Assessing the heat induced changes in major cow and non-cow whey proteins conformation on kinetic and thermodynamic basis

The use of alkaline phosphatase and possible alternative testing to verify pasteurisation of raw milk, colostrum, dairy and colostrum-based products

Pasteurisation of raw milk, colostrum, dairy or colostrum-based products must be achieved using at least 72°C for 15 s, at least 63°C for 30 min or any equivalent combination, such that the alkaline phosphatase (ALP) test immediately after such treatment gives a negative result. For cows' milk, a negative result is when the measured activity is ≤ 350 milliunits of enzyme activity per litre (mU/L) using the ISO standard 11816-1. The use and limitations of an ALP test and possible alternative methods for verifying pasteurisation of those products from other animal species (in particular sheep and goats) were evaluated. The current limitations of ALP testing of bovine products also apply. ALP activity in raw ovine milk appears to be about three times higher and in caprine milk about five times lower than in bovine milk and is highly variable between breeds. It is influenced by season, lactation stage and fat content. Assuming a similar pathogen inactivation rate to cows' milk and based on the available data, there is 95-99% probability (extremely likely) that pasteurised goat milk and pasteurised sheep milk would have an ALP activity below a limit of 300 and 500 mU/L, respectively. The main alternative methods currently used are temperature monitoring using data loggers (which cannot detect other process failures such as cracked or leaking plates) and the enumeration of Enterobacteriaceae (which is not suitable for pasteurisation verification but is relevant for hygiene monitoring). The inactivation of certain enzymes other than ALP may be more suitable for the verification of pasteurisation but requires further study. Secondary products of heat treatment are not suitable as pasteurisation markers due to the high temperatures needed for their production. More research is needed to facilitate a definitive conclusion on the applicability of changes in native whey proteins as pasteurisation markers.

Modulation of Milk Allergenicity by Baking Milk in Foods: A Proteomic Investigation

Cow's milk is considered the best wholesome supplement for children since it is highly enriched with micro and macro nutrients. Although the protein fraction is composed of more than 25 proteins, only a few of them are capable of triggering allergic reactions in sensitive consumers. The balance in protein composition plays an important role in the sensitization capacity of cow's milk, and its modification can increase the immunological response in allergic patients. In particular, the heating treatments in the presence of a food matrix have demonstrated a decrease in the milk allergenicity and this has also proved to play a pivotal role in developing tolerance towards milk. In this paper we investigated the effect of thermal treatment like baking of cow's milk proteins that were employed as ingredients in the preparation of muffins. A proteomic workflow was applied to the analysis of the protein bands highlighted along the SDS gel followed by western blot analyses with sera of milk allergic children in order to have deeper information on the impact of the heating on the epitopes and consequent IgE recognition. Our results show that incorporating milk in muffins might promote the formation of complex milk-food components and induce a modulation of the immunoreactivity towards milk allergens compared to milk baked in the oven at 180 °C for ten minutes. The interactions between milk proteins and food components during heating proved to play a role in the potential reduction of allergenicity as assessed by in vitro tests. This would help, in perspective, in designing strategies for improving milk tolerance in young patients affected from severe milk allergies.

Monitoring the heat-induced structural changes of alkaline phosphatase by molecular modeling, fluorescence spectroscopy and inactivation kinetics investigations

The heat induced conformational changes of calf alkaline phosphatase (ALP) were analyzed using different methods, based on fluorescence spectroscopy, molecular modeling and inactivation studies. Experimental studies were conducted in buffer solution in the temperature range between 25 and 70 °C. Molecular dynamic (MD) simulation provided details on thermally induced changes in ALP structure, highlighting that heating favored the hydrophobic exposure and important alteration of the catalytic site above 60 °C. Additional information to MD data were obtained by using different fluorescence spectroscopy methods, which revealed a complex mechanism of thermal denaturation. Therefore, the emissive properties indicated an unfolding of ALP at temperatures below 60 °C, whereas at higher temperatures, the polypeptides chains fold leading to a higher exposure of Trp residues. In order to establish a structure-function relationship, the results were correlated with inactivation studies of ALP in buffer at pH 9.0. The inactivation data were fitted using a first-order kinetic model, resulting in an activation energy value of 207.26 ± 21.68 kJ · mol(-1).

Ultra-high resolution crystal structure of recombinant caprine β-lactoglobulin

β-Lactoglobulin (βlg) is the most abundant whey protein in the milks of ruminant animals. While bovine βlg has been subjected to a vast array of studies, little is known about the caprine ortholog. We present an ultra-high resolution crystal structure of caprine βlg complemented by analytical ultracentrifugation and small-angle X-ray scattering data. In both solution and crystalline states caprine βlg is dimeric (K(D)<5 μM); however, our data suggest a flexible quaternary arrangement of subunits within the dimer. These structural findings will provide insight into relationships among structural, processing, nutritional and immunological characteristics that distinguish cow's and goat's milk.

Cow's milk with active immunoglobulins against Campylobacter jejuni: effects of temperature on immunoglobulin activity

BACKGROUND

Adult Holstein cows were injected with an antiserum against Campylobacter jejuni and immunoglobulin activities in vitro were determined in blood and milk several weeks after injection. The immunoactivity of immunoglobulins in milk was measured by an ELISA after different temperature-time treatments (60-91°C and 4-3600 s) at laboratory and pilot-plant scales. Kinetic and thermodynamic parameters were determined.

RESULTS

An increase in immunoglobulin activity in milk was detected several days after injection. Optical densities increased by three- to seven-fold in this period. The activity started to decay 4-5 weeks after injection. Immunoglobulins maintained most of their in vitro activity under pasteurisation conditions (72°C and 15 s) and were denatured following first-order kinetics.

CONCLUSIONS

The injection protocol applied allows milk with specific immunoglobulins against Campylobacter jejuni to be obtained. Traditional pasteurisation did not reduce this activity.