Three serious problems have been experienced in the manufacture of low moisture cheese using ultrafiltration (UF)- high fat-loss, excessive moisture retention, and poor cheese texture. In this work the causes of these problems were identified, and means of overcoming them were developed. Coagulation and cheese-making experiments indicated that UF concentration of milk shifts the control of rennet coagulation toward the casein micelle collision rate and away from rennet activity, resulting in formation of a rough-textured curd structure that resists syneresis. Use of 4x whole milk retentate, instead of 5x, improved rennet curd structure, syneresis, and UF cheese texture without reducing protein retention in the cheese. Use of increased rennet and reduced set temperature (26°C) also improved curd structure, syneresis, and cheese texture. Washing of the rennet curd prepared from 4x milk retentate during cheese-making, instead of diafiltration of retentate, was found to improve cheese texture, and cheese moisture below 39% was achieved. UF retentate was inconsistent as a starter medium because it offered no protection against bacteriophage proliferation, and the growth of some strains of Lactococcus lactis was impaired in UF retentate. Commercial, internally-buffered pH-controlled starter media were more consistent than fermented retentate starter when used for making cheese from 4x retentate. Low-pressure homogenization of milk at a temperature between 37°C and 45°C increased fat recovery in UF cheese made from 4x ultrafiltration concentrated milk with minimal damage to cheese texture and syneresis. A procedure was developed for the manufacture of quality, high-yield, low-moisture cheese from 4 times ultrafiltration concentrated whole milk. Fat retention in the cheese was 95% and protein retention was 85%

A processing procedure for the manufacture of directly acidified cottage cheese curd from 16% total solids ultrafiltered retentate was developed. The effects of preacidification of skim milk before ultrafiltration and heat treatment of retentate were investigated to improve the functional and sensory qualities of retentate curd. Retentate directly acidified with phosphoric acid and glucono-delta-lactone to pH 4.7 formed a dense, rubbery curd that could not be handled well in a vat. A heat treatment of 71.1°C for 30 min applied to the retentate resulted in a curd with acceptable handling properties. However, this heat treatment caused the curd to shift in pH, become translucent in appearance, and have a pasty texture. Preacidification of the skim milk to pH 5.8 12 h prior to ultrafiltration, and a less severe heat treatment of 71.1°C for 6 min made a stable curd with good sensory quality. A 3 x 4 x 3 randomized split block design experiment was done to test the effects of preacidification and heat treatment on the properties of retentate curd. Skim milk was pasteurized at 62.8°C for 30 min and split into three lots which were unacidified, phosphoric acid added to pH 6.2, and phosphoric acid added to pH 5.85. The three lots of skim milk were ultrafiltered at 54.4°C to 16% total solids. Each lot was divided into four treatments which were unheated, heated to 71.1°C for 7 s, 76.7°C for 7 s, and 82.2°C for 7 s. Each vat was replicated three times. Cottage cheese pH, total solids, and six sensory attributes were measured. Finished cottage cheeses were evaluated by an expert panel of five judges. Total solids, protein content, and fines content of the whey were also measured. Preacidification treatment at pH 6.2 enhanced curd structure, which increased solids recovery, reduced fines, and improved curd appearance, firmness, and texture. Heat treatments caused softening of the curd and increased moisture content in the curd. Excessive heat treatment caused shattering, fines, and mealiness. The best curd from the experiment was produced from pH 6.2 retentate heat treated at 71.1°C for 7 s. Whey proteins decreased in wheys from retentates heat treated at 76.7°C for 7 sand 82.2°C for 7 s. The effects of heat treatment were more pronounced with increasing acidification.

The heat-induced gelation properties of ultrafiltered (UF) whole milk concentrate were studied under different physical and chemical conditions. total solids concentration, homogenization pressures, heating temperatures, and heating times were found to have a positive correlation with gel strength. The addition of calcium chloride, sodium chloride, or trisodium citrate produced gels of higher strengths and textural properties than the gels obtained with non-salt-treated concentrate. Calcium chloride produced the strongest gels with a cheese-like texture and poor spreadability. Sodium chloride produced gels of intermediate strength with a firm, elastic texture and poor spreadability. Trisodium citrate produced the softest gels with a smooth, creamy texture and good spreadability. A shelf stable 40% total solids UF concentrate was manufactured using ultra-high temperature (UHT) processing by direct steam injection. The pourable concentrate had a shelf life of 75 to 90 days at 23°C and did not have the ability to produce heat-induced gels after a second heating. Addition of calcium chloride, sodium chloride, or trisodium citrate restored the heat-induced gelation of the retentate. However, the gels were weaker and presented different characteristics than did the gels from non-UHT-treated concentrate. Transmission electron microscopy (TEM) studies revealed a relationship between gel firmness and gel ultrastructure of the heat-induced gels. The gels consisted of a network of casein micelles connected with strands of a less dense protein material. The tighter the network the stronger the gel strength. High heating temperatures and calcium chloride addition caused fusion of the casein micelles int he network. Sensory evaluation of two prototype gelled desserts by a general consumer population showed a good potential for the use of the heat-induced gelation property of UF-concentrated whole milk in the development of new gelled dessert applications.

Whole milks were adjusted to pH 5.8, 6.2, or 6. 7 with HCl and batch pasteurized at 63°C for 30 min. Each was concentrated 5:1 (40% total solids) through a single tube polysulfone membrane Abcor ultrafiltration unit. Lactose (L), casein hydrolysate (CH), and one of two brands of yeast extract (YE1, YE2) were added into cooled retentates at 0.1, 0.3, 0.5, 0. 7 or 0.9% and equilibrated overnight at 4°C. Five percent proteinase positive (Prt+) Streptococcus cremoris UC 310+ (v/w) milk based culture was added. Unfortified retentate was also inoculated with 0.1, 0.3, 0.5, 0. 7 or 0.9% starter and pH readings were taken on all samples for 24 h during incubation at 23°C. Similar substrates were inoculated with proteinase negative (Prt-) S. cremoris UC 310-. Lactose had no significant effect on acid production. Casein hydrolysate had a slight positive effect. Yeast extract had a significant effect at all preacidification levels and a significant difference was also noticed between the brands. Mean times required for the proteinase positive culture to reach pH 5.1 in 5x retentate from milk acidified to pH 5.8 were 24, 12, 10, 10, and 24 h for L, CH, YE1, YE2, and the control respectively. Proteinase negative variants of this strain had mean times of >24 h, 14 h, 11 h, 11 h, and >24 h respectively. These time differences were significantly different between Prt+ and Prt- variants. A minimum concentration of 0.2% yeast extract produced the most stimulation while greater quantities provided no additional benefit. Taste panelists were unable to detect yeast extract in retentates fermented by either culture variant.

The problem of age gelation in ultra-high temperature (U1IT) sterilized milk retentate (ultrafiltered 3x concentrated) is investigated in this work. Transmission electron microscopy (1EM), utilizing the microcube encapsulation technique and protocols for immunolocalization of milk proteins, provides insight into the phenomenon of age gelation ofUHT-sterilized, ultrafiltered (UF) milk retentate. Primary antibodies (specific for the native as well as the complexed forms of milk proteins) and secondary antibodies (conjugated to gold probes) are used to elucidate the positions of the milk proteins in various samples of milk from the stage of milking through UHT sterilization and storage for 12 months, by which time gelation had occurred. The movement of the milk proteins is charted and these data are used to determine the role of the proteins in age gelation of UHT-sterilized UF milk retentate. Heat-denatured β-lactoglobulin and α-lactalbumin form complexes within the serum as well as with the casein components of the micelles. UHT sterilization not only denatures β-lactoglobulin and α-lactalbumin, but catalyzes the reaction of these whey proteins and K-casein, leading to the successful formation of the complex. Complexing of β-lactoglobulin and K-casein competitively weakens the complex of K-casein to other casein fractions of the micelle. This leads to migration of K-casein from the micelle to the serum, compromising the role of K-casein in stabilizing the casein proteins within the micellar moiety. The time-dependent loss of K-casein from the micelle would expose the calcium-insoluble micellar αs1-casein and β-casein to the serum calcium. Subsequent to this, some αs1-casein and β-casein are also released from the micelles, and gelation of the milk occurs. No information was obtained on location of αs2-casein. The release of K-casein from the micelles thus apparently represents the critical factor in the phenomenon of age gelation in UHT-sterilized milk concentrates.

Yogurts were made from intermediate-high temperature (100, 110, 120, and 130°C for 4 or 16 s), ultra-high temperature (140°C for 4 or 16 s), and vat heat (82°C for 20 min) treatments of skim milk fortified to 5% protein by either ultrafiltration or the addition of nonfat dry milk (NOM). Whey protein denaturation in heated milks increased with temperature and holding time from indirect plate heating and was highest in vat-heated milks. Whey protein denaturation and yogurt water-holding capacity increased with protein levels in the fortified milks compared to skim milk. Penetrometer gel strength and stirred viscosity in 21 day-old yogurt made from heated ultrafiltered skim milk exceeded those of yogurts made from NOM-fortified skim milk, even though the NOM yogurts contained more solids (13.0 vs 11.4%). Maximum gel strength and viscosity, and least syneresis of yogurts from ultrafiltered and NOM fortified yogurts occurred following intermediate-high temperature treatments of 1 00°C for 16 s, 110°C for 4 or 16 s, and 120°C for 4 s. There was significantly lower whey protein denaturation at these intermediate-high temperatures compared to UHT or vat heating. Gel strength and viscosity were lower and syneresis greater in yogurts from ultrafiltered or NOM-fortified skim milk following UHT treatment compared to yogurts made with intermediate-high temperature treatments or vat heating. The water-holding capacity of yogurts from fortified milks treated at intermediate-high temperatures was comparable to that of yogurts from vatheated milks. Fortification by ultrafiltration, to lower total solids (and without use of stabilizers) resulted in yogurt with higher gel strength and viscosity, and reduced syneresis compared to yogurt from NOM fortification. Yogurt prepared by intermediate-high temperature treatment had comparable or better gel strength and viscosity, and reduced syneresis compared to yogurt prepared by traditional vat heating.

Manufacture of white soft cheese from ultrafiltered whole cows• milk involved acidification of pasteurized homogenized whole milk to pH 6.0 with phosphoric or citric acid. The preacidified milk was ultrafiltered at 54 °C until 60% of original milk weight was removed as permeate, diafiltered with deionized water equal to 38.5% of the original milk and concentrated by UF (4.8 fold) to pre-cheese (38% total solid). The pre-cheese was heated to 76.7°C/16 sec, 71 .l°C/l6 sec (HTST) and 7l.l°C/l5 min (controlled water bath), inoculated with 2% starter culture (Streptococcus cremoris), renneted (10 ml/100 lb retentate) and placed in one pound plastic containers in which coagulation took place (8-10 min). Salt (1 .5%) was added on the top of parchment paper placed under the lid, and the curd was incubated at 85°F. The most acceptable cheese was from ultrafiltered retentate heated for 16 sec at 76.7°C before cheese making. Organoleptic tests showed that samples highest in calcium content ranked highest in acceptability. Acidification with citric acid removed more calcium than phosphoric acid and resulted in softer cheese than the control cheese (non-acidified). Slight bitterness was observed when excessive starter and low salt (NaCl) concentration were used. Addition of salt to the retentate prior to heating caused thickening of the retentate before 70°C was reached. Extending the heating time increased the tendency toward mealiness in the cheese.

Pasteurized skimmilk at 4°C was acidified to pH 5.8 with 85.5% phosphoric acid (136g H3Po4;100 kg skimmilk), then warmed to 54°C and ultrafiltered to a protein concentration 9.1 ± 0.2%. The retentate was heated to 76.5°C for 16 s then cooled to 2°C. Phosphoric acid (85.5%) was added at a rate of 3.41g per kg retentate. The acidified retentate was slowly warmed to 29.5 °C (3°C/5 min) when the pH was checked. The pH at this point was no lower than 5.4. Heating was continued until a temperature of 32.2°C was reached. Glucono delta lactone was added to the retentate (17.6 g/kg retentate) and left undisturbed for approximately 80 min. The curd was cut at pH 4.7 with 0.64 cm curd knives and allowed 10 min for syneresis. Permeate obtained from the same lot of milk was acidified to pH 4.8 (66 g H3Po4;100 kg permeate), then added to the curd at 32.2°C (three parts permeate to four parts retentate) and used as a cooking vehicle. The curd was cooked to 59°C in 90 min. The curd was held at 59°C for 10 min, drained and washed once with ice water. Cream dressing containing 12.5% fat and 3% salt was used at the rate of two parts curd to one part dressing. Control cottage cheese was produced by a direct acid method from the same skimmilk used to produce ultrafiltered curd. Use of ultrafiltered skimmilk retentate for cottage cheese making resulted in 2.24% more curd (corrected to 20% solids) and 2.24% more curd per kg original milk protein than the control. However, satisfactory firmness in UF curd required slightly more than 20% solids in the final product. Sensory evaluations indicated that creamed cottage cheese was not significantly different (p

This study investigated the manufacturing procedures and texture attributes of direct acid set of an unripened, shelf-stable cheese variety produced by the combined technologies of ultrafiltration and ultra-high temperature processing. Product evaluation included physical and chemical properties such as gel strength, syneresis, pH, moisture, protein, and fat. Whole milk was concentrated by ultrafiltration to 30, 35, and 40% total solids. Milk retentate was ultra-high temperature-processed by preheating to 65 or 77°C, sterilized at 141°C for 4 s by direct steam injection, flash cooled to approximately 62 or 72°C, homogenized in two stages at either 13.8/2.1 or 27.6/4.1 MPa, cooled to 38°C, and aseptically packaged. iv sterilized sodium chloride was aseptically added and dissolved in the ultra-filtrated and ultra-high temperature processed retentate to produce .5% final concentration. Autoclaved solutions of citric and lactic acids, or glucono-delta-lactone were added aseptically to the salted retentate to form a soft gel by lowering the pH range from 4.3 to 4.6. The coagulated retentates were stored at room temperature for 6 months. The effects of total solids, homogenization pressures, preheat temperatures, acidulants, and storage time on selected physicochemical properties of the acid gels were determined. Taste panels evaluated selected soft cheese characteristics after 6 months' storage. No statistically significant effect of the total milk solids level on gel firmness was observed. High homogenization pressure and the interaction of high preheat temperature and homogenization pressure produced significantly firmer gel and caused less syneresis. Acidulant types influenced significantly gel strength, syneresis, appearance, and texture. Soft cheeses prepared with citric acid were firmer than those acidified with lactic acid or gluconodelta-lactone. Lactic acid samples produced more syneresis than citric acid cheese samples. Cheese samples prepared with glucono-delta-lactone had the smoothest and least grainy texture, shiny appearance, little or no wheying-off, and a gel strength intermediate between the two other acidulants.