Heat Inactivation of the Alkaline Phosphatase in Human Milk and Colostrum 1.

Time-temperature relationships were developed for heat inactivation of alkaline phosphatase in pooled human milk and colostrum. Heat inactivation of the enzyme in human milk proceeds at the same rate as in cows' milk. The heat sensitivity of the enzyme is slightly greater in human colostrum than in human milk.

Heat Stability of the Bile Salt-Stimulated Lipase in Human Milk Fortified with Sodium Taurocholate 1.

Time-temperature relationships for heat-inactivation of the bile salt-stimulated lipase activity were compared in whole human milk and in the same product fortified to 9 mM/ml with sodium taurocholate. Heat treatments were varied from 45 to 70°C for times ranging from 15s to 40 min. Enzyme activity was more heat stable in human milk fortified with taurocholate than in control samples. The temperature required for the onset of heat inactivation at 30-min holding time was increased from 45°C for control samples to 60°C following addition of taurocholate. A temperature differential of approximately 12°C was required in the fortified milks to produce inactivation equivalent to that observed in the control milks over the heating range studied.

Effect of Film Oxygen Transmission Rate on Lean Color and Microbiological Characteristics of Vacuum-Packaged Beef Knuckles.

Seventy-two beef knuckles were packaged (n = 12) in each of six different bag types with oxygen transmission rates (OTR) of 1, 10, 12, 13, 30 and 400 cc/m2/24 h at 4°C and 100% relative humidity to study brown discoloration of knuckles during refrigerated storage. Knuckles in bag types of OTR of 1 and 12 cc did not discolor as compared to those in bags with higher OTR (30 and 400 cc) probably due to differences in oxygen tension in the package and in the types of bacteria present. Deterioration of lean color of knuckles in some bag types of low OTR appeared associated with large percentages of Leuconostoc mesenteroides in the microflora.

Retail Appearance, Odor and Microbiological Characteristics of Pork Loin Chops Packaged in Different Oxygen-Barrier Films as Affected by Loin Storage Treatment.

Pork loins were fabricated immediately (fresh) or stored in parchment paper for 6 d or stored in vacuum packages for 8 d. Chops were packaged in either a high oxygen-permeable (PVC) film or a high oxygen-barrier film (vacuum) to be displayed 4 d or 2, 6 and 10 d, respectively. High oxygen-barrier (HOB) film was superior to PVC film in maintaining desirable visual properties of chops. Chops had less off-odor in HOB film when they were held no longer than 3 or 4 d in HOB packages compared to extended periods of display. Pork loin chops packaged in high oxygen-barrier film can be displayed up to 6 d if chops are from fresh pork loins. Although visual scores for vacuum-packaged chops were acceptable for 10 d for all storage treatments, chops from the parchment paper and vacuum-packaged storage treatments had off-odors which were limiting factors in achieving long shelf life.

Rapid high-temperature treatment of human milk.

Increasing interest in feeding human milk to low-birth-weight infants raises concern about microbial contamination of milk that is pooled or stored. We examined the effect of rapid high-temperature treatment on bacteria and viruses and on the nutritional and immunologic quality of pooled human milk. Growth of endogenous bacteria and infectivity of added cytomegalovirus were undetectable after heating at 72 degrees C for 15 and 5 seconds, respectively. Folic acid and vitamins B1, B2, B6, and C were not affected, whereas bile salt-stimulated lipase was inactivated by these conditions. The concentration of lactoferrin and secretory IgA, and SIgA antibody activity were not changed by heating at 72 degrees C. Lysozyme concentration and enzymatic activity were increased significantly by heat treatment, suggesting that this component may be largely sequestered in milk. Our findings suggest that rapid high-temperature treatment can reduce microbial contamination without destroying the unique nutritional and immunologic qualities of human milk.

Lipolytic Activity During Storage of Human Milk: Accumulation of Free Fatty Acids 1.

Lipolysis was quantitated during storage of fluid and freezedried human whole and skim milks. Fatty acid accumulation was faster in whole fluid milk stored for 1 week at 4°C than in frozen (-20°C) samples stored for 180 d. The rapid accumulation of fatty acids during 24 h of storage at 4°C was enhanced in previously frozen milk samples. While freeze-dried whole milk showed no lipolysis when stored at -20°C, accumulation of free fatty acids was rapid in samples stored at room temperature. Fluid and freeze-dried skim milk samples exhibited no appreciable lipolysis.

Vacuum Packaging Versus Modified Atmosphere Packaging of Lamb Loins.

Lamb loins were allocated (30 loins/treatment) to three packaging treatments: (a) vacuum-packaged, (b) vacuum-packaged followed immediately by injection of a 20% CO2:80% N2 atmosphere, and (c) vacuum-packaged followed immediately by injection of a 40% CO2:60% N2 atmosphere. Loins in each packaging treatment were then assigned (6 loins/period) to one of five storage periods--0, 7, 14, 21 or 28 d. During storage, the CO2 concentration increased in vacuum packages (initial vs. 21 d) and decreased in modified atmosphere packages (initial vs. 7 or 28 d); O2 concentration was higher in vacuum packages than in modified atmosphere packages at every storage period. Vacuum packaging was superior to modified atmosphere packaging for maintaining desirable appearance of wholesale loins, particularly if the atmosphere contained a high CO2 concentration. Appearance of retail chops was not substantively affected by the method used to package (vacuum vs. modified atmosphere) the wholesale loin from which they originated. Palatability of cooked chops was not affected by packaging method in 28 or 30 comparisons among product from loins that had been stored for 0 to 28 d before organoleptic testing.

Heat Inactivation of Bile Salt-Stimulated Lipase Activity in Human Milk and Colostrum 1.

Time-temperature relationships for heat-inactivation of bile salt-stimulated lipase activity in human milk and colostrum were systematically measured using a pH-stat assay procedure with triolein as substrate. The enzyme was not affected in either menstruum at 45°C for 40 min. The enzyme was destroyed almost instantaneously at 60°C, and was slightly more heat-sensitive in colostrum than in milk. The bile salt-stimulated lipase(s) in human milk was more heat sensitive than lipase in bovine milk.

Lipolytic Activity During Storage of Human Milk: Stability of the Bile Salt-Stimulated Lipase 1.

Bile salt-stimulated lipase activity was monitored in fresh human milk and skim milk during refrigerated (4°C) and frozen (-20°C) storage, and in the lyophilized milks stored at -20°C and at room temperature. Following a sharp initial drop to approximately 77% of the original lipase activity, lipase was relatively stable in frozen or freeze-dried milks during 180 d of storage at -20°C. Activity losses were greatest (P < .05) in freeze-dried whole milks and skim milks stored at room temperature, approximating a 30% loss during 30 d of storage. Lipase activity was stable during refrigerated (4°C) storage of whole milk for 1 week.

Growth of Selected Bacteria in Processed Human Milks 1.

Survival and/or growth of Pseudomonas fluorescens , Micrococcus luteus , Micrococcus sp. 102 and Staphylococcus aureus was studied in raw, frozen, pasteurized or heat-sterilized pooled human skim milks. Growth response of P. fluorescens at 25°C was essentially the same in the untreated and treated milks with an increase in count/ml of 4 log cycles during a 24-h incubation period. Counts (per ml) of S. aureus in raw, pasteurized and frozen milks increased approximately 3 log cycles. Growth of S. aureus in heat-sterilized milk was somewhat less. Micrococcus sp. 102 could not be recovered from raw and frozen milk after incubation at 37°C for 14 and 24 h, respectively. The count (per ml) of this organism in pasteurized milk decreased approximately 2 log cycles during the 24-h incubation period, whereas counts in sterilized milk increased approximately 2 log cycles. In no instance did M. luteus survive in raw, pasteurized or frozen milks at 37°C even for short periods after inoculation. The organism survived in heat-sterilized milk for 14 h at 37°C, but then decreased in numbers until the organism could be recovered from only 1 of 5 pools after 48 h of incubation.

Changes in the Natural Microflora During Incubation of Fresh and Processed Human Milks 1.

Seven pooled human milks, each from at least 6 different breast-feeding mothers (4 weeks post-partum) were studied for microbial population and flora changes during storage at 37°C. Coagulase-negative Staphylococcus spp. constituted a considerable part (39-100%) of the microflora in 6 of 7 pools of fresh milk, with coryneform bacteria, Lactobacillus , Micrococcus and Streptococcus spp. isolated less frequently. Storage of raw milk for 8 h caused a shift in flora favoring the Lactobacillus spp. After 24 h, coagulase-negative Staphylococcus were dominant in 4 of 7 pools, coryneform bacteria in 2 of 7, and Lactobacillus and Micrococcus spp. each in 1 of 7 pools. Low levels of bacteria were detected in 2 of 7 pasteurized pools, consisting of Staphylococcus spp. or yeasts. Freezing of the milk before storage at 37°C had little effect on the aerobic plate counts.

Nutritive value of globin-amino acid and complementary globin-cereal mixtures.

Protein efficiency ratios (PER) were determined using male weanling rats fed diets containing bovine globin alone and with wheat and corn gluten. Simultaneous equations and graphical methods were devised for selecting combinations of globin and cereal proteins to provide optimal and suboptimal profiles of limiting amino acids. Supplementation of the globin with amino acids established isoleucine and methionine as limiting amino acids. Addition of globin, whose amino acid pattern is complementary to that of the cereal proteins, markedly improved the PER values of the proteins. However, growth rates of rats fed various combinations of proteins were not identical, even though PER values differed only slightly. The PER of combined proteins were not predictable from amino acid composition or from correlations between PER and chemical score based on National Research Council (NRC) requirements for essential amino acids. The inability of the optimal mixtures to meet expected nutritional performance clearly indicated that other factors affecting availability of amino acids are implicated. Nevertheless, mutual improvement of two incomplete proteins such as globin and wheat or corn gluten was demonstrated. Addition of globin to widely used diets consisting mainly of corn or wheat can be nutritionally beneficial.

A comparison of heat-induced gel strengths of bovine plasma and egg albumen proteins.

The heat-induced gel strength in suspensions of two types of plasma protein isolates and egg albumen were compared to investigate the use of bovine blood plasma in food systems as a replacement for egg albumen and other proteins. A viscosity index, based on a counter-flow back-extrusion model, was used to measure gel strength. The optimum pH for gel formation was 7.0 for phosphated and nonphosphated plasma protein suspensions and 9.0 for egg albumen. The protein gel strengths were compared at 8% protein concentrations and at their respective pH optima. The gel strength of heated bovine plasma protein suspensions was greater (P < .01) than that of egg albumen, indicating that blood plasma exhibited a binding ability superior to that of egg albumen. The addition of controlled low levels of sodium and calcium increased (P < .05) the binding ability of both plasma protein isolates, while egg albumen showed no changes (P > .05). Greater concentrations substantially decreased (P < .01) the gel strength in both types of heated plasma protein suspensions and egg albumen, revealing that all three protein types exhibited an ionic strength dependency.

Effect of CO2-N2 Atmospheres on the Microbial Flora of Pork.

Pork loins were vacuum-packaged; one group remained vacuum-packaged, other vacuum packages were injected with gas atmospheres of either 20% CO2 + 80% N2 or 40% CO2 + 60% N2. Loins were stored for 7, 14, 21 and 28 days at 1-3 C. After each storage interval, chops were prepared from loins and subjected to 5 days of retail display. Psychrotrophic bacterial counts of lean and fat surfaces of loins stored in 40% CO2 + 60% N2 were frequently significantly lower than counts of comparable sites of vacuum-packaged loins. Lactobacillus counts of the subcutaneous fat cover of loins stored in CO2 + N2 were in most instances (7 of 8 comparisons) significantly higher than those of vacuum-packaged loins; this was true in only 2 of 8 comparisons for the lean surface. Psychrotrophic bacterial counts of chops prepared from loins subjected to the various storage treatments were seldom significantly different. During storage of pork loins, lactobacilli became a predominant part of the microflora and comprised more than 90% of the microflora after 21 days for loins stored in CO2 + N2 and after 28 days for vacuum-packaged loins. Pseudomonas spp. continued to persist to a greater degree in the vacuum-packaged loins than in the loins stored in CO2 + N2.

Physical and Sensory Characteristics of Pork Loins Stored in Vacuum or Modified Atmosphere Packages.

Wholesale pork loins were either vacuum-packaged, packaged in an atmosphere of 20% CO2 + 80% N2 or packaged in an atmosphere of 40% CO2 + 60% N2. After storage, the primal cuts were evaluated visually for muscle color, fat cover appearance, off-odor, lean surface discoloration and overall appearance. Retail cuts fabricated from the wholesale loins were evaluated for surface discoloration and overall appearance during a 5-day retail display period or they were used for sensory panel evaluation. Few significant differences between packaging treatments were found during the storage period for traits evaluated on the primal cuts. Few significant differences between packaging treatments were observed for either retail display data or sensory panel evaluation.

Appearance of Beef, Pork and Lamb Stored in Vacuum or Modified Gas Atmospheres.

Beef, pork and lamb loins were vacuum-packaged as subprimal cuts, vacuum-packaged as reformed subprimal cuts, vacuum-packaged as retail cuts or packaged in modified gas atmospheres as retail cuts. Cuts were stored and evaluated, after 0, 7, 14 or 21 days of storage, for surface discoloration and overall appearance. Gas analysis of the heads pace of packages was also obtained. In all vacuum packaging treatments, the percentage of CO2, increased and the percentage of O2, decreased with increased storage. The gas composition in modified gas atmosphere packages changed little during the 21-day study. Using systems and gas combinations involved in the present study, retail cuts of beef, pork and lamb could not be successfully precut, retail-packaged and stored for 7 to 21 days in vacuum or modified gas atmospheres. Vacuum-packaged retail cuts and retail cuts stored in modified gas atmospheres sustained extensive surface discoloration and were of unsatisfactory appearance, even after only 7 days of storage and 1 day of retail display. Conversely, storage of retail cuts as vacuum-packaged reformed subprimal cuts for 7 to 21 days decreased (P < .05) surface discoloration and improved (P < .05) overall appearance in comparison to retail cuts from loins stored as subprimals for comparable times in vacuum packages.

Microbiology of Beef, Pork and Lamb Stored in Vacuum or Modified Gas Atmospheres.

Beef, pork and lamb loins were vacuum-packaged as subprimal cuts (controls), reformed subprimal cuts and as retail cuts (steaks or chops). Subprimal cuts, reformed subprimal cuts and one group of retail cuts remained vacuum-packaged. Other groups of retail cuts were injected with atmospheres of either 20% CO2 + 80% N2 or 40% CO2 + 60% N2. Cuts were randomly assigned to storage periods of 0-21 days at 2 ± 1 C. At weekly intervals, steaks or chops were removed from each treatment and examined after storage for 5 days under retail display conditions. Psychrotrophic bacterial counts and lactobacilli counts of steaks and chops stored in CO2-N2 atmospheres usually were lower, though not often statistically significant, than those of comparable vacuum-packaged steaks, chops or loins. Psychrotrophic counts of steaks and pork chops, initially held in CO2,-N2 atmospheres and then subjected to retail display, usually were lower than those of comparable steaks and chops that had been vacuum-packaged (without added CO2-N2) or prepared from vacuum-packaged loins.

Ascorbic Acid Stimulation of Diacetyl Production in Mixed-Strain Lactic Acid Cultures.

The effect of three levels of ascorbic acid on diacetyl and acid production by two mixed-strain cultures was investigated. Each culture was grown in nonfat dry milk reconstituted to 11% total solids with 0.1% added sodium citrate. Ascorbic acid concentrations in the milk were 0, 0.10, and 0.25%. Stimulation of diacetyl production was observed at both concentrations of ascorbic acid. The stimulatory effect of ascorbic acid at both concentrations was approximately the same for each culture. Diacetyl production was initiated earlier in samples containing ascorbic acid. Ascorbic acid did not stimulate acid production.

Fat Test Depression During Chilled Storage of Milk Samples in Plastic Containers for Analysis by the Milko-Tester 1.

Ambiguous depressions in fat tests were observed when milk samples were stored before testing by the Milko-Tester procedure. Fat-test depression was augmented by shipping and by chilling samples at the time of collection in an ice-water mixture. The effect was greatest in samples stored in 1-oz. plastic containers and in partially filled plastic bags. The fat-test depression was not significant in samples stored in glass bottles or in plastic containers receiving no refrigeration during the storage period.

Physical and Sensory Characteristics of Pork Packaged in Various Gas Atmospheres.

One hundred and ninety-six boneless pork roasts were vacuum-packaged. Twenty-eight roasts remained vacuum-packaged to serve as controls. The remaining packages were divided into six groups of 28 packages each and injected with one of six gas mixtures: (a) 100% O2, (b) 20% CO2 + 80% N2, (c) 50% CO2 + 50% O2, (d) 20% CO2 + 80% O2, (e) 25% CO2 + 25% O2 + 50% N2 or (f) 51% CO2 + 30% O2 + 18% N2 + 1% CO. Five packages from each packaging treatment were removed from storage after 7, 14, 21, 28 or 35 days. Data collection included gas composition of the intact packages and off-odor, surface discoloration, overall appearance, retail caselife and palatability of cuts. The most prevalent gas in vacuum packages was CO2 with weight percentages of 62-88% during the 35-day storage period. Packages initially injected with an atmosphere containing 100% O2 showed a gradual decrease in O2 and an increase in CO2 with increased storage. Roasts stored in O2-containing atmospheres for 14 and/or 21 days had a higher incidence of off-odor and chops from such roasts had lower overall appearance ratings after 1 day of retail display and lower flavor and overall palatability ratings than comparable vacuum packaged meats. These differences were significant only for roasts stored in modified atmospheres containing high concentrations of O2 and only after extended periods of storage. Data suggest that a modified gas atmosphere of 20% CO2 + 80% N2 is a suitable alternative to vacuum-packaging.