High-pressure-induced changes in bovine milk: a review

High-pressure (HP) treatment of food products is a novel processing technique during which the product is treated in a vessel of suitable strength at a high pressure, generally in the range 100–1000 MPa. As a result, several constituents and properties of the treated product are altered. HP-induced changes in the constituents and properties of milk are arguably among the most extensive of the range of food products studied to date. HP treatment of milk induces solubilization of minerals associated with the casein micelles, denatures whey proteins and, depending on pressure, can either induce aggregation or disruption of the casein micelles. These HP-induced changes in milk constituents affect the properties of the milk; cheesemaking properties of milk can be enhanced considerably, indicating potential application of HP treatment in this area; furthermore, encouraging results have also been reported for HP treatment of milk prior to yogurt manufacture. HP treatment of milk also affects its microflora; however, considerable variation in baroresistance between bacterial species and strains exists. Further applied research appears warranted to establish the full commercial potential of HP treatment of milk.     

Dry kiln scheduling in furniture production

In this paper, a dry kiln scheduling problem from the furniture manufacturing industry is considered. Factory-specified due dates for orders, kiln availability, kiln capacity, and travel time from the kilns to the factories are all incorporated in a model which is formulated as an integer linear program. The objective of the formulation is to minimize the maximum tardiness of orders arriving at the plants by solving a special case of scheduling n independent jobs on m non-identical parallel ciachines. Because of the computational complexity, and the fact that standard integer programming packages appear to perform very poorly on the problem, a heuristic approach is developed. Computational experience is provided which indicates that the heuristic gives very high quality solutions to problems in near real-time.     

Influence of added calcium chloride on the heat stability of unconcentrated and concentrated bovine milk

The influence of added calcium chloride (1–10 mmol/L) on the heat-induced coagulation of skim bovine milk was examined. Unconcentrated milk displayed a pH-heat coagulation time (HCT) profile with a maximum at pH 6.6 and minimum at pH 7.0. Adding calcium chloride to unconcentrated milk progressively reduced the HCT at the maximum, increased the pH at which the maximum occurred and reduced the HCT at pH > 7.0. For concentrated milk, the shape of the pH-HCT profile, that is, a maximum at pH 6.6, was not altered by added calcium chloride, but HCT was reduced progressively with increasing concentration of calcium chloride. Preheating (90°C for 10 min) shifted the maximum in the pH-HCT profile of unconcentrated milk to a more acidic pH, and addition of 5 mmol/L calcium chloride to preheated milk induced changes in heat stability similar to those noted for unheated milk. Addition of calcium chloride to milk prior to preheating strongly reduced the stability of milk against heat-induced coagulation. These data suggest that calcium has a strong destabilizing effect on the stability of milk systems against heat-induced coagulation.     

Foaming properties of milk: A review of the influence of composition and processing

Milk foams can be either desirable, e.g. for cappuccino‐style beverages, or undesirable, e.g. in the reconstitution of milk powders or infant formula. In this article, compositional and processing factors affecting the foaming properties of milk are reviewed. Skim milk foams can be extremely stable, particularly when they are formed at ～40–50°C. The presence of lipids can be detrimental to the formation and stability of milk foams, particularly at a temperature where the milk fat is partially crystalline, e.g. 20°C. The presence of phospholipids, free fatty acids and partial glycerides strongly impairs foaming of milk.     

On optimal and approximate policies for a multistage production/inventory problem

A stochastic multistage production/inventory problem can be solved by an approximate procedure developed by Clark and Scarf. Previous researchers have made comparisons of the solutions obtained by this procedure with optimal solutions obtained by a Markov Decision Process (MDP) solution procedure and found that the Clark-Scarf procedure gives close to optimal solutions. Their experimentation was restricted to two-stage problems. In this paper we extend the comparison to three-stage problems. It is found that the differences in average costs per period grow noticeably as the number of stages of the problem increases. Observations that may facilitate the development of a heuristic procedure to improve the Clark-Scarf solution are given.     

Computation reduction for a large-scale Markov process model to analyse multistage production systems

In order to solve a large-scale Markov decision process which optimizes the control strategy of a multistaged production/inventory system, a computation reduction and memory management system was used. A ‘nuclear’ state space of relatively small size was found to substitute for the original state space. A circular comparison technique and a location index storage method were used to save computer memory used for storing the model     

Influence of added lyophilized butter serum on the heat stability of unconcentrated and concentrated bovine milk

The influence of added lyophilized butter serum on the heat stability of milk was investigated. The addition of lyophilized serum from salted butter to unconcentrated skimmed milk (SM) reduced the heat coagulation time (HCT) at, and increased the pH of, the maximum in the pH–HCT profile and caused disappearance of the minimum. NaCl had similar effects on the heat stability of SM as lyophilized salted butter serum, whereas lyophilized serum from unsalted butter had little effect. The addition of lyophilized salted butter serum to concentrated skimmed milk (CSM) also shifted the pH of maximum heat stability to a higher value and, at certain concentrations, increased the maximum HCT; similar effects were obtained on addition of NaCl, but lyophilized serum from unsalted butter had little effect. These results suggest that the effects of lyophilized serum from salted butter on the heat stability of SM or CSM are due primarily to the presence of a high level of NaCl in this serum.     

Properties of casein micelles cross-linked by transglutaminase

Factors affecting the cross-linking of milk proteins by transglutaminase (TGase) were studied. Cross-linking of caseins in bovine skim milk was optimal over a very wide pH range. The role of micellar calcium phosphate (MCP) in maintaining the integrity of TGase-treated casein micelles was studied by incubating skim milk with 0.01% (w/v) TGase at 30°C for 1–24 h, followed by removal of MCP from untreated or TGase-treated milk by acidification and dialysis. The protein content and profile of the samples were determined by Kjeldahl and SDS-PAGE, respectively. Whey proteins in unheated milk were not susceptible to TGase-induced cross-linking. The higher level of sedimentable protein in MCP-free TGase-treated milk than in MCP-free control milk indicated that TGase treatment partially prevented disintegration of the micelle on removal of MCP, probably due to extensive intramicellar TGase-induced cross-linking of casein molecules which led to the formation of sedimentable covalently bonded casein aggregates.     

Dynamic lot size/sequencing policies in a multi-product,single-machine system

This paper is concerned with the modeling and analysis of a single-machine, multi-product, integrated production–inventory system. A semi-Markov model is developed that incorporates a state-dependent control system. Control optimization is achieved through the use of Markov-renewal programming. Three- and four-product models are developed. The model(s) are exercised over a range of parameters in order to determine the characteristics of the system, and to identify the structure of the optimal control rules of the system. The result is that one can identify simple basic rules of operation that are near-optimal in a dynamic environment, and that make sense intuitively.