Moisture diffusivity of fresh and spoiled tissues measured by thermogravimetric analysis

Presenting author: Luis Vargas

Co-author: Hao Feng

Department of Food Science and Human Nutrition

Softening and spoilage are major factors determining shelf-life of fruits and vegetables. Microbial proliferation and metabolic factors both contribute cell-wall degradation, causing produce tissue softening and deterioration. Around 36 million tons of food waste is generated in the U.S, and 15% of the waste is pre-consumed produce. This creates losses in food, energy, and water, causing environmental issues. Waste produce can be dehydrated and used as a partial replacement of animal feed. Moisture diffusivity (Deff) is the coefficient in the Fick’s law that is important for the analysis, design and optimization of a drying process. This parameter varies depending on product characteristics such as moisture content, processing conditions and internal structure. This study was undertaken to examine changes in moisture diffusivity of fresh and spoiled produce tissues Fresh strawberries (SB) and bell peppers (BP) were obtained from a local retailer. Spoilage was induced by exposure to room temperatures (25±2°C) and 40±5% relative humidity for up to 7 days. Excised samples (0.8×0.8cm) were obtained from fresh and spoiled SB and BP, and dried with hot air at 70°C for 350 minutes. The Deff of SB and BP tissues were determined from drying curves produced with a TA Instruments Q50 thermogravimetric analyzer, using the slope method. Yeast and molds (YM) counts of fresh and spoiled tissues were determined. Spoiled SB had a faster drying rate than the fresh counterpart when stored for 4 days at 25°C. No significant differences in Deff were observed in the first 3(SB) and 5(BP) days of spoilage. Higher Deff in the first falling rate was observed in BP. Up to 4 log CFU/g increase in YM counts after 7 days storage. SEM and µ-CT scan analysis showed differences in microstructure due to spoilage. Produce samples with spoilage had a faster drying rate and thus higher Deff than fresh material, thus less time and energy could be used to dry them into animal feed.