Evaluating consumer affective thresholds in high protein beverages using different approaches : a thesis presented in partial fulfilment of the requirements for the degree of Master of Food Technology at Massey University, Manawatū, New Zealand. EMBARGOED until 27 September 2028.

Abstract

Understanding how sensory attributes influence consumer rejection is critical for guiding the development of functional foods, such as high-protein dairy beverages. This study compared three consumer affective threshold methodologies: paired preference, liking, and binary rejection to determine thresholds for three sensory attributes in protein beverages. Consumers (N=142) performed 2-AFC preference tests and evaluated four sample series: a control and four samples with decreasing sweetness (sucralose at 0–5% sugar equivalence), four with increasing thickness (50– 350 cP), and four with increasing powdery mouthfeel from added whey protein (0–10%). Seven additional samples completed a central composite rotational design to examine sweetness and thickness thresholds simultaneously. Sensory panel descriptive analysis, instrumental characterisation, and ingredient composition were used as stimulus intensity measures. Thresholds varied significantly by methodology, with sweetness thresholds ranging from 1.7% to 4.2% sugar equivalence, thickness thresholds from 245 cP to beyond the tested range, and powderiness thresholds from 3.6% to 8.7% WPC. Consumer segmentation greatly influenced threshold positioning, highlighting individual differences. Sweetness was the strongest driver of rejection, both individually and in combination with thickness. Methodological comparisons demonstrated distinct strengths and limitations, reinforcing the need to tailor threshold methodology selection to research objectives. Paired preference was effective for detecting small changes relative to a control, whereas liking and binary rejection provided greater flexibility in assessing broader acceptability. Integrating consumer reasoning behind acceptability added insights; sensory properties were the primary drivers of acceptability, but factors such as ease of drinking, expected purchase satisfaction, and product expectations also influenced consumer decisions.