Acid Degree Value Research Articles

Effect of Various Direct Ultra-High Temperature Heat Treatments on Flavor of Commercially Prepared Milks

Grae A milk (3.25% fat) was direct UHT processed at 132.2, 143.3, and 137.2°C with 2min preheating and at 137.2°C without preheating for 12s and aseptically packaged in 246-ml Brik Pak cartons in a commercial plant. Samples from each treatment were stored at 25 and 2°C for 24 wk.Changes in acid degree value paralleled the development of stale flavor most closely with a correlation coefficient higher than any of the other tests. Dissolved oxygen might have affected rate of flavor change for UHT milks stored at room temperature. Increases in acidity were slightly greater in UHT samples stored at room temperature than under refrigeration. A combination of acid degree value, dissolved oxygen, and titratable acidity correlated most closely to stale flavor. There was little difference in flavor and concentration of volatile compounds among various heat treatments. Concentrations of acetaldehyde, propanal, n-hexanal, 2-pentanone, 2-hexanone, and 2-heptanone increased more at room temperature than in refrigerated storage; in general, these increases paralleled the stale flavor. Concentrations of the carbonyl compounds measured were far below flavor threshold values when UHT milks were criticized as stale. However, a combination of acetaldehyde, acetone, 2-pentanone, and 2-heptanone were related most closely to stale flavor and could have had an effect on the flavor when all were present.

Effect of Lecithin on Cheese Yield

Cheese manufactured from milk containing three types of lecithin with different acetone-insoluble concentrations were compared with control cheese. A randomized block design with four treatments (three lecithins and one control) was replicated six times in the manufacture of 24 vats of cheese. Commercial lecithins (.05%) were added to the cheese milk at the time of starter addition. Cheese was manufactured by a Colby procedure. Milk was assayed for total solids, fat, total nitrogen, noncasein nitrogen, and acid degree value. Cheese was assayed for solids, acid degree value, and fat. Whey was assayed for total nitrogen, fat, and acid degree value. Milk and cheese weights were to the nearest. 1g. Wet cheese yield increased by an average of 1.9% for cheese containing lecithin. Adjusted whey fats decreased and cheese fat increased slightly (not significant) in lecithin-treated milk and whey surface fat appeared to decrease. No treatment effect was observed for whey total nitrogen or acid degree values of cheese. Whey acid degree values were greater for the STA-SOL UFTM, suggesting that the carrier oil on the whey surface contained some free fatty acids. Apparently, the increased yield was largely due to increased moisture content with a small increase from the milk fat. The resulting increase in fat may be an economic advantage to cheese manufacturers.

Effect of Oxygen on Development of Off-Flavors in Ultrahigh-Temperature Milk

The role of dissolved oxygen as a contributor to flavor deterioration in sterile milk during storage was investigated. Before processing, a concentrated aqueous solution of Tenox-2 was added to half of a batch of pasteurized-homogenized milk to give a final concentration of 400 ppm BHA on a fat basis in the milk. The other half was untreated. Half of each of those batches was treated to reduce oxygen concentrations by a combination of nitrogen sweep and sonication. The remaining two samples (Tenox-2 added and no-Tenox-2) did not receive the deoxygenation treatment. Oxygen levels in the preprocessed deoxygenated milk were lower (4.6 ppm) than those in the untreated milk (6.9 ppm). All four lots were UHT-sterilized at 135°C for 5 s in an indirect UHT system constructed at Kansas State University. Sterilized milk was collected aseptically in a glove box in 250-ml amber glass bottles, which were closed with either Teflon-lined caps or sterile cotton plugs. Samples from each treatment were stored at 7° and 32°C for 4 months. Samples in capped bottles maintained relatively low (<4 ppm) dissolved oxygen concentrations, whereas those in cotton-plugged bottles had relatively high (7–7.5 ppm) dissolved oxygen concentrations. Dissolved oxygen affected the rate of stale flavor development. Sterile milk in bottles with cotton plugs, which had relatively high concentrations of dissolved oxygen during storage, developed a stale flavor sooner and with greater intensity than milks with lower levels of oxygen. However, acetaldehyde, propanal, n-pentanal, and n-hexanal, which are most likely products of lipid oxidation, did not appear to be principal contributors to staling in sterile milk during storage in this study. Furthermore, the stale flavor development did not parallel changes in thiobarbituric acid (TBA) values. Although antioxidant (40 ppm BHA on fat basis from Tenox-2) did retard oxidation slightly, it did not control staling. A decrease in the concentration of several volatile materials throughout the storage period probably was caused by dissipation of the volatile material through the cotton plug or by their interaction with other compounds in the milk. Acid degree values increased in sterile milk at 32°C during prolonged storage, but changes in ADVs did not parallel development of the stale flavor.

Effect of refrigerated storage of milk on the manufacture and quality of Teleme cheese

SummaryTeleme cheese made from milk stored at 4–5 °C for 1–5 d and then pasteurized was compared with that made from unstored control milks. In the raw milks titratable acidity, tyrosine value and acid degree value increased more rapidly in stored milks than in the controls. With pasteurized milks, variations in coagulation times were attributable to levels of psychrotrophs in the corresponding raw milks. Differences were minor for milk fat and N content between cheeses. Curds made from milks stored &gt; 4 d differed markedly from the controls in pH, moisture, N soluble at pH 4·6 and trichloroacetic acid (TCA)-soluble N, but only small differences in levels of casein fragments were detected. Proteolysis in mature cheese (60 d old) made from milk stored &gt; 3 d differed significantly from the controls, and casein fragments were detectable. Off flavour related to excessive protein breakdown developed only in cheese made from milk stored &gt; 4 d. In 60 d old cheeses there was significantly more rancidity in those made from milk stored for &gt; 3 d than in those made from control milk. Unacceptable rancidity became evident at 60 d in cheeses produced from milk stored &gt; 4 d. For Teleme cheesemaking psychrotrophic bacteria multiplying in the milk to levels likely to be encountered in commercial practice are of far greater importance for their lipolytic than for their proteolytic enzymes.

Effects of Lactic Fermentation of Milk on Milk Lipids

ABSTRACTFermentation of whole milk by Lactobacillus acidophilus, Lactobacillus bulguricus and Streptococcus thermophilus resulted in moderate but significant increase in the levels of saturated fatty acids and oleic acid with a concomitant decrease in the levels of linoleic and linolenic acids in the glyceride fraction. Similarly, the increase in the levels of free fatty acids was moderate. There were significant increases in the levels of stearic and oleic acids. Unusual fatty acids of bacterial origin were not detected, and monoglycerides disappeared completely upon fermentation. Changes in cholesterol levels were also not significant. Acid degree value and free fatty acid levels were correlated significantly (r = 0.711). Results indicate that previously reported hypocholestermic effect of fermented milk is not due to changes in the composition of lipid classes investigated.

Fluid Milk Industry in the Central Province of Saudi Arabia

Production, processing, and quality aspects of fluid milk were investigated. Annual production of 36,046, 9,360, and 4,207 metric tons were obtained for raw milk, sterilized milk, and pasteurized milk, respectively. Sterilized milk was made exclusively from recombined milk and constituted 70% of the total processed fluid milk. Only one-third of raw milk was used for manufacture of pasteurized milk and two-thirds for yogurt products. Pasteurized milk was made exclusively from fresh milk. Heat treatment included batch, high-temperature short-time, and ultra-high temperature. The high-temperature short-time pasteurization was predominant. Compositional aspects of raw milk indicated means of 3.09% fat, 3.07% protein, .71% ash, 4.49% lactose, 11.59% total solids, and 8.51% solids-not-fat. The physicochemical analysis of processed fluid milk indicated means of 3.24% fat, 3.30% protein, .73% ash, 4.56% lactose, 11.94% total solids, 8.69% solids-not-fat, 6.59 pH, .14% titratable acidity, .95 acid degree value, 1.3493 refractive index, and 1.0327 specific gravity. Bacteriological analysis showed coliform, Salmonella spp., and Staphylococcus aureus as main contaminants of raw milk. Bacillus cereus and Clostridium perfringens were also detectable but in smaller numbers. Pasteurized milk was of good bacteriological quality and free from detectable antibiotics.

Derancidification of Milk by Adsorption

Among different adsorbents for free fatty acids, that is, metal salt adsorbents, glass fiber, and activated carbon, a column method for carbon adsorption was the best for eliminating free fatty acids from milk produced by lipolysis. Milk was pumped through a jacketed column packed with granular carbon at 60°C. The acid degree value of milk decreased considerably. The temperature and flow rate were critical for derancidification efficiency. Carbon treatment decreased riboflavin but no other components of milk except for a slight decrease (2 to 3%) of protein without affecting its amino acid composition.

Psychrotrophic Bacteria Reduce Cheese Yield

Psychrotrophic strains of Bacillus and Pseudomonas that demonstrated both proteolytic and lipolytic activity were incubated with Grade A milk. The yield of direct-acid cheese manufactured from inoculated milk decreased as psychrotrophic inoculation level increased. Yield reduction resulted from both lipid and protein degradation, and accounted for approximately 45 and 55% of the dry matter loss, respectively. Fat losses were observed from decreased milkfat tests and increased acid degree values. Protein losses were observed from increased non-protein nitrogen and whey nitrogen values. Therefore, cheese yield studies must involve assays of both protein and lipid on a dry matter basis. Acid degree values and fat disappearance in stored milk and total nitrogen in whey were the best indicators of reduction in yields. Although bacterial enumeration, titratable acidity and pH were not good indicators of yield, they may be important in determining when yield loss starts.

Criteria for Optimizing Size and Configuration of Milk Pipelines

To verify various theoretical and practical aspects of milk flow, an experimental milk pipeline was used. Flow instability, characterized by a flooded section of pipeline (that is, formation of milk “slugs”), was dependent on pipeline configuration. Vacuum fluctuations from milk slugs as great fill depths characterized a looped configuration as 28.6 kPa were measured in a dead-end configuration. By contrast, stable flow over a wide range of flow rates, slopes, and. Manning's equation under stable flow conditions accurately predicted flow rate as a function of fill depth, slope, and pipe diameter. Milk Acid Degree Value was higher in milk subjected to slugging. An analysis of effective shear stress on milk suggests a range of fill depths for which milk quality might be maintained. A theoretical model is presented to predict pipeline milk flow as a function of number of cows and rate of unit attaching. A method for pipeline sizing is presented using this model, together with Manning's equation and suitable constraints for fill depth. Current recommendations for pipeline sizing may result in oversized pipeline diameters.

Inhibition of Milk Lipolysis by Lambda Carrageenan

Lambda carrageenan inhibited lipolysis in both raw and homogenized milk. Bulk raw milk samples with and without carrageenan were subjected to both thermal and Waring Blendor activations. Acid degree values revealed that .01 to .05% carrageenan reduced thermally activated lipolysis by 55 to 100% and Waring Blendor activated lipolysis by 36 to 85%. Flavor evaluations by a trained taste panel confirmed the inhibition. Carrageenan (.05%) also reduced the extent of lipolysis produced by the addition of 2% raw skim milk to pasteurized homogenized milk. Carrageenan even inhibited the lipolysis induced by the homogenization of raw milk. Regardless of activation procedure, carrageenan was more effective in inhibiting lipolysis when added before rather than after activation. Addition of carrageenan after lipolysis had occurred did not reduce acid degree values. The inhibitory effect of carrageenan is at least partially from an interaction with lipase. However, it is conceivable that carrageenan may protect the substrate to some extent by partially encapsulating it.

Effect of Process and Temperature During Storage on Ultra-High Temperature Steam-Injected Milk

Milk (3.25% fat) was processed by ultra-high temperature steam injection at 138°C for 20.4s, 149°C for 3.4s, and was packaged aseptically. The ultra-high temperature milk was stored at 24 and 40°C. Fat soluble alkanals were analyzed at start, 8, and 24 wk. Dissolved oxygen content and acid degree values were measured at 4-wk intervals for 24 wkMethanal, propanal, butanal, and nonanal were identified in the two ultra-high temperature samples at start. These compounds decreased during storage at both 24 and 40°C. Dissolved oxygen content increased linearly in samples stored at 24°C but decreased and remained at a minimum in samples stored at 40°C. Acid degree values increased in all samples.

Effects of Processing Conditions on Lipolysis in Milk

Lipolysis, as measured by acid degree value, was observed in processed milk samples. Temperature of pasteurization was a key factor in control of lipase activity. Minimum legal pasteurization was not adequate to prevent lipolysis completely in samples stored for 7 days at 5°C. However, in most cases heating to 76.7°C for 16s did prevent lipolysis from reaching sensory threshold. Varying the holding times from 16 to 24s did not affect lipolysis when temperature was 74.4°C or higher. Varying homogenization pressures from 105 to 211 kg/cm2 did not alter lipolysis significantly. Differences were noted between eight herd milks for extent of prepasteurization lipolysis and thermal inactivation of lipases in these samples.

Heat Resistant Bacterial Lipases and Ultra-High Temperature Sterilization of Dairy Products1,2

Properties of a heat resistant lipase produced by Pseudomonas spp. MC50, a psychrotroph isolated from raw milk, were studied to determine if such enzymes could interfere with successful production of ultra-high temperature sterilized dairy products. In milk MC50 lipase was extremely heat resistant at 100 to 150°C and would be expected to suffer little inactivation during recommended ultra-high temperature processes of 121 to 149°C for .5 to 8s. The optimum temperature for MC50 lipase activity in butter oil emulsion was 40°C, and activity at 20 to 25°C was 27 to 41% of maximum. The optimum pH was pH 8.5 with only 8.3% of maximum activity at pH 6.5 but 43% of maximum activity at pH 7. Lipase activity was greatest in 5% butter oil emulsions, but activity was never less than 65% of maximum over the range of 1 to 10% butter oil. The pH may be the most critical factor in influencing lipase activity in ultra-high temperature sterilized dairy products. Of five batches of normal whole milk and four batches of normal 10% half-and-half subjected to one of three ultra-high temperature sterilization treatments, all exhibited evidence of lipase activity during subsequent storage at room temperature and 40°C. Changes in acid degree values during storage suggested that hydrolytic rancidity could develop in these products in 1 to 7 mo, depending on the ultra-high temperature process and storage temperature. Heat resistant lipases may be common to raw milk and will survive readily most ultra-high temperature sterilization treatments. Although pH may be inhibitory, other factors are suitable to allow lipase activity in dairy products leading to development of rancidity.

Heating and Storing Milk on Dairy Farms Before Pasteurization in Milk Plants

Fresh uncooled raw milk was heated at subpasteurization temperatures through a thin plate heat exchanger and stored in a refrigerated bulk tank at 3±1° C. Equal quantities of heated milk were added to the tank each day or every other day. After 7 days, the stored milk was delivered to a milk processing plant where it was pasteurized. Chemo-biological analysis of the milk before and after pasteurization indicated that the farm-heated milk maintained satisfactory quality after 7 days of storage at 3±1° C. Selected data on the stored milk were comparable to those of regular milk for bacterial counts, acid degree values, and amino acid composition. A consumer panel of 800 persons tasted pasteurized, aged, farmheated (stored) milk, and fresh milk control. About 43% of the panelists expressed no sample preference; 30.8% of the panelists preferred fresh milk.

Effects of Package Temperature and Days of Storage on the Flavor Score of Processed Milk

Shelf-life studies were made on commercially pasteurized milk packaged in fiberboard and blow-mold plastic containers, using two temperatures of storage {4.5 and 7 C) and 0, 7 and 14 days of storage. Quality parameters evaluated were flavor, Standard Plate Count, coliform count, oxidase-positive bacteria count and acid degree value. The data suggest a shelf-life (flavor score ⩾ 36.0) of 2–3 days at 7 C and 7 days at 4.5 C. No significant (P > .01) differences, in the parameters measured, were noted between milk packaged in fiberboard and plastic jugs which were not exposed to fluorescent light. A second phase of this study examined the shelf-life of commercially pasteurized milk packaged in fiberboard containers only. The milks were tested at 0,3,5,7,9,11 and 13 days of storage, using the same parameters noted above. The results suggested a satisfactory shelf-life of 11 and 9 days, respectively, for storage temperatures of 4.5 and 7.0 C.

Effect of a Heat-Resistant Microbial Lipase on Flavor of Ultra-High-Temperature Sterilized Milk

A heat-resistant microbial lipase was added to cows’ milk in different concentrations. After sterilization in a Vacu-Therm Instant Sterilizer the milk was cold-stored at 8°C for 22 days. The acid degree value and flavor changes were followed during storage. The samples containing lipase showed a rapid increase in acid degree value as compared to the reference. The lipase also had a pronounced effect on formation of rancid flavor. The sample with the highest enzyme activity, about .3 units/ml, was perceived as “rancid” after 5 to 8 days. Significant flavor changes appeared in all samples when the acid degree value exceeded 20.

Lipolysis in Milk. I. Determination of Free Fatty Acid and Threshold Value for Lipolyzed Flavor Detection

Two methods, the commonly used “Bureau of Dairy Industries” detergent procedure and a slightly modified version of the Frankel and Tarassuk method, were used to determine the extent of lipolysis in milk. Correlation coefficients were high for both the “Bureau of Dairy Industries” (.95) and the modified Frankel and Tarassuk (.88) methods when acid degree values obtained by each were correlated with time of storage following agitation of the milk. Acid degree values determined by the Bureau of Dairy Industries method correlated highly (.96) with those values by the modified Frankel and Tarassuk method. The linear relationship and high correlation could be used for predicting acid degree values for one method from known values by the other. The threshold for lipolyzed flavor detection in milk was within the range of 4.1 to 4.5 acid degree value as determined by the modified Frankel and Tarassuk method.

Effect of diet and stage of lactation on bovine milk lipolysis

SummaryThe effect of lactation and diet on milk lipoprotein lipase activity (LPL), cell count, serum albumin concentration and free fatty acid levels, expressed in terms of acid degree value (ADV), was examined in 2 experiments. In addition, the ability of blood plasma from cows on different diets to activate LPL was also investigated.Changes in ADV were not consistently associated with changes in LPL, cell count or serum albumin throughout lactation, although results indicated that ADV appeared to be influenced by cell count in early lactation, and by the amount of blood plasma proteins reaching the milk during the remainder of lactation. LPL activity was low in colostrum, but increased rapidly between d 2 and 12 post-partum, reaching a peak at 5 months. Activity was unaffected by diet.There was no effect on ADV of feeding concentrate: hay ratios of 75:25 and 60:40, but ADV was higher in cows fed a low protein diet (crude protein 9%) between 10 and 60 d post-partum, than in cows fed a high protein diet (crude protein 18 %) during the same period. In addition, the blood plasma for cows on the low protein diet had a greater ability to activate LPL although, on the basis of the millk: blood serum albumin ratio, a smaller proportion of blood constituents had reached the milk. The ability of blood plasma to activate LPL was also found to increase with increasing levels of lipoprotein lipid in the blood.

Observations on the influence of high cell count on lipolysis in bovine milk

SummaryThe effect that changes in composition which occur in milks possessing high cell counts have on milk lipolysis has been investigated. High cell counts were produced either by intramammary infusion ofEscherichia coliendotoxin orStreptococcus agalactiaeor by addition of washed cells which were isolated from milk obtained from quarters infused with endotoxin. Free fatty acid levels in milk were measured in terms of acid degree value (ADV) either as initial ADV measured immediately after milking or ADV developed after a prescribed incubation period.There was an increase in initial ADV after the infusion either of endotoxin or ofStr. agalactiaerelative to a control quarter. This increase appeared to be associated with changes in cell count, but in absolute terms the influence of cells on ADV became less as cell count increased. Neither type of infusion had any effect on lipoprotein lipase activity. The addition of washed cells to normal milk resulted in an increase in developed ADV, but the increment was not as large as that produced by the addition of 1% blood serum. When cream and skim-milk from endotoxin-treated quarters and control quarters were mixed in different combinations with and without additional cells, developed ADV was higher in those samples containing endotoxin cream and those with added cells. Milk from a quarter treated with endotoxin was diluted with its own skim-milk to produce different cell counts and ADV was determined after various time intervals at 4 and 37 °C. Lipolysis increased with increasing cell count, but a depression in lipolytic rate was noted after incubation for 6 h at 4 °C and 20 min at 37 °C.The proportion of skim-milk lipoprotein lipase activity in milk serum was larger both in milks possessing high cell counts and in normal milk adjusted to between 5 and 20 mM-NaCl by addition of solid NaCl. These levels of NaCl inhibited lipolysis.The possible direct and indirect effects of high cell count on milk lipolysis are discussed.

Somatic Cells in Milk-Physiological Aspects and Relationship to Amount and Composition of Milk

Somatic cells in milk include epithelial cells from the gland and leukocytes from the blood. Epithelial cells are elevated in very early and late lactation. Leukocytes increase during mastitis infection or injury. They have phagocytic properties and combat invading organisms. Mean somatic cell counts of each milking over a 1-month period for cows with no udder infection, non-pathogens, or pathogens, were 169,500, 225,800, and 997,800 cells per ml, with coeffecients of variation of 94, 66, and 82%. Advanced age, late lactation, and a previous history of mastitis are related to elevated cells. Milk loss in subclinical mastitis is related to somatic cell counts. On a quarter basis, loss started at 500,000 cells per ml, progressed to 7.5% at 1 million, and 30% at 5 million. In cell counting programs associated with monthly testing of individual cows, those cows with two cell counts over 1 million cells per ml produced over 1,000 pounds of milk per lactation less than other cows in the same lactation whose cell count never exceeded 500,000 per ml. Use of cell counting on an individual cow basis improves its usefulness as a management tool for the dairyman compared to bulk tank counts. Literature data suggest the following changes in the milk composition from quarters definitely positive to mastitis screening tests based on somatic cell counts compared to normal quarters (values represent percent of normal): total solids (92), lactose (85), fat (88), total protein (100), caseins (82), whey protein (162), chloride (161), sodium (136), potassium (91), pH (105), lipase activity (116), and acid degree value (183).