Sensory analysis and in vitro assays are the two main methods that researchers use to investigate bitterness and astringency in foods and beverages. Choosing the most suitable method for a particular research question requires an understanding of the differences between these two approaches, as each has advantages and disadvantages. However, the increasingly widespread belief is that both approaches should be used in tandem.

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Sensory analysis is a method of evaluating the taste properties of foods and beverages. This method involves using trained panels of human tasters to evaluate the intensity, quality, and hedonic response (liking or disliking) of specific taste properties such as bitterness and astringency. Sensory analysis is often considered the gold standard for evaluating taste properties because it is the most direct method of assessing how humans perceive taste. It also takes into account the complex interactions between different taste properties, as well as other factors such as aroma, texture, and appearance.

However, sensory analysis does have some limitations. The results can be affected by the individual differences in taste perception among the tasters, as well as their fatigue during the evaluation. Also, sensory analysis is relatively time-consuming and expensive, which limits the number of samples that can be evaluated.

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In the specific case of astringency and bitterness the limitations of sensory analysis can be more critical. Firstly, astringency and bitterness are complex sensations that can vary greatly depending on the individual's sensitivity and personal perception. As such, different tasters may rate the intensity and quality of these attributes differently, leading to inconsistent results. Second, a fully qualified panel is required to distinguish between astringency and bitterness, which are frequently confused by consumers. Additionally, sensory analysis may not be suitable for evaluating highly concentrated or extreme levels of astringency or bitterness, as it can cause discomfort and even pain to the tasters. Lastly, sensory analysis is time-consuming and costly, which limits its applicability for large-scale studies or routine quality control in food and beverage industries.

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Despite all these limitations, sensory analysis remains a valuable tool for evaluating taste attributes in a controlled and systematic manner, and its results can provide useful insights for product development and optimization.

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In vitro assays, on the other hand, are laboratory-based methods of evaluating the taste properties of foods and beverages. These assays involve using chemical or biological techniques to measure the interactions between specific taste compounds and their target receptors (e.g. bitter taste receptors) or biological components involved in the perception mechanism. In vitro assays can provide quantitative data on the bitterness and astringency of foods and beverages and are generally quicker, high-throughput and more cost-effective than sensory analysis.

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Regarding astringency, the most common chemical assays available for assessing astringency in food and beverage is the protein precipitation assay, which involves adding a test solution or beverage to a solution of a protein, such as bovine serum albumin, or more frequently human saliva, and measuring the amount of protein that is precipitated. Since astringent compounds are known to interact with proteins and cause precipitation, the extent of precipitation can be used as an indicator of astringency. However, it is important to note that these assays may not fully capture the complex and dynamic interactions that occur between astringent compounds and proteins in vivo.

Regarding the biological methods, one of the most common methods are the cell-based assays, which involve using human cell lines to evaluate the binding of astringent compounds to cells.

However, in vitro assays have their limitations as well. They often do not take into account the complex interactions between different taste properties, and they can be limited by the availability of specific receptors or other factors that may affect taste perception in humans. Additionally, in vitro assays cannot account for the variation in taste perception among individuals or the variability in the way taste compounds are absorbed and metabolized by the human body.

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In conclusion, both sensory analysis and in vitro assays have their strengths and weaknesses when it comes to studying bitterness and astringency in foods and beverages. Sensory analysis is the most direct method of evaluating taste perception, but it is time-consuming and expensive. In vitro assays are quicker and more cost-effective, but they may not take into account the complex interactions between different taste properties and the variability in taste perception among individuals. Depending on the specific research question, one method may be more appropriate than the other but more recently the simultaneous application of both approaches has been shown to have a huge potential on moving forward to decipher astringency and bitterness perceptions.