Edible coatings to improve storability and enhance nutritional value of strawberries (Fragaria ananassa) and raspberries (Rubus ideaus) Public Deposited

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  • Strawberries {Fragaria ananasa) and raspberries {Rubus ideaus) are good sources ofmany important nutrients, and have great potential to improve human health. However, they are highly perishable and have a very short shelf-life mainly due to the attack of fungi and high respiration rate. Edible coatings, especially chitosan-based coatings have been considered to extend shelf-life of fresh berries by inhibiting the growth of fungi, controlling respiration, and preventing moisture loss through a semi-permeable coating formed on the surface of the berries. In addition, edible coatings may be used as a carrier of functional ingredients to further enhance quality, safety and nutritional value of the product. The objectives of this study were to develop chitosan-based coatings containing high concentration of calcium or vitamin E, to examine the storability of coated berries, and to evaluate the sensory properties of coated fruits. Three 2% chitosan-based coatings including chitosan alone, chitosan containing 5% of Gluconal® CAL (a mixture of calcium lactate and calcium gluconate), and chitosan containing 0.2% of vitamin E (a-tocopheryl acetate) were developed. A 1% acetic acid solution was used as a solvent for dissolving chitosan. Fresh strawberries and raspberries were dipped in the coating solutions twice and dried in the room temperature under blowing air. Berries were then stored at 2°C and 88-89% RH or -23°C for their shelf-life evaluation. Chitosan-based coatings proved to extend shelf-life of fresh strawberries and raspberries up to 2 and 3 weeks, respectively, by reducing the incidence of decay, weight loss, and delaying changes in color, titratable acidity and pH. The coatings also helped maintain quality of frozen strawberries by reducing drip loss and improving firmness. Chitosan coatings containing high concentration of calcium or vitamin E significantly increased the content of these two nutrients in the coated samples. A 100-gram sample of coated berries contain about 34 to 58 mg of calcium or 1.70 to 5.86 mg of vitamin E depending on the type of berries and the time of storage, while uncoated berries only contain 19 to 21 mg of calcium or 0.25 to 1.15 mg of vitamin E. For evaluating the sensory properties of coated berries, four 1% chitosan-based coatings were developed: chitosan dissolved in 0.6% lactic acid, chitosan dissolved in 0.6% acetic acid, chitosan dissolved in 0.6% lactic acid containing 0.2% vitamin E. Consumer test and free-choice profiling trained panel were used to evaluate the sensory properties of the coated strawberries. Both consumer tests of 1 day and 1 week after coating indicated that lactic acid and acetic acid dissolved chitosan coatings increased the appearance acceptance of the strawberries, but coating containing vitamin E decreased appearance of strawberries; chitosan coatings did not change sweetness and firmness compared to the uncoated berries. The 1% chitosan coating solution did not extend the shelflife of the strawberry after 1 week of storage. Trained panel results after storage of 1 week and on the selected samples after storage for 2 and 3 weeks showed that lactic acid dissolved chitosan coatings increased the glossiness of the strawberry, while chitosan coating with vitamin E increased the waxy and white of the strawberries. The trained panel did not detect any astringency in the samples, and vitamin E fortified coating tended to help maintain the overall strawberry flavor of the strawberries compared to other treatments at the same storage time. Overall results indicated that 2% chitosan coatings can extend the shelf-life of fresh berries during cold storage, and 1% chitosan coating helped reduce the astringency of coated strawberries. However, 1% chitosan did not work as effectively as 2% chitosan to protect berries from mold deterioration. More studies are needed to improve the coating technology and make the technique practical and the product acceptable by the consumers.
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