Microdrying: It’s A Berry Good Job
An ongoing project between Washington State University’s department of horticulture and landscape architecture, College of Pharmacy and the International Marketing Program for Agricultural Commodities & Trade (IMPACT) is studying the preservation of antioxidants and other nutritional values through various drying methods of Washington red raspberries.
It is found that microwave drying speeds up the drying time from days to hours without compromising the look or taste of the berry.
Dr. Carter Clary, assistant professor from the department of horticulture and landscape architecture, and Dr. Neal Davies, associate professor in the College of Pharmacy, are working together to discover an effective and economical drying method which retains the excellent nutritional values and fresh characteristics of red raspberries, especially antioxidant levels. “We’re trying to produce a product with better retention of volatiles, aromas and tastes,” said Clary. “One that looks nice and smells and tastes better.” There are four methods which can take days to completely dry a raspberry while compromising the look, taste, smell and nutritional value according to Clary.
The traditional method of drying fruit involves exposing the fruit to mechanical hot air dryers resulting in days of drying time. There are advantages in cost, however the fruit’s composition and appearance is greatly changed, resulting in the biggest disadvantage to traditional drying methods, Clary said. Osmotic dehydration is another method which removes water from the fruit by placing the berry in a sugar solution.
The water concentration is lower outside the berry so the water moves to the lower strength resulting in a loss of water and an infusion of sugar into the fruit, Clary said. Freeze-drying is another method and does a reasonably good job of preserving the fresh characteristics but is an expensive process, Clary said. The fourth method is low pressure dehydration where the fruit is placed in a vacuum and the pressure is lowered, taking less time to dry the fruit, Clary said.
The IMPACT supported microwave-vacuum project is a combination of low pressure dehydration and the addition of a microwave heat source, which significantly speeds up the drying time “from days to hours” Clary said. The drying reaction is taken from the skin of the berry to inside the berry where the benefits of microwave drying methods are shown. The process heats and removes water from all regions of the berry at the same time, which does not compromise the look, taste and other fresh characteristics of the fruit, Clary said.
To compare the microwave-vacuum process to other methods Clary is also using the traditional hot-air drying and freeze drying methods. In a one kilogram sample of red raspberries the hot-air drying method takes four hours to effectively dry the fruit, while the freeze drying process takes 49 hours. Compare these process times to only 90 minutes of drying time for the microwave-vacuum method and a sizeable reduction of processing time has been made. “This method provides the potential to become more economical than other methods,” Clary said. Clary’s drying methods are only one component of the project. Davies is investigating the nutritional aspect of the different drying methods.
Nutritional aspects
“Pharmacy isn’t just about drugs but promoting good health and nutrition, and the impact phytochemicals have on our health,” said Davies. Those phytochemicals come in the form of polyphenols and flavenoids which are related to the major health claims being made about raspberries. Davies, Jaime A. Yanez, a doctoral candidate under Davies, and Esteban Mejia-Meza, a doctoral candidate under Clary, are analyzing the compounds found in the fruit produced by Clary’s drying methods. They are also examining the polyphenol and flavenoid compounds in fresh fruit to form a baseline for the information gathered from the analysis. The study concentrates on seven compounds out of thousands, and the effect the different drying methods have on the compounds, in addition to the overall characteristics of the fruit.
“We observe the changes with each drying method and try to combine the good changes to get a higher compound presence, while trying to make the process more economical,” said Mejia-Meza. The project is also trying to develop a drying method that retains the highest level of antioxidants. Antioxidants are chemicals that reduce oxidative damage to cells and are associated with the aging process, according to Healthline, an online compilation of medical journals.
Antioxidants have also been linked to the prevention of cancer, cardiovascular disease and diabetes, Yanez said. “The study is designed to find out if antioxidants are present, and at what levels for each drying method,” Clary said. Antioxidants can also be supplied to the body through nutritional supplements, such as vitamins A, C, and E, along with selenium and grape seed extract, according to Healthline.
“We are working to identify the health benefits of raspberries and prove the fruit is better for you than the nutritional supplements,” Yanez said. Another component of the study is to target the main industry needs, focusing on an economically efficient product with a high nutritional value that makes the consumer happy, said Yanez.
From research to reality
Clary and Davies are collaborating with Tree Top, Inc., a grower owned apple juice company located in Selah, Washington, US, to create an effective drying method which retains fruit’s nutritional value and fresh look characteristics. The dried fruit, called “fruit inclusions”, are used to increase the nutritional value and marketability of breakfast cereals.
Clary and Davies were approached by Tree Top, Inc. regarding the company’s interest in dried fruits with fresh fruit qualities. Tree Top, Inc. does not produce cereal products but is well on their way to producing dried fruits to be included in cereal products. Tree Top, Inc. first thought freeze dried fruit would be best but later felt freeze dried products were too expensive, Clary said. “If we can prove red raspberries and other fruits maintain high levels of antioxidants throughout the drying method that equals a marketing edge for grower and value-added producers,” Clary said. “It gives Tree Top an “
Another partner in the project is the Washington Red Raspberry Commission. The Commission is hopeful the investment will identify new, cost-effective technology allowing them to sell Washington red raspberries to markets which require a shelf-stable dried product, said Henry Bierlink, executive director of the Washington Red Raspberry Commission. “We sense areas where freezing is not a good option will be open to a dried product and that the bakery market would benefit from a dried berry,” Bierlink said.