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0041-3216/2014/030179-08 Trop. Agric. (Trinidad) Vol. 91 No. 3 July 2014 179
©2014 Trop. Agric. (Trinidad)
Effect of drying method on the chemical composition of
leaves from four tropical tree species
Ayanna Ramsumair1, Victor Mlambo2*, Cicero H. O. Lallo3
1Department of Food Production, Faculty of Food and Agriculture,
The University of the West Indies, St. Augustine, Trinidad & Tobago
2Department of Animal Science, Faculty of Agriculture, Science and Technology,
North-West University, Mmabatho, Mafikeng 2745, South Africa.
3Open Tropical Forages-Animal Production Laboratory, Department of Food Production ,
Faculty of Food and Agriculture, The University of the West Indies, St. Augustine,
Trinidad and Tobago
*Corresponding author: Victor.Mlambo@nwu.ac.za; victormlambo@yahoo.co.uk;
Drying techniques are an important variable in forage evaluation because they affect the accuracy with which
the composition of fresh plant material is determined. This study investigated the effect of five drying methods
(freeze-drying, sun-, shade- and oven-drying (60º C and 70º C) on the chemical composition of leaves from
Trichantera gigantea, Gliricidia sepium, Leucaena leucocephala and Morus alba trees grown in Trinidad. The
objective was to determine the most suitable drying method for laboratory evaluation and for field conservation.
Leaves were harvested and then dried under the five drying methods until constant weight before being milled
for chemical analyses. Dry matter (DM), organic matter (OM), ash, neutral detergent fibre (NDF), acid
detergent fibre (ADF), acid detergent lignin (ADL), nitrogen (N) and acid detergent insoluble nitrogen (ADIN)
were determined. Oven-dried G. sepium and L. leucocephala leaves at 70º C and oven-dried M. alba leaves at 60º
C had the highest NDF concentration. Morus alba and T. gigantea oven-dried (60º C) and G. sepium (70º C) had
the highest ADF concentration compared to sun-dried, shade-dried and freeze-dried leaves. Oven-dried (70°C)
G. sepium and M. alba leaves, oven-dried (60º C) T. gigantea leaves, and shade-dried L. leucocephala leaves had
the highest ADL concentration. When shade-drying and sun-drying methods were compared, leaves dried under
shade had higher ADF, NDF, and ADL concentration. Oven drying (60º C and 70º C) resulted in an overall
reduction in the total N of leaves and an increase in the amount of ADIN present. Shade-dried leaves had the
highest total N concentration and the lowest ADIN concentration. It was concluded that shade drying, as
opposed to sun-drying would be the most suitable method for drying forages for conservation purposes, where
as for laboratory analysis purposes freeze drying would be the most suitable method. Further, oven drying can
be used in place of freeze-drying for those laboratories that cannot afford the capital outlay required to
purchase freeze-drying equipment
Keywords: Sun-drying, shade-drying, freeze-drying, drying temperature, fibre-bound nitrogen, lignin
Increasing livestock production in Trinidad
and Tobago is constrained by the seasonal
variation in forage availability and the high
cost of commercial feeds. These seasonal
fluctuations in quality and quantity of feed
need to be addressed by increasing the
production of tree and shrub type forage
species. However, to effectively utilize these
non-conventional feedstuffs as feed for
animals, conservation and accurate nutritional
assessment of these forages is imperative.
Accurate formulation of diets is directly
related to accuracy of the chemical
compositional analysis of these materials; this
in turn may be affected by the drying method
employed during the processing of forages for
chemical analysis. As such, drying
temperature has been identified as an
important factor in forage evaluation because
there are changes in the nutritional
composition that are effected by different
drying temperatures. Drying is designed to
reduce the moisture content in the feed
thereby inhibiting microbial and enzymatic
reactions allowing feed to be preserved
(McDonald et al. 2002, 536-539). The choice
of drying method/temperature is therefore of
paramount importance as it has a direct effect
on assayable chemical constituents of plant
materials. A number of different drying
techniques are available for use, some of these
cause nutrient losses. Drying forages at
Effect of drying methods on the chemical composition of leaves from four tree species; A. Ramsumair et al.
180 Trop. Agric. (Trinidad) Vol. 91 No. 3 July 2014
temperatures below 30⁰C results in enzymatic
degradation of sugars and subsequent losses
of carbon and dry matter. Such losses are
proportional to the water content of forages
and result from continued enzymatic
respiration during the drying process (Collins
and Coblentz 2007, 583 - 599). Dry matter
losses at higher temperatures are a result of
degradation and volatilization of cellular
constituents. Some of the commonly used
drying methods alter or even destroy certain
chemical constituents. Freeze-drying is
considered to be the gold standard of drying
methods for samples being prepared for
chemical analyses. However, freeze-drying is
an expensive method that is largely
unaffordable in most laboratories in
developing countries. The objective of this
study was to determine appropriate drying
methods for laboratory feed evaluation and
for on-farm feed processing and conservation.
The study was, therefore, designed to answer
the following research questions:
1. Does freeze-drying, oven- (60 and 70°C)
drying, shade-drying and sun-drying
affect the chemical composition of
Gliricidia sepium, Leucaena
leucocephala, Morus alba, and
Trichanthera gigantea tree leaves?
2. Can oven drying at 60°C be used in place
of the gold standard, freeze-drying, for
tree leaves?
3. Is there any difference in the chemical
composition of shade-dried and sun-dried
G. sepium, L. leucocephala, M. alba, and
T. gigantea tree leaves?
4. Does a 10°C oven temperature difference
(oven-drying at 60°C versus 70°C) affect
the chemical composition of these
forages?
Materials and Methods
Study site and harvesting method
Gliricidia sepium, Trichanthera gigantea,
Leucaena leucocephala, and Morus alba trees
were grown in September 2009 at the
University of the West Indies Field Station
(UFS) (latitude 10° 38’N and longitude 61°
23’ W). Topography is moderately flat with
an elevation of 15.2 m above sea level.
Average monthly temperature is 27 °C while
the mean annual rainfall is 1782.9 mm. The
soil type is river estate loam and the soil is
free draining with a pH range of 5.0 – 6.2. In
September 2011, leaves were harvested by
hand from 5 randomly selected individual
trees of each species and placed in labelled
brown paper bags. Harvesting was done early
in the morning to prevent excess moisture
loss.
Drying procedures
Tree leaves from the five individual tree
species were dried using the five different
drying methods: shade-drying (SHD), sun-
drying (SUD), freeze-drying (FD), and oven
(60°C (OD60) and 70°C (OD70) drying. The
five experimental replicates per tree species
were each allocated to one of the five drying
methods. Sun and shade-drying treatments
were done under the protection of a
greenhouse at 30°C. Shade treatment was
achieved by protecting tree leaves from direct
exposure to the sun using cardboard shields.
Freeze-drying was done using a Rotational
Vaccuum Concentrator Christ Freeze dryer
BETA 1-8 LD plus (Martin Christ
Gefriertrocknungsanlagen GmbH, Germany).
Oven-drying was done in a forced-air
ventilated Imperial V Laboratory oven called
(Labline Instruments Inc. IL, USA) at 60°C or
70°C. All drying was done to constant weight
after which dried samples were milled to pass
through a 2-mm sieve using a Wiley Mill
(Glen Creston Ltd, Middlesex, UK) and
stored in brown bags at room temperature
pending chemical analyses.
Chemical analyses
Dry matter (DM) was determined by drying
leaf samples in an oven at 105°C for 12 hours.
Organic matter (OM) was determined as the
loss in sample weight upon ignition at 600°C
for 6 h in a muffle furnace. Neutral detergent
fibre (NDF), acid detergent fibre (ADF) and
acid detergent lignin (ADL) were determined
according to Van Soest et al. (1991, 3583-
Effect of drying methods on the chemical composition of leaves from four tree species; A. Ramsumair et al.
Trop. Agric. (Trinidad) Vol. 91 No. 3 July 2014 181
3597) using the ANKOM2000 Fibre Analyzer
(ANKOM Technology, New York). NDF was
analyzed with α amylase but without sodium
sulphite. Both NDF and ADF were expressed
inclusive of residual ash. ADL was
determined on ADF using 72% sulphuric acid
to solubilize cellulose. Nitrogen was
determined by the Kjeldahl method (AOAC,
2005; method number 984.13). ADIN was
determined by N analysis on the ADF residue,
which had been dried at 40 °C for 48 h.
Statistical analysis
Chemical composition data were analysed
using the general linear models (GLM)
procedure of Minitab for a 4 (tree species) x 5
(drying methods) factorial treatment
arrangement in a completely randomised
experimental design to account for effect of
tree species, drying methods and species x
drying method interaction effects. The linear
model used was:
ijk
ij
jiijk EDTDTY
,
where
Yijk = observation of the dependent variable
ijk;
µ = fixed effect of population mean for the
variable;
Ti = effect of tree species (i = 4; G. sepium, L.
leucocephala, M. alba, and T. gigantea);
Dj = effect of drying method (j = 5; shade-
drying, sun-drying, freeze-drying, oven-
drying at 60°C and oven-drying at 70°C);
(T*D)ij = effect of interaction between species
at level i and drying method at level j;
Eijk = random error associated with
observation ijk.
Results
Drying method caused no significant (P >
0.05) changes in ash content of all tree leaves
(Table 1). However, tree species had
significantly (P < 0.05) different levels of ash.
Trichantera gigantea leaves had the highest
(P < 0.05) ash content (246.7 g/kg DM)
followed by M. alba leaves (135.1 g/kg DM)
across all drying methods.
Tree species and drying method
significantly interacted to influence NDF
content of leaves (Table 2). The results
presented show that sun- and shade-dried
leaves of T. gigantea, G. sepium, and M. alba
had similar (P > 0.05) NDF concentration.
Shade-dried L. leucocephala leaves had
higher NDF content (487.7 g/kg OM)
compared to sun-dried leaves (400.5 g/kg
OM). When oven- (60 or 70°C) or shade-
dried, T. gigantea and L. leucocephala leaves
had the highest NDF content. Morus alba
leaves had consistently the least NDF content
across all drying methods. When oven-drying
at 60°C was compared to oven-drying at
70°C; no differences (P > 0.05) in NDF
content were observed for M. alba leaves,
while drying at 70°C resulted in higher (P <
0.05) NDF content in leaves of G. sepium and
L. leucocephala. However, drying at a higher
temperature resulted in leaves with lower
NDF content for T. gigantea. Comparing the
‘gold standard’ drying method, freeze-drying,
to oven-drying at 60°C revealed that oven-
drying resulted in higher (P < 0.05) levels of
NDF in L. leucocephala, G. sepium, and M.
alba leaves. However, for T. gigantea leaves,
freeze-drying resulted in leaves with higher (P
< 0.05) NDF content compared to oven-
drying at 60°C.
Species and drying method significantly
interacted to influence ADF content of leaves
(Table 3). As observed with NDF content,
sun- and shade-dried leaves of T. gigantea, G.
sepium, and M. alba had similar (P > 0.05)
ADF content. Shade-dried L. leucocephala
leaves had higher ADF content (340.9 g/kg
OM) compared to sun-dried leaves (246.7
g/kg OM). When oven-drying at 60°C was
compared to oven-drying at 70°C; M. alba, L.
leucocephala, and T. gigantea leaves had
similar (P > 0.05) ADF content, while drying
at 70°C resulted in higher (P < 0.05) ADF
content in leaves of G. sepium. Oven-dried
(60°C) T. gigantea, M. alba, and L.
leucocephala leaves had higher (P < 0.05)
ADF content compared to freeze-dried leaves,
while no difference (P > 0.05) in ADF content
was observed for G. sepium leaves.
Comparing tree species, T. gigantea leaves
had the highest (P < 0.05) ADF content across
Effect of drying methods on the chemical composition of leaves from four tree species; A. Ramsumair et al.
182 Trop. Agric. (Trinidad) Vol. 91 No. 3 July 2014
all drying methods except shade-drying.
Under shade-drying, it was L. leucocephala
leaves that had the highest ADF content
(340.9 g/kg DM). Morus alba leaves had the
least ADF content across all drying methods.
Table 1: The effect of drying methods on ash content (g/kg DM) of tree leaves
Drying method1
Tree species
FD
SUD
SHD
OD60
OD70
Trichantera gigantean
232.7C
238.4D
241.2D
267.5C
253.5C
Gliricidia sepium
75.1A
90.0B
93.4B
84.2A
81.6A
Leucaena leucocephala
71.8A
73.7A
65.2A
73.3A
75.1A
Morus alba
126.0B
154.3C
131.5C
122.8B
141.1B
A,B,C In a column, different uppercase superscripts denote significant differences (P < 0.05) between tree species means
within each drying method
1Drying method: FD = Freeze-dried; SUD = Sun-dried; SHD = Shade-dried; OD60 = Oven-dried at 60 0C; OD70 =
Oven-dried at 70 0C
Table 2: The effect of drying methods on neutral detergent fibre expressed exclusive of residual
ash (NDFom) content (g/kg OM) of tree leaves
Drying method1
Tree species
FD
SUD
SHD
OD60
OD70
Trichantera gigantean
568.4dD
494.6aC
485.1aC
536.5cC
512.2bB
Gliricidia sepium
406.7aC
414.4aB
414.7aB
468.0bB
498.5cB
Leucaena leucocephala
377.2aB
400.5bB
487.7cC
478.9cB
512.5dB
Morus alba
269.1aA
273.4Aa
289.8abA
294.8bA
283.8bA
a,b,cIn a row, different lowercase superscripts denote significant differences (P < 0.05) between drying method means
within each tree species
A,B,C In a column, different uppercase superscripts denote significant differences (P< 0.05) between tree species means
within each drying method
1Drying method: FD = Freeze-dried; SUD = Sun-dried; SHD = Shade-dried; OD60 = Oven-dried at 60 0C; OD70 =
Oven-dried at 70 0C
Table 3: The effect of drying methods on acid detergent fibre content (expressed inclusive of
residual ash) (g/kg DM) of tree leaves
Drying method1
Tree species
FD
SUD
SHD
OD60
OD70
Trichantera gigantea
328.3bD
276.0aD
288.0aC
345.4cD
336.8bcD
Gliricidia sepium
248.7bcC
223.5aB
223.4aB
238.6bB
257.0cB
Leucaena leucocephala
223.9aB
246.7cC
340.9bD
304.2dC
288.1dC
Morus alba
165.0aA
185.2bA
191.7bA
195.7bA
191.1bA
a,b,cIn a row, different lowercase superscripts denote significant differences (P < 0.05) between drying method means
within each tree species
A,B,C In a column, different uppercase superscripts denote significant differences (P< 0.05) between tree species means
within each drying method
1Drying method: FD = Freeze-dried; SUD = Sun-dried; SHD = Shade-dried; OD60 = Oven-dried at 60 0C; OD70 =
Oven-dried at 70 0C
Effect of drying methods on the chemical composition of leaves from four tree species; A. Ramsumair et al.
Trop. Agric. (Trinidad) Vol. 91 No. 3 July 2014 183
Table 4: The effect of drying methods on acid detergent lignin (expressed exclusive of residual
ash) content (g/kg OM) of tree leaves
Drying method1
Tree species
FD
SUD
SHD
OD60
OD70
Trichantera gigantea
172.0cC
102.4aB
103.1aB
182.8dD
154.8bC
Gliricidia sepium
104.6abB
99.3abB
109.9bcB
97.3aB
117.7cB
Leucaena leucocephala
95.9aB
100.4aB
187.7cC
151.0bC
152.0bC
Morus alba
17.6aA
16.4aA
22.9aA
22.3Aa
23.8aA
a,b,cIn a row, different lowercase superscripts denote significant differences (P < 0.05) between drying method means
within each tree species
A,B,C In a column, different uppercase superscripts denote significant differences (P< 0.05) between tree species means
within each drying method
1Drying method: FD = Freeze-dried; SUD = Sun-dried; SHD = Shade-dried; OD60 = Oven-dried at 60 0C; OD70 =
Oven-dried at 70 0C
Table 5: The effect of drying method on total and fibre-bound nitrogen (ADIN) content (g/kg
DM) of tree leaves
Drying method1
T. gigantea
G. sepium
L. leucocephala
M. alba
FD
Total N
21.1
30.8
33.9
23.6
ADIN
13.3b
6.19a
4.77ab
1.38a
%2ADIN
63.0
20.1
14.1
5.9
SUD
Total N
21.7
34.1
36.8
19.7
ADIN
8.7a
4.44a
3.15a
1.95a
% ADIN
40.1
13.0
8.6
9.9
SHD
Total N
25.1
33.0
36.1
22.7
ADIN
7.8a
3.93a
8.67b
1.58a
% ADIN
31.1
11.9
24.0
7.0
OD60
Total N
21.1
35.5
33.2
19.4
ADIN
15.5b
4.43a
6.80ab
1.82a
% ADIN
73.5
12.5
20.5
9.4
OD70
Total N
20.8
32.9
35.7
23.3
ADIN
12.0ab
5.84a
6.75ab
1.60a
% ADIN
57.7
17.8
18.9
6.9
a,b,c Within each tree species, different lowercase superscripts denote significant differences (P < 0.05) between drying
method means for tADIN.
1Drying method: FD = Freeze-dried; SUD = Sun-dried; SHD = Shade-dried; OD60 = Oven-dried at 60 0C; OD70 =
Oven-dried at 70 0C; 2% = proportion of ADIN in total N.
Table 4 presents the effect of drying method
on ADL content of tree leaves. Significant
interaction (P < 0.05) between tree species
and drying methods were observed for ADL.
As with NDF and ADF content, sun- and
shade-dried leaves of T. gigantea, G. sepium,
and M. alba had similar (P > 0.05) ADL
content. Shade-dried L. leucocephala leaves
had higher ADL content (187.7 g/kg OM)
compared to sun-dried leaves (100.4 g/kg
OM). Oven-drying at 60°C resulted in leaves
with similar (P < 0.05) ADL levels as freeze-
drying for M. alba and G. sepium leaves.
However, higher (P < 0.05) ADL levels were
observed in oven-dried T. gigantea and L.
leucocephala leaves compared to freeze-dried
ones. The two oven-drying temperatures (60
and 70°C) resulted in similar (P < 0.05) ADL
content in M. alba and L. leucocephala
leaves. However, for G. sepium, oven-drying
at a higher temperature resulted in leaves with
higher ADL content. The opposite was true
for T gigantea leaves. With regards to species
differences, T. gigantea leaves had the highest
ADL content when freeze-dried, sun-dried,
oven-dried at 60°C and oven-dried at 70°C.
Effect of drying methods on the chemical composition of leaves from four tree species; A. Ramsumair et al.
184 Trop. Agric. (Trinidad) Vol. 91 No. 3 July 2014
As seen for NDF, ADF, and ADL, M. alba
leaves had the least ADL content across all
drying methods.
Table 5 presents the effect of drying
methods on both the total N and ADIN (fibre-
bound nitrogen) content of tree leaves.
Inherent tree species differences in terms of
total N concentration have long been
established and hence tree species
comparisons are excluded in Table 5. Drying
method was found to have no significant (P >
0.05) influence on total N content but was
found to affect (P < 0.05) ADIN content. No
comparisons are, therefore, presented for total
N content of leaves. Fibre-bound N content of
leaves was similar (P > 0.05) for shade- and
sun-dried leaves of all tree species except L.
leucocephala. For L. leucocephala leaves,
shade-drying resulted in higher ADIN content
(8.67 g/kg DM) than sun-drying (3.15 g/kg
DM). For all tree species, freeze-drying and
oven-drying at 60°C resulted in leaves with
similar ADIN concentration. Similarly, a
comparison of the two oven-drying
temperatures (60 and 70°C) revealed no
differences (P > 0.05) in ADIN content of
leaves from all tree species. For T. gigantea
leaves, oven-drying at 60°C (73.5 %), oven-
drying at 70°C (57.7 %), and freeze-drying
(63.0 %) resulted in leaves with the highest
proportion of fibre-bound N. For G. sepium,
freeze-dried leaves had the highest proportion
(20.1 %) of fibre-bound N, while for L.
leucocephala, shade-dried leaves had the
highest proportion (24.0 %). Very low
quantities of total N were assayed as ADIN in
M. alba leaves. Oven-drying at 60°C (9.4 %)
and sun-drying (9.9 %) M. alba leaves
resulted in the highest proportion of fibre-
bound N.
Discussion
Sample preparation procedures have been
long known to affect the accuracy of nutrient
composition data (Mayland 1968, 658-659).
One of the most common preparation
procedures in forage analysis is the reduction
in moisture content through various drying
techniques. The main objective for drying
forages prior to chemical analyses is to
provide a reproducible basis for expressing
chemical composition. Drying techniques that
rapidly reduce plant metabolic activity and
preserve macromolecular structures after
harvesting are generally considered to be the
most efficient in reflecting the composition of
fresh samples (Pelletier et al. 2010, 139-150;
Alomar et al. 2003, 191-200). There are
several drying techniques being employed for
this purpose in laboratories. Freeze-drying is
considered to be the gold standard for post-
harvest processing of plant material pending
chemical analyses (Alomar et al. 1999, 309-
319). However, the initial and running costs
for this technique are prohibitive and the
majority of laboratories in developing
countries cannot afford it. Field drying
procedures such as shade and sun-drying are
also known to affect forage quality. In this
study we investigated the effect of drying
techniques on the chemical composition of
leaves from T. gigantea, G. sepium, L.
leucocephala, and M. alba trees, which are
potential feed resources for ruminants.
Significant interactions between drying
technique and type (species) of substrate
mean that general recommendations cannot be
made about optimum drying technique.
Similar NDF, ADF, and ADL concentration
in shade- and sun-dried T. gigantea, G.
sepium, and M. alba leaves indicate that the
drying temperatures did not differ greatly
(30°C under sun-drying and 27°C under
shade-drying) between the two drying
techniques. Indeed, similar drying periods
were observed for sun-dried leaves and shade-
dried leaves. However, differences between
shade- and sun-dried leaves may still exist for
leaf components that easily oxidize upon
direct exposure to light such as β-carotene, a
precursor of vitamin A, and phenolic
compounds (Palmer et al. 2000, 29-40). Under
the shade and sun-drying conditions
investigated in this study, it is unlikely that
the concentration of macro constituents such
as NDF, ADF and ADL would be greatly
affected. However, fibre (NDF, ADF, and
ADL) concentration was observed to be
higher in shade-dried than in sun-dried L.
leucocephala leaves possibly reflecting the
slightly longer period (4 more hours than sun-
Effect of drying methods on the chemical composition of leaves from four tree species; A. Ramsumair et al.
Trop. Agric. (Trinidad) Vol. 91 No. 3 July 2014 185
drying) it took to completely dry the leaves
under shade. Indeed, Pelletier et al. (2010, 140
- 145) report that drying procedures that
rapidly remove moisture from plant material
and thus quickly inhibit plant enzyme activity
are useful in preserving the nutritive attributes
of substrates. Slower rates of drying promote
loss of non-structural carbohydrates, loss of
volatile organic substances, and protein
degradation (Deinum and Maassen 1994, 75-
86). The loss of these cellular contents result
in dried substrates with a higher concentration
of cell wall components as seen in shade-dried
L. leucocephala leaves, which had higher
NDF, ADF, and ADL concentration than sun-
dried leaves. Thus depending on the drying
temperature used and hence the length of time
required to achieve constant weight, drying
would cause losses in water soluble
carbohydrates due to respiration, (Dzowela et
al. 1995, 263-269). Sun-dried leaves would
have had a shorter time in which water is
available for respiration to take place while
shade-drying resulted in prolonged plant
metabolic activity. Under these conditions
soluble carbohydrates from the forage are
consumed by the respiration process
producing carbon dioxide and heat thus
reducing the amount of soluble carbohydrates
and increasing the fibre proportion (Heberer
et al. 1985, 1117-1119). Coblentz and
Hoffman (2008, 1-4) reported that increases in
NDF concentrations occur because cell
solubles are oxidized preferentially during
plant respiration even after harvesting. Fiber
components, such as NDF, ADF, and lignin,
are generally inert during this process, but
their concentrations increase because cell
solubles are reduced due to oxidation. It is,
therefore, expected that slow-drying methods
would result in higher proportions of NDF,
ADF and ADL (Dzowela et al. 1995, 263-
269).
Drying plant material at high
temperatures also result in the formation of
indigestible protein-carbohydrate complexes
called Maillard products, which are assayed as
part of fibre fractions. However, our results
indicate that a 10°C difference in oven-drying
temperature did not cause higher NDF content
in all tree species except T. gigantea. Maillard
reaction is a heat-induced chemical reaction
between protein (amino acids) and sugars.
Maillard products produce a range of odors
and colors in forages, but generally are poorly
characterized nutrients in ruminant nutrition
(Coblentz and Hoffman 2008, 3 - 4).
Therefore drying the forages at higher
temperatures may result in higher fibre
content because of the Maillard products and
lower soluble carbohydrates. These
complexes are poorly soluble in acid and
neutral detergent solutions and their formation
increases at higher temperatures during the
drying process. Maillard products thus
increase the amount of N bound to fibre,
measured as ADIN. Our results indicate no
differences in ADIN content of leaves that
were freeze-dried, oven-dried at 60, and oven-
dried at 70°C. This indicates that the drying
temperatures employed in this study were not
high enough to cause the formation of
Maillard products. The similarity in chemical
composition of leaves between freeze-drying,
and oven-drying (60 and 70°C) is also
exciting as it means that the ‘gold standard’
freeze-drying method can be substituted with
oven-drying at 60 or 70°C in laboratories in
developing countries.
The total N content contained in forage
determines the total amount that would be
available for consumption by animals. Our
results indicate that drying technique did not
affect total N content possibly because the
drying temperatures employed were not high
enough to promote any form of volatilization
of ammonia (Deinum and Maassen 1994, 75-
86). However, this does not rule out the
possibility of changes in the concentration of
N fractions, an important factor in the
nutrition of ruminants since it affects protein
quality. The conversion of true protein to
NPN is a result of proteolysis which occurs in
cut forages and continues through drying
(Pelletier et al. 2010, 139-150). Rapid
proteolysis begins with the breakdown of
plant membranes and the release of proteases
from the vacuole, which represent a complex
mixture of enzymes (McDonald et al. 2002,
538). The formation of NPN increases under
low temperature drying conditions that
prolong the dehydration process thereby
Effect of drying methods on the chemical composition of leaves from four tree species; A. Ramsumair et al.
186 Trop. Agric. (Trinidad) Vol. 91 No. 3 July 2014
allowing proteolytic enzymes enough time to
breakdown true protein.
Conclusion
Since oven drying at 60°C or 70°C did not
differ from freeze-drying, the reference
method, it is concluded that oven-drying can
be used in place of freeze-drying for those
laboratories that cannot afford the capital
outlay required to purchase freeze-drying
equipment. Shade-drying was also found to be
similar to sun-drying as far as fibre, lignin and
N concentration are concerned. Thus for field
drying of tree leaves any one of the two
drying techniques can be employed. However,
it should be noted that shade-drying can
prevent the loss of other heat-labile and
readily oxidized nutrients that were not
measured in this study.
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