Consumer Rejection Threshold of Mung Bean Protein Hydrolysate: Unsweetened and Sweetened Brewed Teas as Test Models

Mung beans (Vigna radiata L.) can be considered an environmentally sustainable food due to their nutritional value, environmental benefits, and their potential in reducing reliance on animal-based proteins. Mung bean protein hydrolysate (MBPH) is a plant-based functional ingredient; however, its application in beverages is restricted by intense bitterness. This study was the first one to determine the consumer rejection threshold (CRT) of MBPH in three beverage matrices [water, unsweetened brewed tea (USBT), and sweetened brewed tea (SBT)] to evaluate how sweetness modulated bitterness perception and, in turn, affected consumer acceptance. Sensory evaluation was conducted with 308 consumers to evaluate acceptance of overall quality and bitter taste (yes/no), hedonic rating (overall liking and liking of taste and bitterness; a 9-point hedonic scale), and preference (a 2-alternative forced-choice, 2-AFC test) of three beverage matrices across MBPH concentrations of 0.0-1.2% (w/v). Acceptance decreased with increasing MBPH concentration across all matrices, with distinct differences in CRT values among samples. Based on overall acceptance, CRT values were 0.40% MBPH for water, 0.48% MBPH for USBT, and 0.80% MBPH for SBT. CRT values based on bitterness liking were lower (0.18-0.64%) compared to those (0.24-0.76%) based on overall taste and overall liking, indicating that bitterness perception was the primary driver of rejection. The 2-AFC results showed consistent preference for control samples; therefore, CRT could not be determined using this method under the experimental condition in this study. Overall, CRT values increased from 0.18-0.48% MBPH for USBT to 0.64-0.80% MBPH for SBT, demonstrating a quantitative shift associated with matrix composition and the presence of sweetness, providing a practical strategy for product developers to enhance the palatability of plant-based beverages containing MBPH.