 
Holographic Sensor). 
A common example of a commercial biosensor is the blood glucose biosensor, which 
uses the enzyme glucose oxidase to break blood glucose down. In doing so it first 
oxidizes glucose and uses two electrons to reduce the FAD (a component of the 
enzyme) to FADH2. This in turn is oxidized by the electrode (accepting two electrons 
from the electrode) in a number of steps. The resulting current is a measure of the 
concentration of glucose. In this case, the electrode is the transducer and the 
enzyme is the biologically active component. 
Recently, arrays of many different detector molecules have been applied in so called 
electronic nose devices; where the pattern of response from the detectors is used to 
fingerprint substance. Current commercial electronic noses, however, do not use 
biological elements. 
Principles of Detection 
Analytical chemistry plays an important role in food quality parameters 
because almost every sector of industry and public service relies on quality control. A 
food quality biosensor is a device, which can respond to some property or properties 
of food and transform the response(s) into a detectable signal, often an electric 
signal. This signal may provide direct information about the quality factor(s) to be 
measured or may have a known relation to the quality factor. There are various kinds 
of biosensors most of which work on the principle of one of the following: 
Electrochemical Biosensors 
Electrochemical biosensors are based on monitoring electroactive species 
that are either produced or consumed by the action of the biological components 
(e.g., enzymes and cells). Transduction of the produced signal can be performed 
using one of several methods under two broad headings: 
? Potentiometric Biosensors 
? Amperometric Biosensors 
 
Potentiometric Biosensors 
These are based on monitoring the potential of a system at a working 
electrode, with respect to an accurate reference electrode, under conditions of 
essentially zero current flow. In process, potentiometric measurements are related to 
the analyte activity (of a target species) in the test sample. Potentiometric biosensors 
can operate over a wide range (usually several orders of magnitude) of 
concentrations. The use of potentiometric biosensors for food quality analysis has 
not been as widely reported as for amperometric sensors. However, some of the 
examples where this approach has been used for food quality analysis include 
estimating monophenolase activity in apple juice, determining the concentration of 
sucrose in soft drinks, measuring isocitrate concentrations in fruit juices, and 
determining urea levels in milk. 
 
Amperometric Biosensors 
The use of amperometric biosensors in signal transduction has proved to be 
the most widely reported using an electrochemical approach. Both “one-shot” 
(disposable) sensors and on-line (multi measurement) devices are commercially 
available, monitoring a wide range of target analytes. In contrast to potentiometric 
devices, the principle operation of amperometric biosensors is defined by a constant 
potential applied between a working and a reference electrode. The applied potential 
results in redox reactions, causing a net current to flow. The magnitude of this 
current is proportional to the concentration of electro active species present in test 
solution and both cathodic (reducing) and anodic (oxidizing) reactions can be 
monitored amperometrically. Most of the amperometric biosensors described use 
enzymes as the biorecognition element. Typically, oxidase and dehydrogenase 
enzymes have been the most frequently exploited catalysts used for these biosensor 
formats. 
Calorimetric Biosensors 
Most of the biochemical reactions are accompanied by either heat absorption 
or production. Sensors based on calorimetric transduction are designed to detect 
heat generated or consumed during a biological reaction; by using sensitive heat 
detection devices. Various biosensors for specific target analytes have been 
constructed. In the field of food quality analysis, uses of such biosensors to detect 
metabolites have been described. 
Optical Biosensors 
These sensors are based on measuring responses to illumination or to light 
emission. Optical biosensors can employ a number of techniques to detect the 
presence of a target analyte and are based on well-founded methods including 
chemiluminescence, fluorescence, light absorbance, phosphoresence, photothermal 
techniques, surface plasmon resonance (SPR), light polarization and rotation, and 
total internal reflectance. For example the use of this technique has been 
demonstrated to detect the presence of allergens, in particular peanuts, during food 
production. 
Acoustic Biosensors 
Piezoelectric quartz crystals can be affected by a change of mass at the 
crystal surface; this phenomenon has been successfully exploited and used to 
develop acoustic biosensors. For practical applications, the surface of the crystal can 
be modified with recognition elements (e.g., antibodies) that can bind specifically to a 
target analyte. 
Immunosensors 
Immunosensors are based on exploiting the specific interaction of antibodies 
with antigens. Typically, immunoassays (such as the enzyme-linked immunosorbent 
assay technique) employ a label (e.g., enzyme, antibody, fluorescent marker) to 
detect the immunological reaction. The use of biosensor platforms, linked to an 
immunoassay format, offers a route to rapid and accurate quantitative measurements 
of target analytes. 
 
Applications of Biosensors 
There are many potential applications of biosensors of various types. The 
main requirements for a biosensor approach to be valuable in terms of research and 
commercial applications are the identification of a target molecule, availability of a 
suitable biological recognition element, and the potential for disposable portable 
detection systems to be preferred to sensitive laboratory-based techniques in some 
situations. Some examples are given below: 
? Glucose monitoring in diabetes patients ?historical market driver 
? Other medical health related targets 
? Environmental applications e.g. the detection of pesticides and river water 
contaminants 
? Remote sensing of airborne bacteria e.g. in counter-bioterrorist activities 
? Detection of pathogens 
? Determining levels of toxic substances before and after bioremediation 
? Detection and determining of organophosphate 
? Routine analytical measurement of folic acid, biotin, vitamin B12 and pantothenic 
acid as an alternative to microbiological assay 
? Determination of drug residues in food, such as antibiotics and growth promoters, 
particularly meat and honey. 
? Drug discovery and evaluation of biological activity of new compounds. 
? Protein engineering in biosensors  
? Detection of toxic metabolites such as mycotoxins 
Utility Biosensors for applications in Agriculture in Food/ Fruit Quality Control 
Quality control is the essential part of a food industry and efficient quality 
assurance is becoming increasingly important. Consumers expect good quality and 
healthy food at a given price; with good shelf life and high safety while food 
inspections require good manufacturing practices, safety, labelling and compliance 
with the regulations. Further, food producers are increasingly asking for efficient 
control methods, in particular through on-line or at-line quality sensors. Their main 
aim is to satisfy the consumer and regulatory requirements and to improve the 
production feasibility, quality sorting, automation and reduction of production cost 
and production time subsequently. 
Biochemical Composition of Fruits 
The quality of soft fruit, in terms of taste, nutrition and consumers acceptance, 
is fundamentally based on the biochemical composition of the fruit. In soft fruits (viz. 
blackcurrant and strawberry) sugar: acid ratios can be used as an important index of 
fruit maturity and act as a determinant of overall fruit. However, sugar: acid ratios are 
infrequently used due to a requirement for specific instrumentation and semi-skilled 
analytical scientists. Today we need a simple and low-cost alternative, which would 
significantly enhance both the number and extent of tests carried out. 
 
Fruit Maturity, Ripening and Quality Relationships 
Fruit maturity at harvest is the most important factor that determines shelf life 
and final fruit quality. If harvested immature then fruits are more subject to shriveling 
and mechanical damage, and are of inferior quality when ripe, whereas overripe 
fruits are liable to become soft and mealy with bland flavour soon after harvest. 
Therefore, fruits harvested either too early or too late in their season are more 
susceptible to post harvest physiological disorders than fruits harvested at proper 
maturity.  
 
Fruits can be divided into two groups:  
1) Fruit that are incapable of enduring their ripening process once picked from the 
plant like berries, cheery, citrus fruits, grapes, lychee, pineapple, pomegranate, 
and tamarillo.  
2) Fruits that can be harvested mature and ripped off the plant like apple, apricot, 
avocado, banana, cherimoya, guava, kiwifruit, mango, nectarine, papaya, 
passion fruit, pear, peach, persimmon, plum, quince, sapodilla, sapota.  
 
Volatile compounds are responsible for the characteristic aroma of fruits and are 
present in extremely small quantities (<100< g/g fresh wt.). The major volatile formed 
is ethylene. Scientists are trying to develop portable instruments with sensors that 
detect volatile production by fruits and hence detecting maturity and quality. Other 
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