Developing healthy snack chips by continuous vacuum belt drying
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Low-fat tortilla chips and sweet potato chips were developed by a continuous vacuum belt drying (CVD) method and compared to those made by deep fat frying (DFF). Quality factors of the products were investigated including oil content, texture attributes, color, sensory properties, shrinkage and nutrient retention. Drying characteristics such as drying time, diffusivity, and drying models were studied in this research. A continuous vacuum drying method was used to develop low-fat tortilla chips and sweet potato chips with good sensory properties. The CVD chips developed an expanded structure and contained 1.57-1.82 g oil/100 g, depending on initial thickness, compared to 33.37-34.80 g oil/100g for DFF chips. Three levels of chip thickness and three levels of plate heating temperature were studied to show how the drying conditions affected the quality of tortilla chips and the amount of energy consumed. Several drying models were investigated to test their applicability to CVD tortilla chips. The models can be used to predict drying times and optimize drying processes, and provide insight into the mechanisms of drying and the importance of product properties. Model was developed from the drying rate curves that incorporated a characteristic drying coefficient [k(t)] that varied with time. All models had good agreement between experimental data and predicted data, with r2>0.98. With consideration of other goodness-of-fit indicators (SSE and χ2), results showed that the model that incorporated k(t) gave the best fit. The color, texture, microstructure, and β-carotene content of CVD sweet potato chips were studied and compared to DFF chips. The results showed that continuous vacuum belt drying gives good color and nutrient retention in the sweet potato chips, and that CVD chips had similar texture attributes to those prepared by deep fat frying. Low temperature (100°C) vacuum dried products had the most similar color values (L* C* H*) to fresh sweet potatoes. Chips dried at a sequence of temperatures (T-mix=140/120/100°C) had the lowest hardness and highest fracturability, and were most similar to DFF chips.