Effects of four different cooking methods on anthocyanins, total phenolics and antioxidant activity of black rice.

BACKGROUND: Two cultivars of black rice were investigated for the effects of different cooking methods on anthocyanins, total phenolic compounds and antioxidant activities. RESULTS: There was a significant loss of anthocyanins during cooking: roasting resulted in the greatest decrease (94%), followed by steaming (88%), pan-frying (86%) and boiling (77%). Contents of phenolic compounds decreased drastically after cooking, with significantly lower retention in the black rice cultivar that had higher amylose content. DPPH radical-scavenging activity of black rice decreased after cooking. In contrast, metal-chelating activity increased significantly after cooking. Anthocyanins showed a high positive correlation with total phenolic compounds (r2 = 0.936) but a significant negative correlation with metal-chelating activity (r2 = 0.6107). CONCLUSION: The results indicate that cooking degraded anthocyanins and other phenolic compounds, but with a concomitant increase in phenolics from possible degradation of anthocyanins, which resulted in the enhancement of metal-chelating activity.

Optimizing oxidative stability and quality in fish balls: the synergistic effects of cooking methods and turmeric powder addition.

This study examined the effects of cooking methods (boiling, steaming, pan-frying, oven-roasting, and microwave cooking) and turmeric powder (TP) addition on the physicochemical properties and oxidative stability of fish balls. Higher cooking temperatures increased moisture evaporation. Pre-cooking before freezing reduced hydroperoxide and malondialdehyde levels in fish balls over 4 months of storage, especially noticeable in boiled, pan-fried, and oven-roasted fish balls. Additionally, TP addition significantly improved the total reducing capacity of the fish balls, an effect that persisted even after cooking. Consequently, hydroperoxide and malondialdehyde levels decreased during storage, with a more pronounced effect observed in steamed and microwave-cooked fish balls. Principal component analysis identified distinct clusters based on cooking methods and TP addition, categorizing the fish balls into three groups, and highlighting the complex interplay between these two factors. These findings offer valuable insights into extending the shelf life of fish balls through optimized antioxidant and cooking methods.

Effects of Sweet Potato Powder Selected Based on the Polar Paradox Hypothesis on Oil Oxidation in the Preparation of Deep-Fried Croquettes.

This study investigated whether sweet potato powder (SPP) and purple SPP (PSPP) could prevent oil oxidation during deep-frying. A volume of soybean oil was repetitively used for deep-frying croquettes coated with either SPP or PSPP. An aliquot of the fried oil was collected (SPP and PSPP oils) before and after each frying to analyze moisture and lipid oxidation products (LOPs). With increasing numbers of frying, the moisture content in oils significantly increased without an appreciable difference between SPP and PSPP oils. The total oxidation values reflecting primary and secondary LOPs also significantly increased. However, the values were higher for PSPP oils despite the much higher antioxidant activity of the polar extracts from PSPP compared to SPP. This was attributed to the presence of transition metals. PSPP oils seemed to have association colloids whose interfaces were occupied more with polar antioxidants, thereby transition metals were easily reduced and their pro-oxidative activity increased. The polar paradox hypothesis stating that polar antioxidants are more effective in preventing lipid oxidation in bulk oil is not always applicable to real foods due to various food matrices.

Methods to improve rice protein dispersal at moderate pH.

Dispersion of rice protein (RP) at a neutral pH is highly important for its application in the food industry. We analyzed the solubility of RP at different pH conditions and found higher solubility at pH < 3 and pH > 8 than at a neutral pH. Furthermore, at pH 2, the RP solubility improved from 30 to 63% with sonication; however, the samples precipitated when the pH was increased from 2 to 7. To circumvent this, anionic pectin and sodium alginate were added to the RP solution at pH 2. Pectin formed a complex with RP at pH 2, showing a shift in the zeta-potential from 17.3 mV (RP only) to - 1.0 mV (RP plus 1% pectin). Interestingly, the formation of this RP-pectin complex allowed RP to remain dispersed when the pH was increased to 7. Moreover, a stable emulsion could be prepared using the RP-pectin complex as an emulsifier.

Preparation and characterization of water/oil and water/oil/water emulsions containing biopolymer-gelled water droplets.

The purpose of this study was to create water-in-oil (W/O) and water-in-oil-in-water (W/O/W) emulsions containing gelled internal water droplets. Twenty weight percent W/O emulsions stabilized by a nonionic surfactant (6.4 wt % polyglycerol polyricinoleate, PGPR) were prepared that contained either 0 or 15 wt % whey protein isolate (WPI) in the aqueous phase, with the WPI-containing emulsions being either unheated or heated (80 degrees C for 20 min) to gel the protein. Optical microscopy and sedimentation tests did not indicate any significant changes in droplet characteristics of the W/O emulsions depending on WPI content (0 or 15%), shearing (0-7 min at constant shear), thermal processing (30-90 degrees C for 30 min), or storage at room temperature (up to 3 weeks). W/O/W emulsions were produced by homogenizing the W/O emulsions with an aqueous Tween 20 solution using either a membrane homogenizer (MH) or a high-pressure valve homogenizer (HPVH). For the MH the mean oil droplet size decreased with increasing number of passes, whereas for the HPVH it decreased with increasing number of passes and increasing homogenization pressure. The HPVH produced smaller droplets than the MH, but the MH produced a narrower particle size distribution. All W/O/W emulsions had a high retention of water droplets (>95%) within the larger oil droplets after homogenization. This study shows that W/O/W emulsions containing oil droplets with gelled water droplets inside can be produced by using MH or HPVH.

Parboiling improved oxidative stability of milled white rice during one-year storage.

Parboiling was investigated to improve the long-term oxidative stability of milled white rice beyond its current application to paddy brown rice. White rice was steamed at 105°C for 20 min, 120°C for 5 min, or 120°C for 20 min without soaking in water, followed by drying at 70°C for 3 h. During oneyear storage at 25 and 4°C, acid value as an index of oxidative deterioration of rice remained relatively constant in parboiled rice samples, while significant increases were observed in raw rice with higher acid values at 25°C compared with 4°C. This indicates that the parboiling improved the oxidative stability of white rice over the long period of time even at room temperature, therefore it can be an efficient alternative to retard the oxidative deterioration of white rice.

Influence of Sulfur Fertilization on the Antioxidant Activities of Onion Juices Prepared by Thermal Treatment.

Two onions (Sulfur-1 and Sulfur-4) cultivated with different sulfur applications were thermally processed to elucidate the effects of heat treatment on browning index and antioxidant activity. Sulfur-4 onion had higher sulfur content compared with the Sulfur-1 onion. After thermal processing, browning intensity was different between the two onions juices, with lower values observed for Sulfur-4 onion juice. This suggests that sulfur inhibits the Maillard browning reaction. The total reducing capacity of the juices increased at higher thermal processing temperatures; however, it was also lower in the Sulfur-4 onion juice. This suggests that the heat treatment of onions enhanced their antioxidant activity, but the effect was offset in the Sulfur-4 onion juice presumably due to higher sulfur content. This study indicates that sulfur, a core element for the functionality of onions, can decrease the antioxidant activity of thermally processed onions because of its potential as a Maillard reaction inhibitor.

Aglycone Isoflavones and Exopolysaccharides Produced by Lactobacillus acidophilus in Fermented Soybean Paste.

Bioconversion of aglycone-formed isoflavones from glycoside-formed isoflavones by commercial lactic acid bacteria in fermented soybean paste was evaluated. Enterococcus faecium KCTC 13410 showed the most resistant capacity and Lactobacillus acidophilus KCTC 3925 had a sensitive susceptibility at a high NaCl concentration (13.2%) in fermented soybean paste. Among the 5 strains tested, Lac. acidophilus KCTC 3925 showed the highest relative ratio of aglycone-formed isoflavones to total isoflavones in fermented soybean paste. Production of exopolysaccarides (EPS) by lactic acid bacteria was compared using de Man, Rogosa, and Sharpe medium containing 1% sucrose at 37°C for 48 h. Among the 5 lactic acid bacteria, Lac. acidophilus KCTC 3925 and Lactobacillus rhamnosus KCTC 3929 were investigated to produce EPS. Based on the results concerning growing susceptibility and conversion of aglycone-formed isoflavones/EPS production, it is anticipated that Lac. acidophilus KCTC 3925 may be used for preparation of Cheonggukjang, which contains relative low NaCl content.

Influence of environmental stresses on stability of O/W emulsions containing cationic droplets stabilized by SDS-fish gelatin membranes.

Oil-in-water (O/W) emulsions containing small oil droplets (d32 approximately 0.22 microm) stabilized by sodium dodecyl sulfate (SDS)-fish gelatin (FG) membranes were produced by an electrostatic deposition technique. A primary emulsion containing anionic SDS-coated droplets (zeta approximately -40 mV) was prepared by homogenizing oil and emulsifier solution using a high-pressure valve homogenizer (20 wt % corn oil, 0.46 wt % SDS, 100 mM acetic acid, pH 3.0). A secondary emulsion containing cationic SDS-FG-coated droplets (zeta approximately +30 mV) was formed by diluting the primary emulsion with an aqueous fish gelatin solution (10 wt % corn oil, 0.23 wt % SDS, 100 mM acetic acid, 2.00 wt % fish gelatin, pH 3.0). The stabilities of primary and secondary emulsions with the same oil concentration to thermal processing, ionic strength, and pH were assessed by measuring particle size distribution, zeta potential, microstructure, destabilized oil, and creaming stability. The droplets in secondary emulsions had good stability to droplet aggregation at holding temperatures from 30 to 90 degrees C for 30 min, [NaCl] < or = 100 mM, and pH values from 3 to 8. This study shows that the ability to generate emulsions containing droplets stabilized by multilayer interfacial membranes comprised of two or more types of emulsifiers, rather than a single interfacial layer comprised of one type of emulsifier, may lead to the development of food products with improved stability to environmental stresses.

Food types and frying frequency affect the lipid oxidation of deep frying oil for the preparation of school meals in Korea.

200 soybean oils used in school meals for deep frying were investigated to elucidate factors influencing lipid oxidation in the oils. The mean levels of moisture along with primary and secondary lipid oxidation products were significantly different among the oils used by the six schools. When comparing lipid oxidation products of frying oils used for four different food groups (vegetables, fish, meat or carbohydrate-rich foods), differences were found among them, with the values for the carbohydrate-rich group being the lowest. The vegetable group was higher in the contents of conjugated dienes and trienes, and lower for those of hydroperoxides and malondialdehyde. The mean values of malondialdehyde and p-anisidine value for the fish group were greater than those of the other groups. The levels of conjugated trienes and malondialdehyde increased with the frying frequency. These findings indicate that food types and frequency of frying play a role in determining the oil oxidation in deep fried foods in schools.

Seasonal variations of fatty acid compositions in various Korean shellfish.

Seasonal variations of fatty acids in various Korean shellfish were investigated in relation to the changes in total fatty acids contents, the ratio of polyunsaturated fatty acids to saturated fatty acids (P/S), and that of n-3 fatty acids to n-6 fatty acids (n-3/n-6). A distinct seasonal pattern was found in total fatty acids contents with maximal values in early summer and minimal values in late summer. The percentage of monounsaturated fatty acids was lowest in most species throughout the year. In summer months, the proportion of polyunsaturated fatty acids decreased while that of saturated fatty acids increased. The major contributing factor to the seasonal variation of polyunsaturated fatty acids was n-3 fatty acids. These results led to the lowest levels of P/S and n-3/n-6 in summer. Nevertheless, the data suggest that bivalve shellfish would be excellent sources of n-3 fatty acids, especially eicosapentaenoic acid and docosahexaenoic acid.

Release properties of gel-type W/O/W encapsulation system prepared using enzymatically-modified starch.

A gel-based encapsulation system was developed by incorporating W/O/W emulsions and 4-α-glucanotransferase (4αGTase) treated starch capable of thermoreversible gel formation, and its physical and release characteristics were investigated as functions of preparation conditions and temperature. Release properties of the W/O/W gels were affected by stability and encapsulation efficiency (EE) of W/O/W emulsions embedded within. Lower EE caused by longer sonication time increased fast release dye portion, which resulted in higher dye release rate, even though emulsion stability improved at longer sonication time. Lower dye release rate of W/O/W gels prepared with relatively higher W/O volume fractions slightly increased as temperature increased from room temperature to 90 °C. However, samples prepared with relatively lower W/O volume fractions showed higher dye release rate and a larger increase at 90 °C. The 4αGTase-treated starch gel improved W/O/W emulsion stability and thus retarded dye release even at 90 °C.

Antioxidant and Anti-inflammatory Activities of Butanol Extract of Melaleuca leucadendron L.

Melaleuca leucadendron L. has been used as a tranquilizing, sedating, evil-dispelling and pain-relieving agent. We examined the effects of M. leucadendron L. extracts on oxidative stress and inflammation. M. leucadendron L. was extracted with methanol (MeOH) and then fractionated with chloroform (CHCl3) and butanol (BuOH). Antioxidant activity of the MeOH extract and BuOH fraction were higher than that of both α-tocopherol and butyrated hydroxytoluene (BHT). Total phenol content in the extracts of M. leucadendron L., especially the BuOH fraction, well correlated with the antioxidant activity. The anti-inflammatory activity of BuOH extracts were investigated by lipopolysaccharide (LPS)-induced nitric oxide (NO) and prostaglandin E2 (PGE2) production, and cyclooxygenase-2 (COX-2) expression in RAW 264.7 macrophages. The BuOH fraction significantly inhibited LPS-induced NO and PGE2 production. Furthermore, BuOH extract of M. leucadendron L. inhibited the expression of COX-2 and iNOS protein without an appreciable cytotoxic effect on RAW264.7 cells. The extract of M. leucadendron L. also suppressed the phosphorylation of inhibitor κBα (IκBα) and its degradation associated with nuclear factor-κB (NF-κB) activation. Furthermore, BuOH fraction inhibited LPS-induced NF-κB transcriptional activity in a dose-dependent manner. These results suggested that M. leucadendron L. could be useful as a natural anti-oxidant and anti-inflammatory resource.

Fatty Acid Composition as a Predictor for the Oxidation Stability of Korean Vegetable Oils with or without Induced Oxidative Stress.

This study was designed to investigate whether the fatty acid composition could make a significant contribution to the oxidation stability of vegetable oils marketed in Korea. Ten kinds, 97 items of vegetable oils that were produced in either an industrialized or a traditional way were collected and analyzed for their fatty acid compositions and lipid oxidation products, in the absence or presence of oxidative stress. Peroxidability index (PI) calculations based on the fatty acid composition ranged from 7.10 to 111.87 with the lowest value found in olive oils and the highest in perilla oils. In the absence of induced oxidative stress, malondialdehyde (MDA), the secondary lipid oxidation product, was generated more in the oils with higher PI (r=0.890), while the tendency was not observed when the oils were subjected to an oxidation-accelerating system. In the presence of the oxidative stress, the perilla oils produced in an industrialized manner generated appreciably higher amounts of MDA than those produced in a traditional way, although both types of oils presented similar PIs. The results implicate that the fatty acid compositions could be a predictor for the oxidation stability of the vegetable oils at the early stage of oil oxidation, but not for those at a later stage of oxidation.

Effect of emulsifier type on droplet disruption in repeated shirasu porous glass membrane homogenization.

The influence of various emulsifier types (anionic, nonionic, and zwitterionic) on the mean particle size, transmembrane flux, and membrane fouling in repeated membrane homogenization using a Shirasu porous glass (SPG) membrane has been investigated. Oil-in-water (O/W) emulsions (40 wt % corn oil stabilized by 0.06-2 wt % sodium dodecyl sulfate (SDS) or 0.1-2 wt % Tween 20 at pH 3 or 0.5-2 wt % beta-lactoglobulin (beta-Lg) at pH 7) were prepared by passing coarsely emulsified feed mixtures five times through the membrane with a mean pore size of 8.0 microm under the transmembrane pressure of 100 kPa. The flux increased as the number of passes increased, tending to a maximum limiting value. The maximum flux for the Tween 20-stabilized emulsions (5-47 m3.m(-2).h(-1)) was smaller than that for the SDS-stabilized emulsions (29-60 m3.m(-2).h(-1)) because less energy was needed for the disruption of a SDS-stabilized droplet due to the lower interfacial tension. The mean particle size after five passes was 4.1-6.8 and 6.4-8.7 mum for 0.1-2 wt % SDS and Tween 20, respectively. The flux in the presence of beta-Lg was much smaller than that in the presence of SDS and Tween 20, which was a consequence of more pronounced membrane fouling, due to the protein adsorption to the membrane surface. After five passes through the membrane, the fouling resistance in the presence of 2 wt % beta-Lg (1.1 x 10(10) 1/m) was 2 orders of magnitude higher than that for 0.5 wt % Tween 20 and an order of magnitude higher than the membrane resistance. If a clean membrane was used in the fifth pass, a 2-fold reduction of the fouling resistance was observed.

Estimated intakes of isoflavones and coumestrol in Korean population.

The dietary intakes and sources of isoflavones and coumestrol were estimated for each age group of Koreans based on data from the Korean Nutrition Survey conducted in 1998. For quantitative data on the levels of isoflavones and coumestrol, our previous study monitoring phytoestrogens in 220 Korean leguminous foodstuffs was employed and the median value for each food was adopted. The total isoflavones and coumestrol intake per capita was estimated as 23.3 mg/day, which constituted 14.2 mg daidzein, 6.7 mg genistein, 0.9 mg glycitein, 1.0 mg formononetin, 0.2 mg biochanin A, and 0.3 mg coumestrol. The top five foods arrowroot, soybean paste, tofu, soybean, and soybean sprout contributed to 88.2% of isoflavone intake, with the corresponding intake from each food being 8.3 mg/day, 4.9 mg/day, 2.6 mg/day, 2.5 mg/day, and 2.0 mg/day, respectively. Starting at age 3-6, the contributions of fermented soy products to the isoflavones intakes were around 30%. Soybean sprout was a major source of coumestrol intake in Koreans. Slight differences in the preference of these foods were observed among the various age groups. As regards the total isoflavone intakes, the highest value was 33.6 mg/day for people age 30-49, followed by age 50-64 (26.4 mg/day), 20-29 (21.0 mg/day), >or=65 (18.8 mg/day), 1-2 (14.5 mg/day), 7-12 (12.4 mg/day), 13-19 (10.1 mg/day), and 3-6 (8.9 mg/day). The intake levels are likely to be exceeded in groups who have preferably consumed high phytoestrogen-containing foods such as soy-protein-based infant formula and arrowroot.