Incorporating Polyphenols In Baked Products

Health Benefits of Polyphenols

Polyphenols have long been associated with health and with improvement in nutrition for humans and animals. A number of human foods and pet foods extol the virtues of these compounds in general or focus on a particular type as a major benefit (Williamson, 2017). The main benefits are listed here:-

1. Antioxidant Properties: Polyphenols are powerful antioxidants, capable of neutralizing free radicals that can cause oxidative stress and damage to cells. The inclusion of polyphenol-rich ingredients in baked goods, such as berries or dark chocolate, can enhance the antioxidant capacity of these foods, potentially offering health benefits to consumers.
2. Anti-inflammatory Effects: Chronic inflammation is a precursor to many diseases, including cardiovascular diseases, diabetes, and cancer. Polyphenols can modulate inflammatory pathways, reducing the risk of chronic diseases. Baked goods containing polyphenol-rich ingredients might therefore contribute to an anti-inflammatory diet.
3. Potential Anti-carcinogenic Properties: Certain polyphenols, like flavonoids and phenolic acids, have been studied for their potential to inhibit the growth of cancer cells. While the baking process may alter their structure, some polyphenols retain their bioactivity even after being subjected to heat, thus contributing to the preventive aspect of cancer.
4. Cardioprotective Benefits: Polyphenols can improve endothelial function, reduce blood pressure, and inhibit platelet aggregation. Incorporating polyphenol-rich ingredients in baked goods, such as nuts or seeds, may help in maintaining cardiovascular health.
5. Improved Digestive Health: Polyphenols may act as prebiotics, promoting the growth of beneficial gut bacteria. Baked foods that include polyphenol-rich ingredients can contribute to a healthier gut microbiome, which is linked to better overall health.

Influence on Food Quality

Food quality is affected by a number of factors but here are the main ones listed:-

1. Flavour and Aroma: Polyphenols can significantly influence the flavour profile of baked goods. They often impart astringency and bitterness, which can be desirable in certain products like dark chocolate and certain breads. The Maillard reaction, a chemical reaction between amino acids and reducing sugars that occurs during baking, can also be influenced by polyphenols, leading to a complex array of flavours and aromas.
2. Colour and Appearance: Polyphenols contribute to the colour of many foods through their interaction with other components during the baking process. For instance, anthocyanins, a type of polyphenol found in berries, can impart a vibrant colour to baked goods, making them visually appealing.
3. Texture and Mouthfeel: The presence of polyphenols can affect the texture of baked products. They can interact with proteins and starches, influencing the dough’s rheological properties and the final product’s texture. For example, the addition of polyphenol-rich ingredients like nuts can add crunch, while fruit purees can contribute moisture and softness.

Food quality is a a function of a number of factors including the ingredients used and the processing required. When it comes to baked foods, wholegrain cereals are generally recognised as being healthier than those that have been refined. The main reason is the presence of greater amounts of phenolics and dietary fibre. Even though processing alters the properties of the ingredients there is enough polyphenol left to exert an impact on the food. The phenolics are the main antioxidants and help protect food componentry but when ingested have diverse nutritional benefits.

Challenges in Baking with Polyphenols

The benefits as well as the issues associated with polyphenols in baked goods is of considerable interest (Ou et al., 2019)  and they are summarized here:-

1. Thermal Stability: One of the primary challenges of incorporating polyphenols in baked goods is their thermal stability. Many polyphenols are sensitive to heat and can degrade during baking, leading to a loss of their beneficial properties. It is well established that compounds will break down on heating as the polyphenols used in cereals which are commonly used in baking suffer the same fate. What is not so well established is which ones and to what degree. The main phenolic compounds in cereals are ferulic and coumaric acids. The amount of free phenolic acids in general increases at the expense of the bound polyphenolics (Abdel-Aal & Rabalski, 2013). On that basis baking raises the amount of freely formed polyphenolics. Other compounds behave slightly differently.  For example, catechins in green tea are known to degrade at high temperatures, which can reduce their antioxidant capacity.
2. Interaction with Other Ingredients: Polyphenols can interact with other ingredients in the dough, such as proteins and carbohydrates. These interactions can sometimes result in the formation of complexes that may reduce the bioavailability of polyphenols, thereby diminishing their potential health benefits.
3. Bitterness and Astringency: While these attributes can be desirable in certain products, they can also be a drawback. The bitterness and astringency of some polyphenols can be off-putting to consumers, especially in sweeter baked goods. Balancing these flavours to create a palatable product can be challenging.
4. Consistency and Uniformity: Ensuring consistent quality in baked goods containing polyphenols can be difficult. Variations in polyphenol content and composition, depending on the source and processing methods of the ingredients, can lead to inconsistencies in flavour, colour, and texture
5. Natural Sources of Polyphenols: Polyphenols are invariably bound in the natural state by esterification to oligo- or polysaccharides and
   form bridges between the polymer chains in the kernel. Their freedom to operate in any food during processing and through their bioavailability for absorption is dependent on their degree of release from the bound state at any time during processing and storage. 

Potential Drawbacks of Polyphenols in Baked Foods

1. Reduced Bioavailability: Most polyphenols show low stability on heating so it is of little surprise that they will be retained adequately in the food. Likewise then, the bioavailability of polyphenols can be significantly affected by the baking process. Heat can lead to the degradation or transformation of polyphenolic compounds, making them less absorbable by the human body. Additionally, polyphenols can bind to dietary fiber, proteins, or minerals, reducing their absorption.
2. Antinutritional Factors: Some polyphenols can act as antinutrients by binding to minerals like iron, calcium, and zinc, thus inhibiting their absorption. This can be particularly concerning for individuals who rely on baked goods as a significant part of their diet, potentially leading to mineral deficiencies. There are cases of polyphenols such as catechols forming benzoquinone which induces tumours and leukaemia even. Compounds such as quercetin, chlorogenic acid and caffeic acid will form catechol when heated (Ravber et al., 2016) so baking may not be as attractive a proposition if the level of such reaction products becomes a health issue.
3. Impact on Shelf Life: While polyphenols have antioxidant properties that can extend the shelf life of baked products by inhibiting lipid oxidation, they can also be susceptible to oxidation themselves. This can result in changes in colour, flavour, and overall quality over time.
4. Sensory Acceptance: As mentioned earlier, the strong flavours associated with some polyphenols can limit their use in certain types of baked goods. The bitterness and astringency might not be well-received by all consumers, especially in products traditionally expected to be sweet. One of the main issues is the impact on colour as well as texture (Almaski et al., 2017).
5. Cost and Accessibility: Polyphenol-rich ingredients can sometimes be more expensive and less accessible than their conventional counterparts. This can increase the cost of production and potentially the retail price of the final product, making it less accessible to a broader audience.

The key aspect though is that even when the polyphenol content is reduced there is still enough to produce a considerable benefit.

Examples Of Polyphenol Addition

Bread is one of our most important staples. Fortification of bread with iron, with vitamins, fibre and other minerals has been a common theme of product developers and nutritionists seeking opportunities to improve the value and quality of this food. Those ideas have naturally extended to other baked foods in due course.

Fibre has long been added to food and there are numerous example to cite. They’ve also been added along with polyphenols as when shortbread biscuits were enriched with a ‘coarse fraction’ of barley flour (Verado et al., 2011). They assessed the stability of the biscuits compared to a control using just ordinary what flour. It is a good example of how particular grain fractions such as flour contain a range of components which all bring particular unique benefits. The same type of contribution is made from other grains in the form of oat flour, buckwheat etc. Many of these health benefits are put down to the presence of beta-glucans which have well established heart health claims associated with them. However, the presence of polyphenols too such as the flavan-3-ols cannot be overlooked either. Adding the barley flour fraction raised the level of flavan-3-ols from 0.6 mg/100g in the biscuit to 4.3 mg/100g. That was almost a 10 fold rise. The baking process caused the loss of 2/3rds of the flavan-3-ol content which illustrates how susceptible many of these polyphenols are to heat processing of any sort. The stability results were mixed which is another illustration of whether addition improved the functional performance of the biscuit. In this case lipid oxidation rose over the 1 year lifetime of the biscuit.

One study examined the addition of three polyphenols – rosmarinic acid, resveratrol, and epicatechin at two concentrations (0.02% and 0.2%) which were baked at three different temperatures of 150, 170, and 190 ºC (Ou et al., 2017). As in other examples the baking temperature affected the retention of the polyphenols. The individual levels vary – rosmarinic acid is highly stable whilst only 27% and 10% of resveratrol and epicatechin remained when there was 10 minutes baking at 190C. What is interesting is how the polyphenols reduced the amount of particular coloured products such as  fluorescent advanced glycation end products (AGEs). Presumably, those polyphenols which were least stable were also interacting with compounds which normally produce such coloured endproducts. Likewise, compounds such as glyoxal and methylglyoxal were also being destroyed by reaction with resveratrol and epicatechin. Glyoxal and methylglyoxal are intimately involved in Maillard browning reactions as well as generating AGEs.  The benefit of these polyphenols is in removing toxic compounds from the baked food.

Waste materials from fruit and vegetable processing are good sources of polyphenols. Muffins are highly popular because of their versatility and the range of different ingredients that can be added to them.  Muffins have been fortified with apple peel to provide both dietary fibre and phenolics. These muffins retained about 61, 57, 53, 44 and 20% of quercetin glycosides, catechins, chlorogenic acid, phloridzin and cyanidin galactoside (Rupasinghe et al., 2008). Muffins have also been a useful test material for examining the addition of fruit pomace such as blackcurrant, strawberry, raspberry and sour cherry to levels of 50g/kg. There were baked in two types of oven – conventional and halogen at three different temperatures (Gornas et al., 2016). As expected the anthocyanins are the most unstable compounds although they are protected to some extent when bound up in the fruit matrix. Unfortunately, between 35 and 97% of the anthocyanin content is lost. Fortunately, flavonol glycosides are retained to some degree with at worst 21% loss. The amount of free ellagic acid was increased in strawberry and raspberry pomace based muffins and increases in amount as the baking time rose. That fits with much earlier studies that had proved the same point years ago but it does indicate how valuable even waste materials are.

The addition of tea and green tea in particular is also of interest. Tea has been a strong cultural ingredient of various cake formulations such as bara brith for example.  Green Tea Extract (GTE) is made up of polyphenols from green tea, including catechins, which make up 30% of the dry weight of green tea leaves. There are many different polyphenolic catechins in green tea: (−) epicatechin (EC), (−) epicatechin-3-gallate (ECG), (−) epigallocatechin (EGC), (−) epigallocatechin-3-gallate (EGCG), (−) gallocatechin gallate (GCG), (+) catechin, and (+) gallocatechin (GC) (Zaveri, 2006).  Baking as it is known is a process used anyway in green tea processing to produce black tea. Whilst the changes in polyphenol content are understood the same benefits could be imparted to baked foods containing tea (Wang et al., 2022). Green tea powder has been added to sponge cakes at levels of 10,20 and 30% of the wheat flour with a control of no added green tea. Generally, a number of functional and sensory properties altered as the addition level increases. The viscosity and specific gravity of the batter increased as did sensory factors such as hardness and chewiness. The critical polyphenol was catechin which showed good antioxidant activity which was retained with storage of the cake. Up to 20% addition of green tea was feasible before the sensory properties of the cake became unpleasant (Lu et al., 2010).

Green tea may also be a suitable agent for reducing acrylamide formation. One of the key catechins which is epigallocatechin (EGCG) has been shown to do just this in baked bread (Fu et al., 2018). Its addition to cupcakes too which are similar to muffins in many respects has also been beneficial. As well as baking whereby food is cooked in air, it is also possible to produce baked products by frying which is actually a form of dehydration. It is used to cook doughnuts for example (Ngan et al., 2023).

Innovative Approaches and Future Directions

Methods to improve the stability and incorporation of polyphenols during food processing are being addressed (Cao et al., 2021).

Encapsulation Techniques

To address the stability and bioavailability issues, encapsulation techniques are being explored. Encapsulation can protect polyphenols from degradation during baking and ensure their release in the gastrointestinal tract, enhancing bioavailability. Encapsulation generally improves the bioavailability of these compounds simply because their solubility in food systems is so poor. Nanoencapsulation, nanoparticle carriage, nanoemulsions and other nano-technologies may well be the the best methods for delivering these compounds. They have been examined thoroughly by Rashidinejad et al., (2021). Narayan et al., (2024) have encapsulated epigallocatechin gallate in starch nanoparticles.  All types of encapsulating material are being explored especially if they have a ‘green’ perspective. That means they are lower cost and have less impact on the environment.

Pectin is robust during baking but may be too resistant to breakdown in the gut. However, it is a potential material for consideration (Rosales & Fabi, 2023). A green technology benefit might be using  waste-derived carbohydrates as encapsulating agents. The carbohydrates in mind would be  starch, sodium alginate and carrageenan which are derived from algae processing and plant processing  generally (Samborska et al., 2021).

Bilayer emulsions are obtained by combining oppositely charged components at the oil/water interface through electrostatic deposition. The additional protection is provided by a multilayer system. At the moment the main interest is in providing a fat-like sensation for low fat cakes but they could provide a suitable encapsulant of polyphenols in the process.

1. Optimized Baking Processes: Adjusting baking times and temperatures, as well as incorporating specific ingredients that stabilize polyphenols, can help retain their beneficial properties. For instance, using lower baking temperatures or shorter baking times can minimize the degradation of heat-sensitive polyphenols.
2. Fermentation: The use of fermentation in baked goods can enhance the bioavailability of polyphenols. Fermentation can break down complex polyphenolic compounds into simpler, more absorbable forms, potentially increasing their health benefits.
3. Fortification and Blending: Blending polyphenol-rich ingredients with other functional components like fiber, proteins, or probiotics can create a synergistic effect, enhancing the overall health benefits of the baked product.
4. Consumer Education: Educating consumers about the potential health benefits of polyphenol-rich baked goods can create a demand for these products. Awareness campaigns and clear labeling can help consumers make informed choices, promoting the inclusion of polyphenol-rich foods in their diet.

The incorporation of polyphenols in baked foods presents a unique blend of opportunities and challenges. On the positive side, polyphenols can enhance the nutritional profile of baked goods, offering antioxidant, anti-inflammatory, and cardioprotective benefits. They also contribute to the flavour, colour, and texture of the final product, making it more appealing. However, the thermal instability of polyphenols, their potential interactions with other ingredients, and the possible antinutritional effects pose significant challenges. Additionally, issues related to sensory acceptance and cost can limit the widespread adoption of polyphenol-enriched baked products.

To fully harness the benefits of polyphenols in baked foods, ongoing research and innovation are crucial. Techniques like encapsulation, fermentation, and optimized baking processes offer promising solutions to the challenges faced. Ultimately, a balanced approach that considers both the positive and negative aspects of polyphenols will be essential for the successful incorporation of these compounds into baked goods, enhancing both their health benefits and consumer appeal.

References

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