Jonathan Pratt Rowe
Cassava, taro, and breadfruit are critical food sources indigenous to the Pacific islands. Because they serve as the main source of energy for 500 million people, their availability is vital to the survival of these people. In addition to the energy provided, these plants also provide essential vitamins and minerals. Generally, cassava, taro, and breadfruit are grown with relative ease and abundance. Their physical and chemical properties, however, are not conducive to storage, and as a result, much is wasted.
In times of shortage (drought, hurricane, blights), the use of preserved cassava, taro, and breadfruit can be significant in the sustaining of life. Through use of a solar-drier, we have developed methods suitable for the long-term storage of these plant foods.
Our objective was to develop a drying and storage method that would provide the people of the Pacific Islands with a safe, quality preserved food.
Various methods of solar-drying were tested, with measurements of water activity (Aw), temperature, and relative humidity (RH) being taken at various times. Upon drying, the fruit pieces were sealed in Mylar™ bags with oxygen absorbers. Subsequent measurements of Aw and headspace oxygen content were taken periodically after storage.
Results indicate that solar-drying is an effective means of preservation in the Pacific Islands. Aw levels were generally the same as the initial measure levels (.4-.6). Headspace oxygen content was minimal in each sample (below .05%), indicating the oxygen absorbers were effective.
These results show an environment more suitable for the long-term storage of cassava, taro, and breadfruit. Such long-term storage will provide the people of the Pacific Islands with supplies of usable food in times of shortage as well as provide a means for storage of highly perishable products.
Justification
In 1984, the FAO issued a bulletin entitled Traditional post-harvest technology of perishable tropical staples. The main theme of this document was to emphasize the need for an interaction of the traditional methods of post-harvest technology with modern scientific concepts. “Traditional knowledge, especially of the post-harvest technology of these perishable staples, has remained largely untapped, but possibilities exist for the interaction of modern scientific concepts with these traditional systems.” Since this bulletin was issued, very little has been done from the scientific community to answer this need.
To adequately assess the need for post-harvest technology and long-term storage of food products the principle of food security must be understood. The FAO defines food security as the insurance that “all people at all times have both physical and economic access to the basic food they need.” In the area of the Pacific Islands, there are two main obstacles to achieving food security: 1. Economic instability, and 2. Natural disasters.
Political and economic instability are unfortunate characteristics of many developing countries throughout the world. For example, two coups have taken place in Fiji in the past twenty years – in 1987 and 2000. Such instability affects the people’s “economic access to the food they need.”
Emergency situations, of course, also pertain to natural disasters. These disasters may include tropical depressions, typhoons, floods, droughts, and blights. Such disasters can quickly destroy these staple crops of breadfruit, cassava, and taro. The frequency and impact of these natural disasters is often over-looked by the world community.
The most likely way to overcome these obstacles is use of the staple carbohydrates in the Pacific Islands. The three main staples include breadfruit, cassava, and taro. These products are the chief carbohydrate contributors to the diets of 500-700 million people worldwide.
In the Pacific Islands, the breadfruit tree (Artocarpus altilis) fruits more or less continually, with fruit in all stages of development being present on the tree year round. There are, however, two or three main fruiting periods. The fruit itself ranges in spherical size from 10-20 cm in diameter, depending on the variety.
Cassava (Manihot esculenta) is an annual root crop, requiring 8 months of ideal conditions to produce a crop. A good sized root is usually around 35 cm long, with a 5 cm diameter. Fresh roots usually contain around 30% starch, with very little protein. Because of high levels of cyanogenic glucosides, fresh cassava requires some form of processing before it can be consumed.
Taro (Colocasia esculenta) is an edible aroid, with the underground “corm” portion being utilized for its starchy composition. This corm can grow to be over 30 cm and, in addition to carbohydrates, provide other important vitamins and minerals such as Vitamins C and B1, and iron. Taro typically requires about 8-9 months for suitable growth.
Typically, these crops grow readily in the Pacific Islands. As previously illustrated, however, emergency situations (both economic and natural disasters) are prevalent in this area of the world. Food security is not achieved when food is only available in ideal conditions. Food security can be achieved when these staples are preserved for use in such emergency situations.
There are, unfortunately, challenges to the preservation of breadfruit, cassava, and taro. These products have extremely high moisture content and water activity (as high as 0.99). This provides the water necessary for enzymatic activity and microbial growth.
In addition, environmental conditions also present an obstacle in preservation. The climate of the Pacific Islands is usually hot and humid, and many lack refrigeration capabilities. Environmental factors, when combined with the product water activity, create an ideal environment for enzymatic activity and microbial growth. Because of this, shelf-life of these staples is typically 1-3 days.
Recall again the economic and natural disaster problems: a 1-3 day shelf-life of staple carbohydrates does not achieve food security. Consider the following headlines from a Fiji newspaper, all taken from the exact same day in May 2004: “Bugs raid rural farms,” and “Villagers await extra food assistance.” Both of these problems came as a direct result of recent flooding in the area. The villagers needed food assistance because “the plantations along the river… were destroyed.” Another article, still from the same day, was titled, “Reservoir runs dry.” A portion of the population is recovering from devastating floods, while another portion is “praying for a heavy downpour to solve current water problems.” In the Pacific Islands, preservation methods must be employed to extend the shelf-life of staples beyond 1-3 days.
The FAO bulletin referenced earlier points out that “there exist possibilities for the injection of modern scientific concepts into these traditional [post-harvest] systems…”
Traditional methods of preservation include drying, fermentation, leaving the crop in the ground, and storage in cellars. While extending the shelf-life beyond the typical three days, these traditional methods (excluding drying) are not suitable for long-term storage. In these methods, the negatives outweigh the positives from the perspective of long-term storage.
Drying appears to be the most feasible method for long-term storage. As previously noted, the main cause for rapid deterioration is the high water activity and moisture content of these staples. Drying, of course, presents a preservation method that lowers these values. In addition, drying is a simple method not requiring extensive training or time by the laborer. Specifically, solar-drying utilizes a natural source of energy: the sun. In areas where others sources of energy are not easily obtained, solar energy can be harvested with a solar-dryer. Not only is this energy effective, but is also an inexpensive source of energy.
The objectives of this project were two-fold:
1. Using indigenous crops (breadfruit, cassava, and taro), create a shelf-stable product suitable for long-term storage
2. Regarding solar-dryer processing: design a simple solar-dryer that can be built and used in a village-type setting; and develop a use manual for the dryer and its operation.
Solar-Dryer Construction
Design of the solar-dryer used in this research was based on previous designs, with modifications made to better suit the circumstances unique to this research. Construction of this dryer took place in Suva, Fiji; special care was taken to use materials available in the Pacific Islands. Consideration was also given to the costs involved with construction. With all materials purchased in Fiji, the overall price of construction totaled between $180 and 200 U.S. dollars. This price is appropriate for group or village use, but may be too expensive for individual families.
Construction of a homemade solar panel utilizes the efficiency of solar energy. When left in the sun, the combination of clear plexiglass and black screens create an environment with high temperatures. As the temperature of the air increases, the density decreases, causing the air to rise. This process creates a natural convective airflow through the drying racks. This airflow is benefited by air vents located at the top of the dryer and an opening at the bottom of the solar panel.
During the drying process, as temperatures inside the dryer increased, relative humidity within the dryer decreased. For example, comparison of data loggers inside and outside the dryers on a typical day reveals that the dryer increases drying temperature (88.7ºF to 115.6ºF), while lowering the relative humidity (55.4% to 35.9%).
Detailed procedures for the construction of the solar-dryer can be obtained by contacting the author.
Drying Methodology
In order to increase desirability of the finished product, attempts to conform to traditional customs were made in the processing of the foods. In order for drying to take place at reasonable rates, however, some changes have been made. With every product, it was important that the beginning food was fresh; use of a poor beginning product leads to a poor finished product.
Breadfruit, cassava, and taro were prepared for drying by first peeling the fruit in the traditional or customary manner. Rinsing the products is typically necessary before and/or after peeling.
The next step, the peeling of the products, introduces variances from traditional methods of preparation. Breadfruit is sliced so that each peace is approximately 1 cm in thickness. During or after slicing, the seeded center section of the breadfruit will need to be removed. Taro is sliced in a similar manner, with each slice ranging in thickness from 7-10 mm. In typical cooking methods, these pieces are sliced thicker; for drying purposes the thickness was reduced.
To prepare cassava for drying, it must first be cut into sections 5-8 cm long. From these sections cut the cassava so that it is no more than 13 mm at its thickest part. The cassava will dry at a quicker rate if it is sliced similar to breadfruit and taro. Most consumers, however, are accustomed to the longer (5-8 cm) sections.
After slicing, a single layer of pieces were spread across the drying rack. The amount of product on each rack (or in the dryer) does have an effect on the total drying time. Throughout the drying process, the racks within the dryer may be rotated periodically to dry pieces in a uniform manner.
In order to achieve optimal drying conditions in the dryer, the entire solar-dryer requires rotation throughout the day. To create the most effective drying environment, the plastic face of the dryer should be in direct sunlight. This is accomplished by periodically rotating the dryer until the side of the dryer and the shadow form a continuous line.
Drying Results
The target water activity (Aw) in this research was 0.6. Generally, a water activity of 0.7 is sufficient for drying, but 0.6 was selected to insure adequate drying. Because of the nature of a solar dryer, actual drying time varied. This is a result of several variables, including the type of product, size of the product, and weather conditions. All things considered, drying to the target water activity of 0.6 took 2-3 of sunny weather.
As noted previously, the purpose of this project was to develop solar dryers that could be utilized in village or group settings. In such settings, water activity cannot be measured with modern instruments. Therefore, descriptions of these products at the target water activity were developed. When dried sufficiently, pieces should snap sharply, and have distinct dry and brittle characteristics. In addition, cracking may occur as products reach the target water activity.
Storage
Storage of the dried products plays a critical role in their future uses. During storage, several factors increased the quality and shelf-life of the product:
Package: For optimal results, Mylar™ pouches (a foil-plastic laminate) are recommended. These pouches will also require a heated sealer to create an airtight environment in the bag. If these packages are not available at stores, they may be obtained through the Church of Jesus Christ of Latter-Day Saints Distribution Services. Alternative methods are available, but these methods will decrease significantly the shelf-life of the product. Such methods include using polyethylene plastic (requiring a heat sealer), or Ziploc™ type sacks. If using an alternative method, creating an airtight environment is crucial.
Oxygen Absorbers: Before sealing the storage package, addition of oxygen absorbing packets is strongly recommended. This packet will absorb whatever oxygen that may be present, and thus reducing the chance of microbial growth. Oxygen absorbers may also be ordered through the Church of Jesus Christ of Latter-Day Saints Distribution Services. These absorbers work best when combined with the Mylar™ pouches, but may also be used with alternative packaging methods.
Environment: The storage environment is important in preserving foods, especially those not packaged in Mylar™. A dark, cool, and dry environment is most suitable for the preservation of dried foods. In contrast, a wet, warm, and/or sunlit area will decrease the shelf-life of the dried products. In addition, rodents and pests are capable of chewing through most types of packages. To remedy this, an environment free or resistant to rodents and pests is recommended.
Sensory
Before consumption of any of the dried products, rehydration must take place. This was accomplished by soaking the dried products in water for approximately 12 hours. Following this initial soaking, the product is then boiled in new water for 30-40 minutes, or until it reaches the desired texture.
Sensory testing was conducted with 100 panelists on dried and rehydrated taro. Acceptance testing showed that panelists moderately liked the appearance, aroma, flavor, texture, and overall acceptance (a score of 7 on a 9-point hedonic scale). In addition to acceptance testing, panelists were also asked under what circumstances they would eat this product. Under normal circumstances, 73% said they would eat the rehydrated taro. In an emergency situation, 97% responded they would eat the rehydrated taro.
Storage: 1 Year Analysis
After one year of storage in Mylar™ pouches, dried cassava and breadfruit were tested. The oxygen content inside the pouches was found to be below the target of .05%. Water activity measurements of the products indicated a lower water activity than when initially packaged. The combination of low water activity and low oxygen creates excellent storage conditions, preserving the overall quality and desirability of the food.
Conclusion
The objective of this research was to develop a drying and storage method that would provide the people of the Pacific Islands with a safe, quality preserved food. Sensory tests indicated that dried and rehydrated taro is acceptable by the consumer. In the solar dryer, temperatures were raised while relative humidity was lowered in comparison to ambient values. After one year of storage in Mylar™ pouches, water activity remained unchanged, while the oxygen content of the pouch measured below .05%. From this analysis, solar-drying was found to be an effective processing method for the long-term storage of cassava, taro, and breadfruit.