A screening method for the determination of ascorbic acid in fruit juices and soft drinks

A simple and rapid liquid chromatographic method based on a new stationary phase Teknokroma, Tr-010065 Mediterranea sea₁₈ (15 cm × 0.4 cm, id 3 μm), to determine ascorbic acid in beverages is reported. With the proposed method the samples were analysed by direct injection without a previous treatment. The total analysis time does not exceed 6 min. The method showed a good repeatability (RSD < 2%: n = 6) and an excellent sensitivity (LOD = 0.01 mg/l). Seventeen samples were analysed, including fruit juices, soft drinks and isotonic beverages. Ascorbic acid contents ranged from 6.6 to 840 mg/l. The ascorbic acid stability in some beverages during their shelf-life was also evaluated. Degradation of about 54% was observed in a tea drink.     

Development of an integrated approach for the stability testing of flavonoids and ascorbic acid in powders

An integrated approach for determining the stability of flavonoids and ascorbic acid in powders was developed. A rapid analyte solubility procedure was used to decide whether HPLC, GLC, or NMR would best serve to measure the stability of each flavonoid. Both the flavonoid under study and ascorbic acid were measured in one analysis with any of the determinative methods. Seventeen flavonoids of differing types, as well as ascorbic acid, were evaluated to establish the approach. The effects of storage relative humidity (RH) on the stability of several flavonoid powders with and without ascorbic acid were then determined. Quercetin, luteolin, taxifolin, naringenin, and naringin were stable for up to 8 weeks in RHs up to 98%, and ascorbic acid was significantly destroyed in the presence of quercetin, luteolin, and taxifolin at 98% RH. Both grape anthocyanins and ascorbic acid were unstable in the presence of each other at 98% RH. The integrated approach could be used for shelf-life testing of powdered flavonoids under a variety of storage conditions.     

Rapid detection of cows' milk in sheeps' and goats' milk by a species-specific polymerase chain reaction technique

A polymerase chain reaction (PCR) assay was developed for the specific identification of cows' milk in sheep's and goats' milk by using primers targeting the mitochondrial 12S rRNA gene. The use of a forward primer complementary to a conserved DNA sequence, along with a reverse primer specific for cow, yielded a 223-bp fragment from cows' milk DNA, whereas no amplification signal was obtained in sheep's and goats' milk DNA. The technique was applied to raw, pasteurized, and sterilized milk binary mixtures of cow-sheep and cow-goat, enabling the specific detection of cows' milk with a good sensitivity threshold (0.1%). The proposed PCR assay represents a rapid and straightforward method applicable to the authentication of milk and other dairy products in routine analysis.     

Effect of pasteurisation on ascorbic acid,dehydroascorbic acid,tocopherols and fatty acids in pooled mature human milk

Ascorbic and dehydroascorbic acids (vitamin C), tocopherols (vitamin E) and unsaturated fatty acids are heat-sensitive and therefore, their concentrations in human milk could be affected by pasteurisation. Here we determined the concentrations of ascorbic acid plus dehydroascorbic acid, ascorbic acid alone, and α- and γ-tocopherols, and the percentages of fatty acids in samples of human milk after pasteurisation by a slow (62.5 °C, 30 min) or fast heating (100 °C, 5 min) procedure. Both methods led to a significant decrease in the concentrations of ascorbic acid plus dehydroascorbic acid (12% and 29%), ascorbic acid (26% and 41%), α-tocopherol (17% and 34%) and γ-tocopherol (13% and 32%), respectively. However, milk fatty acids, including the polyunsaturated long-chain fatty acids, were unaffected by the two methods. On the basis of these observations, we recommend that human milk be treated using a slow pasteurisation. In addition, we propose ascorbic acid as a marker of the degree of heat treatment.     

Effects of glucagon infusions on protein and amino acid composition of milk from dairy cows

Changing the composition of milk proteins and AA affects the nutritional and physical properties of dairy products. Intravenous infusions of glucagon decreases milk protein production and concentration by promoting the use of gluconeogenic blood AA for hepatic glucose synthesis. Little is known about how the diversion of AA to gluconeogenesis affects the composition of milk proteins and AA. The objective was to quantify changes in composition of milk protein and AA in response to i.v. glucagon infusions. Three separate experiments were used: 1) 8 Holstein cows were fed ad libitum and infused with glucagon at 10 mg/d for 14 d, 2) 7 Holstein cows were feed restricted and infused with glucagon at 10 mg/d for 14 d, and 3) 4 Brown Swiss cows were infused with glucagon at 5 and 10 mg/d for 2 d each. Milk and milk component yields and milk protein and amino acid composition of samples, collected with blood samples at the first and last day of the glucagon infusion period, were compared with those collected 1 d before and after the glucagon infusion period. Glucagon infusions decreased milk protein production and concentration in each experiment by at least 0.2 ± 0.05 kg/d and 4 ± 0.4 g/L, respectively. The decrease was accompanied by changes in milk protein composition, the most consistent being an increase in κ-casein (1.68 ± 0.27%). Overall, glucagon infusions resulted in higher proportions of κ-casein and α_S2-casein (1.34 ± 0.51%) and smaller proportions of α_S1-casein (−3.83 ± 1.75%) and α-lactalbumin (−0.91 ± 0.32%). Glucagon had little impact on milk AA composition except an increase in glycine (0.26 ± 0.11%). The results suggest that milk protein synthesis is regulated by many factors including AA and glucose availability.     

Antioxidant mechanisms of Trolox and ascorbic acid on the oxidation of riboflavin in milk under light

Antioxidant activities and the mechanism of water-soluble Trolox and ascorbic acid on the oxidation of riboflavin in milk were studied. Trolox or ascorbic acid at 0, 100, 250, 500, or 1000 ppm was added to milk with or without added 50 ppm riboflavin and stored under light at 27 °C. Headspace oxygen was analysed by GC and Trolox, ascorbic acid, and riboflavin were determined by HPLC. The headspace oxygen of milk with added 50 ppm riboflavin depleted faster than that of milk without added riboflavin (p < 0.05). Trolox and ascorbic acid decreased during storage under light and riboflavin was completely destroyed within 24 h. As the concentration of Trolox or ascorbic acid increased, the riboflavin loss decreased. Riboflavin, Trolox, and ascorbic acid competed to react with singlet oxygen which was formed in the presence of riboflavin under light. Trolox and ascorbic acid protected riboflavin in milk under light by reacting with singlet oxygen.     

Quantitative modelling approaches for ascorbic acid degradation and non-enzymatic browning of orange juice during ultrasound processing

The objective of this study was to develop a deterministic modelling approach for non-enzymatic browning (NEB) and ascorbic acid (AA) degradation in orange juice during ultrasound processing. Freshly squeezed orange juice was sonicated using a 1500 W ultrasonic processor at a constant frequency of 20 kHz and processing variables of amplitude level (24.4–61.0 μm), temperature (5–30 °C) and time (0–10 min). The rate constants of the NEB and AA were estimated by a primary model (zero and first order) while their relationship with respect to the processing factors was tested for a number of models, i.e., second order polynomial, different types of Ratkowsky-type model, and an Arrhenius-type model. The non-monotonic behaviour of NEB has been described more accurately by the use of a polynomial model. The rate constants of AA were described by a similar type of model having a monotonic behaviour. A synergistic effect of temperature for different amplitudes on the rate constant of both NEB and AA was observed, while an antagonistic effect of amplitude on the rate of NEB was evident. The models with the best fit were integrated to produce contour plots for the combined amplitude and temperature. The constructed contour plots illustrate that low temperatures and intermediate amplitudes, i.e., 42.7 μm, result in lower NEB and AA deterioration and consequently better quality orange juice. The overall developed modelling approaches exploit quality data in order to identify the optimal processing regions for eliminating quality deterioration of orange juice during ultrasound processing which is of high importance to the food industry.     

Effects of week of lactation and genetic selection for milk yield on milk fatty acid composition in Holstein cows

Control (CL) and select line (SL) dairy cows (n = 22) managed identically but differing in milk yield (>4100 kg/305 d) were used to determine differences in milk fatty acid profile as lactation progressed. Milk yield was recorded daily and milk samples were collected during wk 1, 4, 8, 12, and 16 postpartum for milk composition analysis. Milk samples from wk 1, 8, and 16 were also analyzed for fatty acid composition. Select-line cows produced more milk (44.4 vs. 31.2 kg/d) and milk components than CL cows during the 16-wk period. There was no difference in rate of milk yield increase, but peak milk yield for SL cows was greater and occurred later in lactation. There were no differences in milk SCC or milk fat, protein, or lactose content. Selection for milk yield did not affect the content of most individual milk fatty acids; however, compared with CL, SL cows had a reduced Delta(9)-desaturase system and tended to produce milk with lower monounsaturated fatty acid content. Selection for milk yield did not affect milk fatty acid origin but the percentage of de novo fatty acids increased and preformed fatty acids decreased as lactation progressed. Milk fat trans-11 18:1 and cis-9,trans-11 conjugated linoleic acid increased with progressing lactation (10.7 vs. 14.1 and 3.1 vs. 5.4 mg/g, or 31 and 76%, respectively) and were correlated strongly among wk 1, 8, and 16 of lactation. Temporal changes in the Delta(9)-desaturase system occurred during lactation but these changes were not correlated with milk fat cis-9,trans-11 conjugated linoleic acid content. Results indicate prolonged genetic selection for milk yield had little effect on milk fatty acid composition, but milk fatty acid profiles varied markedly by week of lactation.     

固相萃取-高效液相色谱测定奶粉中磺胺类抗生素残留

建立了测定奶粉中磺胺嘧啶和磺胺甲噁唑的固相萃取-高效液相色谱法。奶粉溶于水后经亚铁氰化钾和醋酸锌溶液处理后离心去除脂肪,过C18柱,用水淋洗,甲醇洗脱,洗脱液用于高效液相色谱分析。采用C18柱,流动相为甲醇∶0.08%乙酸=40∶60,检测波长272nm,流速0.8mL/min。结果表明,两种磺胺药物在0.05～1μg/mL的范围内线性良好,回收率为96.8%～97.5%。本方法具有灵敏度高,重复性好等特点。     

Feeding a C16:0-enriched fat supplement increased the yield of milk fat and improved conversion of feed to milk

Previous work has indicated that dietary palmitic acid (C16:0) may increase milk fat yield. The effect of a dietary C16:0-enriched fat supplement on feed intake, yield of milk and milk components, and feed efficiency was evaluated in an experiment with a crossover arrangement of treatments with 25-d periods. A fermentable starch challenge on the last 4 d of each period was utilized as a split-plot within period. Sixteen mid-lactation Holstein cows (249 ± 33 d in milk) were assigned randomly to treatment sequence. Treatments were either a C16:0-enriched (~85% C16:0) fat supplement (fatty acid treatment, FAT, 2% dry matter) or a control diet (CON) containing no supplemental fat. Diets containing dry ground corn grain were fed from d 1 through 21 of each period. On the last 4 d of each period, dry ground corn was replaced by high-moisture corn grain on an equivalent dry matter basis to provide a fermentable starch challenge. Response variables were averaged for d 18 to 21 (immediately before the fermentable starch challenge) and d 22 to 25 (during the fermentable starch challenge). We observed no treatment effects on milk yield or milk protein yield. The FAT treatment increased milk fat concentration from 3.88 to 4.16% and fat yield from 1.23 to 1.32 kg/d compared with CON. The FAT treatment decreased dry matter intake by 1.4 kg/d and increased conversion of feed to milk (3.5% fat-corrected milk yield/dry matter intake) by 8.6% compared with CON. The increase in milk fat yield by FAT was entirely accounted for by a 27% increase in 16-carbon fatty acid output into milk. Yields of de novo and preformed fatty acids were not affected by FAT relative to CON. The fermentable starch challenge did not affect milk fat concentration or yield. Results demonstrate the potential for a dietary C16:0-enriched fat supplement to improve milk fat concentration and yield as well as efficiency of conversion of feed to milk. Further studies are required to verify and extend these results and to determine whether responses are similar across different diets and levels of milk production.     

Effects of selenium form on blood and milk selenium concentrations,milk component and milk fatty acid composition in dairy cows

BACKGROUND: Human health may be improved if milk with a favorable fatty acid composition and Se concentration is ingested. The present study is to determine how a basal diet supplemented with daily 5 mg Se as Se‐enriched yeast (SY) or sodium selenite (SS) affects the fatty acid composition and Se concentration of bovine milk. The effects of Se form on blood Se concentration, erythrocyte glutathione peroxidase 1 (GPx1) activity, serum GPx3 activity and milk yield and component were also studied. RESULTS: Both Se forms, when compared to control group, increased Se concentrations of blood (P < 0.01) and milk (P < 0.01), erythrocyte GPx1 activity (P < 0.05) and milk percentages of polyunsaturated fatty acids (PUFA) (P < 0.05) and cis‐9,cis‐12 linoleic acid (P < 0.05). Cows supplemented with SY had higher Se levels in blood (P < 0.01) and milk (P < 0.01) and percentage of PUFA in milk (P < 0.05) when compared with those supplemented with SS. Milk yield, milk component and serum GPx3 activity were not significantly affected by Se form. CONCLUSION: Supplementation of diet with SY appears to be of more benefit than SS in producing favorable milk with high PUFA and Se concentrations. Copyright © 2010 Society of Chemical Industry     

Determination of ascorbic and isoascorbic acid in beverages and additives to meat products by capillary isotachophoresis

 A isotachophoretic method with conductivity detection was developed to directly determine ascorbic acid in food samples. The leading electrolyte contained hydrochloric acid (10 mmol/l), β-alanine (pH 3.0), and methylhydroxyethylcellulose (0.1%). The terminating electrolyte was 5 mmol/l caproic acid. The method is suitable for determining ascorbic acid in juice, beers, and as additives to meat products. The method was also applied for the determination of isoascorbic acid in additives to meat products. Received: 21 February 2000 / Revised version: 15 May 2000     

Survey of the fatty acid composition of retail milk in the United States including regional and seasonal variations

Consumers are increasingly aware that food components have the potential to influence human health maintenance and disease prevention, and dietary fatty acids (FA) have been of special interest. It has been 25 years since the last survey of US milk FA composition, and during this interval substantial changes in dairy rations have occurred, including increased use of total mixed rations and byproduct feeds as well as the routine use of lipid and FA supplements. Furthermore, analytical procedures have improved allowing greater detail in the routine analysis of FA, especially trans FA. Our objective was to survey US milk fat and determine its FA composition. We obtained samples of fluid milk from 56 milk processing plants across the US every 3 mo for one year to capture seasonal and geographical variations. Processing plants were selected based on the criteria that they represented 50% or more of the fluid milk produced in that area. An overall summary of the milk fat analysis indicated that saturated fatty acids comprised 63.7% of total milk FA with palmitic and stearic acids representing the majority (44.1 and 18.3% of total saturated fatty acids, respectively). Unsaturated fatty acids were 33.2% of total milk FA with oleic acid predominating (71.0% of total unsaturated fatty acids). These values are comparable to those of the previous survey in 1984, considering differences in analytical techniques. Trans FA represented 3.2% of total FA, with vaccenic acid being the major trans isomer (46.5% of total trans FA). Cis-9, trans-11 18:2 conjugated linoleic acid represented 0.55% total milk FA, and the major n-3 FA (linolenic acid, 18:3) composed 0.38%. Analyses for seasonal and regional effects indicated statistical differences for some FA, but these were minor from an overall human nutrition perspective as the FA profile for all samples were numerically similar. Overall, the present study provides a valuable database for current FA composition of US fluid milk, and results demonstrate that the milk fatty acid profile is remarkably consistent across geographic regions and seasons from the perspective of human dietary intake of milk fat.     

Technical note: Rapid method for determination of amino acids in milk

A rapid method for measurement of amino acids in milk was developed and validated. The method included a first step of milk protein hydrolysis, followed by the derivatization and separation of amino acids by HPLC. Six combinations of hydrolysis agent and temperature-time conditions were compared with a reference method; derivatization procedures as well as HPLC separation were improved. Hydrolysis of milk samples with 6 N HCl at 160°C for 60 min resulted in no significantly differences compared with the reference method but allowed the analysis of a greater number of milk samples in a short time. In addition, this method was characterized by high precision, low repeatability uncertainty, and high accuracy for all amino acids evaluated; the recovery mean value of the single amino acids was 98.38%. The proposed method is, therefore, accurate, simple, rapid, and suitable for large numbers of milk samples.     

Effect of linoleic acid and dietary vitamin E supplementation on sustained conjugated linoleic acid production in milk fat from dairy cows

Conjugated linoleic acid (CLA; cis-9,trans-11 18:2), a bioactive fatty acid (FA) found in milk and dairy products, has potential human health benefits due to its anticarcinogenic and antiatherogenic properties. Conjugated linoleic acid concentrations in milk fat can be markedly increased by dietary manipulation; however, high levels of CLA are difficult to sustain as rumen biohydrogenation shifts and milk fat depression (MFD) is often induced. Our objective was to feed a typical Northeastern corn-based diet and investigate whether vitamin E and soybean oil supplementation would sustain an enhanced milk fat CLA content while avoiding MFD. Holstein cows (n = 48) were assigned to a completely randomized block design with repeated measures for 28 d and received 1 of 4 dietary treatments: (1) control (CON), (2) 10,000 IU of vitamin E/d (VE), (3) 2.5% soybean oil (SO), and (4) 2.5% soybean oil plus 10,000 IU of vitamin E/d (SO-VE). A 2-wk pretreatment control diet served as the covariate. Milk fat percentage was reduced by both high-oil diets (3.53, 3.56, 2.94, and 2.92% for CON, VE, SO, and SO-VE), whereas milk yield increased significantly for the SO-VE diet only, thus partially mitigating MFD by oil feeding. Milk protein percentage was higher for cows fed the SO diet (3.04, 3.05, 3.28, and 3.03% for CON, VE, SO, and SO-VE), implying that nutrient partitioning or ruminal supply of microbial protein was altered in response to the reduction in milk fat. Milk fat concentration of CLA more than doubled in cows fed the diets supplemented with soybean oil, with concurrent increases in trans-10 18:1 and trans-11 18:1 FA. Moreover, milk fat from cows fed the 2 soybean oil diets had 39.1% less de novo synthesized FA and 33.8% more long-chain preformed FA, and vitamin E had no effect on milk fat composition. Overall, dietary supplements of soybean oil caused a reduction in milk fat percentage and a shift in FA composition characteristic of MFD. Supplementing diets with vitamin E did not overcome the oil-induced reduction in milk fat percentage or changes in FA profile, but partially mitigated the reduction in fat yield by increasing milk yield.     

Effects of lauric and myristic acids on ruminal fermentation, production, and milk fatty acid composition in lactating dairy cows

The objectives of this experiment were to investigate the effects of lauric (LA) and myristic (MA) acids on ruminal fermentation, production, and milk fatty acid (FA) profile in lactating dairy cows and to identify the FA responsible for the methanogen-suppressing effect of coconut oil. The experiment was conducted as a replicated 3 × 3 Latin square. Six ruminally cannulated cows (95 ± 26.4 DIM) were subjected to the following treatments: 240 g/cow per day each of stearic acid (SA, control), LA, or MA. Experimental periods were 28 d and cows were refaunated between periods. Lauric acid reduced protozoal counts in the rumen by 96%, as well as acetate, total VFA, and microbial N outflow from the rumen, compared with SA and MA. Ruminal methane production was not affected by treatment. Dry matter intake was reduced 35% by LA compared with SA and MA, which resulted in decreased milk yield. Milk fat content also was depressed by LA compared with SA and MA. Treatment had no effect on milk protein content. All treatments increased milk concentration of the respective treatment FA. Concentration of C12:0 was more than doubled by LA, and C14:0 was increased (45%) by MA compared with SA. Concentration of milk FA < C16 was 20% lower for LA than MA. Concentrations of trans 18:1 FA (except trans 12) and CLA isomers were increased by LA compared with SA and MA. Overall, the concentrations of saturated FA in milk fat were reduced, and that of > C16 FA and MUFA were increased, by LA compared with the other treatments. In this study, LA had profound effects on ruminal fermentation, mediated through inhibited microbial populations, and decreased DMI, milk yield, and milk fat content. Despite the significant decrease in protozoal counts, however, LA had no effect on ruminal methane production. Thus, the antimethanogenic effect of coconut oil, observed in related studies, is likely due to total FA application level, the additive effect of LA and MA, or a combination of both. Both LA and MA modified milk FA profile significantly.     

Effects of changes in dietary amino acid balance on milk yield and mammary function in dairy cows

Two experiments were conducted to determine whether longer-term deficiencies in the supply of limiting amino acids would be accompanied by a decline in mammary function (total DNA, cell proliferation rate and activities of key enzymes), and whether this would adversely affect the cow's ability to respond to a return to a nutritionally adequate diet. The first experiment was performed in early/mid lactation, and the second, using the same cows, was carried out in mid/late lactation. A control group of six cows were given a grass silage-cereal diet containing fish meal as the sole protein supplement (amino acid adequate) throughout the experiments, whereas another group of six cows in treatment received the control diet for 2 wk (lactation wk 5 and 6) and then were changed to a diet in which the fish meal was replaced by an equivalent amount of protein as feather meal (amino acid deficient) for 6 wk before returning to the fish meal diet for 4 wk (Experiment 1). After a rest period of 5 wk, the experimental procedure was repeated (Experiment 2). Although there was a fall in milk yield as lactation advanced, leading to lower milk yields in Experiment 2, the marked difference in milk yield between treatments was similar for the two stages of lactation (21% vs 16% in Experiment 1 and 2, respectively). In both experiments, the marked fall of milk yield in cows given the feather meal diet was completely recovered by a return to the fish meal diet. Despite the markedly lower milk yield with the amino acid-deficient diet, however, there was no clear evidence of corresponding changes in measurements of mammary function.     

紫外分光光度法和高效液相色谱法测定Maillard体系中抗坏血酸含量的比较

在抗坏血酸/半胱氨酸Maillard体系中,探讨了简单、快速、准确测定抗坏血酸含量的方法。用偏磷酸溶液作为提取剂,比较了紫外分光光度法和高效液相色谱法(HPLC)测定Maillard体系中抗坏血酸的含量。结果表明:紫外分光光度法和HPLC标准曲线线性关系良好,线性范围分别为0~14μg/mL和0~100μg/mL,两种方法相关系数R均达到0.999,平均回收率分别为111%和99.7%。使用两种方法测定三组平行样时,结果相近,误差较小。说明Maillard体系中紫外分光光度法测定抗坏血酸含量时干扰较小,且相比之下其更为简单快捷,适合Maillard体系中的抗坏血酸含量的测定。      

Development of a rapid mitochondrial DNA extraction method for species identification in milk and milk products

Isolation of mitochondrial DNA (mtDNA) from milk offers an effective way to monitor aspects of quality control and traceability to ensure food safety. A few methods of DNA isolation from milk have been reported, but many of them are time consuming and expensive. Here, we report a rapid, simple, and efficient method of mtDNA extraction from raw and processed milk (pasteurized, retorted, and UHT milk) to generate substrate for analysis using any PCR analysis platform. Various techniques used for the separation of mitochondria were explored and combined with a sodium dodecyl sulfate method for mtDNA extraction from raw and processed milk. The optimized protocol supports the efficient amplification of mtDNA independent of sample origin and is sufficiently straightforward to allow its widespread adoption by industry.     

Nutrient content of milk and milk products: Vitamins of the B complex and vitamin C in retail creams,ice creams and milk shakes

A study was undertaken to update and extend information on the water-soluble vitamin content of creams, ice creams and take-away milk shakes on retail sale in the UK. The concentration of water-soluble vitamins in creams reflected to varying extents the level of fat and the type of heat processing. The concentration of vitamins in both dairy and non-dairy ice creams were generally similar. The amounts of vitamins in milk shakes were similar to those in pasteurised milk.