H. KENT STUTZ, GERALD J. SILVERMAN Food Sciences Lab., U.S. Army Natick Research & Development Command Natick, MA 0 1760 WILLIAM M. SPIRA CRL-DACCA, Department of State and ROBERT E. LEVIN Dept. of Food Science & Technology, University of Massachusetts, Amherst. MA A Research Note AN APPARATUS FOR COLLECTING VOLATILES AND MAINTAINING A CONSTANT OXYGEN CONCENTRATION ABSTRACT An apparatus is described which is capable of controlling oxygen con- centrations during the spoilage of ground beef. The apparatus re- sponded sensitively to high and low oxygen demands and could be sanitized. INTRODUCTION IN A PREVIOUS STUDY on the volatiles produced during the spoilage of poultry (Freeman .et al., 1976) the oxygen concen- tration was not regulated. In the present study on raw, ground beef, it was thought desirable to assess the influence of this variable during spoilage. In order to accomplish this objective an apparatus was required which would be capable of (1) establishing and maintaining precise oxygen concentrations; (2) collecting volatiles for chemical analysis by entrappment on porous polymers (Jennings, 1972) or by temperature fractionation (Merritt et al., 1959); and (3) capable of being sanitized. The apparatus described below satisfactorily fulfilled these requirements for experiments lasting up to 10 days. EXPERIMENTAL A SCHEMATIC of the apparatus is presented in Figure 1. The sample (N) is contained in a 1000 ml flask (I). The two sections of the flask are sealed with an “0” ring and secured by a clamp. The top of the sample flask has ports for admitting oxygen (P), removing head space volatiles (R) and for the insertion of an oxygen probe (S). In establishing the desired oxygen concentration, the sample (N) in the flask is initially flushed with nitrogen, followed by the introduction of an oxygen-nitrogen mixture (40% 0, , 60% N, ; Matheson Gas Prod- ucts, Gloucester, MA). The signal from the oxygen probe (L) (Bio Marine Industries, Devan, PA) is conveyed to the control unit (C). A detailed schematic of the apparatus for regulating oxygen con- centration by the control unit (C) is presented in the insert of Figure 1. The signal from the oxygen probe drives a modified strip recorder (1, Ominographic model 3000, Houston Instruments, Inc., Bellaire, TX). The modification consists of attaching a microswitch (2) to the recorder frame on a bar positioned parallel to the path along which the pen is driven. The location of the microswitch is adjustable and its location determines the desired oxygen concentration. Whenever micro- bial activity lowers the oxygen concentration below that desired, the movement of the recorder pen closes the microswitch and energizes a 6v d.c. circuit. The 6v d.c. circuit consists of a 6 volt battery (3), a second micro- switch (8) which is activated by a continuously rotating timing cam (4) (General Time, model P1022A1, Thompson, CT) and a 6 volt d.c. contactor. During periods of oxygen demand when the switch on the recorder (2) is closed, the momentary closing of switch 8 energizes contactor 5 which in turn simultaneously opens solenoids 6 and 7, (Skinner Elec. Co., Model B2DA1052, New Britain, CT). Oxygen is introduced into the system through solenoid 6 and the effluent volatiles are released through solenoid 7. Synchronizing the action of the two 658-JOURNAL OF FOOD SCIENCE-Volume 43 (1978) solenoids prevents atmospheric oxygen from diffusing back into the1 system and minimizes the build-up of internal pressure. The oxygen-nitrogen gas mixture entering the system through solenoid 6 is regulated by a flow meter (D) (Model 100, Fisher and Porter Co., Warminster, PA), filtered (E) (type 33G Balston Inc., Lexington, MA) to remove microorganisms and particulate matter, humidified by passage through water (G) and finally enters the oxygen mixing chamber (H) for distribution to individual sample containers (I). The entry of the oxygen-nitrogen gas mixture into the flask (I) flushes the head space volatiles through port R and a Porapak Q trap (F) (Water Associates, Milford, MA). Organic compounds in the head space are retained on the trap for gas chromotographic-mass spectro- photometric analysis. Two other appropriate probes (K, M) (Orion Research Inc., Cambridge, MA) measure pH and Eh. The signals from’ the probes for oxygen, pH and Eh, are monitored by an electronic scanner (Orion Research Corp., Cambridge, MA) and data acquisition of these measurements is accomplished by a digitizer (B) (Orion Research Corp., Cambridge, MA). The Data are recorded on tape (A) and also collected by a computer (PDP-15, Digital Corp., Maynard, MA). DISCUSSION BY CAREFULLY ADJUSTING the rate of feed and the cam (4), oxygen concentrations, as shown in Figure 2, can be main- tained at the desired levels in spite of the fact that the oxygen demand is extremely low during the initial portion of then experiment and increases rapidly as spoilage appr0aches.i During this experiment, conducted at 10°C in an atmospheres of 18% oxygen, 72% nitrogen, the unit maintained an oxygen concentration within 0.25% of the desired concentration. By! having the computer monitor and compile the frequency andi duration that the oxygen valve is operative, as noted by the’ closing of the recorder switch (2), a measure of the oxygen demand during spoilage can be compiled (Fig. 2). Oxygen demand is shown to continuously increase during its initial 90-95 hr of storage, before decreasing. Oxygen concentra- tions ranging from 2-18s have been maintained for experi- ments of up to 10 days duration. As indicated in Figure 1 the manifold (H) and the sample flask (I) are maintained in an incubator. The experiments in this study were usually run below ambient temperature, usually at 10°C, and therefore little difficulty has been experi- enced in maintaining saturation of the oxygen-nitrogen mixture. At higher temperatures sparging within the incubator may be necessary. REFERENCES Freeman, L.R., Silverman, G.J., Angelini, P.. Merritt, C. and Es&en, W.G. 1976. Volatiles produced by microorganisms isolated from refrigerated chicken at spoilage. Appl. & Environ. Microbial. 32: 222. Jennings, W.G. 1972. The changing field of flavor chemistry. Food Technol. 26: 25. Merritt, C. Jr.. Bresnick, S.R., Bazinet, M.L., Walsh, J.T. and Angelini, P. 1959. Determination of volatile components of food stuffs. Techniaues and their auDlication to studies of irradiated beef. Aeric. & Food-Chem. 7: 784: MS received 6120177; revised 9/24/V; accepted 9/30/77.