Effect of Gamma Irradiation on the Physicochemical Properties of Rye 1

Effect of Gamma Irradiation on the Physicochemical Properties of 1 MUHAMMAD SIDDIQUE JAMI, M. H. PUBOLS, and JAMES McGINNIS Department of Animal Sciences, Washington State University, Pullman, Washington 99164 (Received for publication September 5, 1978) ABSTRACT The effect of irradiation ( 60 Co) on the nutritional value of rye war determined using a chick growth assay. In vitro irradiation increased significantly the solubility of rye solids in water. Total protein (N X 6.25) was not changed appreciably by irradiation but its solubility in water was increased. Compared with non-irradiated rye, the ph of irradiated rye suspension in water was reduced. In vitro digestibility of irradiated rye protein determined by a mixture of trypsin, chymotrypsin, and peptidase was increased. Solubility of carbohydrate from rye in water was increased and viscosity of a water extract was decreased by irradiation. In vitro a-amylolysis of water extracts of the grain indicated no beneficial effect of gamma irradiation for a-amylase activity. In vitro enzymatic digestibility of a diet containing 62.55% irradiated rye was enhanced by a combined pepsin-pancreatin treatment over a non-irradiated rye containing dye. Dry feces, expressed as percentage of dry matter consumed, were less for chicks fed irradiated rye diets than for those fed nonirradiated rye diets. The nutritional value of rye, based on a chick growth assay, was significantly increased by gamma irradiation ( 60 Co). Irradiation of rye decreased nitrogen and mineral excretion by chicks in relation to intake of these nutrients. INTRODUCTION (Secale cereale) has the potential of being an important cereal grain. It can be grown to advantage in areas and climates where wheat and corn either cannot be grown or yield poorly. Several workers (Jones et al., 1948; Kalmykov, 1968; Janicki and Kowalczyk, 1966) have noted that rye protein has a higher biological value than that of wheat or corn. contains 4.54% lysine as a percent of the protein as compared to 2.9% for wheat (Kalmykov, 1968). This higher lysine content of rye can be important especially in non-ruminant nutrition where this amino acid is often growth limiting. It is known that exposure to gamma irradiation can retard proliferation of spoilage microorganisms or destroy them completely in foods depending on the intensity (Libby and Black, 1978) and that physicochemical characteristics of macronutrients can be altered by this treatment of foods (Nene et al., 1975). These effects of gamma irradiation make it a useful method of food sterilization and preservation. Hickman et al. (1964) reported no harmful 1980 Poultry Science 59:253-257 effects on growth, reproductive performance, or progeny health of four successive generations of rats fed gamma irradiated wheat (.02 -.2 Mrad 60 Co). Digestibility and biological values of corn protein or wheat gluten for rats were not affected by 2.8 or 9.3 Mrad of radiation (Metta and Johnson, 1959). The changes in physicochemical characteristics of food nutrients exposed to gamma irradiation affect their nutritional value. Read et al. (1958) reported improvement in weight gain of rats fed irradiated corn (2.79 Mrad) and cereal bar (5.58 Mrad). The improvement, the authors concluded, was caused by partial breakdown of the biological components of corn and cereal bar. Moran et al. (1968) reported that gamma irradiation of wheat bran (.05-5 Mrad) significantly increased protein and phosphorus utilization by chicks. McGinnis et al. (1978) reported increases in weights of chicks fed gamma irradiated rye (1.88 and 6.2 Mrad) over those fed nonirradiated rye. The studies reported herein were undertaken to examine the mechanisms involved in the improvement of nutritional value of rye exposed to gamma irradiation. 1 Scientific Paper No. 5187. College of Agriculture Research Center, Washington State University, Pullman, WA. Project No. 0107. PROCEDURE Biological assay. Day-old broiler chicks 253

254 J AMI ET AL. hatched from Washington State University stock (Hubbard White Rock X White Mountain) were used in the assay. The birds were randomly distributed in groups of 10 to provide 5 males and 5 females. Three groups were randomly assigned to each experimental diet. The chicks were reared in electrically heated, wire-floored battery brooders. Battery heating elements were set to give a temperature of approximately 95 C at chick height for the first week and lowered to 27 C for the rest of the experimental period. Composition of the basal diet is given in Table 1. A corn based diet was used as a control, with rye or gamma irradiated rye (10 Mrad) being substituted for corn in the experimental diets. Feed and water were supplied ad libitum. Birds and feed were weighed at the start of the experiment, at 1 week, and at 2 weeks, at which time the experiment was terminated. Feces condition was evaluated by more than one person by visually scoring the amount of feces adhering to the wire floors. Feces for different analyses were collected every other day throughout the experimental period. Immediately after collection, the feces were transferred onto stainless steel trays and dried in a force draft oven at 90 C for 18 hr. Dry feces were weighed as soon as they came to room temperature, ground to a fine powder, and stored in polyethelene bags at 5 C. The data on body weight and feed efficien- TABLE 1. Composition of basal diet Ingredient (%) Grain (corn or rye) 62.55 Soybean meal (47.5% protein) 25.00 Fish meal (65% protein) 3.00 Meat and bonemeal (50% protein) 3.00 Animal fat 2.00 Dried whey 1.00 Dehydrated alfalfa (18% protein) 1.10 Iodized salt.23 Dicalcium phosphate.77 Limestore.90 Vitamin premix a.25 Trace mineral premixb.05 DL-methionine.15 Supplies the following per kilogram: vitamin A, 2,200,000 IU; vitamin D?, 660,000 ICU; vitamin E, 1,760 mg; riboflavin, 1,320 mg; D-pantothenic acid, 1,619 mg; niacin, 8,880 mg; choline chloride, 230,780 mg; vitamin B 12, 4.4 mg. Supplies the following mg/kg: Mn, 50; Fe, 50; Cu, 5;Zn, 50; I, 1.5; Ca, 60; Co, 5. cy were analyzed statistically by analysis of variance and the means were compared using Duncan's multiple range test (Duncan, 1955). Other data were not statistically analyzed. Protein solubility. To study the protein solubility, 5 g rye or gamma-irradiated rye (ground to pass a 40 mesh screen) was suspended with 75 ml deionized water and shaken on a wrist action shaker for 30 min at room temperature. The suspension was centrifuged at 3,000 Xg for 10 min. The nitrogen content of the supernatant (soluble nitrogen) and pellet (insoluble nitrogen) were determined by the Kjeldahl method, which was also used for the determination of N in feeds and feces. Viscosity determination. A 5 ml aliquot of the supernatant prepared for protein determination was transferred into an Ostwald viscometer. The time (measured in seconds) required for the supernatant to flow from the upper to the lower mark was regarded as an index of the viscosity of a sample at room temperature (21 C). Reducing sugar determination. For the measurement of reducing sugar, 5 g rye or gamma-irradiated rye (ground to pass a 40 mesh screen) was suspended with 75 ml deionized water and shaken on a wrist action shaker for 30 min at room temperature. A crystal of thymol was added to the suspension to retard microbial growth prior to incubation of the suspension at 41 C for 18 hr. Thereafter, the suspension was again shaken for 10 min at room temperature and centrifuged at 3,000 Xg for 10 min. Reducing sugars were estimated in the supernatant by the 3,5-dinitrosalicylic acid method of Bernfield (1951) and expressed as percentage maltose equivalent of the dry matter of the sample. In vitro a-amylolysis. Amylolysis of rye and gamma-irradiated rye carbohydrate by using a-amylase (which was partially purified from an acetone powder of chick pancreas in our laboratory) was estimated in the supernatant prepared as described above. The reducing sugars were measured by the 3,5-dinitrosalicylic acid method of Bernfield (1951). Enzymatic Determination of Insoluble, Indigestible Residue. Insoluble indigestible residue contents of diets containing 62.55% of rye, gamma-irradiated rye or corn were determined by the method of Hellendoorn (1972) which involves a combined pepsin-pancreatic treatment. Pepsin used in this study was purchased from Sigma Chemical Co. (from hog

GAMMA IRRADIATION OF RYE 255 stomach mucosa, Cat. No. P-7012). An acetone powder of chick pancreas was prepared in our laboratory and used for pancreatin. The only modification made in this method was the use of uncooked diets (ground to pass a 40 mesh screen) instead of beans. In Vitro Enzymatic Digestibility. The enzymes used in this aspect of the study were purchased from Sigma Chemical Co. and were as follows: trypsin (from hog pancreas, Cat. No. T-0134), chymotrypsin (from bovine pancreas, Cat. No. C-4129), and peptidase (from hog intestinal mucosa, Cat. No. P-7500). The in vitro digestibility was studied by using the multienzyme technique (Hsu, 1977). Ash Determination. Ash content of feed containing 62.55% rye, gamma irradiated rye or corn, and feces of chicks fed these diets were determined by using AOAC procedure (1970). Fecal ash was expressed as percentage of ash intake. Calculations. The fecal dry matter excreted by chicks was measured by making total collection of feces over a two-week experimental period as already described. It was expressed as percentage of dry matter intake using the following formula: Total wt. of dry feces Total wt. of dry feed consumed X 100 Total nitrogen excreted by chicks was expressed as percentage of nitrogen intake according to the following formula: Total wt. of dry feces X N (in feces) X 100 Total wt. of dry feed consumed X % N (in feed) Grain and treatment Ash excreted in the feces was expressed as percentage of the ash intake according to the following formula: Total wt. of dry feces X ash (in feces) Total wt. of dry feed consumed X % ash (in feed) X 100 The residue was obtained by drying a 30 ml aliquot of the supernatant at 102 C (for 18 hr) was used to calculate the total soluble solids. RESULTS AND DISCUSSION Biological Assay. A significant reduction in body weight was seen in chicks fed the rye containing diet compared with those fed a corn based diet (Table 2). Supplemental penicillin alleviated this growth reduction and increased feed efficiency significantly. Body weights and feed efficiency of chicks fed the diet containing gamma irradiated rye were significantly greater than for those fed the rye containing diets with or without penicillin. Addition of penicillin to diets containing gamma irradiated rye increased the chick growth significantly, and weights of chicks fed penicillin supplemented gamma irradiated rye diets were equal to those fed the penicillin supplemented corn based diets. However, addition of penicillin to diets containing gamma irradiated rye or corn did not effect a significant improvement in feed efficiency. The low mortality encountered was random and not associated with any particular treatment. These observations are in agreement with those of McGinnis et al. (1978). A significant TABLE 2. Average chick weight, feed efficiency, and screen score for the biological assay Diet description Gamma-irradiated rye (10 Mrad) Gamma-irradiated rye (10 Mrad) Corn Corn Coefficient of variability Procaine penicillin (50 ppm) _ - 14-day average chick weight (g) 142.0 a 183.3 b 206.4 C 241.5 d 231.7 d 247.5 d 4.49% Average gain/feed.52^.64 b.68 c.70 c.69 c.71 = 2.68% Average screen score 1 3.80 4.00 3.90 3.90.30.27 Scoring procedure: 0 = clean; 1 = almost clean; 2 = light; 3 = medium; 4 = heavy. a ' ' c ' Means within a column followed by the same superscript letter are not significantly different (P<.05).

256 JAMI ET AL. TABLE 3. Radiation effect on various properties'* of rye or diets containing 62.55% rye and on fecal excretion of dry matter, N a and ashb Properties (Control) Gammairradiated rye Viscosity of a water extract (seconds) 258.00 ± 1.15 C 144.00 ± 2.31 c ph of a water extract 6.20 ±.013 5.80 ±.022 Water soluble fraction (% of dry matter) 17.17 ±.037 22.26 ±.06 Total protein (N X 6.25;% of dry matter) 10.50 ±.09 10.20 ±.08 Soluble protein (% of total protein) 39.80.23 45.80 ±.12 Reducing sugar (equivalent of maltose; % of dry matter) 8.86 ±.42 15.80 ±.51 Reducing sugar liberated by a-amylase (% of dry matter) 16.16 ±.54 22.00 ±.59 In vitro protein digestibility (multienzyme complex) 78.31 ±.27 80.48 ±.74 Insoluble, indigestible residue of diets containing 62.55% grain 22.30 ±.64 18.50 ±.4 Fecal dry matter (% of dry matter intake) 40.50 ±.5 34.00 ±1.0 Fecal N(% of N-intake) 58.55 ±1.0 46.11 ± 1.2 Fecal ash (% of ash intake) 53.89 ± 2.12 44.63 ± 2.53 Ash retained/weight gain.05 ±.003.048 ±.0040 a Values presented are averages of 3 replicates. Values presented are averages of 2 replicates. c Standard error of mean. growth response of chicks fed gamma irradiated rye over supplemental penicillin suggests that different types of growth stimulation are caused by gamma irradiation and penicillin. Neither supplemental penicillin nor gamma irradiation of rye improved the fecal condition. The mechanism involved in improving the nutritional value of rye by gamma irradiation is not established. The following results illustrate some of the effects of gamma irradiation on rye grain. In Vitro Studies. Results of in vitro studies are presented in Table 3. Gamma irradiation (20 Mrad) effected a marked reduction in the viscosity of a water extract of rye suggesting the degradation of some large molecules of biological materials in rye. There was a decrease in ph caused by gamma irradiation. Total protein content was unaffected. Gamma irradiation did not change the susceptibility of rye carbohydrate to hydrolysis by a-amylase. This is not in agreement with the observation of Nene et al. (1975) who found an increase in the action of a-amylase on the carbohydrates of red gram exposed to gamma irradiation. In vitro protein digestibility of rye proteins was increased slightly by gamma irradiation. Insoluble, indigestible residue of a diet containing 62.55% of rye was decreased by gamma irradiation of the grain. Chicks fed gamma irradiated rye showed a marked reduction on the excretion of dry matter, fecal nitrogen, and fecal ash compared with those fed nonirradiated rye. The results indicated that gamma irradiation degrades or denatures the growth depressing component(s) of rye and effects some physicochemical changes in nutrients such as carbohydrates and proteins. An increase in reducing sugar equivalents and decrease in ph of a water suspension of irradiated rye suggest such changes. However, it is not possible at this time to suggest specifically the mode of irradiation action. REFERENCES Association of Official Analytical Chemists, 1970. Official methods of analysis. 11th ed. Washington, DC. Bernfield, P., 1951. Enzymes of starch degradation and synthesis. Adv. Enzymol. 12:379. Duncan, D. B 1955. Multiple range and multiple F test. Biometrics 11:1 42. Hellendoorn, E. W., 1972. Enzymatic determination of insoluble, indigestible residue of beans. Pages 321 324. in Nutritional improvement of food legumes by breeding. M. Milner, ed. Protein Advisory Group of the United Nations System. UN, New York, NY. Hickman, J. R., D. L. A. McLean, and F. J. Ley, 1964. Rat feeding studies on wheat treated with gamma irradiation. 1. Reproduction. Food Cosmet. Toxicol. 2:15-20. Hsu, H. W., D. L. Vavak, L. D. Satterlee, and G. A. Miller, 1977. A multienzyme technique for estimating protein digestibility. J. Food Sci. 42:1269-1273. Janicki, J., and J. Kowalczyk, 1966. Nutritional value

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