Phenolic compounds from coffee by-products and application in the food and pharmaceutical industries -

Phenolic compounds from coffee by-products and application in the food and pharmaceutical industries

The presence of phenolic compounds, caffeine, and flavonoids in coffee and its by-products has attracted attention with respect to their applications in foods and pharmaceutical matrices, especially considering the bioactive potential of these molecules. These by-products can be used as ingredients to reduce the environmental impact of coffee production, add value to coffee waste, and provide wider options for consumers who are increasingly seeking foods with “natural” and bioactive ingredients. The main phenolic compounds reported in coffee by-products are chlorogenic acid and its derivatives. Bioactive compounds from these by-products can be used in the production of beverages, dairy products, and baking products as antioxidants and colorants, as well as in the pharmaceutical industry; in addition, they have applications in anti-aging and anti-wrinkle products and as protective agents in different cosmetics.

Methods

The pre-processing stages of green coffee involve fruit harvesting, drying, processing, and storage, all of which are extremely important because they have a decisive influence on the final quality of the product. After harvesting, selection, and cleaning, the beans are processed using different methods, which are described as dry, semi-dry, or wet. The dry method consists of cleaning and drying the whole cherry and is carried out with the skin and pulp attached to the fruit. The skin, pulp, mucilage, and parchment comprise a fraction known as the coffee husk, which is the main by-product of the dry processing method. Coffee husk represents 40–50% of the dried fruits. Thus, coffee husks are probably the main residues of coffee handling and processing. After these processing steps, the dried grains are stored for post-processing and are ready for roasting.

Green coffee beans represent approximately 50% of the fruit mass. The external components are 7–8% skin, 29% pulp, 12% parchment, and 1–2% silverskin, the last being the residue produced after the roasting process. The coffee pulp is composed of carbohydrates (35–85%), soluble fibers (31%), minerals (3–11%), and proteins (5–11%). It is also rich in insoluble dietary fibers and can contain phytochemicals, such as tannins (5–9%) and cyanidins (20%). The parchment is composed of α-cellulose (40–49%), hemicelluloses (25–32%), lignin (33–35%), and fiber (0.5–1%).

Phenolic compounds in coffee by-products The residues from coffee processing (husk, pulp, parchment, and silverskin) contain a lot of bioactive compounds and nutrients with potential biological effects; thus, they are interesting from a food technological perspective. The composition of phenolic compounds in the pulp is similar to that of green coffee because it is rich in chlorogenic, caffeic, ferulic, and coumaric acids. The parchment contains chlorogenic acid, vanillic acid, protocatechuic acid, p-coumaric acid, and caffeine.

Extraction techniques The opportunity to recover bioactive compounds from coffee by-products to diversify and add value to the production chain and also to reduce the waste management costs associated with the disposal of large volumes of industrial waste is challenging. Therefore, one of the possible best uses of these residues is the extraction of phenolic compounds because of their high commercial value and potential health benefits.

Solid–liquid extraction agitation Solvent extraction to obtain bioactive compounds is a widespread technique used in industry. This technique can be applied to many different matrices and combined with different solvents and heating to promote mass transfer. The most common solvents employed in this type of extraction are water and ethanol, either separately or in combination. One of the disadvantages of this method is the possibility of the degradation of heat-sensitive compounds.

Solid–liquid continuous extraction soxhlet extraction Solid–liquid continuous extraction is a widely used method for separating and purifying the components of mixtures and is performed based on the polarity of the solvent used. This technique involves multiple extraction steps, long extraction times, and high amounts of solvents. This method involves heating the solvent until it evaporates, causing the generated steam to condense and drip onto the sample. When the solvent reaches the level of the siphon, it is released with all soluble substances according to their polarity. The process is continued for a few hours to enrich the solvent with the sample components having appropriate affinity.

Uses of phenolic compounds from coffee by-products The phytochemicals present in coffee by-products that positively affect the physiological function of the body have important technological functions. In addition, the bioactive compounds described in this review could have additional roles in preserving and extending the shelf life of food products and have applications as additives or ingredients with antioxidant and antimicrobial activity in the food industry.

Antimicrobial activity Antimicrobials kill microorganisms or inhibit their growth. They have several mechanisms of action and types (natural or synthetic) and are crucial in controlling bacterial infections. However, because of the increase in bacterial resistance, as well as the search for increasingly natural foods, there is a growing search for natural antimicrobial agents. Thus, the incorporation of active dual-purpose compounds in coffee by-products further supports their use in food applications as functional ingredients

Antioxidant activity Phenolic compounds are antioxidants that are present in or can be added to foods at low concentrations to delay or inhibit the production of free radicals and the oxidation of nutritional compounds. Currently, the use of synthetic antioxidants in the food industry is being questioned because it has been suggested that some antioxidants could be toxic; therefore, the search for natural alternatives with antioxidant properties is underway. Phytochemical compounds in coffee by-products are used in the food industry because of their antioxidant potential

Prebiotics: Prebiotics are non-digestible, selectively fermented short-chain carbohydrates that allow specific compositional and activity changes to the gastrointestinal microbiota. The aim of these products is to increase the well-being and health of the consumer. The by-products generated after the processing of green coffee beans are rich in prebiotic oligosaccharides, dietary fibers, ash, minerals, proteins, and polyphenols (trigonelline, caffeine, theobromine, and theophylline) and can be exploited for application as a food ingredient. Green coffee beans contain 50–54% carbohydrates and polysaccharides, consisting mainly of mannans/galactomannans, arabinogalactans-proteins, and cellulose, up to a maximum of 50% of the dry weight of the beans.

Coffee extracts and their by-products contain bioactive compounds with functional properties, such as anti-inflammatory, neuroprotective, antimicrobial, and anticancer effects. There are a variety of products for sale on the market that contain formulations based on coffee extracts or their by-products.

Reference:

Bondam, A.F., da Silveira, D.D., dos Santos, J.P. and Hoffmann, J.F., 2022. Phenolic compounds from coffee by-products: Extraction and application in the food and pharmaceutical industries. Trends in Food Science & Technology.