“THE RINDS OF TREE PHILIPPINE CITRUS FRUITS”
This study was conducted to test and compare the potential of essential oils obtained from the rinds of three selected Philippine citrus fruits (pomelo, perante, and dalanghita) in controlling “golden” kuhol. The study also determined some of physico-chemic’al properties of the essential oils.
The essential oils were obtained using the mean distillation method. For each sample, three concentrations of essential oils (5 percent, 10 percent, and 15 percent) were prepared. Comparable boiling points, refractive indices, and degrees of volatility of the essential oils suggest that the essential oils exhibit similar properties. Saponification and iodine numbers revealed that the degree of unsaturation of the essential oils were comparable. Results also showed that the essential oils from the rinds of pomelo, perante, and dalanghita posed similar molluscicidal activity.
I na country where rice cultivation is one of the main sources of livelihood for the people, it is important that a new and effective measure of protecting the crops • be carefully and continuously implemented. One of the major dreaded rice pests throughout the Philippines is the golden snail (Pomaceae canalienlataL.), or golden kuhol. In the past, farmers used to apply different kinds of molluscicidal, such as Methiocarb, Niclosamide, Metaldehyde, and those containing organotin compounds to control golden snail and prevent it from infesting rice crops. However, due to the high costs and high toxicity of these chemicals to other aquatic organisms, molluscicides were banned. Another primary concern was that the golden snail became immune with those different kinds of molluscicides after several exposures. Previous studies revealed that some indigenous plants are potential molluscicides. These include tubing kamaisa (Groton tiglium), sambong (Conyza balsamifera), taba-taba (Jatropa curcas), lagtang (Menispernum cocculus), red pepper (Capsicum frutescens), and tubli (Derris philippinensis). Among the latest plants studied was the calamansi (Citrus mitts L.). It was also reported that volatile oil extracted from the fruit rind was found to be an effective molluscicide against newly hatched golden kuhol. Citrus fruits such as pomelo (Citrus maxima L.), perante (Citrus aurantium L.) and dalanghita (Citrus nobilis L.) contain essential oils that can be potential molluscicides. A study on the molluscicidal activity of citrus fruits may help the farmers in finding a new way of controlling golden kuhol and preventing crop infestation.
REVIEW OF RELATED LITERATURE
Essential Oils Essential oils have been produced and used for flavoring, incense, and medicinal purposes for many centuries now. The sources of these oils are diverse, including flower petals, spices, pine oil, turpentine, and citrus fruit peels. Essential oils have an active role in plant defense. They sometimes possess toxic properties linked to the protection of the species. Some that smell nice to insects may be unpleasant for other insects; this is useful for the plant as defense against parasites or other animals, which would damage the plant. The essence evaporated from the plant is therefore considered a defense mechanism from infections, because of the bactericidal, fungicidal, and ascaricidal action of several oils. In 2001, essential oils from the rinds of calamansi were found to be effective as molluscicide against golden kuhol.
Cultivation of the Golden Kuhol Matured golden snails (kuhol) were fed with kangkong leaves until they laid their eggs. The eggs were then allowed to hatch, and the five day-old golden snails were subjected to bioassay test. Extraction of Bioactive Components About half kilogram of fresh rind samples (pomelo or suha, perante or kaheL and mandarins or dalanghita) were around using a blender. Distilled water, as much as half the volume of the sample. was added. After the grinding process, the mixture was thoroughly squeezed and filtered with cheesecloth. The filtered juices were rled in a distilling flask and subjected to steam distillation. The essential oils collected in the receiver immersed in crushed ice were separated by using a separatory funnel: these were dried with sodium sulfate and measured afterw. ard. The moisture-free oils were then stored in amber a.-4oral bottles and placed in the refrigeraor to prevent decomposition of the components. The percentage yields of the sampl.es were computed in terms of the Yohime-weight percent. Determination of the Physico-Chemicai Properties of the Essential oils B: qg Paint About 1 milliliter (mL) each of the essential oils were poured into – eptaate micro test tubes with a capillary tube closed at one end. The samples were completely immersed in a 100-mL oil bath, which was heated slowly with constant stirring. The average boiling point of each of the – were determined and recorded_ Refractive Index Oze to two drops of each of the samples at a wmperature of 20°C was placed or_ the surface of the prism of a hand —1:-toireeter. The instrument readinz – Brix, B) was conrert 712 the table found in The C— – Is of Analysis of the Association of Official Analytical Chemists (AOAC). Degree of Volatility The degree of volatility of the essential oils at different environmental temperatures within a fixed exposure time was determined following the procedures used by Brandares (1987). Previously oven-dried Petri dishes were weighed and approximately 0.3 mL of the samples was introduced by means of a micropipette. The samples were reweighed. One sample (each of the oils) was exposed to room temperature, the second sample to direct sunlight, and the third was placed inside the refrigerator. The temperature under which the three samples were exposed as well as the initial time of exposure was recorded. The- samples were again weighed after three hours to determine the loss of weight. The procedure of saponification and iodine number analyses were obtained from AOAC (1980). Molluscicidal Activity of the Essential Oils For each sample, three different concentrations of the essential oils were prepared: T, (5 percent), T, ( 10 percent) and T, (15 percent). To each concentration prepared, 10 young (five day-old) golden kuhol were placed. Three replicates were done for each concentration. Mortality rate and percent survivals were determined every two, four, six, eight, and 10 hours. For the positive (+) control, the commercial molluscicide SnailkilR was used and the above procedure was also followed. Water was used as the negative (—) control.
Physical Properties of the Essential Oils The physical characteristics of the essential oils obtained from the rinds of the samples are summarized in Table 1. The essential oils were all colorless and had the characteristic fragrance of the samples. The percentage yields for essential oils of the three samples were found to be comparable. The analysis of variance shows that the essential oils from the rinds of the three samples contain comparable amounts of total dissolved substances based on the refractive index values. Table 1. Percentage Yield and Physical Characteristics of Essential Oils from Pomelo, Perante, and Dalanghita
The “golden” snail, Pomaceae canalienlata L.
* Values with the same superscript letters are not significantly different The degree of volatility of the essential oils was done to determine the effect of different environmental temperatures on the essential oils’ stability and also served as a way to measure the degree of unsaturation.