Heat stability of betacyanins in red beet juice and in betanin solutions

Summary The losses of red pigments during heating and their regeneration after heating were investigated in red beet juice and pure betanin solutions. The experiments were carried out with equal access of oxygen and a similar level of the initial content of the pigment. The presence of heavy metal ions in trace amounts had a great destructive influence on the pigment in solutions of pure betanin. In red beet juice compounds which decrease and compounds which increase the retention of betanin both occured during heating and regeneration. The group of compounds that decrease betanin stability included some metal ions, e.g. Cu(II) and Fe(III), along with certain amino acids. The negative influence of the metal ions in beet juice decreased probably due to the presence of metal-complexing agents.

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Stabilität der Betacyane während der Erhitzung des Rote-Beete-Saftes und der Betanin-Lösungen

Zusammenfassung Es wurden die Verluste an rotem Farbstoff im Rote-Beete-Saft und in Betanin-Lösungen während der Erhitzung mit der Regeneration des Farbstoffes in den erhitzten Proben verglichen. Die Versuche wurden bei gleichem Sauerstoffdruck und bei vergleichbarer Menge des Farbstoffes zu Beginn durchgeführt. Die Anwesenheit von Spuren an Schwermetallen in den Lösungen von reinem Betanin wirkt zerstörend auf den Farbstoff. Im Rote-Beete-Saft treten sowohl Verbindungen auf, die die Betanin-Retention während der Erhitzung und die Regeneration vermehren, wie auch solche, die sie vermindern. Zur Gruppe der Verbindungen, die die Stabilität von Betanin verringern, gehören die Ionen einiger Schwermetalle wie Cu(II) und Fe(III) und einige Aminosäuren. Die negative Wirkung der Metallionen im Saft wird wahrscheinlich durch Anwesenheit metallkomplexierender Verbindungen vermindert.

     

Heat stability of buttermilk

Buttermilk prepared on a laboratory scale from raw cream, or on a commercial scale from flash-pasteurized cream (90 degrees C for 1 to 2 s), exhibited a type B heat coagulation time-pH profile (i.e., stability increased as a function of pH). The high heat stability of buttermilk in the pH range of the minimum of a type A milk (pH approximately 6.8 to 7.0) appears to be related to differences in the serum phase constituents (i.e., a low calcium and beta-Lg concentration and a high nonmicellar kappa-CN content).     

Heat stability of milk

The heat stability of milk has been the subject of a considerable amount of research for about a century. This research has been aimed mainly at understanding the effects of compositional and processing factors on heat stability and elucidating the mechanisms of protein coagulation. This paper provides an overview of the factors that influence the pH dependence of the heat stability of normal and concentrated milks. The principal heat-induced changes in the milk system that contribute to coagulation are discussed. Current knowledge of the mechanisms of heat coagulation in normal and concentrated milks is also reviewed.     

亚麻籽油的热稳定性研究

通过加热试验,研究了亚麻籽油的热稳定性。结果表明:在高温加热条件下,亚麻籽油中α-亚麻酸含量有所降低,总反式脂肪酸的含量提高;在200℃和250℃条件下保持120 min后,亚麻籽油中α-亚麻酸的含量分别下降了6.1%和57.7%,总反式酸的含量分别为4.47%和20.89%。说明亚麻籽油作为烹调用油,烹调温度在200℃以下比较合适,加热时间不宜过长。     

Heat stability of transglutaminase-treated milk

Heat-induced coagulation of unconcentrated (9%, w/w) and concentrated (18%, w/w) reconstituted skim milk was determined after incubation with transglutaminase (TGase). Cross-linking ∼20% of κ-casein strongly increased the heat stability of unconcentrated milk at pH >6.9, presumably by preventing heat-induced dissociation of κ-casein, whereas increased heat stability of unconcentrated milk at pH 6.6–6.8 was only observed when >80% of casein was cross-linked. Treatment with TGase reduced heat stability of unconcentrated milk at pH <6.6, presumably due to the increased susceptibility of partially cross-linked casein micelles to coagulation arising from heat-induced acidification. A low degree of cross-linking increased the heat stability of concentrated milk at pH >6.8, but more extensive cross-linking progressively reduced heat stability. The degree of cross-linking studied did not increase the heat-stability of concentrated milk at its natural pH. The outcomes of this study substantiate the crucial roles of heat-induced acidification and casein dissociation in heat stability of milk.     

Heat stability of peroxidases from orange

Soluble and ionically bound peroxidases have been obtained from orange juice and the albedo. A high level of peroxidase activity was present in the albedo. Non-linear heat inactivation was observed for orange peroxidases. The bound peroxidases were particularly heat stable and regenerated when held at 30°C following heat inactivation. A small amount of regeneration was observed for orange soluble peroxidases.     

Decomposition of betacyanins and betaxanthins by heat and pH changes

Authors investigated the decomposition of the main beetroot colourings betanin and vulgaxanthin I as a function of temperature and pH value in acetate and citrate buffer solutions, in a temperature-range between 60 °C and 80 °C and pH range of 3.3–6.2. The temperature dependence of betain decomposition is characterized by a Q₁₀ value of 2.23 ± 0.45, and the reaction rate was doubled by reducing the pH value from 6.2 to 3.3 independent from the type of acid used. Also the interaction between temperature and pH value on colour decomposition was verified. Investigations were carried out at low oxygen content, and under this conditions the reaction was exactly described - considering the time interval of 20 min - by a linear function at 60 °C, pH value 3.3–6.2 and by an exponential function at 70 °C and 80 °C and pH 3.3–4.65. Activation energy for betain degradation is 77.5 ± 6.76 kJ/mol.     

水牛奶乳清蛋白的热稳定性

以水牛奶为材料,利用native-PAGE和SDS-PAGE,通过不同温度和加热条件下总乳清蛋白和单体蛋白质量浓度的变化,研究水牛奶乳清蛋白的热稳定性。结果表明:水牛奶乳清蛋白在native-PAGE条件下只有β-LG一条条带,在SDS-PAGE条件下得到4条单体乳清蛋白条带;随着提取温度和时间的增加,水牛奶单体乳清蛋白和总乳清蛋白质量浓度均呈下降趋势,说明水牛奶乳清蛋白热稳定性较差;4种乳清单体蛋白中,α-LA的热稳定性最好,IG的热稳定性最差,热稳定性顺序为:α-LAβ-LGBSAIG。     

Heat stability of ochratoxin A in pig products

Swedish blood-pudding, kidneys, muscular tissue and adipose tissue from pigs, naturally contaminated with ochratoxin A, were analysed for ochratoxin A before and after cooking. Frying temperatures were 150–160°C. On average about 20% of the toxin was lost during cooking. In the adipose tissue no toxin was lost.     

Heat stability and calcium bioavailability of calcium-fortified milk

The objective of the study was to fortify calcium in cow milk in order to prepare calcium-enriched heat-stable milk for individuals who may not ingest enough calcium to meet minimum daily requirements. Therefore, cow milk was fortified with calcium at the rate of 50 mg/100 ml using three salts of calcium, viz. calcium chloride, calcium lactate and calcium gluconate. Upon addition of calcium salts, there was a marked drop in the pH and heat stability. However, restoration of pH to the original value with the addition of disodium phosphate stabilized the fortified milk and enhanced its heat stability over unfortified milk. The maximum in heat stability (HCT) of calcium-fortified cow milk samples remained slightly higher than that of unfortified milk. Metabolic study on mice revealed that calcium bioavailability of cow milk fortified with calcium lactate and calcium gluconate and stabilized with disodium phosphate was slightly higher than unfortified cow milk. Fortification of cow milk with calcium and restoration of its pH resulted in a calcium to phosphorus ratio still greater than one, which is considered ideal for retention of calcium in the body.     

Heat stability of milk supplemented with calcium chloride

Calcium chloride (0-25 mM) was added to skim milk powder that was reconstituted to 9% total solids. Heat stability was evaluated between 60 and 120°C for different times by observing whether samples had coagulated, and by measuring the amount of sediment and residual protein in the centrifuged supernatant. Milk samples were also dialyzed during their respective heat treatments to recover the soluble phase at different temperatures to measure pH and ionic calcium. The transition conditions between good and poor heat stability were established for different calcium chloride concentrations and temperatures. As temperature increased, coagulation occurred at lower levels of added calcium chloride. The transition was quite distinct at higher temperatures but less so at lower temperatures; it was initiated by an increase in sediment formation before a firm coagulum was formed. Both pH and ionic calcium decreased in dialysates as temperature increased. No coagulation was observed if Ca(2+) was <0.5 mM and pH was >6.3 in dialysates taken at their respective coagulation temperatures. Being able to measure pH and ionic calcium at high temperatures will allow better understanding of factors affecting heat stability. Electrophoresis of the supernatants permitted identification of the protein fractions participating in the coagulation process. When coagulation was observed below 80°C, substantial amounts of undenatured β-lactoglobulin and α-lactalbumin were found in the supernatant, as well as some soluble casein fractions. All the major whey protein and casein fractions were found in the sediment.     

The effect of heating conditions on losses and regeneration of betacyanins

Summary The losses of Betacyanins during heating at 90 °C and their regeneration after heating were investigated in red beet juice and solutions of pure betanin in different buffers. It was found that the regeneration of pigments during storage of heated samples is greater at 5 °C than at 20 °C. The time, in which the pigments reach the maximum concentration is different for juice and pure betanin solutions. The influence of the type of buffer and its concentration on heating in the absence of oxygen is insignificant, on the other hand the influence is distinctly marked when the betanin heated in the presence of oxygen. When heated in the presence of air, the betanin losses are influenced by the rate of diffusion of oxygen from the air.

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Einflu der Erhitzungsbedingungen auf Verluste und Regeneration der Betacyanine

Zusammenfassung Die Verluste an Betacyaninen während der Erhitzung auf 90 °C und ihre Regeneration nach dem Erhitzen wurden in Rote-Beete-Saft und in verschieden gepufferten reinen Betanin-Lösungen untersucht. Bei 5 °C ist die Regeneration der Farbstoffe besser als bei 20 °C. Die Zeit bis zur maximalen Regeneration der Farbstoffe ist für den Saft und für die Betanin-Lösungen unterschiedlich. Pufferart und -konzentration sind unter sauerstofffreien Bedingungen unwesentlich; bei Anwesenheit von Sauerstoff üben sie indessen einen merklichen Einflu aus. Beim Erhitzen in Gegenwart von Sauerstoff werden die Betanin-Verluste von der Diffusionsgeschwindigkeit des Luftsauerstoffs beeinflußt.

     

Heat stability and reactivation of mare milk lysozyme.

Mare milk and aqueous solution of mare milk lysozyme were incubated for variable times between 30 C and 100 C at pH 3, 6, or 9. Lysozyme activity was stable at acid and neutral pH and labile at alkaline pH. Some of the results show the existence of a reactivation process in mare's milk and in aqueous solution. reaching 30 to 40% after incubation of the aqueous solution at 4 C for 20 days at pH 3 or 6.     

Heat stability of reconstituted, protein-standardized skim milk powders

We determined the effects of standardization material, protein content, and pH on the heat stability of reconstituted milk made from low-heat (LH) and medium-heat (MH) nonfat dry milk (NDM). Low-heat and MH NDM were standardized downward from 35.5% to 34, 32, and 30% protein by adding either edible lactose powder (ELP) or permeate powder (PP) from skim milk ultrafiltration. These powders were called standardized skim milk powders (SSMP). The LH and MH NDM and SSMP were reconstituted to 9% total solids. Furthermore, subsamples of reconstituted NDM and SSMP samples were set aside to measure heat stability at native (unadjusted) pH, and the rest were adjusted to pH 6.3 to 7.0. Heat stability is defined as heat coagulation time at 140°C of the reconstituted LH or MH NDM and SSMP samples. The entire experiment was replicated 3 times at unadjusted pH values and 2 times at adjusted pH values. At an unadjusted pH, powder type, standardization material, and protein content influenced the heat stability of the samples. Heat stability for reconstituted LH NDM and SSMP was higher than reconstituted MH NDM and SSMP. Generally, decreased heat stability was observed in reconstituted LH or MH SSMP as protein content was decreased by standardization. However, adding ELP to MH SSMP did not significantly change its heat stability. When pH was adjusted to values between 6.3 and 7.0, powder type, standardization material, and pH had a significant effect on heat stability, whereas protein content did not. Maximum heat stability was noted at pH 6.7 for both reconstituted LH NDM and SSMP samples, and at pH 6.6 for both reconstituted MH NDM and SSMP samples. Furthermore, for samples with adjusted pH, higher heat stability was observed for reconstituted LH SSMP containing PP compared with reconstituted milk from LH SSMP containing ELP. However, no statistical difference was observed in the heat stability of reconstituted milk from MH NDM and MH SSMP samples. We conclude that powder type (LH or MH) and effect of standardization material (ELP or PP) can help explain differences in heat stability. The difference in the heat stability of powder type may be associated with the difference in the pH of maximum heat stability and compositional differences in the standardization material (ELP or PP).     

Heat stability of whey protein ingredients based on state diagrams

A state diagram approach was used to compare heat stability among whey protein ingredients. Solutions were thermal processed and solubility, turbidity, and colloidal structure (sol, precipitate, or gel) were plotted against the variables of pH (3–7) and protein concentration (1–10%, w/w) to form state diagrams. Each of the whey protein ingredients produced state diagrams with unique patterns in the protein concentrations associated with colloidal structures and in heat stability regions. Relative heat stability among ingredients depended on the pH-thermal processing combination, in that patterns observed at pH ≤ 4.5 were not equivalent to patterns produced at pH > 4.5. Heating at temperatures of <100 °C for extended time did not produce the same results as heating at > 100 °C for short times. State diagrams were able to differentiate among the whey protein ingredients, but absolute values were determined by the heating treatment.     

Heat stability of plasmin (milk proteinase) and plasminogen

The effect of heating on plasmin activity in various media, including phosphate buffer pH 7.0, skim milk, blood plasma, solutions of casein and solutions of whey proteins were investigated. Plots of log residual activity v. heating time were linear at all temperatures from 63 to 143 degrees C. In buffer solutions the presence of casein led to substantial substrate protection, the Arrhenius plots being linear both in the presence and absence of casein. The activation energy, Ea, for the inactivation reaction, was 62.4 kJ/mol in buffer alone and 58.4 kJ/mol with casein present at 25 mg/ml. In skim milk, despite the presence of casein at a similar concentration, plasmin was no more stable to heat than in buffer alone, and a curved Arrhenius plot was obtained indicating a more complex inactivation mechanism. Heating in the presence of proteins having free -SH groups accelerated the inactivation of plasmin. The role of -SH groups was confirmed by experiments with added alpha-lactalbumin, in which no free -SH groups occur, and reduced carboxymethylated beta-lactoglobulin, both of which were without effect. In blood plasma, plasmin was less stable to heat than in buffer (pH 7.0) or in skim milk. Plasminogen behaved very similarly to plasmin either when activated to plasmin with urokinase before heating or when activated afterwards. A hypothesis is presented to describe the heat inactivation and denaturation of plasmin. Technologically important findings are that in skim milk plasmin was largely unaffected by pasteurization conditions and 30-40% of its activity remained even after ultra high temperature processing conditions.     

酯型儿茶素的热稳定性及其上染蚕丝效果

为阐明酯型儿茶素的氧化聚合作用及其对蚕丝染色效果的影响,采用超高效液相色谱串联四极杆飞行时间质谱分析了表没食子儿茶素没食子酸酯（EGCG）、没食子儿茶素没食子酸酯（GCG）和表儿茶素没食子酸酯（ECG）等儿茶素染液的热稳定性。结果表明：儿茶素受热不稳定,转化程度也有差异;单一成分时,ECG的转化率最高,GCG的最低;多种成分共存时,GCG和ECG的协同效应较强,转化率相近。研究EGCG、GCG和ECG在蚕丝上的着色效果发现：EGCG、GCG 和ECG等比例染色时,蚕丝对酯型儿茶素的吸附率为ECG＞GCG＞EGCG;不同比例混染时,蚕丝对酯型儿茶素的吸附率相近,EGCG与GCG的着色能力较ECG强。可见ECG的热稳定性不会影响蚕丝的吸附率,且其着色程度较浅,因而更适于用作植物染色剂。