Spoiled biological materials are biological materials which have been affected or degraded by processes such as chemical decay, enzymatic decay, bacteriological decay or autodegradation. Degradation or decay typically is associated with or accompanied by the production of gases or vapors (offgassing) and may occur at any temperature. For example, biological materials such as fish, seafood, meats, poultry, eggs and dairy products may decay even when refrigerated.

Laboratory methods for detection of spoiled biological material are known. Typically, these methods involve preparing a sample and performing an analysis by standard analytical or microbiological techniques. For example, the presence of histamine, putrescine or cadaverine may be determined by gas or liquid chromatography in conjunction with mass spectroscopy or fluorescence detection. However, as set forth in Analvtical Chemistrv. Vol. 65, No. 12, June 15, 1993, the food industry still needs an objective, non-laboratory technique for performing an accurate quality analysis of biological material immediately prior to the purchase, packaging or consumption of the material. For example, quality control in the fish packing industry currently relies on human sensory assessments to determine the quality and freshness of fish and fishery products. This method is limited by factors including the inspector's health and level of training, competing odors within the packing plant, lapses in the inspector's concentration, loss of the inspector's sensitivity due to nasal fatigue,

limited assessment rates and the inability to detect sub-threshold levels of compounds associated with spoilage. Each of these factors may compromise the quality of the fish being packaged by resulting in a failure to detect unacceptable fish.

Early approaches to automated chemical inspection such as Fine et al., U.S. Patent No. 5,318,911 (the '911 patent), col. 9, lines 40-42, suggest that amines could be detected as indicators of spoilage in fish. However, investigations have shown that amines are typically present in spoiled biological material in the form of salts, which are non-volatile. Accordingly, to produce detectable quantities of amines, the amines must be released by either adding a basic solution to the biological material to place the material at an appropriate pH or by heating the material. For obvious reasons, either of these approaches would risk degrading the quality of the fish or other biological material or, at the least, hastening its decomposition. Accordingly, amines are not considered to be spoilage by-products that are suitable for detection by a method in which altering the biological material is undesirable.

The Alexus (TM) bottle inspection systems developed and marketed by Thermedics Detection Inc., the assignee of the present application, are described in the above-referenced '911 patent and have been shown to detect dead animals and insects in refillable plastic bottles. These systems inject a sodium carbonate solution (i.e., a basic solution) into each bottle as part of the inspection process and heat the vapor sample prior to reacting the sample in a chemiluminescence chamber. Hence, it is believed that these systems are detecting amines produced by the dead animals or insects.

fii-fliπna-ry of the Invention In one aspect, generally, the invention features automatic, real time detection of spoilage of biological material, particularly animal matter such as fish, seafood, meats, poultry, eggs or dairy products. In a preferred embodiment, a sample of volatile compounds, referred to herein as a vapor sample, is obtained from a region in or near the biological material. For example, when the material is fish, the vapor sample may be obtained from the gills of the fish and may include compounds of relatively high vapor pressure which can be drawn or sucked substantially without altering the fish being sampled. The vapor sample may then be analyzed to produce an electrical signal that indicates a degree to which spoilage by-products such as sulfur compounds are present in the sample. Thereafter, the biological material may be determined to be spoiled and unacceptable when the degree to which spoilage by-products (e.g., sulfur compounds) are present in the sample, as indicated by the electrical signal, exceeds predetermined threshold levels.

The method is particularly useful for real time detection of spoilage of biological material that are moving on a conveyor, substantially without altering the biological material from which samples are taken. For example, the method may be used to detect spoilage of fish when the fish is positioned on a conveyor moving at a rate on the order of 0.2 meters per second. In general, the method quickly determines whether a fish is acceptable so that a system operator may remove an unacceptable fish from the conveyor. To accomplish this, the method makes the acceptability determination in less than five seconds and preferably in less than one second. The acceptability determination is typically made without stopping or slowing movement of the conveyor.

As used herein, volatile compounds are gaseous spoilage by-products that are subject to detection by the method of the invention and are detectable in, above, or around spoiled biological materials. Volatile compounds include various sulfur compounds (e.g., methyl mercaptan, dimethyl sulfide, dimethyl disulfide, sulfur dioxide or hydrogen sulfide), aldehydes, ketones, carbonyls, alcohols (e.g., l,5-octadien-3-ol or ethanol) , aromatic compounds (e.g., naphthalene, cresol, indole or phenol), esters, organic acids and other compounds produced by processes of degradation of biological materials. When the biological material is fish, the predominant volatile compounds are sulfur compounds.

As also used herein, real time analyses are analyses that produce immediate results (i.e. within several seconds of initiation of the analysis) . Real time analyses therefore produce results faster than do laboratory methods.

In one approach, the vapor sample is reacted in a chemiluminescence chamber to produce radiant energy.

Thereafter, the electrical signal is produced based on a level of radiant energy detected. Typically, the sample is reacted with ozone (0 ₃ ) in the chemiluminescence chamber. Alternatively, the sample may be reacted with nitrogen dioxide (N0 ₂ ) or other compounds to generate a chemiluminescent reaction.

In the chemiluminescent detection of spoilage by¬ products, radiant energy having wavelengths greater than or equal to 190 nanometers, and, typically, less than 900 nanometers is monitored. For example, methyl mercaptan (CH ₃ SH) , dimethyl sulfide (CH ₃ SCH ₃ ) , dimethyl disulfide (CH ₃ SSCH ₃ ) , sulfur dioxide (S0 ₂ ) and hydrogen sulfide (H ₂ S) , four substances that have been found to be excellent indicators of spoilage in fish and other biological material, produce excited species which emit

radiant energy having wavelengths in the range from about 300 to 500 nanometers when reacted with ozone in a chemiluminescence chamber. When compounds are detectable at ambient temperature, there is no need to alter them prior to ozone reaction and a pyrolyzer is therefore unnecessary for their detection. Hence, the temperature of the vapor sample may be maintained at ambient, or not heated to a high temperature (e.g., not above 150°C) . However, some enhancement of the signal may be obtained by heating to 350°C or higher. Moreover, for compounds that have extremely low freezing points (e.g., -85 ^β C) , residues of vapor samples are easily purged from detection lines and the detection lines need not be heated. When biological materials are spoiled to a degree at which the electrical signal exceeds a threshold level, an indication such as an audible horn or a flashing light is provided to notify a system operator that the biological material is unacceptable and to thereby enable the system operator to remove or dispose of the material. Alternatively, a mechanical rejection system may be employed to automatically remove or dispose of unacceptable material.

The threshold level for unacceptability may be adjusted based on the intended use of the biological material. For example, when the biological material is fish, a lower threshold that would reject fish that is decomposed to a degree at which flavor would be affected could be used when the fish is meant for human consumption while a higher threshold that would reject fish only when it is decomposed to a degree at which safety of consumption would be affected could be used when the fish is meant for use as, for example, filler in animal foods. Similarly, multiple thresholds levels could be used to categorize the fish into different

levels of "freshness" or non-spoilage, with each level being intended for a different use.

When the biological material is fish or other products that are subject to contamination by certain hydrocarbons such as diesel fuel, the method may also include producing a second electrical signal that indicates a degree to which specific hydrocarbons are present in the vapor sample. The biological material may be determined to be contaminated with hydrocarbons and unacceptable when hydrocarbons are present in the vapor sample, as indicated by the second electrical signal, to a degree that exceeds a second predetermined threshold level. Thus, biological material is rejected when it is contaminated with hydrocarbons or it is spoiled to an unacceptable level. Typically, hydrocarbons are detected by reacting a portion of the vapor sample in a fluorescence chamber or photoionization detector to produce radiant energy. Thereafter, the second electrical signal is produced based on a level of radiant energy detected.

In another aspect, generally, the invention features an apparatus for detecting spoilage of biological material such as fish. The apparatus includes a sample probe configured to obtain a vapor sample from a region in or near the biological material and one or more detectors connected to the sample probe for receipt of the sample. Each detector is configured to produce an electrical signal that indicates a degree to which spoilage by-products such as sulfur compounds are present in the sample. A processor is electrically connected to the detectors for receipt of the electrical signals and is configured to determine that biological material is spoiled when the degree to which spoilage by-products are present in the sample, as indicated by the electrical signals, exceeds predetermined threshold levels.

The detector may include a chemiluminescence chamber and a photomultiplier tube positioned to detect radiant energy produced by reaction of the sample in the chamber. The photomultiplier tube may be configured to produce the electrical signal based on a level of radiant energy detected. The detector may also include an ozonator connected to the chamber to supply ozone to the chemiluminescence chamber for reaction with the sample. As an alternative, the detector may include a source of N0 ₂ or another gas that produces a chemiluminescent reaction, with the gas source being connected to supply reagent gas to the chamber.

A filter may be positioned between the photomultiplier tube and the chemiluminescence chamber to limit the wavelengths detectable by the photomultiplier tube. Examples of suitable filters include a quartz filter that passes wavelengths greater than about 190 nanometers or a bandpass filter that passes wavelengths in a range such as the range from about 190 to 900 nanometers.

In some cases, the apparatus is configured for inspection of biological material such as fish as the material moves on a conveyor. To accomplish this, the sample probe is configured to permit samples to be obtained from moving material, and the processor and detector are configured to determine whether the biological material is spoiled before the conveyor has moved a substantial distance.

Typically, the apparatus also includes one or more indicator lights on the sample probe, and a horn. The horn is sounded and an indicator light is flashed when spoiled biological material is detected. The indicator lights may also be used to provide other information such as system status.

To detect certain hydrocarbons, particularly those that fluoresce at temperatures below about 100°C but do not react with ozone or nitrogen dioxide to produce detectable chemiluminescence at such temperatures, the detector may also include a pulse fluorescence chamber and a second photomultiplier tube. The photomultiplier tube may be positioned to detect radiant energy produced by the vapor sample in the pulse fluorescence chamber and configured to produce a second electrical signal based on a level of radiant energy detected. In this case, the processor is typically configured to determine that the biological material is contaminated with hydrocarbons when the degree to which specific hydrocarbons are present, as indicated by the second electrical signal, exceeds a second threshold level.

The tip of the sample probe may be heated to a temperature in the range from ambient to about 150°C (typically about 50°C) to aid release of the vapor sample from the fish or other biological material when the biological material is completely or partially frozen. The heated tip also reduces buildup of diesel fuel or other contaminants on the tip.

The apparatus may also include a flow control unit positioned between the detector and the sample probe. The flow control unit is connected to the processor and configured to permit the processor to automatically check the integrity of the sample probe and the detector. Typically, the processor performs the integrity check by controlling valves in the flow control unit to provide known test gases to the detector and thereafter monitoring signals produced by the detector.

The invention may be configured in other ways to identify volatile spoilage by-products of particular interest. Detectors may include analytical detectors such as chemiluminescence, fluorescence, and

photoionization detectors as well as detectors based on ion mobility spectrometry, mass spectrometry, infrared detection, flame ionization, flame photometric detection, thermal conductivity, nitrogen/phosphorous detection, electron capture, ultraviolet detection or polymer conductance, and may also include refractometers or any other suitable detector. Some detectors are inherently specific to certain compounds of interest and may be used without separation of the vapor sample into components. Nonselective detectors may be made selective for particular compounds of interest by pretreatment or separation techniques for those compounds. For example, compounds from the vapor sample may be trapped by absorbent, cryogenic or temperature means, or may be separated by filters. Similarly, gas chromatography

(GC) , particularly high speed GC, may be used to isolate compounds of interest. The detectors may be used alone or in combination with other detectors. In addition, measurements of vapors may be correlated to a quantity of spoilage inducing organisms.

The volatile spoilage by-products described herein could also be detected by other means. For example, the compounds could be detected through chemical reactions that result in a visually detectable change in color. In this case, a strip or sheet of paper, plastic or the like would be impregnated with a color changing compound. The impregnated strip or sheet would then be wiped over (or waved around) biological materials such as fish, seafood, meats, poultry, eggs and dairy products. If the strip or sheet changed color after exposure to the biological material, this would indicate that the biological material was spoiled. For example, as is well known in the art, pH paper turns color due to the reaction of its impregnated compounds with hydrogen ions. This approach to detection would be particularly useful in that it

would provide a low cost, consumer-oriented approach that would permit consumers to evaluate the quality of materials immediately prior to consumption.

As described below, a particular example of the invention is the use thereof in the fish processing industry to detect spoilage of fish and, in some cases, diesel fuel or other contamination in the fish or on the production line. In a currently preferred method, a chemiluminescence, fluorescence or photoionization detector is employed. These detectors can readily identify spoilage by-products and contamination compounds in real time and do not require the fish or the volatile compounds to be treated prior to detection.

Brief Description of the Drawing Fig. 1 is a side view of an inspection system suitable for inspecting biological materials such as fish.

Fig. 2 is a top view of the inspection system of Fig. l. Fig. 3 is a simplified view, partially in block diagram form, of the inspection system of Fig. l.

Fig. 4 is a flow diagram of a valve arrangement of the inspection system of Fig. 1.

Fig. 5 is a block diagram of a first embodiment of an analysis unit of the inspection system of Fig. 1. Fig. 6 is a diagram of a chemiluminescence detector of the analysis unit of Fig. 5.

Fig. 7 is a diagram of a pulse fluorescence detector of the analysis unit of Fig. 5. Fig. 8 is a block diagram of an electronics module of the analysis unit of Fig. 5.

Figs. 9-10 are block diagrams of other embodiments of the analysis unit of the inspection system of Fig. 1.

Fig. 11 is a flow chart of a procedure implemented by a processor of the inspection system of Fig. l.

Figs. 12 and 13 are flow diagrams for a sampling probe of the inspection system of Fig. 1.

With reference to Figs. 1 and 2, an inspection system 10 for inspection of biological material such as fish for spoilage includes a sampling probe 12 and a detection system 14. The sampling probe is connected to the detection system by a flexible, dual-line hose 16. To reduce user fatigue, the sampling probe 12 and the hose 16 are connected to a moveable boom 18 by extendable/retractable support lines 20.

In operation, a user positions the sample probe 12 in the gills 22 or elsewhere on a fish 24 as the fish moves along a conveyor line 26 in the direction indicated by arrow 28. The user then depresses a sample acquisition switch 30 on the sample probe to cause a vapor sample to be drawn from the gills of the fish through the hose 16 to the detection system 14. The vapor sample typically includes air and other gases, and may include vapors of compounds indicative of spoilage and/or hydrocarbon contamination.

As described in detail below, the detection system 14 analyzes the vapor sample provided by line 16 to determine whether the fish 24 is unacceptable due to spoilage or hydrocarbon contamination, or both. If the detection system determines that the fish is unacceptable, the system activates an indicator light 32 on the sample probe 12 and sounds a horn 33 that is mounted on the detection system 14.

The detection system 14 is configured to determine the acceptability of the fish 24 before the fish has moved a substantial distance along the conveyor 26, and

to thereby permit the user or an assistant to remove an unacceptable fish from the conveyor without experiencing any difficulty in identifying the unacceptable fish. For example, if a vapor sample is obtained from the fish at point A on the conveyor, the detection system determines whether the fish is acceptable before the fish reaches point B. The distance between points A and B may be less than five meters and is typically less than one meter. With line speeds on the order of 0.2 meters per second (or a fish per second) , the detection system is preferably configured to determine the acceptability of a fish in less than one second.

With reference also to Fig. 3, sample probe 12 includes a wedge shaped metal tip 34. Fish 24 are typically placed on conveyor 26 immediately after thawing, and may be partially frozen when they reach inspection system 10. Thus, the tip 34 of the probe 12 is heated to a temperature of about 50°C by an AC cartridge heater 35 and a thermocouple 37 to increase vapor emanation from the fish. Heating the tip 34 also prevents adhesion to the tip of contaminants such as hydrocarbons that may be present in the fish. Holes 36 in the tip permit vapor samples to enter the sample probe. The tip 34 is connected to a hand piece 38 of sample probe 12 by a hollow metal shaft 40. Hand piece 38 is constructed of nylon or polyvinyl chloride (PVC) material and is contoured for ease of handling.

As noted above, sample probe 12 includes an indicator light 32. Detection system 14 causes indicator light 32, which is red, to flash when an unacceptable fish is encountered. Sample probe 12 also includes a green indicator light 42 and a yellow indicator light 44. Detection system 14 activates green light 42 when the system is operational. When a system error is encountered, detection system 14 activates red light 32

and yellow light 44. Finally, when a system check is needed, detection system 14 flashes yellow light 44.

Detection system 14 includes three primary components: a flow control unit 46, an analysis unit 48 and a processor 50. The flow control unit 46 is connected between the hose 16 and the analysis unit 48 and controls the flow of the vapor samples into the analysis unit. The analysis unit analyzes the samples and produces electrical signals that relate to their composition. The processor 50 receives the electrical signals and, based on those signals, determines whether a fish is acceptable.

With reference to Figs. 4, 12 and 13, the flow through fish inspection system 10 is controlled by four valves positioned in flow control unit 46. A first valve 52, which is normally open, is connected to the sample acquisition switch 30. Normally (Fig. 12), air flows from flow control unit 46 to sample probe 12 through a first line 54 of hose 16. Line 54 is connected to a purge air source 58 that is located in flow control unit 46. Air flows through line 54 due to a positive pressure in air source 58 relative to probe tip 34. Air flows to analysis unit 48 through a second line 56 of hose 16. Air flows through line 56 due to a negative pressure in analysis unit 48 relative to probe tip 34. As illustrated in Fig. 12, lines 54 and 56 are connected in shaft 40 so that a single line extends into tip 34.

Except during sampling, the flow of gas through line 54 is greater than flow through line 56 (see Figs. 4 and 12) . Accordingly, there is normally flow out of holes 36 of tip 34. This outward flow helps to prevent blockage of holes 36. In addition, the continuous flow through line 56 prevents vapor buildup in that line. When acquisition switch 30 is depressed (see Figs. 4 and 13) , valve 52 is closed and flow through line 54 is

prevented. As a result, a vapor sample is drawn into holes 36 of sample probe 12 and directed to the analysis unit 48 through line 56. Typically, valve 52 is pulsed closed for a controlled period of time such as 200 to 500 milliseconds so that a controlled amount of the vapor sample is provided to the analysis unit.

The remaining three valves are all normally closed. A second valve 60 is positioned between line 54 and a source 62 of test gas such as nitric oxide (NO) , sulfur dioxide (S0 ₂ ) or an NO/S0 ₂ test gas mixture. A third valve 64 is positioned between line 54 and a vent 66. Finally, a fourth valve 68 is positioned between line 54 and line 56.

Processor 50 uses the valves in flow control unit 46 to verify the integrity of system 10 by testing various components of the system. For example, to test operation of sample probe 12, the processor pulses open valve 60 so that test gas passes into line 54. If sample probe 12 is working correctly, some of the test gas will pass through line 54 and return to analysis unit 48 through line 56. Thereafter, the test gas will be detected by analysis unit 48. If sample probe 12 is blocked or otherwise malfunctioning, the test gas will not return to analysis unit 48 and will not be detected. By monitoring the nitric oxide response of the chemiluminescence detector (discussed below) of analysis unit 48 while testing the sample probe, the processor also uses this procedure to test operation of the chemiluminescence detector. To test operation of the pulse fluorescence detector (discussed below) of analysis unit 48, the processor 50 closes valve 52 and opens valves 64 and 68. This causes purge air from source 58 to flow directly into analysis unit 48 (valve 64 is opened to vent excess purge air and test gas directly to the atmosphere) .

Thereafter, the processor pulses open valve 60 so that an NO/S0 ₂ test gas mixture flows into analysis unit 48. If the pulse fluorescence detector is functioning properly, it will detect the S0 ₂ and provide a signal that so indicates to the processor 50. Similarly, if the pulse fluorescence detector is not functioning properly, it will not provide to the processor a signal indicative of S0 ₂ detection. Thus, the processor determines whether the pulse fluorescence detector is functioning properly by monitoring the signal provided thereby.

With reference to Fig. 5, a first embodiment of analysis unit 48 includes a chemiluminescence detector 70, a pulse fluorescence detector 72 and an electronics module 74. In operation, a first portion of the vapor sample from the flow control unit is drawn into the chemiluminescence detector and is reacted with ozone that is produced from a source of oxygen gas (e.g., air or tank of oxygen gas) by an ozonator 76 such as an electrical discharge unit. As discussed in more detail below, the chemiluminescence detector provides an analog electrical signal to the electronics module 74. The magnitude of this signal is related to the composition of the sample and typically increases when the sample includes spoilage by-products such as sulfur compounds. A vacuum source 78 draws the reacted sample and ozone from the chemiluminescence detector and exhausts it to the atmosphere.

A second portion of the sample from the flow control unit is drawn into the pulse fluorescence detector 72. As discussed in more detail below, the pulse fluorescence detector provides an analog electrical signal to the electronics module. The magnitude of this signal is related to the composition of the sample and typically increases when the sample includes certain hydrocarbons. A vacuum source 80 draws the reacted

sample from the pulse fluorescence detector and exhausts them to the atmosphere. Although separate vacuum sources 78 and 80 are shown in the analysis units of Figs. 5 and 9, a single vacuum pump may, if desired, be utilized to draw samples through the chemiluminescence and pulse fluorescence detectors 70 and 72.

With reference to Fig. 6, chemiluminescence detector 70 includes a reaction chamber 82 having a sample inlet 84, a reaction gas inlet 86 and an outlet 88. In chamber 82, the sample reacts with the ozone and produces a chemical species which emits radiant energy. The radiant energy is detected by a photomultiplier tube 90 after the radiant energy passes through a quartz filter 94 that permits radiant energy having wavelengths greater than about 190 nanometers to pass. The photomultiplier tube produces an electrical signal that is proportional to the radiant energy incident thereon. The chemiluminescence detector 70 operates in a manner similar to a standard chemiluminescence detector with the exception that filter 94 passes a wider range of wavelengths than the filters of standard detectors, which are configured to detect primarily infrared energy and typically pass radiant energy having wavelengths greater than 600 nanometers. By passing a wider range of wavelengths, filter 94 permits the photomultiplier tube to also detect radiant energy having wavelengths less than 600 nanometers (e.g., 300 to 500 nanometers), which wavelengths are typical of many spoilage by-products. For example, when dimethyl disulfide, methyl mercaptan, hydrogen sulfide and sulfur dioxide (sulfur compounds that have been found to be excellent indicators of decomposition of organic material) are reacted with ozone, radiant energy having wavelengths in the range from 300 to 500 nanometers is produced. To limit detection to primarily sulfur compounds, a bandpass

filter that passes wavelengths in the 300 to 500 or 300 to 400 nanometer ranges can be substituted for quartz filter 94.

With reference to Fig. 7, pulse fluorescence detector 72 includes a reaction chamber 96 having a sample inlet 98 and an outlet 100. A flash lamp 102 (e.g. a Xenon lamp flashing at a frequency of 83 Hz) directs pulses of radiant energy through a monochrometer 104 that passes radiant energy of a specific wavelength such as 204 nanometers. After passing through the monochrometer, the pulses are passed through a columnator lens 106 that focusses the pulses through the center of the reaction chamber 96. When the pulses encounter certain hydrocarbons (e.g. , diesel fuel) in the reaction chamber, they energize those compounds and cause them to produce radiant energy. This radiant energy is detected by a photomultiplier tube 108 after the radiant energy passes through a focussing lens 110 and a bandpass filter 112 that passes wavelengths in the range from about 300 to 340 nanometers. Use of the monochrometer 104 and bandpass filter 112 permits the pulse fluorescence detector to preferentially detect diesel fuel and similar hydrocarbons. Lens 110 and lens 106 are configured to have the same focal point in the center of the reaction chamber. This configuration maximizes the percentage of radiant energy that is incident on the photomultiplier tube and thereby maximizes the sensitivity of the detector. The photomultiplier tube produces an electrical signal that is proportional to the radiant energy incident thereon.

With reference to Fig. 8, electronics module 74 includes a preamplifier 114 and an analog-to-digital converter 116 that, respectively, amplify the electrical signal from pulse fluorescence detector 72 and convert the amplified analog signal to a digital signal. A

preamplifier 118 and an analog-to-digital converter 120 perform the same functions on the signal from chemiluminescence detector 70. A multiplexer 122 alternately provides the digital signals to processor 50. With reference to Fig. 9, in a second embodiment, an analysis unit 148 includes a pyrolyzer 150 positioned between flow control unit 46 and chemiluminescence detector 70, and is otherwise identical to analysis unit 48. Pyrolyzer 150 is typically a tube constructed of ceramic, quartz, teflon, glass or metal (i.e., nickel or stainless steel) and heated by, for example, electrical resistance heating, to a temperature of about 350°C. In some applications, pyrolyzer 150 improves the sensitivity of the chemiluminescence detector to spoilage by- products.

With reference to Fig. 10., in a third embodiment, an analysis unit 248 includes only a chemiluminescence detector 70 and does not include a pulse fluorescence detector. In this case, an electronics module 274 that receives the electrical signal from the chemiluminescence detector includes a single preamplifier and a single analog-to-digital converter, but does not include a multiplexer. This embodiment is particularly useful when only spoilage by-products need to be detected and there is no need to detect hydrocarbon contaminants.

With reference to Figs. 3 and 11, processor 50, which may be implemented using a standard 8088 microprocessor, controls system 10 according to a procedure 300. Initially, the processor 50 verifies system integrity by performing a system check as discussed above (step 302) . If the system check indicates that a system failure has occurred (step 304) , the processor activates red light 32 and yellow light 44 (step 306) . Thereafter, the processor continues to

monitor system integrity until the problem is resolved (step 302) .

If no failure has occurred (step 304) , the processor initializes a system check timer and activates the green light 42 (step 308) . Next, the processor determines whether acquisition switch 30 has been pressed (step 310) . If so, the processor activates valve 52 and monitors the electrical signals produced by analysis unit 48 (step 312) . (Valve 52 is automatically deactivated after a time delay of about 5 to 1000 milliseconds, but typically about 200 milliseconds. The processor implements a standard peak finding algorithm that looks for changes that occur in the electrical signals when valve 52 is activated. By monitoring only the changes in the signals, the processor eliminates background effects. If a change in either of the electrical signals exceeds a preset threshold level (step 314), the processor flashes the red light 32 and sounds the horn 33 (step 316) . After sounding the horn, or if neither electrical signal has a change that exceeds the threshold level, the processor checks to see whether the acquisition switch has been pressed again (step 310) .

If the acquisition switch has not been pressed, the processor checks to see whether a system verification switch 15 (Fig. 1) has been pressed (step 320) . If so, the processor verifies system integrity as described above (step 302) . If the system verification switch has not been pressed, the processor determines whether the system check timer has expired (step 322) . If so, the processor flashes the yellow light 44 (step 324) and determines whether the acquisition switch has been pressed (step 310) . If the timer has not expired, the processor determines whether the acquisition switch has been pressed (step 310) .

Other embodiments are within the following claims. For example, for certain applications N0 ₂ or other reagent gases can be substituted for 0 ₃ as the reaction gas in the chemiluminescence detector. Similarly, a photoionization detector could be substituted for the chemiluminescence detector or the pulse fluorescence detector. Also, an analysis unit having only a chemiluminescence detector could be configured with a first portion of the input stream passing directly to the chemiluminescence detector and a second portion passing through a ceramic pyrolyzer heated to a temperature of about 1000°C. This pyrolyzer would produce double bond compounds (alkenes) from hydrocarbons in the vapor sample that could then be detected by the chemiluminescence detector.

In a similar approach, an analysis unit having only a pulse fluorescence detector could be configured with a first portion of the input stream passing directly to the pulse fluorescence detector and a second portion passing through a gold or nickel pyrolyzer heated to a temperature between 300°C and 1000°C. This pyrolyzer would convert spoilage by-products in the form of sulfur compounds into SO _z that could then be detected by the pulse fluorescence detector. In another embodiment, the sample acquisition switch could be activated for an extended period during which the electrical signal(s) produced by the analysis unit would be integrated. This embodiment would offer improved sensitivity in exchange for reduced system throughput.

The system described herein could also be used in other applications. For example, the system could be used in sewage plants to detect excessive emission of hydrogen suIfides or other compounds. Similarly, the system could be used to monitor hydrogen sulfide

emissions from a paper plant operating according to the Kraft process. Correlations between volatile compounds detected and an amount of biological organisms present could also be made by the system. In addition, while biological materials have been primarily described as animal matter, plant matter such as, for example, soy beans could also be analyzed to detect spoilage.