Asian Journal of Food Research and Nutrition

Aim: This study was aimed to examine the microbial and sensory quality of tomato powders using different drying methods

Study Design: This study involved the design, fabrication, and performance evaluation of a mixed solar-powered dryer optimized for drying agricultural produce, specifically Roma tomatoes. The solar dryer was constructed with a solar collector and a drying chamber, and the incorporation of forced convection to enhance the drying efficiency. The design parameters were calculated based on climatic data from Makurdi, Nigeria, including solar radiation, wind speed, ambient temperature, and product moisture characteristics. The dryer was evaluated by comparing its performance to traditional sun drying and hybrid drying methods in terms of microbial load, drying efficiency, and sensory quality. Tomato powder produced from the different drying methods were analyzed for microbial counts (yeast, mold, and total viable count), and subjected to sensory evaluation for appearance, aroma, texture, and overall acceptability. The study demonstrated that the solar dryer produced tomato powder with significantly lower microbial load and higher sensory ratings compared to traditional sun drying.

Place and Duration of Study: Department of Food Science and Technology, College of Food Technology and Human Ecology, Joseph Sarwuan Tarka University, between October 2024 to February 2025.

Methodology: An indirect solar dryer with forced convection was designed and constructed using locally sourced materials, including a 250W amorphous solar panel, plexiglass, bimetal thermostat, case fans, and a 200Ah battery. The design parameters—such as collector tilt angle, drying area, airflow rate, energy requirements, and collector efficiency—were calculated based on climatic data from Makurdi, Nigeria. Roma tomatoes were washed, sliced (5 mm thick), and dried using three methods: open sun drying, solar drying, and hybrid solar drying. After drying, the samples were milled into powder and sealed in polythene bags. Microbial analysis (total viable count and fungal count) was conducted using standard plate count methods, while sensory evaluation (appearance, aroma, texture, and overall acceptability) was performed by a trained panel using a 9-point hedonic scale. Performance parameters such as drying efficiency, drying rate, and collector efficiency were also assessed to evaluate the drying effectiveness.

Results: Microbial analysis result showed that the highest total viable count of 4.49^a ± 0.02 log CFU/g was in the raw tomato sample, followed by the sun-dried tomato powder with 4.40^b ± 0.04 log CFU/g, then the solar-dried tomato powder with 4.29^c ± 0.01 log CFU/g and 4.29^c ± 0.01 log CFU/g for the hybrid dried tomato powder.  The Fungal result showed raw tomatoes had the highest count of 3.36^a ± 0.03 log CFU/g, followed by the sun dried tomato powder with 3.29^a ± 0.01 log CFU/g, then the hybrid dried tomato powder with 3.12^b ± 0.06 log CFU/g, and the solar dried tomato powder with 3.11 ^b± 0.03 log CFU/g. Sensory analysis showed that the hybrid dried tomato had the highest score of appearance 8.00^a ±0.71, followed by the solar dried tomato powder with 7.88^a ±0.60 and sun-dried tomato powder with 6.11^b ±0.78. Aroma results showed the hybrid dried tomato and solar dried tomato powder had the same scores of 7.55^a ±0.53 while the sun-dried tomato powder had 6.00^b ±0.0.86. Texture results showed that the hybrid dried tomato powder had the highest score of 7.66^a ±0.50, followed by the solar dried tomato powder with 7.55^a ±0.52 and lastly the sun-dried tomato powder with 6.11^b ±0.60. General acceptability results showed the solar dried tomato powder had the highest score of 7.89^a±0.33, followed by the hybrid dried tomato powder with 7.78^a±0.44, and lastly the sun-dried tomato powder with 7.00^b±0.71.

Conclusion: The samples dried with the solar dryer were more acceptable than those dried by traditional sun-drying due to their considerably lower microbial load and higher sensory attributes.