Enhanced Thermostability of Lactase (<i>Escherichia coli</i>) in Milk

Mahoney, R. R.; Wilder, Teresa

doi:10.1111/j.1365-2621.1987.tb05916.x

Cited by 4 publications

(6 citation statements)

References 8 publications

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“…As shown in Figure 1a,b the "half-life" (time to reduced lactase activity to 50% of its original value) is about 60 min at 45°C and less than 0.5 min at 55°C. Mahoney and Wilder (1987) have reported that a representative value for the half-life of a purified lactase from Escherichia coli heated in phosphate buffer at 60°C (with added NaN 3 and MgCl 2 ) is 1.1 min. They noted that the half-life of lactase somewhat varied with the lot received from the supplier and also declined with the length of storage of the enzyme in both dry and liquid forms.…”

Section: Resultsmentioning

confidence: 99%

Glass Transition and Thermal Stability of Lactase in Low‐Moisture Amorphous Polymeric Matrices

Mazzobre

Buera

Chirife

1997

Biotechnology Progress

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The thermal stability of a commercial preparation of neutral lactase ( -galactosidase) in low-moisture amorphous polymeric matrices of maltodextrin (MD dextrose equivalent (D.E.) ) 10.9) and polyvinylpyrrolidone (PVP; MW 40 000) stored at various temperatures (T) was studied. The main objective was to analyze the usefulness of the glass transition temperature (T g ) as a parameter for predicting the thermal stability of lactase in low-moisture glass-forming matrices. Loss of enzyme activity was observed during storage in glassy conditions (either in PVP or MD matrices), suggesting that, although molecular mobility may be significantly decreased in the glassy state, the protein molecule is still mobile enough to lead to enzyme inactivation. The results indicated that the change from the glassy to the rubbery state of the PVP matrix, where the enzyme was embedded, was not reflected in drastic changes in the temperature dependence of the thermal inactivation rate, as expected if it could be only predicted on the basis of physical changes of the matrices. The plasticizing effect of water is not the only factor to take into account when considering enzymatic stability in heated low-moisture amorphous systems.

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Section: Resultsmentioning

confidence: 99%

Glass Transition and Thermal Stability of Lactase in Low‐Moisture Amorphous Polymeric Matrices

Mazzobre

Buera

Chirife

1997

Biotechnology Progress

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“…Batch C-62 min. Stabilitv lmcasurcd in milk) slowly declined during storage, as previously rep&cd (Mahoney and Wilder, 1987). Accordingly, all data in individual figures or tables wcrc obtained with a single batch of cnzymc (cxccpt whcrc stated), when the change in half-lift from the initial value was less than 10% and not significant at P~0.05.…”

Section: Methodsmentioning

confidence: 57%

“…Enzyme stability in various media was determined as described by Mahoney and Wilder (1987). All media were adjusted to pH 6.5 at the tcmpcrature of stability determination and the final enzyme concentration in the medium tested was 1 ONPG unit/ml, except where noted.…”

Section: Methodsmentioning

confidence: 99%

“…In a recent study (Mahoney and Wilder, 1987) we reported that E. coli lactase was much more stable in nonfat milk than in buffer and that the difference was more than loo-fold in the temperature range 53.5-60°C. Previous work has shown that this enzyme is stabilized against heat denaturation by 2-mercaptoethanol (Craven et al, 1965), 5-phosphorylribose l-pyrophosphate in the presence of 2-mercaptoethanol (Moses and Sharp, 1970) and an unidentified small molecule with a high absorbance at 260nm, present in crude enzyme extracts (Contaxis and Reithel, 1974).…”

Section: Introductionmentioning

confidence: 94%

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Stabilization of Lactase (Escherichia coli) by Milk Components and Related Compounds

Mahoney¹,

Wilder²

1989

Journal of Food Science

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Thermal stability of lactase was I70-fold greater in milk than in phosphate buffer at 60°C. Enhanced stability was due primarily to casein, whose cffcct was largely substrate dependent. Casein or lactose alone had little or no effect, but together they stabilized the enzyme more than 400-fold at 60°C. The relative effectiveness of other proteins, as stabilizers, was: bovine serum albumin >caseinate>ovatbumin>soy isolate > u-lactalbumin > lysozyme. Galactose was much less effective than lactose in promoting stability; sucrose and glucose were ineffective. Stability was dependent upon both lactose concentration and casein concentration, and decreased with increasing enzyme concentration. Dithioerythritol increased stability in buffer but had relatively little effect in milk.

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“…Lactase was also a little more stable in trehalose solution than in liquid buffer. Mahoney and Wilder (1987) have also reported that lactase heated at 60°C was far more stable in fluid milk than could be predicted from its behavior in liquid buffer solution. At 65°C, the heating temperature the activity of lactase in all liquid systems was almost completely lost after about 5 min (1b), although for shorter times, some stabilizing effect of milk was still apparent.…”

Section: Methodsmentioning

confidence: 96%

Glassy State and Thermal Inactivation of Invertase and Lactase in Dried Amorphous Matrices

et al. 1997

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The thermal stability of enzymes lactase and invertase in dried, amorphous matrices of sugars (trehalose, maltose, lactose, sucrose, raffinose) and some other selected systems (casein, PVP, milk) was studied. The glass transition temperature (Tg) was limited as a threshold parameter for predicting enzyme inactivation because (a) enzyme inactivation was observed in glassy matrices, (b) a specific effect of enzyme stabilization by certain matrices particularly trehalose was observed, and (c) enzyme stability appeared to depend on heating temperature (T) "per se" rather than (T-Tg). For these reasons, a protective mechanism by sugars related to the maintenance of the tertiary structure of the enzyme was favored. A rapid loss of enzyme (lactase) activity was observed in heated sucrose systems at T > Tg, and this was attributed to sucrose crystallization since it is known that upon crystallization the protective effect of sugars is lost. Thus, the stabilizing effect could be indirectly affected by the Tg of the matrix, since crystallization of sugars only occurs above Tg. Trehalose model systems (with added invertase) showed an exceptional stability toward "darkening" (e.g., non-enzymatic browning) when heated in the dried state to elevated temperatures and for long periods of time.

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Enhanced Thermostability of Lactase (Escherichia coli) in Milk

Cited by 4 publications

References 8 publications

Glass Transition and Thermal Stability of Lactase in Low‐Moisture Amorphous Polymeric Matrices

Glass Transition and Thermal Stability of Lactase in Low‐Moisture Amorphous Polymeric Matrices

Stabilization of Lactase (Escherichia coli) by Milk Components and Related Compounds

Glassy State and Thermal Inactivation of Invertase and Lactase in Dried Amorphous Matrices

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