Obesity, a global health concern, necessitates reducing sugar and fat intake while maintaining desirable sensory experiences. Common strategies involve sugar substitutes, but these often negatively impact flavor. Alternatively, enhancing perceived sweetness through multisensory approaches or structural modifications shows promise. Previous research demonstrated that altering food structure can affect taste perception; for example, uneven sugar distribution increases sweetness in semi-solid systems, and modifying chocolate-hydrocolloid composites using fused deposition modeling (FDM) amplified sweetness perception. This study explores inkjet printing's potential for precise spatial control of sweeteners, aiming to understand how thaumatin's distribution affects sweetness perception. Inkjet printing offers high precision and allows for creating complex patterns, unlike manual layering techniques. The study used inkjet printing to create different dot patterns of thaumatin on chocolate surfaces, maintaining a constant total thaumatin amount per sample. The goal was to determine how the spatial arrangement of thaumatin impacts sweetness perception, offering a potentially more effective and versatile method for enhancing sweetness compared to traditional manufacturing.

The researchers reviewed existing literature on strategies to reduce sugar and fat in food while maintaining palatable sensory profiles. They highlighted the challenges of using non-nutritive sweeteners due to potential adverse effects on flavor. The literature review covered studies on multisensory approaches to enhance sweetness, such as combining visual or olfactory cues with taste. Furthermore, it addressed the emerging area of using structured food design to manipulate taste perception. Existing research demonstrated that altering food structure, such as creating gradients of sweetness within a gel or altering the macroscopic structure of chocolate-hydrocolloid composites, could lead to a perceived increase in sweetness. The use of additive manufacturing techniques, specifically inkjet printing and fused deposition modeling, to create complex food structures and influence taste perception, was also discussed.

Printable inks were formulated by emulsifying thaumatin (at varying concentrations) in water and incorporating it into a cocoa butter matrix. The rheological and calorimetric properties of these inks were characterized to ensure consistent printing and melting behavior. A high-speed inkjet printing system was employed to create various dot patterns on chocolate surfaces, including uniformly distributed patterns and patterns where thaumatin dots were concentrated at the center or periphery of the sample. Seven samples with different dot patterns and thaumatin concentrations were produced while maintaining a constant total thaumatin amount. A sensory panel (14-17 trained participants) evaluated perceived sweetness intensity at three time points (start, maximum, and end of consumption). A tongue-inspired biomimetic surface was created using additive manufacturing to simulate the melting and distribution of thaumatin dots during consumption. The data were analyzed using two-way ANOVA and a post-hoc Tukey test.

Sensory evaluation revealed a significant increase in perceived sweetness intensity in samples with surface-concentrated thaumatin compared to a reference sample with uniformly distributed thaumatin. The amplification of sweetness perception reached up to 300% at the start and peak of consumption, and 200% at the end, regardless of the specific dot pattern. However, concentrating thaumatin only in the center of the sample resulted in a 24% decrease in maximum sweetness perception compared to peripheral concentration. The findings suggest that both the proximity of thaumatin to taste receptors and its spatial distribution significantly influence sweetness perception. Analysis of the biomimetic tongue surface experiments suggested that the resolution of the micro-structured patterns was too fine for the tongue's oscillatory motion to impact the rapid spread of thaumatin, explaining the lack of significant perceptual differences among micro-structured samples. Conversely, when the distance between the areas rich in thaumatin was larger (mesoscale level), the distinct activation of different regions on the tongue led to altered sweetness perceptions. A linear relationship was observed between the initial stimulus size (contact area between tongue and dots multiplied by thaumatin concentration) and perceived sweetness intensity, indicating that both factors equally affect thaumatin release during oral processing.

The results support the hypothesis that the spatial arrangement of thaumatin significantly impacts sweetness perception. The substantial amplification of sweetness observed when thaumatin is concentrated on the surface demonstrates the potential of this inkjet-based surface structuring technique for enhancing taste perception. The difference in sweetness perception between central and peripheral concentration of thaumatin highlights the importance of considering the spatial arrangement of taste stimuli on the tongue and regional differences in taste sensitivity. The biomimetic tongue model provided insights into the dynamics of thaumatin release during oral processing, which will inform the design of future food structures. The linear correlation between stimulus size and perceived sweetness suggests that the initial contact area and concentration of thaumatin are key factors influencing taste perception. This approach provides a versatile tool for creating foods with tailored sensory experiences.

This study successfully demonstrated the use of inkjet printing to create spatially controlled patterns of thaumatin on chocolate surfaces, resulting in a significant enhancement of sweetness perception. This novel technique provides a powerful tool for food manufacturers to create products with optimized sensory profiles. Future research could explore the application of this technique to other sweeteners and food matrices, investigate the interaction between texture and taste perception in these structured foods, and develop more sophisticated models of taste perception to predict the sensory experience of consumers.

The study's sensory evaluation was conducted at home due to COVID-19 restrictions, which could have introduced variability in testing conditions. Visual differences between the samples may have subtly influenced the sensory perception of the participants, and the influence of hedonic factors on taste perception was not fully accounted for. The biomimetic tongue model simplified the complex dynamics of oral processing, and future studies should incorporate a more comprehensive model of saliva flow and interactions with food structures. The current focus was limited to sweetness; interactions with other tastes remain an avenue for future research.