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Chemical and microbiological changes occurring in orange peels and in the seepage during ensiling
Biological Wastes 21 (1987) 213-220
Chemical and Microbiological Changes Occurring in Orange Peels and in the Seepage During Ensiling* Gilad Ashbell & N o r b e r t o L i s k e r Agricultural Research Organization, The Volcani Center, POB 6, Bet Dagan 50250, Israel (Received 11 August 1986; revised version received 20 November 1986; accepted 8 December 1986)
A BSTRA CT Orange peels at 17"1% and 20"5% dry matter ( D M ) were ensiled in two successive years in 400- and 280-litre barrels for periods of 142 and 131 days, respectively. By the end of the experiments no differences were found in the chemical and microbiological components of ensiled peels in which seepage was allowed to run off and in those in which the seepage was kept inside the containers. At the upper layer of the silages (in contact with air) there was a great development of the microflora and losses were considerable. Seepage was collected and analysed during the fermentation period. Seepage losses were calculated to be as follows: DM, 6.6-10.4%; water-soluble carbohydrates, 10"3 13"1%; glucose, 3"2-10"7%; and total protein, 8"0-8"7%. The rate of seepage release and its chemical changes are described along with the changes in the aerobic microflora of the peels and the seepage.
INTRODUCTION In Israel, orange peels are a part of animal feed rations but their use is restricted to the orange picking season when this by-product of the orange juice industry is available. The amount produced by that time is more than that required for immediate use. Conservation of the peels as silage would permit their use throughout the year. However, ensiling of orange peels can be accompanied by losses of m o r e than 50% on a dry matter (DM) basis * Contribution from the Agricultural Research Organization, TheVolcani Center, Bet Dagan, Israel No. 1780-E, 1986 series. 213 Biological Wastes 0269-7483/87/$03'50 © Elsevier Applied Science Publishers Ltd, England, 1987. Printed in Great Britain
214
Gilad Ashbell, Norberto Lisker
(Ashbell & Donahaye, 1984, 1986), making this conservation technology questionable on an economic basis. Most of the losses are due to gas and seepage release. Gas seems to be released mostly during fermentation, which lasts for a long period and does not stabilize even after some months (Ashbell & Donahaye, 1986). Losses caused by seepage were demonstrated in laboratory trials as being between 18.0% and 29.0% on a DM basis. In previous work (Ashbell & Donahaye, 1984, 1986) experiments were carried out in 30-1itre airtight containers stored at 26°C. In the present study greater amounts (6- to 9-fold) of orange peels were ensiled in containers under farm conditions and a comparative analysis was made between peels kept together with their seepage and those in which the seepage was allowed to drain off. A broader study on seepage was carried out and the influence of aerobic microorganisms on the total losses was also evaluated. It is hoped that these data will enlarge our knowledge of the fermentation dynamics and seepage release in order to prepare a strategy to reduce losses.
METHODS Two trials were carried out in two successive years (1984 and 1985). In trial 1, orange peels silage was prepared with the early season variety 'Shamouti'. Six 400-1itre metal barrels with a polyethylene lining were filled with 280 kg fresh orange peels and placed in the shade under farm conditions from January 24 until June 15 for a 142-day period. The barrels were left open and the upper side was exposed to air. In three barrels a looped drain was located at the base to allow seepage release. The loop in the drainage tube formed a one-way valve which prevented penetration of ambient air. Seepage was collected and analyzed throughout the ensiling period; daily during the first 10 days and subsequently according to the amounts of seepage released. In trial 2, orange peels of the late-season variety 'Valencia' were used. This trial was carried out essentially as described for trial 1 with the following modifications: 220-1itre high-density polyethylene barrels were used for ensiling 180kg of orange peels and the experiment was conducted from April 9 until August 18, for a 131-day period.
Chemical analysis Pooled mixed samples from each group of containers (i.e. three containers with seepage and three containers without) were taken for the analysis from the upper and the middle layers, separately. The dry matter (DM) of the peels (fresh and silage) was determined by
Chemical and microbial changes in ensiled orange peels
215
oven-drying the material at 60°C for 48 h following 24 h at 105°C, and that of the seepage was determined by drying in a vacuum oven at 70°C for 24 h. pH measurement of the peels was performed in the filtrates of 10g wet material blended with 90ml distilled water, and that of the seepage was performed directly without dilution. Total protein (TP) was determined by the Kjeldahl method and was calculated at N x 6.25. Crude fibre (CF), ash and phosphorus were determined according to the AOAC method (1980). Water-soluble carbohydrates (WSC) were determined according to Dubois et al. (1956) and glucose was determined colorimetrically using Sigma's DexB kit. In vitro digestibility was determined according to Tilley & Terry (1963). Biological oxygen demand (BOD) and chemical oxygen demand (COD) were determined according to Anon (1965).
Microbiological analysis Analyses were performed as follows. Twenty grams of peels were placed in 180 ml of 0-09% agar solution and homogenized twice for 1 min in a Waring Blender. The homogenate was successively diluted tenfold with 0-09% agar solution and the number of colony-forming units (CFU) of aerobic bacteria, yeasts and moulds was determined by the addition of premelted Difco Nutrient Agar for determining bacterial CFU, or of Jarvis medium (1973) for determining yeasts and moulds CFU. The plates were incubated at 26°C for one week, minimal C F U which could be determined in peels was 10 2 C F U g- 1 wet weight, and the numbers of C F U were calculated on a DM basis. For seepage a similar procedure was used except that the initial plating was performed directly without any further dilution.
RESULTS Chemical analyses of the fresh orange peels and the silage are given in Table 1. The results show no consistent difference in the chemical constituents of peels kept with their seepage a n d those in which seepage was allowed to drain off. However, differences could be observed between peels from the upper and the middle layers, regardless of the presence of seepage; pH, TP and ash were especially high at the upper layer. CF increased whereas WSC decreased in all cases and glucose almost disappeared during ensiling. DM, which would be expected to increase at the upper layer because of its permanent contact with ambient air, did so in only one case. The digestibility of the fresh peels and the silage was very high, which indicates the high quality of the product. Because of technical problems, losses in trial 2 only
216
Gilad Ashbell, Norberto Lisker TABLE
1
Chemical Analysis of Fresh Orange Peels as Compared with Silages in which Seepage was Kept Inside the Containers or Allowed to Drain off. Samples were Taken from Two Sites: The Upper and the Middle Layer. Unless Stated Otherwise, Results are Presented in Per Cent DM Source o f material
Trial 1 Fresh (control) Silage ( - seepage) upper layer Silage ( - seepage) middle layer Silage ( + seepage) upper layer Silage ( + seepage) middle layer Trial 2 Fresh (control) Silage ( - seepage) upper layer Silage ( - seepage) middle layer Silage ( + seepage) upper layer Silage ( + seepage) middle layer *
DM (%)
pH
17"1
4-9
59.7
Total protein
Crude fibre
Ash
WSC Glucose
In vitro digestibility
5'4
11.4
2.6
34.8
18-1
92'9
7.2
20"9
19.0
11.8
7'0
0.2
NE*
15.2
3-4
7'8
18.2
3'9
16-2
0.3
90'6
14-1
7-5
15'0
18.6
7.5
5.4
0"04
NE
14.2
3"4
7.3
17'1
4.0
4.9
0.4
91.6
20"5
4'3
7"3
11"6
3"9
2 1 " 0 15-2
89-1
17.5
7'7
18-9
15.6
14.0
10.6
0'03
NE
18.1
3.4
8'8
18.1
5.1
17-3
0.05
88.0
20.1
7.2
20.4
14.1
13.3
8-6
0.02
NE
15.4
3"5
9.1
17'1
5"3
16.5
0-03
88.4
N E - - n o t examined.
were measured. Where seepage was kept inside the containers, DM losses were of the order of 36-8 %, while in those where seepage was allowed to run off, DM losses were of the order of 42-5%. The changes in aerobic microflora which occurred during ensiling are presented in Table 2. At the beginning of the experiment no moulds were detected on the peels. The microflora comprised mostly yeasts and bacteria. After one week only the upper layer was examined, since taking samples from the middle layer would have damaged the whole structure in the containers. In trial 1, in the upper layer, there was a great increase in mould CFU and only a small increase in bacteria and yeasts. In trial 2 a similar trend was noted. By the end of the experiments the CFU of bacteria greatly increased while yeasts and moulds did not change considerably. In the middle layer there was a strong decrease in all aerobic microorganisms (Table 2).
Chemical and microbial changes in ensiled orange peels
4'5 L
3.91 I~'3,7
13-
(a)
4.3
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,,
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,,
i i (d)
.-
"t,
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lb"l15 210 25 3~°'4'0' ,50'Bb DAYS
0
l,
5
,
,
. . . .
,
10" 15 20 25 30-40 50 60
Fig. 1. (a) Changes in seepage pH during ensiling. (b) Changes in seepage dry matter during ensiling. (c) Changes in seepage water-soluble carbohydrates during ensiling. (d) Changes in seepage glucose during ensiling.
100 90
z 70
~ 6e o
~
-
=D.M
5o 4o Q ~3o
~
20
10
DAYS
Fig. 2.
Rate of losses of orange peel silage in trial 1.
Gilad Ashbell, Norberto Lisker
218
TABLE
2
Microbiological Analysis of Fresh Orange Peels as Compared with Ensiled Peels (CFU per g DM)"
Organisms
Days after ensiling
Peels ensiled With seepage
Without seepage
Upper layer
Middle layer
Upper layer
Middle layer
106 107 101° 105 108 107 0*
106 -102
105 107 101°
105 -103
10 5
10 6
10 6
-0* 0*
109 108 0*
-0* 0*
--
108
O*
108
O* 104
Trial 1 Bacteria
Yeasts
Moulds
0 8 142 0 8 142 0 8
107
142
108
O*
0
104
104
104
8
109
--
108
--
101° 104 109 10s 0*
102 104 -0* 0*
101° 104 109 106 0*
103 104 -0* 0*
8
103
--
103
--
131
107
Trial 2 Bacteria
131
Yeasts
Moulds
0 8 131 0
0*
108
0*
* At a dilution of 102, no microorganisms could be detected on petri dishes.
Seepage analysis showed similar trends in both trials, with DM content, pH, WSC and glucose decreasing at almost the same rate (Fig. 1). Very little seepage was released after 65-70 days of ensiling. In trial 1 the ratio of fresh peels to seepage was (w:w) 4-1:1-0, whereas, in trial 2, it was 5-5:1-0. Phosphorus content in the seepage D M decreased from 2.9 to 1.5 ppm (data not shown). The rate of loss of orange peel silage ingredients during the experiment is given in Fig. 2 for trial 1 and in Fig. 3 for trial 2. Total DM losses in seepage were 10-4% in trial 1 and 6"6% in trial 2. The BOD and COD found for seepage taken at the second day (Trial 2 only) was 78 300 and 145 200 mg 0 2 litre- 1, respectively. No moulds were detected in the seepage, and bacteria and yeasts C F U decreased during the experiment.
Chemical and microbial changes in ensiled orange peels
219
8O u3
t~ 70
c
~ ~ot-III ra
I
fl/
v D A YS
Fig. 3.
Rate of losses of orange peel silage in trial 2.
DISCUSSION A large volume of seepage was released from the peels during the ensiling period (ca. 1 litre per 5 kg of peels). Seepage was released for a long period, but most of it during the first week. It is possible that the pectin in the peels holds the water and therefore seepage release is gradual during the fermentation period. Seepage in general is known to be one of the most serious causes of water pollution. Seepage from grass silage, for example, has a BOD of the order of 78000mg Oz per litre, which is high and may 500 in domestic sewage (Spillane & O'Shea, 1973). Orange peels seepage has a BOD of the order of 78000rag O2 per litre, which is high and may constitute a pollution problem. In addition, the losses of chemical constituents in the seepage are high; WSC and minerals are wasted during seepage release. Orange peels silage contains usually between 120 and 210g DM per kilogram. Such silage released as much as 25% seepage of its fresh weight and the DM content of this seepage was between 55 and 112 g per kilogram. Woolford (1978) reported that seepage of silage contains soluble nutritive components and in general its D M content ranges from 10 to 100 g kg-1 Total losses in chemical components of ensiled peels are high and it seems that their magnitude depends on the DM content of the fresh peels. The relatively low losses found in trial 2 can be attributed to the lower DM, WSC and glucose contents in the peels in comparison with trial 1. On the other
220
Gilad Ashbell, Norberto Lisker
hand, almost no difference could be observed among the different parameters examined in peels ensiled with their seepage as compared with those peels in which the seepage was allowed to run off. Our assumption was that in silage where the seepage was allowed to run off greater D M losses would occur. That is because the seepage contains a certain a m o u n t of nutrients including acids which are washed off from the peels, that could minimize fermentation losses. In contrast to grass silages, orange peels have a high WSC content. This factor may have a very special influence on the fermentation process. Losses caused by moulds seem to be low. Only the upper layer (top 10-15 cm) was found to be damaged and unsuitable for feeding. Therefore, the optimal silo for ensiling peels will be in such a form that the peels will be in minimum contact with air. (It must be noted that for technical reasons it is impossible to compact the peels.) Since losses caused by moulds are low, it seems that bacteria and yeasts, which can develop under almost anaerobic conditions, are responsible for the continuous gas release and subsequent losses observed. The next step will be to determine the nature o f the almost anaerobic microorganisms which develop during the ensiling period, in order to prevent the losses they may cause. Since no yeasts were found in the middle layer o f the peels silage, it is likely that the heterofermentative lactic acid bacteria are responsible for the continuous gas release. REFERENCES Anon. (1965). Standard methods for the examination of water and waste water. American Public Health Association Inc., New York, NY, 415-21, 510-14. AOAC (1980). Official methods of analysis. (13th edn), Association of Official Analytical Chemists, Washington, DC. Ashbell, G. & Donahaye, E. (1984). Losses in orange peel silage. Agricultural Wastes, 11, 73. Ashbell, G. & Donahaye, E. (1986). Laboratory trials on conservation of orange peel silage. Agricultural Wastes, 15, 133-37. Dubois, M., Giles, K. A., Hamilton, J. K., Rebers, P. A. & Smith, F. (1956). Colorimetric method for determination of sugars and related substances. Analytical Chemistry, 28, 350-6. Jarvis, B. (1973). Comparison of an improved rose bengal chlorotetracyline agar with other media for the selective isolation and enumeration of moulds and yeasts in food. Journal of Applied Bacteriology, 36, 723-27. Spillane, T. A. and O'Shea, J. (1973). A simple way to dispose of silage effluents. Farm and Food (July/August), 80-1. (As cited by Woolford, M. K., in The silage fermentation, M. Dekker Inc., New York, NY.) Tilley, J. M. A. & Terry, R. A. (1963). A two stage technique for the in vitro digestion of forage crops. Journal of British Grassland Society, 18, 104-11. Woolford, M. K. (1978). The problem of silage effluent. Herbage Abstracts, 48, 397-403.
Chemical and Microbiological Changes Occurring in Orange Peels and in the Seepage During Ensiling* Gilad Ashbell & N o r b e r t o L i s k e r Agricultural Research Organization, The Volcani Center, POB 6, Bet Dagan 50250, Israel (Received 11 August 1986; revised version received 20 November 1986; accepted 8 December 1986)
A BSTRA CT Orange peels at 17"1% and 20"5% dry matter ( D M ) were ensiled in two successive years in 400- and 280-litre barrels for periods of 142 and 131 days, respectively. By the end of the experiments no differences were found in the chemical and microbiological components of ensiled peels in which seepage was allowed to run off and in those in which the seepage was kept inside the containers. At the upper layer of the silages (in contact with air) there was a great development of the microflora and losses were considerable. Seepage was collected and analysed during the fermentation period. Seepage losses were calculated to be as follows: DM, 6.6-10.4%; water-soluble carbohydrates, 10"3 13"1%; glucose, 3"2-10"7%; and total protein, 8"0-8"7%. The rate of seepage release and its chemical changes are described along with the changes in the aerobic microflora of the peels and the seepage.
INTRODUCTION In Israel, orange peels are a part of animal feed rations but their use is restricted to the orange picking season when this by-product of the orange juice industry is available. The amount produced by that time is more than that required for immediate use. Conservation of the peels as silage would permit their use throughout the year. However, ensiling of orange peels can be accompanied by losses of m o r e than 50% on a dry matter (DM) basis * Contribution from the Agricultural Research Organization, TheVolcani Center, Bet Dagan, Israel No. 1780-E, 1986 series. 213 Biological Wastes 0269-7483/87/$03'50 © Elsevier Applied Science Publishers Ltd, England, 1987. Printed in Great Britain
214
Gilad Ashbell, Norberto Lisker
(Ashbell & Donahaye, 1984, 1986), making this conservation technology questionable on an economic basis. Most of the losses are due to gas and seepage release. Gas seems to be released mostly during fermentation, which lasts for a long period and does not stabilize even after some months (Ashbell & Donahaye, 1986). Losses caused by seepage were demonstrated in laboratory trials as being between 18.0% and 29.0% on a DM basis. In previous work (Ashbell & Donahaye, 1984, 1986) experiments were carried out in 30-1itre airtight containers stored at 26°C. In the present study greater amounts (6- to 9-fold) of orange peels were ensiled in containers under farm conditions and a comparative analysis was made between peels kept together with their seepage and those in which the seepage was allowed to drain off. A broader study on seepage was carried out and the influence of aerobic microorganisms on the total losses was also evaluated. It is hoped that these data will enlarge our knowledge of the fermentation dynamics and seepage release in order to prepare a strategy to reduce losses.
METHODS Two trials were carried out in two successive years (1984 and 1985). In trial 1, orange peels silage was prepared with the early season variety 'Shamouti'. Six 400-1itre metal barrels with a polyethylene lining were filled with 280 kg fresh orange peels and placed in the shade under farm conditions from January 24 until June 15 for a 142-day period. The barrels were left open and the upper side was exposed to air. In three barrels a looped drain was located at the base to allow seepage release. The loop in the drainage tube formed a one-way valve which prevented penetration of ambient air. Seepage was collected and analyzed throughout the ensiling period; daily during the first 10 days and subsequently according to the amounts of seepage released. In trial 2, orange peels of the late-season variety 'Valencia' were used. This trial was carried out essentially as described for trial 1 with the following modifications: 220-1itre high-density polyethylene barrels were used for ensiling 180kg of orange peels and the experiment was conducted from April 9 until August 18, for a 131-day period.
Chemical analysis Pooled mixed samples from each group of containers (i.e. three containers with seepage and three containers without) were taken for the analysis from the upper and the middle layers, separately. The dry matter (DM) of the peels (fresh and silage) was determined by
Chemical and microbial changes in ensiled orange peels
215
oven-drying the material at 60°C for 48 h following 24 h at 105°C, and that of the seepage was determined by drying in a vacuum oven at 70°C for 24 h. pH measurement of the peels was performed in the filtrates of 10g wet material blended with 90ml distilled water, and that of the seepage was performed directly without dilution. Total protein (TP) was determined by the Kjeldahl method and was calculated at N x 6.25. Crude fibre (CF), ash and phosphorus were determined according to the AOAC method (1980). Water-soluble carbohydrates (WSC) were determined according to Dubois et al. (1956) and glucose was determined colorimetrically using Sigma's DexB kit. In vitro digestibility was determined according to Tilley & Terry (1963). Biological oxygen demand (BOD) and chemical oxygen demand (COD) were determined according to Anon (1965).
Microbiological analysis Analyses were performed as follows. Twenty grams of peels were placed in 180 ml of 0-09% agar solution and homogenized twice for 1 min in a Waring Blender. The homogenate was successively diluted tenfold with 0-09% agar solution and the number of colony-forming units (CFU) of aerobic bacteria, yeasts and moulds was determined by the addition of premelted Difco Nutrient Agar for determining bacterial CFU, or of Jarvis medium (1973) for determining yeasts and moulds CFU. The plates were incubated at 26°C for one week, minimal C F U which could be determined in peels was 10 2 C F U g- 1 wet weight, and the numbers of C F U were calculated on a DM basis. For seepage a similar procedure was used except that the initial plating was performed directly without any further dilution.
RESULTS Chemical analyses of the fresh orange peels and the silage are given in Table 1. The results show no consistent difference in the chemical constituents of peels kept with their seepage a n d those in which seepage was allowed to drain off. However, differences could be observed between peels from the upper and the middle layers, regardless of the presence of seepage; pH, TP and ash were especially high at the upper layer. CF increased whereas WSC decreased in all cases and glucose almost disappeared during ensiling. DM, which would be expected to increase at the upper layer because of its permanent contact with ambient air, did so in only one case. The digestibility of the fresh peels and the silage was very high, which indicates the high quality of the product. Because of technical problems, losses in trial 2 only
216
Gilad Ashbell, Norberto Lisker TABLE
1
Chemical Analysis of Fresh Orange Peels as Compared with Silages in which Seepage was Kept Inside the Containers or Allowed to Drain off. Samples were Taken from Two Sites: The Upper and the Middle Layer. Unless Stated Otherwise, Results are Presented in Per Cent DM Source o f material
Trial 1 Fresh (control) Silage ( - seepage) upper layer Silage ( - seepage) middle layer Silage ( + seepage) upper layer Silage ( + seepage) middle layer Trial 2 Fresh (control) Silage ( - seepage) upper layer Silage ( - seepage) middle layer Silage ( + seepage) upper layer Silage ( + seepage) middle layer *
DM (%)
pH
17"1
4-9
59.7
Total protein
Crude fibre
Ash
WSC Glucose
In vitro digestibility
5'4
11.4
2.6
34.8
18-1
92'9
7.2
20"9
19.0
11.8
7'0
0.2
NE*
15.2
3-4
7'8
18.2
3'9
16-2
0.3
90'6
14-1
7-5
15'0
18.6
7.5
5.4
0"04
NE
14.2
3"4
7.3
17'1
4.0
4.9
0.4
91.6
20"5
4'3
7"3
11"6
3"9
2 1 " 0 15-2
89-1
17.5
7'7
18-9
15.6
14.0
10.6
0'03
NE
18.1
3.4
8'8
18.1
5.1
17-3
0.05
88.0
20.1
7.2
20.4
14.1
13.3
8-6
0.02
NE
15.4
3"5
9.1
17'1
5"3
16.5
0-03
88.4
N E - - n o t examined.
were measured. Where seepage was kept inside the containers, DM losses were of the order of 36-8 %, while in those where seepage was allowed to run off, DM losses were of the order of 42-5%. The changes in aerobic microflora which occurred during ensiling are presented in Table 2. At the beginning of the experiment no moulds were detected on the peels. The microflora comprised mostly yeasts and bacteria. After one week only the upper layer was examined, since taking samples from the middle layer would have damaged the whole structure in the containers. In trial 1, in the upper layer, there was a great increase in mould CFU and only a small increase in bacteria and yeasts. In trial 2 a similar trend was noted. By the end of the experiments the CFU of bacteria greatly increased while yeasts and moulds did not change considerably. In the middle layer there was a strong decrease in all aerobic microorganisms (Table 2).
Chemical and microbial changes in ensiled orange peels
4'5 L
3.91 I~'3,7
13-
(a)
4.3
~,,
oX..,
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3.5
,*
217
~
(b)
'.
\
7
o--o
-+..-e-- -;i--e,.,
X
'
;~,"L.eo-- \ , ~ .... e-...+.-"
5 e-o
~3
I
l l; i ,
i ~:, . . . . , (C)
70 60 ~ r-, ~ ~ c: 5C 3
(J
4c
Jl, 45 ~ 40 k .c [~ ~ 30 ~,
3C
,,
o--
20
--0
10
-,,
~, i TRIAL1 ...... TRIAL2
,,
i i (d)
.-
"t,
' ~ / o
2c ;
lb"l15 210 25 3~°'4'0' ,50'Bb DAYS
0
l,
5
,
,
. . . .
,
10" 15 20 25 30-40 50 60
Fig. 1. (a) Changes in seepage pH during ensiling. (b) Changes in seepage dry matter during ensiling. (c) Changes in seepage water-soluble carbohydrates during ensiling. (d) Changes in seepage glucose during ensiling.
100 90
z 70
~ 6e o
~
-
=D.M
5o 4o Q ~3o
~
20
10
DAYS
Fig. 2.
Rate of losses of orange peel silage in trial 1.
Gilad Ashbell, Norberto Lisker
218
TABLE
2
Microbiological Analysis of Fresh Orange Peels as Compared with Ensiled Peels (CFU per g DM)"
Organisms
Days after ensiling
Peels ensiled With seepage
Without seepage
Upper layer
Middle layer
Upper layer
Middle layer
106 107 101° 105 108 107 0*
106 -102
105 107 101°
105 -103
10 5
10 6
10 6
-0* 0*
109 108 0*
-0* 0*
--
108
O*
108
O* 104
Trial 1 Bacteria
Yeasts
Moulds
0 8 142 0 8 142 0 8
107
142
108
O*
0
104
104
104
8
109
--
108
--
101° 104 109 10s 0*
102 104 -0* 0*
101° 104 109 106 0*
103 104 -0* 0*
8
103
--
103
--
131
107
Trial 2 Bacteria
131
Yeasts
Moulds
0 8 131 0
0*
108
0*
* At a dilution of 102, no microorganisms could be detected on petri dishes.
Seepage analysis showed similar trends in both trials, with DM content, pH, WSC and glucose decreasing at almost the same rate (Fig. 1). Very little seepage was released after 65-70 days of ensiling. In trial 1 the ratio of fresh peels to seepage was (w:w) 4-1:1-0, whereas, in trial 2, it was 5-5:1-0. Phosphorus content in the seepage D M decreased from 2.9 to 1.5 ppm (data not shown). The rate of loss of orange peel silage ingredients during the experiment is given in Fig. 2 for trial 1 and in Fig. 3 for trial 2. Total DM losses in seepage were 10-4% in trial 1 and 6"6% in trial 2. The BOD and COD found for seepage taken at the second day (Trial 2 only) was 78 300 and 145 200 mg 0 2 litre- 1, respectively. No moulds were detected in the seepage, and bacteria and yeasts C F U decreased during the experiment.
Chemical and microbial changes in ensiled orange peels
219
8O u3
t~ 70
c
~ ~ot-III ra
I
fl/
v D A YS
Fig. 3.
Rate of losses of orange peel silage in trial 2.
DISCUSSION A large volume of seepage was released from the peels during the ensiling period (ca. 1 litre per 5 kg of peels). Seepage was released for a long period, but most of it during the first week. It is possible that the pectin in the peels holds the water and therefore seepage release is gradual during the fermentation period. Seepage in general is known to be one of the most serious causes of water pollution. Seepage from grass silage, for example, has a BOD of the order of 78000mg Oz per litre, which is high and may 500 in domestic sewage (Spillane & O'Shea, 1973). Orange peels seepage has a BOD of the order of 78000rag O2 per litre, which is high and may constitute a pollution problem. In addition, the losses of chemical constituents in the seepage are high; WSC and minerals are wasted during seepage release. Orange peels silage contains usually between 120 and 210g DM per kilogram. Such silage released as much as 25% seepage of its fresh weight and the DM content of this seepage was between 55 and 112 g per kilogram. Woolford (1978) reported that seepage of silage contains soluble nutritive components and in general its D M content ranges from 10 to 100 g kg-1 Total losses in chemical components of ensiled peels are high and it seems that their magnitude depends on the DM content of the fresh peels. The relatively low losses found in trial 2 can be attributed to the lower DM, WSC and glucose contents in the peels in comparison with trial 1. On the other
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Gilad Ashbell, Norberto Lisker
hand, almost no difference could be observed among the different parameters examined in peels ensiled with their seepage as compared with those peels in which the seepage was allowed to run off. Our assumption was that in silage where the seepage was allowed to run off greater D M losses would occur. That is because the seepage contains a certain a m o u n t of nutrients including acids which are washed off from the peels, that could minimize fermentation losses. In contrast to grass silages, orange peels have a high WSC content. This factor may have a very special influence on the fermentation process. Losses caused by moulds seem to be low. Only the upper layer (top 10-15 cm) was found to be damaged and unsuitable for feeding. Therefore, the optimal silo for ensiling peels will be in such a form that the peels will be in minimum contact with air. (It must be noted that for technical reasons it is impossible to compact the peels.) Since losses caused by moulds are low, it seems that bacteria and yeasts, which can develop under almost anaerobic conditions, are responsible for the continuous gas release and subsequent losses observed. The next step will be to determine the nature o f the almost anaerobic microorganisms which develop during the ensiling period, in order to prevent the losses they may cause. Since no yeasts were found in the middle layer o f the peels silage, it is likely that the heterofermentative lactic acid bacteria are responsible for the continuous gas release. REFERENCES Anon. (1965). Standard methods for the examination of water and waste water. American Public Health Association Inc., New York, NY, 415-21, 510-14. AOAC (1980). Official methods of analysis. (13th edn), Association of Official Analytical Chemists, Washington, DC. Ashbell, G. & Donahaye, E. (1984). Losses in orange peel silage. Agricultural Wastes, 11, 73. Ashbell, G. & Donahaye, E. (1986). Laboratory trials on conservation of orange peel silage. Agricultural Wastes, 15, 133-37. Dubois, M., Giles, K. A., Hamilton, J. K., Rebers, P. A. & Smith, F. (1956). Colorimetric method for determination of sugars and related substances. Analytical Chemistry, 28, 350-6. Jarvis, B. (1973). Comparison of an improved rose bengal chlorotetracyline agar with other media for the selective isolation and enumeration of moulds and yeasts in food. Journal of Applied Bacteriology, 36, 723-27. Spillane, T. A. and O'Shea, J. (1973). A simple way to dispose of silage effluents. Farm and Food (July/August), 80-1. (As cited by Woolford, M. K., in The silage fermentation, M. Dekker Inc., New York, NY.) Tilley, J. M. A. & Terry, R. A. (1963). A two stage technique for the in vitro digestion of forage crops. Journal of British Grassland Society, 18, 104-11. Woolford, M. K. (1978). The problem of silage effluent. Herbage Abstracts, 48, 397-403.