The University of the West Indies, at Mona, Jamaica Homepage

The University of the West Indies

at Mona, Jamaica

Dr. Cliff Riley, Dr. Andrew wheatley, Professor Helen Asemota

Faculty of Medical Sciences

The Best Research Publication: Article

Yam Glorious Yam

Yam Eaten Everywhere

The yam (Dioscorea sp.) is an edible root crop that is mainly grown in the tropics. The tuber forms a major component in the diet of millions of the world’s population in Africa, Southeast Asia, the Pacific and the Caribbean as a source of digestible carbohydrate. There are over 24 cultivars of yams grown in Jamaica, belonging to five species, namely: white yams, soft yam, yellow yam, yampie, and Chinese yam. There are also the non-edible yams which are referred to as “wild yams.” They are usually found in the wild and grow mainly in the limestone regions of the island. The main use of yam is as food, usually eaten boiled or roasted. The nutrient content of the tuber is 50-85 % starch, 3-8% protein, 2-5% fiber, 2-7 % ash, and 0.2-0.7% fat of the dry tuber. Starch is the major carbohydrate reserve in yam tubers. It is occurs as a tasteless, odorless, fine white powder in its dried extracted form. Despite its high carbohydrate content, mainly in the form of starch, yam is not listed among the most common sources of industrial starch which is primarily obtained from corn, potato, wheat, tapioca and rice. This is primarily due to the lack of adequate information on the properties, suitability and functionality in its products..

Dr. Cliff Riley viewing substance in flask.

Dr. Cliff Riley viewing substance in flask
[View larger]

Need for Industrial Exploitation of Yams

Over 100,000 tonnes of yams are produced annually in Jamaica (down from 200,000 tonnes in 2000). However only about 5 % is exported with losses of up to 40 % of the total production reported. These losses amounts to over US 20 million annually. This has significantly affected revenue generation in the agricultural sector, primarily farmers, exporters and processors. These losses are primarily due to the poor storageability of the yam tubers. However, the quantities and revenue lost during storage can be prevented if immediately after harvest their starches are extracted and used as ingredients in tablets, capsules, granules and other products. This could reduce the amount of yam that would normally be discarded or lost during storage, increase revenue generation and reduce the country’s demand for imported starches for use in pharmaceutical products. With this in mind the UWI researchers embarked on investigating the physicochemical properties of yam starches and their effectiveness as binders in paracetamol granules, tablets and capsules in a bid to stimulate industrial applications by local manufacturers, primarily in those in the pharmaceutical industry.

STARCH PROPERTIES AND IMPACT ON PHARMACEUTICAL PRODUCTS

Properties such as granule size, shape, specific surface area, sensitivity to moisture, density, swelling power, purity, reactivity, porosity among others play an important role in the use and functionality of starches in finished pharmaceutical products. If the properties of starch from different plant sources are strikingly different, they may impact significantly on processing and product quality and may be a potential source of differences in brand/generic product performance or even in batch-to-batch and lotto- lot variation in the same product formulated with different starches. In addition, these differences in material properties may impact on the quality of starch products and their performance in dosage forms (pharmaceutical products). Paracetamol, one of the most popular analgesic (pain relief) and antipyretic (body temperature reduction) drug, is of poor aqueous solubility (1 in 70 parts of water, BP). Hence, its paediatric solution formulations invariably incorporate alcohol based co-solvents. Apart from the limited stability of aqueous drug products, recent demand by the paediatricians for alcohol-free paracetamol formulation has necessitated consideration of alternative dosage formulation. Presently, no commercial paracetamol granule for reconstitution appears to be on the market, especially in the tropics where extremes of climatic conditions could compromise shelf-stability of liquid preparations.

Dr.Riley and Dr. Wheatley conducting experiments.

Dr. Cliff Riley and Dr. Andrew Wheatley conducting experiments.
[View larger]

PERFORMANCE IN PARACETAMOL SOLID DOSAGES (TABLETS AND GRANULES)

Starches from five local cultivars namely; Round leaf yellow yam (RY), Sweet yam (SY), Negro yam (NY), Chinese yam (CY) and Bitter yam (BY) were extracted, purified and their physical and chemical properties evaluated. The starches were then incorporated as binders in pediatric granules for reconstitution using paracetamol as the active pharmaceutical ingredient (paracetamol [2.5 % w/w], starch [2.5 and 10 % w/w] and sucrose [20 % w/w]) and rate of paracetamol release determined in vitro (outside a host). British Pharmacopeia corn starch (CS) was used as the control binder. The physicochemical properties of the yam starches were found to be dependent on the botanic (plant species) source with identifiable differences observed among the cultivars studied. Apart from the potential effects of these properties on processability, consistency of content and physical characteristics of pharmaceutical products, reasonable correlations were established between these properties and the rate of paracetamol release. Properties such as starch granule size, surface tension, specific surface area and viscosity are positively correlated with the rate of paracetamol release. The dissolution of paracetamol from granules formulated with different yam starches is significantly affected by the properties of the starches and the concentration used as binder. Granules formulated with starch from CY and BY have faster rate of paracetamol dissolution when used as binders compared to those formulated with RY, NY, SY and official corn starch. Paracematol granules formulated with Chinese yam and Bitter yam starches had dissolution times of 2.2 minutes and 2.6 minutes respectively at a starch concentration of 2.5 % compared to that with corn starch (4.55 minutes). This indicates that tablets and granules formulated with Chinese yam and Bitter yam starches could release the active ingredient twice as fast as those containing official corn starch leading to faster relief from the condition being treated for. Hence, careful consideration of starch botanic source in starch binder selection is essential in order to obtain the required drug dissolution rate while preserving other desirable physical properties of the granules.

INDUSTRIAL SIGNIFICANCE

The work presented will have far reaching impact on stakeholders in the agricultural sector, the pharmaceutical industry and consumers of pharmaceuticals.


Cliff Riley is a researcher in the Department of Basic Medical Sciences (Biochemistry Section) and the Biotechnology Centre. His primary areas of research includes; Polymer Chemistry, Pharmaceutics, Biotechnology, and Diabetes Management.cliff.riley@uwimona.edu.jm

Andrew Wheatley is a lecturer in the Department of Basic Medical Sciences (Biochemistry Section) and the Biotechnology Centre. His major areas of research interest includes; Biotechnology, Diabetes Management, Biochemistry and Natural Products.andrew.wheatley@uwimona.edu.jm

Helen Asemota is a professor of Biochemistry and Molecular Biology in the Department of Basic Medical Sciences (Biochemistry Section) and the Biotechnology Centre. Her major areas of research focus include; Nanobiology, Biotechnology, Natural Products and Biochemistry. helen.asemota@uwimona.edu.jm