*5.3.1 Interaction with proteins*

In food matrices, PC interaction with proteins may affect their physicochemical properties, and consequently, their sensory characteristics. The sensory implications of PC interaction with proteins are not just centered on taste. Indeed, these interactions can also influence the appearance (e.g. haze, color), aroma and texture of food products.

One of the most known effect of this interaction is haze formation in some plantbased beverages like beer, wine and fruit juice [138]. Consumers expect that these beverages are clear (free of turbidity) and to remain so during the shelf life of the product. The development of haze in beverages results in the formation of insoluble particles of colloidal or larger size that can be detected visually. This is often noted as a negative attribute affecting their acceptance and the likelihood of this product to be purchased again. Astringency and bitterness are also affected by the development of haze. Indeed, red wine astringency can be reduced by the addition of some fining agents (ovalbumin, gluten proteins or yeast protein extract) which remove reactive compounds capable of haze formation [139]. Also, in beers, the interaction between PC and malt proteins causes haze and flocculation which can be modulated by adding some fining agents that will help in the process of clarification [140]. However, fining agents should be used appropriately as they could also compromise

the flavor and the overall quality of the final product. Moreover, the use of fining agents can also remove a considerable amount of PC compromising their potential health benefits. Another example of PC interaction with proteins in beverages is the case of tea. In fact, tea astringency can be rectified by the addition of milk in which PC (flavan-3-ols) interact with milk proteins (casein and whey protein) [141].

Grace and colleagues [142] studied the effect of the fortification of soy protein isolate with concentrated PC-rich fruits and vegetables (muscadine grape and kale) by sensory analysis. These authors observed that the appearance of the incorporations had resulted in different colors, a purple-red powder for the incorporation with muscadine due to the presence of anthocyanins, and a mid-intensity green with kale caused by chlorophyll incorporation into the matrix. Also, panel evaluators indicated that unfortified protein formed clumps in the mouth, while the fortified muscadine and kale matrices presented a creamy consistency in the mouth. Furthermore, the panel evaluators mentioned that muscadine-protein matrix presented a pleasant flavor with delicate notes of grape aroma, slight astringency, no bitterness, and low sourness in comparison with unfortified soy protein. On the other hand, soy protein fortified with kale showed a reminiscent flavor of cooked beans, moderate sweetness, low sourness, and no bitterness.

In all these examples above mentioned, PC interact with proteins in food matrices, contributing to a lower amount of PC available to interact with oral cavity constituents, including salivary proteins, resulting in a decrease of astringency perception [143] and also bitter taste.

#### *5.3.2 Interaction with lipids*

Contrary to PC-protein interactions that have been widely studied, interactions with other food constituents such as lipids are lacking a deeper and comprehensive research. The main references to the interaction between PC and food lipids concern on plant oils, especially olive oil. Bitterness is a key sensory attribute in olive oil determining its acceptability. However, the lipid matrix composition seems to be a determinant factor on the perception of bitter taste. García-Mesa and colleagues [144] demonstrated that two virgin oil matrices spiked with the same level of PC were able to produce different effects on bitterness, depending on the degree of unsaturation of the olive oil matrix. The most unsaturated matrices resulted in softer sensations and reduced bitterness in comparison with the less unsaturated ones.

The interest on using PC as food additives in food lipid matrices has also been growing. Indeed, lipid oxidation is the main source for food quality deterioration and generation of undesirable odors and flavors, compromising shelf-life, changing texture and color and reducing the nutritional value of food [4]. The use of green tea catechins as food additives with antioxidant properties is a good tool to increase the shelf life and to decrease the susceptibility of oxidative damage of food products. Furthermore, as previously referred, tea PC are able to interact with milk proteins suggesting a good retention in the cheese matrix [145]. Giroux and colleagues [145] evaluated the effect of green tea extract enrichment on the texture and organoleptic properties of Cheddar cheese during storage. The main effects observed were a decrease in the typical cheddar flavor, an increase in the global flavor intensity and astringency, color changes and increase in hardness. Nevertheless, the impact of green tea enrichment was dependent on the concentration used.

#### *5.3.3 Interaction with carbohydrates*

The first evidence of the interaction between PC and carbohydrates can be observed in fruits in which they interact in plant cell wall. Several classes of PC

#### *Eat Tasty and Healthy: Role of Polyphenols in Functional Foods DOI: http://dx.doi.org/10.5772/intechopen.96577*

have already been described to interact with carbohydrates such as anthocyanins, phenolic acids and procyanidins [143].

In the case of red wine, PC are the main contributors to color, astringency and bitterness. Several authors have reported that yeast mannoproteins interaction with PC have numerous effects on wine sensory properties, namely on color stabilization [146], reduction of astringency [147] and increased body and mouthfeel [148]. In fact, the formation of PC-carbohydrate complexes influences their association with salivary proteins leading to a decrease on astringency perception. The same reduction trend on astringency was observed for other matrices, in which soluble pectins were added to persimmon fresh juice, resulting in the complexation with soluble tannins [149]. The interaction between PC and carbohydrates depends on their structure and physicochemical properties (e.g., ionic character and viscosity). Indeed, carbohydrates which present higher viscosity can greatly affect sensorial properties. Peleg and coworkers [150] observed that the increase of viscosity of a PC-rich cranberry juice by the addition of carboxymethyl cellulose lowered the perceived astringency at 25 °C.

In conclusion, interactions between PC and macronutrients can occur in food items and impact their sensory properties. The design of new foods with high nutrient content, tasty and affordable could be a good tool to increase the consumption of these bioactive compounds. However, the creation of these foods without comprising quality, sensory properties and functionality remains a big challenge.

At the end, most of the studies based on supplementation of food products with extracts, or with food industry by-products rich in PC are somehow empiric approaches. They find an optimal dose of an extract, by-product or waste or able to have a high expected (functional/biological) activity while the negative side-effects (e.g. low loaf volume, undesirable taste properties and textural characteristics) are minimized. While this trial-error has led to some successful examples, the use of this knowledge by the food industry depends on a more systematic approach. A deep and extensive characterization of the PC profile of the extracts, by-products and wastes should be a critical point in these studies. Furthermore, consistent data regarding the binding of the PC with food matrix components, the effect of cooking practices as well as the final bioactivities are lacking. These topics will be a valuable tool to align tastiness to healthiness in a systematic and reliable way to aid food industry towards the development of functional and clean label food.
