Effect of newly developed tunnel dryer on shelf-life of dried fruits under ambient and chilled condition

Abstract

The CSIR-FRI is engaged in a collaborative project with the German Technical Cooperation (GTZ) Office in Ghana as part of the on-going Market Oriented Agriculture Programme (MOAP) of the Ministry of Food and Agriculture of Ghana. One of the activities of this CSIR-FRII GTZ / MOAP collaboration has developed a cost-effective drying facility for processing fruits and vegetables. This is a tunnel dryer which operates on hot-air generated through steam which is circulated round the tunnel. As part of test-running of this dryer, samples of banana, coconut, mango, papaya and pineapple slices produced by Nature's Best Fruit Limited were dried in this dryer and the shelf-lives stabilities of the dried products assessed over a period of one year under two storage conditions. Nature's Best Fruits Limited is one of the private entrepreneur through whom the CSIR-FRII GTZI MOAP project is assessing the technical feasibilities of the technologies it is developing. The two storage conditions used were room temperature 28 ± 2°C and chilled-room temperature 18± 2°C all at humidity conditions of 78 ± 4% RH. The shelf-life indices monitored over the 12 month period were the physico-chemical, microbiological and sensorial properties of the stored products. Under the physico-chemical properties, moisture contents remained relatively stable throughout the storage period averaging from 3.13,10.89, 11.56,12.05 to 12.29 %, respectively for dried coconut, papaya, mango, banana and pineapple. The corresponding water activity values were equally stable ranging between 0.54 and 0.56. These low water contents accounts for the microbiological stability of the products throughout the storage period. The absence of coliforms, E. coli, Staph and Salmonella is an indication that good hygienic and manufacturing practices were strictly adhered to by the Nature's Best Fruits Ltd during the production of the samples. The colours as measured using the trismulus system of all the products stored under the chilled room condition were much brighter and more acceptable than those under the room temperature conditions. Non-enzymatic browning was much more pronounced in the banana slices than the rest of the products. There was no significant deterioration in the Vitamin A and C contents of the dried fruits. The total soluble solids (indicated by the Brix) and pH remained unchanged during the whole period of storage. The free fatty acid levels of the coconut slices even at the end of 12 month's storage were within internationally acceptable levels for commercial desiccated coconut. A trained panel of 15 used to monitor the sensory parameters of the stored samples gave relatively high scores for taste, smell, mouth-feel, hand-feel and overall acceptability sensory parameters for the first 8 months. The results of colour parameter were consistent for the pineapple, mango, papaya and coconut samples especially under the chilled-room storage condition but slightly variable under the room temperature condition. From the 8th month, the scores for the sensorial parameters started decreasing significantly especially for products under the room temperature conditions. In particular, the colour score for the dried banana slices was very low. All the dried products passed the microbial and physico-chemical and sensorial specifications by the Organic Food Production Act (www.organicGuide.com) as well as the specifications of the present importing company of Nature's Best Fruits Ltd which is the Meridian Organic Foods Company of Stuttgart, Germany. The conclusion is that the optimal shelf-life duration for dried pineapples, papaya, mango and coconut, established through this study, under the room condition (average 29 DC and 75 % RH) was 8 months whilst that for the chilled-room temperature (average 19 DC and 75 % RH) condition is 12 month. The shelf-life duration for dried banana slices established under both storage conditions was 8 months