| Summary: | The dairy sector is of great economic importance worldwide, and it has always been extremely competitive in terms of product portfolio innovation. In order to respond to new consumer trends, such as products with particular nutritional profiles and products with added health benefits, this industry has had to adapt its portfolio accordingly. Also, the numbers concerning food waste are very high, with about 1/3 of the food destined to human consumption being lost worldwide; in Portugal, 17% of the annual food production is estimated to become food waste. In the cheese production sector, generated waste includes cheese surpluses or their off-standards items. These cheese by-products were valorised in this dissertation project by serving as basic ingredient for the development of a group of novel dairy products, with innovative taste features and nutritionally enhanced characteristics. That was achieved by the formulation of a melted cheese base (MCB) - a paste of melted cheese in gelatinized starch (or other hydrocolloids including xanthan gum and guar gum), having milk as the fluid vehicle. These MCBs were the distinctive ingredient for ulterior incorporation in the final products, where Emmental cheese was the cheese type selected for most of the research work, due to its properties. Besides cheese, the MCBs also included agents able to stabilize its dispersed state after cooling. In order to avoid the emulsifying salts common in processed cheeses, hydrocolloids were used instead. The main ones were native corn starch (CS) and waxy rice starch (WRS), that also worked as thickeners and stabilizers of the MCBs. It was shown that the starch suspension in milk should be heated past the gelatinization temperature (85 ºC for CS and 90 ºC for WRS) before cheese addition, so that the final MCB formulation could reveal ideal textural characteristics. A study on the interactions involved in holding the protein structure in cheese (Emmental) was also made using solutions of different dissociating agents at different concentrations and combinations. To quantify the solubilized protein, a modification of a spectrophotometric-based method that can be employed to quantify total protein in cheese was developed, with statistically similar results (p>0.05) to those obtained by the Kjeldahl method. The results showed that caseins in the Emmental cheese are held together by a set of hydrophobic interactions, hydrogen bonds, and electrostatic bonds, including ionic bonds, with hydrogen bonds having an important role, comparable to hydrophobic interactions, a conclusion not commonly reported for cheese structures. The last part of this project entailed the development of two novel dairy products, namely, yogucheeses corresponding to yogurts fortified with cheese, and novel ricotta-type fresh cheeses. For the yogucheeses, cheese (Emmental) and CS or WRS were used in the MCB formulations. These MCBs were mixed with further milk in different proportions, before addition of starter culture and fermentation, in order to create samples with different proportions of MCB to further analyse. The products were characterised in terms of macronutrient composition, physical and chemical properties. In the end, the incorporation of CS and WRS, combined with the incorporation of ripened cheese, created yogurt samples with a firmer gel structure, lower syneresis, and higher viscosity. All the yogurts were stable throughout a period of 14 days, with no alterations in their visual aspect and syneresis behaviour. For the ricotta-type fresh cheeses, MCBs were made using two cheese types (Emmental and Ewe’s cheeses) and using CS or WRS. Afterwards, the MCB wase diluted with milk and then renneted, so that the novel fresh cheeses could be obtained. These samples were characterised in terms of macronutrient composition, physical and chemical properties, as well as sensory properties. The fresh cheese developed had a balanced nutritional content, and a texture similar to many commercial fresh cheese types, or spreadable processed cheeses. Gel formation of the initial mixture was hindered above a certain incorporation of ripened cheese, but this was overcome by the addition of skim milk powder (SMP) to the preparation. Starch and SMP both reduced syneresis of the renneted gel. As for the sensory attributes of the products, according to a consumer panel, the preference was higher for a more solid texture and with the flavour of a traditional cow’s cheese. Both these products were manufactured using our MCB formulation. This alternative strategy for utilization of cheese can contribute to food surplus minimization, while bringing additional nutrients and specific flavours to these products. Since ingredients that are not compatible with clean label designation were not used, as well as sweeteners of any kind, these products are consistent with the consumer trends existing nowadays and are in alignment with the sustainable development goals. In conclusion, this thesis project presents research that led to a novel line of dairy products, economically and environmentally interesting, as well as rewarding, being also in line with the recent consumers’ trends and demands for more sustainable and health-promoting foods, all while contributing to the circular economy, since the product formulation uses cheese surpluses, which ultimately reduces food waste.
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