Direct Steam Injection Research Articles

Association of β-Lactoglobulin and β-Lactalbumin with the Casein Micelles in Skim Milk Heated in an Ultra-high Temperature Plant

Abstract Skim milk was subjected to various time–temperature treatments using a direct steam injection (DSI) system in a pilot-scale ultra-high temperature (UHT) plant. The heated samples were ultracentrifuged and the supernatants analysed using quantitative polyacrylamide gel electrophoresis to determine the extent of denaturation of β-lactoglobulin (β-lg) and α-lactalbumin (α-la) and their association with the casein micelles. The extent of β-lg and α-la denaturation and association increased with an increase in both heating time and temperature; the rate of association was markedly less than that of denaturation. The association behaviour was affected by heating temperature; during the initial stages of heating in the range 80–130°C, mainly β-lg appeared to associate with the casein micelles, but after prolonged heating, α-la began to associate with the micelle. In contrast, below 80°C both β-lg and α-la appeared to associate simultaneously with the micelles. The maximum level of association of α-la varied with heating temperature, ∼40% of total in the range 95–130°C and ∼55% below 90°C. For β-lg, the maximum level of association was ∼55% of total regardless of the temperature. A pseudo-first-order model was used to calculate the reaction kinetics of the association of β-lg with the casein micelle.

Kinetics of Denaturation and Aggregation of Whey Proteins in Skim Milk Heated in an Ultra-high Temperature (UHT) Pilot Plant

Skim milk was subjected to various temperature–time (70–130°C for 3–1800 s) treatments in a pilot-scale ultra-high temperature (UHT) plant using a direct steam injection (DSI) system. The rates of denaturation and aggregation of β-lactoglobulin (β-lg) and α-lactalbumin (α-la) were determined by quantitative polyacrylamide gel electrophoresis while that of immunoglobulin G (IgG) was determined by affinity chromatography. The order of reaction, the rate constant and the activation energy were determined for the denaturation of β-lg, α-la and IgG using non-linear regression methods. The kinetic parameters obtained for β-lg and α-la showed a marked temperature dependence. Aggregation of β-lg mainly involved the formation of intermolecular disulphide linkages at all temperatures studied, while the aggregation of α-la, particularly below 80°C, appeared to also involve hydrophobic interactions. The kinetic parameters obtained for β-lg aggregation, due to disulphide bond formation, were similar to those observed for β-lg denaturation.

Effect of different heat treatments on the strong binding interactions between whey proteins and milk fat globules in whole milk

SummaryThe heat-induced binding of whey proteins to milk fat globule membranes in whole milk was investigated by quantitative electrophoresis and laser scanning densitometry. Both α-lactalbumin and β-lactoglobulin bound to the surfaces of fat globules when milk was heated in a water bath in the temperature range 65–85 °C. The interaction behaviour of α-lactalbumin did not seem to change with temperature, and the total amount of protein bound was ∼ 0·2 mg/g fat contained in the cream. The quantity of βlactoglobulin interacting with the milk fat globules increased with temperature from 02 to 0·7 mg/g fat between 65° and 85 °C. Even in whole milk heated at batch pasteurization temperatures (60–65 °C), α-lactalbumin and β-lactoglobulin were found attached to the fat globules. The interactions of the whey proteins with intact fat globule membranes were also investigated in milk heated in an industrial system (a pilot scale UHT and high temperature short time module), and the results were compared with those from the laboratory treatment (simple batch heating). The binding of the whey proteins to fat globules differed between milk heated by UHT using indirect steam heating or direct steam injection (DSI). However, the surface load in milk treated by DSI was not comparable to that of milk treated by batch heating or indirect steam heating, because of the changes in fat globule size and membrane composition caused by the DSI process.

Design of Stable Steam Injectors for Continuous Heating

Continuous direct steam injection systems are used in industry to rapidly raise the temperature of process streams either for heating or for sterilization purposes. High heat transfer rates can be achieved using this method, as compared with other methods e.g. shell and tube heat exchangers. Currently, there are no rational procedures available for designing steam injectors for stable operation. Flow visualization studies and pressure measurements have shown that three flow regimes ; bubbling, jetting and intermittent steam/water flow exist, in direct steam injection into continuously flowing water. These flow regimes are a function of process conditions and orifice diameter. A semi-quantitative flow regime map for a range of process conditions has been drawn up. Bubbly flows give rise to the highest levels of noise due to bubble oscillations. This type of flow should therefore be avoided. The most stable flow regime, in terms of noise levels generated and hydrodynamic considerations is the jetting regime. Models have been derived for each flow regime ; good agreement is found between experimental and theoretical data. A dimensionless number (Bubble/Jet number) has been defined, which can be used to predict transitions between bubbling and jetting flows. This dimensionless number, together with the flow regime map can be used to design stable, relatively quiet steam injection systems.

Sensory and Microbial Quality of Milk Processed for Extended Shelf Life by Direct Steam Injection

Heat treatments of milk between 100 and 145°C produce a new type of product with a shelf life of 15 to 30 days at 7°C, which is termed extended shelf life (ESL) milk. Little information is available on the safety and sensory qualities of this product. Extended shelf life milk is being processed commercially to expand the distribution area of fluid milk products. After arrival at market, this product still has the shelf life of a pasteurized product. In this study milk was processed by direct steam injection at temperatures between 100 and 140°C for 4 or 12 s. Holding time did not significantly affect the sensory quality of the milk. A trained taste panel found cooked flavor and other off flavors varied significantly with increasing processing temperature and storage time. There were no significant differences noted in cooked or off flavors between 132 and 140°C. Psychrotrophic Bacillus species were isolated from milk processed at and below 132°C, while no organisms were isolated from milk processed at temperatures at or above 134°C. Consumer preference panels indicated consumers preferred milk processed at 134°C for 4 s to ultrahigh-temperature (UHT) processed milk, although there was a slight preference for high-temperature short-time processed (HTST) milk compared to milk processed at 134°C for 4 s. Higher temperatures had a less destructive effect on lipase activity, while storage time did not significantly affect lipase activity.

Effects of a Low Concentration of Added Plasmin on Ultra-High Temperature Processed Milk

The relationship between proteolysis and gelation was studied in UHT-processed milk following the aseptic addition of the enzyme plasmin at a concentration of .15 mg/L. Individual 250-ml containers of commercially processed (direct steam injection, 134.4°C for 14.2s) milk were used. The milk was injected with plasmin 1 wk after processing and stored at room temperature (–23°C). Over a 6-mo period, the milk was examined for changes in appearance, pH, apparent viscosity, gel formation, enzymatic activity, and casein breakdown. Control milk samples did not gel during the test period. The milk containers that received the plasmin addition began to form a gel at 90 d of storage, and this gelation was accompanied by an increase in apparent viscosity. In the samples with added plasmin, enzyme activity was detected using the chromogenic substrate, H-D-valyl-L-leucyl-L-lysyl-4-nitroanilide (S-2251), and casein breakdown was apparent as examined by SDS-PAGE. It appeared that the added plasmin preferentially attacked ßbeta;- and α-caseins over κ-casein. The evidence supports a relationship between a low level of plasmin activity and the gelation of UHT milk.

Isolation and partial purification of astringent compounds from ultra-high temperature sterilized milk

SummaryAstringent off-flavours were observed in commercial samples of UHT-milk heated by direct-steam injection. The off-flavour components from these milk samples were isolated by the chloroform-methanol extraction procedure of Harwalkar & Elliott. The astringent-tasting components in these extracts were partly purified by isoelectric precipitation at pH 7·0 and by size exclusion chromatography on Sephadex G-50 columns. The extracted off-flavour components and the partly purified samples were further analysed by FPLC using a Mono-Q anion exchange column and PAGE. The FPLC and PAGE patterns of the extracts from astringent and non-astringent samples of milk showed marked differences and the astringent flavour correlated with one of the fractions resolved by FPLC. This fraction was found to be heterogeneous by PAGE. The astringent off-flavours in UHT-sterilized milk were γ-casein-like breakdown products of casein.

Effect of Ultra-High-Temperature Steam Injection Upon Constituents of Skim Milk

Raw skim milk was heated to 143±1 C by direct steam injection, held for 8 to 10 s, and vacuum cooled. Analyses of different chemical characteristics of ultra-high-temperature processed skim milk showed a decrease in pH, titratable acidity, and ionized calcium as compared to the control; sialic acid and active sulfhydryls increased. Increases in sialic acid and sulfhydryls might be due to unfolding of protein moieties thus exposing: 1) glycoproteins containing sialic acid and 2) buried sulfhydryls and/or reduction of disulfide bridges in milk proteins. Alteration of the native protein was determined by two techniques: 1) isolation procedures for specific proteins and 2) electrophoretic and densitometric techniques. Casein micelles were most resistant to alteration of their structure while whey proteins, especially β-lactoglobulins, were very susceptible to structural changes. These structural changes may be related to sedimentation and flavor problems associated with ultra-high-temperature milks.

ASEPTIC PROCESSING AND PACKAGING OF MILK

The commercial aspects of aseptic processing and packaging of milk showing only a slow rise in the market are assessed. The paper describes three types of process plant, the indirect plate heat exchanger, indirect tubular heat exchanger and direct steam injection plants and the various advantages are evaluated. Simplification of plants with the removal of de‐gassers, flash cooling vessels etc. is emphasized in the modern indirect plant which will heat, cool and homogenize as simply as possible. Differences between operation of a UHT carton dairy and an average bottling dairy are described. (Editor's summary)

Effect of Psychrotrophic Bacteria from Raw Milk on Milk Proteins and Stability of Milk Proteins to Ultrahigh Temperature Treatment

The effects of psychrotroph growth in raw milk on proteins of mils and on the response of milk proteins to heat treatments with ultrahigh temperature were studied. Ten gram-negative psychrotrophs isolated from raw milk readily attacked raw milk proteins. Kappa- and beta-casein were most susceptible although some of the isolates also attacked the whey proteins. Detectable proteolysis did not require large psychrotroph populations. A 10 to 20% decrease in kappa-casein during 2 days at 5 C accompanied growth of one isolate to a population of only 10,000/ml. Growth of psychrotrophs in raw milk predisposed the proteins to deleterious effects of ultrahigh temperature treatments. Ultrahigh temperature treatment by direct steam injection had little effect on raw milk caseins and decreased alpha-lactalbumin and beta-lactoglobulin by 21% and 34%, respectively. Milk that had undergone proteolysis exhibited decreased detectable kappa-, beta-, and alphas-caseins and increased loss of beta-lactoglobulin as a result of ultrahigh temperature treatment. Milk suffering extensive kappa-casein degradation coagulated during ultrahigh temperature treatment. Coagulation during or shortly after heating increased with severity of heat treatment and size of psychrotroph population.

Effect of Ultra-high Temperature Steam Injection on Flavor Acceptability of Whole and Fortified Skim Milks

Whole milk (3.25% fat and 9% solids-not-fat) and low-fat fortified milk (.9% fat and 11% solids-not-fat) were processed in a No-Bac Aro-Vac equipped with an ultra-high-temperature direct steam injector. Milk was preheated to 71C and then heated to 107, 121, 135, or 143C and held for 1.5 or 5s. Samples were also heated to 135 or 143C and held for 8 or 10s. Samples were stored at 1.7 and 7.2C and analyzed by a taste panel at 2, 9, 16, 23, and 30 days. Both triangular and preference tests were used. After 30 days of storage at 72.2C, whole milk and fortified low-fat milk heated at 135 and 143C fcr 10s were acceptable. Storage at 1.7C for 30 days resulted in flavor scores between acceptable and good for all processing temperatures and times. Acceptable milk can be produced by ultra-high-temperature direct steam injection.

Effects of ultra-high-temperature (UHT) processing and of subsequent storage on the vitamin content of milk

SummaryThe vitamin content of ultra-high-temperature (UHT) processed milk was compared with that of the original raw milk. Three processes were used. In the first, which caused no change in oxygen content, the milk was heated and cooled in a plate-type heat exchanger. In the second, the milk was again heated indirectly and then evaporatively cooled, leaving in the milk about one-third of the initial oxygen content. In the third process the milk was heated by direct steam injection and cooled by evaporation and contained little or no residual oxygen.On processing and during subsequent storage for 90 days there was no loss of vitamin A, carotene, vitamin E, thiamine, riboflavine, pantothenic acid, biotin or nicotinic acid. There was little or no loss of vitamin B6or vitamin B12on processing, but up to 50% of each of these vitamins was lost during 90 days' storage. All the dehydroascorbic acid (DHA) and about 20% of the ascorbic acid (AA) was lost on processing. There was no further loss of AA during 90 days’ storage when no residual oxygen was present, but in milks containing more than about 1 ppm oxygen all the AA was lost within 14 days. About 20% of the folic acid was lost on processing; thereafter, as with ascorbic acid, the extent of the loss on storage depended on the residual oxygen content of the milk: in the absence of oxygen the folic acid was stable.

Poduction of Sulfur Compounds in Skimmilk Heated by Direct Steam Injection

Summary The effects of direct steam injection heating on the development of heat-activated sulfur compounds in skimmilk were studied over a temperature and time range of 190 to 300 F and 2 to 150 sec. The heat activation of sulfhydryl groups, as measured by silver titration, followed a direct relationship to heating-temperatures in those samples held for 2 sec. At 20 and 150 sec, maximum responses to temperature were observed followed by a decrease, when vacuum cooling was used, as the temperature of heating increased. It was determined that much of the decrease in titration values above the critical treatment resulted from volatilization of sulfur compounds.

Direct-Steam Injection System for Processing Fluid Milk Products

Summary A steam-injection system for heating fluid milk products is described in which temperatures are automatically and accurately maintained as high as 300F. Holding times are varied by adjustments in the length of the holding tube. Thus, accurate heat treatments of fluid products can be provided over a wide range of total treatments. The system is very adaptable for research and commercial use because of the wide range of treatments and volumes possible with the equipment. The system has been used for the commercial processing of fluid milk and ice cream mixes in conjunction with a high-temperature short-time pasteurizer. It has also proved very useful in research on fluid milk, ice cream mix, and skimmilk for cultured milk products. The vacuum system is being used to provide quantities of volatile materials from milk for identification purposes. The entire system is cleaned easily in-place and should be very adaptable to an automated process.

Use of Direct Steam Injection in Food Processing

Use of Direct Steam Injection in Food Processing

Disinfecting Garbage in Truck Bodies by Direct Steam Injection

Disinfecting Garbage in Truck Bodies by Direct Steam Injection

Direct Steam-Injection Continuous Starch-Cooker

A number of different continuous starch-cooking devices are available for the production of starch-based textile pastes and sizes. This paper discusses the advantages and operation of a simple, direct steam-injection type made from standard piping. Characteristics of pastes produced with this type of cooker are also discussed.