Enzymatic Synthesis of l‐Ascorbyl Fatty Acid Esters Under Ultrasonic Irradiation and Comparison of Their Antioxidant Activity and Stability

A series of novel l ‐ascorbyl fatty acid esters were synthesized by catalization of Novozym^® 435 under ultrasonic irradiation and characterized by infrared spectroscopy, electrospray ionization mass spectra, and nuclear magnetic resonance. Their properties especially antioxidant activity and stability were investigated. The results showed that the reducing power, the scavenging activity of hydroxyl radical and 2,2‐diphenyl‐1‐picrylhydrazyl radical were decreased with the increase of the number of carbon atoms in fatty acid. The hydroxyl radical scavenging activity and reducing power of l ‐ascorbyl saturated fatty acid esters were better than that of tert‐butylhydroquinone. The induction period in lipid oxidation of l ‐ascorbyl saturated fatty acid esters and tert‐butylhydroquinone were longer than that of l ‐ascorbyl unsaturated fatty acid esters and l ‐ascorbic acid both in soybean oil and lard. Besides, the l ‐ascorbyl fatty acid esters showed different stabilities in different conditions by comparing with l ‐ascorbic acid, and the l ‐ascorbyl saturated fatty acid esters were more stable than l ‐ascorbyl unsaturated fatty acid esters in ethanol solution.     

Enzymatic Synthesis of Ascorbyl Palmitate in Organic Solvents: Process Optimization and Kinetic Evaluation

This work is focused on the optimization of reaction parameters for the synthesis of ascorbyl palmitate catalyzed by Candida antarctica lipase in different organic solvents. The sequential strategy of experimental designs proved to be useful in maximizing the conditions for product conversion in tert-butanol system using Novozym 435 as catalyst. The optimum production were achieved at ascorbic acid to palmitic acid mole ratio of 1:9, stirring rate of 150 rpm, 70 °C, enzyme concentration of 5 wt.% at 17 h of reaction, resulting in an ascorbyl palmitate conversion of about 67%. Reaction kinetics for ascorbyl palmitate production showed that very satisfactory reaction conversions (∼56%) could be achieved in short reaction times (6 h). The kinetic empirical model proposed showed ability to satisfactory represents and predict the experimental data.     

Optimisation of enzymatic esterification of soybean oil deodoriser distillate

The enzymatic esterification of free fatty acids from soybean oil deodoriser distillate with ethanol, catalysed by immobilised fungal lipase, was studied. The extent of conversion of free fatty acids to ethyl esters was optimised using a response surface methodology obtained through a second‐order factorial experimental design. The variables studied were reaction temperature (30–70 °C), enzyme concentration (7–23%) and ethanol/free fatty acid molar ratio (0.3–3.7:1). The optimal reaction conditions achieved were temperature from 46.4 to 53.6 °C, enzyme concentration from 13.6 to 16.5% and ethanol/free fatty acid molar ratio from 1.7 to 2.3:1, with conversions above 88%. No significant tocopherol losses were observed during the process. In conclusion, enzymatic fatty acid esterification was shown to be a technically viable process. © 2001 Society of Chemical Industry     

Lipase-catalysed production of triacylglycerols enriched in pinolenic acid at the sn-2 position from pine nut oil

BACKGROUND: The purpose of this study was to produce triacylglycerols (TAGs) enriched in pinolenic acid (PLA) at the sn‐2 position using the principle of acyl migration, from the pine nut oil containing PLA esterified exclusively at the sn‐3 position. RESULTS: Two types of lipase‐catalysed reactions, i.e. redistribution and reesterification of fatty acids, were successively performed using seven commercially available lipases as biocatalysts. Of the lipases tested, Novozym 435 and Lipozyme TL IM were effective biocatalysts for positioning PLA at the sn‐2 location. These biocatalysts were selected for further evaluation of the effects of reaction parameters, such as temperature and water content on the migration of PLA residues to the sn‐2 position and TAG content. For both lipases, a significant decrease in TAG content was observed after the lipase‐catalysed redistribution of fatty acids for both lipases. The reduced TAG content could be enhanced up to approx. 92%, through lipase‐catalysed re‐esterification of the hydrolysed fatty acids under vacuum. CONCLUSION: TAG enriched in PLA at the sn‐2 position was synthesised from pine nut oil via lipase‐catalysed redistribution and re‐esterification of fatty acid residues using Lipozyme TL IM and Novozym 435 as biocatalysts. Copyright © 2011 Society of Chemical Industry     

Concentration of n‐3 polyunsaturated fatty acids in cholesterol‐reduced cod‐liver oil by lipases

This study was conducted to elucidate the effects of different lipases originated from Candida rugosa (CR), porcine pancreas (PP) and Aspergillus niger (AN) on the degree of hydrolysis (DH) in cholesterol‐reduced cod‐liver oil (87.5%) and evaluate the changes in n‐3 polyunsaturated fatty acid concentrations in the oil hydrolysed by the lipases. The lipase‐catalysed hydrolysis of cholesterol‐reduced cod‐liver oil was performed at 37 °C for 8 h. Among all the lipase samples studied, DH in the oil after lipase‐catalysed hydrolysis followed the decreasing order: CR lipase (70.01%) > PP lipase (26.18%) > AN lipase (18.57%). Triacylglycerol levels in the oil hydrolysed by all the lipases studied decreased, while mono‐ and diacylglycerol levels increased during lipase‐catalysed hydrolysis. The eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) concentrations in cholesterol‐reduced cod‐liver oil hydrolysed by the CR lipase were remarkably higher than those by the PP or AN lipase. Thus, it is suggested in this study that the CR lipase appears to be most suitable for producing and n‐3 polyunsaturated fatty acids including EPA and DHA concentrates from cholesterol‐reduced cod‐liver oil.     

Pectin methyl esterase treatment on high‐methoxy pectin for making fruit jam with reduced sugar content

BACKGROUND: Pectin methyl esterase (PME) has been postulated to catalyse the transacylation reaction between pectin molecules. The present study aimed to prove the occurrence of this reaction. The feasibility of applying PME‐catalysed transacylation between high‐methoxy pectin molecules in making fruit jam with reduced sugar content was also investigated. RESULTS: PME treatment increased the turbidity and particle size in pectin solution and the molecular weight of pectin, while it decreased the number of methoxy ester linkages and the intensity of the CH₃ absorption peak in the Fourier transform infrared spectrum without changes in the number of total ester linkages in pectin molecules. These findings support the occurrence of PME‐catalysed transacylation between pectin molecules. Higher values of hardness, gumminess and chewiness were found in a jam containing PME‐treated citrus pectin (10 g L^?1) and sugar (350 g L^?1) as compared with either a jam containing untreated citrus pectin (10 g L^?1) and sugar (350 g L^?1) or strawberry jam containing pectin (10 g L^?1) from the fruit and sugar (650 g L^?1). CONCLUSION: The demand for sugar in jam making can be greatly reduced by the use of PME‐treated high‐methoxy pectin. Copyright © 2012 Society of Chemical Industry     

Inhibitory effect of rice bran extract on polyphenol oxidase of potato and banana

Rice bran was extracted with water and its effects on potato and banana polyphenol oxidase (PPO) were investigated. Rice bran extract (RBE), conc. 0.3 g mL^?1, exhibited PPO inhibition in potato and banana PPO with % inhibition of 69.31% and 47.63%, respectively (P ≤ 0.05). RBE showed a concentration‐dependent inhibition on potato and banana PPO. RBE (conc. 0.3 g mL^?1) inhibited potato PPO higher than ascorbic acid, citric acid, NaCl and EDTA (final conc. 20 mg L^?1); and it also inhibited banana PPO higher than citric acid, NaCl and EDTA (final conc. 20 mg L^?1), respectively. The combination of RBE with citric acid or ascorbic acid appeared to be additive inhibitory effect on banana and potato PPO. Kinetic study of the inhibition on potato and banana PPO by RBE showed that RBE was a mixed‐type inhibitor; however, RBE appeared to be able to act directly on enzyme structure rather than substrate structure.     

The influence of vitamin E supplementation on yeast fermentation

Ethanol is a well‐known toxic metabolite of yeast, affecting cell growth, and it is a major factor responsible for reduced ethanol production. Therefore, yeast strains that can withstand high ethanol concentrations are highly desirable. The effects of vitamin E supplementation and enhanced cell membrane fluidity in ethanol fermentations were studied. The results showed that ethanol tolerance was significantly improved by vitamin E supplementation, which correlated with the increased level of polyunsaturated fatty acids. The data showed that, after 0.1 g L^?1 vitamin E was added to the highest ethanol concentration, one could attain 118.7 g L^?1, in contrast to 106.4 g L^?1. The experimental results indicated that the increase in vitamin E suppressed unsaturated fatty acid oxidation, resulting in enhanced ethanol tolerance and increased production yield. Copyright © 2016 The Institute of Brewing & Distilling     

Turbidity potentials of single long‐chain fatty acids and gelatinised starch in synthetic lautering wort

The turbidity potentials of long‐chain fatty acids as well as gelatinised starch were investigated in synthetic lautering wort to determine their contribution to turbidity according to concentration. Synthetic wort proved to be a standardised and reproducible model solution. Concentration series of gelatinised starch and single long‐chain fatty acids as pure substances showed high correlations between concentrations and turbidity levels of turbidity 11° and turbidity 90° measurements. Gelatinised barley starch has the turbidity potential of 0.04 EBC/(mg L^?1) on turbidity 11° levels. Regarding long‐chain fatty acids, saturated fatty acids showed distinctly higher turbidity potentials on turbidity 11° (≥0.32 EBC/(mg L^?1) and turbidity 90° (≥0.15 EBC/(mg L^?1) than unsaturated fatty acids. The turbidity potential of the saturated fatty acids corresponded with their chain lengths, with stearic acid (18:0) showing the highest turbidity potential. However, the impact on turbidity is primarily determined by concentration and not by turbidity potential.     

超声辅助脂肪酶催化L-抗坏血酸脂肪酸酯的合成

采用猪油和抗坏血酸为原料,通过单因素试验和正交试验,研究超声作用对酶促转酯化反应合成抗坏血酸脂肪酸酯的影响,并确定其最佳反应条件。结果表明,最佳反应条件为:叔戊醇为溶剂,Novozym 435用量20%(抗坏血酸质量百分比),抗坏血酸与猪油物质的量的比1:3,超声功率350W,超声频率59kHz,反应时间9h,在此条件下,抗坏血酸脂肪酸酯转化率达到88.00%。超声处理不仅可以提高产物产率(从71%提高到88%),还可以大大缩短反应时间(从32h降低到9h)。超声条件下Novozym 435有良好的操作稳定性,反应6批次后,酶活还保持在比较高的水平。     

Biochemical,microbiological and sensory changes in shrimp (Panaeus aztecus) dipped in different solutions using face‐centred central composite design

Biochemical, microbiological and sensory changes during shelf‐life at ?1 °C were determined in shrimp (Panaeus aztecus) previously dipped in ascorbic acid, citric acid, potassium sorbate and 4‐hexyl resorcinol solutions using face‐centred central composite design. Microbiological count, trimethylamine and hypoxantine production were measured. The lowest level of the total psychrotrophic bacteria, hypoxantine and trimethylamine were found in samples dipped in all containing chemicals solutions comparing to control treatment. Sensory studies showed that treatment A (ascorbic acid 4.50, citric acid 0.12, potassium sorbate 18.60 and 4‐hexyl resorcinol 0.25, all g L^?1) and B (ascorbic acid 4.37, citric acid 1.26, potassium sorbate 7.03 and 4‐hexyl resorcinol 0.25, all g L^?1) did not alter the typical sensory features of shrimp and were effective at delaying the bitter off‐flavour formation for 26 days. This study constitutes a promising alternative to extent shelf‐life of shrimp kept at ?1 °C without freezing.     

Kinetics of the Thermal Degradation of Patulin in the Presence of Ascorbic Acid

Degradation of the mycotoxin patulin between 25 and 85 °C without and with added ascorbic acid was studied, and the effectiveness of linear and nonlinear models for predicting reaction rates was compared. In agreement with previous reports, ascorbic acid significantly increased (P ≤ 0.05) the rate of patulin degradation at all temperatures studied. The data for patulin degradation in the absence of ascorbic acid were adequately modeled using a zero‐order linear kinetic model. However, the predictive abilities of zero and higher‐order linear models were not adequate to describe the more complex reactions that likely occurred when ascorbic acid was added. In contrast, the nonlinear Weibull model adequately described the patulin‐ascorbic acid reaction throughout the temperature range studied. Zero‐order rate constants and Weibull scale values for each of the respective reactions followed the Arrhenius law. Activation energies of 58.7 ± 3.9 and 29.6 ± 1.9 kJ mol^?1 for the reaction without and with ascorbic acid, respectively, confirmed decreased patulin stability in the presence of ascorbic acid and suggested that the mechanisms for the 2 degradation reactions were different.     

Lipase-catalyzed acylation of <Emphasis Type="SmallCaps">l</Emphasis>-carnitine with conjugated linoleic acid in [Bmim]PF<Subscript>6</Subscript> ionic liquid

Improving significantly the acylation reaction of l-carnitine with conjugated linoleic acid catalyzed by lipase needs to select an efficient and suitable reaction medium that is not only polar but also hydrophobic. [Bmim]PF₆ which is satisfied with the above two requirements was applied as the reaction medium. The optimal reaction conditions were: Novozyme 435 as the catalyst, 5:1 of molar ratio of fatty acid to l-carnitine, 40 g L⁻¹ lipase, 0.22 a_W of initial water activity, 125 g L⁻¹ molecular sieves (they were added within 0–3 h of reaction time), 60 °C of reaction temperature, 200 rpm of rotation speed, 32 h of reaction time. The overall conversion could reach 98.27%. The conversion in [Bmim]PF₆ was 2.13 and 1.56 times higher than that in acetonitrile and in solvent-free system, respectively. The lipase in the present work could be used eight times. [Bmim]PF₆ as the reaction medium was better than acetonitrile and solvent-free system.     

A proposed mechanism for the inhibition of soybean lipoxygenase by β‐carotene

The inhibition mechanism of soybean lipoxygenase (LOX) by β‐carotene was studied. Addition of β‐carotene into the reaction mixture decreased the rate of conjugated diene formation. Increasing the concentration of β‐carotene in the reaction mixture resulted in a decrease in the rate of conjugated diene formation. Although the rate of conjugated diene formation was lower in the presence of β‐carotene, the same amounts of linoleic acid hydroperoxides were formed by the enzyme at the end of the reaction, both with and without β‐carotene in the reaction medium. The rates of conjugated diene formation for 40, 20, 10 and 4 U mL^?1 LOX enzyme were almost equal to zero when the concentrations of β‐carotene were 20, 17.5, 15 and 10 µmol L^?1 in model reaction systems, respectively. β‐Carotene directly influences the amount of enzyme in the reaction medium available for the catalytic conversion of linoleic acid into corresponding hydroperoxides. The results obtained here suggest that β‐carotene reacts with linoleyl radical (L^?) at the beginning of the chain reaction, preventing the accumulation of conjugated diene forms (LOO^?, LOO^? and LOOH). Since L^? transforms back to its original form of LH, the enzyme cannot complete the chain reaction and thus remains at inactive Fe(II) form. Copyright © 2005 Society of Chemical Industry     

Biosynthesis of ascorbyl benzoate in organic solvents and study of its antioxygenic and antimicrobial properties

Ascorbyl benzoate was synthesized through lipase-catalyzed esterification in organic media, and its properties studied. A series of organic solvents with a log P from −1.30 to 2.50 were investigated, in which cylcohexanone (log P = 0.96) was found to be the most suitable. The optimum reaction conditions in cylcohexanone were pH 6.0, a_w 0.33, a substrate concentration form 0.06 M to 0.1 M, 65 °C, and above 150 rpm speeds of shaking. Experimental results also demonstrated that benzoic acid was not an ideal substrate of lipase, which led to low conversion rates, but its limitation could be overcome by excess l-ascorbic acid. Schaal oven test illustrated that the antioxidant activity of ascorbyl benzoate was comparable to that of ascorbyl palmitate, and minimal inhibitory concentration (MIC) data showed that its antimicrobial activity was weaker than that of benzoic acid.     

Phenolic acids from malt are efficient acetylcholinesterase and butyrylcholinesterase inhibitors

Anticholinesterase activities of mashes produced using wheat (‘Wheat Pale’) or barley malts (‘Pilsner’, ‘Pale Ale’, ‘Munich Light’, ‘Carahell’ or ‘Carared’) were studied by spectrophotometric method. The highest inhibition of acetylcholinesterase and butyrylcholinesterase was observed at 52 °C and/or 64 °C, followed by a decrease or stabilization of the activity at 72 °C. Changes in the total phenolics content in the test mashes were correlated with changes in the acetylcholinesterase and/or butyrylcholinesterase activities. Phenolic acids were singled out from phenolic compounds for more detailed studies owing to their simplicity and structural similarity to well‐known cholinesterase inhibitors. The main phenolic acids in the test malts were ferulic, gallic, p‐coumaric and vanillic acids followed by chlorogenic, caffeic, syringic, p‐OH‐benzoic, sinapic and protocatechuic acids. The anticholinesterase activities of the phenolic acids were studied using model standard solutions at concentrations similar to the maximal content of these compounds in the test mashes. Among the phenolic acids, p‐coumaric acid had the largest share in the anticholinesterase activity, even though it was present in the test mashes at a significantly lower concentration (~0.38 mm L^?1) than ferulic acid (~1.00 mm L^?1). Sinapic acid and p‐OH‐benzoic acid (0.03 and 0.01 mm L^?1, respectively) were equally efficient inhibitors as ferulic acid at ~1.00 mm L^?1. This preliminary study should be extended to other phenolic compounds from malt (wort) in the near future. Copyright © 2012 The Institute of Brewing & Distilling     

APPLICATION OF A NEW CONTINUOUS FLOW SPECTROPHOTOMETRIC METHOD FOR THE CHARACTERIZATION OF POLYPHENOL OXIDASE NATURALLY IMMOBILIZED ON COCONUT FIBER

The association of continuous flow injection and spectrophotometry affords a simple, novel and rapid way of monitoring continuously the activity of naturally immobilized enzymes in their natural environment, thus eliminating cumbersome purification. The method was applied to determine the activity of polyphenol oxidase (PPO) enzymes naturally immobilized on coconut (Cocus nucifera, L.) fiber tissues. Maximum enzyme activity occurred at a temperature of 25C and at pH 6.0 using catechol as substrate. Thermal stability was assayed in a temperature range of 20 to 75C. The PPO exhibited excellent thermal stability, with only 50% loss in its activity at 75C after 4.3 min exposure. For catechol apparent Michaelis‐Menten constant (apparent Km), apparent Vmax and the apparent activation energy were 9.1 × 10^?3 mol L^?1, 0.20 abs min^?1 and 10.5 kcal mol^?1, respectively. The immobilized PPO showed high activity for o‐diphenols. The reactivity order was caffeic acid > pyrogallol > catechol. Complete inhibition of the enzyme was observed with 1 × 10^?3 mol L^?1 concentration of cyanide, thiourea, L‐cysteine, ascorbic acid, sodium sulfite, nitrates of cadmium, zinc and mercury, individually. Benzoic acid, 3‐hydroxy‐benzoic acid, 4‐acetamidephenol, sodium azide, resorcinol, L‐cystine and EDTA at equal concentrations inhibited PPO partially.     

Ligustrazine formation in Zhenjiang aromatic vinegar: changes during fermentation and storing process

BACKGROUND: Zhenjiang aromatic vinegar is one of the most well‐known traditional fermented vinegars in China. Previously, a alkylpyrazine named ligustrazine was found as a bioactive compound in Zhenjiang aromatic vinegar. However, the generating mechanism of ligustrazine during the fermentation and storing process of vinegar was unknown. In this study, the changes in ligustrazine and its synthesis precursors (diacetyl and acetoin) in the industrial process were investigated by gas chromatography–mass spectrometry. RESULTS: During the fermentation process, ligustrazine was first detected at the fifth day, and content reached 75.90 µg g^?1 when fermentation was complete. During the storage process, the content of ligustrazine increased with storage time, and the content in 6‐year‐old vinegar reached 696.63 mg L^?1, which was about 20 times higher than raw vinegar (34.7 mg L^?1). This may be attributed to the conversion of precursors to ligustrazine through the Maillard reaction as precursor contents decreased during the storage process. CONCLUSION: Results of this study showed that ligustrazine in vinegar was mainly formed during the storage process, and the fermentation process was regarded as the accumulation stage of precursors for ligustrazine synthesis. Copyright © 2011 Society of Chemical Industry     

Optimization of hot water extraction of roselle juice using response surface methodology: a comparative study with other extraction methods

Roselle has regained the attention of many fruit juice manufacturers in Malaysia as a product that contains high ascorbic acid and anthocyanins. However, ascorbic acid and anthocyanin pigments can be easily destroyed during processing of fruit juice. Therefore, in the present study, the effects of different processing methods, namely hot water extraction (HWE), hot water blending, cold water blending and screw press, on the changes in anthocyanins and ascorbic acid contents of roselle juice were evaluated. The anthocyanins and ascorbic acid contents of roselle were determined using the pH differential method and high‐performance liquid chromatography respectively. The physico‐chemical characteristics and sensory properties of roselle juice were also evaluated. The results of the study indicate that the HWE method is the most effective extraction method, resulting in high anthocyanins and ascorbic acid contents of 43 g l^?1 (as delphinidin‐3‐glucoside) and 2.34 g kg^?1 respectively. The optimum juice extraction conditions were 3.5 h at 60 °C. Copyright © 2003 Society of Chemical Industry