Packaging modifications for protecting flavor of extended-shelf-life milk from light.

The effectiveness of titanium dioxide (TiO2)-loaded high-density polyethylene (HDPE) to reduce light-induced oxidation of extended-shelf-life milk (2% total fat) was studied. The objective was to determine differences over time in sensory quality, vitamin retention, and oxidative chemistry as a function of packaging and retail light exposure duration. Effectiveness of packaging for protecting milk quality was assessed by sensory evaluation (triangle tests, untrained panel), changes in volatile compounds, thiobarbituric reactive substances (TBARS), and riboflavin concentration. Milk (2%) was stored in HDPE packages consisting of TiO2 at 3 levels (low: 0.6%; medium: 1.3%; high: 4.3%) at 3 °C for up to 43 d. Light-protected (translucent, foil-wrapped) and light-exposed (translucent) HDPE packages served as controls. The high TiO2-HDPE package provided protection similar to light-protected control package through d 22 of light exposure, with less consistent performance by the medium TiO2 package. The TBARS increased in all treatments during storage. Under the experimental conditions used, a TBARS value of 1.3mg/L could be considered the limiting sensory threshold for differentiating oxidized milk from light-protected milk. Riboflavin concentration decreased 10.5% in the light-protected control and 28.5% in the high TiO2 packaged milk past 29 d of light exposure, but losses were greater than 40% for all other packages. The high TiO2 package protected riboflavin concentration from degradation and controlled aldehyde concentration throughout the test period.

Oxidative stability of an extended shelf-life dairy-based beverage system designed to contribute to heart health.

Skim milk, butter-derived aqueous phase, butter oil, and fish oil (3 levels) were used to produce UHT pasteurized n-3 fatty acid-fortified beverages (3.1% fat, 3.9% protein, and 11.5% total solids) with targeted deliveries of 200, 500, and 800 mg of eicosapentaenoic acid and docosahexaenoic acid (combined total) per 250 mL (8 fl oz) serving. Microbial quality, emulsion stability, and oxidation of lipids over 35 d of storage at 4 °C were evaluated. Conjugated diene hydroperoxides were below 1% throughout storage and were found at highest concentrations around d 21 of storage for all formulations. Volatile analysis indicated an increase in 1-penten-3-ol in the n-3 fortified dairy-based beverage systems during storage. Triangle tests were conducted to determine if consumers could detect a difference in aroma, compared with commercially processed aseptically packaged milk. The beverage system with targeted delivery of 500 mg of eicosapentaenoic acid + docosahexaenoic acid per 250-mL serving was not different in aroma compared with commercially available UHT processed milk. This formulation delivered 432 mg of heart-healthy n-3 fatty acids per 250-mL serving on d 35 and was microbiologically and physically stable throughout the 35-d refrigerated storage period.

Consumer perception and sensory effect of oxidation in savory-flavored yogurt enriched with n-3 lipids.

The objective of this study was to determine the effects of different oils (butter, fish, and oxidized fish) on sensory characteristics of a savory [chile-lime (CL)] low-fat yogurt using descriptive (unstructured line scales, 5 attributes) and affective (hedonic) sensory testing methods. Yogurts were each manufactured at low [1.1-1.2% total fat; 0.43% added oil (wt/wt)] or high [1.6% total fat; 1% added oil (wt/wt)] levels of fish oil, with high levels of fish oil targeted to deliver 145 mg of docosahexaenoic acid+eicosapentaenoic acid/170 g of yogurt. In a preliminary study, untrained panelists (n=31), using triangle tests, did not discriminate between low levels of fish and butter oils in unflavored yogurts but could discern yogurt with oxidized fish oil, even at the low level. Trained panelists (n=12) described lower lime and acid flavor characteristics in CL-flavored yogurts containing 1% oxidized fish oil compared with yogurts containing low levels of oxidized fish oil and low or high levels of butter and fish oils. Oxidized flavor was higher in CL-flavored yogurts with oxidized fish oil (low and high) and with the high level of fish oil. Consumer ratings (n=100; 9-point hedonic scale; 9="like extremely) of overall acceptability and flavor acceptability were bimodally distributed, with overall means between 4 and 5 ("neither like nor dislike") for CL-flavored yogurt with butter or fish oils (high level). The upper 50% of responses for yogurt with butter or fish oil were 6.51 and 6.31, respectively, for overall acceptability ("like slightly"), and 7.02 and 6.56, respectively, for flavor acceptability. A large segment of consumers may be interested in incorporating heart-healthy n-3 lipids in their diets through frequent consumption of a savory yogurt enriched with n-3 fatty acids.

Glycosylation of kappa-casein. I. Localization and characterization of sialyltransferase in bovine mammary gland.

A sialyltransferase (CMP-N-acetylneuraminate:D-galactosyl-glycoprotein N-acetylneuraminyltransferase, EC 2.4.99.1) which attaches N-acetylneuraminic acid to the terminal end of the carbohydrate chain of kappa-casein was found to be concentrated in Golgi apparatus-enriched fractions of bovine mammary gland. Maximum sialyltransferase activity was obtained at pH 5.5 and 37 degrees C in the presence of 1 mM dithiothreitol and Triton X-100. A Km of 0.19 mg asialo-kappa-casein/ml (0.01 mM) was obtained for the sialyltransferase. Native kappa-casein also served as acceptor for N-acetylneuraminic acid transferase of Golgi apparatus-enriched fractions although at a slower rate than did asialo-kappa-casein. The sialyltransferase has a divalent cation requirement for maximum activity which was best satisfied by the presence of 10 mM Mn2+.

Effect of feeding organic acids on selected intestinal content measurements at varying times postweaning in pigs.

Pigs weaned at 21 d of age (n = 72) were fed a 20% CP corn-soybean meal-based diet (control) with 1.5% fumaric or 1.5% citric acid added to observe the effect of these acids on the pH, chloride ion concentration (Cl-), VFA profile, and microflora population in the stomach, jejunum, cecum, and lower colon contents at -2, 0, 3, 7, 14, and 21 d postweaning. Feeding organic acids had no appreciable effect (P greater than .10) on stomach jejunum, cecum, or lower colon pH, Cl-, VFA profile, or microflora populations, except for increasing the concentration of fumaric acid in the stomachs of pigs fed fumaric acid. The pH of the gastrointestinal tract generally decreased from -2 to 21 d postweaning with no corresponding change in Cl- over time. No age effects on total anaerobic culture counts were observed except in the stomach, where counts decreased from -2 to 3 d postweaning. Clostridia counts generally decreased after weaning in all intestinal sections. Lactobacillus counts were usually lower at d 0 and 3 and greatest at d 7 postweaning in the stomach, jejunum, and lower colon, but no age effect was observed for concentration of cecum lactobacilli. Escherichia coli counts generally increased after weaning to 3 and 7 d postweaning. Intestinal content measurements were affected by postweaning age but were not affected by feeding organic acids.

Processing effects on physicochemical properties of creams formulated with modified milk fat.

Type of thermal process [high temperature, short time pasteurization (HTST) or ultra-high temperature pasteurization (UHT)] and homogenization sequence (before or after pasteurization) were examined for influence on the physicochemical properties of natural cream (20% milk fat) and creams formulated with 20% low-melt, fractionated butteroil emulsified with skim milk, or buttermilk and butter-derived aqueous phase. Homogenization sequence influenced physicochemical makeup of the creams. Creams homogenized before pasteurization contained more milk fat surface material, higher phospholipid levels, and less protein at the milk fat interface than creams homogenized after pasteurization. Phosphodiesterase I activity was higher (relative to protein on lipid globule surface) when cream was homogenized before pasteurization. Creams formulated with skim milk and modified milk fat had relatively more phospholipid adsorbed at the milk fat interface. Ultra-high-temperature-pasteurized natural and reformulated creams were higher in viscosity at all shear rates investigated compared with HTST-pasteurized creams. High-temperature, short time-pasteurized natural cream was more viscous than HTST-pasteurized reformulated creams at most shear rates investigated. High-temperature, short time-pasteurized creams had better emulsion stability than UHT-pasteurized creams. Cream formulated with buttermilk had creaming stability most comparable to natural cream, and cream formulated with skim milk and modified butteroil was least stable to creaming. Most creams feathered in a pH range of 5.00 to 5.20, indicating that they were moderately stable to slightly unstable emulsions. All processing sequences yielded creams within sensory specifications with the exception of treatments homogenized before UHT pasteurization and skim milk formulations homogenized after UHT pasteurization.

Effect of bovine plasmin on alpha-S1-B and kappa-A caseins.

Both alpha-S1- and kappa-caseins were incubated at 37 C in the presence of bovine plasmin (.28 mg/ml) prepared from fresh blood plasma. The electrophoretic pattern of kappa-casein A was unchanged following 60-min incubation with plasmin. However, the electrophoretic band corresponding to alpha-S1-casein B gradually disappeared during the initial 30-min incubation with plasmin. Proteolysis was accompanied by the formation of one polypeptide band with electrophoretic mobility slightly slower than alpha-S1-casein B and several bands with faster electrophoretic mobilities. Two of the faster electrophoretic bands contained phosphorus. Estimates of molecular weights were 20,500, 12,300, and 10,300 daltons for three of these early degradation products of alpha-S1-casein B by plasmin.

Activity of lysosomal enzymes in murine mammary tissue through pregnancy, lactation, and involution.

Murine mammary tissue homogenates obtained during pregnancy, lactation, and involution were assayed for activities of two lysosomal marker enzymes, acid phosphatase, and N-acetyl-beta-D-glucosaminidase. Acid phosphatase activity per milligram protein was relatively constant through pregnancy and lactation, although a decrease was detected at parturition. Acid phosphatase activity per milligram deoxyribonucleic acid was also stable through pregnancy and lactation except for a peak of activity during lactogenesis. Acid phosphatase activity per gram wet weight also remained stable during pregnancy and lactation, but activity was significantly higher during lactation than pregnancy. Glucosaminidase activity, whether expressed as milligrams deoxyribonucleic acid of milligrams protein, tended to decrease during pregnancy, decreased further with lactogenesis, and remained significantly lower throughout lactation. Glucosaminidase activity per gram wet weight increased as pregnancy progressed and slowly decreased through lactogenesis to midpregnancy levels, which remained stable throughout the remainder of lactation. Both acid phosphatase and glucosaminidase activities were slightly higher at the end of lactation, and both decreased within 24 h of weaning. Significant increases in activities of both enzymes were observed from d 1 to 4 of involution.

Characterization of small intestinal mucus glycoproteins from pigs of various ages.

1. The mucus from 2-day-old and 3-week-old pigs was separated into polymeric mucus glycoprotein, degraded mucus glycoprotein subunit, and low-molecular-weight glycoprotein. 2. The low-molecular-weight glycoprotein fraction contained significant amount of mannose. 3. The degraded mucus glycoprotein subunit and the low-molecular-weight glycoprotein decreased in the mucus from older pigs.

Distribution of the lysosomal enzyme aryl sulfatase in murine mammary tissue through pregnancy, lactation, and involution.

Mammary tissue from 44 primiparous mice at various stages of pregnancy, lactation, and involution were stained for aryl sulfatase (lysosomal marker enzyme) activity and prepared for electron microscopy. Stereological techniques were used to determine the distribution of lysosomes per unit of cytoplasmic area in mammary epithelial cells. The number of primary lysosomes (containing only enzyme) was stable throughout the study, except for a temporary increase following parturition. Secondary lysosomes (containing substrate undergoing active digestion) designated as either telolysosomes or dense bodies were more frequent in mammary epithelial cells from animals in the late involution and early pregnancy stages than in lactating animals. However, telolysosomes did increase temporarily at the onset of lactation and casein micelles were identified within secondary lysosomes throughout the lactation stage. The frequencies for endoplasmic reticulum and Golgi apparatus containing aryl sulfatase reaction product were highest in secretory cells, when these structures were predominant. Shifts in lysosomal populations throughout the study suggests that lysosomes may have an active role within the mammary epithelial cells during differentiation and secretion as well as during involution.

Lactose and major milk proteins are present in secretory vesicle-rich fractions from lactating mammary gland.

Preparations enriched in apparently intact secretory vesicles were isolated from homogenates of lactating rat and bovine mammary tissue by differential and density gradient centrifugation in isoosmotic media. Morphologically these preparations consisted nearly entirely of vesicles of varying sizes, at least some of which contained casein micelles. Endoplasmic reticulum vesicles, Golgi apparatus cisterna and dictyosomes, mitochondria, peroxisomes, lysosomes, and nuclei were not observed in secretory vesicle-rich fractions. Vesicle preparations were enriched in lactose relative to total membrane fractions from mammary gland. The galactosyltransferase of lactose synthase (UDPgalactose: D-glucose 4 beta-galactosyl-transferase, EC 2.4.1.22) was also present in secretory vesicle preparations, alphas1- and beta-caseins, alpha-lactalbumin, and beta-lactoglobulin, the major secretory proteins of differentiated mammary epithelial cells, were identified as constituents of vesicle-rich fractions from bovine mammary gland. These observations suggest that the major carbohydrate and major proteins of milk are compartmentalized into secretory vesicles and are secreted by exocytotic fusion of secretory vesicles with the apical plasma membrane.

Electrophoretic and biochemical comparison of casein and whey protein from porcine colostrum and milk.

Porcine colostrum casein contained at least one major polypeptide band in both acid gel and sodium dodecyl sulfate gel electrophoresis that did not appear in patterns of casein prepared from porcine milk. In sodium dodecyl sulfate gel patterns, this polypeptide possessed a molecular weight of 62,000 and stained positively with "Stains-all" but not with periodic acid-Schiff reagent. Several minor caseins that appeared in acid and alkaline gel patterns from colostrum could not be detected in casein prepared from milk. Seven minor polypeptides in sodium dodecyl sulfate gel patterns of whey proteins prepared from porcine colostrum could not be detected in milk. Identical acid and alkaline gel patterns were obtained for whey proteins prepared from colostrum and milk. Only the sodium dodecyl sulfate gel electrophoretic pattern of casein prepared from milk, and possibly the alkaline gel electrophoretic pattern of whey protein prepared from milk, contained polypeptides not in patterns from colostrum. Total phosphorus contents of colostrum and milk casein were 2.96% and 3.78%. Casein prepared from porcine colostrum contained almost twice as much hexosamine and slightly elevated N-acetylneuraminic acid as casein prepared from milk. Hexose content was nearly equivalent. Whey protein prepared from milk contained more total hexose than casein prepared from colostrum, whereas N-acetylneuraminic acid and hexosamine contents were nearly equivalent.

Isolation of functionally active acini from bovine mammary gland.

Conditions to obtain high yields of intact acini from lactating bovine mammary glands and certain structural and functional characteristics of isolated acini were investigated. A two-factor experiment with three collagenase concentrations (100, 150, and 200 mg/100 ml) and incubation periods (40, 60, and 90 min) demonstrated that increases in both factors significantly increased net acini yield. Largest amounts of acini obtained, based on content of deoxyribonucleic acid, were 10.3% of the original tissue. Morphologically, fractions consisted primarily of acini or large cell clumps, and nearly all cells excluded trypan blue. Acini cultured in complete nutrient medium incorporated radioactive leucine into proteins. When acini were incubated in medium without supplemental amino acids, specific activity of synthesized proteins was correlated negatively with incubation time. During pulse labeling with radioactive L-leucine over 16 min, true labeling of acinar proteins occurred after 4 min. Sequential kinetics of pulse-chase labeling demonstrated a response pattern unique to the in vitro acinar system. Acinar protein synthesis was inhibited by cycloheximide and strongly stimulated by by 3',5'-cyclic adenosine monophosphate.

Comparison of lectin receptor and membrane coat-associated glycoproteins of milk lipid globule membranes.

1. Glycoproteins of bovine (Bos taurus) and human (Homo sapiens) milk lipid globule membranes were characterized by ability to bind lectins after electrophoretic separation. 2. Seven lectin receptor glycoproteins were detected in bovine and five in human milk lipid globule membranes. Bovine and human globule membrane glycoproteins differed in ability to interact with certain lectins. 3. Two major nonionic detergent insoluble glycoproteins were present in bovine and human lipid globule membrane; these constituents had apparent molecular weights of 155,000 and 69,000. Detergent-insoluble polypeptides with similar or identical electrophoretic mobilities were found in milk lipid globule membranes from four other species, rat (Rattus norvegicus), sheep (Ovis aries), pig (Sus scrofa) and goat (Capra hircus). Tryptic peptide mapping revealed these polypeptides to be nonidentical among species.

Foods and Food Ingredients for Prevention of Diarrheal Disease in Children in Developing Countries.

Increased awareness of the morbidity and mortality attributed to diarrheal disease among children under 5 years of age in developing countries has led to a variety of approaches aimed toward prevention. In this review, foods and food ingredients which appear to be most effective in prevention of diarrheal disease in infants are considered. The effect of each of the following potential food or food ingredient categories on the control or prevention of diarrheal disease is discussed: human milk components, antibodies, probiotics, and fermented foods.

Plasmin-mediated proteolysis of casein in bovine milk.

Plasminogen was found to be present in bovine milk by crossreactivity between rabbit antiserum to plasminogen and casein prepared from milk by acid precipitation. This result was further supported by recovery of intact 125I-labeled plasminogen from rabbit milk after its intravenous injection. Freshly isolated whole bovine casein was observed to undergo slow autoproteolysis at 37 degrees C. Polyacrylamide gel electrophoresis revealed gradual disappearance of major caseins accompanied by appearance and increase in intensity of numerous electrophoretic bands. This autoproteolysis was inhibited by low concentrations of epsilon-aminocaproic acid (0.1 mM) and diisopropyl fluorophosphate (1 mM); catalytic amounts of urokinase accelerated the process. Autoproteolysis of isolated bovine beta-casein was shown by both urea and sodium dodecyl sulfate gel electrophoresis to result in formation of gamma 1- and gamma 2-caseins. Similar electrophoretic bands were formed when beta-casein was degraded by plasmin prepared from bovine blood serum. These results support the hypothesis that bovine plasmin occurs in milk and is identical to alkaline milk protease.

Probiotic culture survival and implications in fermented frozen yogurt characteristics.

Low-fat ice cream mix was fermented with probiotic-supplemented and traditional starter culture systems and evaluated for culture survival, composition, and sensory characteristics of frozen product. Fermentations were stopped when the titratable acidity reached 0.15% greater than the initial titratable acidity (end point 1) or when the pH reached 5.6 (end point 2). Mix was frozen and stored for 11 wk at -20 degrees C. The traditional yogurt culture system contained the strains Streptococcus salivarius ssp. thermophilus and Lactobacillus delbrueckii ssp. bulgaricus. The probiotic-supplemented system contained the traditional cultures as well as Bifidobacterium longum and Lactobacillus acidophilus. We compared recovery of Bifodobacterium by three methods, a repair-detection system with roll-tubes and plates on modified bifid glucose medium and plates with maltose + galactose reinforced clostridial medium. Culture bacteria in both systems did not decrease in the yogurt during frozen storage. The roll-tube method with modified bifid glucose agar and repair detection system provided at least one-half log10 cfu/ml higher recovery of B. longum compared with recoveries using modified bifid glucose agar or maltose + galactose reinforced clostridial agar on petri plates. No change in concentrations of lactose or protein for products fermented with either culture system occurred during storage. Acid flavor was more intense when product was fermented to pH 5.6, but yogurt flavor was not intensified. The presence of probiotic bacteria in the supplemented system seemed to cause no differences in protein and lactose concentration and sensory characteristics.