Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / An in vivo digestibility experiment was conducted to evaluate the influence of degradable nitrogen source and feeding frequency on the digestion process and utilization of kikuio grass hay. Eight castrated male lamb (35 ± 4 Kg live weight) maintained in individual metabolic cage, were used in a 2x2 factorial experiment according to a replicated 4x4 Latin Square design. Treatments tested were the combination of two supplement feeding frequencies: once (morning) or twice (morning and aftermoon) daily, and two supplements, based on cassava meal plus calcium caseinate or cassava meal plus urea. For all treatments kikuio hay was fed ad. Libitum and the supplements were fed at a rate of 7 g/Kg live weight daily. Animals supplemented twice day consumed higher quantity of the gross fractions, either in absolute values or in proportion to live weight or metabolic weight (P<0,05) and they tended to consume higher quantity of digestible energy and to synthesize more microbial protein (P<0,10). Feeding frequency did not influence the digestibility. When calcium caseinate was fed animal tended (P<0,10) to have higher dry matter intake in relation to live weight and higher organic matter intake in relation to metabolic weight. There was interaction between nitrogen source × frequency of supplementation on intake of both digestible organic matter and digestible energy. Animals receiving supplement with calcium caseinate twice a day and supplemented with urea once a day have higher intake of theses fractions. Animals supplemented once a day presented higher rumen sugar concentration (P<0,05), but pH as well as ammonia and peptides + aminoacid concentration were not affected by supplementation frequencys. Higher concentrations of NH3 and lower concentrations of pep+aa were observed in animals supplemented with urea (P<0,05). The supplement feeding frequency did not influence the digestion process and forage utilization when the nitrogen source was urea, but when the nitrogen source was calcium caseinate, supplementation twice daily improves intake and nutrients offer to the animals. / Para avaliar se as freqüências de oferta de suplemento, com diferentes tipos de nitrogênio degradável, influenciam os processos de digestão e a utilização do feno de uma gramínea tropical, foi realizado um estudo de digestibilidade in vivo, utilizando oito ovinos machos castrados (PV médio 35 ± 4 Kg), mantidos em gaiolas de metabolismo individuais em um delineamento duplo quadrado latino 4x4 em um esquema fatorial 2x2. Como volumoso foi utilizado feno de capim quicuio (Pennisetum clandestinum) com 70 dias de rebrota, como suplemento foi utilizada uma mistura a base de farinha de mandioca mais uréia ou caseinato de cálcio, além de uma mistura de sal mineral comercial e melaço em pó. Os tratamentos foram duas freqüências de suplementação × duas fontes de nitrogênio. As combinações foram suplementação com farinha de mandioca mais caseinato fornecido uma vez ao dia (manhã) e duas vezes ao dia (manhã e tarde) e suplementação com farinha de mandioca mais uréia uma vez ao dia (manhã) e duas vezes ao dia (manhã e tarde) à nível de 7 g/Kg de PV. O volumoso foi fornecido Ad. Libitum duas vezes ao dia (manhã e tarde). Os animais quando suplementados duas vezes ao dia consumiram maior quantidade das frações brutas, tanto em valores absolutos, como em proporção ao PV ou peso metabólico (P<0,05) e tenderam a consumir maior quantidade de energia digestível e a sintetizar mais proteína microbiana (P<0,10). A freqüência de suplementação não influenciou na digestibilidade e a eficiência da síntese de proteína microbiana. Somente houve uma tendência de quando os animais foram suplementados com caseinato consumirem maior quantidade de matéria seca em relação ao peso vivo e matéria orgânica em g/Kg de peso metabólico (P<0,10), não havendo mais nenhum efeito da suplementação com diferentes fontes de nitrogênio degradável no rúmen. Houve interação fonte de nitrogênio × freqüência de suplementação no consumo de matéria orgânica digestível e energia digestível onde os animais quando recebendo suplemento com caseinato duas vezes ao dia e quando suplementados com uréia uma vez ao dia consumiram mais destas frações. Quando os animais foram suplementados uma vez por dia apresentaram maiores concentrações ruminais de açucares (CHO) (P<0,05), e o pH, amônia (NH3) e peptídeos + aminoácidos (pep+aa) não foram influenciados pelas diferentes freqüências de suplementação. Maiores concentrações ruminais de NH3 e menores de pep+aa foram observadas quando os animais foram suplementados com uréia (P<0,05). A suplementação com farinha de mandioca mais caseinato fornecido duas vezes ao dia manifestou ser superior as demais suplementações, no entanto os mecanismos não ficaram bem estabelecidos, necessitando estudos adicionais.

Orientadores: Rosiane Lopes da Cunha, Ana Carla Kawazoe Sato / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Almentos / Made available in DSpace on 2018-08-18T17:56:49Z (GMT). No. of bitstreams: 1 Costa_AlineAlvaresdaSilva_M.pdf: 2383816 bytes, checksum: 2af9fcfd4c4efd286c4471da25aa7226 (MD5) Previous issue date: 2011 / Resumo: Proteínas são os biopolímeros mais amplamente utilizados nas formulações de emulsões alimentícias como agentes emulsificantes, por serem um aditivo seguro. Com o intuito de entender e melhorar as propriedades emulsificantes das proteínas, inicialmente foram estudadas as macroemulsões óleo-água (O/A) estabilizadas por caseinato de sódio (CN-Na), obtidas em um sistema rotor-estator, sob diferentes concentrações de proteína e condições de pH. Todas as macroemulsões apresentaram separação de fases, devido ao mecanismo de cremeação. Este processo de desestabilização foi reduzido quando existiu o aumento da viscosidade dos sistemas, obtido pela adição de maiores concentrações de proteína e pela redução do pH em direção ao ponto isoelétrico da proteína. Já a utilização da homogeneização a altas pressões promoveu a formação de emulsões cineticamente estáveis, não sendo observada separação de fases com 4% de CN-Na em nenhuma das condições de pH. De modo geral, as emulsões apresentaram comportamento pseudoplástico, com exceção das emulsões estabilizadas com 1% de proteína em pH 5, que se comportaram como fluido dilatante, e em pH 7, como fluido Newtoniano. A redução do pH para os sistemas com 1% de CN-Na levou à desestabilização das emulsões, devido à menor concentração de proteínas adsorvidas não permitirem uma estabilização eletrostática. Foi realizado um tratamento enzimático para melhorar a estabilização das emulsões que separaram de fases em pH ácido. Assim, géis de caseinato de sódio foram reticulados com lacase e ácido ferúlico e as propriedades mecânicas desses géis foram avaliadas. A adição de lacase mediada por ácido ferúlico resultou em géis mais rígidos, firmes e menos deformáveis. As melhores combinações foram selecionadas para o preparo de emulsões O/A estabilizadas com CN-Na com o objetivo de aumentar a estabilidade em pH ácido. O uso desse tratamento enzimático levou a modificações na estrutura da proteína e, com isso, mudanças nas suas propriedades funcionais, o que permitiu o aumento na estabilidade das emulsões. Em geral, essas emulsões tratadas enzimaticamente apresentaram-se mais estáveis, com distribuição de gotas menos polidispersa e com comportamento mais estruturado, apesar do aumento no diâmetro médio das gotas, variando entre 11,79 e 20,17 µm para emulsões em pH 3 contra 6,14 µm medido na emulsão controle (sem tratamento enzimático). Assim, o aumento na estabilidade dessas emulsões deve estar associado ao aumento da viscosidade, que promoveram estabilidade estérica aos sistemas. Portanto, os resultados mostram que foi possível a produção de emulsões ácidas com maior estabilidade a partir do caseinato de sódio, através do tratamento enzimático, originando emulsões com estruturas e propriedades reológicas diferenciadas em comparação com a proteína não reticulada / Abstract: Proteins are biopolymers widely used as a safe additive in the formulation of food emulsions as emulsifying agents. To understand and improve the emulsifying properties of sodium caseinate, initially oil-in-water macroemulsions (O/W) were studied. The emulsions were stabilized by sodium caseinate prepared using a rotor-stator device at different concentrations of protein and pH. All macroemulsions showed phase separation due to the creaming mechanism. This mechanism of destabilization was reduced with the increase of system viscosity, either due to the increase on the concentrations of protein and by the reduction of pH towards to the protein¿s isoelectric point. The use of high-pressure homogenization promoted the formation of stable microemulsions, with no phase separation observed in emulsions with 4% CN-Na. In general, the emulsions exhibited a shear-thinning behavior, except the emulsion containing 1% protein at pH 7, which exhibited Newtonian behavior, and at pH 5, which tended to show a shear-thickening behavior. The reduction of pH in emulsions with 1% CN-Na led to phase separated emulsions, which was attributed to the amount of adsorbed protein, which was insufficient to promote a strong electrostatic repulsion. In order to improve the stabilization of phase separated emulsions at acidic pH, an enzymatic treatment was carried out. Thus, sodium caseinate gels were crosslinked with laccase and ferulic acid and the mechanical properties of these gels were evaluated. The addition of laccase and ferulic acid resulted in gels with increased hardness, firmness and less deformable. The best treatments were selected for the preparation of O/W emulsions stabilized with CN-Na, in order to increase in their stability in acidic pH. The enzymatic treatment caused modifications in the protein structure, resulting in changes of functional properties, which led to an increase in the emulsion stability. In general, these enzymatically treated emulsions were more stable, composed by droplets with lower size distribution and more structured behavior, despite the increased mean droplet diameters (between 11.79 and 20.17 µm for emulsions at pH 3). Thus, the stability increase of these emulsions could be associated to the increase in viscosity, which resulted in steric stability. Results showed that it was possible to produce more stable emulsions containing sodium caseinate in acidic pH using enzymatic treatment, resulting in emulsions with different structures and rheological properties when compared with the non-cross-linked protein / Mestrado / Engenharia de Alimentos / Mestre em Engenharia de Alimentos

Orientadores: Florencia Cecilia Menegalli, Rosiane Lopes da Cunha / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-10T04:44:46Z (GMT). No. of bitstreams: 1 Gozzo_AngelaMaria_D.pdf: 11741135 bytes, checksum: a214a3f6ddbdeaa7712078b8b0f19f2a (MD5) Previous issue date: 2008 / Resumo: Os amidos são adicionados freqüentemente aos alimentos devido as suas propriedades espessantes e de retenção de água, como estabilizantes coloidais e agentes gelificantes. O amaranto é uma cultura de baixo custo, e seu amido, um novo ingrediente com potencial uso industrial. O caseinato de sódio é um sal derivado da caseína amplamente utilizado como emulsificante em alimentos. O estudo de misturas de proteínas e polissacarídeos é de grande interesse, pois tais combinações podem levar a um intervalo de propriedades mais amplo que os géis puros de proteína ou de polissacarídeo. Neste trabalho, as características físico-químicas do amido e as interações entre amido de amaranto/caseinato de sódio, adicionados ou não de sacarose, foram estudadas em sistemas mantidos a 10 °C e pH no ponto isoelétrico. Estas interações foram estudadas através de análises térmicas (gelatinização e retrogradação), de capacidade de retenção de água, sinerese, análise estrutural e comportamento reológico (em cisalhamento oscilatório e em compressão biaxial) da mistura dos biopolímeros e sacarose, durante e após a gelificação. Foram comparados dois métodos de acidificação, um lento, realizado a 10°C e outro rápido, a 90°C. O caseinato de sódio contribuiu para favorecer a característica elástica e viscosa dos sistemas analisados, principalmente na acidificação lenta, porém, o comportamento reológico foi governado principalmente pela velocidade de acidificação, pois os géis formados pelo processo lento apresentaram G¿ e G¿ superiores aos sistemas formados por acidificação rápida. Géis de caseínato - amido formaram estruturas pouco agrupadas, com cadeias ramificadas, cuja rede ficou mais estruturada com o aumento da concentração dos polímeros, sendo que, a porosidade dos géis formados por acidificação lenta foi maior e mais uniformemente distribuída que dos géis formados por acidificação rápida. A sacarose atuou como um agente anti-retrogradante, sendo que, este efeito foi mais importante para a interação sacarose-amilopectina do que para a sacarose-amilose. Apesar de retardar o envelhecimento, a sacarose não atuou fortemente sobre as interações, sendo que as propriedades dos géis mostraram ser mais fortemente dependentes da concentração de biopolímeros e, principalmente, da temperatura de acidificação. Amostras contendo maiores concentrações de amido/caseinato apresentaram maior capacidade de retenção de água (WHC) e menor sinerese. A retrogradação do amido de amaranto não foi elevada, no entanto, valores de DH (re-gelatinização) aumentaram com a concentração de sacarose e tempo de armazenamento e decresceram com a adição de caseinato de sódio / Abstract: The starches are frequently added to the foods owed their properties and water retention, as colloidal emulsion-estabilizing agents. The amaranth is a low cost culture, and his starch, a new ingredient with potential industrial use. The caseinato of sodium is a salt derived of the casein thoroughly used as emulsion in foods. The study proteins and polysaccharide mixtures is of great interest, because such combinations can take the a wider interval of properties than the pure gels of protein or polysaccharide. In this work, the physiochemical characteristics of the starch and the interactions among amaranthus starch-sodium caseinate, added or not of sucrose, were studied in systems maintained at 10 °C and pH in the isoeletric point. These interactions were studied through thermal analyses, water holding capacity, syneresis, structural analysis and behavior rheologic of the biopolymers-sucrose mixture, during and after the gelation. Two acidification methods were compared, one performed at 10°C (slow) and other, at 90°C (fast). The sodium caseinate contributed to favor the elastic and viscous characteristic of the analyzed systems, mainly in the slow acidification, however, the rheologic behavior was governed mainly by the acidification speed, because the gels formed by the slow process presented G' and G" superiors to the systems formed by the fast acidification. Starch-caseínato gels formed structures low contained, with ramified chains, whose net was more structured with the increase of the polymeric concentration, and, the gels porosity formed by slow acidification was larger and more evenly distributed that of gels formed by fast acidification. The sucrose acted as an anti-retrogradation agent, and, this effect went more important for the sucrose- amylopectin interaction than for the sucroseamylose. In spite of delaying the aging, the sucrose didn't act strongly about the interactions, and the gels properties showed to be more strongly dependent of the biopolymers concentration and, mainly, of the acidification temperature. Samples containing larger starch caseinate concentrations presented larger water holding capacity (WHC) and smaller syneresis. The retrogradation of the amaranth starch was not elevated, however, values of DH increased with the sucrose concentration and time of storage and they decreased with the addition of sodium caseinate / Doutorado / Doutor em Engenharia de Alimentos

The present study was aimed at extending our knowledge of the antioxidative properties of the milk protein products, whey protein isolate (WPI) and sodium caseinate (NaCas), in oil-in-water (O/W) emulsions rich in polyunsaturated fatty acids (PUFAs). In particular, the objective was to contribute to our understanding of the compositional and processing factors that influence the oxidative stability of protein-stabilised O/W emulsions. Linoleic acid (approximately 60 %) was used as the lipid for the oil phase (10.6 %). The emulsion samples were usually incubated at 50 °C to accelerate lipid oxidation. Lipid oxidation indicators were lipid hydroperoxides and headspace hexanal, determined by solid phase microextraction (SPME) combined with gas chromatography (GC). WPI- or NaCas-stabilised emulsions were prepared using a wide range of protein concentrations (0.5, 1.0, 2.0, 3.0, 4.0, 7.0 or 10.0 %) at two droplet sizes (d32 = 0.31 and 0.65 µm). In general, higher lipid oxidation levels were found for the larger droplet size. Increasing protein concentration led to a decrease in the lipid oxidation rate. The greatest decrease in lipid hydroperoxide levels (values after 4 h) occurred at up to 4.0 % protein concentration. The greatest decrease in hexanal levels (values after 24 h) occurred at up to 4.0 % protein concentration in WPI emulsions (0.31 µm). The hexanal levels were more independent of the protein concentration in the other emulsion types. The hexanal level decreased at protein concentrations > 4.0 % in NaCas emulsions (0.31 and 0.65 µm) and at protein concentrations > 7.0 % in WPI emulsions (0.65 µm). The difference between lipid hydroperoxide generation in emulsions with small and large droplet sizes decreased with increasing protein concentration. This effect was more pronounced in NaCas emulsions. In general, NaCas was a better inhibitor of lipid oxidation than WPI, but WPI appeared to be the better antioxidant at some droplet size/protein concentration combinations. The protein in the continuous phase, i.e. the unadsorbed protein, played an important role in lipid oxidation. In principal, the lipid hydroperoxide and hexanal levels showed the same development over the continuous phase protein concentration as over the protein concentration in WPI and NaCas emulsions (d32 = 0.31 µm). A low NaCas level in the continuous phase already led to a relatively low hexanal level, whereas a higher WPI level was required. When NaCas solution was added to a WPI emulsion or WPI solution was added to a NaCas emulsion, a synergistic antioxidative effect was observed. The high molecular weight fractions (molecular weight = 12000-14000) of WPI and NaCas contained pro-oxidative metal ions that contributed to lipid oxidation in the emulsions. An enrichment of NaCas emulsions with the low molecular weight fraction of NaCas (with a molecular weight = 12000-14000) notably inhibited lipid oxidation. An enrichment of WPI emulsions with the low molecular weight fraction of WPI (with a molecular weight = 12000-14000) also seemed to inhibit lipid oxidation, but the effect was not significant. The protein solutions were enriched with these fractions before emulsion preparation. Pure WPI solution or mixed WPI/NaCas (1:1, weight/weight) solution with 1.12 or 2.24 % protein concentration was heated at 84 °C for up to 40 min, cooled and then used to prepare emulsions. Lipid oxidation was generally not affected by the heat treatment or the degree of whey protein denaturation. However, at the lower WPI concentration, more hexanal was produced for the longer heating times (20, 30 and 40 min) and this appeared to be connected with the physical instability of the emulsions. Greater oxidative stability was found at the higher protein concentration and when the proteins were mixed, pointing to a possible synergistic antioxidative effect of WPI and NaCas. The addition of the free radical source 2,2’-azobis(2-amidinopropane) dihydrochloride (AAPH) greatly increased the oxygen uptake and the generation of lipid hydroperoxides in the emulsions. The oxidative stability increased with increasing protein concentration (1.0, 4.0 and 7.0 %). NaCas had a greater antioxidative effect than WPI. The inhibition of oxygen uptake appeared to be largely influenced by the free-radical-scavenging activity of the system, determined by the protein type and the protein concentration, as the radicals were produced linearly over time and oxygen was consumed linearly over time. It can therefore be concluded that free-radical-scavenging activity represents a major antioxidative mechanism of the milk proteins. Oxygen was consumed much faster in emulsions than in protein solutions when the same level of AAPH was incorporated. In a WPI (1.0 % protein) emulsion, much lower levels of protein hydroperoxides than of lipid hydroperoxides developed. This pointed to a much greater reactivity of linoleic acid than of the milk proteins with oxygen. In contrast, the exposure of WPI to oxidising linoleic acid in an emulsion (1.0 % protein) or to AAPH in aqueous solution led to oxidative damage of the whey proteins, indicated by the loss of amino acids. The loss of specific amino acids was different for proteins in the continuous phase or cream phase of an emulsion or in WPI solution. The present study confirms the antioxidative potential of WPI and NaCas and gives new insights into their functionality as oxidative stabilisers in O/W emulsions.

The aim of this study was to investigate the impact of the casein microstructure on the molecular diffusion of probes with different sizes and deformabilities. The mobility of molecular flexible ('PEG') and rigid (dendrimer) probes of various sizes was studied in suspensions and gels of NPC and SC at various protein concentrations. Measurements were carried out by NMR, which makes it possible to probe translational mobilities over a distance of 1.5 microns, as well as local mobilities at the molecular scale (several nanometers) through the relaxation times, T2. A coherent model was used and the same mechanism was proposed to describe the diffusion of small probes in both casein dispersions. It is the combination of different factors that should be considered: the ratio of the probe size to the distance between the obstructing particles or the entanglement points, as well as the flexibility of the probe. The rotational diffusion of PEG and dendrimer probes was less hindered than translational diffusion in both casein systems. Different relaxation behaviors were observed between the two casein systems and retardation in T2 relaxation times was highlighted in rennet and acid casein gels. These results are probably related to the local mobility of the matrix. The overall results of this project led to a better understanding of probe mobility in casein systems and made it possible to propose a new model that challenges the previous one proposed by Le Feunteun et al. to describe the diffusion of probes in casein systems.

The present study was aimed at extending our knowledge of the antioxidative properties of the milk protein products, whey protein isolate (WPI) and sodium caseinate (NaCas), in oil-in-water (O/W) emulsions rich in polyunsaturated fatty acids (PUFAs). In particular, the objective was to contribute to our understanding of the compositional and processing factors that influence the oxidative stability of protein-stabilised O/W emulsions. Linoleic acid (approximately 60 %) was used as the lipid for the oil phase (10.6 %). The emulsion samples were usually incubated at 50 °C to accelerate lipid oxidation. Lipid oxidation indicators were lipid hydroperoxides and headspace hexanal, determined by solid phase microextraction (SPME) combined with gas chromatography (GC). WPI- or NaCas-stabilised emulsions were prepared using a wide range of protein concentrations (0.5, 1.0, 2.0, 3.0, 4.0, 7.0 or 10.0 %) at two droplet sizes (d32 = 0.31 and 0.65 µm). In general, higher lipid oxidation levels were found for the larger droplet size. Increasing protein concentration led to a decrease in the lipid oxidation rate. The greatest decrease in lipid hydroperoxide levels (values after 4 h) occurred at up to 4.0 % protein concentration. The greatest decrease in hexanal levels (values after 24 h) occurred at up to 4.0 % protein concentration in WPI emulsions (0.31 µm). The hexanal levels were more independent of the protein concentration in the other emulsion types. The hexanal level decreased at protein concentrations > 4.0 % in NaCas emulsions (0.31 and 0.65 µm) and at protein concentrations > 7.0 % in WPI emulsions (0.65 µm). The difference between lipid hydroperoxide generation in emulsions with small and large droplet sizes decreased with increasing protein concentration. This effect was more pronounced in NaCas emulsions. In general, NaCas was a better inhibitor of lipid oxidation than WPI, but WPI appeared to be the better antioxidant at some droplet size/protein concentration combinations. The protein in the continuous phase, i.e. the unadsorbed protein, played an important role in lipid oxidation. In principal, the lipid hydroperoxide and hexanal levels showed the same development over the continuous phase protein concentration as over the protein concentration in WPI and NaCas emulsions (d32 = 0.31 µm). A low NaCas level in the continuous phase already led to a relatively low hexanal level, whereas a higher WPI level was required. When NaCas solution was added to a WPI emulsion or WPI solution was added to a NaCas emulsion, a synergistic antioxidative effect was observed. The high molecular weight fractions (molecular weight = 12000-14000) of WPI and NaCas contained pro-oxidative metal ions that contributed to lipid oxidation in the emulsions. An enrichment of NaCas emulsions with the low molecular weight fraction of NaCas (with a molecular weight = 12000-14000) notably inhibited lipid oxidation. An enrichment of WPI emulsions with the low molecular weight fraction of WPI (with a molecular weight = 12000-14000) also seemed to inhibit lipid oxidation, but the effect was not significant. The protein solutions were enriched with these fractions before emulsion preparation. Pure WPI solution or mixed WPI/NaCas (1:1, weight/weight) solution with 1.12 or 2.24 % protein concentration was heated at 84 °C for up to 40 min, cooled and then used to prepare emulsions. Lipid oxidation was generally not affected by the heat treatment or the degree of whey protein denaturation. However, at the lower WPI concentration, more hexanal was produced for the longer heating times (20, 30 and 40 min) and this appeared to be connected with the physical instability of the emulsions. Greater oxidative stability was found at the higher protein concentration and when the proteins were mixed, pointing to a possible synergistic antioxidative effect of WPI and NaCas. The addition of the free radical source 2,2’-azobis(2-amidinopropane) dihydrochloride (AAPH) greatly increased the oxygen uptake and the generation of lipid hydroperoxides in the emulsions. The oxidative stability increased with increasing protein concentration (1.0, 4.0 and 7.0 %). NaCas had a greater antioxidative effect than WPI. The inhibition of oxygen uptake appeared to be largely influenced by the free-radical-scavenging activity of the system, determined by the protein type and the protein concentration, as the radicals were produced linearly over time and oxygen was consumed linearly over time. It can therefore be concluded that free-radical-scavenging activity represents a major antioxidative mechanism of the milk proteins. Oxygen was consumed much faster in emulsions than in protein solutions when the same level of AAPH was incorporated. In a WPI (1.0 % protein) emulsion, much lower levels of protein hydroperoxides than of lipid hydroperoxides developed. This pointed to a much greater reactivity of linoleic acid than of the milk proteins with oxygen. In contrast, the exposure of WPI to oxidising linoleic acid in an emulsion (1.0 % protein) or to AAPH in aqueous solution led to oxidative damage of the whey proteins, indicated by the loss of amino acids. The loss of specific amino acids was different for proteins in the continuous phase or cream phase of an emulsion or in WPI solution. The present study confirms the antioxidative potential of WPI and NaCas and gives new insights into their functionality as oxidative stabilisers in O/W emulsions.

The present study was aimed at extending our knowledge of the antioxidative properties of the milk protein products, whey protein isolate (WPI) and sodium caseinate (NaCas), in oil-in-water (O/W) emulsions rich in polyunsaturated fatty acids (PUFAs). In particular, the objective was to contribute to our understanding of the compositional and processing factors that influence the oxidative stability of protein-stabilised O/W emulsions. Linoleic acid (approximately 60 %) was used as the lipid for the oil phase (10.6 %). The emulsion samples were usually incubated at 50 °C to accelerate lipid oxidation. Lipid oxidation indicators were lipid hydroperoxides and headspace hexanal, determined by solid phase microextraction (SPME) combined with gas chromatography (GC). WPI- or NaCas-stabilised emulsions were prepared using a wide range of protein concentrations (0.5, 1.0, 2.0, 3.0, 4.0, 7.0 or 10.0 %) at two droplet sizes (d32 = 0.31 and 0.65 µm). In general, higher lipid oxidation levels were found for the larger droplet size. Increasing protein concentration led to a decrease in the lipid oxidation rate. The greatest decrease in lipid hydroperoxide levels (values after 4 h) occurred at up to 4.0 % protein concentration. The greatest decrease in hexanal levels (values after 24 h) occurred at up to 4.0 % protein concentration in WPI emulsions (0.31 µm). The hexanal levels were more independent of the protein concentration in the other emulsion types. The hexanal level decreased at protein concentrations > 4.0 % in NaCas emulsions (0.31 and 0.65 µm) and at protein concentrations > 7.0 % in WPI emulsions (0.65 µm). The difference between lipid hydroperoxide generation in emulsions with small and large droplet sizes decreased with increasing protein concentration. This effect was more pronounced in NaCas emulsions. In general, NaCas was a better inhibitor of lipid oxidation than WPI, but WPI appeared to be the better antioxidant at some droplet size/protein concentration combinations. The protein in the continuous phase, i.e. the unadsorbed protein, played an important role in lipid oxidation. In principal, the lipid hydroperoxide and hexanal levels showed the same development over the continuous phase protein concentration as over the protein concentration in WPI and NaCas emulsions (d32 = 0.31 µm). A low NaCas level in the continuous phase already led to a relatively low hexanal level, whereas a higher WPI level was required. When NaCas solution was added to a WPI emulsion or WPI solution was added to a NaCas emulsion, a synergistic antioxidative effect was observed. The high molecular weight fractions (molecular weight = 12000-14000) of WPI and NaCas contained pro-oxidative metal ions that contributed to lipid oxidation in the emulsions. An enrichment of NaCas emulsions with the low molecular weight fraction of NaCas (with a molecular weight = 12000-14000) notably inhibited lipid oxidation. An enrichment of WPI emulsions with the low molecular weight fraction of WPI (with a molecular weight = 12000-14000) also seemed to inhibit lipid oxidation, but the effect was not significant. The protein solutions were enriched with these fractions before emulsion preparation. Pure WPI solution or mixed WPI/NaCas (1:1, weight/weight) solution with 1.12 or 2.24 % protein concentration was heated at 84 °C for up to 40 min, cooled and then used to prepare emulsions. Lipid oxidation was generally not affected by the heat treatment or the degree of whey protein denaturation. However, at the lower WPI concentration, more hexanal was produced for the longer heating times (20, 30 and 40 min) and this appeared to be connected with the physical instability of the emulsions. Greater oxidative stability was found at the higher protein concentration and when the proteins were mixed, pointing to a possible synergistic antioxidative effect of WPI and NaCas. The addition of the free radical source 2,2’-azobis(2-amidinopropane) dihydrochloride (AAPH) greatly increased the oxygen uptake and the generation of lipid hydroperoxides in the emulsions. The oxidative stability increased with increasing protein concentration (1.0, 4.0 and 7.0 %). NaCas had a greater antioxidative effect than WPI. The inhibition of oxygen uptake appeared to be largely influenced by the free-radical-scavenging activity of the system, determined by the protein type and the protein concentration, as the radicals were produced linearly over time and oxygen was consumed linearly over time. It can therefore be concluded that free-radical-scavenging activity represents a major antioxidative mechanism of the milk proteins. Oxygen was consumed much faster in emulsions than in protein solutions when the same level of AAPH was incorporated. In a WPI (1.0 % protein) emulsion, much lower levels of protein hydroperoxides than of lipid hydroperoxides developed. This pointed to a much greater reactivity of linoleic acid than of the milk proteins with oxygen. In contrast, the exposure of WPI to oxidising linoleic acid in an emulsion (1.0 % protein) or to AAPH in aqueous solution led to oxidative damage of the whey proteins, indicated by the loss of amino acids. The loss of specific amino acids was different for proteins in the continuous phase or cream phase of an emulsion or in WPI solution. The present study confirms the antioxidative potential of WPI and NaCas and gives new insights into their functionality as oxidative stabilisers in O/W emulsions.

The present study was aimed at extending our knowledge of the antioxidative properties of the milk protein products, whey protein isolate (WPI) and sodium caseinate (NaCas), in oil-in-water (O/W) emulsions rich in polyunsaturated fatty acids (PUFAs). In particular, the objective was to contribute to our understanding of the compositional and processing factors that influence the oxidative stability of protein-stabilised O/W emulsions. Linoleic acid (approximately 60 %) was used as the lipid for the oil phase (10.6 %). The emulsion samples were usually incubated at 50 °C to accelerate lipid oxidation. Lipid oxidation indicators were lipid hydroperoxides and headspace hexanal, determined by solid phase microextraction (SPME) combined with gas chromatography (GC). WPI- or NaCas-stabilised emulsions were prepared using a wide range of protein concentrations (0.5, 1.0, 2.0, 3.0, 4.0, 7.0 or 10.0 %) at two droplet sizes (d32 = 0.31 and 0.65 µm). In general, higher lipid oxidation levels were found for the larger droplet size. Increasing protein concentration led to a decrease in the lipid oxidation rate. The greatest decrease in lipid hydroperoxide levels (values after 4 h) occurred at up to 4.0 % protein concentration. The greatest decrease in hexanal levels (values after 24 h) occurred at up to 4.0 % protein concentration in WPI emulsions (0.31 µm). The hexanal levels were more independent of the protein concentration in the other emulsion types. The hexanal level decreased at protein concentrations > 4.0 % in NaCas emulsions (0.31 and 0.65 µm) and at protein concentrations > 7.0 % in WPI emulsions (0.65 µm). The difference between lipid hydroperoxide generation in emulsions with small and large droplet sizes decreased with increasing protein concentration. This effect was more pronounced in NaCas emulsions. In general, NaCas was a better inhibitor of lipid oxidation than WPI, but WPI appeared to be the better antioxidant at some droplet size/protein concentration combinations. The protein in the continuous phase, i.e. the unadsorbed protein, played an important role in lipid oxidation. In principal, the lipid hydroperoxide and hexanal levels showed the same development over the continuous phase protein concentration as over the protein concentration in WPI and NaCas emulsions (d32 = 0.31 µm). A low NaCas level in the continuous phase already led to a relatively low hexanal level, whereas a higher WPI level was required. When NaCas solution was added to a WPI emulsion or WPI solution was added to a NaCas emulsion, a synergistic antioxidative effect was observed. The high molecular weight fractions (molecular weight = 12000-14000) of WPI and NaCas contained pro-oxidative metal ions that contributed to lipid oxidation in the emulsions. An enrichment of NaCas emulsions with the low molecular weight fraction of NaCas (with a molecular weight = 12000-14000) notably inhibited lipid oxidation. An enrichment of WPI emulsions with the low molecular weight fraction of WPI (with a molecular weight = 12000-14000) also seemed to inhibit lipid oxidation, but the effect was not significant. The protein solutions were enriched with these fractions before emulsion preparation. Pure WPI solution or mixed WPI/NaCas (1:1, weight/weight) solution with 1.12 or 2.24 % protein concentration was heated at 84 °C for up to 40 min, cooled and then used to prepare emulsions. Lipid oxidation was generally not affected by the heat treatment or the degree of whey protein denaturation. However, at the lower WPI concentration, more hexanal was produced for the longer heating times (20, 30 and 40 min) and this appeared to be connected with the physical instability of the emulsions. Greater oxidative stability was found at the higher protein concentration and when the proteins were mixed, pointing to a possible synergistic antioxidative effect of WPI and NaCas. The addition of the free radical source 2,2’-azobis(2-amidinopropane) dihydrochloride (AAPH) greatly increased the oxygen uptake and the generation of lipid hydroperoxides in the emulsions. The oxidative stability increased with increasing protein concentration (1.0, 4.0 and 7.0 %). NaCas had a greater antioxidative effect than WPI. The inhibition of oxygen uptake appeared to be largely influenced by the free-radical-scavenging activity of the system, determined by the protein type and the protein concentration, as the radicals were produced linearly over time and oxygen was consumed linearly over time. It can therefore be concluded that free-radical-scavenging activity represents a major antioxidative mechanism of the milk proteins. Oxygen was consumed much faster in emulsions than in protein solutions when the same level of AAPH was incorporated. In a WPI (1.0 % protein) emulsion, much lower levels of protein hydroperoxides than of lipid hydroperoxides developed. This pointed to a much greater reactivity of linoleic acid than of the milk proteins with oxygen. In contrast, the exposure of WPI to oxidising linoleic acid in an emulsion (1.0 % protein) or to AAPH in aqueous solution led to oxidative damage of the whey proteins, indicated by the loss of amino acids. The loss of specific amino acids was different for proteins in the continuous phase or cream phase of an emulsion or in WPI solution. The present study confirms the antioxidative potential of WPI and NaCas and gives new insights into their functionality as oxidative stabilisers in O/W emulsions.

The present study was aimed at extending our knowledge of the antioxidative properties of the milk protein products, whey protein isolate (WPI) and sodium caseinate (NaCas), in oil-in-water (O/W) emulsions rich in polyunsaturated fatty acids (PUFAs). In particular, the objective was to contribute to our understanding of the compositional and processing factors that influence the oxidative stability of protein-stabilised O/W emulsions. Linoleic acid (approximately 60 %) was used as the lipid for the oil phase (10.6 %). The emulsion samples were usually incubated at 50 °C to accelerate lipid oxidation. Lipid oxidation indicators were lipid hydroperoxides and headspace hexanal, determined by solid phase microextraction (SPME) combined with gas chromatography (GC). WPI- or NaCas-stabilised emulsions were prepared using a wide range of protein concentrations (0.5, 1.0, 2.0, 3.0, 4.0, 7.0 or 10.0 %) at two droplet sizes (d32 = 0.31 and 0.65 µm). In general, higher lipid oxidation levels were found for the larger droplet size. Increasing protein concentration led to a decrease in the lipid oxidation rate. The greatest decrease in lipid hydroperoxide levels (values after 4 h) occurred at up to 4.0 % protein concentration. The greatest decrease in hexanal levels (values after 24 h) occurred at up to 4.0 % protein concentration in WPI emulsions (0.31 µm). The hexanal levels were more independent of the protein concentration in the other emulsion types. The hexanal level decreased at protein concentrations > 4.0 % in NaCas emulsions (0.31 and 0.65 µm) and at protein concentrations > 7.0 % in WPI emulsions (0.65 µm). The difference between lipid hydroperoxide generation in emulsions with small and large droplet sizes decreased with increasing protein concentration. This effect was more pronounced in NaCas emulsions. In general, NaCas was a better inhibitor of lipid oxidation than WPI, but WPI appeared to be the better antioxidant at some droplet size/protein concentration combinations. The protein in the continuous phase, i.e. the unadsorbed protein, played an important role in lipid oxidation. In principal, the lipid hydroperoxide and hexanal levels showed the same development over the continuous phase protein concentration as over the protein concentration in WPI and NaCas emulsions (d32 = 0.31 µm). A low NaCas level in the continuous phase already led to a relatively low hexanal level, whereas a higher WPI level was required. When NaCas solution was added to a WPI emulsion or WPI solution was added to a NaCas emulsion, a synergistic antioxidative effect was observed. The high molecular weight fractions (molecular weight = 12000-14000) of WPI and NaCas contained pro-oxidative metal ions that contributed to lipid oxidation in the emulsions. An enrichment of NaCas emulsions with the low molecular weight fraction of NaCas (with a molecular weight = 12000-14000) notably inhibited lipid oxidation. An enrichment of WPI emulsions with the low molecular weight fraction of WPI (with a molecular weight = 12000-14000) also seemed to inhibit lipid oxidation, but the effect was not significant. The protein solutions were enriched with these fractions before emulsion preparation. Pure WPI solution or mixed WPI/NaCas (1:1, weight/weight) solution with 1.12 or 2.24 % protein concentration was heated at 84 °C for up to 40 min, cooled and then used to prepare emulsions. Lipid oxidation was generally not affected by the heat treatment or the degree of whey protein denaturation. However, at the lower WPI concentration, more hexanal was produced for the longer heating times (20, 30 and 40 min) and this appeared to be connected with the physical instability of the emulsions. Greater oxidative stability was found at the higher protein concentration and when the proteins were mixed, pointing to a possible synergistic antioxidative effect of WPI and NaCas. The addition of the free radical source 2,2’-azobis(2-amidinopropane) dihydrochloride (AAPH) greatly increased the oxygen uptake and the generation of lipid hydroperoxides in the emulsions. The oxidative stability increased with increasing protein concentration (1.0, 4.0 and 7.0 %). NaCas had a greater antioxidative effect than WPI. The inhibition of oxygen uptake appeared to be largely influenced by the free-radical-scavenging activity of the system, determined by the protein type and the protein concentration, as the radicals were produced linearly over time and oxygen was consumed linearly over time. It can therefore be concluded that free-radical-scavenging activity represents a major antioxidative mechanism of the milk proteins. Oxygen was consumed much faster in emulsions than in protein solutions when the same level of AAPH was incorporated. In a WPI (1.0 % protein) emulsion, much lower levels of protein hydroperoxides than of lipid hydroperoxides developed. This pointed to a much greater reactivity of linoleic acid than of the milk proteins with oxygen. In contrast, the exposure of WPI to oxidising linoleic acid in an emulsion (1.0 % protein) or to AAPH in aqueous solution led to oxidative damage of the whey proteins, indicated by the loss of amino acids. The loss of specific amino acids was different for proteins in the continuous phase or cream phase of an emulsion or in WPI solution. The present study confirms the antioxidative potential of WPI and NaCas and gives new insights into their functionality as oxidative stabilisers in O/W emulsions.

The present study was aimed at extending our knowledge of the antioxidative properties of the milk protein products, whey protein isolate (WPI) and sodium caseinate (NaCas), in oil-in-water (O/W) emulsions rich in polyunsaturated fatty acids (PUFAs). In particular, the objective was to contribute to our understanding of the compositional and processing factors that influence the oxidative stability of protein-stabilised O/W emulsions. Linoleic acid (approximately 60 %) was used as the lipid for the oil phase (10.6 %). The emulsion samples were usually incubated at 50 °C to accelerate lipid oxidation. Lipid oxidation indicators were lipid hydroperoxides and headspace hexanal, determined by solid phase microextraction (SPME) combined with gas chromatography (GC). WPI- or NaCas-stabilised emulsions were prepared using a wide range of protein concentrations (0.5, 1.0, 2.0, 3.0, 4.0, 7.0 or 10.0 %) at two droplet sizes (d32 = 0.31 and 0.65 µm). In general, higher lipid oxidation levels were found for the larger droplet size. Increasing protein concentration led to a decrease in the lipid oxidation rate. The greatest decrease in lipid hydroperoxide levels (values after 4 h) occurred at up to 4.0 % protein concentration. The greatest decrease in hexanal levels (values after 24 h) occurred at up to 4.0 % protein concentration in WPI emulsions (0.31 µm). The hexanal levels were more independent of the protein concentration in the other emulsion types. The hexanal level decreased at protein concentrations > 4.0 % in NaCas emulsions (0.31 and 0.65 µm) and at protein concentrations > 7.0 % in WPI emulsions (0.65 µm). The difference between lipid hydroperoxide generation in emulsions with small and large droplet sizes decreased with increasing protein concentration. This effect was more pronounced in NaCas emulsions. In general, NaCas was a better inhibitor of lipid oxidation than WPI, but WPI appeared to be the better antioxidant at some droplet size/protein concentration combinations. The protein in the continuous phase, i.e. the unadsorbed protein, played an important role in lipid oxidation. In principal, the lipid hydroperoxide and hexanal levels showed the same development over the continuous phase protein concentration as over the protein concentration in WPI and NaCas emulsions (d32 = 0.31 µm). A low NaCas level in the continuous phase already led to a relatively low hexanal level, whereas a higher WPI level was required. When NaCas solution was added to a WPI emulsion or WPI solution was added to a NaCas emulsion, a synergistic antioxidative effect was observed. The high molecular weight fractions (molecular weight = 12000-14000) of WPI and NaCas contained pro-oxidative metal ions that contributed to lipid oxidation in the emulsions. An enrichment of NaCas emulsions with the low molecular weight fraction of NaCas (with a molecular weight = 12000-14000) notably inhibited lipid oxidation. An enrichment of WPI emulsions with the low molecular weight fraction of WPI (with a molecular weight = 12000-14000) also seemed to inhibit lipid oxidation, but the effect was not significant. The protein solutions were enriched with these fractions before emulsion preparation. Pure WPI solution or mixed WPI/NaCas (1:1, weight/weight) solution with 1.12 or 2.24 % protein concentration was heated at 84 °C for up to 40 min, cooled and then used to prepare emulsions. Lipid oxidation was generally not affected by the heat treatment or the degree of whey protein denaturation. However, at the lower WPI concentration, more hexanal was produced for the longer heating times (20, 30 and 40 min) and this appeared to be connected with the physical instability of the emulsions. Greater oxidative stability was found at the higher protein concentration and when the proteins were mixed, pointing to a possible synergistic antioxidative effect of WPI and NaCas. The addition of the free radical source 2,2’-azobis(2-amidinopropane) dihydrochloride (AAPH) greatly increased the oxygen uptake and the generation of lipid hydroperoxides in the emulsions. The oxidative stability increased with increasing protein concentration (1.0, 4.0 and 7.0 %). NaCas had a greater antioxidative effect than WPI. The inhibition of oxygen uptake appeared to be largely influenced by the free-radical-scavenging activity of the system, determined by the protein type and the protein concentration, as the radicals were produced linearly over time and oxygen was consumed linearly over time. It can therefore be concluded that free-radical-scavenging activity represents a major antioxidative mechanism of the milk proteins. Oxygen was consumed much faster in emulsions than in protein solutions when the same level of AAPH was incorporated. In a WPI (1.0 % protein) emulsion, much lower levels of protein hydroperoxides than of lipid hydroperoxides developed. This pointed to a much greater reactivity of linoleic acid than of the milk proteins with oxygen. In contrast, the exposure of WPI to oxidising linoleic acid in an emulsion (1.0 % protein) or to AAPH in aqueous solution led to oxidative damage of the whey proteins, indicated by the loss of amino acids. The loss of specific amino acids was different for proteins in the continuous phase or cream phase of an emulsion or in WPI solution. The present study confirms the antioxidative potential of WPI and NaCas and gives new insights into their functionality as oxidative stabilisers in O/W emulsions.