Studies on the occurrence and formation of 1,2-dicarbonyls in honey

The 1,2-dicarbonyl compounds 3-deoxyglucosulose (3-DG), methylglyoxal (MGO) and glyoxal (GO) were measured for the first time in 21 honey samples as the corresponding quinoxalines after derivatization with orthophenylenediamine using RP-HPLC and UV-detection. Compared to 5-hydroxymethylfural (HMF), which was also quantified, and ranged between 0.6 and 44 mg/kg, up to 100-fold higher amounts of 3-DG were found, ranging from 79 to 1,266 mg/kg. During storage of honey at 35 °C and 45 °C, a linear increase of 3-DG was observed. Values for GO and MGO were in the ranges 0.2–2.7 mg/kg and 0.4–5.4 mg/kg respectively, and were not affected by storage. Using semi-preparative RP-HPLC, glucosone, a 1,2-dicarbonyl compound previously unknown to occur in foods was isolated from a honey sample and characterized by LC-MS and NMR spectroscopy.     

Chemical changes in the non-volatile fraction of Brazilian honeys during storage under tropical conditions

The chemical transformations of the non-volatile fraction of Brazilian honeys during storage in tropical condition were monitored. Five systems, namely: 1 – fresh samples; 2 and 3 – samples heated for 3 and 6 months at 35–40 °C; 4 and 5 – samples left under similar conditions to systems 2 and 3, but containing sodium metabisulphite (120 ppm), were tested. The major transformations during storage occurred in the free and lactone acidity, diastase activity and 5-hydroxymethylfurfural (5-HMF) content. Storage modified diastase activity and the content of 5-HMF to an extent that the samples could not remain classified as fresh honey. The action of sodium metabisulphite in the control of the 5-HMF formation seemed to be dependent on other honey characteristics, such as its botanical origin. Sodium metabisulphite also influenced the development of the internal esterification reaction that converts gluconic acid into its corresponding lactone.     

Albumin causes a synergistic increase in the antioxidant activity of green tea catechins in oil-in-water emulsions

Model oil-in-water emulsions containing epicatechin (EC) and epigallocatechin gallate (EGCG) showed a synergistic increase in stability in emulsions containing added albumin. EGCG showed a stronger synergy (35%) with ovalbumin than did EC. Oxidation of the oil was monitored by determining peroxide values and hexanal contents. The effect of bovine serum albumin (BSA) on model oil-in-water emulsions containing each of the green tea catechins [epicatechin gallate (ECG), EGCG, EC and epigallocatechin (EGC)] was studied during storage at 30 °C. The green tea catechins showed moderate antioxidant activity in the emulsions with the order of activity being ECG ≈ EGCG > EC > EGC. Although BSA had very little antioxidant activity in the absence of phenolic antioxidants, the combination of BSA with each of the catechins showed strong antioxidant activity. BSA, in combination with EC, EGCG or EGC, showing the strongest antioxidant activity with good stability after 45 days storage. Model experiments with the catechins stored with BSA in aqueous solutions confirmed that protein–catechin adducts with antioxidant activity were formed between the catechins and protein. The antioxidant activity of the separated protein–catechin adducts increased strongly with storage time and was stronger for EGCG and ECG than for EC or EGC.     

Changes in the antioxidant properties of protein solutions in the presence of epigallocatechin gallate

β-Casein and α-casein showed radical-scavenging activities in aqueous solution, whereas bovine serum albumin (BSA), α-lactalbumin and β-lactoglobulin showed much weaker antioxidant activity, when assessed by the 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) radical-scavenging assay. However, β-casein and α-casein showed reduced antioxidant activity after storage at 30 °C. An increase in radical-scavenging activity and a fall in fluorescence of the protein component were evident after 6 h, when BSA, β-lactoglobulin or casein were mixed with EGCG, and excess EGCG was removed, indicating the formation of a complex with this protein on mixing. Storage of all the proteins with EGCG at 30 °C caused an increase in the antioxidant activity of the isolated protein component after separation from excess EGCG. This showed that EGCG was reacting with the proteins and that the protein-bound catechin had antioxidant properties. The reaction of EGCG with BSA, casein and β-lactoglobulin was confirmed by the loss of fluorescence of the protein on storage, and the increase in UV absorbance between 250 and 400 nm. The increase in antioxidant activity of BSA after storage with EGCG was confirmed by the ferric reducing antioxidant potential (FRAP) and the oxygen radical antioxidant capacity (ORAC) assays.     

Changes in glyoxal and methylglyoxal content in the fried dough twist during frying and storage

Glyoxal (GO) and methylglyoxal (MGO) are important precursors for advanced glycation end products (AGEs) in foods and in vivo, which are also known as reactive carbonyls. Accumulation of AGEs may result in health risk. The effect of frying time and temperature on GO and MGO formation during fried dough twist processing was investigated. The changes in GO and MGO content of fried dough twist were also examined under the different storage condition. Sample extraction, derivatization, and cleanup conditions were evaluated to provide a sample preparation method for GO and MGO analysis by RP-HPLC–DAD. Quantification limits of GO and MGO were 0.01 and 0.02 mg/L for fried dough twist, respectively. The average recovery rate was 89 % with detection relative standard deviation of lower than 5.7 %. During frying and prolonged storage, GO and MGO contents in fried dough twist ranged from 6.5 to 11.8 mg/kg and from 5.1 to 12.0 mg/kg, respectively. The results indicated that content of GO and MGO in fried dough twist depended on the frying time and temperature. For GO, no significant differences (p < 0.05) among the all types of samples were found during the whole process of storage, with the exception of storage temperature after 60-day storage. Changes in MGO occurred during the 60-day storage, indicating storage temperature, oxygen content, lighting, and storage duration, exert a significant effect on the development of the MGO.     

Determination of HMF in roasted flour/oil mixtures and effect of solvent used in the extraction procedure

Roasting of flour in oil or fat to form a roux is a common application in the preparation of many foods. In this study the development of 5-(hydroxymethyl)furfural (5-HMF) during roasting of white flour and oil mixtures prepared at 1:1, 1:2 and 1:3 ratios at 120, 160 and 200 °C was investigated. Extraction of 5-HMF from the solids phase, liquid (oil) phase and mixed phase of the samples was performed using three different solvents (water, ether and CCl₄) to evaluate the suitability of these solvents for improvement of the extraction procedure employed in the analysis method. The 5-HMF concentration was determined by using a reversed-phase HPLC system with a C₁₈ column and a photodiode array detector.     

Response surface methodological study on HMF and fluorescent accumulation in red and white grape juices and concentrates

White and red grape juices and their concentrates were subjected to thermal treatments at different temperatures ranging from 50 to 70 °C at different times. 5-Hydroxymethylfurfural (5-HMF) and fluorescence relative index (FLRI) were measured. Response surface methodology (RSM) was applied to determine the effect of temperature and time on the HMF and FLRI formation at the different Brix (bx) degrees. An increase in temperature (from 50 to 70 °C) and time (from 12 to 192 h) for 15°, 45° and 65° Brix degrees was associated with an increase in HMF and FLRI development of white and red grape juices. HMF formation was higher in white grape juice and concentrates than in red ones. Optimum conditions were confirmed and these fitted the experimental data well. Thus, regression equations can be used to estimate HMF and FLRI values at various Brix degrees for white and red grape juices and concentrates.     

Effect of synthetic antioxidants on storage stability of Khoa – a semi-solid concentrated milk product

Effect of synthetic antioxidants on storage stability of freshly prepared khoa was evaluated. Free fatty acids (FFA), peroxide value (POV) and iodine values (IV) were used to assess the development of rancidity during 30 days of storage of khoa at 25 and 45 °C. Butylated hydroxy anisole (BHA) and butylated hydroxy toluene (BHT) were added to freshly prepared khoa to extend the storage life. After 30 days of storage at 45 °C, freshly prepared khoa containing 200 ppm of BHA and BHT showed lower values of FFA (0.066%, 0.058%) and POVs (23.0, 21.0 meq/kg) than the control samples (FFA 0.320%, POV 127 meq/kg). Iodine values of khoa sample containing 200 ppm of BHA and BHT were 67 and 69 after 30 days storage at 45 °C. However, iodine value of a khoa sample without antioxidant (control) after 30 days of storage at 45 °C was 30. Similarly, khoa samples treated with 100 ppm of BHA, along with 100 ppm of BHT, showed FFA value (19.0%), POV (0.049 meq/kg) and iodine value (72) after storage for 30 days at 45 °C. These results illustrate that synthetic antioxidants inhibited the development of rancidity during storage of khoa. Therefore, storage life of khoa can easily be extended for 30 days by the addition of BHA and BHT.     

Thermally-induced protein–polyphenol co-assemblies: beta lactoglobulin-based nanocomplexes as protective nanovehicles for EGCG

Delivery of sensitive water-soluble compounds in foods is an important challenge. (−)-Epigallocatechin-3-gallate (EGCG), the major catechin in green tea, is a potent antioxidant with numerous attributed health benefits. However, its sensitivity to oxidation limits its enrichment in the diet for preventive medicine. We have studied the possibility of using thermally modified β-lactoglobulin (β-Lg) to form co-assembled nanovehicles for delivery of EGCG, as a model system for delivery of polyphenols by heat-modified proteins. Using fluorescence spectroscopy, DLS and spectrophotometry we found that optimal nano-entrapment is obtained when EGCG is added to preheated (75–85 °C, 20 min) β-Lg solution during cooling and vortexing. The measured association constant with the heated protein was 3.7 × 10⁵ M⁻¹, about 3.5-fold higher than that with the native protein: 1.05 × 10⁵ M⁻¹. Thermally-induced protein-EGCG co-assemblies were smaller than 50 nm, thus excellent transparency was maintained, enabling their application in clear beverages. These complexes conferred considerable protection to EGCG against oxidative degradation: A 33-fold lower initial degradation rate, and a 3.2-fold slower degradation over 8 days were observed for nano-entrapped compared to unprotected EGCG.     

Trapping reactions of reactive carbonyl species with tea polyphenols in simulated physiological conditions

The carbonyl stress that leads to the formation of advanced glycation end products (AGEs) in diabetes mellitus has drawn much attention recently. Reactive alpha-dicarbonyl compounds, such as glyoxal (GO) and methylglyoxal (MGO), have been shown to be a high potential glycation agent in vitro and in vivo. In this study, epicatechins in green tea and theaflavins in black tea were found to be able to reduce the concentration of MGO in physiological phosphate buffer conditions. Modified MGO derivatization for GC/flame ionization detector (FID) method in quantification was systematically conducted. In molar ratio of 3 (MGO/polyphenol), theaflavin-3,3'-digallate (TF3) in theaflavins and (-)-epigallocatechin (EGC) in epicatechins showed the highest MGO reduction at 66.65 and 45.74%, respectively, after 1 h of incubation. In kinetic study (molar ratio of MGO/polyphenol = 1:1), rapid MGO reduction occurred within 10 min. Identities of primary adducts between (-)-epigallocatechin gallate (EGCG) and MGO were determined. Newly generated stereoisomers at the C8 position of EGCG A-ring were isolated with a chiral column, and structurally confirmed by 2-D NMR analyses.     

Storage effects on nutritional quality of commonly consumed cereals

Storage effects on nutritional quality of commonly consumed cereal grains are studied. Freshly harvested wheat, maize and rice grains were stored at 10, 25 and 45 °C for six months. A significant decrease in pH and an increase in titratable acidity was observed during storage of these three cereal grains at 25 and 45 °C. A gradual decline in moisture, total available lysine and thiamine contents was observed during storage. Total available lysine contents decreased by 6.50% and 18.5% in wheat, 14.3% and 20.7% in maize and 23.7% and 34.2% in rice during six months of storage at 25 and 45 °C, respectively. Six month’s storage of rice, maize and wheat grains at 25 and 45 °C resulted in reduction of thiamine contents by 16.7% and 29.2%, 17.2% and 24.1% and 21.4% and 29.5%, respectively. About 36.4–44.4% decrease in total soluble sugars at 45 °C and 9.30–31.8% increase in total soluble sugars were observed at 10 and 25 °C during six months storage of these cereal grains. Protein and starch digestibilities of cereal grains also deceased during six months of storage at 25 and 45 °C. No significant change in nutritional quality was observed during storage of cereal grains at 10 °C.     

Stability of lipids and fatty acids in frozen and gamma irradiated Patagonian toothfish (Dissostichus eleginoides) from the Southwestern Atlantic

Patagonian toothfish were captured in the Southwestern Atlantic Ocean (FAO Zone N° 41). The fatty acid profile of total lipids and the triacylglycerol and phospholipid content of control and irradiated samples (1 and 5 kGy) stored at −18 °C were analyzed at 0 and 293 days post irradiation. The fatty acids are mainly monounsaturated acids (47 g/100 g total fatty acids), the most abundant one being oleic acid (18:1 n-9). This is followed in order of abundance by saturated fatty acids (26 g/100 g total fatty acids), consisting mainly of palmitic acid (16:0). Polyunsaturated fatty acids were less abundant (17 g/100 g total fatty acids) and consisted mainly of eicosapentaeonic (20:5 n-3) and docosahexaenoic (22:6 n-3) acids. Triacylglycerol content was 563.07 mg/mL oil, whereas phospholipids were 11.21 mg/mL oil. Gamma irradiation did not significantly affect the fatty acid profile or triacylglycerol and phospholipid content of P. toothfish stored for 293 days at −18 °C. The results suggest that the species exhibits a marked stability when subjected to irradiation and prolonged storage in the frozen state.     

Effects of modified atmosphere package (MAP) with a silicon gum film window and storage temperature on the quality and antioxidant system of stored Agrocybe chaxingu

Packages of Agrocybe chaxingu with or without silicon gum film windows were flushed with an initial modified atmosphere (MA) 100 mL/L O₂, 100 mL/L CO₂ and balance N₂ and stored at 1 °C and 3 °C, respectively. The changes in gas headspace, sensory, content of malondialdehyde (MDA), generation of superoxide anion, the activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) of mushroom were investigated. A. chaxingu stored in MAP without silicon gum film window at 1 °C had the poorest sensory quality because of chilling injury and physiological injury caused by a combination of storage temperature and poor atmosphere conditions (O₂ under 9 mL/L and CO₂ above 172 mL/L since Day 4). These injuries induced a relatively high content of MDA and generation of superoxide anion. The antioxidant enzyme system, including SOD, CAT and POD, was stimulated, to increase activities and scavenge the reactive oxygen species (ROS) to reduce injury during the initial storage period. However, these injuries also induced senescence of the stored mushroom, which resulted in decreased activities of antioxidant enzyme system. The activities of antioxidant enzyme system of A. chaxingu stored in MAP with silicon gum film window at 3 °C was the most favourable to delay the senescence process in the latter part of storage period, and the mushroom had the best quality to the end of storage.     

Effects of temperature,solid content and pH on the stability of black carrot anthocyanins

Anthocyanin stability of black carrots was studied at various solid contents (11, 30, 45 and 64° Brix) and pHs (4.3 and 6.0) during both heating, at 70–90 °C, and storage at 4–37 °C. Monomeric anthocyanin degradation fitted a first-order reaction model. Degradation of monomeric anthocyanins increased with increasing solid content during heating, while it decreased during storage. For example, at pH 4.3, half-life periods for anthocyanins at 30, 45 and 64° Brix were, respectively, 8.4, 6.9 and 5.2 h during heating at 80 °C and 18.7, 30.8 and 35.9 weeks during storage at 20 °C. At 30–64° Brix, increasing pH from 4.3 to 6.0 enhanced the degradation of anthocyanins during heating. The effect of pH on thermal stability of anthocyanins was also studied at six different pHs (2.5–7.0) in citrate-phosphate buffer solutions and significant decrease in anthocyanin stability was observed at pHs above 5.0. Higher activation energies (E_a) were obtained during heating than during storage with increasing solid contents. At 30–64° Brix, E_a values ranged from 68.8 to 95.1 kJ mol⁻¹ during heating and from 62.1 to 86.2 kJ mol⁻¹ during storage. Q₁₀ values at 20–37 °C were as high as 3.1 at 45° Brix and 3.6 at 64° Brix.     

Effect of high pressure processing on the stability of anthocyanin,ascorbic acid and color of Chinese bayberry juice during storage

The stability of anthocyanin (Cy3Gl) and ascorbic acid (AA) of pressure treated Chinese bayberry (Myrica rubra Sieb. et Zucc.) juice was investigated during storage at temperature of 4 °C and 25 °C. Samples of Chinese bayberry juice (350 mL each, packed with a polyethylene bag) were processed at 400, 500, 600 MPa in room temperature for 10 min. The retention ratio of Cy3Gl and AA content after pressure treatment was more than 98% and 96%, respectively. Both Cy3Gl and AA of pressure treated juice were more stable during storage as compared to those of the untreated control juice. The degradation of Cy3Gl and AA of samples during storage could be described using first order kinetic model. It was observed that there was a significant (p < 0.01) correlation between changes of Cy3Gl and AA content for all tested samples of Chinese bayberry juice during storage.     

Cooking quality of faba bean after storage at high temperature and the role of lignins and other phenolics in bean hardening

Selected physical and chemical characteristics of faba beans (Vicia faba L.) cv. Fiesta were studied after 12 months storage at 5, 15, 25, 37, 45 or 50 °C (±2 °C) in relation to the hard-to-cook phenomenon. In comparison with control (seeds stored at 5 °C), seeds stored at 15 and 25 °C demonstrated non-significant (p?0.05) changes in most of the physical and chemical characteristics including hydration and swelling coefficients, acid detergent fibre, lignin and tannin contents, whereas seeds stored at ?37 °C demonstrated significant changes (p?0.05). Solutes and electrolytes leaching after 18 h soaking substantially increased with increased temperature. Faba bean hardness tested by the hard-to-cook test also increased substantially with increased storage temperature. After 8 h soaking followed by 2 h cooking, the puncture force required for seeds stored at 5 °C was 3.3 N seed⁻¹ whereas seeds stored at 50 °C required a much higher puncture force of 15.2 N seed⁻¹. There was a high negative correlation (r²=0.98) between storage temperature and cooking ability of faba bean. Substantial increases in acid detergent fibre and lignin contents occurred with increased storage temperatures. There was a three-fold increase in lignin content of faba bean stored at 50 °C compared to those stored at 5 °C and it was correlated with bean hardness (r²=0.98). Storage at high temperatures for 12 months led to a substantial reduction in total free phenolics especially in the testa and there was a greater reduction with increasing storage temperature. Reduction in free phenolics was negatively correlated (r²=0.75) with bean hardness.     

Citrus peel extract – A natural source of antioxidant

Citrus peel extract as a natural source of antioxidant was evaluated during 6 months storage of refined corn oil at 25 and 45 °C. Extracts of citrus peel were prepared by refluxing the dried ground peel with ethanol, methanol, acetone, hexane, diethyl ether and dichloromethane. Maximum amount of citrus peel extract was obtained with methanol. Antioxidant activity of methanolic extract was assessed by measuring free fatty acid (FFA) content peroxide value (POV) and iodine value (IV) during 6 months storage of refined corn oil at 25 and 45 °C. After 6 months of storage at 45 °C, corn oil containing 1600 and 2000 ppm citrus peel extract, showed lower FFA contents (1.5% and 1.0%), and POVs (8.38 and 7.0 meq kg⁻¹) and higher iodine values (81, 89) than the control sample (FFA 17.0% POV 101 meq kg⁻¹ IV 47). Refined corn oil containing 200 ppm of butylated hydroxy anisole (BHA) and butylated hydroxy toluene (BHT) showed FFA contents of 2.0% and 1.8%, POVs 17.0 and 12.7 meq kg⁻¹ and IVs 84 and 87, respectively, after 6 months of storage at 45 °C. These results show that methanolic extract of citrus exhibited very strong antioxidant activity, which was almost equal to synthetic antioxidants (BHA and BHA). Therefore, the use of citrus peel extract is recommended as a natural antioxidant to suppress development of rancidity in oils and fats.     

Stability of active components of cardamom oleoresin in co-crystallized sugar cube during storage

Cardamom oleoresin was co-crystallized to formulate flavoured sugar cubes for table top use in tea. The flavoured sugar cubes were packed in two-layer composite and three-layer metalized laminate packaging materials and evaluated for 5 months at relative humidities of 33%, 63% and 93% and temperatures of 5 °C, 25 °C and 45 °C, respectively. The major active components of cardamom oleoresin viz. 1,8-cineole and α-terpinyl acetate in the co-crystallized sugar cubes was quantified by gas chromatography throughout the storage period. The major active components of cardamom in the oleoresin, freshly prepared flavoured sugar cubes, and in sugar cubes stored under extreme condition of storage at 45 °C under all the relative humidities were identified by GCMS. The rate of degradation of 1,8-cineole was higher than α-terpinyl acetate as seen from the kinetic study and activation energy in both the packaging materials under all conditions of storage.     

Antioxidant and antimicrobial effects of garlic in chicken sausage

The antioxidant and antimicrobial effects of equivalent concentrations of fresh garlic (FG), garlic powder (GP) and garlic oil (GO) were investigated against lipid oxidation and microbial growth in raw chicken sausage during storage at 3°C. The antioxidant activities were compared to that of a standard synthetic antioxidant; butylated hydroxyanisole (BHA). The initial mean levels of thiobarbituric acid (TBA) value and peroxide value (POV) were 0.140 and 6.32, respectively. However after 21 days of storage, TBA and POV ranged from 0.151 to 4.92, respectively, in FG (50 g/kg) formulated samples to 0.214 and 8.64, respectively, in GO (0.06 g/kg) formulation. Addition of either garlic or BHA (0.1 g/kg) significantly delayed lipid oxidation when compared with control. The antioxidant activities of the various materials added followed the order FG>GP>BHA>GO. On the other hand, the initial aerobic plate count (APC) in the samples was 4.41 log₁₀ CFU/g. Addition of FG (30 g/kg) or GP (9 g/kg) significantly reduced the APC and, subsequently, the shelf-life of the product was extended to 21 days. However, addition of GO or BHA resulted in no significant difference in APC when compared with control. Sensory analysis indicated that FG had a significant stronger flavor than the other sausage formulations. The results suggest that fresh garlic and garlic powder, through their combined antioxidant and antimicrobial effects, are potentially useful in preserving meat products.     

Fructooligosaccharide fortification of selected fruit juice beverages: Effect on the quality characteristics

Fortification of selected fruit juice beverages (Pineapple, Mango and Orange juice) with fructooligosaccharides (FOSs), a low calorie prebiotic has been discussed. Results indicated that sucrose which is usually used as a sweetener in fruit juice beverages can be partially substituted with FOS without significantly affecting the overall quality. The fruit juice beverages were evaluated for physicochemical and sensory changes during 6 months storage period at ambient (25 ± 2 °C) and refrigeration temperature (4 °C). The pH, total soluble solids, titratable acidity, and colour did not change significantly (P ≥ 0.05) during storage. The initial FOS content of pineapple, mango and orange juice beverages was 3.79, 3.45, and 3.62 g/100 mL. The FOS content of the fruit juice beverages stored at refrigeration temperature was 2.00-2.39 g/100 mL after 6 months of storage and 2.69-3.32, 1.65-2.08 and 0.38-0.58 g/100 mL at the second, fourth and sixth months of storage at ambient temperature respectively. The sensory analysis showed that the beverages were acceptable up to 4 and 6 months storage at ambient and refrigeration temperature respectively.