The effects of Ca concentration and pH on the composition, microstructural, and functional properties of Mozzarella cheese were studied. Cheeses were made using a starter culture (control) or by direct acidification of the milk with lactic acid or lactic acid and glucono-delta-lactone. In each of three trials, four cheeses were produced: a control, CL, and three directly-acidified cheeses, DA1, DA2, and DA3. The cheeses were stored at 4 degrees C for 70 d. The Ca content and pH were varied by altering the pH at setting, pitching, and plasticization. The mean pH at 1 d and the Ca content (mg/g of protein) of the various cheeses were: CL, 5.42 and 27.7; DA1, 5.96 and 21.8; DA2, 5.93 and 29.6; DA3, 5.58 and 28.7. For cheeses with a high pH (i.e., approximately 5.9), reducing the Ca content from 29.6 to 21.8 mg/g of protein resulted in a significant decrease in the protein level and increases in the moisture content and mean level of nonexpressible serum (g/g of protein). Reducing the Ca concentration also resulted in a more swollen, hydrated para-casein matrix at 1 d. The decrease in Ca content in the high-pH cheeses coincided with increases in the mean stretchability and flowability of the melted cheese over the 70-d storage period. The fluidity of the melted cheese also increased when the Ca content was reduced, as reflected by a lower elastic shear modulus and a higher value for the phase angle, delta, of the melted cheese, especially after storage for <12 d. The melt time, flowability, and stretchability of the low-Ca, high-pH DA1 cheese at 1 d were similar to those for the CL cheese after storage for > or = 12 d. In contrast, the mean values for flowability and stretchability of the high-pH, high-Ca DA2 cheese over the 70-d period were significantly lower than those of the CL cheese. Reducing the pH of high-Ca cheese (27.7 to 29.6 mg/g of protein) from -5.95 to 5.58 resulted in higher flowability, stretchability, and fluidity of the melted cheese. For cheeses with similar pH and Ca concentration, the method of acidification had little effect on composition, microstructure, flowability, stretchability, and fluidity of the melted cheese.

Low-moisture Mozzarella cheeses (LMMC), varying in calcium content and pH, were made using a starter culture (control; CL) or direct acidification (DA) with lactic acid or lactic acid and glucono-delta-lactone. The pH and calcium concentration significantly affected the type and extent of proteolysis in Mozzarella cheese during the 70-d storage period at 4 degrees C. For cheeses with a similar pH, reducing the calcium-to-casein ratio from -29 to 22 mg/g of protein resulted in marked increases in moisture content and in primary and secondary proteolysis, as indicated by polyacrylamide gel electrophoresis and higher levels of pH 4.6- and 5%-PTA-soluble N. Increasing the pH of DA cheeses of similar moisture content, from approximately 5.5 to 5.9, while maintaining the calcium-to-casein ratio almost constant at approximately 29 mg/g, resulted in a decrease in primary proteolysis but had no effect on secondary proteolysis. Comparison of CL and DA cheeses with a similar composition showed that the CL cheese had higher levels of alpha(s1)-CN degradation, pH 4.6- and 5%-PTA-soluble N. Analysis of pH 4.6-soluble N extracts by reverse-phase HPLC showed that the CL cheese had higher concentrations of compounds with low retention times, suggesting higher concentrations of low molecular mass peptides and free amino acids.

Low-moisture Mozzarella cheese, in duplicate trials, was ripened at 0, 4, 10 or 15 o C for 70 d. For all temperature treatments, increasing ripening time resulted in significant (P < 0.05) increases in the level of proteolysis as measured by the levels of pH 4.6 soluble-N (pH 4.6SN) and 5% phosphotungstic acid-soluble N (PTA-N). Urea-PAGE electrophoretograms of the pH 4.6-insoluble cheese extracts showed that increasing the storage temperature resulted in an increase in the extent of degradation of α s1 -CN but had little effect on the degradation of β-casein. Increasing the ripening temperature resulted in a significant increase in the mean level of pH 4.6SN and PTA-N over the 70 d ripening period. Reverse-phase HPLC (RP-HPLC) of the pH 4.6-soluble and 70% ethanol-soluble fractions of the pH4.6-soluble cheese extracts indicated a heterogeneous array of peptides. The concentration of early-eluting peptides, representing amino acids and small peptides, increased as the ripening temperature was increased. Ripening / temperature / Mozzarella / composition / proteolysisRésumé -Effets de la température d'affinage sur les fromages de Mozzarella à faible teneur en eau. 1. Composition et protéolyse. Deux lots de fromages de Mozzarella à faible teneur en eau ont été fabriqués et ont été maturés à 0, 4, 10 ou 15 o C pendant 70 jours. À toutes les températures, l'augmentation du temps de maturation a entraîné une augmentation significative (P < 0,05) du niveau de protéolyse comme mesuré par les niveaux d'azote soluble à pH 4,6 (pH 4,6SN) et d'azote soluble dans l'acide phosphotungstique à 5 % (PTA-N). Les électrophorégrammes urée-PAGE des fractions de fromage insolubles à pH 4,6 ont montré que l'augmentation de la température de conservation provoquait une augmentation du niveau de dégradation de la caséine α s1 mais avait peu d'effet sur la dégradation de la caséine β. L'augmentation de la température de maturation a entraîné une augmentation significative des niveaux moyens de pH 4,6SN et PTA-N sur toute la période de 463 Lait 81 (2001) 463-474 © INRA, EDP Sciences, 2001 maturation de 70 jours. L'HPLC en phase inverse de la fraction pH4,6SN et de la fraction soluble dans l'éthanol à 70 % obtenue à partir de pH4,6SN a montré un ensemble hétérogène de peptides. La concentration de peptides élués en premier, représentant des acide aminés et petits peptides, a augmenté quand la température de maturation augmentait. Maturation / température / Mozzarella / composition / protéolyse

-Low-moisture Mozzarella cheeses were made in duplicate and ripened for 70 d at 0, 4, 10 or 15 o C. For all temperatures, advance in ripening time resulted in significant (P < 0.05) decreases in the concentration of intact casein, firmness, melt time and apparent viscosity. In contrast, the flowability and stretchability of the molten cheeses increased significantly during storage. Increasing the ripening temperature from 0 to 15 o C resulted in a significant decrease in the mean concentration of intact casein and a decrease in the level of serum expressed on centrifugation. The latter changes were paralleled by a significant decrease in the mean melt time (time required for shred fusion) of the cheese over the 70 d ripening period, and a significant increase in the mean flowability and reduction in the mean apparent viscosity of the molten cheese. The effect of elevation of storage temperature on the functional attributes of the molten cheese was attributed mainly to the concomitant reduction in the content of intact casein which was negatively correlated with flowability and positively with apparent viscosity and melt time.Ripening / temperature / Mozzarella / functionality / texture Résumé -Effets de la température d'affinage sur les fromages de Mozzarella à faible teneur en eau. 2. Texture et propriétés fonctionnelles. Deux lots de fromages de Mozzarella à faible teneur en eau ont été fabriqués et maturés pendant 70 jours à 0, 4, 10 ou 15 o C. Pour toutes les températures, l'avancée dans le temps de maturation a entraîné une diminution significative (P < 0,05) de la concentration en caséine intacte, de la fermeté, du temps de fusion et de la viscosité apparente. Par opposition, l'aptitude à l'écoulement et au filant des fromages fondus a augmenté significativement pendant le stockage. L'augmentation de la température de maturation de 0 à 15 o C a résulté une diminution significative de la concentration moyenne en caséine intacte et une diminution de la quantité de sérum extraite par centrifugation. Parallèlement à ces derniers changements, on observait une diminution significative des temps moyens de fusion (temps exigé pour la fusion de brins de fromage râpé) au cours 475

No abstract