Temperature and pressure stability of l-ascorbic acid and/or [6s] 5-methyltetrahydrofolic acid: A kinetic study

Processing (i.e. pressure and temperature) stability of l-ascorbic acid (l-AA) and/or [6S]-5-methy-ltetrahydrofolate ([6S]-5-CH₃-H₄folate) was studied on a kinetic basis using different vitamin and initial oxygen concentrations. Stability of both folate and l-AA was enhanced by increasing the vitamin concentration or by decreasing the oxygen concentration. Based on this study, it was concluded that (i) l-AA increased the folate stability during processing; (ii) the molar ratio between l-AA or folate and the initial oxygen content was an important parameter to determine the proportion of aerobic degradation; and (iii) the minimum concentration of l-AA needed to prevent the oxidation of folate was at least 2 times as high as the molar concentration of the initial oxygen content when l-AA exists as a single antioxidant in the system.     

Low‐field NMR: A tool for studying protein aggregation

Low‐field nuclear magnetic resonance (NMR) spin–spin relaxation (T₂) measurements were used to study the denaturation and aggregation of β‐lactoglobulin (β‐LG) solutions of varying concentrations (1–80 g L^?1) as they were heated at temperatures ranging from ambient up to 90 °C. For concentrations of 1–10 g L^?1, the T₂ of β‐LG solutions did not change, even after heating to 90 °C. A decrease in T₂ was only observed when solutions having higher concentrations (20–80 g L^?1) were heated. Circular dichroism (CD) spectroscopy and fluorescence tests using the dye 1‐anilino‐8‐naphthalene sulfonate (ANS) on 0.2 and 1 g L^?1 solutions, respectively, indicated there were changes in the protein's secondary and tertiary conformations when the β‐LG solutions reached 70 °C and above. In addition, dynamic light scattering (DLS) showed that protein aggregation occurred only at concentrations above 10 g L^?1 and for heating at 70 °C and above. The hydrodynamic radius increased as T₂ decreased. When excess 2‐mercaptoethanol was added, the changes in both T₂ and the hydrodynamic radius followed the same trend for all β‐LG protein concentrations between 1 and 40 g L^?1. These observations led to the conclusion that the changes in T₂ were due to protein aggregation, not protein unfolding. Copyright © 2007 Society of Chemical Industry     

Kinetics of (6R,S) 5-formyltetrahydrofolic acid isobaric–isothermal degradation in a model system

Isothermal and isobaric–isothermal degradation kinetics of (6R,S) 5-formyltetrahydrofolic acid (5-CHOH₄PteGlu) was studied at different pH levels in the temperature range from 80 to 110 °C and different pressure–temperature combinations (100–800 MPa and 30–70 °C). The thermal degradation of 5-CHOH₄PteGlu followed first-order kinetics at all pH levels (in the range of pH 3–9.2) studied. 5-CHOH₄PteGlu at pH 7–9.2 was quite stable up to 5–7 h of heating at 80 °C but less stable in more acidic conditions (pH 3.38 and 5). Pressure–temperature degradation of 5-CHOH₄PteGlu could be adequately described by a first-order reaction. In the whole pressure–temperature area studied, the degradation rate constants of 5-CHOH₄PteGlu were enhanced by increasing pressure or increasing temperature. Significant reductions in 5-CHOH₄PteGlu concentration were noticed when pressures above 400 MPa were combined with temperatures above 40 °C. A model to describe the effect of combined pressure and temperature on the 5-CHOH₄PteGlu destruction rate constant was presented.     

Thermofraktographie zur Schnellanalyse von Kunststoffen. 2. Mitt. Identifizierung von Phenolharzen

Thermofractography is suitable for the rapid identification of phenolic resins. 3–4 mg of the material to be investigated are heated in the temperature gradient of 150–450°C. The thermofractogram shows the free phenols of the resin in the range of 150–250°C. The phenols developing through thermolysis from the condensation products appear, depending on the corresponding initial phenol, in the range of 300–450°C. The efficiency of the method is demonstrated on several novolaks and phenolresol.     

Complying with practice codes

As part of a pilot-project programme in the Netherlands to develop 'small' stand-alone expert systems, the IBBC-TNO Institute in Delft has developed BRAM. This is a fire-safety analysis method using artificial intelligence to guide the designer through the practice code requirements. The objectives, the problems and the solutions evolved are discussed in this article.     

Kinetic study on the thermal and pressure degradation of anthocyanins in strawberries

The degradation of anthocyanins (pelargonidin-3-glucoside) in a strawberry paste during high-temperature/high-pressure treatments was investigated over a temperature range of 80–130 °C and a pressure range of 200–700 MPa, compared to 0.1 MPa. A first-order kinetic model fitted well to all data. At constant pressure, anthocyanin concentration decreased as a function of time and the degradation was accelerated at higher temperatures. At constant temperature, anthocyanins were more rapidly degraded as the pressure increased, but the effect of increasing pressure was smaller than the effect of increasing temperature. Temperature dependence of the degradation rate constants, described by the Arrhenius equation, was higher at atmospheric pressure than at elevated pressures, where all activation energies were comparable. Activation volumes, estimated by the Eyring equation, demonstrated a small pressure dependence of the reaction rate constants. Finally, a model to describe the combined temperature–pressure dependence of the degradation rate constants was proposed.     

Behavior of mustard seed (<Emphasis Type="Italic">Sinapis alba</Emphasis> L.) myrosinase during temperature/pressure treatments: a case study on enzyme activity and stability

The activity of myrosinase, an enzyme found mainly in Brassicaceae, is influenced by some intrinsic (e.g. pH, ascorbic acid) and extrinsic (e.g. temperature, pressure) factors. In this study, the effect of intrinsic and extrinsic factors on the activity of mustard seed myrosinase (Sinapis alba L.) was determined in a buffer system and in broccoli juice. Ascorbic acid and to a much lesser extent MgCl₂ were found to enhance the myrosinase activity. In buffer solution, the optimal temperature for myrosinase activity at atmospheric pressure was 60 °C. At elevated pressure, the reaction rate increased until 200 MPa and the optimal temperature shifted to 40 °C in a buffer system. In broccoli juice, mustard seed myrosinase behaved somewhat different compared to the buffer system. The highest enzyme activity was found at 60 °C, both at atmospheric and elevated pressures. In broccoli juice, the enzymatic reaction rate also increased up to pressures of 200 MPa. Enzyme inactivation could be described by first order kinetics.     

High-pressure treatments induce folate polyglutamate profile changes in intact broccoli (Brassica oleraceae L. cv. Italica) tissue

In plant matrices, folates exist largely as folylpoly-γ-glutamates requiring deglutamylation to monoglutamates prior to absorption, which might impair dietary folate bioavailability. This study investigated folylpoly-γ-glutamate stability and conversions in broccoli tissue during thermal (25–90 °C, 30 min) and high-pressure treatments (0.1–600 MPa, 25–45 °C, 30 min) after vacuum packaging. Folates were analyzed based on poly-γ-glutamate side chain length by RP-HPLC. During thermal treatments, folates were stable up to 90 °C, whereas differences in folylpoly-γ-glutamate profiles towards higher conjugated folylpoly-γ-glutamates were observed at elevated temperatures (70–90 °C). High-pressure treatments resulted in significant folate losses (48–78%). Depending on the pressure–temperature combinations studied, folylpoly-γ-glutamates were converted to folylmono- and folyldi-γ-glutamates, which was shown to occur mainly during the initial stages of the high-pressure treatments, i.e. during pressure build-up and subsequent equilibration. Targeted application of high-pressure treatments can hence be applied to obtain broccoli with higher monoglutamate folate content. Implications towards folate bioavailability in relation to the observed folate degradation, however, requires further investigation.     

Influence of pressure/temperature treatments on glucosinolate conversion in broccoli (Brassica oleraceae L. cv Italica) heads

Glucosinolates are a group of secondary plant metabolites that are found in the Brassicaceae family. Upon hydrolysis by the endogenous enzyme myrosinase, a large number of compounds can be formed of which some are potentially anticarcinogenic, while others are largely inactive. Furthermore, some bioactive compounds are unstable. Therefore, it is not only important to determine the type and amount of glucosinolates present or hydrolysed in a given plant, but it is also relevant to investigate the type of hydrolysis products. In this research, the effect of combined pressure–temperature treatments (100–500 MPa, 20–40 °C) on the glucosinolate conversion and the kind of hydrolysis products was studied in broccoli, both during treatment and after autolysis. The results, showed that high pressure can induce glucosinolate hydrolysis during treatment, promote the formation of isothiocyanates after treatment and that relatively more indole oligomers are formed during treatment than during autolysis. These results indicate that pressure treatment limits the loss of glucosinolates and its health beneficial products.