Passion fruit drying using refractance window dryer and evaluation of output powder as ingredient for yogurt
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Passion fruit (Passiflora edulis) has a pleasant flavor, aroma and is high in vitamins and phytochemicals. This makes passion fruits a potential ingredient in various products like yogurt. However, the utilization of passion fruits is limited by their perishability. In this study, the optimum conditions for drying passion fruit puree using refractance window drying technology RWDT) were determined and used to produce passion fruit powder which was evaluated as a flavoring ingredient for yogurt. Response surface methodology (RSM) was used to optimize the drying temperature and time. Moisture content, vitamin C, ß-carotene and total phenolic content and total antioxidant activity were considered as the response variables. Optimal drying temperature and time conditions were found to be 82.5 °C and 60 min, respectively. The respective values for ascorbic acid, moisture, ß- carotene, total antioxidant activity, and total phenolic content under optimal drying conditions were 58.8 mg/100 g solids, 11.1% wb, 8.8 μg retinol activity equivalent (RAE)/100g solids, 367.6 mg/100 g solids vitamin C equivalent (VCE) and 352.2mg/100 g solids gallic acid equivalent (GAE) respectively. All models for prediction of these values were satisfactory and had a non-significant lack of fit (p<0.05). This indicates the suitability of the model in optimizing the refractance window drying operating conditions for the production of quality passion fruit powder. Addition of refractance window dried passion fruit powder to yogurt resulted in a significant reduction in syneresis, increase in viscosity, phytochemicals content and improvement in sensory acceptability, in comparison to plain and commercial flavored yogurts. The results show that the nutritional, nutraceutical and sensory properties of yogurt can be enhanced by addition of refractance window dried passion fruit powder.