Injury and death of frozen Listeria monocytogenes as affected by glycerol and milk components

A cell suspension of Listeria monocytogenes strain Scott A in phosphate buffer solution alone or with added glycerol, milk fat, lactose, or casein was frozen and stored at -18 degrees C. At suitable intervals, samples of cell suspensions were thawed at 35 degrees C and plated on suitable media to distinguish between surviving injured and noninjured cells of L. monocytogenes. Glycerol (2 or 4%) protected L. monocytogenes from death and injury during frozen storage for up to 6 mo; however, when 2% glycerol was present, 30 min of frozen storage had to elapse after completion of freezing before protection against death was evident. During short-term (2 wk or less) frozen storage, lactose, milk fat, and casein, each at 2%, provided better protection to L. monocytogenes than did 2% glycerol. During long-term frozen storage, milk components, each at 2%, protected L. monocytogenes against death and injury, but less than that provided by glycerol. Protection by lactose and milk fat against death during frozen storage was observed during 4 wk and against injury during 5 mo and 4 wk of frozen storage, respectively. Protection by casein against death and injury occurred during frozen storage for up to 6 mo. Salts that simulate milk ultrafiltrate provided almost no protection to L. monocytogenes during freezing and frozen storage. Increasing the concentration of milk fat from 2 to 4% resulted in almost no change in death of L. monocytogenes, but in a decrease in injury only during the first 24 h of frozen storage.(ABSTRACT TRUNCATED AT 250 WORDS)     

Stability of aflatoxin M in milk.

This three-part study was designed to determine aflatoxin M recovery from pasteurized and/or stored cow's milk. (a) Aflatoxin M was added to samples of raw Holstein milk at a concentration of 2.0 mug/liter. Half of each sample then was pasteurized at 63 C for 30 min, and both raw and pasteurized portions were stored at 4 C up to 17 days. (b) Samples of raw milk, pasteurized (77 C, 16 s) skim milk, dry cottage cheese curd, and cottage cheese whey were taken from a commercial operation in an area in which natural contamination had been encountered. (c) Milk from a cow dosed with aflatoxin B1 was stored frozen (-18 C) in bulk and in assay-size sample containers for 120 days. Aflatoxin M was recovered completely after either storage or pasteurization in (a) and (b). In (c), a recovery deficiency was detectable after 68 days of storage, which increased to 45% of the original value by 120 days. These observations differ from those of others in that loss of aflatoxin M was significant after pasteurization or storage of raw milk, totaling 87% loss after 120 days of frozen storage. Aflatoxin M partitioning between curd and whey in the preparation of cottage cheese agrees with more recent studies, but differs from previous reports. Three possible explanations for the differences are offered.     

alpha-Amylase activity in rumen fluid of cows producing milk of low and normal fat content

α-Amylase activity in cell-free rumen fluid from lactating cows was measured by Phadebas amylase test. Effects of handling and storage of rumen fluid on α-amylase activity were determined. Assays of 35,000 × g centrifuged rumen fluid stored at ?18 °C showed good reproducibility, while reproducibility of assays of samples uncentrifuged prior to freezing was poor. In frozen stored samples of rumen fluid centrifuged at 35,000 × g or 3,200 × g, α-amylase activity decreased, whereas in frozen uncentrifuged samples α-amylase activity increased with storage time. α-Amylase activity was high and showed wide variations in one cow with experimentally induced low milk fat syndrome. Enzymatic activity was correlated negatively with rumen pH and positively with total concentration of volatile fatty acids. α-Amylase activity was significantly higher in rumen fluid samples from cows with low milk fat in conventional herds compared to cows with normal milk fat in the same herds. Enzymatic activity showed negative correlation coefficients with milk fat percentage and positive with total viable counts of rumen bacteria and mole percent of rumen propionic acid in the low milk fat cows but not in the cows with normal milk fat. α-Amylase activity in cell-free rumen fluid may be a useful indicator of activity of starch-hydrolyzing rumen microorganisms.     

冻藏条件对人乳脂质及挥发性风味物质的影响

以新鲜人乳为对照(0d),设置-18、-60℃和-60℃快速冷冻(-60℃(Q))3种冻藏条件分别冻藏60 d与180 d,通过测定脂质含量、非酯化脂肪酸(non-esterified fatty acids,NEFA)含量、脂质过氧化物(lipid peroxide,LPO)含量、脂肪酸组成、乳脂肪球微观结构及挥发性...     

Comparative study on breast milk of mothers delivering preterm and term infants--protein, fat and lactose

Milk samples were collected from 35 mothers delivering preterm infants and from 35 mothers delivering term infants at 3 time intervals over the first 3 weeks of lactation. The samples were collected by manual expression from both breasts into polyethylene containers and were frozen at -20 degrees C and stored for analysis. The protein content of preterm milks during the first and second weeks is higher than that of term milk (P less than 0.05). The fat and lactose contents during the first week are slightly more in term milk than in preterm milk. During the third week the fat content of preterm milk is higher but its lactose content was lower. All these differences are not significant. These results are discussed.     

Ultrasonication retains more milk fat globule membrane proteins compared to equivalent shear-homogenization

Ultrasonication, like common shear homogenization, can reduce the milk fat globule size and may change the milk fat globule membrane (MFGM). This work compared the effect of ultrasonication to equivalent shear homogenization on MFGM proteins and lipid-derived volatile components. Results showed that treating milk with ultrasound at 35 kJ/L would realize a similar size distribution of the milk fat globules as shear-homogenization at 20 MPa. Proteomics analysis revealed that in total 192 MFGM proteins were identified and quantified and a number of these proteins were lost after both treatments; however, more MFGM proteins remained after ultrasonication than after shear-homogenization. SDS-PAGE results showed that milk plasma proteins, and especially caseins, were absorbed on the milk fat globules after both treatments. In addition, the amount of the volatile free fatty acids increased after both treatments.Industrial relevance: Ultrasonication, as an innovative food processing technology, in comparison to traditional homogenization, was shown to equally efficiently decrease the MFG size, but lead to less damage to native MFGM proteins, which may be due to its longer homogenization time window. These results increased knowledge on the biochemical changes of milk fat globules after their size reduction and showed that ultrasonication could be used as a novel approach to improve dairy product quality.     

Comparative study on breast milk of mothers delivering preterm and term infants — Protein,fat and lactose

Milk samples were collected from 35 mothers delivering preterm infants and from 35 mothers delivering term infants at 3 time intervals over the first 3 weeks of lactation. The samples were collected by manual expression from both breasts into polyethylene containers and were frozen at ?20 °C and stored for analysis. The protein content of preterm milks during the first and second weeks is higher than that of term milk (P < 0.05) The fat and lactose contents during the first week are slightly more in term milk than in preterm milk. During the third week the fat content of preterm milk is higher but its lactose content was lower. All these differences are not significant. These results are discussed.     

Basic chemical characteristics of fresh, non-packed and vacuum-packed sheep-tail and tail-fat stored frozen for different periods

Fatty tails were obtained after the slaughter of Morkaraman sheep, which are a common breed of fatty-tailed sheep in Turkey. Fat obtained from sheep tails, (called tail-fat) is used either in fresh condition or after frozen storage. This fat is commonly used as a food source in many countries in which fat-tail sheep breeds are raised; but there has been no detailed research on fatty tails or the tail-fat. In this work some quality criteria such as water, fat and nitrogen content, 2-thiobarbituric acid and peroxide numbers, free fatty acids, melting point, iodine and saponification numbers were studied in sheep tails and sheep tail-fat, both in the fresh condition and after storage at -18 ± 1°C for up to 60 days. The effect of vacuum packaging versus storage in netting bags (no-protection, non-packed), was also determined. The fat content of the tails was around 94%. Thus, the tail is a concentrated fat source. Some quality criteria of the tail and the tail-fat were determined and are given in the text. Overall results indicated that both the tail and the tail-fat can be effectively used in various types of food and food processing, especially after performing some technological and refining processing. If the fatty tail has to be stored, it should be vacuum packed and stored frozen. At -18°C, vacuum-packed tail samples could be stored around 45 days, but in the netting bags, this storage period should not exceed 30 days.     

Physiological Activity of Deep-Frozen Concentrates of Leuconostoc Strains

11 strains of Leuconostoc cremoris and 1 strain of Leuconostoc lactis were the subject of investigations. Basing on the evaluation of growth parameters in the different cultivation media and on the diacetyl production ability in milk 2 strains of Leuconostoc cremoris and 1 strain of Leuconostoc lactis were chosen for preparing frozen concentrated biomass. Sterile milk or cream (18% fat) were used as protecting agents. Concentrated biomass was frozen at ?70 °C and stored at ?30 °C for 3 months. The prepared concentrates contained from 1.6 × 10¹¹ to 2.8 × 10¹¹ colony forming units (CFU)/g. Except for one (strain “S”) the strains retained 100% survival. All the strains showed high growth activity after their recovery in milk (3.3 × 10⁸ - 8.4 × 10⁸ CFU/ml). Both protecting agents applied proved to be equally good for preserving viability of the cells and for their acidifying activity. In spite of the protecting agent a decrease in the aroma activity by 25–50% was observed after one month of the biomass storage. Nevertheless, concentrated frozen multicomponent starters containing Leuconostoc strains retained the ability to produce diacetyl and acetoin on the unchanged level during the three months storage period.     

Effect of temperature conditions of the home environment on the physical properties of semi-solid fat products

The effect of temporary storage at room temperature (RT, 23 °C) on the physical properties and the texture of commercially available semi-solid fat products was studied. Three semi-solid fat products, namely, butter, margarine containing milk fat, and fat spread (70 % fat w/w), were maintained at RT for 2 days and then stored at 5 °C for another 2 days, and the changes in their physical properties were evaluated. The texture and sensory analyses showed that the hardness of the butter sample temporarily stored at RT increased. The storage modules (G′) at 5 °C of the butter sample that was temporarily stored at RT were higher than those of the butter stored continuously at 5 °C. Cryo-scanning electron microscopic visualization of the fat crystal network showed that film-like crystal networks linking dispersed water droplets were observed in the butter and margarine temporarily stored at RT. Meanwhile, X-ray diffraction patterns indicated that the regenerated fat crystal network comprised a polymorphic α-2 form, unlike the network in the butter not subjected to RT storage. These results suggest that the storage temperature history in the home environment can increase the hardness of semi-solid fat products containing milk fat because of the reformation of crystal networks in the milk fat triglycerides that were melted under RT.     

Lipolysis and Oxidation in Ultra‐High Temperature Milk Depend on Sampling Month,Storage Duration,and Temperature

During storage, some factors (for example, storage duration and temperature) can affect milk stability and consumer acceptability. Thiobarbituric acid reactive substances (TBARSs), lipid classes, and fatty acid profiles in stored ultra‐high temperature (UHT) milk were analyzed to assess the effects of storage time and temperature on lipid oxidation and lipolysis. With storage duration up to 12 months, the milk fat phase was separated and showed high levels of oxidation and lipolysis, manifested as increased levels of TBARS and free fatty acids. High oxidation levels decreased the percentage of unsaturated fatty acids (UFAs) in triacylglycerol and phospholipids. Higher storage temperatures (20, 30, and 37 °C) resulted in a higher degree of fat aggregation, oxidation, and lipolysis compared with refrigerated storage (4 °C). Additionally, sampling month of raw milk (May, July, and November) affected the lipid profiles of UHT milk during storage, with more UFA oxidized in July than in the other 2 months.     

Effects of refrigeration,freezing and replacement of milk fat by inulin and whey protein concentrate on texture profile and sensory acceptance of synbiotic guava mousses

The effects of refrigeration, freezing and substitution of milk fat by inulin and whey protein concentrate (WPC) on the texture and sensory features of synbiotic guava mousses supplemented with the probiotic, Lactobacillus acidophilus La-5, and the prebiotic fibre oligofructose, were studied. The frozen storage (−18 ± 1 °C), followed by thawing at 4 °C before the analyses, and the complete replacement of the milk fat by inulin plus WPC, led to significant differences in the instrumental texture parameters of mousses (P < 0.05). Nonetheless, these changes did not affect the sensory acceptability of the products studied. The frozen storage may be employed to extend the shelf-life of synbiotic guava mousses. Additionally, to obtain a texture profile similar to the traditional product, the simultaneous addition of inulin and WPC is recommended only for the partial replacement of milk fat in refrigerated and frozen mousses, and the total proportion of both ingredients together should not exceed 2.6%.     

Quality and Emulsion Stability of Milk from Ettawah Crossed Bred Goat During Frozen Storage

Goat milk has specific chemical composition and physical properties. The purpose of this study was to investigate the change of milk quality and emulsion stability during 60 d frozen storage. Milk sample was taken from three Ettawah Crossedbred goats that were divided into three groups. Samples were frozen and stored for 0, 30 and 60 days. At the end of each storage periode, milk sample was thawed in the refrigerator and analyzed for total number of bacteria, chemical (acidity, pH, free fatty acids), physical (alcohol test, clot on boiling test) quality, and emulsion stability. The microbiological and chemical data were analyzed statistically using one way ANOVA, whereas physical quality and emulsion stabilty were expressed qualitatively. There were no change in the total bacteria, acidity, pH and free fatty acid (FFA) of milk during storage, whereas the assessment by 70% alcohol showed positive since 0 d. Emulsions stability changed after 30 d of storage. While, the clot on boiling (COB) test of milk was positive at 60 d of storage. Recommendation is frozen storage of goat milk should not longer than 30 d.     

Retention of Phytochemicals in Fresh and Processed Broccoli

Our objective was to determine whether steam blanching, storage and preparation affected concentrations of sulforaphane (SF), sulforaphane nitrile (SFN), cyanohydroxybutene (CHB), iberin (I) or iberin nitrile (IN) in fresh and frozen broccoli. Broccoli (var. “Arcadia”) was grown in St. Charles, IL over three seasons. Samples were steam blanched (2 min at 93 ± 5°C) within 24h of harvest, frozen and stored at ?20°C up to 90 days, and fresh broccoli was stored at 4°C up to 21 days. Samples were analyzed uncooked or microwave cooked. SF, SFN, I, IN and CHB were determined by GC in dichloromethane extracts from lyophilized samples. Rates of loss for CHB and SF were similar during storage of fresh broccoli. Blanching, storage, and microwave cooking decreased (p < 0.01) concentrations of each compound in fresh and frozen broccoli.     

Effect of grape seed extract on oxidative, color and sensory stability of a pre-cooked, frozen, re-heated beef sausage model system

To compare grape seed extract (GSE) to common antioxidants in a pre-cooked, frozen, stored meat model system sausage was manufactured from lean beef (70%), pork fat (28%), and salt (2%). Antioxidants added for comparison with control included grapeseed extract (100, 300, and 500 ppm), ascorbic acid (AA, 100 ppm of fat) and propyl gallate (PG, 100 ppm of fat). Product was formed into rolls, frozen, sliced into patties, cooked on a flat griddle to 70 °C, overwrapped in PVC, then frozen at - 18 °C for 4 months. GSE- and PG-containing samples retained their fresh cooked beef odor and flavor longer (p < 0.05) than controls during storage. Rancid odor and flavor scores of GSE-containing samples were lower (p < 0.05) than those of controls after 4months of storage. The L* value of all samples increased (p<0.05) during storage. Thiobarbituric acid reactive substances (TBARS) of the control and AA-containing samples increased (p < 0.05); those of GSE-containing samples did not change significantly (p > 0.05) over the storage period.     

Influence of storage and preservation on fossomatic cell count and composition of goat milk

This study was designed to evaluate the effects of different test conditions on the somatic cell count (SCC) and composition of goat milk. To this end, 3600 tests were performed on 1800 aliquots taken from 40 goat milk samples using a combined instrument set-up based on flow cytometry for SCC and Fourier transform infrared analysis for fat, total protein, lactose, total solids, and freezing point determinations. The conditions tested were storage temperature (refrigeration and freezing), use of a preservative [no preservative (NP), azidiol (AZ), and bronopol (BR)], and age of the milk samples at each storage temperature (24 h to 42 d at refrigeration temperature and 21 to 105 d at freezing temperature). Significant effects on logSCC variation were shown by the storage temperature, the preservation treatment, the interaction of storage temperature × preservation treatment, and milk age within the interaction of storage temperature × preservative. Highest counts were recorded in the BR-preserved milk samples (logSCC = 5.877), and lowest counts were recorded in milk samples preserved using AZ (logSCC = 5.803). The use of frozen/thawed samples led to a significantly decreased logSCC for the treatments AZ and NP; the logSCC was not modified when BR-preserved frozen/thawed samples were analyzed. During storage, variations in the SCC observed for BR-preserved samples stored at refrigeration temperature for up to 25 d and at freezing temperature for all times tested were always <10%. The preservation treatment was the main factor affecting the milk composition variables examined. Highest values of most variables were obtained in the BR-preserved samples, and the lowest values were obtained in the AZ-preserved samples. The freezing point was lower in the preserved samples than in the NP samples. The levels of milk constituents recorded in the BR-preserved samples were independent of both the storage temperature and age of milk sample. Our findings indicate that the freezing point of goat milk must be interpreted according to the preservative used.     

Relationships among dietary roasted soybeans, milk components, and spontaneous oxidized flavor of milk.

Relationships among dietary roasted whole soybeans (RSB), milk fatty acid profile, and the development of spontaneous oxidized flavor of milk were investigated by using 20 commercial dairy herds. Diets contained 0 to 15.3% of dry matter as RSB. Concentrations of dietary RSB were correlated positively with concentrations of C18:2 and C18:3 in milk fat. Concentrations of alpha-tocopherol, beta-carotene, and ascorbic acid in milk decreased from 0 to 3 d of storage (4 degrees C), and oxidized flavor in milk increased linearly between 0 and 8 d of storage. Milk fatty acid profile did not change during storage. The development of oxidized flavor at 8 d postsampling was correlated (r) with increased concentrations in milk fat of C18:2 (0.49), C18:3 (0.55), total polyunsaturated milk fatty acids (0.50), and dietary concentrations of RSB (0.38). Multiple regression was used to quantify relationships between variables and oxidized flavor (samples stored 8 d). All significant models included milk concentrations of Cu and dehydroascorbic acid. Concentrations of C18:2, C18:3, or total polyunsaturated fatty acids in milk fat, or dietary RSB concentrations, and interactions of those variables with Cu were included in individual models. Milk with high concentrations of polyunsaturated fatty acids and Cu were most susceptible to oxidation. Feeding RSB increased polyunsaturated fatty acid concentrations in milk fat, which increased the likelihood of oxidized flavor, especially when milk had high concentrations of Cu.     

Effect of different storage conditions on coagulating properties and cheese quality of Withania coagulans extract

The effects of different storage conditions on the coagulating properties of extracts of Withania coagulans berries were investigated in terms of coagulation time, pH and quality attributes of cheese prepared from buffalo milk. The extracts were stored under different conditions, viz. room temperature (27 ± 3 °C), refrigerated storage (4 °C), frozen storage (?20 °C) and lyophilisation. The milk‐coagulating activity of the plant extracts was measured on a fortnightly basis for a period of 5 months. There was a nonsignificant change in pH and the milk coagulating properties of the lyophilised extract. Physiochemical analysis revealed that cheese prepared with lyophilised extract retained the highest content of ash (2.3%), fat (23.8%), total solids (48.7%) and crude protein (22.7%), and resulted in the highest cheese yield (17.6%) compared to other tested treatments. Thus, it is concluded that lyophilisation has good potential for storage of vegetable extract coagulants.     

Evaluation of increased vitamin D fortification in high-temperature, short-time-processed 2% milk, UHT-processed 2% fat chocolate milk, and low-fat strawberry yogurt

The objective of this study was to determine the effect of increased vitamin D fortification (250 IU/serving) of high-temperature, short-time (HTST)-processed 2% fat milk, UHT-processed 2% fat chocolate milk, and low-fat strawberry yogurt on the sensory characteristics and stability of vitamin D during processing and storage. Three replicates of HTST pasteurized 2% fat milk, UHT pasteurized 2% fat chocolate milk, and low-fat strawberry yogurt were manufactured. Each of the 3 replicates for all products contained a control (no vitamin D fortification), a treatment group with 100 IU vitamin D/serving (current level of vitamin D fortification), and a treatment group with 250 IU vitamin D/serving. A cold-water dispersible vitamin D₃ concentrate was used for all fortifications. The HTST-processed 2% fat milk was stored for 21 d, with vitamin D analysis done before processing and on d 0, 14, and 21. Sensory analysis was conducted on d 14. The UHT-processed 2% fat chocolate milk was stored for 60 d, with vitamin D analysis done before processing and on d 0, 40, and 60. Sensory analysis was conducted on d 40. Low-fat strawberry yogurt was stored for 42 d, with vitamin D analysis done before processing, and on d 0, 28, and 42. Sensory analysis was conducted on d 28. Vitamin D levels in the fortified products were found to be similar to the target levels of fortification (100 and 250 IU vitamin D per serving) for all products, indicating no loss of vitamin D during processing. Vitamin D was also found to be stable over the shelf life of each product. Increasing the fortification of vitamin D from 100 to 250 IU/serving did not result in a change in the sensory characteristics of HTST-processed 2% fat milk, UHT-processed 2% fat chocolate milk, or low-fat strawberry yogurt. These results indicate that it is feasible to increase vitamin D fortification from 100 to 250 IU per serving in these products.     

UHT乳贮藏期间理化特性和感官品质的变化

为探讨超高温瞬时杀菌(ultra-high temperature instantaneous sterilization,UHT)乳的营养价值随贮藏时间的变化,对不同贮藏期UHT乳的理化特性和感官品质进行监测。在6个月的贮藏期内,UHT乳中脂肪、蛋白质、乳糖以及固形物的总量并无明显变化,维生素C和泛酸的含量均损失了约25%,游离氨基酸和钙离子分别增加了5.35%和6.73%。不同贮藏期UHT乳的黏度变化不显著(P>0.05),但粒径大小强烈依赖于贮藏时间,乳脂肪球和酪蛋白胶束的尺寸在贮藏初期分别增加了约38 nm和14 nm,然后分别稳定在约173 nm和612 nm。贮藏1个月的UHT乳样品在风味和口感方面整体表现较好,贮藏6个月后,UHT乳的感官品质大幅下降,出现了许多不良风味。