Effect of Water Activity and Microwave Heating on the Physicochemical Properties of Mexican Red Chili Peppers ( <i>Capsicum annum</i> L.): <i>De Árbol</i> and <i>Guajillo</i>

ABSTRACT Red chili peppers are important ingredients in different gastronomies around the world; they need to be exported free of pathogenic bacteria. The objective of this study was to evaluate how water activity affects microwave heating for De Árbol and Guajillo red chili peppers and their physicochemical properties. Chilis were adjusted to three values of water activity ( a w ) ~0.4, 0.5, and 0.7 in humidity chambers with oversaturated salt solutions. Adjusted samples were subjected to microwave (MW) heating (2450 MHz, 300 W) to reach 70°C, reported as temperature to control Salmonella in low moisture foods. Dielectric properties and penetration depth were determined to assure sufficient wave penetration. The MW heating was followed by a cooling stage with forced air. Decreasing in a w resulted in increasing heating time to achieve the target temperature. Also, moisture content was decreased after treatment ( p &lt; 0.05) but accomplishing the Mexican standard for moisture content in chilis. With MW heating and water condition, De Arbol chilis exhibited moisture content between 5.88% and 6.14% (w.b.), while Guajillo chilis had values between 10.16% and 15.33% (w.b.). Color remained mostly unchanged for De Árbol chilis ( p &gt; 0.05), with net color difference (Δ E ) lower than 10. Under the studied conditions, MW application is a suitable alternative for De Árbol and Guajillo chili varieties, maintaining the physical characteristics required for their trade.