Effect of drying method on the chemical composition of leaves from four tropical tree species

Abstract

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.