Effective use of multimedia (MM) in instructional design is critical for student learning, especially for large lecture introductory courses. This study used a mixed-method approach to explore the effect of food science supporting course materials that utilized different MM formats, designed with Cognitive Theory of Multimedia Learning (CTML) methods, on cognitive load as explained by perceived mental effort (PME) scores combined with students' perceptions. College students (n = 182) were randomized into 1 of 3 MM groups: audio + text + graphics (Group 1-ATG); text + graphics (Group 2-TG); or video + audio + text + graphics (Group 3-VATG). Participants answered a demographic survey and prior knowledge questionnaire before viewing 3 food science supporting course materials (that is, food laws, quality assurance, and sensory tests) and completed the PME instrument and open-ended questions online in a noncontrolled setting. For quantitative data, PME scores were compared among MM groups and content types using analysis of variance (ANOVA). For qualitative data, content analysis was applied to identify extraneous cognitive load (ECL)-related descriptors from students' open-ended question responses, which were used to explain quantitative survey findings. Overall, students in Group 2-TG had lower PME scores than Groups 1-ATG and 3-VATG (P < 0.05) and participants in Group 2-TG provided less ECL-related comments than those in the other 2 groups. Across MM groups, students showed higher PME scores after reviewing the quality assurance course material (P < 0.05). Additionally, despite higher PME scores, students from Groups 1-ATG and 3-VATG would take another course with these MM formats. Practical Implications: This study investigated the appropriate use of CTML methods when designing supporting course materials with various MM formats for asynchronous learning. The findings showed that instructors should consider different effects of MM formats when designing online course materials. In addition, instructors should apply mixed-method approach to evaluate effects of MM design on students' perceived cognitive load levels that cannot be fully understood with only quantitative survey data.