Recovery and Application of Whey Proteins in Conventional and Nonconventional Food Systems
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Recovery and application of whey proteins in conventional and nonconventional food systems Dissertation submitted to the Faculty of Science and Technology, University of Coimbra, to the Degree of Doctor in Philosophy (PhD) in Chemical Engineering, specialization in Chemical Processes Marta Helena Fernandes Henriques 2012 Work financially supported by under the program Bolsas de Doutoramento (SFRH/ BD/ 36645/ 2007) Dedico este trabalho aos meus pais: Maria Helena Fernandes e Luis Henriques Obrigada por tudo… Abstract Whey is the liquid that separates from the curd during cheese or casein manufacture. It is the main by-product of the cheese industry (≈9 L of whey per 1 kg of cheese), representing a serious environmental problem (BOD = 35-45 g/L). Its disposal or waste management involves high investments and operational costs that provide no profits for the cheese producers. However, whey is an important source of proteins with a high functional, nutritional and biological value, thus justifying its commercial use. Conventional practices for the valorisation of whey comprise the manufacture of dried products such as whey powder, whey protein concentrate (WPC) and isolate (WPI) and lactose, using concentration processes such as reverse osmosis and evaporation, or ultrafiltration followed by spray-drying of the retentates and/or permeates. However, the high costs associated with the dehydration step mean that these technologies cannot be used in the medium/small scale industries which represent 79% of the dairy sector in Portugal and a significant volume of the business (37%). This thesis focuses on the development of innovative solutions for the valorisation of whey, in particular whey proteins, in medium/small scale cheese production. Batch ultrafiltration (UF) and diafiltration (DF) were used to produce liquid whey protein concentrates (LWPC) and dehydrated whey protein concentrates (WPC) of bovine and ovine origin. The products obtained were applied to food products, namely fresh cheese and set yogurt, to partially replace conventional ingredients, and as a raw material in lactic gels to produce innovative dairy products. Nonconventional applications were also explored, such as the production of films and coatings with bioactive properties. v vi The effects of the production process configurations and operational conditions on the characteristics of liquid and dry whey protein concentrate products were evaluated. Bovine LWPC with protein contents ranging from 61% to 87% (dry basis) were obtained. Diafiltration performed in volume reduction mode produced the best results in terms of protein content (20% higher than in the UF process) and purity. The ovine products (LWPC and WPC) had higher protein yields (62-84%, dry basis), making them more attractive for valorisation. It is common practice in the industrial manufacture of cheese and yogurt to increase the total solids content by applying skimmed milk powder, caseinates or protein concentrate powders in order to increase production yields and overcome syneresis problems. However, a less expensive alternative is to use LWPC, although this has not yet been explored in yogurts and or fully investigated in cheese. The production of fresh cheese and set yogurt incorporating various levels of LWPC proved to be an asset, not only by increasing production yields but also by improving the functional and nutritional properties of the final products. With regard to fresh cheese, the incorporation of LWPC increased product stability during storage and spontaneous syneresis reduction. No differences were found in texture between the conventional and tested products, although sensorial attributes were affected by the amount of LWPC that was incorporated, which indicates that this is an essential parameter to control. Only high levels of incorporation penalise product acceptance. The good performance of bovine LWPC in yogurt, the higher protein content of ovine LWPC and the fact that this type of whey is available from national producers led to an evaluation of their use in yogurts. Yogurts produced from bovine milk incorporating (bovine and ovine) LWPC and ovine yogurts were compared to conventional bovine yogurts. It was found that the incorporation of LWPC in set yogurts helps to reduce hardness, gumminess and viscosity, and consequently increases syneresis. These results indicate that a more open gel structure with a lower water retention capacity was produced. Moreover, the modest syneresis values obtained for all the formulations tested (typical of yogurts with an high total solids content) revealed the high functionality (gelation capacity) of LWPC. The protein content in ovine yogurts was significantly higher them in bovine yogurts with or without the incorporation of LWPC. On a sensorial level, no differences were found between the conventional bovine yogurts and those incorporating LWPC, indicating that regardless of the origins of the LWPC (bovine or ovine) the sensorial properties of set yogurts were not affected. However, differences were detected for ovine yogurts, which received a poor classification in the preference test. vii One very attractive market opportunity, which has not yet been explored, is the use of LWPC as a raw material in the manufacture of innovative products. Its high protein content and the well- established functional and nutritional value of its proteins are good indicators per se of its high added value. The physicochemical, textural and rheological properties of thermal gels produced from LWPC were evaluated in terms of the type of LWPC (skimmed or unskimmed, produced by ultrafiltration, or skimmed produced by diafiltration), protein concentration (5% and 7%, dry basis) and pH (4 and 7). Non-defatted LWPC, high protein concentrations and lower pH values lead to stronger thermal gels. LWPC produced by diafiltration at pH 7 with a 5% protein concentration did not produce solid structures, probably due to the lower intermolecular interactions prevailing under these conditions. All acid gels produced by bacterial fermentation (yogurt type) and by glocono-δ-lactone (GDL) acidification (dessert type) showed viscoleastic behaviour, regardless to skimmed milk powder (SMP) fortification. The yogurt type gels were the weakest gels. It was concluded that, depending on the gelation process adopted and the manufacturing conditions, products with specific chemical and rheological properties could be obtained. This versatility enables the desired product to be manufactured with the appropriate characteristics. Increasing environmental concerns about replace synthetic polymers with natural ones is stimulating research into new materials, particularly those obtained from nonconventional sources such as agro-residues. Whey proteins may be included in this premise. The research carried out so far in this field has used WPI as the base material and the solvent casting method to produce edible films and coatings. However, this research studied the performance of WPC as a less expensive alternative to WPI and the application of UV irradiation to promote film modification. The chemical composition of the film and the modification method affected the physicochemical, optical and barrier properties in specific ways. Using WPC with 50% protein and 40% lactose resulted in the production of films with attractive functional properties. The colour of the films was slightly penalised by the presence of lactose, but the film transparency remained within the range of values obtained for commercial synthetic films (oriented polypropylene (OPP) and polyethylene (PE)). UV irradiation enabled films to be produced with increased hydrophobicity and less moisture content. However, their greater solubility may limit their applicability under high humidity conditions. The molecular structure observed by FTIR revealed the presence of weaker chemical bonds between the formulation components using UV modification, which leads to less thermally stable films. The mechanical properties were not viii affected by the modification method, although their modest tensile strength and Young´s modulus in comparison to the synthetic films may restrict their applications. Edible coatings with antimicrobial activity were applied to semi-cured cheeses serving as a food model. Under these conditions, both the coating modification method and antimicrobiological coating activity were evaluated by monitoring the physicochemical, microbiological and sensorial properties of the cheese during ripening. Uncoated cheeses and cheeses coated with commercial polyvinyl alcohol (PVA) coatings served as negative and positive controls. The type of modification influenced the performance of the edible whey protein coatings. In comparison with commercial coatings, the antimicrobial coatings produced using both heat denaturation and UV irradiation showed similar or better results with regard to preventing cheese dehydration and the microbiological control of Staphylococcus spp., Pseudomonas spp., Enterobacteriaceae, yeasts and moulds. No sensorial differences were detected between cheeses with antimicrobial edible whey protein coatings and those with commercial coatings. The results are very promising in terms of effectively replacing commercial coatings with natural ones. The work presented in this thesis showed the great potential for using whey protein in less complex processes in the medium/small cheese industries to partially solve the environmental problem of whey at relatively low operational and investment costs.