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INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
24 hours. Samples were withdrawn until practically all the lat,ex had been removed. The remainder waa vented into a beaker. A clear unemulsified liquid was obtained, which immediately began to eject a vapor from solution. After approximately 5 minutes, the evolution had almost stopped and an orange viscous liquid with a molasses-like consistency, much lighter than the latex, remained. These results indicate that, up to 44.5y0 conversion, two distinct liquid phases are present. Apparently the two phases tend to separate fairly rapidly by the time the samples are used. All samples were properly stabilized and all had been aged from several days to several weeks by the time they were used. Either of these conditions may have had an effect on the stability of the emulsions. This type of densitometer and the method of operation provide a ready and positive method of detecting the existence of more than one phase.
The disappearance of the two phases OCCUJ'S at about 45% conversion. The initial reactor pressure during polymerization first begins t o drop at nearly this same conversion. The rate of heat evolution reaches a maximum, and the heat transfer coefficients pass through a minimum at about this point or at slightly higher conversions. These phenomena appear to indicate that a separate liquid phase of the unreacted monomers does not exist beyond this conversion. ACKNOWLEDGMENT
The author wishes to acknowledge the help of G. P. Baumann, J. L. Beecher, G. M. Davidson, F. W. Dittman, W. L. Kranich, J. L. Olsen, and J. L. Zabel, in the design, construction, and operation of the various densitometers employed in this project.
RANCIDITY OF BACON.. The effects of antioxidants-(1) nordihydroguaiaretic acid (NDGA), (2) d-isoascorbyl palmitate, soybean lecithin, and mixed tocopherols, and (3) gossypol i n five different concentrations-in retarding the development of peroxides in slices of unsmolied and smoked bacon were studied and compared with corresponding slices receiving no treatment. The antioxidants dissolved i n vegetable oils were applied to the surface of the slices. This study showed that all of the antioxidants were effective in retarding the development of peroxides, the effectiveness of the gossypol varying with the concentration used. The induction or keeping period for the treated slices was three to five times longer than for those receiving no antioxidants. Smoking retards the development of rancidity i n bacon, while light promotes its development.
T
HE development of rancidity, particularly during the warmer months, markedly shortens the time during which cured pork can be stored without becoming unpalatable. The investigation reported here is part of extensive research undertaken to find improved.methods of controlling rancidity development in cured pork, which would increase the value of these cured cuts by preventing waste and improving palatability. The quality is determined when served &the table. Recent studies on and developments in the use of antioxidants (2-11,14) suggest their application in the prevention of rancidity in pork. Certain of these antioxidants have shown remarkable powers in stabilizing lard and oils. Mattill, Olcott, and Golumbic (1, 2, 7, 9, 10) made extensive investigations on the chemical characteristics of antioxidants. They determined oxygenic indices of many antioxidants and demonstrated that lard can be stabilized by these materials. Lundberg et al. (6) recently showed that with lard, nordihydroguaiaretic acid (NDGA) has powerful antioxidant properties which are enhanced when used in combination with ascorbic acid, Riemenschneider et al. (11) showed synergistic effects in retarding rancidity development when certain combinations of antioxidants are added to lard. Similar results were obtained by adding the antioxidants that supplement those occurring naturally in the products. White ( I B , f 7 ) in studying the factors affecting the development of rancidity in bacon found considerable variation in stability from slab to slab. Wrapping in aluminum foil, storing at 18" t o -23O C.,and thawing in brine or pickle were most effective in retarding rancidity. Smoking also imparted antioxidant effects. The changes in rancidity development were determined
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Vol. 37, No. 12
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Efect of Antioxidants F. H. SMITH, D. E. BRADY, AND R. E. COMSTOCK North Carolina Agricultural Experiment Station, Raleigh, N . C.
by the peroxide and free fatty acid content. The peroxides developed rapidly during curing while the free fatty acid developed a t a uniform rate during curing and storage. White concluded that rancidity was largely due to oxidation, since the free fatty acid content was low throughout the study. He also found that, of the several methods studied for measuring rancidity, peroxide values were most reliable. A modified Kreis test gave results that were highly correlated with the peroxide values. The first part of this paper deals with a study of the effects of light and two antioxidants on rancidity development of bacon as estimated by peroxide values, expressed as milliequivalent8 per kilogram of fat. The second part describes further studies on the use of three antioxidants in controlling rancidity development of the same product. I.
EFFECT OF LIGHT AND ANTIOXIDANTS
This experiment was designed to compare the rate of rancidity development in cured bacon sliced 5 mm. thick: (1) untreated; (2)treated with antioxidant A, 0.02% nordihydroguaiaretic acid (NDGA) in hydrogenated vegetable oil; and (3) treated with antioxidant B, a hydrogenated vegetable oil containing 0.06% d-isoascorbyl palmitate, 0.06% soybean lecithin, and 0.01% mixed tocopherols. The cornpanson was made at room temperature (approximately 80" F.) both in the light and in the dark. The bacon came from a hog fed a large amount of soybeans, and hence the fat was very oily. The bacon was cured with a mixture consisting of 8 pounds of salt, 3 pounds of brown aug&r, 3 ounces of saltpeter, and 5 gallons of water per 100 pounds of meat. After curing for 10 days, the bacon was given a light smoking and stored for 180 days in a dark room at 34' to 36' F. Slices were cut from the slab and randomized before treatment. Six of the randomized slices were dipped in each of the melted antioxidants (60' C.) and hung on a small rack along with eiX slices receiving no treatment. This rack was placed on a table and exposed at room temperature to light coming through two
INDUSTRIAL AND E N G I N E E R I N G C H E M I S T R Y
December, 1945
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Stansby (16) and expressed in milliequivalents of peroxide per kilogram of fat. The effects of the various t r e a t m e n t s a r e presented graphically in Figure 1. The average peroxide values for slices treated with antioxidants A and B were significantly' lower a t all intervals of storage in both light and dark than the controls receiving no treatment. The average peroxide values of the controls increased with time a t a uniform rate, and the significantly accountable differences between storage in light and dark were nearly the same at all time intervals. This suggests that the induct i o n period f o r u n t r e a t e d bacon may be prolonged by storing in the dark; but when this period is over, rancidity develops as rapidly in the dark as in the light. The average peroxide values for the slices of bacon treated with antioxidant B were less at each time interval than for those
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Figure 1. I3lT-t of Antioxidants on Rancidity Development in Sliced Bacon 0.02% nordihydroguaiaretic acid i n hydrogenated vegetable oil B. 0.06% d-iwslcmbyl palmitate. 0.06% aogbean lecithin, and 0.01% mixed tocohperola in hydrogenated vegetable oil C. Control I. Initial peroxide r d u e of bacon
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large windows. Another rack having the same number of slices with identical treatments was placed in a dark cabinet in the same room. A similar number of slices were treated and stored in the same way on the following day. Eight slices which were used to determine the initial peroxide value a t the beginning of the experiment gave an average of 6.8. At 7, 14, and 21 days, peroxide values were determined on four slices receiving each treatment, stored in both light and dark. After the rinds were removed, the slices were placed in 250-ml. beakers and heated in an oven for 3 hours a t 75" C. The fat was then expressed with a m a l l fruit press and filtered, with slight suction, through a small wad of cotton placed in the constricted stem of a funnel. About 1 gram of the melted fat was put in a tared flask, having a ground glass stopper, and weighed. Peroxide values were determined by the hydrochloric acid method of Both this and the following experiment were derigned to allow statistical analysis of the resulting data. Differencee indicated as significant had a probability of occurrence through chance of less than 6%. Difference stated to be highly significant had a probability of chance occurrence of 1% or lesa. 1
