Characterization of the physical, microbiological, and chemical properties of sonicated raw bovine milk.

Innovative processing technologies, such as ultrasonication, can change the properties of milk, allowing for the improvement or development of dairy foods. Yet taking bench-scale equipment to pilot plant scale has been challenging. Raw milk, standardized to 3% fat and warmed to inlet temperatures of 42 or 54°C, was exposed to continuous, high-intensity, low-frequency ultrasonication (16/20 kHz, 1.36 kW/pass) at flow rates of 0.15, 0.30, and 0.45 L/min that resulted in resident times within the reaction cell of 6, 3, and 2 min per pass, respectively. Multiple passes (3, 5, and 7, respectively) were required to obtain a total exposure time of 14 to 18 min. Evaluation of fat droplet sizes, enzyme coagulation properties, and microstructure of milk and milk gels, as well as determining compositional and lipid properties, were conducted to determine the potential of the ultrasound system to effectively modify milk. Laser scanning particle sizing and confocal microscopy showed that the largest droplets (2.26 ± 0.13 µm) found in raw milk were selectively reduced in size with a concomitant increase in the number of submicron droplets (0.37 ± 0.06 µm), which occurred sooner when exposed to shorter bursts of ultrasonication (0.45 L/min flow rates) and at an inlet temperature of 54°C. Ultrasound processing with milk entering at 42°C resulted in faster gelling times and firmer curds at 30 min; however, extended processing at inlet temperature of 54°C reduced curd firmness and lengthened coagulation time. This showed that ultrasonication altered protein-protein and protein-lipid interactions, thus the strength of the enzyme-set curds. Scanning electron microscopy revealed a denser curd matrix with less continuous and more irregular shaped and clustered strands, whereas transmission electron microscopy showed submicron lipid droplets embedded within the protein strands of the curd matrix. Processing at inlet temperature of 54°C with flow rates of 0.30 and 0.45 L/min also reduced the total aerobic bacterial count by more than 1 log cfu/mL, and the number of psychrophiles below the limit of detection (10 cfu/mL) for this study. Ultrasonication exposures of 14 to 18 min had minimal effect on the milk composition, fatty acid profiles, and lipid heat capacity and enthalpy. The findings show that this continuous ultrasound system, which is conducive to commercial scale-up, modifies the physical and functional properties of milk under the parameters used in this study and has potential use in dairy processing.

The effects of microfluidization on the physical, microbial, chemical, and coagulation properties of milk.

This work examines the use of mild heat treatments in conjunction with 2-pass microfluidization to generate cheese milk for potential use in soft cheeses, such as Queso Fresco. Raw, thermized, and high temperature, short time pasteurized milk samples, standardized to the 3% (wt/wt) fat content used in cheesemaking, were processed at 4 inlet temperature and pressure conditions: 42°C/75 MPa, 42°C/125 MPa, 54°C/125 MPa, and 54°C/170 MPa. Processing-induced changes in the physical, chemical, and microbial properties resulting from the intense pressure, shear, and cavitation that milk experiences as it is microfluidized were compared with nonmicrofluidized controls. A pressure-dependent increase in exit temperature was observed for all microfluidized samples, with inactivation of alkaline phosphatase in raw and thermized samples at 125 and 170 MPa. Microfluidization of all samples under the 4 inlet temperature and processing pressure conditions resulted in a stable emulsion of fat droplets ranging from 0.390 to 0.501 µm, compared with 7.921 (control) and 4.127 (homogenized control) µm. Confocal imaging showed coalescence of scattered fat agglomerates 1 to 3 µm in size during the first 24 h. We found no changes in fat, lactose, ash content or pH, indicating the major components of milk remained unaffected by microfluidization. However, the apparent protein content was reduced from 3.1 to 2.2%, likely a result of near infrared spectroscopy improperly identifying the micellar fragments embedded into the fat droplets. Microbiology results indicated a decrease in mesophilic aerobic and psychrophilic milk microflora with increasing temperature and pressure, suggesting that microfluidization may eliminate bacteria. The viscosities of milk samples were similar but tended to be higher after treatment at 54°C and 125 or 170 MPa. These samples exhibited the longest coagulation times and the weakest gel firmness, indicating that formation of the casein matrix, a critical step in the production of cheese, was affected. Low temperature and pressure (42°C/75 MPa) exhibited similar coagulation properties to controls. The results suggest that microfluidization at lower pressures may be used to manufacture high-moisture cheese with altered texture whereas higher pressures may result in novel dairy ingredients.

A behavioral mechanism for resting site selection by pupae in three mosquito species.

Pupae of Aedes aegypti, Ae. triseriatus and Culex restuans dive less frequently when resting in a concave meniscus than when resting in open water. They also tend to terminate diving after contacting submerged vertical surfaces, increasing their chances of surfacing in a concave meniscus. As a result pupae tend to rest in concave menisci associated with emergent vertical surfaces, a behavioral adaptation by which they probably conserve energy and avoid predation.

In vitro interaction of quinidine with kaolin and pectin.

The adsorption of quinidine onto kaolin was studied as a function of pH in aqueous solutions in which the ionic strength was adjusted to 0.1. The interaction of quinidine with pectin also was investigated in water and in phosphate buffer; the buffer pH and ionic strength were adjusted to 6.5 and 0.1, respectively. The in vitro results indicated that quinidine was adsorbed onto kaolin. At the highest concentration studied, the extent of adsorption increased from 3.64 mg of quinidine adsorbed/g of adsorbent at pH 2.4 to an average of 5.81 mg/g in the pH 5.5-7.5 range. In the presence of electrolytes, the interaction of quinidine with pectin was relatively small (3-13% bound) as compared to studies performed in water (66-90% bound). The data indicate that some quinidine may be adsorbed when this drug is administered concurrently with kaolin-pectin preparations.