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.     

Antioxidant capacities of α-tocopherol,trolox, ascorbic acid,and ascorbyl palmitate in riboflavin photosensitized oil-in-water emulsions

Antioxidant capacities of α-tocopherol, trolox, ascorbic acid, and ascorbyl palmitate at 0.01, 0.1, and 1.0 mM in riboflavin photosensitized oil-in-water (O/W) emulsions were determined using headspace oxygen depletion, lipid hydroperoxide, and headspace volatile analyses. After 32 h visible light irradiation, headspace oxygen in O/W emulsions without adding antioxidants, with 1.0 mM α-tocopherol, trolox, ascorbic acid, and ascorbyl palmitate decreased to 18.50%, 18.85%, 16.01%, 17.92%, and 19.88%, respectively, whereas those samples in the dark were 20.74%. Trolox and ascorbic acid acted as prooxidants while their lipophilic counterparts, α-tocopherol and ascorbyl palmitate, respectively showed antioxidant properties. Similar antioxidative or prooxidative properties of the tested compounds can be observed in the results of lipid hydroperoxides and headspace volatiles. However, the prooxidant and antioxidant properties of the tested compounds were not clearly shown at 0.01 and 0.1 mM concentration. Both the type and concentration of antioxidants influenced the antioxidant capacities in riboflavin photosensitized O/W emulsions.     

Determination of aromatic amino acid content in cooked meat by derivative spectrophotometry: Implications for nutritional quality of meat

The technique of second derivative spectrophotometry was used to determine the level and the heat stability of the three aromatic amino acids (tryptophan, tyrosine and phenylalanine) in bovine meat (M. Longissimus thoraci). This paper presents a method which measures the second derivative absorbance values at a wavelength specifically assigned to each aromatic amino acid with corrections for the interference from other amino acids at the same wavelength. Three cooking temperatures were tested in this study (60, 100 and 140 °C). Due to important cooking losses, results differ slightly according to the method of calculation (level expressed by gram of wet meat or by gram of proteins). Whatever the calculation method, heating at 60 °C had little effect on aromatic acid levels while higher temperatures had a dramatic effect on aromatic amino acids stability. The stability of the three aromatic amino acids during cooking decreased in the order tryptophan > phenylalanine > tyrosine.     

Evaluation of Antioxidant or Prooxidant Properties of Selected Amino Acids Using In Vitro Assays and in Oil‐in‐Water Emulsions Under Riboflavin Sensitization

The antioxidant properties of selected amino acids were tested using in vitro assays and oil‐in‐water (O/W) emulsions under riboflavin (RF) photosensitization. Headspace oxygen content, lipid hydroperoxides, and conjugated dienes were determined for the degree of oxidation. Riboflavin photosensitization was adapted as the oxidation driving force. In vitro assays showed that cysteine had the highest antioxidant properties followed by tryptophan and tyrosine. However, in O/W emulsions under RF photosensitization, tyrosine inhibited lipid oxidation whereas tryptophan acted as a prooxidant. Tryptophan accelerated the rates of oxidation in O/W emulsion without RF. The antioxidant properties of amino acids differed depending on the antioxidant determination methods, oxidation driving forces, and food matrices.     

Effects of lipophilic and hydrophilic antioxidants in oil-in-water emulsions under chlorophyll photosensitization

Antioxidative or prooxidative properties of α-tocopherol, Trolox, ascorbic acid, and ascorbyl-palmitate at the concentration of 0.1 and 1.0 mM were determined in oil-in-water (O/W) emulsions under chlorophyll photosensitization. Headspace oxygen depletion, lipid hydroperoxides, and headspace volatile analyses were conducted to determine the oxidative stability of O/W emulsions. For 32 h visible light irradiation, depleted headspace oxygen content in O/W emulsions were in the order of samples containing Trolox, ascorbic acid, ascorbyl palmitate, α-tocopherol, without antioxidants under light, and samples in the dark, which implies that all the added compounds acted prooxidant. These prooxidative properties of added compounds can be observed in the results of lipid hydroperoxides and headspace volatiles. Samples containing ascorbic acid and ascorbyl palmitate retained higher chlorophyll content than those containing Trolox up to 16 h. Increases of concentration of Trolox, ascorbic acid, and ascorbyl palmitate from 0.1 to 1.0 mM increased the lipid oxidation products whereas α-tocopherol decreased the degree of lipid oxidation implying α-tocopherol may not share the same prooxidant mechanisms compared to other compounds in chlorophyll sensitized O/W emulsions.     

Comparison of bioactive components in GABA tea and green tea produced in Taiwan

The aim of this study is to investigate the bioactive components of GABA (γ-aminobutyric acid) tea as compared with green tea produced in Taiwan. Using in total 56 tea samples (28 green tea and 28 GABA tea), moisture content, Hunter L, a and b values, phenolic compounds, amino acids including GABA, fatty acids and ascorbic acid were determined. The results showed that moisture, total free amino acids, crude fat, Hunter L value, total nitrogen, free fatty acids and reducing sugar did not differ significantly between GABA tea and green tea. However, GABA tea had higher Hunter a and b values, while green tea had higher total catechin and ascorbic acid contents (p < 0.05). Of major catechins, epicatechin and epigallocatechin gallate were found to be lower in GABA tea than in green tea. For free amino acids, GABA, alanine, ammonia, lysine, leucine and isoleucine were found to be significantly higher in GABA tea, while the glutamic acid, aspartic acid, and phenylalanine were higher in green tea (p < 0.05). Theanine, tryptophan, valine, threonine and methionine were not found to be different between the two kinds of tea.     

Effect of amino acids on the formation of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in creatinine/phenylalanine and creatinine/phenylalanine/4-oxo-2-nonenal reaction mixtures

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) formation in mixtures of creatinine, phenylalanine, amino acids and 4-oxo-2-nonenal was studied, to analyse the role of amino acids on the generation of this heterocyclic aromatic amine. When oxidised lipid was absent, cysteine, serine, aspartic acid, threonine, asparagine, tryptophan, tyrosine, proline, and methionine increased significantly (p < 0.05) the amount of PhIP formed in comparison to the control. When lipid was present, only the addition of methionine, glycine, and serine increased significantly (p < 0.05) the amount of PhIP produced, while histidine, cysteine, lysine, tryptophan, tyrosine, and alanine reduced significantly (p < 0.05) PhIP. These results may be a consequence of the different competitive reactions that occur. Thus, in the absence of lipids, thermal decomposition of the amino acids produced reactive carbonyls that converted phenylalanine into phenylacetaldehyde as a key step in the formation of PhIP. When oxidised lipid was present, amino acids competed with phenylalanine for the lipid, and amino acid degradation products were formed, among which alpha-keto acids seemed to play a role in these reactions. These results suggest that PhIP can be produced by several alternative reaction pathways from all major food components, including amino acids and lipids, in addition to carbohydrates.     

Kinetics for Singlet Oxygen Formation by Riboflavin Photosensitization and the Reaction between Riboflavin and Singlet Oxygen

ABSTRACT: The formation of singlet oxygen by riboflavin and the kinetics and mechanisms of riboflavin degradation in aqueous solution under light were determined. The singlet oxygen formation rate by riboflavin was 2.31 μmole oxygen/mL headspace/h of serum bottle. The degradations of riboflavin were 66% in D₂O and 40% in H₂O, respectively, under light after 24 h. The results indicate that singlet oxygen is involved in riboflavin destruction under light. The riboflavin destructions were 94.0% and 15.7% with 0 mM or 160 mM ascorbic acid, respectively, under light after 96 h. The reaction rate between riboflavin and singlet oxygen was 1.01 × 10¹⁰/M/s, which is a diffusion-controlled reaction rate. This explains the extremely fast degradation of riboflavin in foods under light. Ascorbic acid and sodium azide reduce the degradation of riboflavin under light with different quenching mechanisms. Ascorbic acid quenched both singlet oxygen and excited triplet riboflavin. Sodium azide quenched only the singlet oxygen in riboflavin solution with a quenching rate of 1.547 × 10⁷/M/s. With the involvement of both the Type-I and Type-II mechanisms in the riboflavin degradation under light, singlet oxygen quencher alone could not protect the riboflavin from degradation completely. Addition of ascorbic acid can protect riboflavin oxidation in foods exposed to light.     

Effect of γ-radiation on green onion DNA integrity: Role of ascorbic acid and polyphenols against nucleic acid damage

The effect of γ-radiation on green onion DNA integrity, phenol content, oxygen radical absorbance capacity, employing pyrogallol red and fluorescein as probes, as well as ascorbic acid content has been evaluated. Measurements using thiazole orange-DNA fluorescence and agarose gel electrophoresis show that γ-radiation does not lead to an apparent DNA change in green onion. However, it was readily cleaved upon irradiation from the previously isolated nucleic acid. Furthermore, green onion exposure to γ-radiation produces slight increases in the polyphenol concentrations (163–188 μM Trolox eq.) and a decrease in the oxygen radical absorbance using fluorescein (from 245 to 200 Trolox eq.) Interestingly, a high ascorbic acid content (364 μM), which decreases by 40% after γ-ray exposure was measured by using pyrogallol-red-based oxygen radical absorbance capacity induction times from green onion aqueous extracts. Thus, our results suggest that ascorbic acid present in green onion plays a fundamental role in the plant antioxidant response toward γ-radiation exposure, while polyphenols remain largely unchanged, as revealed from oxygen radical absorbance capacity, employing pyrogallol red.     

Effect of cooking on protein oxidation in n-3 polyunsaturated fatty acids enriched beef. Implication on nutritional quality

The effect of cooking on protein oxidation was investigated in M. Longissimus thoracis of eight Normand cows fed during a 100 days finishing period with two different diets: a conventional diet (concentrate/straw based diet) and a diet rich in n-3 polyunsaturated fatty acids (PUFAs), obtained by addition to the conventional diet of a mixture of extruded linseed and extruded rapeseed. After 11 days storage, at 4 °C under vacuum, meat was cooked by applying jets of steam. Three experimental heating treatments were tested: two with constant surface temperatures of 65 and 96 °C during 300 s, and one with a continuous increasing surface temperature up to 207 °C. Protein oxidation was evaluated by the measurement of carbonyls, aromatic amino acids, and free thiols content. The formation of Schiff bases due to the reaction of proteins with aldehydic products of the lipid oxidation was also evaluated. Cooking resulted in a significant increase of carbonyl groups and Schiff bases as well as a significant degradation of tyrosine and tryptophan. Nevertheless, enrichment of the animal diet in n-3 PUFAs had minor effects on protein oxidation induced by cooking which are unlikely to be of nutritional significance.     

Effects of Riboflavin Photosensitized Oxidation on the Volatile Compounds of Soymilk

ABSTRACT: Soymilks with or without added riboflavin in serum bottles were stored under light or in dark at 20 °C. The headspace oxygen and volatile compounds were determined by gas chromatography. Riboflavin had significant effects on the headspace oxygen depletion and volatile compounds formation in soymilk under light ( P < 0.05). Riboflavin did not have significant effects on the formation of volatile compounds and the depletion of headspace oxygen in dark ( P > 0.05). The volatile compounds increased under light, but not in dark as the added riboflavin increased. Storage temperature at 4 °C or 20 °C did not have significant difference in the effect of riboflavin on the headspace oxygen depletion in soymilk under light. Hexanal, an important beany flavor compound, was identified as the major volatile compound in the riboflavin photosensitized soymilk. Singlet oxygen oxidation was involved in the formation of volatile compounds in soymilk under light. Hexanal could be formed by singlet oxygen oxidation. Ascorbic acid, a quencher for singlet oxygen and the excited triplet sensitizer, significantly inhibited the formation of hexanal and total volatiles in soymilk under light.     

Oxidative modification of amino acids in porcine myofibrillar protein isolates exposed to three oxidizing systems

Susceptibility of amino acids in myofibrillar protein isolate (MPI) exposed to three oxidizing matrixes commonly encountered in muscle foods was compared. MPI suspensions (20 mg protein/mL) in 15 mM piperazine-N,N bis(2-ethane sulphonic acid) buffer (pH 6.0) were oxidized with an iron-catalyzed oxidizing system (IOS, 0.01 mM FeCl₃, 0.1 mM ascorbic acid, 0.0–10.0 mM H₂O₂), a lipid-oxidizing system (LOS, 0.0–10.0 mM linoleic acid, 3750 units of lipoxidase/mL), or a metmyoglobin (MetMb) oxidizing system (MOS, 0.0–0.5 mM H₂O₂/MetMb) for 24 h at 4 °C. Changes were quantitatively analyzed by determining amino acids on a reverse-phase liquid chromatographic (LC) system. In IOS, the amount of cysteine, methionine and tyrosine decreased (P < 0.05) with increasing [H₂O₂]. In LOS, only cysteine and methionine were lowered at increasing linoleic acid concentrations. In MOS, the quantity of alanine, cysteine, glycine, histidine, leucine and lysine, as well as the total amount of amino acids were significantly reduced at high concentrations of MetMb/H₂O₂. The results suggest that under typical meat processing conditions, iron- and metmyoglobin-catalyzed reactions play a major role in the oxidation of amino acids in muscle proteins.     

Comparative amino acid and fatty acid compositions of edible gums kondagogu (Cochlospermum gossypium) and karaya (Sterculia urens)

Gum karaya and gum kondagogu are the two important commercial tree gums of India. The amino acids and fatty acid profiles of gum kondagogu and gum karaya were investigated by preparing their corresponding N-O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) derivatives for amino acids and direct trans-esterification of methyl esters for fatty acids and their subsequent analysis by a GC–MS method. The amino acids, such as, alanine, valine, methionine, tyrosine and tryptophan, were not detected in gum karaya as they were in gum kondagogu. Interestingly, the aspartic acid content (72.8 ± 3.45 μg/g) of gum kondagogu was higher than that of gum karaya (64.2 ± 2.44 μg/g). The ratios of saturated to unsaturated fatty acid in gum kondagogu and gum karaya were found to be 5:1, and 6.6:1, respectively. Among the unsaturated fatty acids, linoleic acid (1.8 ± 0.12 μg/g) and γ-linolenic acid (0.8 ± 0.05 μg/g) were detected only in gum kondagogu. Arachidic acid was not detected in gum karaya. Additionally, the presence of linoleic acid and γ-linolenic acid in gum kondagogu reinforces its nutritional value.     

Application of Leaching Model to Describe Potato Nutrient Losses in Hot Water Blanching

Nutritive losses of hot water blanched potatoes were studied. The potatoes lost significant amounts of some amino acids-glutamic acid, aspartic acid, valine, phenylalanine, arginine, methionine and tryptophan. They also lost a significant amount of gamma-amino butyric acid. The concentration of the water soluble vitamins, ascorbic acid, riboflavin, thiamin, and niacin was significantly reduced. A leaching model, with diffusion as the rate controlling step, successfully predicted losses of these vitamins as a function of process parameters.     

Chemical characterization of Chinese chive seed (Allium tuberosum Rottl.)

Chinese chive seeds (Allium tuberosum Rottl.) (grown in China) were investigated. Density, thousand-grain weight, and hectolitre weight of seeds were 1.27 g/cm³, 4.9 g, and 71 kg/100 l, respectively. The results showed that Chinese chive seeds contained high amounts of oil (15.8%), dietary fibre (18.2%) and crude protein (12.3%). Oil of seeds was composed of 10.1% saturated and 90.0% unsaturated fatty acids. Linoleic(69.1%) and palmitic (7.0%) were the most abundant unsaturated and saturated fatty acids, respectively. Chinese chive seeds contained 4.5 mg/kg of thiamin, 2.8 mg/kg of riboflavin and 55.1 mg/kg of niacin. The mineral contents of the seed of A. tuberosum, for iron, calcium and zinc, were 580 mg/kg, 1328 and 80.8 mg/kg, respectively. Analysis of the amino acid content of Chinese chive seed revealed that it was a rich source of the essential amino acids, isoleucine, tryptophan and lysine. The study revealed that Chinese chive seeds had high levels of nutritionally important components, such as oil, minerals and essential amino acids.     

Changes of Headspace Volatiles in Milk with Riboflavin Photosensitization

ABSTRACT:  Effects of fluorescent light, riboflavin, ascorbic acid, sodium azide, and butylated hydroxyanisole (BHA) on the volatiles in milk at 4 °C were determined using a combination of headspace-solid phase microextraction (HS-SPME), gas chromatography (GC), and mass spectrometry (MS). Pentanal, hexanal, heptanal, and dimethyl disulfide were formed only in the milk stored under light and increased significantly as the duration of light exposure increased from 0 to 8 h and the concentration of added riboflavin increased from 5 to 50 ppm ( P  < 0.05). As fat content in milk increased, peak areas of pentanal, hexanal, and heptanal increased significantly ( P  < 0.05) while those of dimethyl disulfide did not change significantly ( P  > 0.05). Sodium azide prevented the formation of dimethyl disulfide in milk, implying that dimethyl disulfide can be formed through singlet oxygen oxidation (type II pathway). Addition of ascorbic acid and BHA reduced the formation of hexanal, heptanal, and dimethyl disulfide significantly ( P  < 0.05). Generation mechanisms of pentanal seem to be different from those of hexanal and heptanal in milk. Both singlet oxygen oxidation (type II pathway) and free radicals (type I pathway) play important roles in the formation of light-induced volatiles in milk.     

QUENCHING MECHANISMS AND KINETICS OF CAROTENOIDS IN RIBOFLAVIN PHOTOSENSITIZED SINGLET OXYGEN OXIDATION OF VITAMIN D2

The oxidation of vitamin D₂ in a solution of 12% water, 88% acetone and 15 ppm ribqflavin under light or dark was studied by measuring the headspace oxygen. Ribofiavin accelerated the oxidation of vitamin D₂ by singlet oxygen under light, but did not affect vitamin D₂ oxidation under dark. Quenching mechanisms and kinetics within the range of 0–20 ppm β‐cawtene or fucoxanthin and with 0–80 ppm retinyl acetate or retinol on 15 ppm riboflavin photosensitized singlet oxygen oxidation of vitamin D₂ were also studied. The rate of singlet oxygen formation by 15 ppm riboflavin was 1.78 umole oxygen/mL headspace‐hour. The reaction rate constant of vitamin D₂ with singlet oxygen was 2.2 times 10⁷ M^?1A s^?1. The carotenoids minimized the oxidation of vitamin D₂ by quenching singlet oxygen. The total quenching rate constants of retinol, retinyl acetate, jucoxanthin and ft‐carotene were in the order of 1.22 times 10⁸, 5.98 times 10⁸, 1.78 times 10⁹ and 5.00 times 10⁹M^?1. s^?1 respectively, which suggests that as the number of double bonds of carotenoids increases, the quenching rate constant ofcarotenoid increases.     

Effect of frozen storage duration and cooking on physical and oxidative changes in M. Gastrocnemius pars interna and M. Iliofiburalis of Rhea americana

This study was conducted to evaluate the effect of frozen storage time (30, 60, 90 or 180 days) and cooking (100 °C, 30 min) on the physical characteristics and oxidative stability of M. Gastrocnemius pars interna (GN) and M. Iliofiburalis (IF) of rhea americana. Physical parameters measured included thawing and cooking loss, colour parameters (L*a*b*), while oxidation was assessed by determining the TBA-RS, carbonyl and aromatic amino acid content. Prolonged frozen storage of rhea meat decreased lightness (L*), yellowness (b*), and increased the discoloration parameter hue angle and redness a*. During storage, muscle IF was more prone to lipid and myoglobin oxidation than muscle GN. Cooking loss declined with the increase of storage time and was higher in GN than in IF muscle. With cooking, TBA-RS, carbonyl content, and aromatic amino acids (phenylalanine, tyrosine, and tryptophan) were highly affected, but the extent of oxidation ranged according to muscle and duration of frozen storage.     

Effects of α-, γ-, and δ-Tocopherols on Oxidative Stability of Soybean Oil

The effectts of 0, 100, 250, 500 and 1000 ppm of α-, γ-, or δ-tocopherol on oxidative stability of purified soybean oil in the dark at 55°C were studied. We measured peroxide value and headspace oxygen consumption in the samples. Purified soybean oil was prepared by liquid column chromatography. Tocopherols acted as antioxidants or prooxidants depending on their concentration. Optimum concentrations of α -, γ -, and δ– tocopherols to increase oxidative stability was 100, 250 and 500 ppm, respectively. The tocopherols had significant prooxidant effect (P < 0.05) at higher concentrations above this.     

Effects of chlorophyll photosensitisation on the oxidative stability in oil-in-water emulsions

Effects of chlorophyll photosensitisation on the oxidative stability of oil-in-water (O/W) emulsions were determined by analysing headspace oxygen content, lipid hydroperoxides, and headspace volatiles. The roles of transition metals and singlet oxygen were tested by adding ethylenediaminetetraacetic acid (EDTA) and sodium azide, respectively. Emulsions with chlorophylls and visible light irradiation had significantly high lipid hydroperoxides and headspace volatiles and low headspace oxygen content (p < 0.05) after 32 h while samples without light irradiation did not show any significant changes (p > 0.05). Sodium azide did not show clear antioxidant capacities in O/W emulsion systems rather showed prooxidant properties at some concentration. Addition of EDTA, a metal chelator, accelerated the rates of lipid oxidation in a concentration dependent manner. EDTA may enhance the stability of chlorophylls in O/W emulsions and the resulting higher chlorophyll concentrations may generate more singlet oxygen thus accelerating the rates of lipid oxidation.