## 3 Formulations of Green Tea Extracts and EGCG in Food Industry  
Three types of tea products are manufactured from Camellia sinensis in the food industry: black tea (78%), green tea (20%), and oolong (2%) [19]. Green tea can be obtained in the traditional manufacturing process, where the leaves are harvested, withered, rolled, and then quickly treated with high temperature (steamed or heated) to hamper enzymatic degradation of polyphenols and other bioactive components [20]. The infusion of green tea is known as one of the most popular beverages in the world due to its pleasant aroma and taste. In addition, its regular drinking can provide many health benefits, which are mostly due to a high concentration of catechins, primarily EGCG, known for its antioxidant properties [21].  
Green tea extract containing EGCG can also be found in many food products due to the growing interest in its use as a dietary supplement and food preservative. The purchase of diverse groceries containing a green tea extract is becoming more popular among consumers worldwide. This can especially be seen in ready-to-eat meals (also containing meat), cereals, bakery products, salad dressings, mayonnaise, margarine, oils (vegetable, marine, frying), and various beverages (soft drinks, energy drinks, juices). In many studies performed on food products containing green tea extract or isolated EGCG, poor stability during storage and oral bioavailability of catechins were highlighted [22]. The main limitation of the widespread use of EGCG is its low stability. EGCG quickly decomposes under the influence of light, temperature, changes in pH, or in the presence of oxygen. The main reactions of EGCG breakdown are epimerization and autooxidation [2; 3]. It was also found that EGCG is unstable when it is sterilized at high temperatures. For this reason, uncommon novel methods should be employed instead of high-temperature sterilization. This would include ionizing radiation or the filtration method followed by freeze-drying [22].  
Green tea extracts and isolated EGCG have been combined with food additives such as vitamin C, xylitol, sucrose, citric acid, butylated hydroxytoluene (dibutylhydroxytoluene, BHT), and EDTA. They were also dispersed in milk, as well as drinks from soy and rice, and citrus juices, such as orange, grapefruit, lemon, and lime. In all these studies, the stability and bioavailability of obtained formulations were assessed. In detail, formulations of green tea extract with ascorbic acid and xylitol or sucrose increased intestinal transport of EGCG [23; 24]. Additionally, the digestive recovery of green tea catechins was either increased or decreased by various common food additives, one such being citrus juices which causes a significant increase [25]. Incorporating powdered green tea extract into food components can also affect the stability of EGCG, making it critical to consider any additional component in a final product due to this potential interaction and influence [26]. Following this issue, [PERSON] et al. obtained a dry apple food product enriched with green tea extract (green tea extract-fortified product), which presented good stability over one month [27].