Use of different thermal indices to assess the quality of pasteurized milks

 Lactoperoxidase activity and lactulose, furosine and undenatured whey protein contents were determined in Spanish commercial milks labelled as pasteurized (group A) and high-temperature pasteurized (group B), in order to assess their quality. Three samples of group A and all of the samples of group B were lactoperoxidase negative. Most samples of group A had measurable amounts of lactulose, even though their concentrations of undenatured β-lactoglobulin were higher than 2600 mg/l. In general, samples of group B showed higher lactulose and furosine and lower undenatured whey protein contents. High levels of furosine and lactulose accompanied by high levels of undenatured β-lactoglobulin could indicate the addition of milk heated at high temperatures, whereas high levels of furosine and relatively low levels of lactulose may have been due to the presence of reconstituted milk powder. Received: 29 June 1998     

Use of different thermal indices to assess the quality of pasteurized milks

 Lactoperoxidase activity and lactulose, furosine and undenatured whey protein contents were determined in Spanish commercial milks labelled as pasteurized (group A) and high-temperature pasteurized (group B), in order to assess their quality. Three samples of group A and all of the samples of group B were lactoperoxidase negative. Most samples of group A had measurable amounts of lactulose, even though their concentrations of undenatured β-lactoglobulin were higher than 2600 mg/l. In general, samples of group B showed higher lactulose and furosine and lower undenatured whey protein contents. High levels of furosine and lactulose accompanied by high levels of undenatured β-lactoglobulin could indicate the addition of milk heated at high temperatures, whereas high levels of furosine and relatively low levels of lactulose may have been due to the presence of reconstituted milk powder.     

Improvement of the ammonia measurement using a clarifying reagent and application to evaluate heat damage in commercial milk samples

The enzymatic Boehringer procedure for ammonia measurement in milk was improved to be rapid and simple using a clarifying reagent without any pretreatment of the sample. A good correlation (r=0.99, n=36) existed between the proposed enzymatic method (EM) and the specific electrode method (SEM) when applied on raw and commercial milk samples. The repeatability of the EM applied to UHT milk was satisfactory with a relative standard deviation of 5.4% (n=26). The EM was used to evaluate heat damage in commercial half-skimmed pasteurised, direct or indirect or unlabelled UHT and in-bottle sterilised milk. The EM was well correlated with absorbance at 340 nm (A₃₄₀) of transparent modified milk (r=0.97, n=42), with lactulose determined by HPLC and by capillary electrophoresis (r=0.95, n=17 and r=0.95, n=26, respectively). All parameters differentiated significantly (P<0.001) between pasteurised, UHT- and in-bottle sterilised milk, and also direct-UHT and indirect-UHT samples. More intensive heat treatment produced higher contents of ammonia, lactulose and A₃₄₀ values.     

Heating Milk: A Study on Mutagenicity

The mutagenicity of heated milk and model systems was investigated by the Ames mutagenicity assay. Heating varied from pasteurization to in-bottle sterilization to ultra-high-temperature (UHT) heat-treatment. No mutagenic response was found in heated milk or model systems. Early Maillard reaction products formed in heated milk or milk-resembling model systems apparently did not show mutagenic activity in the Ames-test. Milk that was burnt to the pan was also investigated. Chloroform and ethanol extracts of this milk showed mutagenic activity. Evidence showed this was due to Maillard reaction products. The antimutagenic activity of casein, reported in earlier studies, was confirmed.     

Effects of overprocessing on heat damage of UHT milk

Formation of lactulose, furosine, galactosyl-|*beta*|-pyranone and lysinoalanine was studied in UHT milk samples produced by either direct or indirect heating on industrial plants and by indirect heating on a pilot plant. In particular, the effects of severe sterilization conditions, different proportions of milk recirculation, and storage of the finished product (23 °C for up to 90 days) have been investigated on the levels of the above molecules in UHT milk. An extensive increase of the values of all the indicators occurred when severe heat process was applied, but no direct relation was found between their levels and the nominal time–temperature conditions. Lactulose and furosine levels confirmed to be strictly correlated in UHT milk. In case of overheating or high proportion (60%) of milk recirculation, galactosyl-|*beta*|-pyranone formation was strongly enhanced, proving that also the advanced Maillard reaction takes place extensively, which is not detected by furosine value. Formation of lysinoalanine in UHT drinking milk on storage was pointed out for the first time. Lysinoalanine proved to be the most sensitive index of storage conditions among the four parameters studied. Data suggest that a realistic defence of UHT milk quality can be achieved only by fixing upper limits to heat damage parameters. Besides avoiding unjustified milk overheating, this approach may allow manipulations, like reprocessing expired milk, to be pointed out.     

Phosphatase activity levels in pasteurized goats' milk

A study of the effect of pasteurization on goats' milk took place in order to compare the effectiveness of two pasteurization processes (low and high pasteurization) by assessing the procedure microbiologically and biochemically. The results revealed that both pasteurization processes were effective, showing microbial destruction of approximately 100%. With regard to the determination of phosphatase activity to monitor pasteurization, data in both cases were higher than the limit established for a well pasteurized milk, according to the method used. Machine milked milk showing a lower microbial content nearly achieved the standard level by batch pasteurization, 0.75 μg phenol/ml, but 2.5 μg phenol/ml by the high temperature short time (HTST) method. Phosphatase activity levels of 1.8 and 4.3 μg phenol/ml were the mean values obtained for low and high pasteurization respectively. Our results lead to the conclusion that the batch method for pasteurization of goats' milk is more efficient in terms of total bacterial count than the HTST method. Furthermore, the technique used for the determination of phosphatase activity does not seem to be adequate for pasteurization control of goats' milk, since in very rare situations were we able to attain the limit established.     

Evaluation of heat-induced changes in Spanish commercial milk: hydroxymethylfurfural and available lysine content

Hydroxymethyfurfural (HMF) content and loss of available lysine were measured as indices of heat damage in various Spanish commercial milks (pasteurized, UHT sterilized and in-bottle sterilized milks) with similar processing dates. HMF level was determined by the traditional colorimetric procedure and by the reversed-phase HPLC method. Available lysine was measured by an alternative method with o -phthaldialdehyde as fluorescent marker. A significative relationship has been found between the HMF content and loss of available lysine and both are suitable for use as heat-induced indices. When loss of lysine ( y ) was expressed as percentage and HMF ( x ) as μ m , the function of the correlation line was, y =0.47x−0.089 ( r =0.958, P <,0.005).     

β-乳球蛋白对VE热稳定性的影响

为改善超高温瞬时灭菌(ultra-high temperature instantaneous sterilization,UHT)乳中VE的热稳定性,以 β-乳球蛋白(β-lactoglobulin,β-LG)和VE为材料制备复合物,探究β-LG对VE热稳定性的影响.通过浊度、粒径、Zeta电位、扫描电子显微镜、十二...     

Effects of heating temperatures and addition of reconstituted milk on the heat indicators in milk

The objective of the present study was to evaluate the effect of heating temperatures and reconstituted milk on heat treatment indicators in milk by comparing the heat damage between raw milk and raw milk plus reconstituted milk (composite milk). The contents of lactulose, furosine, beta-lactoglobulin, and lactoperoxidase were determined after the heat indicators were heated to 65 to 115 °C for 15 s both in raw milk and composite milk. In the raw milk, the lactulose and furosine contents increased with increased heating temperature, while the beta-lactoglobulin content and lactoperoxidase activity decreased. The lactulose and furosine contents were increased after the addition of reconstituted milk. The reconstituted milk also significantly (P < 0.05) reduced the concentration of beta-lactoglobulin in the milk. Both heat treatment and an addition of reconstituted milk decreased the lactoperoxidase activity significantly (P < 0.05), and the lactoperoxidase activity was undetectable at 85 °C. The ratios of lactulose to furosine in pasteurized milk were higher than that in composite pasteurized milk. It is concluded that lactulose, furosine, and beta-lactoglobulin are suitable indicators of high heat pasteurization or raw milk, while lactoperoxidase may be used in monitoring mild heat pasteurization. Practical Application: Adequate heat treatment is necessary to destroy the microbes in raw milk. However, excessive heat treatment can result in inactivation of active compounds or loss of nutrients. The present study showed that the concentrations of lactulose, furosine, beta-lactoglobulin, and the activity of lactoperoxidase are sensitive to processing temperature and can serve as indicators of milk pasteurization.     

Ribonucleosides: Chemical parameters for controlling the heat treatment of milk

From experimental findings concerning changes in the contents of ribonucleosides - which belong to the group of minor milk constituents - in heat-treated milk it can be concluded that the concentrations of cytidine, guanosine and inosine present in raw milk show a multifold increase in milk which has been subjected to thermization and holder pasteurization, whereas the adenosine level decreases. On the other hand, these enzyme- (e.g. adenosine deaminase, alkaline phosphatase) catalysed changes in the content of unmodified ribonucleosides in milk are not observed in milk samples after short- and long-time pasteurization, high temperature pasteurization, ultra-high heating and sterilization. The changes in milk ribonucleoside contents found in these heating regions are mainly attributable to the catalytic activity of the milk enzymes in the course of the heating-up phase. During short- and long-time-, as well as high temperature pasteurization i.e. in the whole pasteurization region, changes in the nucleoside levels correlating with processing temperature and holding time were not observed since in these heating regions milk enzymes, such as adenosine deaminase and alkaline phosphatase, are inactivated. Hence, in the whole region of pasteurization neither enzyme-induced degradation- and conversion reactions nor thermally induced chemical degradation reactions take place with respect to unmodified ribonucleosides. However, with sterilization values exceeding F₀ = 30 min thermally induced hydrolytic effects are observed in UHT milk samples which lead in particular to an increase in adenosine contents. Comparable observations were made as regards cytidine, guanosine, inosine and adenosine contents in sterilized milk samples. Summing up, it can be concluded that from the viewpoint of dairy technology cytidine, guanosine and mainly inosine can be taken into account as chemical parameters for detecting thermization and, in particular, holder pasteurization. For characterizing heat treatment in the region of pasteurization, high temperature pasteurization, UHT heating and sterilization unmodified ribonucleosides of milk appear to be unsuited. The studies on the Dimroth-rearrangement under heating conditions of thermization and holder pasteurization, as well as short-, long-time- and high-temperature pasteurization, ultra-high heating and sterilization have shown that N⁶-methyladenosine, which is the resulting product of the rearrangement, is suited to be used as chemical parameter for controlling milk heat-treatment under time-temperature conditions with sterilization values (F₀) lying between ≈0.4 and 22 min. N⁶-methyladenosine is, thus, suited to be used as a chemical parameter for detecting heat treatment in the upper range of high temperature pasteurization, the whole range of UHT heating and the lower range of sterilization (as normally applied in dairies). From the viewpoint of dairy technology N⁶-methyladenosine is, thus, suited to be used as a further chemical parameter mainly for characterizing the upper range of UHT heating and the lower range of sterilization of heat-treated milk.     

常见热杀菌方式对关中羊乳品质的影响

采用5种常用热杀菌方式处理关中羊乳,即低温长时巴氏杀菌(65 ℃/30 min)、高温短时巴氏杀菌(72 ℃/15 s)、超巴氏杀菌(95 ℃/5 min)、高温高压灭菌(121 ℃/20 min)和超高温瞬时灭菌(137 ℃/7 s),在测定蛋白沉淀率、酒精稳定性、pH、红度值、粘度和脂肪球变化基础上,结合内源荧光光谱和聚丙烯酰胺凝胶电泳(SDS-PAGE)分析,探究热杀菌处理对关中羊乳品质的影响。结果表明,高温高压灭菌羊乳蛋白沉淀率最高、酒精稳定性最差、pH明显下降、红度值明显增大,但5种杀菌方式对粘度没有显著影响(p>0.05);羊乳脂肪球经巴氏杀菌和超巴氏杀菌后,表观直径略微增大,而高温高压灭菌和超高温瞬时灭菌,尤其是高温高压灭菌则导致其明显变小;荧光光谱表明,高温高压灭菌羊乳蛋白结构改变最大,内源荧光强度剧烈升高;电泳显示,巴氏杀菌(65 ℃/30 min和72 ℃/15 s)对羊乳酪蛋白和乳清蛋白影响较小,超巴氏杀菌(95 ℃/5 min)乳清蛋白开始变性、聚集或部分降解,高温高压灭菌和超高温瞬时灭菌,尤其是高温高压灭菌则使乳清蛋白明显降解甚至消失,酪蛋白出现聚集和解聚。结果表明,高温高压灭菌和超高温瞬时灭菌,尤其是高温高压灭菌对关中羊乳品质影响较大,超巴氏杀菌影响次之,而巴氏杀菌则对其影响较小。     

Conversion of Isoflavone Glycosides to Aglycones in SoyLife and Soymeal Using β-glycosidase

ABSTRACT: Conversion of isoflavones from glycosides to aglycones in SoyLife and soymeal using varying concentrations of β-glycosidase, and different pH conditions and temperatures was investigated. The best conditions for the conversion of glycosides to aglycones were pH 5.0, 50 °C, and 5 h incubation with 5 units β-glycosidase/g Soy Life and 1.5 units/g soymeal. Under these conditions, the amount of genistein, daidzein, and glycitein in Soy Life treated with β-glycosidase were 4.22, 11.52, and 11.85 μmol/g compared to untreated controls of 0.26, 0.97, and 4.43 μmol/g, respectively. In soymeal, the amounts were 3.21, 2.02, and 2.12 μmol/g compared to untreated controls of 1.23, 1.25, and 1.51 μmol/g, respectively. Mole percent recovery of genistein was 87% in Soy Life and 80% in soymeal, respectively.     

Analysis of galactosylisomaltol in milk systems using HPLC

While performing the HPLC separation of hydroxymethyfurfural (HMF) from in-bottle sterilised milk samples, two unknown compounds, named by us as Fig. 1, Fig. 2, Fig. 4

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Fig. 1. Classical separation of total and free (dotted line) HMF of (a) a skimmed in-bottle sterilised milk (Stork, 120°C/14 min), and (b) isolated fraction of pFig. 1, Fig. 2, Fig. 4.

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Fig. 2. (a) DAD spectrum of chromatographic peaks corresponding to pFig. 1, Fig. 2, Fig. 4, HMF and pFig. 1, Fig. 2; (b) spectrum of a freeze-dried fraction of pFig. 1, Fig. 2, Fig. 4.

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Fig. 4. Degradation of a pFig. 1, Fig. 2, Fig. 4 solution (0.75 μg/ml) dissolved in water (♦) and oxalic acid solution 0.3 N (▴) and 0.6 N (□) up to 60 min in a boiling water bath.

and Fig. 1, Fig. 2, were observed. Preliminary data indicated that the amount of compound Fig. 1, Fig. 2, Fig. 4 in the samples was dependent on the intensity of the heat treatment applied to milk. Compound Fig. 1, Fig. 2, Fig. 4 was isolated from heated solutions of lactose/caseinate and milk, and purified by semi-preparative rp-HPLC. Applying HPLC-DAD, UV, IR, GC–MS and NMR analysis it was possible to identify it as galactosylisomaltol. The analysis of HMF and galactosylisomaltol enables to follow simultaneously, the Amadori product degradation through 1,2- or 2,3-enolisation in milk systems. Higher levels of galactosylisomaltol were found in in-bottle sterilised samples as compared with UHT-treated and pasteurised milks. Galactosylisomaltol was not found either in raw or pasteurised milk.     

Deterioration of protein fraction by Maillard reaction in dietetic milks.

The development of the Maillard reaction in pasteurized, UHT and in-bottle sterilized dietetic milks was studied. In these products damage caused by heat treatments could increase as a result either of the addition of various ingredients or of manufacturing processes that alter their content of reducing carbohydrates. Protein damage was evaluated by measuring furosine by reversed-phase ion-paired HPLC. The levels of furosine detected made it possible to assess the amounts of biologically unavailable lysine. In all milks analysed blocked lysine values were < 340-350 mg/g total lysine, the level at which lysine becomes the limiting amino acid in milk. Pasteurized dietetic milks had levels of blocked lysine similar to that in ordinary pasteurized cows' milk. In some UHT and in-bottle sterilized dietetic milks their different composition resulted in an increase in the blocked lysine content. In some in-bottle sterilized milks, protein damage greatly reduces the beneficial effects of milk as a dietary supplement. Lactose-free milks, which are more susceptible to protein deterioration because of their higher content of reducing carbohydrates, were also analysed after storage at 20 degrees C and at < or = 4 degrees C. At the end of their recommended storage times, they contained limited amounts of blocked lysine only if they had been stored at < or = 4 degrees C.     

Energy Use for Continuous Thermal Processing of Milk

Energy use in a direct heat/vacuum cooling system was evaluated and compared to an indirect unit during start-up, sterilization, and milk processing. Product flow rates were 606-1325 L/hr. Process temperatures were 138 and 149°C. Energy for start-up was 1.7 to 2.9 x 10⁵ kJ for the direct; 0.9 to 1.4 x 10⁵ kJ, indirect. Energy for 30 min sterilization was 4.0 to 5.6 x 10⁵ kJ for direct; 2.3 to 3.7 x 10⁵ kJ, indirect. Product processing energy was 357.9-436.8 kJ/kg for indirect; 547.8-697.6 kJ/kg direct. Greater heat recovery potential and fewer pumps made the indirect system less energy intensive. Methods of energy conservation are suggested.     

Maillard Reaction in Microwave Cooking: Comparison of Early Maillard Products in Conventionally and Microwave-Heated Milk

The impact of microwave cooking on the formation of early Maillard products was investigated and compared with the effect of conventional cooking, using milk as a test system. Experiments were carried out at controlled temperatures of 80°C and 90°C, respectively, at holding times up to 420min. Furosine, hydroxymethylfurfural (HMF) and lactulose, which are all established indicators to estimate heat damage, were determined. The concentrations of all the heating indicators increased with increasing heating time. For example in the 90°C test series the furosine values rose from 34mglitre⁻¹ (0·5h) to 94mglitre⁻¹ (2h holding time) in the milk heated by microwaves and from 35mglitre⁻¹ (0·5h) to 96mg litre⁻¹ (2h) in the conventionally heated milk. None of the reaction products showed significant differences as between the microwave heating and conventional cooking methods.     

两种加热介质分别采用间接式杀菌的比较

杀菌分为直接式与间接式杀菌两种。直接式杀菌目前在国内应用不多,间接式杀菌比较多见。间接式杀菌根据所采用的加热介质的不同又分为蒸汽间接加热与高温水间接加热杀菌两种。以生产能力为1000kg/h用于牛奶杀菌,就采用两种不同加热介质的杀菌进行比较。     

Effects of Maillard reaction conditions on the antigenicity of α-lactalbumin and β-lactoglobulin in whey protein conjugated with maltose

The effects of Maillard reaction conditions (weight ratio of protein to sugar, temperature and time) on the antigenicity of α-lactalbumin (α-LA) and β-lactoglobulin (β-LG) in conjugates of whey protein isolate (WPI) with maltose were investigated. Response surface methodology was used to establish models to predict the antigenicity of α-LA and β-LG and find an optimal reaction condition under which the antigenicity of α-LA and β-LG reduces to minimum value. Conjugating WPI with maltose was an effective way to reduce the antigenicity of α-LA and β-LG. The antigenicity of α-LA decreased from 32.25 μg mL⁻¹ to 10.91 μg mL⁻¹. And the antigenicity of β-LG decreased from 272.4 μg mL⁻¹ to 38.17 μg mL⁻¹. Temperature had the greatest effect on the antigenicity of α-LA, while weight ratio of WPI to maltose was the most significant factor on the antigenicity of β-LG.     

Quantification of Lactulose and Epilactose in the Presence of Lactose in Milk using a dual HPLC analysis

The valuable lactose derivatives lactulose and epilactose can be derived from lactose either by the Lobry de Bruyn-Alberda van Ekenstein transformation during heat treatments or by enzymatic conversion using cellobiose 2-epimerases (EC 5.1.3.11). The chromatographic determination of lactose, lactulose, and epilactose in milk is challenging, due to the variable ratio of the three saccharides and their similar retention properties. In this work, a dual high-performance liquid chromatography (HPLC) analysis for the quantification of lactose, lactulose, and epilactose in milk samples was developed and validated. The samples originated from an enzymatic lactose conversion using the cellobiose 2-epimerase from Caldicellulosiruptor saccharolyticus. Application of this enzyme led to the formation of high lactulose concentrations (28.0 g/L) in milk. The dual HPLC analysis utilized a combination of two chromatographic separation techniques, configured in two parallel systems. After precolumn derivatization, the samples were analyzed as follows: Method 1 determined the concentration of lactose and epilactose using a C₁₈ column with an ion-pair reagent as eluent, coupled with a UV detector. Method 2 determined the concentration of lactulose using a trimodal stationary phase (hydrophilic interaction, anion- and cation-exchange properties) with acetonitrile/ammonium formiate buffer as eluent, coupled with an evaporative light scattering detector. Both methods were validated in terms of linearity, precision and recovery. The revealing detection limits in the milk samples were 3.32 mg/L for lactose, 4.73 mg/L for epilactose and 139 mg/L for lactulose. The dual HPLC analysis presented allows accurate lactose, lactulose, and epilactose separation in complex food matrices such as milk.     

Identification of proteolytic bacteria from thai traditional fermented foods and their allergenic reducing potentials

ABSTRACT:  This study aimed to identify proteolytic bacteria from Thai traditional fermented foods and investigate their allergenic reducing potentials to wheat and milk allergens. Nine bacteria were isolated from fermented foods as follows: fermented soybean seeds (Thua Nao), fermented soybean paste (Thua Nao), wheat flour dough of steamed stuffed bun (Sa La Pao), and soaked rice from Thai fermented rice-noodle (Kha Nhom Jeen) processing. Both phenotypic and genotypic identifications were used in this study. It was found that all isolates were Gram-positive rods. Seven isolates were matched and identified as Bacillus subtilis by both techniques, and the remaining 2 isolates were phenotypically and genotypically identified as B. licheniformis and B. subtilis , respectively. The concentrated crude enzyme of B. subtilis DB and SR could reduce allergenicity of gliadin by hydrolyzing the allergenic gliadin fragments detected by immunoblotting. Furthermore, the enzyme of B. subtilis DB could also reduce allergenicity of β-lactoglobulin (β-LG) detected by hydrolyzing the major allergenic epitope of β-LG at Gln³⁵-Ser³⁶ position. B. subtilis DB and SR can be applied for the production of hypoallergenic wheat flour or milk food products.