Showing papers by "Christophe Lacroix published in 1998"

High nisin Z production by Lactococcus lactis UL719 in whey permeate with aeration

Abstract: The influence of controlled pH (5.0–6.5) and initial dissolved oxygen level (0–90% air saturation) on nisin Z production in a yeast extract/Tween 80-supplemented whey permeate (SWP) was examined during batch fermentations with citrate positive Lactococcus lactis subsp. lactis UL719. The total activity corresponding to the sum of soluble and cell-bound activities, as measured by a critical dilution method, was more than 50% lower at pH 5.0 than in the range 5.5–6.5, although the specific production decreased as pH increased. A maximum nisin Z activity of 8200 AU/ml (4100IU/ml) was observed in the supernatant after 8h of culture for pH ranging from 5.5 to 6.5. Prolonging the culture beyond 12h decreased this activity at pH 6.0 and 6.5 but not at pH 5.5 or 5.0. A corresponding increase in cell-bound activity was probably due to adsorption of soluble bacteriocin to the cell wall. Aeration increased cell-bound and total activity to maximum values of 32800 and 41000 AU/ml (16400 and 20500IU/ml), respectively, with an initial level of 60% air saturation after 24h of incubation at pH 6.0. The specific production at 60% or 90% initial air saturation was eight-fold higher than at 0%.

Effet de l'incorporation des protéines du lactosérum dénaturées et microparticulées dans le cheddar jeune

Abstract: EtTect of incorporation of denatured and microparticulated whey protein in young Cheddar cheese. Two whey protein concentrates (WPC) heat-denatured at pH 4.2 (WPC 4.2) and at pH 6.7 (WPC 6.7) and microparticulated were used for the production of Cheddar cheese. Three micro-productions of Cheddar were made in triplicate: one with a control milk and the other two with milks in which the WPC 4.2 and WPC 6.7 ingredients were respectively added. The total amount of proteins was increased by 0.5 kgflOO kg of milk (0.5%). The expe- rimental cheeses had a significant higher yield, i.e., 4.3% with WPC 4.2 and 5.2% with WPC 6.7, than the control cheese, at a 37% constant moisture. Cheeses manufactured under these procedures were lower in fat and had a higher moisture content than the control chee se. Electronic micro- scopy shows that the control cheese had a more compact structure than the experimental cheeses. © InralElsevier, Paris. denaturation / whey protein / microfluidization / cheese yield