Sittiwat Lertsiri

Comparison of determination method for volatile compounds in Thai soy sauce

Abstract Dynamic headspace (DHS) sampling, direct solvent extraction (DSE) and vacuum simultaneous steam distillation–solvent extraction (V–SDE) were used for sample preparation in volatile compound analysis in Thai soy sauce. The extracts obtained from two brands were then analyzed by gas chromatography-mass spectrometry (GC–MS). A comparative study of volatile compounds obtained from these preparation techniques was performed. Some similarities were observed among different characteristic volatile profiles obtained from each preparation technique. Highly volatile compounds were detected only by DHS whereas DSE and V–SDE gave a wide spectrum of chemical classes of compounds detected. Moreover, differences of volatile compounds detected from both soy sauces were noted. This might be due to the differences of production process employed and strains of microorganism used.

Co-culturing of Pichia guilliermondii enhanced volatile flavor compound formation by Zygosaccharomyces rouxii in the model system of Thai soy sauce fermentation.

The roles of salt-tolerant yeasts such as Zygosaccharomyces rouxii, Candida versatilis, and Candida etchellsii in the production of volatile flavor compounds (VFCs) in soy sauce fermentation have been well documented. However, the knowledge of VFC production by other salt-tolerant yeasts is still limited. In this work, the roles of Z. rouxii and Pichia guilliermondii strains in VFC production were investigated in moromi medium as a model system for soy sauce fermentation. Inoculation of a single culture of either Z. rouxii or P. guilliermondii as well as co-cultures of these two yeasts into moromi medium showed increased numbers of viable yeast at around 0.7 to 1.9 log CFU/mL after 7days of cultivation at 30°C. During cultivation, both single and co-cultures displayed survival over a 7-day time period, compared with the controls (no culture added). Overall, yeast inoculation enhanced the production of VFCs in the moromi media with higher amounts of ethanol, alcohols, furanones, esters, aldehyde, acid, pyrone and phenols, known as important characteristic flavor compounds in soy sauce. Moreover, the co-culture produced more alcohols, furanones, esters, maltol and benzoic acid than the single culture of Z. rouxii.

Changes in volatile aroma compounds of organic fragrant rice during storage under different conditions.

BACKGROUND Aroma of fragrant rice greatly affects palatability as well as consumer acceptability. Loss of desirable volatile compounds such as 2-acetyl-1-pyrroline (2-AP) and increase in volatile lipid oxidation products in aged rice have been reported. The aim of this study was to monitor the changes in key volatile compounds of organic red fragrant rice cv. Hom Daeng during storage. Effects of packaging material, storage temperature and time were evaluated using solid phase microextraction/gas chromatography/mass spectrometry. RESULTS Thirteen key volatile compounds including ten lipid oxidation products were monitored. For samples vacuum packed in Nylon/LLDPE pouches at ambient temperature, significant increases in hexanal, 2-pentylfuran, 1-octanol and 4-vinyl guaiacol and significant decreases in 2-AP and geranyl acetone were found after the second month (P< or =0.05). Vacuum packing in OPP/Al/LLDPE pouches or storage at 15 degrees C better retarded the formation of volatile lipid oxidation products and greater retained desirable odorants, including 2-AP. However, accumulation of lipid oxidation products and 4-vinyl guaiacol was apparent after the sixth month under these storage conditions. CONCLUSION A greater extent and higher rate of undesirable changes in volatile compounds were found in samples stored under Nylon/LLDPE/ambient temperature condition. Nevertheless, this condition is acceptable for the retail trade of organic rice in Thailand. Storage conditions using reduced temperature or better packaging materials may be more appropriate for exported rice or superior-grade fragrant rice to better maintain the desirable rice aroma.

PHOSPHOLIPID HYDROPEROXIDES AND LIPID PEROXIDATION IN LIVER AND PLASMA OF ODS RATS SUPPLEMENTED WITH ALPHA -TOCOPHEROL AND ASCORBIC ACID

Forty-five mutant male ODS rats, unable to synthesize ascorbic acid, were fed nine diets containing 5, 50 or 250 mg of vitamin E/kg diet and 150, 300 or 900 mg of vitamin C/kg diet for 21 days. The concentrations of vitamins C and E increased in liver and plasma in relation to the level of these vitamins in the diet. Vitamin C dietary supplementation increased the plasma vitamin E content at low levels of vitamin E intake, supporting the concept of an in vivo synergism between both antioxidant vitamins. Vitamin C, at the dietary levels studied, did not affect the lipid peroxidation. Vitamin E decreased liver and plasma endogenous levels of thiobarbituric acid-reactive substances and liver sensitivity to non-enzymatic lipid peroxidation. This was confirmed by a highly specific assay of lipid hydroperoxides using high performance liquid chromatography with chemiluminescence detection. The hepatic concentration of both phosphatidylcholine and phosphatidylethanolamine hydroperoxides decreased as the vitamin E content of the diet increased. The results show for the first time the capacity of vitamin E to protest against peroxidation of major phospholipids in vivo under basal unstressed conditions.

Luminol chemiluminescent determination of hydrogen peroxide at picomole levels using high-performance liquid chromatography with a cation-exchange resin gel column

Abstract The optimum conditions of high-performance liquid chromatography combined with luminol chemiluminescence detection were established for the determination of hydrogen peroxide at picomole levels using a cation-exchange gel column. The gel column with distilled water as the mobile phase allowed a good separation of H 2 O 2 without causing any irreversible binding of H 2 O 2 to the column surface. The detection limit and the quantification limit of H 2 O 2 were 4 and 6–600 pmol, respectively. The suitability of the present method was verified by the determination of H 2 O 2 present in coffee drinks.

Development of a genetic sexing strain in Bactrocera carambolae (Diptera: Tephritidae) by introgression of sex sorting components from B. dorsalis, Salaya1 strain

BackgroundThe carambola fruit fly, Bactrocera carambolae Drew & Hancock is a high profile key pest that is widely distributed in the southwestern ASEAN region. In addition, it has trans-continentally invaded Suriname, where it has been expanding east and southward since 1975. This fruit fly belongs to Bactrocera dorsalis species complex. The development and application of a genetic sexing strain (Salaya1) of B. dorsalis sensu stricto (s.s.) (Hendel) for the sterile insect technique (SIT) has improved the fruit fly control. However, matings between B. dorsalis s.s. and B. carambolae are incompatible, which hinder the application of the Salaya1 strain to control the carambola fruit fly. To solve this problem, we introduced genetic sexing components from the Salaya1 strain into the B. carambolae genome by interspecific hybridization.ResultsMorphological characteristics, mating competitiveness, male pheromone profiles, and genetic relationships revealed consistencies that helped to distinguish Salaya1 and B. carambolae strains. A Y-autosome translocation linking the dominant wild-type allele of white pupae gene and a free autosome carrying a recessive white pupae homologue from the Salaya1 strain were introgressed into the gene pool of B. carambolae. A panel of Y-pseudo-linked microsatellite loci of the Salaya1 strain served as markers for the introgression experiments. This resulted in a newly derived genetic sexing strain called Salaya5, with morphological characteristics corresponding to B. carambolae. The rectal gland pheromone profile of Salaya5 males also contained a distinctive component of B. carambolae. Microsatellite DNA analyses confirmed the close genetic relationships between the Salaya5 strain and wild B. carambolae populations. Further experiments showed that the sterile males of Salaya5 can compete with wild males for mating with wild females in field cage conditions.ConclusionsIntrogression of sex sorting components from the Salaya1 strain to a closely related B. carambolae strain generated a new genetic sexing strain, Salaya5. Morphology-based taxonomic characteristics, distinctive pheromone components, microsatellite DNA markers, genetic relationships, and mating competitiveness provided parental baseline data and validation tools for the new strain. The Salaya5 strain shows a close similarity with those features in the wild B. carambolae strain. In addition, mating competitiveness tests suggested that Salaya5 has a potential to be used in B. carambolae SIT programs based on male-only releases.

Pyrone hydroperoxide formation during the Maillard reaction and its implication in biological systems

Hydroperoxide formation during Maillard reaction (amino-carbonyl reaction) was investigated using luminol-chemiluminescence-high performance liquid chromatography (CL-HPLC). From the equimolar reaction mixture of 1 M beta-alanine/D-glucose in phosphate buffer (pH 8.0) at 95 degrees C, two hydroperoxides and H2O2 were detected as chemiluminescent products in CL-HPLC, and the yields were proportional to the browning development. One of these hydroperoxides was isolated and identified as 3-hydroxy-5-hydroperoxy-2-methyl-5,6-dihydropyran-4-one (HMDP, pyrone hydroperoxide) by fast atom bombardment mass spectrometry. The HMDP formation was also confirmed in L-lysine/D-glucose and in bovine serum albumin/D-glucose with the physiological incubation at 37 degrees C for 4 days and 3 wk, respectively. Incubation at 37 degrees C of human plasma containing 5.5-25.0 mM of D-glucose for 60 h showed the glucose concentration-dependent formation of HMDP (10-35 microM of H2O2 equivalence). The HMDP was negative to thiobarbituric acid reaction and was degraded by peroxidases such as horseradish peroxidase, Athromyces ramosus peroxidase, heated cytochrome c, and microperoxidase. The results strongly suggested the formation of such hydroperoxide even in biological Maillard reaction termed as glycation, and implied its contribution in pathogenesis and oxidative lesions associated with hyperglycemia.

Glutaminase-producing Meyerozyma (Pichia) guilliermondii isolated from Thai soy sauce fermentation

In this study, 34 yeast isolates were obtained from koji and moromi samples of Thai soy sauce fermentation. However, the most interesting yeast strain was isolated from the enriched 2 month-old (M2) moromi sample and identified as Meyerozyma (Pichia) guilliermondii EM2Y61. This strain is a salt-tolerant yeast that could tolerate up to 20% (w/v) NaCl and produce extracellular and cell-bound glutaminases. Interestingly, its glutaminases were more active in 18% (w/v) NaCl which is a salt concentration in moromi. The extracellular glutaminases activity was found to be much higher than that of cell-bound glutaminase. The highest specific activity and stability of the extracellular glutaminase were found in 18% (w/v) NaCl at pH4.5 and 37°C. A challenge test by adding partially-purified extracellular glutaminase from M. guilliermondii EM2Y61 into 1 month-old (M1) moromi sample showed an increased conversion of L-glutamine to L-glutamic acid. This is the first report of glutaminase producing M. guilliermondii isolated from the moromi of Thai soy sauce fermentation. The results suggested the potential application of M. guilliermondii EM2Y61 as starter yeast culture to increase l-glutamic acid during soy sauce fermentation.

Chemical and Organoleptic Comparison of Fish Sauce Made from Cold Water Species and Typical Thai Fish Sauce

ABSTRACT Organoleptic and chemical properties of fish sauce made experimentally from the four cold water fish species–Arctic capelin, Atlantic herring, Atlantic cod and blue whiting–were compared with three first grade commercial fish sauces made from tropical anchovies. Although the flavor of the fish sauces made from cold water species were judged as inferior to the flavor of the tropical fish sauces, the blue whiting and Atlantic herring sauces obtained fair ranking. Chemical analyses revealed that sugar had been added in all the three commercial sauces. Although sugar is added during blending just before bottling, flavor enhancing chemical reactions, between amino groups and reducing sugars, probably occur during storage of the final product. Accordingly, this procedure should be adapted also in preparation of fish sauce from cold water species.

The occurrence of a novel hydrophilic hydroperoxide, 3-hydroxy-5-hydroperoxy-2-methyl-5,6-dihydropyran-4-one, as a reactive glycation product in human plasma

This study describes the occurrence of 3-hydroxy-5-hydroperoxy-2-methyl-5,6-dihydropyran-4-one (HMDP) in plasma obtained from normal subjects and patients with type 2 diabetes. We have shown previously that HMDP is a novel hydrophilic hydroperoxide formed in the in vitro Maillard reaction that could be analyzed using ultrasensitive chemiluminescence detection-high-performance liquid chromatography (CL-HPLC). The HMDP concentration was 273+/-227 nmol/l in normal subjects and 656+/-535 nmol/l in patients with diabetes. The HMDP concentration was proportional to the plasma glucose concentration level (r=0.640; P<0.01) but not with the glycated hemoglobin level. To investigate the in vivo effects of HMDP, a range of concentrations of the compound was incubated for different time periods with human serum albumin and lipoproteins. HMDP was found to induce denaturation of these macromolecules by modifying lysine residues and causing cross-linking and polymerization of proteins. In the presence of metal ions such as iron and copper, HMDP induced peroxidative degradation of lipoprotein lipids as measured by an elevation in thiobarbituric acid reactive substances (TBARS) concentration. These results suggested that HMDP is produced as a consequence of both hyperglycemia and increased oxidative stress, and may have the potential to contribute to the pathogenesis of arterial complications in diabetes mellitus.