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The effect of treatment with urea, sorbic acid, or dehydration on orange peel silage
Animal Feed Science and Technology, 20 (1988) 335-342
335
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
Short C o m m u n i c a t i o n
The Effect of Treatment with Urea, Sorbic Acid, or Dehydration on Orange Peel Silage Z.G. W E I N B E R G
l,G. P A H L O W
~, B. D I N T E R s and G. A S H B E L L
I
~Department of Stored Products, Feed Conservation Laboratory, AgriculturalResearch Organization, The Volcani Center, Bet Dagan 50250 (Israel) 2Instituteof Grassland and Forage Research, Federal Research Center o[Agriculture (FAL), Braunschweig D-3300 (F.R.G.) (Received 8 April 1987; accepted for publication 30 December 1987)
ABSTRACT Weinberg, Z.G., Pahlow, G., Dinter, B. and AshbeU, G., 1988. The effectof treatment with urea, sorbic acid,or dehydration on orange peel silage.Anita. Feed Sci. Technol.,20: 335-342. The purpose of this work was to study the effects of 1% urea, 0.05% sorbic acid (SA) and moderate dehydration (by oven at 35°C for I h) on the ensilingprocess of orange peels and on reducing fermentation losses. Fresh peels of the various treatments, in 10-kg triplicates,were ensiled in speciallydesigned anaerobic containers for 35 days. Chemical and microbial analyses were performed on the peels and on seepage samples taken during the ensilingperiod. The dominant microbial populations of the peel silagewere lactobacilli(10s g per D M ) and yeasts (105 g per D M ) and the major fermentation product was ethanol (18% in D M of the control silage).There were differencesbetween the treatments, with SA being the only treatment effective in reducing D M losses to 15%, compared with> 30% for the other treatments. Chemical results indicate a more efficientfermentation process with SA.
INTRODUCTION
Orange peels, a by-product of the orange juice industry, are highly nutritious (on a dry matter, D M , basis) and can serve as fodder (Braverman, 1949). In the past, when energy costs were lower, it was economical to conserve this material by drying. A m m e r m a n et al. (1967), Vijchulata et al. (1980) and Chen et al. (1981) used dried citruspulp and citruscondensed molasses as an energy source in rations for ruminants and obtained good results with regard to the animals' performance. Another method of conservation of the citruspeels would Contribution from the AgriculturalResearch Organization, The Volcani Center, Bet Dagan, Israel No. 1894-E, 1986 series.
0377-8401/88/$03.50
© 1988 Elsevier Science Publishers B.V.
336
be ensiling. However, the peels lose much of their nutritive value very rapidly during ensiling, due to undesirable fermentation. In a previous study, Ashbell et al. (1987) showed that most of the loss is due to gas release occurring during the first week of storage. Under Israeli conditions, peels can be stored in the dairy farm for fresh feeding for up to 1 week until consumed and lose much of their DM content even during that period. Furthermore, during the picking season, the peels are produced at a rate greater than that required for use directly as fodder, so they must be conserved for longer storage. In the case of ensiling, peels may lose as much as 50% of their original DM content (Ashbell and Donahaye, 1984). Ashbell et al. (1987) showed that, in addition to lactic acid bacteria, the microflora of the peels (fresh or ensiled) consists of large numbers of yeasts and lactate-fermenting yeasts which probably bring about the great losses in DM. In order to improve fermentation in orange peel silage, selective means should be employed that would inhibit these detrimental yeast populations. In the present work, we studied the effects of urea, sorbic acid (SA) and partial dehydration on losses and quality of orange peel silage. These treatments were chosen in order to affect the peel microflora and thus to improve the fermentation process. Urea was used since it was reported to improve the aerobic stability of silages (probably as an ammonia generator) and to improve the nitrogen content of the final product (McDonald, 1981 ). SA is known to possess antimycotic activity. Dehydration was tested since previous preliminary experiments (unpublished) showed that even slight increase in DM content by a few percent resulted in reduced fermentation losses. MATERIALS A N D M E T H O D S
Experimental Fresh orange peels (variety Shamouti) of the various treatments, in triplicate, were ensiled and stored in specially designed anaerobic containers, 10 kg in each, as described by Ashbell et al. (1987). The containers were stored at a constant ambient temperature of 21 + 1 ° C. Containers and seepage weights were recorded on Days 1, 2, 3, 4, 5, 7, 9, 11, 15, 18, 24, 30 and 35 of ensiling. Gas weight losses were calculated from the difference between total weight loss and seepage weight release. Fresh aliquots from the seepage from each treatment were used for chemicl analyses on these days. On Day 35, all the containers were opened and peel samples were taken with a special edged metal pipe, 40 mm in diameter.
Treatments (I) Control: I0 kg of peel in each container were ensiled with no additives or treatment.
337
(2) Urea: 1% of urea powder (w:w) was mixed thoroughly by hand with the fresh peel before ensiling. (3) SA: 0.05% SA (Sigma ~R)) (w:w) was mixed thoroughly by hand with the fresh peel before ensiling. (4) Dehydration: 40 kg of fresh peel were spread on 8 metal trays (67×43 cm), ca. 5 kg on each, and dried for 1 h at 35 ° C in an air convection oven. The peels lost 8.5 _+0.3% of their original weight.
Chemical analysis Analyses of the fresh peels, after 35 days ofensiling and of seepage included the determination of pH, DM, ash, water-soluble carbohydrates (WSC), volatile fatty acids (VFA) and lactic acid (LA). The methods employed in this analysis are described in detail in Ashbell et al. (1987)
Microbial analysis This was carried out on fresh and ensiled peels (from Day 0 and Day 35, respectively) and on seepage from Days 15 and 24 after ensiling. This included the determination of lactic acid bac~ria (LAB), lactate-assimilating yeasts, enterobacteria and clostridial spores. The methods used in this analysis are also described in Ashbell et al. (1987).
Biological oxygen demand (BOD) and chemical oxygen demand (COD) These were determined on the control seepage from Day 2, according to the method described (Anon., 1965).
In vitro digestibility This was determined according to Tilley and Terry (1963). RESULTS
The chemical properties of the fresh and ensiled peels are listed in Table 1. In general, the urea-treated and dehydrated peel silages were not markedly different from the control silage. The SA-treated silage, however, was very different from the other silages. Residual WSC in the ensiled peels was between 9.4 and 12.3% in DM, except for the SA treatment where it remained at a high level of 22 % in DM. In this silage (SA), the lowest levels of ethanol and acetic acid were detected. However, LA levels were similar to the other peel silages.
338
TABLE1 Chemicalanalysisofthe orangepeels (freshand silage,after35 days) Treatment
pH
Percent in D M
Fresh Silage PereentDM
WSC
Lactic acid
Ethanol
Acetic acid
Fresh Silage Fresh Silage Fresh Silage Fresh Silage Fresh Silage Control l%urea 0.05% sorbic acid Dehydration
4.1 4.1 4.0 4.2
3.6 3.7 3.5 3.5
17.2 17.8 18.2 19.3
14.2 14.1 16.1 14.6
41.2 9.4 35.3 9.9 3 9 . 0 22.0 3 8 . 0 12.3
0.9 0.6 0.4 0.6
1.8 2.5 2.3 2.3
<0.1 <0.1 <0.1 <0.1
16.5 13.4 7.0 16.0
<0.1 2.8 <0.1 3.0 <0.1 1.2 <0.1 9.2
TABLE 2 Dry matterlosses(means± SD )oforangepeelsilage Treatment
Percent D M loss in seepage
Percent D M loss as gas a
Total D M loss
Seepage release weight (g per container)
Control 1% urea 0.05% sorbic acid Dehydration
5.6 6.0 5.7 3.5
25.7 28.1 15.4 30.6
31.3 +- 1.4 34.1 ___0.4 21.1 +_0.9 34.1 +_0.2
1273.5 ± 132.8 1273.9 ± 20.5 926.9 _+115.9 836.9 +_ 18.5
~Calculated.
The digestibilityof the fresh and ensiled peels in all treatments was very high and varied between 85.2 and 89.2% in D M . The D M losses are given in Table 2. The control, urea-treated and dehydrated peels lostabout one-third of the D M content of the fresh peels,whereas the SA-treated peels lost only about one-fifth (of the D M ) . Total seepage weights were highest in the control and urea-treated peels and smaller in the SA-treated and dehydrated peels. Seepage release was most intensive on Day 2 after ensiling and most seepage was released within 1 week after ensiling. D M content in the seepage varied from 11.8 to 13.4% in the beginning, decreased after 3 days and varied from 5.6 to 8.4% until the end of the experiment. This was similar for all treatments. Most of the D M losses in all treatments are attributed to gas losses.This is in agreement with previous findings (Ashbell and Donahaye, 1986; Ashbell et al.,1987). The BOD and COD of the seepage were 58 600 and 108 850 mg 02 1-1, respectively. Since fermentation products of the peels were determined only 35 days after
339
ensiling, the dynamics can be followed only in the changes occurring in the seepage. The effluent, however, was exposed to oxygen during the night of collecting the samples and thus certain oxidative processes could occur in this material, which still contained high numbers of active organisms (see Table 4). Seepage analysis revealed that ethanol was the major fermentation product. The highest levels of ethanol were found in the control seepage (on the first week even more than 80% in DM) and the lowest levels were found in the seepage of the SA treated peels. The concentration of ethanol decreased after reaching a maximum level 1 week after ensiling. LA contents in the seepage of the various treatments increased with time of ensiling for all treatments and ranged between 9 and 14% in DM of the seepage (Day 35). Acetic acid contents increased with time for all treatments and ranged from 4 to 12% in DM. SA treatment resulted in the lowest, and the control treatment in the highest, contents. Results of the microbial analysis of the peels and seepage are given in Tables 3 and 4. The dominant populations in the fresh peels were lactobacilli, lactateassimilating yeasts (LAY) and enterobacteria. The log number of colonyforming units g-1 DM (CFU) of each population was ca. 5.0. On Day 35, the log number of the lactobacilli increased to ca. 8.0 in all treatments. Since the counts for the total number of yeasts and the LAY in particular did not differ as much as in forage crops, where the total count can be 1000 times higher, at least during the first weeks only data on the LAY are given in Tables 3 and 4. The numbers of LAY did not change much throughout ensiling except in the dehydrated peels, where the log number decreased slightly, to 3.6. EnterobacTABLE 3 Microflora of the fresh and ensiled orange peels (log CFU g-1 DM)a Treatment
LactobaciUi
Lactateassimilating Fresh Silage yeasts (LAY)
Moulds b
Enterobacteria
Clostridia
Fresh Silage Fresh
Silage
Fresh Silage
1.2 1.6 1.2 0.7
0 0 0 0
1.6 0 0 0
Fresh Silage Control 1% urea 0.05% sorbic acid Dehydration
5.1 4.7 5.0 4.8
8.3 8.4 8.0 7.3
5.2 4.9 4.9 4.9
"CFU, colony-forming units. bMoulds appeared on the L A Y plates.
4.4 5.5 4.3 3.6
0 0 0 0
4.8 4.7 4.7 4.6
0 0 0 0
340 TABLE 4 Microfloraof the orangepeel seepage (logCFU g-1 DM)a
Treatment
Lactobacilliafter (days) 15
Control 1% urea 0.05% sorbicacid Dehydration
8.7 8.5 8.7 8.6
24 8.4 9.4 8.8 7.8
Lactate-assimilatingyeasts after (days) 35 8.3 8.7 8.1 7.8
15
24
35
6.1 7.6 6.7 7.3
3.9 6.3 6.3 7.4
5.3 5.0 4.5 5.4
aCFU = colony-formingunits. teria, moulds and clostridiawere found (in small numbers) only in the fresh peels. In the seepage (Table 4), the microflora on Days 15, 24 and 35 was similar to the microflora of the peel on Day 35, except for the yeasts, which were higher in the seepage than in the urea-treated peels and in the dehydrated peels. The texture of the control peel silage was pasty (mushy), the urea-treated and dehydrated peels were somewhat firmer, and the SA-treated peels maintained the best structure. DISCUSSION In order to reduce losses in orange peel silage, several treatments were tried with the aim of inhibiting yeast activity and improving fermentation. The least losses were achieved with SA, in which seepage release was less than in the control or urea-treated peels. This is in spite of the fact that the SA did not decrease the yeast populations much. The number of LAY in the SA seepage (Day 35) was somewhat less than in the other seepages. Sorbic acid is known to have antimycotic or fungistatic effects and it could be that it affected the yeasts' activity rather than the yeast counts. Urea, which is sometimes added to silages as a stabilizer (McDonald, 1981 ), did not reduce losses and also did not affect the yeast count. Dehydration was aimed at reducing the water content of the peels and improving fermentation. This treatment increased the DM content by only 2%. Dehydration led to the least seepage release, but losses were comparable to those in the control. It could be that the temperature at which the dehydration was performed (35 ° C ) enhanced the development of undesirable micro-organisms and/or activated enzymes such as pectinase which resulted in loss of structure and enhanced losses. The main idea behind this treatment was to examine the effect of various industrial methods (during juice extraction) that would yield drier peels.
341
For the control, urea-treated and dehydrated peels, L A formation was more or less the inverse of the decrease in percent W S C . With the S A treatment, percent W S C did not decrease to the same extent as with the other treatments, but L A formation was comparable to the other treatments. This might indicate a more efficientfermentation with this treatment. This was confirmed by the V F A analysis which indicated a mostly homolactic conversion of the sugars to rather high amounts of L A and the effective inhibition of yeast metabolism, leading to far lower ethanol and C02 production. Previous experiments indicated that chemical and microbial changes occurring in the peels during the ensiling period are reflected by the chemical and microbial changes in the seepage. Seepage microflora at an early stage of ensiling (Day 15 ) was already similar to the microflora of the peels tested on Day 35. This confirms our previous impression (Ashbell et al.,1987) that most changes in the peel silage occur very rapidly. Indeed, most seepage release occurred within 5 days of ensiling in all treatments tested. In this experiment, the extent of seepage release was relativelysmall in comparison with previous data, probably due to smaller hydrostatic pressure buildup in our experimental containers. In larger containers, seepage release was more intensive (Ashbell and Donahaye, 1986). Silage seepage is among the most serious water pollutants (Woolford, 1984 ). In this experiment, the B O D and C O D values of the seepage were also very high, probably due to the high concentration of W S C . From this study, it appears that S A was the most efficienttreatment with regard to loss reduction and fermentation pattern of the orange peel silage. Several more treatments are currently being tested in our laboratory to improve further the fermentation process and to minimize losses. The most promising treatments will be elaborated on (various concentrations of intensities),firstin experiments under laboratory conditions and then on a commercial scale.
REFERENCES Ammerman, C.B., Neal, F.C., Palmer, A.Z., Moore, J.E. and Arrington, L.R., 1967. Comparative nutritional value of pelleted and regular dried citrus pulp when fed at different levels to finishing steers. Dep. Anita. Sci. Mimeogr. Pep. AN 67-7, University of Florida, Gainesville, FL. Anonymous, 1965. American Public Health Association. In: Standard Methods for the Examination of Water and Wastewater. New York, pp. 415-421,520-514. AshbeU, G. and Donahaye, E., 1984. Losses in orange peel silage.Agric. Wastes, 11: 73-77. Ashbell,G. and Donahaye, E., 1986.Laboratory trialson conservationsof orange peelsilage.Agric. Wastes, 15: 133-137. Ashbell, G., Pahlow, G., Dinter, B. and Weinberg, Z.G., 1987. Dynamics of orange fermentation during ensiling.J. Appl. Bacteriol.,63: 275-279.
342 Braverman, S.B., 1949. Miscellaneous citrus products. In: S.B. Braverman (Editor), Citrus Products. Interecience, New York, pp. 351-356. Chen, M.C., Ammerman, C.B., Henry, P.R., Palmer, A.Z. and Long, S.K., 1981. Citrus condensed molassed solubles as an energy source for ruminants. J. Anita. Sci., 53: 253-259. McDonald, P., 1981. Silage additives. In: P. McDonald (Editor), The Biochemistry of Silage. Wiley, Chichester, pp. 157-158. Tilley, J.M. and Terry, R.A., 1963. A two-stage technique for the in vitro digestion of forage crops. J. Br. Grassl. Soc., 18: 104-111. Vijchulata, P., Henry, P.R., Ammerman, C.B., Potter, S.G., Palmer, A.Z. and Becker, H.N., 1980. Effect of dried citrus pulp and cage layer manure in combination with monensin on performance and tissue mineral composition in finishing steers. J. Anita. Sci., 50: 1022-1030. Woo[ford, M.K., 1984. Source of loss in silage. In: M.K. Woo[ford (Editor), The Silage Fermentation. Marcel Dekker, New York, p. 173.
335
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
Short C o m m u n i c a t i o n
The Effect of Treatment with Urea, Sorbic Acid, or Dehydration on Orange Peel Silage Z.G. W E I N B E R G
l,G. P A H L O W
~, B. D I N T E R s and G. A S H B E L L
I
~Department of Stored Products, Feed Conservation Laboratory, AgriculturalResearch Organization, The Volcani Center, Bet Dagan 50250 (Israel) 2Instituteof Grassland and Forage Research, Federal Research Center o[Agriculture (FAL), Braunschweig D-3300 (F.R.G.) (Received 8 April 1987; accepted for publication 30 December 1987)
ABSTRACT Weinberg, Z.G., Pahlow, G., Dinter, B. and AshbeU, G., 1988. The effectof treatment with urea, sorbic acid,or dehydration on orange peel silage.Anita. Feed Sci. Technol.,20: 335-342. The purpose of this work was to study the effects of 1% urea, 0.05% sorbic acid (SA) and moderate dehydration (by oven at 35°C for I h) on the ensilingprocess of orange peels and on reducing fermentation losses. Fresh peels of the various treatments, in 10-kg triplicates,were ensiled in speciallydesigned anaerobic containers for 35 days. Chemical and microbial analyses were performed on the peels and on seepage samples taken during the ensilingperiod. The dominant microbial populations of the peel silagewere lactobacilli(10s g per D M ) and yeasts (105 g per D M ) and the major fermentation product was ethanol (18% in D M of the control silage).There were differencesbetween the treatments, with SA being the only treatment effective in reducing D M losses to 15%, compared with> 30% for the other treatments. Chemical results indicate a more efficientfermentation process with SA.
INTRODUCTION
Orange peels, a by-product of the orange juice industry, are highly nutritious (on a dry matter, D M , basis) and can serve as fodder (Braverman, 1949). In the past, when energy costs were lower, it was economical to conserve this material by drying. A m m e r m a n et al. (1967), Vijchulata et al. (1980) and Chen et al. (1981) used dried citruspulp and citruscondensed molasses as an energy source in rations for ruminants and obtained good results with regard to the animals' performance. Another method of conservation of the citruspeels would Contribution from the AgriculturalResearch Organization, The Volcani Center, Bet Dagan, Israel No. 1894-E, 1986 series.
0377-8401/88/$03.50
© 1988 Elsevier Science Publishers B.V.
336
be ensiling. However, the peels lose much of their nutritive value very rapidly during ensiling, due to undesirable fermentation. In a previous study, Ashbell et al. (1987) showed that most of the loss is due to gas release occurring during the first week of storage. Under Israeli conditions, peels can be stored in the dairy farm for fresh feeding for up to 1 week until consumed and lose much of their DM content even during that period. Furthermore, during the picking season, the peels are produced at a rate greater than that required for use directly as fodder, so they must be conserved for longer storage. In the case of ensiling, peels may lose as much as 50% of their original DM content (Ashbell and Donahaye, 1984). Ashbell et al. (1987) showed that, in addition to lactic acid bacteria, the microflora of the peels (fresh or ensiled) consists of large numbers of yeasts and lactate-fermenting yeasts which probably bring about the great losses in DM. In order to improve fermentation in orange peel silage, selective means should be employed that would inhibit these detrimental yeast populations. In the present work, we studied the effects of urea, sorbic acid (SA) and partial dehydration on losses and quality of orange peel silage. These treatments were chosen in order to affect the peel microflora and thus to improve the fermentation process. Urea was used since it was reported to improve the aerobic stability of silages (probably as an ammonia generator) and to improve the nitrogen content of the final product (McDonald, 1981 ). SA is known to possess antimycotic activity. Dehydration was tested since previous preliminary experiments (unpublished) showed that even slight increase in DM content by a few percent resulted in reduced fermentation losses. MATERIALS A N D M E T H O D S
Experimental Fresh orange peels (variety Shamouti) of the various treatments, in triplicate, were ensiled and stored in specially designed anaerobic containers, 10 kg in each, as described by Ashbell et al. (1987). The containers were stored at a constant ambient temperature of 21 + 1 ° C. Containers and seepage weights were recorded on Days 1, 2, 3, 4, 5, 7, 9, 11, 15, 18, 24, 30 and 35 of ensiling. Gas weight losses were calculated from the difference between total weight loss and seepage weight release. Fresh aliquots from the seepage from each treatment were used for chemicl analyses on these days. On Day 35, all the containers were opened and peel samples were taken with a special edged metal pipe, 40 mm in diameter.
Treatments (I) Control: I0 kg of peel in each container were ensiled with no additives or treatment.
337
(2) Urea: 1% of urea powder (w:w) was mixed thoroughly by hand with the fresh peel before ensiling. (3) SA: 0.05% SA (Sigma ~R)) (w:w) was mixed thoroughly by hand with the fresh peel before ensiling. (4) Dehydration: 40 kg of fresh peel were spread on 8 metal trays (67×43 cm), ca. 5 kg on each, and dried for 1 h at 35 ° C in an air convection oven. The peels lost 8.5 _+0.3% of their original weight.
Chemical analysis Analyses of the fresh peels, after 35 days ofensiling and of seepage included the determination of pH, DM, ash, water-soluble carbohydrates (WSC), volatile fatty acids (VFA) and lactic acid (LA). The methods employed in this analysis are described in detail in Ashbell et al. (1987)
Microbial analysis This was carried out on fresh and ensiled peels (from Day 0 and Day 35, respectively) and on seepage from Days 15 and 24 after ensiling. This included the determination of lactic acid bac~ria (LAB), lactate-assimilating yeasts, enterobacteria and clostridial spores. The methods used in this analysis are also described in Ashbell et al. (1987).
Biological oxygen demand (BOD) and chemical oxygen demand (COD) These were determined on the control seepage from Day 2, according to the method described (Anon., 1965).
In vitro digestibility This was determined according to Tilley and Terry (1963). RESULTS
The chemical properties of the fresh and ensiled peels are listed in Table 1. In general, the urea-treated and dehydrated peel silages were not markedly different from the control silage. The SA-treated silage, however, was very different from the other silages. Residual WSC in the ensiled peels was between 9.4 and 12.3% in DM, except for the SA treatment where it remained at a high level of 22 % in DM. In this silage (SA), the lowest levels of ethanol and acetic acid were detected. However, LA levels were similar to the other peel silages.
338
TABLE1 Chemicalanalysisofthe orangepeels (freshand silage,after35 days) Treatment
pH
Percent in D M
Fresh Silage PereentDM
WSC
Lactic acid
Ethanol
Acetic acid
Fresh Silage Fresh Silage Fresh Silage Fresh Silage Fresh Silage Control l%urea 0.05% sorbic acid Dehydration
4.1 4.1 4.0 4.2
3.6 3.7 3.5 3.5
17.2 17.8 18.2 19.3
14.2 14.1 16.1 14.6
41.2 9.4 35.3 9.9 3 9 . 0 22.0 3 8 . 0 12.3
0.9 0.6 0.4 0.6
1.8 2.5 2.3 2.3
<0.1 <0.1 <0.1 <0.1
16.5 13.4 7.0 16.0
<0.1 2.8 <0.1 3.0 <0.1 1.2 <0.1 9.2
TABLE 2 Dry matterlosses(means± SD )oforangepeelsilage Treatment
Percent D M loss in seepage
Percent D M loss as gas a
Total D M loss
Seepage release weight (g per container)
Control 1% urea 0.05% sorbic acid Dehydration
5.6 6.0 5.7 3.5
25.7 28.1 15.4 30.6
31.3 +- 1.4 34.1 ___0.4 21.1 +_0.9 34.1 +_0.2
1273.5 ± 132.8 1273.9 ± 20.5 926.9 _+115.9 836.9 +_ 18.5
~Calculated.
The digestibilityof the fresh and ensiled peels in all treatments was very high and varied between 85.2 and 89.2% in D M . The D M losses are given in Table 2. The control, urea-treated and dehydrated peels lostabout one-third of the D M content of the fresh peels,whereas the SA-treated peels lost only about one-fifth (of the D M ) . Total seepage weights were highest in the control and urea-treated peels and smaller in the SA-treated and dehydrated peels. Seepage release was most intensive on Day 2 after ensiling and most seepage was released within 1 week after ensiling. D M content in the seepage varied from 11.8 to 13.4% in the beginning, decreased after 3 days and varied from 5.6 to 8.4% until the end of the experiment. This was similar for all treatments. Most of the D M losses in all treatments are attributed to gas losses.This is in agreement with previous findings (Ashbell and Donahaye, 1986; Ashbell et al.,1987). The BOD and COD of the seepage were 58 600 and 108 850 mg 02 1-1, respectively. Since fermentation products of the peels were determined only 35 days after
339
ensiling, the dynamics can be followed only in the changes occurring in the seepage. The effluent, however, was exposed to oxygen during the night of collecting the samples and thus certain oxidative processes could occur in this material, which still contained high numbers of active organisms (see Table 4). Seepage analysis revealed that ethanol was the major fermentation product. The highest levels of ethanol were found in the control seepage (on the first week even more than 80% in DM) and the lowest levels were found in the seepage of the SA treated peels. The concentration of ethanol decreased after reaching a maximum level 1 week after ensiling. LA contents in the seepage of the various treatments increased with time of ensiling for all treatments and ranged between 9 and 14% in DM of the seepage (Day 35). Acetic acid contents increased with time for all treatments and ranged from 4 to 12% in DM. SA treatment resulted in the lowest, and the control treatment in the highest, contents. Results of the microbial analysis of the peels and seepage are given in Tables 3 and 4. The dominant populations in the fresh peels were lactobacilli, lactateassimilating yeasts (LAY) and enterobacteria. The log number of colonyforming units g-1 DM (CFU) of each population was ca. 5.0. On Day 35, the log number of the lactobacilli increased to ca. 8.0 in all treatments. Since the counts for the total number of yeasts and the LAY in particular did not differ as much as in forage crops, where the total count can be 1000 times higher, at least during the first weeks only data on the LAY are given in Tables 3 and 4. The numbers of LAY did not change much throughout ensiling except in the dehydrated peels, where the log number decreased slightly, to 3.6. EnterobacTABLE 3 Microflora of the fresh and ensiled orange peels (log CFU g-1 DM)a Treatment
LactobaciUi
Lactateassimilating Fresh Silage yeasts (LAY)
Moulds b
Enterobacteria
Clostridia
Fresh Silage Fresh
Silage
Fresh Silage
1.2 1.6 1.2 0.7
0 0 0 0
1.6 0 0 0
Fresh Silage Control 1% urea 0.05% sorbic acid Dehydration
5.1 4.7 5.0 4.8
8.3 8.4 8.0 7.3
5.2 4.9 4.9 4.9
"CFU, colony-forming units. bMoulds appeared on the L A Y plates.
4.4 5.5 4.3 3.6
0 0 0 0
4.8 4.7 4.7 4.6
0 0 0 0
340 TABLE 4 Microfloraof the orangepeel seepage (logCFU g-1 DM)a
Treatment
Lactobacilliafter (days) 15
Control 1% urea 0.05% sorbicacid Dehydration
8.7 8.5 8.7 8.6
24 8.4 9.4 8.8 7.8
Lactate-assimilatingyeasts after (days) 35 8.3 8.7 8.1 7.8
15
24
35
6.1 7.6 6.7 7.3
3.9 6.3 6.3 7.4
5.3 5.0 4.5 5.4
aCFU = colony-formingunits. teria, moulds and clostridiawere found (in small numbers) only in the fresh peels. In the seepage (Table 4), the microflora on Days 15, 24 and 35 was similar to the microflora of the peel on Day 35, except for the yeasts, which were higher in the seepage than in the urea-treated peels and in the dehydrated peels. The texture of the control peel silage was pasty (mushy), the urea-treated and dehydrated peels were somewhat firmer, and the SA-treated peels maintained the best structure. DISCUSSION In order to reduce losses in orange peel silage, several treatments were tried with the aim of inhibiting yeast activity and improving fermentation. The least losses were achieved with SA, in which seepage release was less than in the control or urea-treated peels. This is in spite of the fact that the SA did not decrease the yeast populations much. The number of LAY in the SA seepage (Day 35) was somewhat less than in the other seepages. Sorbic acid is known to have antimycotic or fungistatic effects and it could be that it affected the yeasts' activity rather than the yeast counts. Urea, which is sometimes added to silages as a stabilizer (McDonald, 1981 ), did not reduce losses and also did not affect the yeast count. Dehydration was aimed at reducing the water content of the peels and improving fermentation. This treatment increased the DM content by only 2%. Dehydration led to the least seepage release, but losses were comparable to those in the control. It could be that the temperature at which the dehydration was performed (35 ° C ) enhanced the development of undesirable micro-organisms and/or activated enzymes such as pectinase which resulted in loss of structure and enhanced losses. The main idea behind this treatment was to examine the effect of various industrial methods (during juice extraction) that would yield drier peels.
341
For the control, urea-treated and dehydrated peels, L A formation was more or less the inverse of the decrease in percent W S C . With the S A treatment, percent W S C did not decrease to the same extent as with the other treatments, but L A formation was comparable to the other treatments. This might indicate a more efficientfermentation with this treatment. This was confirmed by the V F A analysis which indicated a mostly homolactic conversion of the sugars to rather high amounts of L A and the effective inhibition of yeast metabolism, leading to far lower ethanol and C02 production. Previous experiments indicated that chemical and microbial changes occurring in the peels during the ensiling period are reflected by the chemical and microbial changes in the seepage. Seepage microflora at an early stage of ensiling (Day 15 ) was already similar to the microflora of the peels tested on Day 35. This confirms our previous impression (Ashbell et al.,1987) that most changes in the peel silage occur very rapidly. Indeed, most seepage release occurred within 5 days of ensiling in all treatments tested. In this experiment, the extent of seepage release was relativelysmall in comparison with previous data, probably due to smaller hydrostatic pressure buildup in our experimental containers. In larger containers, seepage release was more intensive (Ashbell and Donahaye, 1986). Silage seepage is among the most serious water pollutants (Woolford, 1984 ). In this experiment, the B O D and C O D values of the seepage were also very high, probably due to the high concentration of W S C . From this study, it appears that S A was the most efficienttreatment with regard to loss reduction and fermentation pattern of the orange peel silage. Several more treatments are currently being tested in our laboratory to improve further the fermentation process and to minimize losses. The most promising treatments will be elaborated on (various concentrations of intensities),firstin experiments under laboratory conditions and then on a commercial scale.
REFERENCES Ammerman, C.B., Neal, F.C., Palmer, A.Z., Moore, J.E. and Arrington, L.R., 1967. Comparative nutritional value of pelleted and regular dried citrus pulp when fed at different levels to finishing steers. Dep. Anita. Sci. Mimeogr. Pep. AN 67-7, University of Florida, Gainesville, FL. Anonymous, 1965. American Public Health Association. In: Standard Methods for the Examination of Water and Wastewater. New York, pp. 415-421,520-514. AshbeU, G. and Donahaye, E., 1984. Losses in orange peel silage.Agric. Wastes, 11: 73-77. Ashbell,G. and Donahaye, E., 1986.Laboratory trialson conservationsof orange peelsilage.Agric. Wastes, 15: 133-137. Ashbell, G., Pahlow, G., Dinter, B. and Weinberg, Z.G., 1987. Dynamics of orange fermentation during ensiling.J. Appl. Bacteriol.,63: 275-279.
342 Braverman, S.B., 1949. Miscellaneous citrus products. In: S.B. Braverman (Editor), Citrus Products. Interecience, New York, pp. 351-356. Chen, M.C., Ammerman, C.B., Henry, P.R., Palmer, A.Z. and Long, S.K., 1981. Citrus condensed molassed solubles as an energy source for ruminants. J. Anita. Sci., 53: 253-259. McDonald, P., 1981. Silage additives. In: P. McDonald (Editor), The Biochemistry of Silage. Wiley, Chichester, pp. 157-158. Tilley, J.M. and Terry, R.A., 1963. A two-stage technique for the in vitro digestion of forage crops. J. Br. Grassl. Soc., 18: 104-111. Vijchulata, P., Henry, P.R., Ammerman, C.B., Potter, S.G., Palmer, A.Z. and Becker, H.N., 1980. Effect of dried citrus pulp and cage layer manure in combination with monensin on performance and tissue mineral composition in finishing steers. J. Anita. Sci., 50: 1022-1030. Woo[ford, M.K., 1984. Source of loss in silage. In: M.K. Woo[ford (Editor), The Silage Fermentation. Marcel Dekker, New York, p. 173.