La stérilisation déstabilisant les protéines laitières acidifiées, des stabilisants sont généralement ajoutés. L’objectif de cette thèse était de comprendre les mécanismes physico-chimiques induits par l’acidification de formules laitières puis de rechercher des voies de stabilisation clean label pour les caséines acidifiées et traitées UHT. Des analyses décrivant la minéralisation, la charge de surface, l’hydratation et les modifications chimiques des caséines ont été mises en œuvre pour étudier leur stabilité.À l’échelle pilote, les caséines étaient plus stables à pH > 5,8 (entre pH 6,7 et 3,7), à basse température (8 versus 42°C), dans une formule riche en protéines (7 versus 3,2 %) et acidifiées par acide citrique (versus lactique). La meilleure stabilité dans ces conditions (parmi 140 combinaisons) s’expliquerait par des diminutions de répulsions électrostatiques, hydrophobes et de diffusion ainsi que par des augmentations de pouvoir tampon et de calcium chélaté par le citrate.Cependant, un traitement de 120°C / 15 s déstabilisait les micelles de caséines dès pH 6,2. L’ajout de matière grasse n’apportait pas d’amélioration. La lactosylation a ensuite été étudiée pour diminuer le pHi des caséines et donc les stabiliser à pH acide. Un prétraitement thermique (90°C / 60 min) à pH 7,5 avec du lactose leur a été appliqué dans différents environnements physico-chimiques. Les niveaux de lactosylation des caséines en milieu dilué étaient faibles mais augmentés avec une forte concentration en lactose (150 g/L) ou en milieu sec. Ce prétraitement appliqué en présence d’une concentration élevée en caséines (50 g/L) ou en minéraux -teneur en perméat triplée) améliorait davantage la stabilisation thermique des protéines acidifiées que la lactosylation seule. Cela s'exliquerait par un pouvoir tampon supérieur lié à cet environnement plus riche. / As sterilization destabilizes acidified dairy proteins, stabilizers are usually added. The objective of this thesis was to understand the physicochemical mechanisms induced by the acidification of dairy formulas and to look for clean label solutions to stabilize for acidified and heat treated caseins. To study their stability, the mineralization, surface charge, hydration and chemical modifications of caseins were characterized.At the pilot scale, caseins were more stable at pH > 5.8 (between pH 6.7 and 3.7), low temperature (8 versus 42°C), in formulas which were enriched in proteins (7 versus 3.2 %) and acidified with citric acid (versus lactic). This set of conditions (amid 140 combinations) would be the best to preserve the stability of proteins because it would correspond to a decrease of electrostatic and hydrophobic repulsions and of diffusion and to an increase of buffer strength and of citrate-chelated calcium content.However, a heat treatment at 120°C during 15 s destabilized casein micelles from pH 6.2 whatever the set of conditions. Adding fat did not bring any improvement.Next, lactosylation was studied to decrease the pHi of caseins so as to stabilize them at acidic pH. A heat pretreatment (90°C/60 min) at pH 7.5 in the presence of lactose was applied to casein micelles in several physicochemical environments. Lactosylation rates of casein in aqueous conditions were low but they were increased with high lactose content (150 g/L) or in dry conditions. This heat pretreatment, implemented with a high casein (50 g/L) or mineral (triple-concentrated permeate content) concentration improved even more the heat stability of acidified proteins than lactosylation only. This could be explained by higher buffer strength due to this richer environnement

O objetivo do estudo foi determinar a composição e as características físico-químicas (pH, acidez, estabilidade ao álcool, sólidos totais, gordura, lactose, teor de extrato seco desengordurado e proteína total), contagem de células somáticas (CCS) e as frações de caseína (α-S1, α-S2, β e κ) dos leites identificados como leite instável não ácido (LINA) e de leites estáveis à prova de álcool a 78% (v/v). A amostragem contemplou todas as propriedades leiteiras fornecedoras de leite de um laticínio localizado no município de Casa Branca - Estado de São Paulo, nos meses de março, maio, julho e setembro de 2007. Considerou-se, como critério de identificação de LINA, a amostra de leite de conjunto de cada propriedade que apresentasse instabilidade à prova do álcool a 72% (v/v) e acidez inferior a 18ºD. Do total de amostras instáveis ao teste do álcool a 72% (v/v), 64,77% foram identificadas como LINA. A freqüência de amostras de LINA variou de acordo com o mês de amostragem, indicando uma possível influência sazonal sobre a ocorrência deste problema nos rebanhos analisados. No mês de julho, a incidência de LINA foi maior, coincidindo com o período seco, quando a disponibilidade e a qualidade das forragens são reduzidas. No mês de setembro, época de chuvas em que ocorre maior oferta de forragens de melhor qualidade, a incidência de LINA diminuiu. Em julho, houve um aumento significativo nos níveis de gordura, lactose e CCS, observando-se, porém, uma diminuição significativa nas concentrações de proteína bruta nas amostras. Neste mês, notou-se também uma menor concentração de κ-caseína no LINA, embora as diferenças entre as caseínas α-S1, α-S2, β e κ do LINA e do leite estável não tenham sido significativas nos meses de amostragem. Os resultados evidenciaram que a ocorrência de LINA é freqüente nos rebanhos leiteiros da região estudada, o que pode acarretar perdas significativas à indústria de laticínios e aos produtores devido ao descarte do leite. / The aim of this study was to determinate the composition and the physical-chemical characteristics (pH, acidity, alcohol stability, total solids, fat, lactose, non fat solids and total protein), somatic cells counts (SCC) and casein fractions (α-S1, α-S2, β and κ) of unstable non-acid and stable milks at the alcohol test at 78% (v/v). Samples were collected from all the dairy farms that provide milk to a dairy plant located in Casa Branca - São Paulo State. Sampling procedures were done on March, May, July and September 2007. Milk samples from each dairy farm presenting instability to alcohol test at 72% (v/v) and acidity less than 18ºD were considered as unstable non-acid milk. From the total of unstable samples to alcohol test at 72% (v/v), 64.77% were identified as unstable non-acid milk. The frequency of unstable non-acid milk samples varied according the month of sampling, hence indicating a possible seasonal influence on the occurrence of this problem in the dairy herds studied. On July, the incidence of unstable non-acid milk was higher, coinciding with the dry season, when the quality and availability of forage are reduced. On September, at rainfall season, when the availability and quality of forage are better, the incidence of unstable non-acid milk decreased. There was a significant increase in the levels of fat, lactose and SSC in samples collected on July, although a significant decrease was observed in the concentrations of total protein. In this month, a lower concentration of κ-casein was also noted in unstable non-acid milks. However, the differences between the α-S1, α-S2, β and κ casein of unstable non-acid milk and stable milk were not significant in all sampling months. Results showed that the occurrence of unstable non-acid milk is common in dairy herds in the studied area, which can cause significant losses to the dairy industry and dairy farms due to the discharging of milk.

O objetivo do estudo foi determinar a composição e as características físico-químicas (pH, acidez, estabilidade ao álcool, sólidos totais, gordura, lactose, teor de extrato seco desengordurado e proteína total), contagem de células somáticas (CCS) e as frações de caseína (α-S1, α-S2, β e κ) dos leites identificados como leite instável não ácido (LINA) e de leites estáveis à prova de álcool a 78% (v/v). A amostragem contemplou todas as propriedades leiteiras fornecedoras de leite de um laticínio localizado no município de Casa Branca - Estado de São Paulo, nos meses de março, maio, julho e setembro de 2007. Considerou-se, como critério de identificação de LINA, a amostra de leite de conjunto de cada propriedade que apresentasse instabilidade à prova do álcool a 72% (v/v) e acidez inferior a 18ºD. Do total de amostras instáveis ao teste do álcool a 72% (v/v), 64,77% foram identificadas como LINA. A freqüência de amostras de LINA variou de acordo com o mês de amostragem, indicando uma possível influência sazonal sobre a ocorrência deste problema nos rebanhos analisados. No mês de julho, a incidência de LINA foi maior, coincidindo com o período seco, quando a disponibilidade e a qualidade das forragens são reduzidas. No mês de setembro, época de chuvas em que ocorre maior oferta de forragens de melhor qualidade, a incidência de LINA diminuiu. Em julho, houve um aumento significativo nos níveis de gordura, lactose e CCS, observando-se, porém, uma diminuição significativa nas concentrações de proteína bruta nas amostras. Neste mês, notou-se também uma menor concentração de κ-caseína no LINA, embora as diferenças entre as caseínas α-S1, α-S2, β e κ do LINA e do leite estável não tenham sido significativas nos meses de amostragem. Os resultados evidenciaram que a ocorrência de LINA é freqüente nos rebanhos leiteiros da região estudada, o que pode acarretar perdas significativas à indústria de laticínios e aos produtores devido ao descarte do leite. / The aim of this study was to determinate the composition and the physical-chemical characteristics (pH, acidity, alcohol stability, total solids, fat, lactose, non fat solids and total protein), somatic cells counts (SCC) and casein fractions (α-S1, α-S2, β and κ) of unstable non-acid and stable milks at the alcohol test at 78% (v/v). Samples were collected from all the dairy farms that provide milk to a dairy plant located in Casa Branca - São Paulo State. Sampling procedures were done on March, May, July and September 2007. Milk samples from each dairy farm presenting instability to alcohol test at 72% (v/v) and acidity less than 18ºD were considered as unstable non-acid milk. From the total of unstable samples to alcohol test at 72% (v/v), 64.77% were identified as unstable non-acid milk. The frequency of unstable non-acid milk samples varied according the month of sampling, hence indicating a possible seasonal influence on the occurrence of this problem in the dairy herds studied. On July, the incidence of unstable non-acid milk was higher, coinciding with the dry season, when the quality and availability of forage are reduced. On September, at rainfall season, when the availability and quality of forage are better, the incidence of unstable non-acid milk decreased. There was a significant increase in the levels of fat, lactose and SSC in samples collected on July, although a significant decrease was observed in the concentrations of total protein. In this month, a lower concentration of κ-casein was also noted in unstable non-acid milks. However, the differences between the α-S1, α-S2, β and κ casein of unstable non-acid milk and stable milk were not significant in all sampling months. Results showed that the occurrence of unstable non-acid milk is common in dairy herds in the studied area, which can cause significant losses to the dairy industry and dairy farms due to the discharging of milk.