Ensiling leaves of Taro (Colocasia esculenta (L.) Shott) with sugar cane molasses
 

Chittavong Malavanh, T R Preston^*and Brian Ogle^**

Faculty of Agriculture, National University of Laos (NUOL),
Vientiane city,Lao PDR
malavanc@yahoo.com
^* UTA, TOSOLY, AA #48, Socorro, Santander, Colombia
^** SwedishUniversity of Agricultural Sciences, Department of Animal Nutrition and Management,
PO Box 7024, 750 07, Uppsala, Sweden

Abstract

An experiment was carried out at laboratory scale to determine the optimum level of molasses for ensiling taro (Colocasia esculenta (L.) Shott) leaves. The leaves were collected from Nongveng village, near Vientiane City in Laos, and were chopped into small pieces (2 to 3 cm) and ensiled in plastic bags (capacity 2 kg) with levels of sugarcane molasses of 0, 2, 4 and 6% (dry matter [DM] basis). The mean total sugar content (°Brix) of the molasses was 77. Each molasses level was repeated five times, corresponding to ensiling periods of 0, 7, 14, 21 and 28 days. At each ensiling date samples were taken for determination of pH, DM, ammonia nitrogen (NH₃-N), water extractable DM and N, and total N. Physical characteristics, such as smell and colour, were observed and recorded.

After 7 days the colour for all treatments had changed from green to yellow-brown and was darker at higher levels of molasses. Each treatment had an acceptable smell. The pH values for all treatments were around 6 at day 0 and then quickly fell below 5, the value being dependent on ensiling time and the level of molasses (P<0.05). At day 0 the concentration of NH3-N was very low on all treatments, but from 7 days onwards the concentration had increased with the time of ensiling on all treatments; the highest value was 5,900 mg/kg DM on the 0% level of molasses at 28 days. The ammonia-N concentration decreased as the level of molasses increased. Ensiling for 28 days with 4% molasses reduced oxalate concentration from 2.20 to 0.37% of DM.

A level of 4% molasses and an ensiling period of between 14 and 21 days appeared to be the most appropriate procedures for ensiling Taro leaves as determined by pH, ammonia concentration and water extractable DM and N.

Key words: ammonia, Colocasia esculenta (L.) Shott, ensiling, leaves, nitrogen, pH, taro, water extractable DM and N

Introduction

Leaves from Taro (Colocasia esculenta (L.) Schott) are rich in vitamins and minerals. They are a good source of thiamin, riboflavin, iron, phosphorus and zinc, and a very good source of vitamin B6, vitamin C, niacin, potassium, copper and manganese. Oxalic acid may be present in the corm, however, and especially in the leaves (http://en.wikipedia.org/wiki/Taro). The leaves can be chopped and ensiled to considerably reduce undesirable substances in Taro, which thus becomes more palatable.

Ensiling is the preservation of forage (or crop residue or by-product) of high moisture content based on a lactic acid (ideally) fermentation under anaerobic conditions (Moran 2005; McDonald et al 2002). It has been shown that ensiled fish and shrimp by-products can be preserved for several months (Levin 1994; Ly et al 2000). The silage can then be used as feed for livestock (Lien et al 1994; Khieu et al 2000; Ly et al 2000; Ngoan 2002). Recent research in Laos has shown that Golden Apple Snail flesh can be successfully preserved for at least 24 weeks by ensiling with an additive mixture of molasses and rice bran and then successfully used as feed for growing pigs (Kaensombath 2005). The main function of a silage additive is to increase the nutritional value or improve fermentation (Ohio Sate University Extension 2001). Molasses is a good and cheap additive and is available in Vientiane Province. It has a high soluble carbohydrate content of about 700 g/kg DM and has been shown to increase the dry matter and lactic acid content, and to reduce the pH and ammonia levels in treated silages (McDonald et al 2002). However, according to Ohio State University Extension (2001), molasses should not be added to wet silage (<35% dry matter) because of increased seepage losses

The objective of this experiment was to determine the optimum level of molasses additive for ensiling Taro leaves.
 

Materials and Methods

Location

The experiment was conducted in the Laboratory of the Faculty of Agriculture, National University of Laos (NUOL), Vientiane City, Laos, from May to June 2006.

Procedure

Leaves of Taro (Colocasia esculenta) were purchased from Nongveng village, near Vientiane City. They were chopped into small pieces (2 to 3 cm) and ensiled in plastic bags (capacity 2 kg) with levels of sugar cane molasses of 0, 2, 4 and 6% (DM basis). The bags were sealed to prevent air contamination and then put into plastic buckets to exclude mice and prevent external mechanical damage and stored at room temperature (20-30^oC). The mean total sugar content (°Brix) of the molasses was 77.0. Each molasses level was repeated five times, corresponding to ensiling periods of 0, 7, 14, 21 and 28 days.

Measurements

Samples were taken to analyze for total and water extractable DM and N, and fermentation characteristics such as pH and NH₃-N. Water soluble DM and N was determined by the methods described by Ly and Preston (1997). Physical characteristics, such as smell and colour, were observed and recorded. N, crude fibre, NH3-N and oxalic acid were determined according to AOAC (1990) and DM by micro-wave radiation (Undersander et al 1993).

Statistical analysis

The data were analyzed using the general linear model option of Minitab (version 14) ANOVA software (MINITAB 2000). Sources of variation were treatments and error.

Results

Chemical composition of the taro leaves and molasses

The chemical characteristics of the fresh taro leaves and molasses are shown in Table 1.

Physical characteristics

Initially, the Taro leaf silage at 0% molasses had a green colour, but for the other treatments the colour rapidly started to change from green to brown. After 7 days the color for all treatments had changed to yellow-brown, and was darker at higher levels of molasses. The color did not change further in the treatments with molasses added, but the colour of the Taro leaf silage at the 0% level changed to yellow-brown at 21 days, and became even darker at 28 days. All silages had a good smell throughout.

Changes in chemical composition and pH with time of ensiling

The pH values for all treatments were around 6 at day 0 and then fell below 5 in all treatments after 14 days, except for the 0% molasses treatment (Figure 1; Table 2). The pH values further decreased with time of ensiling (P<0.05) and level of molasses (P<0.05). For example, at the 4% level of molasses the pH value was 4.0 at 21 days (Figure 1). The DM content of al the silages was some 6 percentage units higher than in the fresh leaves.

At day 0 the concentration of NH3-N was very low on all treatments (Figure 2). After 7 days the concentration increased with the time of ensiling on all treatments (P<0.05); the highest value recorded was 1.3 g/kg DM on the 0% level of molasses at 28 days. The ammonia-N concentration decreased in proportion to the level of molasses (Figure 2; Table 2). After ensiling for 28 days with 4% molasses added oxalate concentration was reduced from 2.20 to 0.30% of DM.

The proportion of the DM solubilised by water extraction was not affected by ensiling time, but increased with the increasing level of molasses (P<0.05) (Table 2 and 3 and Figure 3).

The proportion of the total N extracted by water increased both with length of ensiling and the level of molasses (Tables 2 and 3 and Figure 4), and was highest at the 4 and 6% levels (P<0.05).

Table 3. Effect of molasses level on the chemical composition of ensiled Taro leaves at 28 days of ensiling
	Molasses, %				SEM	P-value
	0	2	4	6
pH	5.90a	5.40a	4.80b	4.70b	0.15	0.001
DM, %	22.2a	20.6b	21.4a	22.5a	0.44	0.037
NH3-N, mg/kg DM	989a	863ab	689bc	60c	48.4	0.001
NH3-N in total N, %	3.53a	3.05ab	2.55bc	2.24c	0.20	0.003
N, % DM	2.80	2.80	2.70	2.70	0.05	0.061
WV-DM, % DM	29.3b	30.8b	44.0a	46.6a	2.01	0.001
WV-N, % DM	30.8b	35.2ab	42.2a	42.2a	2.23	0.008
Oxalic acid, %			0.30
a,b,c Mean values within rows with different superscript letters are significantly different (P<0.05)

Discussion

According to McDonald et al (2002), if the material to be ensiled has a relatively low DM content, it is advisable to use an additive with high dry matter content, which was the case in the present study. The higher DM content of the silage (20 to 24%) compared with the fresh leaves (16% DM) was probably the result of wilting during transport from the village and subsequent chopping at the university. The pH values for all treatments were around 6.0 initially, and then fell quite rapidly, because any oxygen trapped between the forage particles is eliminated as a result of the respiration of the plant material and the anaerobic activities of bacteria start to dominate. The plant enzymes are also active during this initial phase, provided the pH is still within the normal range for fresh material (pH 6.0-6.5) (Moran 2005). However, after 14 days the pH values had fallen to below 5.0, except in the treatment without any addition of molasses. A successful fermentation will see the number of lactic acid producing bacteria dominate under anaerobic conditions and when there is a readily-fermentable substrate such as molasses, reducing the pH to 3.5 to 4.5 (Moran, 2005), as was also the case in the present study.

During the 28 days of ensiling, there were only very slight changes in the chemical composition of the Taro leaf silage, which is in agreement with several previous studies. McDonald et al (2002) reported that losses of DM of less than 5% during ensiling are acceptable. The slight decrease in CP content was because there is normally some deamination of amino acids that occurs during fermentation (McDonald et al 2002). Lin et al (1988) also concluded that the general nutrient values (including metabolizable energy), fatty acid composition and amino acid contents (including the proportion of essential amino acids) in silages of mixtures of sweet potato roots and maize meal did not change during ensiling. Ruiz (1982) showed that the dry matter content of sweet potato foliage silages did not change by adding roots (up to 1.2%) or urea (up to 1.6%).

The oxalate content of the raw leaves of taro (Colocasia esculenta (var.) Schott) was reported as being 236 mg oxalate/100 g wet matter (Savage et al 2006), which is similar to the value of 2.20% of DM found in our study. Ensiling for 28 days with 4% molasses reduced the oxalate concentration to 0.30% of DM, a reduction of 86%. This is in agreement with Tiep et al (2006), who reported that ensiling Alocasia macrorrhiza leaves with rice bran and molasses reduced calcium oxalate content by 78.8%.

The increase in the concentration of ammonia-N during the first 7 days of ensiling is in accordance with the report of McDonald et al (2002) that proteolytic organisms (mainly Clostridia) are active while the pH is still relatively high (falling only from 6.50 to 5.80 in the first 7 days) resulting in breakdown of protein to amino acids, amines and ammonia. After 7 days there was no further increase in ammonia-N concentration. The reduction in ammonia-N due to addition of molasses was probably because the higher the concentration of molasses the faster was the reduction in the pH of the silage (see Figure 1). Part of the increase in water soluble DM due to addition of molasses can be explained by the effect of the molasses per se, as most of the compounds in molasses (sugars and minerals) are water-soluble. However, at the 4 and 6% molasses levels the increase in water-extractable DM was almost 100%, which implies that under these conditions (4 and 6% molasses) the ensiling process had stimulated partial breakdown of some of the components in the taro leaves. Similar effects were seen in the proportions of water-extractable N, which increased by more than 50% due to the addition of the molasses.

Conclusions

• A level of 4% molasses and an ensiling period of from 14 to 21 days appeared to be the most appropriate for ensiling taro leaves, as determined by pH and ammonia and oxalic acid concentration.

Acknowledgements

We are very grateful to the Swedish International Development Cooperation Agency, Department for Research Cooperation (Sida-SAREC) through the regional MEKARN Project, for the financial support of this study.

I would also like to thank the Faculty of Agriculture, National University of Laos for allowing and helping me to carry out this experiment. The authors thank Mr Bounlerth Syvilai for analytical assistance in the laboratory of the Faculty of Agriculture.

References

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